GRAPHICS: Improve color bit depth conversion

Data is no longer truncated it so should be more accurate. See pull request #486 for more info.

1 files changed, 125 insertions, 7 deletions

diff --git a/graphics/pixelformat.h b/graphics/pixelformat.h
index 792833a8e3..00db6702fc 100644
--- a/graphics/pixelformat.h
+++ b/graphics/pixelformat.h
@@ -27,6 +27,97 @@
 
 namespace Graphics {
 
+/** Template to expand from an n-bit component to an 8-bit component */
+template<int depth>
+struct ColorComponent {
+};
+
+template<>
+struct ColorComponent<0> {
+	static inline uint expand(uint value) {
+		return 0;
+	}
+};
+
+template<>
+struct ColorComponent<1> {
+	static inline uint expand(uint value) {
+		value &= 1;
+		return value |
+		       (value << 1) |
+		       (value << 2) |
+		       (value << 3) |
+		       (value << 4) |
+		       (value << 5) |
+		       (value << 6) |
+		       (value << 7);
+	}
+};
+
+template<>
+struct ColorComponent<2> {
+	static inline uint expand(uint value) {
+		value &= 3;
+		return value |
+		       (value << 2) |
+		       (value << 4) |
+		       (value << 6);
+	}
+};
+
+template<>
+struct ColorComponent<3> {
+	static inline uint expand(uint value) {
+		value &= 7;
+		return (value << 5) |
+		       (value << 2) |
+		       (value >> 1);
+	}
+};
+
+template<>
+struct ColorComponent<4> {
+	static inline uint expand(uint value) {
+		value &= 15;
+		return value |
+		       (value << 4);
+	}
+};
+
+template<>
+struct ColorComponent<5> {
+	static inline uint expand(uint value) {
+		value &= 31;
+		return (value << 3) |
+		       (value >> 2);
+	}
+};
+
+template<>
+struct ColorComponent<6> {
+	static inline uint expand(uint value) {
+		value &= 63;
+		return (value << 2) |
+		       (value >> 4);
+	}
+};
+
+template<>
+struct ColorComponent<7> {
+	static inline uint expand(uint value) {
+		value &= 127;
+		return (value << 1) |
+		       (value >> 6);
+	}
+};
+
+template<>
+struct ColorComponent<8> {
+	static inline uint expand(uint value) {
+		return value & 255;
+	}
+};
+
 /**
  * A pixel format description.
  *
@@ -91,16 +182,16 @@ struct PixelFormat {
 	}
 
 	inline void colorToRGB(uint32 color, uint8 &r, uint8 &g, uint8 &b) const {
-		r = ((color >> rShift) << rLoss) & 0xFF;
-		g = ((color >> gShift) << gLoss) & 0xFF;
-		b = ((color >> bShift) << bLoss) & 0xFF;
+		r = expand(rBits(), color >> rShift);
+		g = expand(gBits(), color >> gShift);
+		b = expand(bBits(), color >> bShift);
 	}
 
 	inline void colorToARGB(uint32 color, uint8 &a, uint8 &r, uint8 &g, uint8 &b) const {
-		a = (aBits() == 0) ? 0xFF : (((color >> aShift) << aLoss) & 0xFF);
-		r = ((color >> rShift) << rLoss) & 0xFF;
-		g = ((color >> gShift) << gLoss) & 0xFF;
-		b = ((color >> bShift) << bLoss) & 0xFF;
+		a = (aBits() == 0) ? 0xFF : expand(aBits(), color >> aShift);
+		r = expand(rBits(), color >> rShift);
+		g = expand(gBits(), color >> gShift);
+		b = expand(bBits(), color >> bShift);
 	}
 
 	//////////////////////////////////////////////////////////////////////
@@ -142,6 +233,33 @@ struct PixelFormat {
 	inline uint aMax() const {
 		return (1 << aBits()) - 1;
 	}
+
+	/** Expand a given bit-depth component to a full 8-bit component */
+	static inline uint expand(uint bits, uint color) {
+		switch (bits) {
+		case 0:
+			return ColorComponent<0>::expand(color);
+		case 1:
+			return ColorComponent<1>::expand(color);
+		case 2:
+			return ColorComponent<2>::expand(color);
+		case 3:
+			return ColorComponent<3>::expand(color);
+		case 4:
+			return ColorComponent<4>::expand(color);
+		case 5:
+			return ColorComponent<5>::expand(color);
+		case 6:
+			return ColorComponent<6>::expand(color);
+		case 7:
+			return ColorComponent<7>::expand(color);
+		case 8:
+			return ColorComponent<8>::expand(color);
+		}
+
+		// Unsupported
+		return 0;
+	}
 };
 
 } // End of namespace Graphics