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PNGLoader: Templatize the unfiltering functions to reduce branchiness.

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This also allows us to dodge processing alpha values in non-alpha PNGs
without a branch.
This commit is contained in:
Andreas Kling 2019-03-21 16:40:40 +01:00
parent cfc521d57e
commit cd1afde48c
Notes: sideshowbarker 2024-07-19 14:58:43 +09:00 
Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/cd1afde48c7
1 changed files with 103 additions and 37 deletions
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140
SharedGraphics/PNGLoader.cpp
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@ -137,7 +137,7 @@ RetainPtr<GraphicsBitmap> load_png(const String& path)
return bitmap;
}
static byte paeth_predictor(int a, int b, int c)
[[gnu::always_inline]] static inline byte paeth_predictor(int a, int b, int c)
{
int p = a + b - c;
int pa = abs(p - a);
@ -161,6 +161,81 @@ union [[gnu::packed]] Pixel {
};
static_assert(sizeof(Pixel) == 4);
template<bool has_alpha, byte filter_type>
[[gnu::always_inline]] static inline void unfilter_impl(const GraphicsBitmap& bitmap, int y)
{
if constexpr (filter_type == 1) {
auto* pixels = (Pixel*)bitmap.scanline(y);
for (int i = 0; i < bitmap.width(); ++i) {
auto& x = pixels[i];
swap(x.r, x.b);
Pixel a;
if (i != 0) a.rgba = bitmap.scanline(y)[i - 1];
x.r += a.r;
x.g += a.g;
x.b += a.b;
if constexpr (has_alpha)
x.a += a.a;
}
return;
}
if constexpr (filter_type == 2) {
auto* pixels = (Pixel*)bitmap.scanline(y);
for (int i = 0; i < bitmap.width(); ++i) {
auto& x = pixels[i];
swap(x.r, x.b);
Pixel b;
if (y != 0) b.rgba = bitmap.scanline(y - 1)[i];
x.r += b.r;
x.g += b.g;
x.b += b.b;
if constexpr (has_alpha)
x.a += b.a;
}
return;
}
if constexpr (filter_type == 3) {
auto* pixels = (Pixel*)bitmap.scanline(y);
for (int i = 0; i < bitmap.width(); ++i) {
auto& x = pixels[i];
swap(x.r, x.b);
Pixel a;
Pixel b;
if (i != 0) a.rgba = bitmap.scanline(y)[i - 1];
if (y != 0) b.rgba = bitmap.scanline(y - 1)[i];
x.r = x.r + ((a.r + b.r) / 2);
x.g = x.g + ((a.g + b.g) / 2);
x.b = x.b + ((a.b + b.b) / 2);
if constexpr (has_alpha)
x.a = x.a + ((a.a + b.a) / 2);
}
return;
}
if constexpr (filter_type == 4) {
auto* pixels = (Pixel*)bitmap.scanline(y);
for (int i = 0; i < bitmap.width(); ++i) {
auto& x = pixels[i];
swap(x.r, x.b);
Pixel a;
Pixel b;
Pixel c;
if (i != 0) a.rgba = bitmap.scanline(y)[i - 1];
if (y != 0) b.rgba = bitmap.scanline(y - 1)[i];
if (y != 0 && i != 0) c.rgba = bitmap.scanline(y - 1)[i - 1];
x.r += paeth_predictor(a.r, b.r, c.r);
x.g += paeth_predictor(a.g, b.g, c.g);
x.b += paeth_predictor(a.b, b.b, c.b);
if constexpr (has_alpha)
x.a += paeth_predictor(a.a, b.a, c.a);
}
}
}
[[gnu::noinline]] static void unfilter(PNGLoadingContext& context)
{
{
@ -196,42 +271,33 @@ static_assert(sizeof(Pixel) == 4);
auto filter = context.scanlines[y].filter;
if (filter == 0)
continue;
for (int i = 0; i < context.width; ++i) {
auto& x = (Pixel&)context.bitmap->scanline(y)[i];
swap(x.r, x.b);
Pixel a;
Pixel b;
if (i != 0) a.rgba = context.bitmap->scanline(y)[i - 1];
if (y != 0) b.rgba = context.bitmap->scanline(y - 1)[i];
if (filter == 1) {
x.r += a.r;
x.g += a.g;
x.b += a.b;
if (context.has_alpha())
x.a += a.a;
} else if (filter == 2) {
x.r += b.r;
x.g += b.g;
x.b += b.b;
if (context.has_alpha())
x.a += b.a;
} if (filter == 3) {
x.r = x.r + ((a.r + b.r) / 2);
x.g = x.g + ((a.g + b.g) / 2);
x.b = x.b + ((a.b + b.b) / 2);
if (context.has_alpha())
x.a = x.a + ((a.a + b.a) / 2);
} if (filter == 4) {
Pixel c;
if (y != 0 && i != 0) c.rgba = context.bitmap->scanline(y - 1)[i - 1];
x.r += paeth_predictor(a.r, b.r, c.r);
x.g += paeth_predictor(a.g, b.g, c.g);
x.b += paeth_predictor(a.b, b.b, c.b);
if (context.has_alpha())
x.a += paeth_predictor(a.a, b.a, c.a);
}
if (filter == 1) {
if (context.has_alpha())
unfilter_impl<true, 1>(*context.bitmap, y);
else
unfilter_impl<false, 1>(*context.bitmap, y);
continue;
}
if (filter == 2) {
if (context.has_alpha())
unfilter_impl<true, 2>(*context.bitmap, y);
else
unfilter_impl<false, 2>(*context.bitmap, y);
continue;
}
if (filter == 3) {
if (context.has_alpha())
unfilter_impl<true, 3>(*context.bitmap, y);
else
unfilter_impl<false, 3>(*context.bitmap, y);
continue;
}
if (filter == 4) {
if (context.has_alpha())
unfilter_impl<true, 4>(*context.bitmap, y);
else
unfilter_impl<false, 4>(*context.bitmap, y);
continue;
}
}
}