michael@0: #define R16_BITS     5
michael@0: #define G16_BITS     6
michael@0: #define B16_BITS     5
michael@0: 
michael@0: #define R16_SHIFT    (B16_BITS + G16_BITS)
michael@0: #define G16_SHIFT    (B16_BITS)
michael@0: #define B16_SHIFT    0
michael@0: 
michael@0: #define MASK 0xff
michael@0: #define ONE_HALF 0x80
michael@0: 
michael@0: #define A_SHIFT 8 * 3
michael@0: #define R_SHIFT 8 * 2
michael@0: #define G_SHIFT 8
michael@0: #define A_MASK 0xff000000
michael@0: #define R_MASK 0xff0000
michael@0: #define G_MASK 0xff00
michael@0: 
michael@0: #define RB_MASK 0xff00ff
michael@0: #define AG_MASK 0xff00ff00
michael@0: #define RB_ONE_HALF 0x800080
michael@0: #define RB_MASK_PLUS_ONE 0x10000100
michael@0: 
michael@0: #define ALPHA_8(x) ((x) >> A_SHIFT)
michael@0: #define RED_8(x) (((x) >> R_SHIFT) & MASK)
michael@0: #define GREEN_8(x) (((x) >> G_SHIFT) & MASK)
michael@0: #define BLUE_8(x) ((x) & MASK)
michael@0: 
michael@0: // This uses the same dithering technique that Skia does.
michael@0: // It is essentially preturbing the lower bit based on the
michael@0: // high bit
michael@0: static inline uint16_t dither_32_to_16(uint32_t c)
michael@0: {
michael@0:     uint8_t b = BLUE_8(c);
michael@0:     uint8_t g = GREEN_8(c);
michael@0:     uint8_t r = RED_8(c);
michael@0:     r = ((r << 1) - ((r >> (8 - R16_BITS) << (8 - R16_BITS)) | (r >> R16_BITS))) >> (8 - R16_BITS);
michael@0:     g = ((g << 1) - ((g >> (8 - G16_BITS) << (8 - G16_BITS)) | (g >> G16_BITS))) >> (8 - G16_BITS);
michael@0:     b = ((b << 1) - ((b >> (8 - B16_BITS) << (8 - B16_BITS)) | (b >> B16_BITS))) >> (8 - B16_BITS);
michael@0:     return ((r << R16_SHIFT) | (g << G16_SHIFT) | (b << B16_SHIFT));
michael@0: }
michael@0: 
michael@0: static inline uint16_t dither_8888_to_0565(uint32_t color, pixman_bool_t toggle)
michael@0: {
michael@0:     // alternate between a preturbed truncation and a regular truncation
michael@0:     if (toggle) {
michael@0: 	return dither_32_to_16(color);
michael@0:     } else {
michael@0: 	return convert_8888_to_0565(color);
michael@0:     }
michael@0: }