1 2 /* 3 * Copyright 2006 The Android Open Source Project 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 9 10 #ifndef SkAntiRun_DEFINED 11 #define SkAntiRun_DEFINED 12 13 #include "SkBlitter.h" 14 15 /** Sparse array of run-length-encoded alpha (supersampling coverage) values. 16 Sparseness allows us to independently compose several paths into the 17 same SkAlphaRuns buffer. 18 */ 19 20 class SkAlphaRuns { 21 public: 22 int16_t* fRuns; 23 uint8_t* fAlpha; 24 25 /// Returns true if the scanline contains only a single run, 26 /// of alpha value 0. 27 bool empty() const { 28 SkASSERT(fRuns[0] > 0); 29 return fAlpha[0] == 0 && fRuns[fRuns[0]] == 0; 30 } 31 32 /// Reinitialize for a new scanline. 33 void reset(int width); 34 35 /** 36 * Insert into the buffer a run starting at (x-offsetX): 37 * if startAlpha > 0 38 * one pixel with value += startAlpha, 39 * max 255 40 * if middleCount > 0 41 * middleCount pixels with value += maxValue 42 * if stopAlpha > 0 43 * one pixel with value += stopAlpha 44 * Returns the offsetX value that should be passed on the next call, 45 * assuming we're on the same scanline. If the caller is switching 46 * scanlines, then offsetX should be 0 when this is called. 47 */ 48 SK_ALWAYS_INLINE int add(int x, U8CPU startAlpha, int middleCount, U8CPU stopAlpha, 49 U8CPU maxValue, int offsetX) { 50 SkASSERT(middleCount >= 0); 51 SkASSERT(x >= 0 && x + (startAlpha != 0) + middleCount + (stopAlpha != 0) <= fWidth); 52 53 SkASSERT(fRuns[offsetX] >= 0); 54 55 int16_t* runs = fRuns + offsetX; 56 uint8_t* alpha = fAlpha + offsetX; 57 uint8_t* lastAlpha = alpha; 58 x -= offsetX; 59 60 if (startAlpha) { 61 SkAlphaRuns::Break(runs, alpha, x, 1); 62 /* I should be able to just add alpha[x] + startAlpha. 63 However, if the trailing edge of the previous span and the leading 64 edge of the current span round to the same super-sampled x value, 65 I might overflow to 256 with this add, hence the funny subtract (crud). 66 */ 67 unsigned tmp = alpha[x] + startAlpha; 68 SkASSERT(tmp <= 256); 69 alpha[x] = SkToU8(tmp - (tmp >> 8)); // was (tmp >> 7), but that seems wrong if we're trying to catch 256 70 71 runs += x + 1; 72 alpha += x + 1; 73 x = 0; 74 lastAlpha += x; // we don't want the +1 75 SkDEBUGCODE(this->validate();) 76 } 77 78 if (middleCount) { 79 SkAlphaRuns::Break(runs, alpha, x, middleCount); 80 alpha += x; 81 runs += x; 82 x = 0; 83 do { 84 alpha[0] = SkToU8(alpha[0] + maxValue); 85 int n = runs[0]; 86 SkASSERT(n <= middleCount); 87 alpha += n; 88 runs += n; 89 middleCount -= n; 90 } while (middleCount > 0); 91 SkDEBUGCODE(this->validate();) 92 lastAlpha = alpha; 93 } 94 95 if (stopAlpha) { 96 SkAlphaRuns::Break(runs, alpha, x, 1); 97 alpha += x; 98 alpha[0] = SkToU8(alpha[0] + stopAlpha); 99 SkDEBUGCODE(this->validate();) 100 lastAlpha = alpha; 101 } 102 103 return SkToS32(lastAlpha - fAlpha); // new offsetX 104 } 105 106 SkDEBUGCODE(void assertValid(int y, int maxStep) const;) 107 SkDEBUGCODE(void dump() const;) 108 109 /** 110 * Break the runs in the buffer at offsets x and x+count, properly 111 * updating the runs to the right and left. 112 * i.e. from the state AAAABBBB, run-length encoded as A4B4, 113 * Break(..., 2, 5) would produce AAAABBBB rle as A2A2B3B1. 114 * Allows add() to sum another run to some of the new sub-runs. 115 * i.e. adding ..CCCCC. would produce AADDEEEB, rle as A2D2E3B1. 116 */ 117 static void Break(int16_t runs[], uint8_t alpha[], int x, int count) { 118 SkASSERT(count > 0 && x >= 0); 119 120 // SkAlphaRuns::BreakAt(runs, alpha, x); 121 // SkAlphaRuns::BreakAt(&runs[x], &alpha[x], count); 122 123 int16_t* next_runs = runs + x; 124 uint8_t* next_alpha = alpha + x; 125 126 while (x > 0) { 127 int n = runs[0]; 128 SkASSERT(n > 0); 129 130 if (x < n) { 131 alpha[x] = alpha[0]; 132 runs[0] = SkToS16(x); 133 runs[x] = SkToS16(n - x); 134 break; 135 } 136 runs += n; 137 alpha += n; 138 x -= n; 139 } 140 141 runs = next_runs; 142 alpha = next_alpha; 143 x = count; 144 145 for (;;) { 146 int n = runs[0]; 147 SkASSERT(n > 0); 148 149 if (x < n) { 150 alpha[x] = alpha[0]; 151 runs[0] = SkToS16(x); 152 runs[x] = SkToS16(n - x); 153 break; 154 } 155 x -= n; 156 if (x <= 0) { 157 break; 158 } 159 runs += n; 160 alpha += n; 161 } 162 } 163 164 /** 165 * Cut (at offset x in the buffer) a run into two shorter runs with 166 * matching alpha values. 167 * Used by the RectClipBlitter to trim a RLE encoding to match the 168 * clipping rectangle. 169 */ 170 static void BreakAt(int16_t runs[], uint8_t alpha[], int x) { 171 while (x > 0) { 172 int n = runs[0]; 173 SkASSERT(n > 0); 174 175 if (x < n) { 176 alpha[x] = alpha[0]; 177 runs[0] = SkToS16(x); 178 runs[x] = SkToS16(n - x); 179 break; 180 } 181 runs += n; 182 alpha += n; 183 x -= n; 184 } 185 } 186 187 private: 188 SkDEBUGCODE(int fWidth;) 189 SkDEBUGCODE(void validate() const;) 190 }; 191 192 #endif 193
