in Support/STBImage/include/stb_image.h [4879:5051]
static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp)
{
stbi_uc palette[1024], pal_img_n=0;
stbi_uc has_trans=0, tc[3]={0};
stbi__uint16 tc16[3];
stbi__uint32 ioff=0, idata_limit=0, i, pal_len=0;
int first=1,k,interlace=0, color=0, is_iphone=0;
stbi__context *s = z->s;
z->expanded = NULL;
z->idata = NULL;
z->out = NULL;
if (!stbi__check_png_header(s)) return 0;
if (scan == STBI__SCAN_type) return 1;
for (;;) {
stbi__pngchunk c = stbi__get_chunk_header(s);
switch (c.type) {
case STBI__PNG_TYPE('C','g','B','I'):
is_iphone = 1;
stbi__skip(s, c.length);
break;
case STBI__PNG_TYPE('I','H','D','R'): {
int comp,filter;
if (!first) return stbi__err("multiple IHDR","Corrupt PNG");
first = 0;
if (c.length != 13) return stbi__err("bad IHDR len","Corrupt PNG");
s->img_x = stbi__get32be(s); if (s->img_x > (1 << 24)) return stbi__err("too large","Very large image (corrupt?)");
s->img_y = stbi__get32be(s); if (s->img_y > (1 << 24)) return stbi__err("too large","Very large image (corrupt?)");
z->depth = stbi__get8(s); if (z->depth != 1 && z->depth != 2 && z->depth != 4 && z->depth != 8 && z->depth != 16) return stbi__err("1/2/4/8/16-bit only","PNG not supported: 1/2/4/8/16-bit only");
color = stbi__get8(s); if (color > 6) return stbi__err("bad ctype","Corrupt PNG");
if (color == 3 && z->depth == 16) return stbi__err("bad ctype","Corrupt PNG");
if (color == 3) pal_img_n = 3; else if (color & 1) return stbi__err("bad ctype","Corrupt PNG");
comp = stbi__get8(s); if (comp) return stbi__err("bad comp method","Corrupt PNG");
filter= stbi__get8(s); if (filter) return stbi__err("bad filter method","Corrupt PNG");
interlace = stbi__get8(s); if (interlace>1) return stbi__err("bad interlace method","Corrupt PNG");
if (!s->img_x || !s->img_y) return stbi__err("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) return stbi__err("too large", "Image too large to decode");
if (scan == STBI__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) return stbi__err("too large","Corrupt PNG");
// if SCAN_header, have to scan to see if we have a tRNS
}
break;
}
case STBI__PNG_TYPE('P','L','T','E'): {
if (first) return stbi__err("first not IHDR", "Corrupt PNG");
if (c.length > 256*3) return stbi__err("invalid PLTE","Corrupt PNG");
pal_len = c.length / 3;
if (pal_len * 3 != c.length) return stbi__err("invalid PLTE","Corrupt PNG");
for (i=0; i < pal_len; ++i) {
palette[i*4+0] = stbi__get8(s);
palette[i*4+1] = stbi__get8(s);
palette[i*4+2] = stbi__get8(s);
palette[i*4+3] = 255;
}
break;
}
case STBI__PNG_TYPE('t','R','N','S'): {
if (first) return stbi__err("first not IHDR", "Corrupt PNG");
if (z->idata) return stbi__err("tRNS after IDAT","Corrupt PNG");
if (pal_img_n) {
if (scan == STBI__SCAN_header) { s->img_n = 4; return 1; }
if (pal_len == 0) return stbi__err("tRNS before PLTE","Corrupt PNG");
if (c.length > pal_len) return stbi__err("bad tRNS len","Corrupt PNG");
pal_img_n = 4;
for (i=0; i < c.length; ++i)
palette[i*4+3] = stbi__get8(s);
} else {
if (!(s->img_n & 1)) return stbi__err("tRNS with alpha","Corrupt PNG");
if (c.length != (stbi__uint32) s->img_n*2) return stbi__err("bad tRNS len","Corrupt PNG");
has_trans = 1;
if (z->depth == 16) {
for (k = 0; k < s->img_n; ++k) tc16[k] = (stbi__uint16)stbi__get16be(s); // copy the values as-is
} else {
for (k = 0; k < s->img_n; ++k) tc[k] = (stbi_uc)(stbi__get16be(s) & 255) * stbi__depth_scale_table[z->depth]; // non 8-bit images will be larger
}
}
break;
}
case STBI__PNG_TYPE('I','D','A','T'): {
if (first) return stbi__err("first not IHDR", "Corrupt PNG");
if (pal_img_n && !pal_len) return stbi__err("no PLTE","Corrupt PNG");
if (scan == STBI__SCAN_header) { s->img_n = pal_img_n; return 1; }
if ((int)(ioff + c.length) < (int)ioff) return 0;
if (ioff + c.length > idata_limit) {
stbi__uint32 idata_limit_old = idata_limit;
stbi_uc *p;
if (idata_limit == 0) idata_limit = c.length > 4096 ? c.length : 4096;
while (ioff + c.length > idata_limit)
idata_limit *= 2;
STBI_NOTUSED(idata_limit_old);
p = (stbi_uc *) STBI_REALLOC_SIZED(z->idata, idata_limit_old, idata_limit); if (p == NULL) return stbi__err("outofmem", "Out of memory");
z->idata = p;
}
if (!stbi__getn(s, z->idata+ioff,c.length)) return stbi__err("outofdata","Corrupt PNG");
ioff += c.length;
break;
}
case STBI__PNG_TYPE('I','E','N','D'): {
stbi__uint32 raw_len, bpl;
if (first) return stbi__err("first not IHDR", "Corrupt PNG");
if (scan != STBI__SCAN_load) return 1;
if (z->idata == NULL) return stbi__err("no IDAT","Corrupt PNG");
// initial guess for decoded data size to avoid unnecessary reallocs
bpl = (s->img_x * z->depth + 7) / 8; // bytes per line, per component
raw_len = bpl * s->img_y * s->img_n /* pixels */ + s->img_y /* filter mode per row */;
z->expanded = (stbi_uc *) stbi_zlib_decode_malloc_guesssize_headerflag((char *) z->idata, ioff, raw_len, (int *) &raw_len, !is_iphone);
if (z->expanded == NULL) return 0; // zlib should set error
STBI_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 (!stbi__create_png_image(z, z->expanded, raw_len, s->img_out_n, z->depth, color, interlace)) return 0;
if (has_trans) {
if (z->depth == 16) {
if (!stbi__compute_transparency16(z, tc16, s->img_out_n)) return 0;
} else {
if (!stbi__compute_transparency(z, tc, s->img_out_n)) return 0;
}
}
if (is_iphone && stbi__de_iphone_flag && s->img_out_n > 2)
stbi__de_iphone(z);
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 (!stbi__expand_png_palette(z, palette, pal_len, s->img_out_n))
return 0;
} else if (has_trans) {
// non-paletted image with tRNS -> source image has (constant) alpha
++s->img_n;
}
STBI_FREE(z->expanded); z->expanded = NULL;
// end of PNG chunk, read and skip CRC
stbi__get32be(s);
return 1;
}
default:
// if critical, fail
if (first) return stbi__err("first not IHDR", "Corrupt PNG");
if ((c.type & (1 << 29)) == 0) {
#ifndef STBI_NO_FAILURE_STRINGS
// not threadsafe
static char invalid_chunk[] = "XXXX PNG chunk not known";
invalid_chunk[0] = STBI__BYTECAST(c.type >> 24);
invalid_chunk[1] = STBI__BYTECAST(c.type >> 16);
invalid_chunk[2] = STBI__BYTECAST(c.type >> 8);
invalid_chunk[3] = STBI__BYTECAST(c.type >> 0);
#endif
return stbi__err(invalid_chunk, "PNG not supported: unknown PNG chunk type");
}
stbi__skip(s, c.length);
break;
}
// end of PNG chunk, read and skip CRC
stbi__get32be(s);
}
}