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fix: Port upstream 1.1.0-rc fixes (glyph null-safety, PNGdec wide image buffer)

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Cherry-pick two bug fixes from upstream PR #992:

- fix(GfxRenderer): Null-safety in getSpaceWidth/getTextAdvanceX to
  prevent Load access fault when bold/italic font variants lack certain
  glyphs (upstream 3e2c518)
- fix(PNGdec): Increase PNG_MAX_BUFFERED_PIXELS to 16416 for 2048px
  wide images and add pre-decode buffer overflow guard (upstream b8e743e)

Co-authored-by: Cursor <cursoragent@cursor.com>
This commit is contained in:
cottongin
2026-02-19 13:20:30 -05:00
parent 0fda9031fd
commit c1b8e53138
3 changed files with 46 additions and 5 deletions
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38
lib/Epub/Epub/converters/PngToFramebufferConverter.cpp
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@@ -90,6 +90,32 @@ int32_t pngSeekWithHandle(PNGFILE* pFile, int32_t pos) {
constexpr size_t PNG_DECODER_APPROX_SIZE = 44 * 1024; // ~42 KB + overhead
constexpr size_t MIN_FREE_HEAP_FOR_PNG = PNG_DECODER_APPROX_SIZE + 16 * 1024; // decoder + 16 KB headroom
// PNGdec keeps TWO scanlines in its internal ucPixels buffer (current + previous)
// and each scanline includes a leading filter byte.
// Required storage is therefore approximately: 2 * (pitch + 1) + alignment slack.
// If PNG_MAX_BUFFERED_PIXELS is smaller than this requirement for a given image,
// PNGdec can overrun its internal buffer before our draw callback executes.
int bytesPerPixelFromType(int pixelType) {
switch (pixelType) {
case PNG_PIXEL_TRUECOLOR:
return 3;
case PNG_PIXEL_GRAY_ALPHA:
return 2;
case PNG_PIXEL_TRUECOLOR_ALPHA:
return 4;
case PNG_PIXEL_GRAYSCALE:
case PNG_PIXEL_INDEXED:
default:
return 1;
}
}
int requiredPngInternalBufferBytes(int srcWidth, int pixelType) {
// +1 filter byte per scanline, *2 for current+previous lines, +32 for alignment margin.
int pitch = srcWidth * bytesPerPixelFromType(pixelType);
return ((pitch + 1) * 2) + 32;
}
// Convert entire source line to grayscale with alpha blending to white background.
// For indexed PNGs with tRNS chunk, alpha values are stored at palette[768] onwards.
// Processing the whole line at once improves cache locality and reduces per-pixel overhead.
@@ -304,6 +330,18 @@ bool PngToFramebufferConverter::decodeToFramebuffer(const std::string& imagePath
LOG_DBG("PNG", "PNG %dx%d -> %dx%d (scale %.2f), bpp: %d", ctx.srcWidth, ctx.srcHeight, ctx.dstWidth, ctx.dstHeight,
ctx.scale, png->getBpp());
const int pixelType = png->getPixelType();
const int requiredInternal = requiredPngInternalBufferBytes(ctx.srcWidth, pixelType);
if (requiredInternal > PNG_MAX_BUFFERED_PIXELS) {
LOG_ERR("PNG",
"PNG row buffer too small: need %d bytes for width=%d type=%d, configured PNG_MAX_BUFFERED_PIXELS=%d",
requiredInternal, ctx.srcWidth, pixelType, PNG_MAX_BUFFERED_PIXELS);
LOG_ERR("PNG", "Aborting decode to avoid PNGdec internal buffer overflow");
png->close();
delete png;
return false;
}
if (png->getBpp() != 8) {
warnUnsupportedFeature("bit depth (" + std::to_string(png->getBpp()) + "bpp)", imagePath);
}