Add premultiplied blending

src/modules/graphics/Graphics.cpp

@@ -121,6 +121,7 @@ namespace graphics
 		{ "additive", Graphics::BLEND_ADDITIVE },
 		{ "subtractive", Graphics::BLEND_SUBTRACTIVE },
 		{ "multiplicative", Graphics::BLEND_MULTIPLICATIVE },
+		{ "premultiplied", Graphics::BLEND_PREMULTIPLIED },
 	};
 
 	StringMap<Graphics::BlendMode, Graphics::BLEND_MAX_ENUM> Graphics::blendModes(Graphics::blendModeEntries, sizeof(Graphics::blendModeEntries));

src/modules/graphics/Graphics.h

@@ -54,6 +54,7 @@ namespace graphics
 			BLEND_ADDITIVE,
 			BLEND_SUBTRACTIVE,
 			BLEND_MULTIPLICATIVE,
+			BLEND_PREMULTIPLIED,
 			BLEND_MAX_ENUM
 		};
 

src/modules/graphics/opengl/Graphics.cpp

@@ -659,6 +659,8 @@ namespace opengl
 			glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 		else if (mode == BLEND_MULTIPLICATIVE)
 			glBlendFunc(GL_DST_COLOR, GL_ONE_MINUS_SRC_ALPHA);
+		else if (mode == BLEND_PREMULTIPLIED)
+			glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
 		else // mode == BLEND_ADDITIVE || mode == BLEND_SUBTRACTIVE
 			glBlendFunc(GL_SRC_ALPHA, GL_ONE);
 	}
@@ -684,8 +686,12 @@ namespace opengl
 			return BLEND_ADDITIVE;
 		else if (src == GL_SRC_ALPHA && dst == GL_ONE_MINUS_SRC_ALPHA) // && equation == GL_FUNC_ADD
 			return BLEND_ALPHA;
-		else // src == GL_DST_COLOR && dst == GL_ONE_MINUS_SRC_ALPHA && equation == GL_FUNC_ADD
+		else if (src == GL_DST_COLOR && dst == GL_ONE_MINUS_SRC_ALPHA) // && equation == GL_FUNC_ADD
 			return BLEND_MULTIPLICATIVE;
+		else if (src == GL_ONE && dst == GL_ONE_MINUS_SRC_ALPHA) // && equation == GL_FUNC_ADD
+			return BLEND_PREMULTIPLIED;
+			
+		return BLEND_MAX_ENUM; // Should never be reached.
 	}
 
 	Graphics::ColorMode Graphics::getColorMode()