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LibGfx/PNG: Respect the tRNS chunk transparency with color type 2

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For PNG color type 2 (TrueColor), if there's a tRNS chunk, it specifies
an R/G/B triplet in the image bit depth. This triplet acts as the
transparency value, and should yield transparent pixels wherever that
specific color value is present.

We now support this. :^)
This commit is contained in:
Andreas Kling 2022-02-14 17:55:35 +01:00
parent 5c7f11f1cd
commit f7f7aa6986
Notes: sideshowbarker 2024-07-17 18:48:30 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/f7f7aa6986
1 changed files with 37 additions and 5 deletions
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42
Userland/Libraries/LibGfx/PNGLoader.cpp
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@ -54,6 +54,8 @@ struct [[gnu::packed]] Triplet {
T r;
T g;
T b;
bool operator==(Triplet const& other) const = default;
};
template<typename T>
@ -313,6 +315,24 @@ ALWAYS_INLINE static void unpack_triplets_without_alpha(PNGLoadingContext& conte
}
}
template<typename T>
ALWAYS_INLINE static void unpack_triplets_with_transparency_value(PNGLoadingContext& context, Triplet<T> transparency_value)
{
for (int y = 0; y < context.height; ++y) {
auto* triplets = reinterpret_cast<const Triplet<T>*>(context.scanlines[y].data.data());
for (int i = 0; i < context.width; ++i) {
auto& pixel = (Pixel&)context.bitmap->scanline(y)[i];
pixel.r = triplets[i].r;
pixel.g = triplets[i].g;
pixel.b = triplets[i].b;
if (triplets[i] == transparency_value)
pixel.a = 0x00;
else
pixel.a = 0xff;
}
}
}
NEVER_INLINE FLATTEN static ErrorOr<void> unfilter(PNGLoadingContext& context)
{
// First unpack the scanlines to RGBA:
@ -352,12 +372,24 @@ NEVER_INLINE FLATTEN static ErrorOr<void> unfilter(PNGLoadingContext& context)
}
break;
case 2:
if (context.bit_depth == 8) {
unpack_triplets_without_alpha<u8>(context);
} else if (context.bit_depth == 16) {
unpack_triplets_without_alpha<u16>(context);
if (context.palette_transparency_data.size() == 6) {
if (context.bit_depth == 8) {
unpack_triplets_with_transparency_value<u8>(context, Triplet<u8> { context.palette_transparency_data[0], context.palette_transparency_data[2], context.palette_transparency_data[4] });
} else if (context.bit_depth == 16) {
u16 tr = context.palette_transparency_data[0] | context.palette_transparency_data[1] << 8;
u16 tg = context.palette_transparency_data[2] | context.palette_transparency_data[3] << 8;
u16 tb = context.palette_transparency_data[4] | context.palette_transparency_data[5] << 8;
unpack_triplets_with_transparency_value<u16>(context, Triplet<u16> { tr, tg, tb });
} else {
VERIFY_NOT_REACHED();
}
} else {
VERIFY_NOT_REACHED();
if (context.bit_depth == 8)
unpack_triplets_without_alpha<u8>(context);
else if (context.bit_depth == 16)
unpack_triplets_without_alpha<u16>(context);
else
VERIFY_NOT_REACHED();
}
break;
case 6: