(svn r11076) -Fix: MakeTransparent of 32bpp blitter used 0..100; using 0..255 makes it much faster (frosch)

-Fix: ComposeColourXXX could work a tiny bit faster when using 256, not 255 as value to divide with; downside is that it can give alpha errors (frosch)

src/blitter/32bpp_anim.cpp

@@ -59,7 +59,7 @@ void Blitter_32bppAnim::Draw(Blitter::BlitterParams *bp, BlitterMode mode, ZoomL
 
 					/* Make the current color a bit more black, so it looks like this image is transparent */
 					if (src->a != 0) {
-						*dst = MakeTransparent(*dst, 75);
+						*dst = MakeTransparent(*dst, 192);
 						*anim = bp->remap[*anim];
 					}
 					break;
@@ -90,7 +90,7 @@ void Blitter_32bppAnim::DrawColorMappingRect(void *dst, int width, int height, i
 	if (pal == PALETTE_TO_TRANSPARENT) {
 		do {
 			for (int i = 0; i != width; i++) {
-				*udst = MakeTransparent(*udst, 60);
+				*udst = MakeTransparent(*udst, 154);
 				*anim = 0;
 				udst++;
 				anim++;

src/blitter/32bpp_base.hpp

@@ -48,15 +48,19 @@ public:
 	 */
 	static inline uint ComposeColourRGBA(uint r, uint g, uint b, uint a, uint current)
 	{
+		if (a == 0) return current;
+		if (a >= 255) return ComposeColour(0xFF, r, g, b);
+
 		uint cr, cg, cb;
 		cr = GB(current, 16, 8);
 		cg = GB(current, 8,  8);
 		cb = GB(current, 0,  8);
 
+		/* The 256 is wrong, it should be 255, but 256 is much faster... */
 		return ComposeColour(0xFF,
-												(r * a + cr * (255 - a)) / 255,
+												(r * a + cr * (256 - a)) / 256,
-												(g * a + cg * (255 - a)) / 255,
+												(g * a + cg * (256 - a)) / 256,
-												(b * a + cb * (255 - a)) / 255);
+												(b * a + cb * (256 - a)) / 256);
 	}
 
 	/**
@@ -64,24 +68,28 @@ public:
 	*/
 	static inline uint ComposeColourPA(uint colour, uint a, uint current)
 	{
+		if (a == 0) return current;
+		if (a >= 255) return (colour | 0xFF000000);
+
 		uint r, g, b, cr, cg, cb;
-		r  = GB(colour,   16, 8);
+		r  = GB(colour,  16, 8);
-		g  = GB(colour,   8,  8);
+		g  = GB(colour,  8,  8);
-		b  = GB(colour,   0,  8);
+		b  = GB(colour,  0,  8);
 		cr = GB(current, 16, 8);
 		cg = GB(current, 8,  8);
 		cb = GB(current, 0,  8);
 
+		/* The 256 is wrong, it should be 255, but 256 is much faster... */
 		return ComposeColour(0xFF,
-												(r * a + cr * (255 - a)) / 255,
+												(r * a + cr * (256 - a)) / 256,
-												(g * a + cg * (255 - a)) / 255,
+												(g * a + cg * (256 - a)) / 256,
-												(b * a + cb * (255 - a)) / 255);
+												(b * a + cb * (256 - a)) / 256);
 	}
 
 	/**
 	* Make a pixel looks like it is transparent.
 	* @param colour the colour already on the screen.
-	* @param amount the amount of transparency, times 100.
+	* @param amount the amount of transparency, times 256.
 	* @return the new colour for the screen.
 	*/
 	static inline uint MakeTransparent(uint colour, uint amount)
@@ -91,7 +99,7 @@ public:
 		g = GB(colour, 8,  8);
 		b = GB(colour, 0,  8);
 
-		return ComposeColour(0xFF, r * amount / 100, g * amount / 100, b * amount / 100);
+		return ComposeColour(0xFF, r * amount / 256, g * amount / 256, b * amount / 256);
 	}
 
 	/**

src/blitter/32bpp_simple.cpp

@@ -40,7 +40,7 @@ void Blitter_32bppSimple::Draw(Blitter::BlitterParams *bp, BlitterMode mode, Zoo
 					 *  we produce a result the newgrf maker didn't expect ;) */
 
 					/* Make the current color a bit more black, so it looks like this image is transparent */
-					if (src->a != 0) *dst = MakeTransparent(*dst, 75);
+					if (src->a != 0) *dst = MakeTransparent(*dst, 192);
 					break;
 
 				default:
@@ -60,7 +60,7 @@ void Blitter_32bppSimple::DrawColorMappingRect(void *dst, int width, int height,
 	if (pal == PALETTE_TO_TRANSPARENT) {
 		do {
 			for (int i = 0; i != width; i++) {
-				*udst = MakeTransparent(*udst, 60);
+				*udst = MakeTransparent(*udst, 154);
 				udst++;
 			}
 			udst = udst - width + _screen.pitch;