add BLEND_WEIGHTED_MULTIPLY and BLEND_INVERT_DEST blend modes

stepmania/src/Actor.cpp

@@ -1175,6 +1175,8 @@ void Actor::SetBlendModeString( const RString &s )
 {
 	if     (s.EqualsNoCase("normal"))	this->SetBlendMode( BLEND_NORMAL );
 	else if(s.EqualsNoCase("add"))		this->SetBlendMode( BLEND_ADD );
+	else if(s.EqualsNoCase("weightedmultiply")) this->SetBlendMode( BLEND_WEIGHTED_MULTIPLY );
+	else if(s.EqualsNoCase("invertdest")) this->SetBlendMode( BLEND_INVERT_DEST );
 	else if(s.EqualsNoCase("noeffect"))	this->SetBlendMode( BLEND_NO_EFFECT );
 	else	ASSERT(0);
 }

stepmania/src/RageDisplay_OGL.cpp

@@ -1416,6 +1416,14 @@ void RageDisplay_OGL::SetBlendMode( BlendMode mode )
 {
 	glEnable(GL_BLEND);
 
+	if( GLExt.glBlendEquation != NULL )
+	{
+		if( mode == BLEND_INVERT_DEST )
+			GLExt.glBlendEquation( GL_FUNC_SUBTRACT );
+		else
+			GLExt.glBlendEquation( GL_FUNC_ADD );
+	}
+
 	switch( mode )
 	{
 	case BLEND_NORMAL:
@@ -1424,6 +1432,16 @@ void RageDisplay_OGL::SetBlendMode( BlendMode mode )
 	case BLEND_ADD:
 		glBlendFunc( GL_SRC_ALPHA, GL_ONE );
 		break;
+	case BLEND_WEIGHTED_MULTIPLY:
+		/* output = 2*(dst*src).  0.5,0.5,0.5 is identity; darker colors darken the image,
+		 * and brighter colors lighten the image. */
+		glBlendFunc( GL_DST_COLOR, GL_SRC_COLOR );
+
+		break;
+	case BLEND_INVERT_DEST:
+		/* out = src - dst.  The source color should almost always be #FFFFFF, to make it "1 - dst". */
+		glBlendFunc( GL_ONE, GL_ONE );
+		break;
 	case BLEND_NO_EFFECT:
 		/* XXX: Would it be faster and have the same effect to say glDisable(GL_COLOR_WRITEMASK)? */
 		glBlendFunc( GL_ZERO, GL_ONE );

stepmania/src/RageTypes.h

@@ -3,7 +3,7 @@
 #ifndef RAGETYPES_H
 #define RAGETYPES_H
 
-enum BlendMode { BLEND_NORMAL, BLEND_ADD, BLEND_NO_EFFECT, BLEND_INVALID };
+enum BlendMode { BLEND_NORMAL, BLEND_ADD, BLEND_WEIGHTED_MULTIPLY, BLEND_INVERT_DEST, BLEND_NO_EFFECT, BLEND_INVALID };
 enum CullMode { CULL_BACK, CULL_FRONT, CULL_NONE };
 enum ZTestMode { ZTEST_OFF, ZTEST_WRITE_ON_PASS, ZTEST_WRITE_ON_FAIL };
 enum PolygonMode { POLYGON_FILL, POLYGON_LINE };