1 #define R16_BITS 5 2 #define G16_BITS 6 3 #define B16_BITS 5 4 5 #define R16_SHIFT (B16_BITS + G16_BITS) 6 #define G16_SHIFT (B16_BITS) 7 #define B16_SHIFT 0 8 9 #define MASK 0xff 10 #define ONE_HALF 0x80 11 12 #define A_SHIFT 8 * 3 13 #define R_SHIFT 8 * 2 14 #define G_SHIFT 8 15 #define A_MASK 0xff000000 16 #define R_MASK 0xff0000 17 #define G_MASK 0xff00 18 19 #define RB_MASK 0xff00ff 20 #define AG_MASK 0xff00ff00 21 #define RB_ONE_HALF 0x800080 22 #define RB_MASK_PLUS_ONE 0x10000100 23 24 #define ALPHA_8(x) ((x) >> A_SHIFT) 25 #define RED_8(x) (((x) >> R_SHIFT) & MASK) 26 #define GREEN_8(x) (((x) >> G_SHIFT) & MASK) 27 #define BLUE_8(x) ((x) & MASK) 28 29 // This uses the same dithering technique that Skia does. 30 // It is essentially preturbing the lower bit based on the 31 // high bit dither_32_to_16(uint32_t c)32static inline uint16_t dither_32_to_16(uint32_t c) 33 { 34 uint8_t b = BLUE_8(c); 35 uint8_t g = GREEN_8(c); 36 uint8_t r = RED_8(c); 37 r = ((r << 1) - ((r >> (8 - R16_BITS) << (8 - R16_BITS)) | (r >> R16_BITS))) >> (8 - R16_BITS); 38 g = ((g << 1) - ((g >> (8 - G16_BITS) << (8 - G16_BITS)) | (g >> G16_BITS))) >> (8 - G16_BITS); 39 b = ((b << 1) - ((b >> (8 - B16_BITS) << (8 - B16_BITS)) | (b >> B16_BITS))) >> (8 - B16_BITS); 40 return ((r << R16_SHIFT) | (g << G16_SHIFT) | (b << B16_SHIFT)); 41 } 42 dither_8888_to_0565(uint32_t color,pixman_bool_t toggle)43static inline uint16_t dither_8888_to_0565(uint32_t color, pixman_bool_t toggle) 44 { 45 // alternate between a preturbed truncation and a regular truncation 46 if (toggle) { 47 return dither_32_to_16(color); 48 } else { 49 return convert_8888_to_0565(color); 50 } 51 } 52