1
2/*
3 * Copyright 2011 Google Inc.
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8#include "SkDither.h"
9
10/*  The base dither matrix we use to derive optimized ones for 565 and 4444
11
12    { 0,  32, 8,  40, 2,  34, 10, 42 },
13    { 48, 16, 56, 24, 50, 18, 58, 26 },
14    { 12, 44, 4,  36, 14, 46, 6,  38 },
15    { 60, 28, 52, 20, 62, 30, 54, 22 },
16    { 3,  35, 11, 43, 1,  33, 9,  41 },
17    { 51, 19, 59, 27, 49, 17, 57, 25 },
18    { 15, 47, 7,  39, 13, 45, 5,  37 },
19    { 63, 31, 55, 23, 61, 29, 53, 21 }
20
21    The 4444 version only needs 4 bits, and given that we can reduce its size
22    since the other 4x4 sub pieces all look the same once we truncate the bits.
23
24    The 565 version only needs 3 bits for red/blue, and only 2 bits for green.
25    For simplicity, we store 3 bits, and have the dither macros for green know
26    this, and they shift the dither value down by 1 to make it 2 bits.
27 */
28
29#ifdef ENABLE_DITHER_MATRIX_4X4
30
31const uint8_t gDitherMatrix_4Bit_4X4[4][4] = {
32    {  0,  8,  2, 10 },
33    { 12,  4, 14,  6 },
34    {  3, 11,  1,  9 },
35    { 15,  7, 13,  5 }
36};
37
38const uint8_t gDitherMatrix_3Bit_4X4[4][4] = {
39    {  0,  4,  1,  5 },
40    {  6,  2,  7,  3 },
41    {  1,  5,  0,  4 },
42    {  7,  3,  6,  2 }
43};
44
45#else   // used packed shorts for a scanlines worth of dither values
46
47const uint16_t gDitherMatrix_4Bit_16[4] = {
48    0xA280, 0x6E4C, 0x91B3, 0x5D7F
49};
50
51const uint16_t gDitherMatrix_3Bit_16[4] = {
52    0x5140, 0x3726, 0x4051, 0x2637
53};
54
55#endif
56
57