Rethink 2x src alpha->color doubling. Fixes #3379.

GPU/GLES/FragmentShaderGenerator.cpp

@@ -234,33 +234,14 @@ static bool IsColorTestTriviallyTrue() {
 	}
 }
 
-static bool CanDoubleSrcBlendMode() {
+static bool AlphaToColorDoubling() {
 	if (!gstate.isAlphaBlendEnabled()) {
 		return false;
 	}
-
-	int funcA = gstate.getBlendFuncA();
-	int funcB = gstate.getBlendFuncB();
-	if (funcA != GE_SRCBLEND_DOUBLESRCALPHA) {
-		funcB = funcA;
-		funcA = gstate.getBlendFuncB();
-	}
-	if (funcA != GE_SRCBLEND_DOUBLESRCALPHA) {
-		return false;
-	}
-
-	// One side should be doubled.  Let's check the other side.
-	// LittleBigPlanet, for example, uses 2.0 * src, 1.0 - src, which can't double.
-	// Persona 2 uses the same function, which is the reason for its darkness. It only ever passes
-	// 1.0 as src alpha though, so in effect it's a color doubling.
-	switch (funcB) {
-	case GE_DSTBLEND_SRCALPHA:
-	case GE_DSTBLEND_INVSRCALPHA:
-		return false;
-
-	default:
-		return true;
-	}
+	// 2x alpha in the source function = source color doubling.
+	// We don't really need to care about the dest alpha function - sure we can't handle
+	// the doubling dest ones, but there's nothing we can do about that.
+	return (gstate.getBlendFuncA() == GE_SRCBLEND_DOUBLESRCALPHA);
 }
 
 // Here we must take all the bits of the gstate that determine what the fragment shader will
@@ -275,9 +256,8 @@ void ComputeFragmentShaderID(FragmentShaderID *id) {
 		bool enableFog = gstate.isFogEnabled() && !gstate.isModeThrough();
 		bool enableAlphaTest = gstate.isAlphaTestEnabled() && !IsAlphaTestTriviallyTrue() && !g_Config.bDisableAlphaTest;
 		bool enableColorTest = gstate.isColorTestEnabled() && !IsColorTestTriviallyTrue();
-		bool enableColorDoubling = gstate.isColorDoublingEnabled();
+		bool enableColorDoubling = gstate.isColorDoublingEnabled() || AlphaToColorDoubling();
 		// This isn't really correct, but it's a hack to get doubled blend modes to work more correctly.
-		bool enableAlphaDoubling = CanDoubleSrcBlendMode();
 		bool doTextureProjection = gstate.getUVGenMode() == GE_TEXMAP_TEXTURE_MATRIX;
 		bool doTextureAlpha = gstate.isTextureAlphaUsed();
 		ReplaceAlphaType stencilToAlpha = ReplaceAlphaWithStencil();
@@ -303,7 +283,6 @@ void ComputeFragmentShaderID(FragmentShaderID *id) {
 		id->d[0] |= (enableFog & 1) << 15;
 		id->d[0] |= (doTextureProjection & 1) << 16;
 		id->d[0] |= (enableColorDoubling & 1) << 17;
-		id->d[0] |= (enableAlphaDoubling & 1) << 18;
 		id->d[0] |= (stencilToAlpha) << 19;
 
 		if (stencilToAlpha != REPLACE_ALPHA_NO) {
@@ -381,9 +360,12 @@ void GenerateFragmentShader(char *buffer) {
 	bool enableFog = gstate.isFogEnabled() && !gstate.isModeThrough() && !gstate.isModeClear();
 	bool enableAlphaTest = gstate.isAlphaTestEnabled() && !IsAlphaTestTriviallyTrue() && !gstate.isModeClear() && !g_Config.bDisableAlphaTest;
 	bool enableColorTest = gstate.isColorTestEnabled() && !IsColorTestTriviallyTrue() && !gstate.isModeClear();
-	bool enableColorDoubling = gstate.isColorDoublingEnabled() && gstate.isTextureMapEnabled();
+
+	// If alpha doubling is enabled, we double the color value instead. Otherwise alpha 255 doubled will have no effect.
+	// TODO: Why the texturemapenabled check?
+	bool enableColorDoubling = (gstate.isColorDoublingEnabled() && gstate.isTextureMapEnabled()) || AlphaToColorDoubling();
+
 	// This isn't really correct, but it's a hack to get doubled blend modes to work more correctly.
-	bool enableAlphaDoubling = CanDoubleSrcBlendMode();
 	bool doTextureProjection = gstate.getUVGenMode() == GE_TEXMAP_TEXTURE_MATRIX;
 	bool doTextureAlpha = gstate.isTextureAlphaUsed();
 	ReplaceAlphaType stencilToAlpha = ReplaceAlphaWithStencil();
@@ -547,12 +529,8 @@ void GenerateFragmentShader(char *buffer) {
 		}
 
 		// Color doubling happens after the color test.
-		if (enableColorDoubling && enableAlphaDoubling) {
-			WRITE(p, "  v = v * 2.0;\n");
-		} else if (enableColorDoubling) {
+		if (enableColorDoubling) {
 			WRITE(p, "  v.rgb = v.rgb * 2.0;\n");
-		} else if (enableAlphaDoubling) {
-			WRITE(p, "  v.a = v.a * 2.0;\n");
 		}
 
 		if (enableFog) {