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/*
* Copyright 2006 The Android Open Source Project
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkAntiRun_DEFINED
#define SkAntiRun_DEFINED
#include "SkBlitter.h"
#include "SkTo.h"
/** Sparse array of run-length-encoded alpha (supersampling coverage) values.
Sparseness allows us to independently compose several paths into the
same SkAlphaRuns buffer.
*/
class SkAlphaRuns {
public:
int16_t* fRuns;
uint8_t* fAlpha;
// Return 0-255 given 0-256
static inline SkAlpha CatchOverflow(int alpha) {
SkASSERT(alpha >= 0 && alpha <= 256);
return alpha - (alpha >> 8);
}
/// Returns true if the scanline contains only a single run,
/// of alpha value 0.
bool empty() const {
SkASSERT(fRuns[0] > 0);
return fAlpha[0] == 0 && fRuns[fRuns[0]] == 0;
}
/// Reinitialize for a new scanline.
void reset(int width);
/**
* Insert into the buffer a run starting at (x-offsetX):
* if startAlpha > 0
* one pixel with value += startAlpha,
* max 255
* if middleCount > 0
* middleCount pixels with value += maxValue
* if stopAlpha > 0
* one pixel with value += stopAlpha
* Returns the offsetX value that should be passed on the next call,
* assuming we're on the same scanline. If the caller is switching
* scanlines, then offsetX should be 0 when this is called.
*/
SK_ALWAYS_INLINE int add(int x, U8CPU startAlpha, int middleCount, U8CPU stopAlpha,
U8CPU maxValue, int offsetX) {
SkASSERT(middleCount >= 0);
SkASSERT(x >= 0 && x + (startAlpha != 0) + middleCount + (stopAlpha != 0) <= fWidth);
SkASSERT(fRuns[offsetX] >= 0);
int16_t* runs = fRuns + offsetX;
uint8_t* alpha = fAlpha + offsetX;
uint8_t* lastAlpha = alpha;
x -= offsetX;
if (startAlpha) {
SkAlphaRuns::Break(runs, alpha, x, 1);
/* I should be able to just add alpha[x] + startAlpha.
However, if the trailing edge of the previous span and the leading
edge of the current span round to the same super-sampled x value,
I might overflow to 256 with this add, hence the funny subtract (crud).
*/
unsigned tmp = alpha[x] + startAlpha;
SkASSERT(tmp <= 256);
alpha[x] = SkToU8(tmp - (tmp >> 8)); // was (tmp >> 7), but that seems wrong if we're trying to catch 256
runs += x + 1;
alpha += x + 1;
x = 0;
SkDEBUGCODE(this->validate();)
}
if (middleCount) {
SkAlphaRuns::Break(runs, alpha, x, middleCount);
alpha += x;
runs += x;
x = 0;
do {
alpha[0] = SkToU8(CatchOverflow(alpha[0] + maxValue));
int n = runs[0];
SkASSERT(n <= middleCount);
alpha += n;
runs += n;
middleCount -= n;
} while (middleCount > 0);
SkDEBUGCODE(this->validate();)
lastAlpha = alpha;
}
if (stopAlpha) {
SkAlphaRuns::Break(runs, alpha, x, 1);
alpha += x;
alpha[0] = SkToU8(alpha[0] + stopAlpha);
SkDEBUGCODE(this->validate();)
lastAlpha = alpha;
}
return SkToS32(lastAlpha - fAlpha); // new offsetX
}
SkDEBUGCODE(void assertValid(int y, int maxStep) const;)
SkDEBUGCODE(void dump() const;)
/**
* Break the runs in the buffer at offsets x and x+count, properly
* updating the runs to the right and left.
* i.e. from the state AAAABBBB, run-length encoded as A4B4,
* Break(..., 2, 5) would produce AAAABBBB rle as A2A2B3B1.
* Allows add() to sum another run to some of the new sub-runs.
* i.e. adding ..CCCCC. would produce AADDEEEB, rle as A2D2E3B1.
*/
static void Break(int16_t runs[], uint8_t alpha[], int x, int count) {
SkASSERT(count > 0 && x >= 0);
// SkAlphaRuns::BreakAt(runs, alpha, x);
// SkAlphaRuns::BreakAt(&runs[x], &alpha[x], count);
int16_t* next_runs = runs + x;
uint8_t* next_alpha = alpha + x;
while (x > 0) {
int n = runs[0];
SkASSERT(n > 0);
if (x < n) {
alpha[x] = alpha[0];
runs[0] = SkToS16(x);
runs[x] = SkToS16(n - x);
break;
}
runs += n;
alpha += n;
x -= n;
}
runs = next_runs;
alpha = next_alpha;
x = count;
for (;;) {
int n = runs[0];
SkASSERT(n > 0);
if (x < n) {
alpha[x] = alpha[0];
runs[0] = SkToS16(x);
runs[x] = SkToS16(n - x);
break;
}
x -= n;
if (x <= 0) {
break;
}
runs += n;
alpha += n;
}
}
/**
* Cut (at offset x in the buffer) a run into two shorter runs with
* matching alpha values.
* Used by the RectClipBlitter to trim a RLE encoding to match the
* clipping rectangle.
*/
static void BreakAt(int16_t runs[], uint8_t alpha[], int x) {
while (x > 0) {
int n = runs[0];
SkASSERT(n > 0);
if (x < n) {
alpha[x] = alpha[0];
runs[0] = SkToS16(x);
runs[x] = SkToS16(n - x);
break;
}
runs += n;
alpha += n;
x -= n;
}
}
private:
SkDEBUGCODE(int fWidth;)
SkDEBUGCODE(void validate() const;)
};
#endif
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