/// D translation of stb_image-1.33 (http://nothings.org/stb_image.c)
///
/// This port only supports:
/// $(UL
///   $(LI PNG 8-bit-per-channel only.)
///   $(LI JPEG baseline (no JPEG progressive).)
///   $(LI GIF.)
///   $(LI BMP non-1bpp, non-RLE.)
/// )
///
/// TODO:
/// $(UL
///   $(LI Support a range as input.)
///  )

//============================    Contributors    =========================
//
// Image formats                                Optimizations & bugfixes
// Sean Barrett (jpeg, png, bmp)                Fabian "ryg" Giesen
// Nicolas Schulz (hdr, psd)
// Jonathan Dummer (tga)                     Bug fixes & warning fixes
// Jean-Marc Lienher (gif)                      Marc LeBlanc
// Tom Seddon (pic)                             Christpher Lloyd
// Thatcher Ulrich (psd)                        Dave Moore
// Won Chun
// the Horde3D community
// Extensions, features                            Janez Zemva
// Jetro Lauha (stbi_info)                      Jonathan Blow
// James "moose2000" Brown (iPhone PNG)         Laurent Gomila
// Ben "Disch" Wenger (io callbacks)            Aruelien Pocheville
// Martin "SpartanJ" Golini                     Ryamond Barbiero
// David Woo

module gfm.image.stb_image;

import core.stdc.stdlib;
import core.stdc..string;

import ae.utils.graphics.image;
import ae.utils.graphics.color;



/// The one function you probably want to use.
/// Loads an image from a static array.
/// Because probing has been removed from stb_image, parsing is optimistic 
/// and might throw internally before finding the right image format.
/// Throws: $(D STBImageException) on error.
Image!RGBA loadImage(const(ubyte[]) imageData)
{
    import gfm.image.stb_image;
    import core.stdc..string;

    void[] data = cast(void[])imageData;
    int width, height, components;
    ubyte* decoded = stbi_load_from_memory(data, width, height, components, 4);
    scope(exit) stbi_image_free(decoded);

    // stb_image guarantees that ouput will always have 4 components when asked
    // Fortunately they are already RGBA

    // allocates result
    Image!RGBA loaded;
    loaded.size(width, height);

    // copy pixels (here they are contiguous in each case)
    memcpy(loaded.pixels.ptr, decoded, width * height * 4);
    return loaded; // this uses the GC to give up ownership
}

enum STBI_VERSION = 1;

/// The exception type thrown when loading an image failed.
class STBImageException : Exception
{
    public
    {
        @safe pure nothrow this(string message, string file =__FILE__, size_t line = __LINE__, Throwable next = null)
        {
            super(message, file, line, next);
        }
    }
}

enum : int
{
   STBI_default    = 0, // only used for req_comp
   STBI_grey       = 1,
   STBI_grey_alpha = 2,
   STBI_rgb        = 3,
   STBI_rgb_alpha  = 4
};

// define faster low-level operations (typically SIMD support)


uint stbi_lrot(uint x, uint y)
{
    return (x << y) | (x >> (32 - y));
}

// stbi structure is our basic context used by all images, so it
// contains all the IO context, plus some basic image information
struct stbi
{
   uint img_x, img_y;
   int img_n, img_out_n;

   int buflen;
   ubyte[128] buffer_start;

   const(ubyte) *img_buffer;
   const(ubyte) *img_buffer_end;
   const(ubyte) *img_buffer_original;
}


// initialize a memory-decode context
void start_mem(stbi *s, const(ubyte)*buffer, int len)
{
   s.img_buffer = buffer;
   s.img_buffer_original = buffer;
   s.img_buffer_end = buffer+len;
}

void stbi_rewind(stbi *s)
{
   // conceptually rewind SHOULD rewind to the beginning of the stream,
   // but we just rewind to the beginning of the initial buffer, because
   // we only use it after doing 'test', which only ever looks at at most 92 bytes
   s.img_buffer = s.img_buffer_original;
}


ubyte *stbi_load_main(stbi *s, int *x, int *y, int *comp, int req_comp)
{
    try
    {
        stbi_jpeg_test(s);
        stbi_rewind(s);
        return stbi_jpeg_load(s,x,y,comp,req_comp);
    }
    catch(STBImageException e)
    {
        stbi_rewind(s);
    }

    try
    {
        stbi_png_test(s);
        stbi_rewind(s);
        return stbi_png_load(s,x,y,comp,req_comp);
    }
    catch(STBImageException e)
    {
        stbi_rewind(s);
    }

    try
    {
        stbi_bmp_test(s);
        stbi_rewind(s);
        return stbi_bmp_load(s,x,y,comp,req_comp);
    }
    catch(STBImageException e)
    {
        stbi_rewind(s);
    }

    try
    {
        stbi_gif_test(s);
        stbi_rewind(s);
        return stbi_gif_load(s,x,y,comp,req_comp);
    }
    catch(STBImageException e)
    {
        stbi_rewind(s);
    }

    throw new STBImageException("Image not of any known type, or corrupt");
}

/// Loads an image from memory.
/// Throws: STBImageException on error.
ubyte* stbi_load_from_memory(void[] buffer, out int width, out int height, out int components, int requestedComponents)
{
   stbi s;
   start_mem(&s, cast(ubyte*)buffer.ptr, cast(int)(buffer.length));
   return stbi_load_main(&s, &width, &height, &components, requestedComponents);
}

/// Frees an image loaded by stb_image.
void stbi_image_free(void *retval_from_stbi_load)
{
    free(retval_from_stbi_load);
}

/// Load an image from memory and puts it in a ae.utils.graphics.image.Image.
/// Throws: STBImageException on error.
Image!RGBA stbiLoadImageAE(void[] buffer)
{
    int width, height, components;
    ubyte* data = stbi_load_from_memory(buffer, width, height, components, 4);
    ubyte[] range = data[0..width*height*4];
    scope(exit) stbi_image_free(data);

    auto result = Image!RGBA(width, height);
    size_t length = width * height * RGBA.sizeof;
    result.pixels[] = cast(RGBA[])(data[0..length]);
    return result;
}

//
// Common code used by all image loaders
//

enum : int
{
   SCAN_load=0,
   SCAN_type,
   SCAN_header
};


int get8(stbi *s)
{
   if (s.img_buffer < s.img_buffer_end)
      return *s.img_buffer++;

   return 0;
}

int at_eof(stbi *s)
{
   return s.img_buffer >= s.img_buffer_end;
}

ubyte get8u(stbi *s)
{
   return cast(ubyte) get8(s);
}

void skip(stbi *s, int n)
{
   s.img_buffer += n;
}

int getn(stbi *s, ubyte *buffer, int n)
{
   if (s.img_buffer+n <= s.img_buffer_end) {
      memcpy(buffer, s.img_buffer, n);
      s.img_buffer += n;
      return 1;
   } else
      return 0;
}

int get16(stbi *s)
{
   int z = get8(s);
   return (z << 8) + get8(s);
}

uint get32(stbi *s)
{
   uint z = get16(s);
   return (z << 16) + get16(s);
}

int get16le(stbi *s)
{
   int z = get8(s);
   return z + (get8(s) << 8);
}

uint get32le(stbi *s)
{
   uint z = get16le(s);
   return z + (get16le(s) << 16);
}

//
//  generic converter from built-in img_n to req_comp
//    individual types do this automatically as much as possible (e.g. jpeg
//    does all cases internally since it needs to colorspace convert anyway,
//    and it never has alpha, so very few cases ). png can automatically
//    interleave an alpha=255 channel, but falls back to this for other cases
//
//  assume data buffer is malloced, so malloc a new one and free that one
//  only failure mode is malloc failing

ubyte compute_y(int r, int g, int b)
{
   return cast(ubyte) (((r*77) + (g*150) +  (29*b)) >> 8);
}

ubyte *convert_format(ubyte *data, int img_n, int req_comp, uint x, uint y)
{
    int i,j;
    ubyte *good;

    if (req_comp == img_n) return data;
    assert(req_comp >= 1 && req_comp <= 4);

    good = cast(ubyte*) malloc(req_comp * x * y);
    if (good == null) {
        free(data);
        throw new STBImageException("Out of memory");
    }

    for (j=0; j < cast(int) y; ++j) {
        ubyte *src  = data + j * x * img_n   ;
        ubyte *dest = good + j * x * req_comp;

        // convert source image with img_n components to one with req_comp components;
        // avoid switch per pixel, so use switch per scanline and massive macros
        switch (img_n * 8 + req_comp)
        {
            case 1 * 8 + 2:
                for(i=x-1; i >= 0; --i, src += 1, dest += 2)
                    dest[0] = src[0], dest[1] = 255;
                break;
            case 1 * 8 + 3:
                for(i=x-1; i >= 0; --i, src += 1, dest += 3)
                    dest[0]=dest[1]=dest[2]=src[0];
                break;
            case 1 * 8 + 4:
                for(i=x-1; i >= 0; --i, src += 1, dest += 4)
                    dest[0]=dest[1]=dest[2]=src[0], dest[3]=255;
                break;
            case 2 * 8 + 1:
                for(i=x-1; i >= 0; --i, src += 2, dest += 1)
                    dest[0]=src[0];
                break;
            case 2 * 8 + 3:
                for(i=x-1; i >= 0; --i, src += 2, dest += 3)
                    dest[0]=dest[1]=dest[2]=src[0];
                break;
            case 2 * 8 + 4:
                for(i=x-1; i >= 0; --i, src += 2, dest += 4)
                    dest[0]=dest[1]=dest[2]=src[0], dest[3]=src[1];
                break;
            case 3 * 8 + 4:
                for(i=x-1; i >= 0; --i, src += 3, dest += 4)
                    dest[0]=src[0],dest[1]=src[1],dest[2]=src[2],dest[3]=255;
                break;
            case 3 * 8 + 1:
                for(i=x-1; i >= 0; --i, src += 3, dest += 1)
                    dest[0]=compute_y(src[0],src[1],src[2]);
                break;
            case 3 * 8 + 2:
                for(i=x-1; i >= 0; --i, src += 3, dest += 2)
                    dest[0]=compute_y(src[0],src[1],src[2]), dest[1] = 255;
                break;
            case 4 * 8 + 1:
                for(i=x-1; i >= 0; --i, src += 4, dest += 1)
                    dest[0]=compute_y(src[0],src[1],src[2]);
                break;
            case 4 * 8 + 2:
                for(i=x-1; i >= 0; --i, src += 4, dest += 2)
                    dest[0]=compute_y(src[0],src[1],src[2]), dest[1] = src[3];
                break;
            case 4 * 8 + 3:
                for(i=x-1; i >= 0; --i, src += 4, dest += 3)
                    dest[0]=src[0],dest[1]=src[1],dest[2]=src[2];
                break;
            default: assert(0);
        }
    }

    free(data);
    return good;
}

//
//  "baseline" JPEG/JFIF decoder (not actually fully baseline implementation)
//
//    simple implementation
//      - channel subsampling of at most 2 in each dimension
//      - doesn't support delayed output of y-dimension
//      - simple interface (only one output format: 8-bit interleaved RGB)
//      - doesn't try to recover corrupt jpegs
//      - doesn't allow partial loading, loading multiple at once
//      - still fast on x86 (copying globals into locals doesn't help x86)
//      - allocates lots of intermediate memory (full size of all components)
//        - non-interleaved case requires this anyway
//        - allows good upsampling (see next)
//    high-quality
//      - upsampled channels are bilinearly interpolated, even across blocks
//      - quality integer IDCT derived from IJG's 'slow'
//    performance
//      - fast huffman; reasonable integer IDCT
//      - uses a lot of intermediate memory, could cache poorly
//      - load http://nothings.org/remote/anemones.jpg 3 times on 2.8Ghz P4
//          stb_jpeg:   1.34 seconds (MSVC6, default release build)
//          stb_jpeg:   1.06 seconds (MSVC6, processor = Pentium Pro)
//          IJL11.dll:  1.08 seconds (compiled by intel)
//          IJG 1998:   0.98 seconds (MSVC6, makefile provided by IJG)
//          IJG 1998:   0.95 seconds (MSVC6, makefile + proc=PPro)

// huffman decoding acceleration
enum FAST_BITS = 9;  // larger handles more cases; smaller stomps less cache

struct huffman
{
   ubyte[1 << FAST_BITS] fast;
   // weirdly, repacking this into AoS is a 10% speed loss, instead of a win
   ushort[256] code;
   ubyte[256] values;
   ubyte[257] size;
   uint[18] maxcode;
   int[17] delta;   // old 'firstsymbol' - old 'firstcode'
}

struct jpeg
{
   stbi *s;
   huffman[4] huff_dc;
   huffman[4] huff_ac;
   ubyte[64][4] dequant;

// sizes for components, interleaved MCUs
   int img_h_max, img_v_max;
   int img_mcu_x, img_mcu_y;
   int img_mcu_w, img_mcu_h;

// definition of jpeg image component
   struct img_comp_
   {
      int id;
      int h,v;
      int tq;
      int hd,ha;
      int dc_pred;

      int x,y,w2,h2;
      ubyte *data;
      void *raw_data;
      ubyte *linebuf;
   }

   img_comp_[4] img_comp;

   uint         code_buffer; // jpeg entropy-coded buffer
   int            code_bits;   // number of valid bits
   ubyte          marker;      // marker seen while filling entropy buffer
   int            nomore;      // flag if we saw a marker so must stop

   int scan_n;
   int[4] order;
   int restart_interval, todo;
}


int build_huffman(huffman *h, int *count)
{
   int i,j,k=0,code;
   // build size list for each symbol (from JPEG spec)
   for (i=0; i < 16; ++i)
      for (j=0; j < count[i]; ++j)
         h.size[k++] = cast(ubyte) (i+1);
   h.size[k] = 0;

   // compute actual symbols (from jpeg spec)
   code = 0;
   k = 0;
   for(j=1; j <= 16; ++j) {
      // compute delta to add to code to compute symbol id
      h.delta[j] = k - code;
      if (h.size[k] == j) {
         while (h.size[k] == j)
            h.code[k++] = cast(ushort) (code++);
         if (code-1 >= (1 << j))
             throw new STBImageException("Bad code lengths, corrupt JPEG");
      }
      // compute largest code + 1 for this size, preshifted as needed later
      h.maxcode[j] = code << (16-j);
      code <<= 1;
   }
   h.maxcode[j] = 0xffffffff;

   // build non-spec acceleration table; 255 is flag for not-accelerated
   memset(h.fast.ptr, 255, 1 << FAST_BITS);
   for (i=0; i < k; ++i) {
      int s = h.size[i];
      if (s <= FAST_BITS) {
         int c = h.code[i] << (FAST_BITS-s);
         int m = 1 << (FAST_BITS-s);
         for (j=0; j < m; ++j) {
            h.fast[c+j] = cast(ubyte) i;
         }
      }
   }
   return 1;
}

void grow_buffer_unsafe(jpeg *j)
{
   do {
      int b = j.nomore ? 0 : get8(j.s);
      if (b == 0xff) {
         int c = get8(j.s);
         if (c != 0) {
            j.marker = cast(ubyte) c;
            j.nomore = 1;
            return;
         }
      }
      j.code_buffer |= b << (24 - j.code_bits);
      j.code_bits += 8;
   } while (j.code_bits <= 24);
}

// (1 << n) - 1
static immutable uint[17] bmask=[0,1,3,7,15,31,63,127,255,511,1023,2047,4095,8191,16383,32767,65535];

// decode a jpeg huffman value from the bitstream
int decode(jpeg *j, huffman *h)
{
   uint temp;
   int c,k;

   if (j.code_bits < 16) grow_buffer_unsafe(j);

   // look at the top FAST_BITS and determine what symbol ID it is,
   // if the code is <= FAST_BITS
   c = (j.code_buffer >> (32 - FAST_BITS)) & ((1 << FAST_BITS)-1);
   k = h.fast[c];
   if (k < 255) {
      int s = h.size[k];
      if (s > j.code_bits)
         return -1;
      j.code_buffer <<= s;
      j.code_bits -= s;
      return h.values[k];
   }

   // naive test is to shift the code_buffer down so k bits are
   // valid, then test against maxcode. To speed this up, we've
   // preshifted maxcode left so that it has (16-k) 0s at the
   // end; in other words, regardless of the number of bits, it
   // wants to be compared against something shifted to have 16;
   // that way we don't need to shift inside the loop.
   temp = j.code_buffer >> 16;
   for (k=FAST_BITS+1 ; ; ++k)
      if (temp < h.maxcode[k])
         break;
   if (k == 17) {
      // error! code not found
      j.code_bits -= 16;
      return -1;
   }

   if (k > j.code_bits)
      return -1;

   // convert the huffman code to the symbol id
   c = ((j.code_buffer >> (32 - k)) & bmask[k]) + h.delta[k];
   assert((((j.code_buffer) >> (32 - h.size[c])) & bmask[h.size[c]]) == h.code[c]);

   // convert the id to a symbol
   j.code_bits -= k;
   j.code_buffer <<= k;
   return h.values[c];
}

// combined JPEG 'receive' and JPEG 'extend', since baseline
// always extends everything it receives.
int extend_receive(jpeg *j, int n)
{
   uint m = 1 << (n-1);
   uint k;
   if (j.code_bits < n) grow_buffer_unsafe(j);

   k = stbi_lrot(j.code_buffer, n);
   j.code_buffer = k & ~bmask[n];
   k &= bmask[n];
   j.code_bits -= n;

   // the following test is probably a random branch that won't
   // predict well. I tried to table accelerate it but failed.
   // maybe it's compiling as a conditional move?
   if (k < m)
      return (-1 << n) + k + 1;
   else
      return k;
}

// given a value that's at position X in the zigzag stream,
// where does it appear in the 8x8 matrix coded as row-major?
static immutable ubyte[64+15] dezigzag =
[
    0,  1,  8, 16,  9,  2,  3, 10,
   17, 24, 32, 25, 18, 11,  4,  5,
   12, 19, 26, 33, 40, 48, 41, 34,
   27, 20, 13,  6,  7, 14, 21, 28,
   35, 42, 49, 56, 57, 50, 43, 36,
   29, 22, 15, 23, 30, 37, 44, 51,
   58, 59, 52, 45, 38, 31, 39, 46,
   53, 60, 61, 54, 47, 55, 62, 63,
   // let corrupt input sample past end
   63, 63, 63, 63, 63, 63, 63, 63,
   63, 63, 63, 63, 63, 63, 63
];

// decode one 64-entry block--
int decode_block(jpeg *j, short[64] data, huffman *hdc, huffman *hac, int b)
{
   int diff,dc,k;
   int t = decode(j, hdc);
   if (t < 0)
       throw new STBImageException("Bad huffman code, corrupt JPEG");

   // 0 all the ac values now so we can do it 32-bits at a time
   memset(data.ptr,0,64*(data[0]).sizeof);

   diff = t ? extend_receive(j, t) : 0;
   dc = j.img_comp[b].dc_pred + diff;
   j.img_comp[b].dc_pred = dc;
   data[0] = cast(short) dc;

   // decode AC components, see JPEG spec
   k = 1;
   do {
      int r,s;
      int rs = decode(j, hac);
      if (rs < 0)
         throw new STBImageException("Bad huffman code, corrupt JPEG");
      s = rs & 15;
      r = rs >> 4;
      if (s == 0) {
         if (rs != 0xf0) break; // end block
         k += 16;
      } else {
         k += r;
         // decode into unzigzag'd location
         data[dezigzag[k++]] = cast(short) extend_receive(j,s);
      }
   } while (k < 64);
   return 1;
}

// take a -128..127 value and clamp it and convert to 0..255
ubyte clamp(int x)
{
   // trick to use a single test to catch both cases
   if (cast(uint) x > 255) {
      if (x < 0) return 0;
      if (x > 255) return 255;
   }
   return cast(ubyte) x;
}

int f2f(double x)
{
    return cast(int)(x * 4096 + 0.5);
}

int fsh(int x)
{
    return x << 12;
}

// derived from jidctint -- DCT_ISLOW
void IDCT_1D(int s0, int s1, int s2, int s3, int s4, int s5, int s6, int s7,
             out int t0, out int t1, out int t2, out int t3,
             out int x0, out int x1, out int x2, out int x3)
{
   int p1,p2,p3,p4,p5;
   p2 = s2;
   p3 = s6;
   p1 = (p2+p3) * f2f(0.5411961f);
   t2 = p1 + p3*f2f(-1.847759065f);
   t3 = p1 + p2*f2f( 0.765366865f);
   p2 = s0;
   p3 = s4;
   t0 = fsh(p2+p3);
   t1 = fsh(p2-p3);
   x0 = t0+t3;
   x3 = t0-t3;
   x1 = t1+t2;
   x2 = t1-t2;
   t0 = s7;
   t1 = s5;
   t2 = s3;
   t3 = s1;
   p3 = t0+t2;
   p4 = t1+t3;
   p1 = t0+t3;
   p2 = t1+t2;
   p5 = (p3+p4)*f2f( 1.175875602f);
   t0 = t0*f2f( 0.298631336f);
   t1 = t1*f2f( 2.053119869f);
   t2 = t2*f2f( 3.072711026f);
   t3 = t3*f2f( 1.501321110f);
   p1 = p5 + p1*f2f(-0.899976223f);
   p2 = p5 + p2*f2f(-2.562915447f);
   p3 = p3*f2f(-1.961570560f);
   p4 = p4*f2f(-0.390180644f);
   t3 += p1+p4;
   t2 += p2+p3;
   t1 += p2+p4;
   t0 += p1+p3;
 }

alias stbi_dequantize_t = ubyte;

// .344 seconds on 3*anemones.jpg
void idct_block(ubyte *out_, int out_stride, short[64] data, stbi_dequantize_t *dequantize)
{
   int i;
   int[64] val;
   int*v = val.ptr;
   stbi_dequantize_t *dq = dequantize;
   ubyte *o;
   short *d = data.ptr;

   // columns
   for (i=0; i < 8; ++i,++d,++dq, ++v) {
      // if all zeroes, shortcut -- this avoids dequantizing 0s and IDCTing
      if (d[ 8]==0 && d[16]==0 && d[24]==0 && d[32]==0
           && d[40]==0 && d[48]==0 && d[56]==0) {
         //    no shortcut                 0     seconds
         //    (1|2|3|4|5|6|7)==0          0     seconds
         //    all separate               -0.047 seconds
         //    1 && 2|3 && 4|5 && 6|7:    -0.047 seconds
         int dcterm = d[0] * dq[0] << 2;
         v[0] = v[8] = v[16] = v[24] = v[32] = v[40] = v[48] = v[56] = dcterm;
      } else {
         int t0, t1, t2, t3, x0, x1, x2, x3;
         IDCT_1D(d[ 0]*dq[ 0],d[ 8]*dq[ 8],d[16]*dq[16],d[24]*dq[24],
                 d[32]*dq[32],d[40]*dq[40],d[48]*dq[48],d[56]*dq[56],
                 t0, t1, t2, t3, x0, x1, x2, x3);
         // constants scaled things up by 1<<12; let's bring them back
         // down, but keep 2 extra bits of precision
         x0 += 512; x1 += 512; x2 += 512; x3 += 512;
         v[ 0] = (x0+t3) >> 10;
         v[56] = (x0-t3) >> 10;
         v[ 8] = (x1+t2) >> 10;
         v[48] = (x1-t2) >> 10;
         v[16] = (x2+t1) >> 10;
         v[40] = (x2-t1) >> 10;
         v[24] = (x3+t0) >> 10;
         v[32] = (x3-t0) >> 10;
      }
   }

   for (i=0, v=val.ptr, o=out_; i < 8; ++i,v+=8,o+=out_stride) {

      // no fast case since the first 1D IDCT spread components out
      int t0, t1, t2, t3, x0, x1, x2, x3;
      IDCT_1D(v[0],v[1],v[2],v[3],v[4],v[5],v[6],v[7], t0, t1, t2, t3, x0, x1, x2, x3);
      // constants scaled things up by 1<<12, plus we had 1<<2 from first
      // loop, plus horizontal and vertical each scale by sqrt(8) so together
      // we've got an extra 1<<3, so 1<<17 total we need to remove.
      // so we want to round that, which means adding 0.5 * 1<<17,
      // aka 65536. Also, we'll end up with -128 to 127 that we want
      // to encode as 0..255 by adding 128, so we'll add that before the shift
      x0 += 65536 + (128<<17);
      x1 += 65536 + (128<<17);
      x2 += 65536 + (128<<17);
      x3 += 65536 + (128<<17);
      // tried computing the shifts into temps, or'ing the temps to see
      // if any were out of range, but that was slower
      o[0] = clamp((x0+t3) >> 17);
      o[7] = clamp((x0-t3) >> 17);
      o[1] = clamp((x1+t2) >> 17);
      o[6] = clamp((x1-t2) >> 17);
      o[2] = clamp((x2+t1) >> 17);
      o[5] = clamp((x2-t1) >> 17);
      o[3] = clamp((x3+t0) >> 17);
      o[4] = clamp((x3-t0) >> 17);
   }
}


enum MARKER_none = 0xff;

// if there's a pending marker from the entropy stream, return that
// otherwise, fetch from the stream and get a marker. if there's no
// marker, return 0xff, which is never a valid marker value
ubyte get_marker(jpeg *j)
{
   ubyte x;
   if (j.marker != MARKER_none) { x = j.marker; j.marker = MARKER_none; return x; }
   x = get8u(j.s);
   if (x != 0xff) return MARKER_none;
   while (x == 0xff)
      x = get8u(j.s);
   return x;
}

// in each scan, we'll have scan_n components, and the order
// of the components is specified by order[]
bool RESTART(int x)
{
    return (x >= 0xd0) && (x <= 0xd7);
}

// after a restart interval, reset the entropy decoder and
// the dc prediction
void reset(jpeg *j)
{
   j.code_bits = 0;
   j.code_buffer = 0;
   j.nomore = 0;
   j.img_comp[0].dc_pred = j.img_comp[1].dc_pred = j.img_comp[2].dc_pred = 0;
   j.marker = MARKER_none;
   j.todo = j.restart_interval ? j.restart_interval : 0x7fffffff;
   // no more than 1<<31 MCUs if no restart_interal? that's plenty safe,
   // since we don't even allow 1<<30 pixels
}

int parse_entropy_coded_data(jpeg *z)
{
   reset(z);
   if (z.scan_n == 1) {
      int i,j;
      short[64] data;
      int n = z.order[0];
      // non-interleaved data, we just need to process one block at a time,
      // in trivial scanline order
      // number of blocks to do just depends on how many actual "pixels" this
      // component has, independent of interleaved MCU blocking and such
      int w = (z.img_comp[n].x+7) >> 3;
      int h = (z.img_comp[n].y+7) >> 3;
      for (j=0; j < h; ++j) {
         for (i=0; i < w; ++i) {
            if (!decode_block(z, data, z.huff_dc.ptr+z.img_comp[n].hd, z.huff_ac.ptr+z.img_comp[n].ha, n)) return 0;
            idct_block(z.img_comp[n].data+z.img_comp[n].w2*j*8+i*8, z.img_comp[n].w2, data, z.dequant[z.img_comp[n].tq].ptr);
            // every data block is an MCU, so countdown the restart interval
            if (--z.todo <= 0) {
               if (z.code_bits < 24) grow_buffer_unsafe(z);
               // if it's NOT a restart, then just bail, so we get corrupt data
               // rather than no data
               if (!RESTART(z.marker)) return 1;
               reset(z);
            }
         }
      }
   } else { // interleaved!
      int i,j,k,x,y;
      short[64] data;
      for (j=0; j < z.img_mcu_y; ++j) {
         for (i=0; i < z.img_mcu_x; ++i) {
            // scan an interleaved mcu... process scan_n components in order
            for (k=0; k < z.scan_n; ++k) {
               int n = z.order[k];
               // scan out an mcu's worth of this component; that's just determined
               // by the basic H and V specified for the component
               for (y=0; y < z.img_comp[n].v; ++y) {
                  for (x=0; x < z.img_comp[n].h; ++x) {
                     int x2 = (i*z.img_comp[n].h + x)*8;
                     int y2 = (j*z.img_comp[n].v + y)*8;
                     if (!decode_block(z, data, z.huff_dc.ptr+z.img_comp[n].hd, z.huff_ac.ptr+z.img_comp[n].ha, n)) return 0;
                     idct_block(z.img_comp[n].data+z.img_comp[n].w2*y2+x2, z.img_comp[n].w2, data, z.dequant[z.img_comp[n].tq].ptr);
                  }
               }
            }
            // after all interleaved components, that's an interleaved MCU,
            // so now count down the restart interval
            if (--z.todo <= 0) {
               if (z.code_bits < 24) grow_buffer_unsafe(z);
               // if it's NOT a restart, then just bail, so we get corrupt data
               // rather than no data
               if (!RESTART(z.marker)) return 1;
               reset(z);
            }
         }
      }
   }
   return 1;
}

int process_marker(jpeg *z, int m)
{
   int L;
   switch (m) {

      case MARKER_none: // no marker found
         throw new STBImageException("Expected marker, corrupt JPEG");

      case 0xC2: // SOF - progressive
          throw new STBImageException("JPEG format not supported (progressive)");

      case 0xDD: // DRI - specify restart interval
         if (get16(z.s) != 4)
             throw new STBImageException("Bad DRI len, corrupt JPEG");
         z.restart_interval = get16(z.s);
         return 1;

      case 0xDB: // DQT - define quantization table
         L = get16(z.s)-2;
         while (L > 0) {
            int q = get8(z.s);
            int p = q >> 4;
            int t = q & 15,i;
            if (p != 0)
               throw new STBImageException("Bad DQT type, corrupt JPEG");
            if (t > 3)
               throw new STBImageException("Bad DQT table, corrupt JPEG");
            for (i=0; i < 64; ++i)
               z.dequant[t][dezigzag[i]] = get8u(z.s);
            L -= 65;
         }
         return L==0;

      case 0xC4: // DHT - define huffman table
         L = get16(z.s)-2;
         while (L > 0) {
            ubyte *v;
            int[16] sizes;
            int i;
            int m_ = 0;
            int q = get8(z.s);
            int tc = q >> 4;
            int th = q & 15;
            if (tc > 1 || th > 3)
                throw new STBImageException("Bad DHT header, corrupt JPEG");
            for (i=0; i < 16; ++i) {
               sizes[i] = get8(z.s);
               m_ += sizes[i];
            }
            L -= 17;
            if (tc == 0) {
               if (!build_huffman(z.huff_dc.ptr+th, sizes.ptr)) return 0;
               v = z.huff_dc[th].values.ptr;
            } else {
               if (!build_huffman(z.huff_ac.ptr+th, sizes.ptr)) return 0;
               v = z.huff_ac[th].values.ptr;
            }
            for (i=0; i < m_; ++i)
               v[i] = get8u(z.s);
            L -= m_;
         }
         return L==0;

      default:
         break;
   }
   // check for comment block or APP blocks
   if ((m >= 0xE0 && m <= 0xEF) || m == 0xFE) {
      skip(z.s, get16(z.s)-2);
      return 1;
   }
   return 0;
}

// after we see SOS
int process_scan_header(jpeg *z)
{
   int i;
   int Ls = get16(z.s);
   z.scan_n = get8(z.s);
   if (z.scan_n < 1 || z.scan_n > 4 || z.scan_n > cast(int) z.s.img_n)
      throw new STBImageException("Bad SOS component count, Corrupt JPEG");

   if (Ls != 6+2*z.scan_n)
      throw new STBImageException("Bad SOS length, Corrupt JPEG");

   for (i=0; i < z.scan_n; ++i) {
      int id = get8(z.s), which;
      int q = get8(z.s);
      for (which = 0; which < z.s.img_n; ++which)
         if (z.img_comp[which].id == id)
            break;
      if (which == z.s.img_n) return 0;
      z.img_comp[which].hd = q >> 4;
      if (z.img_comp[which].hd > 3)
         throw new STBImageException("Bad DC huff, Corrupt JPEG");
      z.img_comp[which].ha = q & 15;
      if (z.img_comp[which].ha > 3)
         throw new STBImageException("Bad AC huff, Corrupt JPEG");
      z.order[i] = which;
   }
   if (get8(z.s) != 0)
      throw new STBImageException("Bad SOS, Corrupt JPEG");
   get8(z.s); // should be 63, but might be 0
   if (get8(z.s) != 0)
      throw new STBImageException("Bad SOS, Corrupt JPEG");

   return 1;
}

int process_frame_header(jpeg *z, int scan)
{
   stbi *s = z.s;
   int Lf,p,i,q, h_max=1,v_max=1,c;
   Lf = get16(s);         if (Lf < 11) throw new STBImageException("Bad SOF len, Corrupt JPEG");
   p  = get8(s);          if (p != 8) throw new STBImageException("JPEG format not supported: 8-bit only"); // JPEG baseline
   s.img_y = get16(s);   if (s.img_y == 0) throw new STBImageException("No header height, JPEG format not supported: delayed height"); // Legal, but we don't handle it--but neither does IJG
   s.img_x = get16(s);   if (s.img_x == 0) throw new STBImageException("0 width, corrupt JPEG"); // JPEG requires
   c = get8(s);
   if (c != 3 && c != 1) throw new STBImageException("Bad component count, corrupt JPEG");    // JFIF requires
   s.img_n = c;
   for (i=0; i < c; ++i) {
      z.img_comp[i].data = null;
      z.img_comp[i].linebuf = null;
   }

   if (Lf != 8+3*s.img_n) throw new STBImageException("Bad SOF len, corrupt JPEG");

   for (i=0; i < s.img_n; ++i) {
      z.img_comp[i].id = get8(s);
      if (z.img_comp[i].id != i+1)   // JFIF requires
         if (z.img_comp[i].id != i)  // some version of jpegtran outputs non-JFIF-compliant files!
            throw new STBImageException("Bad component ID, corrupt JPEG");
      q = get8(s);
      z.img_comp[i].h = (q >> 4);  if (!z.img_comp[i].h || z.img_comp[i].h > 4) throw new STBImageException("Bad H, corrupt JPEG");
      z.img_comp[i].v = q & 15;    if (!z.img_comp[i].v || z.img_comp[i].v > 4) throw new STBImageException("Bad V, corrupt JPEG");
      z.img_comp[i].tq = get8(s);  if (z.img_comp[i].tq > 3) throw new STBImageException("Bad TQ, corrupt JPEG");
   }

   if (scan != SCAN_load) return 1;

   if ((1 << 30) / s.img_x / s.img_n < s.img_y) throw new STBImageException("Image too large to decode");

   for (i=0; i < s.img_n; ++i) {
      if (z.img_comp[i].h > h_max) h_max = z.img_comp[i].h;
      if (z.img_comp[i].v > v_max) v_max = z.img_comp[i].v;
   }

   // compute interleaved mcu info
   z.img_h_max = h_max;
   z.img_v_max = v_max;
   z.img_mcu_w = h_max * 8;
   z.img_mcu_h = v_max * 8;
   z.img_mcu_x = (s.img_x + z.img_mcu_w-1) / z.img_mcu_w;
   z.img_mcu_y = (s.img_y + z.img_mcu_h-1) / z.img_mcu_h;

   for (i=0; i < s.img_n; ++i) {
      // number of effective pixels (e.g. for non-interleaved MCU)
      z.img_comp[i].x = (s.img_x * z.img_comp[i].h + h_max-1) / h_max;
      z.img_comp[i].y = (s.img_y * z.img_comp[i].v + v_max-1) / v_max;
      // to simplify generation, we'll allocate enough memory to decode
      // the bogus oversized data from using interleaved MCUs and their
      // big blocks (e.g. a 16x16 iMCU on an image of width 33); we won't
      // discard the extra data until colorspace conversion
      z.img_comp[i].w2 = z.img_mcu_x * z.img_comp[i].h * 8;
      z.img_comp[i].h2 = z.img_mcu_y * z.img_comp[i].v * 8;
      z.img_comp[i].raw_data = malloc(z.img_comp[i].w2 * z.img_comp[i].h2+15);
      if (z.img_comp[i].raw_data == null) {
         for(--i; i >= 0; --i) {
            free(z.img_comp[i].raw_data);
            z.img_comp[i].data = null;
         }
         throw new STBImageException("Out of memory");
      }
      // align blocks for installable-idct using mmx/sse
      z.img_comp[i].data = cast(ubyte*) (( cast(size_t) z.img_comp[i].raw_data + 15) & ~15);
      z.img_comp[i].linebuf = null;
   }

   return 1;
}

// use comparisons since in some cases we handle more than one case (e.g. SOF)
bool DNL(int x) { return x == 0xdc; }
bool SOI(int x) { return x == 0xd8; }
bool EOI(int x) { return x == 0xd9; }
bool SOF(int x) { return x == 0xc0 || x == 0xc1; }
bool SOS(int x) { return x == 0xda; }

int decode_jpeg_header(jpeg *z, int scan)
{
   int m;
   z.marker = MARKER_none; // initialize cached marker to empty
   m = get_marker(z);
   if (!SOI(m)) throw new STBImageException("No SOI, corrupt JPEG");
   if (scan == SCAN_type) return 1;
   m = get_marker(z);
   while (!SOF(m))
   {

      if (!process_marker(z,m)) return 0;
      m = get_marker(z);



      while (m == MARKER_none)
      {
         // some files have extra padding after their blocks, so ok, we'll scan
         if (at_eof(z.s)) throw new STBImageException("No SOF, corrupt JPEG");
         m = get_marker(z);
      }
   }
   if (!process_frame_header(z, scan)) return 0;
   return 1;
}

int decode_jpeg_image(jpeg *j)
{
   int m;
   j.restart_interval = 0;
   if (!decode_jpeg_header(j, SCAN_load)) return 0;
   m = get_marker(j);
   while (!EOI(m)) {
      if (SOS(m)) {
         if (!process_scan_header(j)) return 0;
         if (!parse_entropy_coded_data(j)) return 0;
         if (j.marker == MARKER_none ) {
            // handle 0s at the end of image data from IP Kamera 9060
            while (!at_eof(j.s)) {
               int x = get8(j.s);
               if (x == 255) {
                  j.marker = get8u(j.s);
                  break;
               } else if (x != 0) {
                  return 0;
               }
            }
            // if we reach eof without hitting a marker, get_marker() below will fail and we'll eventually return 0
         }
      } else {
         if (!process_marker(j, m)) return 0;
      }
      m = get_marker(j);
   }
   return 1;
}

// static jfif-centered resampling (across block boundaries)

alias resample_row_func = ubyte* function(ubyte *out_, ubyte *in0, ubyte *in1, int w, int hs);

ubyte div4(int x)
{
    return cast(ubyte)(x >> 2);
}

ubyte *resample_row_1(ubyte *out_, ubyte *in_near, ubyte *in_far, int w, int hs)
{
   return in_near;
}

ubyte* resample_row_v_2(ubyte *out_, ubyte *in_near, ubyte *in_far, int w, int hs)
{
   // need to generate two samples vertically for every one in input
   int i;
   for (i=0; i < w; ++i)
      out_[i] = div4(3*in_near[i] + in_far[i] + 2);
   return out_;
}

ubyte*  resample_row_h_2(ubyte *out_, ubyte *in_near, ubyte *in_far, int w, int hs)
{
   // need to generate two samples horizontally for every one in input
   int i;
   ubyte *input = in_near;

   if (w == 1) {
      // if only one sample, can't do any interpolation
      out_[0] = out_[1] = input[0];
      return out_;
   }

   out_[0] = input[0];
   out_[1] = div4(input[0]*3 + input[1] + 2);
   for (i=1; i < w-1; ++i) {
      int n = 3*input[i]+2;
      out_[i*2+0] = div4(n+input[i-1]);
      out_[i*2+1] = div4(n+input[i+1]);
   }
   out_[i*2+0] = div4(input[w-2]*3 + input[w-1] + 2);
   out_[i*2+1] = input[w-1];

   return out_;
}

ubyte div16(int x)
{
    return cast(ubyte)(x >> 4);
}


ubyte *resample_row_hv_2(ubyte *out_, ubyte *in_near, ubyte *in_far, int w, int hs)
{
   // need to generate 2x2 samples for every one in input
   int i,t0,t1;
   if (w == 1) {
      out_[0] = out_[1] = div4(3*in_near[0] + in_far[0] + 2);
      return out_;
   }

   t1 = 3*in_near[0] + in_far[0];
   out_[0] = div4(t1+2);
   for (i=1; i < w; ++i) {
      t0 = t1;
      t1 = 3*in_near[i]+in_far[i];
      out_[i*2-1] = div16(3*t0 + t1 + 8);
      out_[i*2  ] = div16(3*t1 + t0 + 8);
   }
   out_[w*2-1] = div4(t1+2);

   return out_;
}

ubyte *resample_row_generic(ubyte *out_, ubyte *in_near, ubyte *in_far, int w, int hs)
{
   // resample with nearest-neighbor
   int i,j;
   in_far = in_far;
   for (i=0; i < w; ++i)
      for (j=0; j < hs; ++j)
         out_[i*hs+j] = in_near[i];
   return out_;
}

int float2fixed(double x)
{
    return cast(int)((x) * 65536 + 0.5);
}

// 0.38 seconds on 3*anemones.jpg   (0.25 with processor = Pro)
// VC6 without processor=Pro is generating multiple LEAs per multiply!
void YCbCr_to_RGB_row(ubyte *out_, const ubyte *y, const ubyte *pcb, const ubyte *pcr, int count, int step)
{
   int i;
   for (i=0; i < count; ++i) {
      int y_fixed = (y[i] << 16) + 32768; // rounding
      int r,g,b;
      int cr = pcr[i] - 128;
      int cb = pcb[i] - 128;
      r = y_fixed + cr*float2fixed(1.40200f);
      g = y_fixed - cr*float2fixed(0.71414f) - cb*float2fixed(0.34414f);
      b = y_fixed                            + cb*float2fixed(1.77200f);
      r >>= 16;
      g >>= 16;
      b >>= 16;
      if (cast(uint) r > 255) { if (r < 0) r = 0; else r = 255; }
      if (cast(uint) g > 255) { if (g < 0) g = 0; else g = 255; }
      if (cast(uint) b > 255) { if (b < 0) b = 0; else b = 255; }
      out_[0] = cast(ubyte)r;
      out_[1] = cast(ubyte)g;
      out_[2] = cast(ubyte)b;
      out_[3] = 255;
      out_ += step;
   }
}

// clean up the temporary component buffers
void cleanup_jpeg(jpeg *j)
{
   int i;
   for (i=0; i < j.s.img_n; ++i) {
      if (j.img_comp[i].data) {
         free(j.img_comp[i].raw_data);
         j.img_comp[i].data = null;
      }
      if (j.img_comp[i].linebuf) {
         free(j.img_comp[i].linebuf);
         j.img_comp[i].linebuf = null;
      }
   }
}

struct stbi_resample
{
   resample_row_func resample;
   ubyte* line0;
   ubyte* line1;
   int hs,vs;   // expansion factor in each axis
   int w_lores; // horizontal pixels pre-expansion
   int ystep;   // how far through vertical expansion we are
   int ypos;    // which pre-expansion row we're on
} ;

ubyte *load_jpeg_image(jpeg *z, int *out_x, int *out_y, int *comp, int req_comp)
{
   int n, decode_n;
   // validate req_comp
   if (req_comp < 0 || req_comp > 4)
       throw new STBImageException("Internal error: bad req_comp");
   z.s.img_n = 0;

   // load a jpeg image from whichever source
   if (!decode_jpeg_image(z)) { cleanup_jpeg(z); return null; }

   // determine actual number of components to generate
   n = req_comp ? req_comp : z.s.img_n;

   if (z.s.img_n == 3 && n < 3)
      decode_n = 1;
   else
      decode_n = z.s.img_n;

   // resample and color-convert
   {
      int k;
      uint i,j;
      ubyte *output;
      ubyte*[4] coutput;

      stbi_resample[4] res_comp;

      for (k=0; k < decode_n; ++k) {
         stbi_resample *r = &res_comp[k];

         // allocate line buffer big enough for upsampling off the edges
         // with upsample factor of 4
         z.img_comp[k].linebuf = cast(ubyte*) malloc(z.s.img_x + 3);
         if (!z.img_comp[k].linebuf)
         {
             cleanup_jpeg(z);
             throw new STBImageException("Out of memory");
         }

         r.hs      = z.img_h_max / z.img_comp[k].h;
         r.vs      = z.img_v_max / z.img_comp[k].v;
         r.ystep   = r.vs >> 1;
         r.w_lores = (z.s.img_x + r.hs-1) / r.hs;
         r.ypos    = 0;
         r.line0   = r.line1 = z.img_comp[k].data;

         if      (r.hs == 1 && r.vs == 1) r.resample = &resample_row_1;
         else if (r.hs == 1 && r.vs == 2) r.resample = &resample_row_v_2;
         else if (r.hs == 2 && r.vs == 1) r.resample = &resample_row_h_2;
         else if (r.hs == 2 && r.vs == 2) r.resample = &resample_row_hv_2;
         else                               r.resample = &resample_row_generic;
      }

      // can't error after this so, this is safe
      output = cast(ubyte*) malloc(n * z.s.img_x * z.s.img_y + 1);
      if (!output) { cleanup_jpeg(z); throw new STBImageException("Out of memory"); }

      // now go ahead and resample
      for (j=0; j < z.s.img_y; ++j) {
         ubyte *out_ = output + n * z.s.img_x * j;
         for (k=0; k < decode_n; ++k) {
            stbi_resample *r = &res_comp[k];
            int y_bot = r.ystep >= (r.vs >> 1);
            coutput[k] = r.resample(z.img_comp[k].linebuf,
                                     y_bot ? r.line1 : r.line0,
                                     y_bot ? r.line0 : r.line1,
                                     r.w_lores, r.hs);
            if (++r.ystep >= r.vs) {
               r.ystep = 0;
               r.line0 = r.line1;
               if (++r.ypos < z.img_comp[k].y)
                  r.line1 += z.img_comp[k].w2;
            }
         }
         if (n >= 3) {
            ubyte *y = coutput[0];
            if (z.s.img_n == 3) {
               YCbCr_to_RGB_row(out_, y, coutput[1], coutput[2], z.s.img_x, n);
            } else
               for (i=0; i < z.s.img_x; ++i) {
                  out_[0] = out_[1] = out_[2] = y[i];
                  out_[3] = 255; // not used if n==3
                  out_ += n;
               }
         } else {
            ubyte *y = coutput[0];
            if (n == 1)
               for (i=0; i < z.s.img_x; ++i) out_[i] = y[i];
            else
               for (i=0; i < z.s.img_x; ++i) *out_++ = y[i], *out_++ = 255;
         }
      }
      cleanup_jpeg(z);
      *out_x = z.s.img_x;
      *out_y = z.s.img_y;
      if (comp) *comp  = z.s.img_n; // report original components, not output
      return output;
   }
}

ubyte* stbi_jpeg_load(stbi *s, int *x, int *y, int *comp, int req_comp)
{
   jpeg j;
   j.s = s;
   return load_jpeg_image(&j, x,y,comp,req_comp);
}

void stbi_jpeg_test(stbi *s)
{
   jpeg j;
   j.s = s;
   int r = decode_jpeg_header(&j, SCAN_type);
   if (r == 0)
       throw new STBImageException("Couldn't decode JPEG header");
}


// public domain zlib decode    v0.2  Sean Barrett 2006-11-18
//    simple implementation
//      - all input must be provided in an upfront buffer
//      - all output is written to a single output buffer (can malloc/realloc)
//    performance
//      - fast huffman

// fast-way is faster to check than jpeg huffman, but slow way is slower
enum ZFAST_BITS = 9; // accelerate all cases in default tables
enum ZFAST_MASK = ((1 << ZFAST_BITS) - 1);

// zlib-style huffman encoding
// (jpegs packs from left, zlib from right, so can't share code)
struct zhuffman
{
   ushort[1 << ZFAST_BITS] fast;
   ushort[16] firstcode;
   int[17] maxcode;
   ushort[16] firstsymbol;
   ubyte[288] size;
   ushort[288] value;
} ;

int bitreverse16(int n)
{
  n = ((n & 0xAAAA) >>  1) | ((n & 0x5555) << 1);
  n = ((n & 0xCCCC) >>  2) | ((n & 0x3333) << 2);
  n = ((n & 0xF0F0) >>  4) | ((n & 0x0F0F) << 4);
  n = ((n & 0xFF00) >>  8) | ((n & 0x00FF) << 8);
  return n;
}

int bit_reverse(int v, int bits)
{
   assert(bits <= 16);
   // to bit reverse n bits, reverse 16 and shift
   // e.g. 11 bits, bit reverse and shift away 5
   return bitreverse16(v) >> (16-bits);
}

int zbuild_huffman(zhuffman *z, ubyte *sizelist, int num)
{
   int i,k=0;
   int code;
   int[16] next_code;
   int[17] sizes;

   // DEFLATE spec for generating codes
   memset(sizes.ptr, 0, sizes.sizeof);
   memset(z.fast.ptr, 255, z.fast.sizeof);
   for (i=0; i < num; ++i)
      ++sizes[sizelist[i]];
   sizes[0] = 0;
   for (i=1; i < 16; ++i)
      assert(sizes[i] <= (1 << i));
   code = 0;
   for (i=1; i < 16; ++i) {
      next_code[i] = code;
      z.firstcode[i] = cast(ushort) code;
      z.firstsymbol[i] = cast(ushort) k;
      code = (code + sizes[i]);
      if (sizes[i])
         if (code-1 >= (1 << i))
            throw new STBImageException("Bad codelength, corrupt JPEG");
      z.maxcode[i] = code << (16-i); // preshift for inner loop
      code <<= 1;
      k += sizes[i];
   }
   z.maxcode[16] = 0x10000; // sentinel
   for (i=0; i < num; ++i) {
      int s = sizelist[i];
      if (s) {
         int c = next_code[s] - z.firstcode[s] + z.firstsymbol[s];
         z.size[c] = cast(ubyte)s;
         z.value[c] = cast(ushort)i;
         if (s <= ZFAST_BITS) {
            int k_ = bit_reverse(next_code[s],s);
            while (k_ < (1 << ZFAST_BITS)) {
               z.fast[k_] = cast(ushort) c;
               k_ += (1 << s);
            }
         }
         ++next_code[s];
      }
   }
   return 1;
}

// zlib-from-memory implementation for PNG reading
//    because PNG allows splitting the zlib stream arbitrarily,
//    and it's annoying structurally to have PNG call ZLIB call PNG,
//    we require PNG read all the IDATs and combine them into a single
//    memory buffer

struct zbuf
{
   const(ubyte) *zbuffer;
   const(ubyte) *zbuffer_end;
   int num_bits;
   uint code_buffer;

   ubyte *zout;
   ubyte *zout_start;
   ubyte *zout_end;
   int   z_expandable;

   zhuffman z_length, z_distance;
} ;

int zget8(zbuf *z)
{
   if (z.zbuffer >= z.zbuffer_end) return 0;
   return *z.zbuffer++;
}

void fill_bits(zbuf *z)
{
   do {
      assert(z.code_buffer < (1U << z.num_bits));
      z.code_buffer |= zget8(z) << z.num_bits;
      z.num_bits += 8;
   } while (z.num_bits <= 24);
}

uint zreceive(zbuf *z, int n)
{
   uint k;
   if (z.num_bits < n) fill_bits(z);
   k = z.code_buffer & ((1 << n) - 1);
   z.code_buffer >>= n;
   z.num_bits -= n;
   return k;
}

int zhuffman_decode(zbuf *a, zhuffman *z)
{
   int b,s,k;
   if (a.num_bits < 16) fill_bits(a);
   b = z.fast[a.code_buffer & ZFAST_MASK];
   if (b < 0xffff) {
      s = z.size[b];
      a.code_buffer >>= s;
      a.num_bits -= s;
      return z.value[b];
   }

   // not resolved by fast table, so compute it the slow way
   // use jpeg approach, which requires MSbits at top
   k = bit_reverse(a.code_buffer, 16);
   for (s=ZFAST_BITS+1; ; ++s)
      if (k < z.maxcode[s])
         break;
   if (s == 16) return -1; // invalid code!
   // code size is s, so:
   b = (k >> (16-s)) - z.firstcode[s] + z.firstsymbol[s];
   assert(z.size[b] == s);
   a.code_buffer >>= s;
   a.num_bits -= s;
   return z.value[b];
}

int expand(zbuf *z, int n)  // need to make room for n bytes
{
   ubyte *q;
   int cur, limit;
   if (!z.z_expandable)
      throw new STBImageException("Output buffer limit, corrupt PNG");
   cur   = cast(int) (z.zout     - z.zout_start);
   limit = cast(int) (z.zout_end - z.zout_start);
   while (cur + n > limit)
      limit *= 2;
   q = cast(ubyte*) realloc(z.zout_start, limit);
   if (q == null)
      throw new STBImageException("Out of memory");
   z.zout_start = q;
   z.zout       = q + cur;
   z.zout_end   = q + limit;
   return 1;
}

static immutable int[31] length_base = [
   3,4,5,6,7,8,9,10,11,13,
   15,17,19,23,27,31,35,43,51,59,
   67,83,99,115,131,163,195,227,258,0,0 ];

static immutable int[31] length_extra =
[ 0,0,0,0,0,0,0,0,1,1,1,1,2,2,2,2,3,3,3,3,4,4,4,4,5,5,5,5,0,0,0 ];

static immutable int[32] dist_base = [ 1,2,3,4,5,7,9,13,17,25,33,49,65,97,129,193,
257,385,513,769,1025,1537,2049,3073,4097,6145,8193,12289,16385,24577,0,0];

static immutable int[32] dist_extra =
[ 0,0,0,0,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,13,13];

int parse_huffman_block(zbuf *a)
{
   for(;;) {
      int z = zhuffman_decode(a, &a.z_length);
      if (z < 256) {
         if (z < 0)
             throw new STBImageException("Bad Huffman code, corrupt PNG");
         if (a.zout >= a.zout_end) if (!expand(a, 1)) return 0;
         *a.zout++ = cast(ubyte) z;
      } else {
         ubyte *p;
         int len,dist;
         if (z == 256) return 1;
         z -= 257;
         len = length_base[z];
         if (length_extra[z]) len += zreceive(a, length_extra[z]);
         z = zhuffman_decode(a, &a.z_distance);
         if (z < 0) throw new STBImageException("Bad Huffman code, corrupt PNG");
         dist = dist_base[z];
         if (dist_extra[z]) dist += zreceive(a, dist_extra[z]);
         if (a.zout - a.zout_start < dist) throw new STBImageException("Bad dist, corrupt PNG");
         if (a.zout + len > a.zout_end) if (!expand(a, len)) return 0;
         p = a.zout - dist;
         while (len--)
            *a.zout++ = *p++;
      }
   }
}

int compute_huffman_codes(zbuf *a)
{
   static immutable ubyte[19] length_dezigzag = [ 16,17,18,0,8,7,9,6,10,5,11,4,12,3,13,2,14,1,15 ];
   zhuffman z_codelength;
   ubyte[286+32+137] lencodes;//padding for maximum single op
   ubyte[19] codelength_sizes;
   int i,n;

   int hlit  = zreceive(a,5) + 257;
   int hdist = zreceive(a,5) + 1;
   int hclen = zreceive(a,4) + 4;

   memset(codelength_sizes.ptr, 0, codelength_sizes.sizeof);
   for (i=0; i < hclen; ++i) {
      int s = zreceive(a,3);
      codelength_sizes[length_dezigzag[i]] = cast(ubyte) s;
   }
   if (!zbuild_huffman(&z_codelength, codelength_sizes.ptr, 19)) return 0;

   n = 0;
   while (n < hlit + hdist) {
      int c = zhuffman_decode(a, &z_codelength);
      assert(c >= 0 && c < 19);
      if (c < 16)
         lencodes[n++] = cast(ubyte) c;
      else if (c == 16) {
         c = zreceive(a,2)+3;
         memset(lencodes.ptr+n, lencodes[n-1], c);
         n += c;
      } else if (c == 17) {
         c = zreceive(a,3)+3;
         memset(lencodes.ptr+n, 0, c);
         n += c;
      } else {
         assert(c == 18);
         c = zreceive(a,7)+11;
         memset(lencodes.ptr+n, 0, c);
         n += c;
      }
   }
   if (n != hlit+hdist) throw new STBImageException("Bad codelengths, corrupt PNG");
   if (!zbuild_huffman(&a.z_length, lencodes.ptr, hlit)) return 0;
   if (!zbuild_huffman(&a.z_distance, lencodes.ptr+hlit, hdist)) return 0;
   return 1;
}

int parse_uncompressed_block(zbuf *a)
{
   ubyte[4] header;
   int len,nlen,k;
   if (a.num_bits & 7)
      zreceive(a, a.num_bits & 7); // discard
   // drain the bit-packed data into header
   k = 0;
   while (a.num_bits > 0) {
      header[k++] = cast(ubyte) (a.code_buffer & 255); // wtf this warns?
      a.code_buffer >>= 8;
      a.num_bits -= 8;
   }
   assert(a.num_bits == 0);
   // now fill header the normal way
   while (k < 4)
      header[k++] = cast(ubyte) zget8(a);
   len  = header[1] * 256 + header[0];
   nlen = header[3] * 256 + header[2];
   if (nlen != (len ^ 0xffff)) throw new STBImageException("Zlib corrupt, corrupt PNG");
   if (a.zbuffer + len > a.zbuffer_end) throw new STBImageException("Read past buffer, corrupt PNG");
   if (a.zout + len > a.zout_end)
      if (!expand(a, len)) return 0;
   memcpy(a.zout, a.zbuffer, len);
   a.zbuffer += len;
   a.zout += len;
   return 1;
}

int parse_zlib_header(zbuf *a)
{
   int cmf   = zget8(a);
   int cm    = cmf & 15;
   /* int cinfo = cmf >> 4; */
   int flg   = zget8(a);
   if ((cmf*256+flg) % 31 != 0) throw new STBImageException("Bad zlib header, corrupt PNG"); // zlib spec
   if (flg & 32) throw new STBImageException("No preset dict, corrupt PNG"); // preset dictionary not allowed in png
   if (cm != 8) throw new STBImageException("Bad compression, corrupt PNG");  // DEFLATE required for png
   // window = 1 << (8 + cinfo)... but who cares, we fully buffer output
   return 1;
}

// @TODO: should statically initialize these for optimal thread safety
__gshared ubyte[288] default_length;
__gshared ubyte[32] default_distance;

void init_defaults()
{
   int i;   // use <= to match clearly with spec
   for (i=0; i <= 143; ++i)     default_length[i]   = 8;
   for (   ; i <= 255; ++i)     default_length[i]   = 9;
   for (   ; i <= 279; ++i)     default_length[i]   = 7;
   for (   ; i <= 287; ++i)     default_length[i]   = 8;

   for (i=0; i <=  31; ++i)     default_distance[i] = 5;
}

__gshared int stbi_png_partial; // a quick hack to only allow decoding some of a PNG... I should implement real streaming support instead
int parse_zlib(zbuf *a, int parse_header)
{
   int final_, type;
   if (parse_header)
      if (!parse_zlib_header(a)) return 0;
   a.num_bits = 0;
   a.code_buffer = 0;
   do {
      final_ = zreceive(a,1);
      type = zreceive(a,2);
      if (type == 0) {
         if (!parse_uncompressed_block(a)) return 0;
      } else if (type == 3) {
         return 0;
      } else {
         if (type == 1) {
            // use fixed code lengths
            if (!default_distance[31]) init_defaults();
            if (!zbuild_huffman(&a.z_length  , default_length.ptr  , 288)) return 0;
            if (!zbuild_huffman(&a.z_distance, default_distance.ptr,  32)) return 0;
         } else {
            if (!compute_huffman_codes(a)) return 0;
         }
         if (!parse_huffman_block(a)) return 0;
      }
      if (stbi_png_partial && a.zout - a.zout_start > 65536)
         break;
   } while (!final_);
   return 1;
}

int do_zlib(zbuf *a, ubyte *obuf, int olen, int exp, int parse_header)
{
   a.zout_start = obuf;
   a.zout       = obuf;
   a.zout_end   = obuf + olen;
   a.z_expandable = exp;

   return parse_zlib(a, parse_header);
}

ubyte *stbi_zlib_decode_malloc_guesssize(const(ubyte) *buffer, int len, int initial_size, int *outlen)
{
   zbuf a;
   ubyte *p = cast(ubyte*) malloc(initial_size);
   if (p == null) return null;
   a.zbuffer = buffer;
   a.zbuffer_end = buffer + len;
   if (do_zlib(&a, p, initial_size, 1, 1)) {
      if (outlen) *outlen = cast(int) (a.zout - a.zout_start);
      return a.zout_start;
   } else {
      free(a.zout_start);
      return null;
   }
}

ubyte *stbi_zlib_decode_malloc(const(ubyte) *buffer, int len, int *outlen)
{
   return stbi_zlib_decode_malloc_guesssize(buffer, len, 16384, outlen);
}

ubyte *stbi_zlib_decode_malloc_guesssize_headerflag(const(ubyte) *buffer, int len, int initial_size, int *outlen, int parse_header)
{
   zbuf a;
   ubyte *p = cast(ubyte*) malloc(initial_size);
   if (p == null) return null;
   a.zbuffer = buffer;
   a.zbuffer_end = buffer + len;
   if (do_zlib(&a, p, initial_size, 1, parse_header)) {
      if (outlen) *outlen = cast(int) (a.zout - a.zout_start);
      return a.zout_start;
   } else {
      free(a.zout_start);
      return null;
   }
}

int stbi_zlib_decode_buffer(ubyte* obuffer, int olen, const(ubyte)* ibuffer, int ilen)
{
   zbuf a;
   a.zbuffer = ibuffer;
   a.zbuffer_end = ibuffer + ilen;
   if (do_zlib(&a, obuffer, olen, 0, 1))
      return cast(int) (a.zout - a.zout_start);
   else
      return -1;
}

ubyte *stbi_zlib_decode_noheader_malloc(const(ubyte) *buffer, int len, int *outlen)
{
   zbuf a;
   ubyte *p = cast(ubyte*) malloc(16384);
   if (p == null) return null;
   a.zbuffer = buffer;
   a.zbuffer_end = buffer+len;
   if (do_zlib(&a, p, 16384, 1, 0)) {
      if (outlen) *outlen = cast(int) (a.zout - a.zout_start);
      return a.zout_start;
   } else {
      free(a.zout_start);
      return null;
   }
}

int stbi_zlib_decode_noheader_buffer(ubyte *obuffer, int olen, const(ubyte) *ibuffer, int ilen)
{
   zbuf a;
   a.zbuffer = ibuffer;
   a.zbuffer_end = ibuffer + ilen;
   if (do_zlib(&a, obuffer, olen, 0, 0))
      return cast(int) (a.zout - a.zout_start);
   else
      return -1;
}

// public domain "baseline" PNG decoder   v0.10  Sean Barrett 2006-11-18
//    simple implementation
//      - only 8-bit samples
//      - no CRC checking
//      - allocates lots of intermediate memory
//        - avoids problem of streaming data between subsystems
//        - avoids explicit window management
//    performance
//      - uses stb_zlib, a PD zlib implementation with fast huffman decoding


struct chunk
{
   uint length;
   uint type;
}

uint PNG_TYPE(ubyte a, ubyte b, ubyte c, ubyte d)
{
   return (a << 24) + (b << 16) + (c << 8) + d;
}

chunk get_chunk_header(stbi *s)
{
   chunk c;
   c.length = get32(s);
   c.type   = get32(s);
   return c;
}

static int check_png_header(stbi *s)
{
   static immutable ubyte[8] png_sig = [ 137, 80, 78, 71, 13, 10, 26, 10 ];
   for (int i = 0; i < 8; ++i)
   {
       ubyte headerByte = get8u(s);
       ubyte expected = png_sig[i];
       if (headerByte != expected)
           throw new STBImageException("Bad PNG sig, not a PNG");
   }
   return 1;
}

struct png
{
   stbi *s;
   ubyte *idata;
   ubyte *expanded;
   ubyte *out_;
}


enum : int
{
   F_none=0, F_sub=1, F_up=2, F_avg=3, F_paeth=4,
   F_avg_first, F_paeth_first
}

static immutable ubyte[5] first_row_filter =
[
   F_none, F_sub, F_none, F_avg_first, F_paeth_first
];

static int paeth(int a, int b, int c)
{
   int p = a + b - c;
   int pa = abs(p-a);
   int pb = abs(p-b);
   int pc = abs(p-c);
   if (pa <= pb && pa <= pc) return a;
   if (pb <= pc) return b;
   return c;
}

// create the png data from post-deflated data
static int create_png_image_raw(png *a, ubyte *raw, uint raw_len, int out_n, uint x, uint y)
{
   stbi *s = a.s;
   uint i,j,stride = x*out_n;
   int k;
   int img_n = s.img_n; // copy it into a local for later
   assert(out_n == s.img_n || out_n == s.img_n+1);
   if (stbi_png_partial) y = 1;
   a.out_ = cast(ubyte*) malloc(x * y * out_n);
   if (!a.out_) throw new STBImageException("Out of memory");
   if (!stbi_png_partial) {
      if (s.img_x == x && s.img_y == y) {
         if (raw_len != (img_n * x + 1) * y) throw new STBImageException("Not enough pixels, corrupt PNG");
      } else { // interlaced:
         if (raw_len < (img_n * x + 1) * y) throw new STBImageException("Not enough pixels, corrupt PNG");
      }
   }
   for (j=0; j < y; ++j) {
      ubyte *cur = a.out_ + stride*j;
      ubyte *prior = cur - stride;
      int filter = *raw++;
      if (filter > 4) throw new STBImageException("Invalid filter, corrupt PNG");
      // if first row, use special filter that doesn't sample previous row
      if (j == 0) filter = first_row_filter[filter];
      // handle first pixel explicitly
      for (k=0; k < img_n; ++k) {
         switch (filter) {
            case F_none       : cur[k] = raw[k]; break;
            case F_sub        : cur[k] = raw[k]; break;
            case F_up         : cur[k] = cast(ubyte)(raw[k] + prior[k]); break;
            case F_avg        : cur[k] = cast(ubyte)(raw[k] + (prior[k]>>1)); break;
            case F_paeth      : cur[k] = cast(ubyte) (raw[k] + paeth(0,prior[k],0)); break;
            case F_avg_first  : cur[k] = raw[k]; break;
            case F_paeth_first: cur[k] = raw[k]; break;
            default: break;
         }
      }
      if (img_n != out_n) cur[img_n] = 255;
      raw += img_n;
      cur += out_n;
      prior += out_n;
      // this is a little gross, so that we don't switch per-pixel or per-component
      if (img_n == out_n) {

         for (i=x-1; i >= 1; --i, raw+=img_n,cur+=img_n,prior+=img_n)
            for (k=0; k < img_n; ++k)
            {
               switch (filter) {
                  case F_none:  cur[k] = raw[k]; break;
                  case F_sub:   cur[k] = cast(ubyte)(raw[k] + cur[k-img_n]); break;
                  case F_up:    cur[k] = cast(ubyte)(raw[k] + prior[k]); break;
                  case F_avg:   cur[k] = cast(ubyte)(raw[k] + ((prior[k] + cur[k-img_n])>>1)); break;
                  case F_paeth:  cur[k] = cast(ubyte) (raw[k] + paeth(cur[k-img_n],prior[k],prior[k-img_n])); break;
                  case F_avg_first:    cur[k] = cast(ubyte)(raw[k] + (cur[k-img_n] >> 1)); break;
                  case F_paeth_first:  cur[k] = cast(ubyte) (raw[k] + paeth(cur[k-img_n],0,0)); break;
                  default: break;
               }
            }
      } else {
         assert(img_n+1 == out_n);

         for (i=x-1; i >= 1; --i, cur[img_n]=255,raw+=img_n,cur+=out_n,prior+=out_n)
            for (k=0; k < img_n; ++k)
            {
               switch (filter) {
                  case F_none:  cur[k] = raw[k]; break;
                  case F_sub:   cur[k] = cast(ubyte)(raw[k] + cur[k-out_n]); break;
                  case F_up:    cur[k] = cast(ubyte)(raw[k] + prior[k]); break;
                  case F_avg:   cur[k] = cast(ubyte)(raw[k] + ((prior[k] + cur[k-out_n])>>1)); break;
                  case F_paeth:  cur[k] = cast(ubyte) (raw[k] + paeth(cur[k-out_n],prior[k],prior[k-out_n])); break;
                  case F_avg_first:    cur[k] = cast(ubyte)(raw[k] + (cur[k-out_n] >> 1)); break;
                  case F_paeth_first:  cur[k] = cast(ubyte) (raw[k] + paeth(cur[k-out_n],0,0)); break;
                  default: break;
               }
            }
      }
   }
   return 1;
}

int create_png_image(png *a, ubyte *raw, uint raw_len, int out_n, int interlaced)
{
   ubyte *final_;
   int p;
   int save;
   if (!interlaced)
      return create_png_image_raw(a, raw, raw_len, out_n, a.s.img_x, a.s.img_y);
   save = stbi_png_partial;
   stbi_png_partial = 0;

   // de-interlacing
   final_ = cast(ubyte*) malloc(a.s.img_x * a.s.img_y * out_n);
   for (p=0; p < 7; ++p) {
      static immutable int[7] xorig = [ 0,4,0,2,0,1,0 ];
      static immutable int[7] yorig = [ 0,0,4,0,2,0,1 ];
      static immutable int[7] xspc = [ 8,8,4,4,2,2,1 ];
      static immutable int[7] yspc = [ 8,8,8,4,4,2,2 ];
      int i,j,x,y;
      // pass1_x[4] = 0, pass1_x[5] = 1, pass1_x[12] = 1
      x = (a.s.img_x - xorig[p] + xspc[p]-1) / xspc[p];
      y = (a.s.img_y - yorig[p] + yspc[p]-1) / yspc[p];
      if (x && y) {
         if (!create_png_image_raw(a, raw, raw_len, out_n, x, y)) {
            free(final_);
            return 0;
         }
         for (j=0; j < y; ++j)
            for (i=0; i < x; ++i)
               memcpy(final_ + (j*yspc[p]+yorig[p])*a.s.img_x*out_n + (i*xspc[p]+xorig[p])*out_n,
                      a.out_ + (j*x+i)*out_n, out_n);
         free(a.out_);
         raw += (x*out_n+1)*y;
         raw_len -= (x*out_n+1)*y;
      }
   }
   a.out_ = final_;

   stbi_png_partial = save;
   return 1;
}

static int compute_transparency(png *z, ubyte[3] tc, int out_n)
{
   stbi *s = z.s;
   uint i, pixel_count = s.img_x * s.img_y;
   ubyte *p = z.out_;

   // compute color-based transparency, assuming we've
   // already got 255 as the alpha value in the output
   assert(out_n == 2 || out_n == 4);

   if (out_n == 2) {
      for (i=0; i < pixel_count; ++i) {
         p[1] = (p[0] == tc[0] ? 0 : 255);
         p += 2;
      }
   } else {
      for (i=0; i < pixel_count; ++i) {
         if (p[0] == tc[0] && p[1] == tc[1] && p[2] == tc[2])
            p[3] = 0;
         p += 4;
      }
   }
   return 1;
}

int expand_palette(png *a, ubyte *palette, int len, int pal_img_n)
{
   uint i, pixel_count = a.s.img_x * a.s.img_y;
   ubyte *p;
   ubyte *temp_out;
   ubyte *orig = a.out_;

   p = cast(ubyte*) malloc(pixel_count * pal_img_n);
   if (p == null)
      throw new STBImageException("Out of memory");

   // between here and free(out) below, exitting would leak
   temp_out = p;

   if (pal_img_n == 3) {
      for (i=0; i < pixel_count; ++i) {
         int n = orig[i]*4;
         p[0] = palette[n  ];
         p[1] = palette[n+1];
         p[2] = palette[n+2];
         p += 3;
      }
   } else {
      for (i=0; i < pixel_count; ++i) {
         int n = orig[i]*4;
         p[0] = palette[n  ];
         p[1] = palette[n+1];
         p[2] = palette[n+2];
         p[3] = palette[n+3];
         p += 4;
      }
   }
   free(a.out_);
   a.out_ = temp_out;

   return 1;
}

int parse_png_file(png *z, int scan, int req_comp)
{
   ubyte[1024] palette;
   ubyte pal_img_n=0;
   ubyte has_trans=0;
   ubyte[3] tc;
   uint ioff=0, idata_limit=0, i, pal_len=0;
   int first=1,k,interlace=0;
   stbi *s = z.s;

   z.expanded = null;
   z.idata = null;
   z.out_ = null;

   if (!check_png_header(s)) return 0;

   if (scan == SCAN_type) return 1;

   for (;;) {
      chunk c = get_chunk_header(s);
      switch (c.type) {
         case PNG_TYPE('I','H','D','R'): {
            int depth,color,comp,filter;
            if (!first) throw new STBImageException("Multiple IHDR, corrupt PNG");
            first = 0;
            if (c.length != 13) throw new STBImageException("Bad IHDR len, corrupt PNG");
            s.img_x = get32(s); if (s.img_x > (1 << 24)) throw new STBImageException("Very large image (corrupt?)");
            s.img_y = get32(s); if (s.img_y > (1 << 24)) throw new STBImageException("Very large image (corrupt?)");
            depth = get8(s);  if (depth != 8)        throw new STBImageException("8bit only, PNG not supported: 8-bit only");
            color = get8(s);  if (color > 6)         throw new STBImageException("Bad ctype, corrupt PNG");
            if (color == 3) pal_img_n = 3; else if (color & 1) throw new STBImageException("Bad ctype, corrupt PNG");
            comp  = get8(s);  if (comp) throw new STBImageException("Bad comp method, corrupt PNG");
            filter= get8(s);  if (filter) throw new STBImageException("Bad filter method, corrupt PNG");
            interlace = get8(s); if (interlace>1) throw new STBImageException("Bad interlace method, corrupt PNG");
            if (!s.img_x || !s.img_y) throw new STBImageException("0-pixel image, corrupt PNG");
            if (!pal_img_n) {
               s.img_n = (color & 2 ? 3 : 1) + (color & 4 ? 1 : 0);
               if ((1 << 30) / s.img_x / s.img_n < s.img_y) throw new STBImageException("Image too large to decode");
               if (scan == SCAN_header) return 1;
            } else {
               // if paletted, then pal_n is our final components, and
               // img_n is # components to decompress/filter.
               s.img_n = 1;
               if ((1 << 30) / s.img_x / 4 < s.img_y) throw new STBImageException("Too large, corrupt PNG");
               // if SCAN_header, have to scan to see if we have a tRNS
            }
            break;
         }

         case PNG_TYPE('P','L','T','E'):  {
            if (first) throw new STBImageException("first not IHDR, corrupt PNG");
            if (c.length > 256*3) throw new STBImageException("invalid PLTE, corrupt PNG");
            pal_len = c.length / 3;
            if (pal_len * 3 != c.length) throw new STBImageException("invalid PLTE, corrupt PNG");
            for (i=0; i < pal_len; ++i) {
               palette[i*4+0] = get8u(s);
               palette[i*4+1] = get8u(s);
               palette[i*4+2] = get8u(s);
               palette[i*4+3] = 255;
            }
            break;
         }

         case PNG_TYPE('t','R','N','S'): {
            if (first) throw new STBImageException("first not IHDR, cCorrupt PNG");
            if (z.idata) throw new STBImageException("tRNS after IDAT, corrupt PNG");
            if (pal_img_n) {
               if (scan == SCAN_header) { s.img_n = 4; return 1; }
               if (pal_len == 0) throw new STBImageException("tRNS before PLTE, corrupt PNG");
               if (c.length > pal_len) throw new STBImageException("bad tRNS len, corrupt PNG");
               pal_img_n = 4;
               for (i=0; i < c.length; ++i)
                  palette[i*4+3] = get8u(s);
            } else {
               if (!(s.img_n & 1)) throw new STBImageException("tRNS with alpha, corrupt PNG");
               if (c.length != cast(uint) s.img_n*2) throw new STBImageException("bad tRNS len, corrupt PNG");
               has_trans = 1;
               for (k=0; k < s.img_n; ++k)
                  tc[k] = cast(ubyte) get16(s); // non 8-bit images will be larger
            }
            break;
         }

         case PNG_TYPE('I','D','A','T'): {
            if (first) throw new STBImageException("first not IHDR, corrupt PNG");
            if (pal_img_n && !pal_len) throw new STBImageException("no PLTE, corrupt PNG");
            if (scan == SCAN_header) { s.img_n = pal_img_n; return 1; }
            if (ioff + c.length > idata_limit) {
               ubyte *p;
               if (idata_limit == 0) idata_limit = c.length > 4096 ? c.length : 4096;
               while (ioff + c.length > idata_limit)
                  idata_limit *= 2;
               p = cast(ubyte*) realloc(z.idata, idata_limit); if (p == null) throw new STBImageException("outofmem, cOut of memory");
               z.idata = p;
            }
            if (!getn(s, z.idata+ioff,c.length)) throw new STBImageException("outofdata, corrupt PNG");
            ioff += c.length;
            break;
         }

         case PNG_TYPE('I','E','N','D'): {
            uint raw_len;
            if (first) throw new STBImageException("first not IHDR, corrupt PNG");
            if (scan != SCAN_load) return 1;
            if (z.idata == null) throw new STBImageException("no IDAT, corrupt PNG");
            z.expanded = stbi_zlib_decode_malloc_guesssize_headerflag(z.idata, ioff, 16384, cast(int *) &raw_len, 1);
            if (z.expanded == null) return 0; // zlib should set error
            free(z.idata); z.idata = null;
            if ((req_comp == s.img_n+1 && req_comp != 3 && !pal_img_n) || has_trans)
               s.img_out_n = s.img_n+1;
            else
               s.img_out_n = s.img_n;
            if (!create_png_image(z, z.expanded, raw_len, s.img_out_n, interlace)) return 0;
            if (has_trans)
               if (!compute_transparency(z, tc, s.img_out_n)) return 0;
            if (pal_img_n) {
               // pal_img_n == 3 or 4
               s.img_n = pal_img_n; // record the actual colors we had
               s.img_out_n = pal_img_n;
               if (req_comp >= 3) s.img_out_n = req_comp;
               if (!expand_palette(z, palette.ptr, pal_len, s.img_out_n))
                  return 0;
            }
            free(z.expanded); z.expanded = null;
            return 1;
         }

         default:
            // if critical, fail
            if (first) throw new STBImageException("first not IHDR, corrupt PNG");
            if ((c.type & (1 << 29)) == 0) {

               throw new STBImageException("PNG not supported: unknown chunk type");
            }
            skip(s, c.length);
            break;
      }
      // end of chunk, read and skip CRC
      get32(s);
   }
}

ubyte *do_png(png *p, int *x, int *y, int *n, int req_comp)
{
   ubyte *result=null;
   if (req_comp < 0 || req_comp > 4)
      throw new STBImageException("Internal error: bad req_comp");
   if (parse_png_file(p, SCAN_load, req_comp)) {
      result = p.out_;
      p.out_ = null;
      if (req_comp && req_comp != p.s.img_out_n) {
         result = convert_format(result, p.s.img_out_n, req_comp, p.s.img_x, p.s.img_y);
         p.s.img_out_n = req_comp;
         if (result == null) return result;
      }
      *x = p.s.img_x;
      *y = p.s.img_y;
      if (n) *n = p.s.img_n;
   }
   free(p.out_);      p.out_    = null;
   free(p.expanded); p.expanded = null;
   free(p.idata);    p.idata    = null;

   return result;
}

ubyte *stbi_png_load(stbi *s, int *x, int *y, int *comp, int req_comp)
{
   png p;
   p.s = s;
   return do_png(&p, x,y,comp,req_comp);
}

void stbi_png_test(stbi *s)
{
   int r = check_png_header(s);
   if (r == 0)
       throw new STBImageException("Couldn't decode PNG header");
}

// Microsoft/Windows BMP image

void stbi_bmp_test(stbi *s)
{
    if (get8(s) != 'B') throw new STBImageException("Couldn't decode BMP header");
    if (get8(s) != 'M') throw new STBImageException("Couldn't decode BMP header");
    get32le(s); // discard filesize
    get16le(s); // discard reserved
    get16le(s); // discard reserved
    get32le(s); // discard data offset
    int sz = get32le(s);
    if (sz == 12 || sz == 40 || sz == 56 || sz == 108)
        return;

    throw new STBImageException("Couldn't decode BMP header");
}


// returns 0..31 for the highest set bit
int high_bit(uint z)
{
   int n=0;
   if (z == 0) return -1;
   if (z >= 0x10000) n += 16, z >>= 16;
   if (z >= 0x00100) n +=  8, z >>=  8;
   if (z >= 0x00010) n +=  4, z >>=  4;
   if (z >= 0x00004) n +=  2, z >>=  2;
   if (z >= 0x00002) n +=  1, z >>=  1;
   return n;
}

int bitcount(uint a)
{
   a = (a & 0x55555555) + ((a >>  1) & 0x55555555); // max 2
   a = (a & 0x33333333) + ((a >>  2) & 0x33333333); // max 4
   a = (a + (a >> 4)) & 0x0f0f0f0f; // max 8 per 4, now 8 bits
   a = (a + (a >> 8)); // max 16 per 8 bits
   a = (a + (a >> 16)); // max 32 per 8 bits
   return a & 0xff;
}

int shiftsigned(int v, int shift, int bits)
{
   int result;
   int z=0;

   if (shift < 0) v <<= -shift;
   else v >>= shift;
   result = v;

   z = bits;
   while (z < 8) {
      result += v >> z;
      z += bits;
   }
   return result;
}

ubyte *bmp_load(stbi *s, int *x, int *y, int *comp, int req_comp)
{
   ubyte *out_;
   uint mr=0,mg=0,mb=0,ma=0, fake_a=0;
   ubyte[4][256] pal;
   int psize=0,i,j,compress=0,width;
   int bpp, flip_vertically, pad, target, offset, hsz;
   if (get8(s) != 'B' || get8(s) != 'M') throw new STBImageException("not BMP, Corrupt BMP");
   get32le(s); // discard filesize
   get16le(s); // discard reserved
   get16le(s); // discard reserved
   offset = get32le(s);
   hsz = get32le(s);
   if (hsz != 12 && hsz != 40 && hsz != 56 && hsz != 108) throw new STBImageException("unknown BMP, BMP type not supported: unknown");
   if (hsz == 12) {
      s.img_x = get16le(s);
      s.img_y = get16le(s);
   } else {
      s.img_x = get32le(s);
      s.img_y = get32le(s);
   }
   if (get16le(s) != 1) throw new STBImageException("bad BMP");
   bpp = get16le(s);
   if (bpp == 1) throw new STBImageException("monochrome, BMP type not supported: 1-bit");
   flip_vertically = (cast(int) s.img_y) > 0;
   s.img_y = abs(cast(int) s.img_y);
   if (hsz == 12) {
      if (bpp < 24)
         psize = (offset - 14 - 24) / 3;
   } else {
      compress = get32le(s);
      if (compress == 1 || compress == 2) throw new STBImageException("BMP RLE, BMP type not supported: RLE");
      get32le(s); // discard sizeof
      get32le(s); // discard hres
      get32le(s); // discard vres
      get32le(s); // discard colorsused
      get32le(s); // discard max important
      if (hsz == 40 || hsz == 56) {
         if (hsz == 56) {
            get32le(s);
            get32le(s);
            get32le(s);
            get32le(s);
         }
         if (bpp == 16 || bpp == 32) {
            mr = mg = mb = 0;
            if (compress == 0) {
               if (bpp == 32) {
                  mr = 0xffu << 16;
                  mg = 0xffu <<  8;
                  mb = 0xffu <<  0;
                  ma = 0xffu << 24;
                  fake_a = 1; // @TODO: check for cases like alpha value is all 0 and switch it to 255
               } else {
                  mr = 31u << 10;
                  mg = 31u <<  5;
                  mb = 31u <<  0;
               }
            } else if (compress == 3) {
               mr = get32le(s);
               mg = get32le(s);
               mb = get32le(s);
               // not documented, but generated by photoshop and handled by mspaint
               if (mr == mg && mg == mb) {
                  // ?!?!?
                  throw new STBImageException("bad BMP");
               }
            } else
               throw new STBImageException("bad BMP");
         }
      } else {
         assert(hsz == 108);
         mr = get32le(s);
         mg = get32le(s);
         mb = get32le(s);
         ma = get32le(s);
         get32le(s); // discard color space
         for (i=0; i < 12; ++i)
            get32le(s); // discard color space parameters
      }
      if (bpp < 16)
         psize = (offset - 14 - hsz) >> 2;
   }
   s.img_n = ma ? 4 : 3;
   if (req_comp && req_comp >= 3) // we can directly decode 3 or 4
      target = req_comp;
   else
      target = s.img_n; // if they want monochrome, we'll post-convert
   out_ = cast(ubyte*) malloc(target * s.img_x * s.img_y);
   if (!out_) throw new STBImageException("Out of memory");
   if (bpp < 16) {
      int z=0;
      if (psize == 0 || psize > 256) { free(out_); throw new STBImageException("invalid, Corrupt BMP"); }
      for (i=0; i < psize; ++i) {
         pal[i][2] = get8u(s);
         pal[i][1] = get8u(s);
         pal[i][0] = get8u(s);
         if (hsz != 12) get8(s);
         pal[i][3] = 255;
      }
      skip(s, offset - 14 - hsz - psize * (hsz == 12 ? 3 : 4));
      if (bpp == 4) width = (s.img_x + 1) >> 1;
      else if (bpp == 8) width = s.img_x;
      else { free(out_); throw new STBImageException("bad bpp, corrupt BMP"); }
      pad = (-width)&3;
      for (j=0; j < cast(int) s.img_y; ++j) {
         for (i=0; i < cast(int) s.img_x; i += 2) {
            int v=get8(s),v2=0;
            if (bpp == 4) {
               v2 = v & 15;
               v >>= 4;
            }
            out_[z++] = pal[v][0];
            out_[z++] = pal[v][1];
            out_[z++] = pal[v][2];
            if (target == 4) out_[z++] = 255;
            if (i+1 == cast(int) s.img_x) break;
            v = (bpp == 8) ? get8(s) : v2;
            out_[z++] = pal[v][0];
            out_[z++] = pal[v][1];
            out_[z++] = pal[v][2];
            if (target == 4) out_[z++] = 255;
         }
         skip(s, pad);
      }
   } else {
      int rshift=0,gshift=0,bshift=0,ashift=0,rcount=0,gcount=0,bcount=0,acount=0;
      int z = 0;
      int easy=0;
      skip(s, offset - 14 - hsz);
      if (bpp == 24) width = 3 * s.img_x;
      else if (bpp == 16) width = 2*s.img_x;
      else /* bpp = 32 and pad = 0 */ width=0;
      pad = (-width) & 3;
      if (bpp == 24) {
         easy = 1;
      } else if (bpp == 32) {
         if (mb == 0xff && mg == 0xff00 && mr == 0x00ff0000 && ma == 0xff000000)
            easy = 2;
      }
      if (!easy) {
         if (!mr || !mg || !mb) { free(out_); throw new STBImageException("bad masks, corrupt BMP"); }
         // right shift amt to put high bit in position #7
         rshift = high_bit(mr)-7; rcount = bitcount(mr);
         gshift = high_bit(mg)-7; gcount = bitcount(mr);
         bshift = high_bit(mb)-7; bcount = bitcount(mr);
         ashift = high_bit(ma)-7; acount = bitcount(mr);
      }
      for (j=0; j < cast(int) s.img_y; ++j) {
         if (easy) {
            for (i=0; i < cast(int) s.img_x; ++i) {
               int a;
               out_[z+2] = get8u(s);
               out_[z+1] = get8u(s);
               out_[z+0] = get8u(s);
               z += 3;
               a = (easy == 2 ? get8(s) : 255);
               if (target == 4) out_[z++] = cast(ubyte) a;
            }
         } else {
            for (i=0; i < cast(int) s.img_x; ++i) {
               uint v = (bpp == 16 ? get16le(s) : get32le(s));
               int a;
               out_[z++] = cast(ubyte) shiftsigned(v & mr, rshift, rcount);
               out_[z++] = cast(ubyte) shiftsigned(v & mg, gshift, gcount);
               out_[z++] = cast(ubyte) shiftsigned(v & mb, bshift, bcount);
               a = (ma ? shiftsigned(v & ma, ashift, acount) : 255);
               if (target == 4) out_[z++] = cast(ubyte) a;
            }
         }
         skip(s, pad);
      }
   }
   if (flip_vertically) {
      ubyte t;
      for (j=0; j < cast(int) s.img_y>>1; ++j) {
         ubyte *p1 = out_ +      j     *s.img_x*target;
         ubyte *p2 = out_ + (s.img_y-1-j)*s.img_x*target;
         for (i=0; i < cast(int) s.img_x*target; ++i) {
            t = p1[i], p1[i] = p2[i], p2[i] = t;
         }
      }
   }

   if (req_comp && req_comp != target) {
      out_ = convert_format(out_, target, req_comp, s.img_x, s.img_y);
      if (out_ == null) return out_; // convert_format frees input on failure
   }

   *x = s.img_x;
   *y = s.img_y;
   if (comp) *comp = s.img_n;
   return out_;
}

ubyte *stbi_bmp_load(stbi *s, int *x, int *y, int *comp, int req_comp)
{
   return bmp_load(s, x,y,comp,req_comp);
}

// *************************************************************************************************
// GIF loader -- public domain by Jean-Marc Lienher -- simplified/shrunk by stb
struct stbi_gif_lzw
{
   short prefix;
   ubyte first;
   ubyte suffix;
}

struct stbi_gif
{
   int w,h;
   ubyte *out_;                 // output buffer (always 4 components)
   int flags, bgindex, ratio, transparent, eflags;
   ubyte[4][256]  pal;
   ubyte[4][256] lpal;
   stbi_gif_lzw[4096] codes;
   ubyte *color_table;
   int parse, step;
   int lflags;
   int start_x, start_y;
   int max_x, max_y;
   int cur_x, cur_y;
   int line_size;
}

void stbi_gif_test(stbi *s)
{
    int sz;
    if (get8(s) != 'G' || get8(s) != 'I' || get8(s) != 'F' || get8(s) != '8')
        throw new STBImageException("Couldn't decode GIF header");
    sz = get8(s);
    if (sz != '9' && sz != '7')
        throw new STBImageException("Couldn't decode GIF header");
    if (get8(s) != 'a')
        throw new STBImageException("Couldn't decode GIF header");
}

void stbi_gif_parse_colortable(stbi *s, ubyte[4][256] pal, int num_entries, int transp)
{
   int i;
   for (i=0; i < num_entries; ++i) {
      pal[i][2] = get8u(s);
      pal[i][1] = get8u(s);
      pal[i][0] = get8u(s);
      pal[i][3] = transp ? 0 : 255;
   }
}

int stbi_gif_header(stbi *s, stbi_gif *g, int *comp, int is_info)
{
   ubyte version_;
   if (get8(s) != 'G' || get8(s) != 'I' || get8(s) != 'F' || get8(s) != '8')
      throw new STBImageException("not GIF, corrupt GIF");

   version_ = get8u(s);
   if (version_ != '7' && version_ != '9')    throw new STBImageException("not GIF, corrupt GIF");
   if (get8(s) != 'a')                      throw new STBImageException("not GIF, corrupt GIF");

   g.w = get16le(s);
   g.h = get16le(s);
   g.flags = get8(s);
   g.bgindex = get8(s);
   g.ratio = get8(s);
   g.transparent = -1;

   if (comp != null) *comp = 4;  // can't actually tell whether it's 3 or 4 until we parse the comments

   if (is_info) return 1;

   if (g.flags & 0x80)
      stbi_gif_parse_colortable(s,g.pal, 2 << (g.flags & 7), -1);

   return 1;
}

void stbi_out_gif_code(stbi_gif *g, ushort code)
{
   ubyte *p;
   ubyte *c;

   // recurse to decode the prefixes, since the linked-list is backwards,
   // and working backwards through an interleaved image would be nasty
   if (g.codes[code].prefix >= 0)
      stbi_out_gif_code(g, g.codes[code].prefix);

   if (g.cur_y >= g.max_y) return;

   p = (&g.out_[g.cur_x + g.cur_y]);
   c = &g.color_table[g.codes[code].suffix * 4];

   if (c[3] >= 128) {
      p[0] = c[2];
      p[1] = c[1];
      p[2] = c[0];
      p[3] = c[3];
   }
   g.cur_x += 4;

   if (g.cur_x >= g.max_x) {
      g.cur_x = g.start_x;
      g.cur_y += g.step;

      while (g.cur_y >= g.max_y && g.parse > 0) {
         g.step = (1 << g.parse) * g.line_size;
         g.cur_y = g.start_y + (g.step >> 1);
         --g.parse;
      }
   }
}

ubyte *stbi_process_gif_raster(stbi *s, stbi_gif *g)
{
   ubyte lzw_cs;
   int len, code;
   uint first;
   int codesize, codemask, avail, oldcode, bits, valid_bits, clear;
   stbi_gif_lzw *p;

   lzw_cs = get8u(s);
   clear = 1 << lzw_cs;
   first = 1;
   codesize = lzw_cs + 1;
   codemask = (1 << codesize) - 1;
   bits = 0;
   valid_bits = 0;
   for (code = 0; code < clear; code++) {
      g.codes[code].prefix = -1;
      g.codes[code].first = cast(ubyte) code;
      g.codes[code].suffix = cast(ubyte) code;
   }

   // support no starting clear code
   avail = clear+2;
   oldcode = -1;

   len = 0;
   for(;;) {
      if (valid_bits < codesize) {
         if (len == 0) {
            len = get8(s); // start new block
            if (len == 0)
               return g.out_;
         }
         --len;
         bits |= cast(int) get8(s) << valid_bits;
         valid_bits += 8;
      } else {
         int code_ = bits & codemask;
         bits >>= codesize;
         valid_bits -= codesize;
         // @OPTIMIZE: is there some way we can accelerate the non-clear path?
         if (code_ == clear) {  // clear code
            codesize = lzw_cs + 1;
            codemask = (1 << codesize) - 1;
            avail = clear + 2;
            oldcode = -1;
            first = 0;
         } else if (code_ == clear + 1) { // end of stream code
            skip(s, len);
            while ((len = get8(s)) > 0)
               skip(s,len);
            return g.out_;
         } else if (code_ <= avail) {
            if (first) throw new STBImageException("no clear code, corrupt GIF");

            if (oldcode >= 0) {
               p = &g.codes[avail++];
               if (avail > 4096)        throw new STBImageException("too many codes, corrupt GIF");
               p.prefix = cast(short) oldcode;
               p.first = g.codes[oldcode].first;
               p.suffix = (code_ == avail) ? p.first : g.codes[code_].first;
            } else if (code_ == avail)
               throw new STBImageException("illegal code in raster, corrupt GIF");

            stbi_out_gif_code(g, cast(ushort) code);

            if ((avail & codemask) == 0 && avail <= 0x0FFF) {
               codesize++;
               codemask = (1 << codesize) - 1;
            }

            oldcode = code_;
         } else {
            throw new STBImageException("illegal code in raster, corrupt GIF");
         }
      }
   }
}

void stbi_fill_gif_background(stbi_gif *g)
{
   int i;
   ubyte *c = g.pal[g.bgindex].ptr;
   // @OPTIMIZE: write a dword at a time
   for (i = 0; i < g.w * g.h * 4; i += 4) {
      ubyte *p  = &g.out_[i];
      p[0] = c[2];
      p[1] = c[1];
      p[2] = c[0];
      p[3] = c[3];
   }
}

// this function is designed to support animated gifs, although stb_image doesn't support it
ubyte *stbi_gif_load_next(stbi *s, stbi_gif *g, int *comp, int req_comp)
{
   int i;
   ubyte *old_out = null;

   if (g.out_ == null) {
      if (!stbi_gif_header(s, g, comp,0))     return null; // failure_reason set by stbi_gif_header
      g.out_ = cast(ubyte*) malloc(4 * g.w * g.h);
      if (g.out_ == null)                      throw new STBImageException("Out of memory");
      stbi_fill_gif_background(g);
   } else {
      // animated-gif-only path
      if (((g.eflags & 0x1C) >> 2) == 3) {
         old_out = g.out_;
         g.out_ = cast(ubyte*) malloc(4 * g.w * g.h);
         if (g.out_ == null)                   throw new STBImageException("Out of memory");
         memcpy(g.out_, old_out, g.w*g.h*4);
      }
   }

   for (;;) {
      switch (get8(s)) {
         case 0x2C: /* Image Descriptor */
         {
            int x, y, w, h;
            ubyte *o;

            x = get16le(s);
            y = get16le(s);
            w = get16le(s);
            h = get16le(s);
            if (((x + w) > (g.w)) || ((y + h) > (g.h)))
               throw new STBImageException("bad Image Descriptor, corrupt GIF");

            g.line_size = g.w * 4;
            g.start_x = x * 4;
            g.start_y = y * g.line_size;
            g.max_x   = g.start_x + w * 4;
            g.max_y   = g.start_y + h * g.line_size;
            g.cur_x   = g.start_x;
            g.cur_y   = g.start_y;

            g.lflags = get8(s);

            if (g.lflags & 0x40) {
               g.step = 8 * g.line_size; // first interlaced spacing
               g.parse = 3;
            } else {
               g.step = g.line_size;
               g.parse = 0;
            }

            if (g.lflags & 0x80) {
               stbi_gif_parse_colortable(s,g.lpal, 2 << (g.lflags & 7), g.eflags & 0x01 ? g.transparent : -1);
               g.color_table = &g.lpal[0][0];
            } else if (g.flags & 0x80) {
               for (i=0; i < 256; ++i)  // @OPTIMIZE: reset only the previous transparent
                  g.pal[i][3] = 255;
               if (g.transparent >= 0 && (g.eflags & 0x01))
                  g.pal[g.transparent][3] = 0;
               g.color_table = &g.pal[0][0];
            } else
               throw new STBImageException("missing color table, corrupt GIF");

            o = stbi_process_gif_raster(s, g);
            if (o == null) return null;

            if (req_comp && req_comp != 4)
               o = convert_format(o, 4, req_comp, g.w, g.h);
            return o;
         }

         case 0x21: // Comment Extension.
         {
            int len;
            if (get8(s) == 0xF9) { // Graphic Control Extension.
               len = get8(s);
               if (len == 4) {
                  g.eflags = get8(s);
                  get16le(s); // delay
                  g.transparent = get8(s);
               } else {
                  skip(s, len);
                  break;
               }
            }
            while ((len = get8(s)) != 0)
               skip(s, len);
            break;
         }

         case 0x3B: // gif stream termination code
            return cast(ubyte*) 1;

         default:
            throw new STBImageException("unknown code, corrupt GIF");
      }
   }
}

ubyte *stbi_gif_load(stbi *s, int *x, int *y, int *comp, int req_comp)
{
   ubyte *u = null;
   stbi_gif g={0};

   u = stbi_gif_load_next(s, &g, comp, req_comp);
   if (u == cast(void *) 1) u = null;  // end of animated gif marker
   if (u) {
      *x = g.w;
      *y = g.h;
   }

   return u;
}