Correct a couple spots where inaccurate integer math was used for col…

…or mult
coornio · Jan 15, 2025 · c1f0614 · c1f0614
1 parent 0f45afe
commit c1f0614
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Showing 2 changed files with 8 additions and 8 deletions.
diff --git a/src/Assistants/Typedefs.hpp b/src/Assistants/Typedefs.hpp
@@ -80,8 +80,8 @@ struct alignas(4) RGBA {
 	constexpr operator u32() const noexcept { return R << 24 | G << 16 | B << 8 | A; }
 };
 
-inline constexpr u8 ChannelPremul(const u8 color, const u8 alpha) noexcept {
-	return ((color * (alpha | alpha << 8)) + 0x8080) >> 16;
+inline constexpr u8 IntColorMult(const u8 color1, const u8 color2) noexcept {
+	return ((color1 * (color2 | color2 << 8)) + 0x8080) >> 16;
 }
 
 template <typename T, typename E>

diff --git a/src/Systems/CHIP8/Cores/MEGACHIP.cpp b/src/Systems/CHIP8/Cores/MEGACHIP.cpp
@@ -393,8 +393,8 @@ void MEGACHIP::initializeFontColors() noexcept {
 }
 
 RGBA MEGACHIP::blendPixel(RGBA src, RGBA dst) const noexcept {
-	src.A = (src.A * mTexture.opacity) >> 8 & 0xFF;
-	if (src.A == 0x00) [[unlikely]] { return dst; }
+	src.A = IntColorMult(src.A, mTexture.opacity);
+	if (src.A == 0x0) [[unlikely]] { return dst; }
 
 	RGBA out{
 		intBlendAlgo(src.R, dst.R),
@@ -405,9 +405,9 @@ RGBA MEGACHIP::blendPixel(RGBA src, RGBA dst) const noexcept {
 	if (src.A < 0xFF) {
 		const auto dW{ static_cast<u8>(~src.A) };
 
-		out.R = 0xFF & ChannelPremul(dst.R, dW) + ChannelPremul(out.R, src.A);
-		out.G = 0xFF & ChannelPremul(dst.G, dW) + ChannelPremul(out.G, src.A);
-		out.B = 0xFF & ChannelPremul(dst.B, dW) + ChannelPremul(out.B, src.A);
+		out.R = 0xFF & IntColorMult(dst.R, dW) + IntColorMult(out.R, src.A);
+		out.G = 0xFF & IntColorMult(dst.G, dW) + IntColorMult(out.G, src.A);
+		out.B = 0xFF & IntColorMult(dst.B, dW) + IntColorMult(out.B, src.A);
 		out.A = 0xFF & std::min(src.A + ((dst.A * dW) >> 8), 0xFF);
 	}
 
@@ -423,7 +423,7 @@ void MEGACHIP::setNewBlendAlgorithm(const s32 mode) noexcept {
 
 		case BlendMode::MULTIPLY:
 			intBlendAlgo = [](const u8 src, const u8 dst)
-				noexcept { return static_cast<u8>((src * dst) >> 8); };
+				noexcept { return IntColorMult(src, dst); };
 			break;
 
 		default: