Analytic AntiAlias for Convex Shapes

src/core/SkScan_AAAPath.cpp

Index: src/core/SkScan_AAAPath.cpp
diff --git a/src/core/SkScan_AAAPath.cpp b/src/core/SkScan_AAAPath.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..e5b8c57d5fa9366ef44e7c04d10093a726c6ccc7
--- /dev/null
+++ b/src/core/SkScan_AAAPath.cpp
@@ -0,0 +1,1279 @@
+/*
+ * Copyright 2016 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.
+ */
+
+#include "SkAntiRun.h"
+#include "SkBlitter.h"
+#include "SkEdge.h"
+#include "SkAnalyticEdge.h"
+#include "SkEdgeBuilder.h"
+#include "SkGeometry.h"
+#include "SkPath.h"
+#include "SkQuadClipper.h"
+#include "SkRasterClip.h"
+#include "SkRegion.h"
+#include "SkScan.h"
+#include "SkScanPriv.h"
+#include "SkTemplates.h"
+#include "SkTSort.h"
+#include "SkUtils.h"
+
+///////////////////////////////////////////////////////////////////////////////
+
+/*
+
+The following is a high-level overview of our analytic anti-aliasing
+algorithm. We consider a path as a collection of line segments, as
+quadratic/cubic curves are converted to small line segments. Without loss of
+generality, let's assume that the draw region is [0, W] x [0, H].
+
+Our algorithm is based on horizontal scan lines (y = c_i) as the previous
+sampling-based algorithm did. However, our algorithm uses non-equal-spaced
+scan lines, while the previous method always uses equal-spaced scan lines,
+such as (y = 1/2 + 0, 1/2 + 1, 1/2 + 2, ...) in the previous non-AA algorithm,
+and (y = 1/8 + 1/4, 1/8 + 2/4, 1/8 + 3/4, ...) in the previous
+16-supersampling AA algorithm.
+
+Our algorithm contains scan lines y = c_i for c_i that is either:
+
+1. an integer between [0, H]
+
+2. the y value of a line segment endpoint
+
+3. the y value of an intersection of two line segments
+
+For two consecutive scan lines y = c_i, y = c_{i+1}, we analytically computes
+the coverage of this horizontal strip of our path on each pixel. This can be
+done very efficiently because the strip of our path now only consists of
+trapezoids whose top and bottom edges are y = c_i, y = c_{i+1} (this includes
+rectangles and triangles as special cases).
+
+We now describe how the coverage of single pixel is computed against such a
+trapezoid. That coverage is essentially the intersection area of a rectangle
+(e.g., [0, 1] x [c_i, c_{i+1}]) and our trapezoid. However, that intersection
+could be complicated, as shown in the example region A below:
+
++-----------\----+
+|            \  C|
+|             \  |
+\              \ |
+|\      A       \|
+| \              \
+|  \             |
+| B \            |
++----\-----------+
+
+However, we don't have to compute the area of A directly. Instead, we can
+compute the excluded area, which are B and C, quite easily, because they're
+just triangles. In fact, we can prove that an excluded region (take B as an
+example) is either itself a simple trapezoid (including rectangles, triangles,
+and empty regions), or its opposite (the opposite of B is A + C) is a simple
+trapezoid. In any case, we can compute its area efficiently.
+
+In summary, our algorithm has a higher quality because it generates ground-
+truth coverages analytically. It is also faster because it has much fewer
+unnessasary horizontal scan lines. For example, given a triangle path, the
+number of scan lines in our algorithm is only about 3 + H while the
+16-supersampling algorithm has about 4H scan lines.
+
+*/
+
+///////////////////////////////////////////////////////////////////////////////
+
+inline void addAlpha(SkAlpha& alpha, SkAlpha delta) {
+    SkASSERT(alpha + (int)delta <= 0xFF);
+    alpha += delta;
+}
+
+class AdditiveBlitter : public SkBlitter {
+public:
+    virtual ~AdditiveBlitter() {}
+
+    virtual SkBlitter* getRealBlitter(bool forceRealBlitter = false) = 0;
+
+    virtual void blitAntiH(int x, int y, const SkAlpha antialias[], int len) = 0;
+    virtual void blitAntiH(int x, int y, const SkAlpha alpha) = 0;
+    virtual void blitAntiH(int x, int y, int width, const SkAlpha alpha) = 0;
+
+    void blitAntiH(int x, int y, const SkAlpha antialias[], const int16_t runs[]) override {
+        SkDEBUGFAIL("Please call real blitter's blitAntiH instead.");
+    }
+
+    void blitV(int x, int y, int height, SkAlpha alpha) override {
+        SkDEBUGFAIL("Please call real blitter's blitV instead.");
+    }
+
+    void blitH(int x, int y, int width) override {
+        SkDEBUGFAIL("Please call real blitter's blitH instead.");
+    }
+
+    void blitRect(int x, int y, int width, int height) override {
+        SkDEBUGFAIL("Please call real blitter's blitRect instead.");
+    }
+
+    void blitAntiRect(int x, int y, int width, int height,
+                      SkAlpha leftAlpha, SkAlpha rightAlpha) override {
+        SkDEBUGFAIL("Please call real blitter's blitAntiRect instead.");
+    }
+
+    virtual int getWidth() = 0;
+};
+
+// We need this mask blitter because it significantly accelerates small path filling.
+class MaskAdditiveBlitter : public AdditiveBlitter {
+public:
+    MaskAdditiveBlitter(SkBlitter* realBlitter, const SkIRect& ir, const SkRegion& clip,
+            bool isInverse);
+    ~MaskAdditiveBlitter() {
+        fRealBlitter->blitMask(fMask, fClipRect);
+    }
+
+    // Most of the time, we still consider this mask blitter as the real blitter
+    // so we can accelerate blitRect and others. But sometimes we want to return
+    // the absolute real blitter (e.g., when we fall back to the old code path).
+    SkBlitter* getRealBlitter(bool forceRealBlitter) override {
+        return forceRealBlitter ? fRealBlitter : this;
+    }
+
+    // Virtual function is slow. So don't use this. Directly add alpha to the mask instead.
+    void blitAntiH(int x, int y, const SkAlpha antialias[], int len) override;
+
+    // Allowing following methods are used to blit rectangles during aaa_walk_convex_edges
+    // Since there aren't many rectangles, we can still break the slow speed of virtual functions.
+    void blitAntiH(int x, int y, const SkAlpha alpha) override;
+    void blitAntiH(int x, int y, int width, const SkAlpha alpha) override;
+    void blitV(int x, int y, int height, SkAlpha alpha) override;
+    void blitRect(int x, int y, int width, int height) override;
+    void blitAntiRect(int x, int y, int width, int height,
+                      SkAlpha leftAlpha, SkAlpha rightAlpha) override;
+
+    int getWidth() override { return fClipRect.width(); }
+
+    static bool canHandleRect(const SkIRect& bounds) {
+        int width = bounds.width();
+        int64_t rb = SkAlign4(width);
+        // use 64bits to detect overflow
+        int64_t storage = rb * bounds.height();
+
+        return (width <= MaskAdditiveBlitter::kMAX_WIDTH) &&
+               (storage <= MaskAdditiveBlitter::kMAX_STORAGE);
+    }
+
+    // Return a pointer where pointer[x] corresonds to the alpha of (x, y)
+    inline uint8_t* getRow(int y) {
+        if (y != fY) {
+            fY = y;
+            fRow = fMask.fImage + (y - fMask.fBounds.fTop) * fMask.fRowBytes - fMask.fBounds.fLeft;
+        }
+        return fRow;
+    }
+
+private:
+    // so we don't try to do very wide things, where the RLE blitter would be faster
+    static const int kMAX_WIDTH = 32;
+    static const int kMAX_STORAGE = 1024;
+
+    SkBlitter*  fRealBlitter;
+    SkMask      fMask;
+    SkIRect     fClipRect;
+    // we add 2 because we can write 1 extra byte at either end due to precision error
+    uint32_t    fStorage[(kMAX_STORAGE >> 2) + 2];
+
+    uint8_t*    fRow;
+    int         fY;
+};
+
+MaskAdditiveBlitter::MaskAdditiveBlitter(SkBlitter* realBlitter, const SkIRect& ir, const SkRegion& clip,
+                                         bool isInverse) {
+    SkASSERT(canHandleRect(ir));
+    SkASSERT(!isInverse);
+
+    fRealBlitter = realBlitter;
+
+    fMask.fImage    = (uint8_t*)fStorage + 1; // There's 1 extra byte at either end of fStorage
+    fMask.fBounds   = ir;
+    fMask.fRowBytes = ir.width();
+    fMask.fFormat   = SkMask::kA8_Format;
+
+    fY = ir.fTop - 1;
+    fRow = nullptr;
+
+    fClipRect = ir;
+    if (!fClipRect.intersect(clip.getBounds())) {
+        SkASSERT(0);
+        fClipRect.setEmpty();
+    }
+
+    memset(fStorage, 0, fMask.fBounds.height() * fMask.fRowBytes + 2);
+}
+
+void MaskAdditiveBlitter::blitAntiH(int x, int y, const SkAlpha antialias[], int len) {
+    SkFAIL("Don't use this; directly add alphas to the mask.");
+}
+
+void MaskAdditiveBlitter::blitAntiH(int x, int y, const SkAlpha alpha) {
+    SkASSERT(x >= fMask.fBounds.fLeft -1);
+    addAlpha(this->getRow(y)[x], alpha);
+}
+
+void MaskAdditiveBlitter::blitAntiH(int x, int y, int width, const SkAlpha alpha) {
+    SkASSERT(x >= fMask.fBounds.fLeft -1);
+    uint8_t* row = this->getRow(y);
+    for (int i=0; i<width; i++) {
+        addAlpha(row[x + i], alpha);
+    }
+}
+
+void MaskAdditiveBlitter::blitV(int x, int y, int height, SkAlpha alpha) {
+    if (alpha == 0) {
+        return;
+    }
+    SkASSERT(x >= fMask.fBounds.fLeft -1);
+    // This must be called as if this is a real blitter.
+    // So we directly set alpha rather than adding it.
+    uint8_t* row = this->getRow(y);
+    for (int i=0; i<height; i++) {
+        row[x] = alpha;
+        row += fMask.fRowBytes;
+    }
+}
+
+void MaskAdditiveBlitter::blitRect(int x, int y, int width, int height) {
+    SkASSERT(x >= fMask.fBounds.fLeft -1);
+    // This must be called as if this is a real blitter.
+    // So we directly set alpha rather than adding it.
+    uint8_t* row = this->getRow(y);
+    for (int i=0; i<height; i++) {
+        memset(row + x, 0xFF, width);
+        row += fMask.fRowBytes;
+    }
+}
+
+void MaskAdditiveBlitter::blitAntiRect(int x, int y, int width, int height,
+        SkAlpha leftAlpha, SkAlpha rightAlpha) {
+    blitV(x, y, height, leftAlpha);
+    blitV(x + 1 + width, y, height, rightAlpha);
+    blitRect(x + 1, y, width, height);
+}
+
+class RunBasedAdditiveBlitter : public AdditiveBlitter {
+public:
+    RunBasedAdditiveBlitter(SkBlitter* realBlitter, const SkIRect& ir, const SkRegion& clip,
+            bool isInverse);
+    ~RunBasedAdditiveBlitter();
+
+    SkBlitter* getRealBlitter(bool forceRealBlitter) override;
+
+    void blitAntiH(int x, int y, const SkAlpha antialias[], int len) override;
+    void blitAntiH(int x, int y, const SkAlpha alpha) override;
+    void blitAntiH(int x, int y, int width, const SkAlpha alpha) override;
+
+    int getWidth() override;
+
+private:
+    SkBlitter* fRealBlitter;
+
+    /// Current y coordinate
+    int         fCurrY;
+    /// Widest row of region to be blitted
+    int         fWidth;
+    /// Leftmost x coordinate in any row
+    int         fLeft;
+    /// Initial y coordinate (top of bounds).
+    int         fTop;
+
+    // The next three variables are used to track a circular buffer that
+    // contains the values used in SkAlphaRuns. These variables should only
+    // ever be updated in advanceRuns(), and fRuns should always point to
+    // a valid SkAlphaRuns...
+    int         fRunsToBuffer;
+    void*       fRunsBuffer;
+    int         fCurrentRun;
+    SkAlphaRuns fRuns;
+
+    int         fOffsetX;
+
+    inline bool check(int x, int width) {
+        #ifdef SK_DEBUG
+        if (x < 0 || x + width > fWidth) {
+            SkDebugf("Ignore x = %d, width = %d\n", x, width);
+        }
+        #endif
+        return (x >= 0 && x + width <= fWidth);
+    }
+
+    // extra one to store the zero at the end
+    inline int getRunsSz() const { return (fWidth + 1 + (fWidth + 2)/2) * sizeof(int16_t); }
+
+    // This function updates the fRuns variable to point to the next buffer space
+    // with adequate storage for a SkAlphaRuns. It mostly just advances fCurrentRun
+    // and resets fRuns to point to an empty scanline.
+    inline void advanceRuns() {
+        const size_t kRunsSz = this->getRunsSz();
+        fCurrentRun = (fCurrentRun + 1) % fRunsToBuffer;
+        fRuns.fRuns = reinterpret_cast<int16_t*>(
+            reinterpret_cast<uint8_t*>(fRunsBuffer) + fCurrentRun * kRunsSz);
+        fRuns.fAlpha = reinterpret_cast<SkAlpha*>(fRuns.fRuns + fWidth + 1);
+        fRuns.reset(fWidth);
+    }
+
+    // Blitting 0xFF and 0 is much faster so we snap alphas close to them
+    inline SkAlpha snapAlpha(SkAlpha alpha) {
+        return alpha > 247 ? 0xFF : alpha < 8 ? 0 : alpha;
+    }
+
+    inline void flush() {
+        if (fCurrY >= fTop) {
+            SkASSERT(fCurrentRun < fRunsToBuffer);
+            for (int x = 0; fRuns.fRuns[x]; x += fRuns.fRuns[x]) {
+                // It seems that blitting 255 or 0 is much faster than blitting 254 or 1
+                fRuns.fAlpha[x] = snapAlpha(fRuns.fAlpha[x]);
+            }
+            if (!fRuns.empty()) {
+                // SkDEBUGCODE(fRuns.dump();)
+                fRealBlitter->blitAntiH(fLeft, fCurrY, fRuns.fAlpha, fRuns.fRuns);
+                this->advanceRuns();
+                fOffsetX = 0;
+            }
+            fCurrY = fTop - 1;
+        }
+    }
+
+    inline void checkY(int y) {
+        if (y != fCurrY) {
+            this->flush();
+            fCurrY = y;
+        }
+    }
+};
+
+RunBasedAdditiveBlitter::RunBasedAdditiveBlitter(SkBlitter* realBlitter, const SkIRect& ir, const SkRegion& clip,
+                                 bool isInverse) {
+    fRealBlitter = realBlitter;
+
+    SkIRect sectBounds;
+    if (isInverse) {
+        // We use the clip bounds instead of the ir, since we may be asked to
+        //draw outside of the rect when we're a inverse filltype
+        sectBounds = clip.getBounds();
+    } else {
+        if (!sectBounds.intersect(ir, clip.getBounds())) {
+            sectBounds.setEmpty();
+        }
+    }
+
+    const int left = sectBounds.left();
+    const int right = sectBounds.right();
+
+    fLeft = left;
+    fWidth = right - left;
+    fTop = sectBounds.top();
+    fCurrY = fTop - 1;
+
+    fRunsToBuffer = realBlitter->requestRowsPreserved();
+    fRunsBuffer = realBlitter->allocBlitMemory(fRunsToBuffer * this->getRunsSz());
+    fCurrentRun = -1;
+
+    this->advanceRuns();
+
+    fOffsetX = 0;
+}
+
+RunBasedAdditiveBlitter::~RunBasedAdditiveBlitter() {
+    this->flush();
+}
+
+SkBlitter* RunBasedAdditiveBlitter::getRealBlitter(bool forceRealBlitter) {
+    return fRealBlitter;
+}
+
+void RunBasedAdditiveBlitter::blitAntiH(int x, int y, const SkAlpha antialias[], int len) {
+    checkY(y);
+    x -= fLeft;
+
+    if (x < 0) {
+        len += x;
+        antialias -= x;
+        x = 0;
+    }
+    len = SkTMin(len, fWidth - x);
+    SkASSERT(check(x, len));
+
+    if (x < fOffsetX) {
+        fOffsetX = 0;
+    }
+
+    fOffsetX = fRuns.add(x, 0, len, 0, 0, fOffsetX); // Break the run
+    for (int i = 0; i < len; i += fRuns.fRuns[x + i]) {
+        for (int j = 1; j < fRuns.fRuns[x + i]; j++) {
+            fRuns.fRuns[x + i + j] = 1;
+            fRuns.fAlpha[x + i + j] = fRuns.fAlpha[x + i];
+        }
+        fRuns.fRuns[x + i] = 1;
+    }
+    for (int i=0; i<len; i++) {
+        addAlpha(fRuns.fAlpha[x + i], antialias[i]);
+    }
+}
+void RunBasedAdditiveBlitter::blitAntiH(int x, int y, const SkAlpha alpha) {
+    checkY(y);
+    x -= fLeft;
+
+    if (x < fOffsetX) {
+        fOffsetX = 0;
+    }
+
+    if (this->check(x, 1)) {
+        fOffsetX = fRuns.add(x, 0, 1, 0, alpha, fOffsetX);
+    }
+}
+
+void RunBasedAdditiveBlitter::blitAntiH(int x, int y, int width, const SkAlpha alpha) {
+    checkY(y);
+    x -= fLeft;
+
+    if (x < fOffsetX) {
+        fOffsetX = 0;
+    }
+
+    if (this->check(x, width)) {
+        fOffsetX = fRuns.add(x, 0, width, 0, alpha, fOffsetX);
+    }
+}
+
+int RunBasedAdditiveBlitter::getWidth() { return fWidth; }
+
+///////////////////////////////////////////////////////////////////////////////
+
+// Return the alpha of a trapezoid whose height is 1
+static inline SkAlpha trapezoidToAlpha(SkFixed l1, SkFixed l2) {
+    SkASSERT(l1 >= 0 && l2 >= 0);
+    return ((l1 + l2) >> 9);
+}
+
+// The alpha of right-triangle (a, a*b), in 16 bits
+static inline SkFixed partialTriangleToAlpha16(SkFixed a, SkFixed b) {
+    SkASSERT(a <= SK_Fixed1);
+    // SkFixedMul_lowprec(SkFixedMul_lowprec(a, a), b) >> 1
+    // return ((((a >> 8) * (a >> 8)) >> 8) * (b >> 8)) >> 1;
+    return (a >> 11) * (a >> 11) * (b >> 11);
+}
+
+// The alpha of right-triangle (a, a*b)
+static inline SkAlpha partialTriangleToAlpha(SkFixed a, SkFixed b) {
+    return partialTriangleToAlpha16(a, b) >> 8;
+}
+
+static inline SkAlpha getPartialAlpha(SkAlpha alpha, SkFixed partialHeight) {
+    return (alpha * partialHeight) >> 16;
+}
+
+static inline SkAlpha getPartialAlpha(SkAlpha alpha, SkAlpha fullAlpha) {
+    return ((uint16_t)alpha * fullAlpha) >> 8;
+}
+
+// For SkFixed that's close to SK_Fixed1, we can't convert it to alpha by just shifting right.
+// For example, when f = SK_Fixed1, right shifting 8 will get 256, but we need 255.
+// This is rarely the problem so we'll only use this for blitting rectangles.
+static inline SkAlpha f2a(SkFixed f) {
+    SkASSERT(f <= SK_Fixed1);
+    return getPartialAlpha(0xFF, f);
+}
+
+// Suppose that line (l1, y)-(r1, y+1) intersects with (l2, y)-(r2, y+1),
+// approximate (very coarsely) the x coordinate of the intersection.
+static inline SkFixed approximateIntersection(SkFixed l1, SkFixed r1, SkFixed l2, SkFixed r2) {
+    if (l1 > r1) { SkTSwap(l1, r1); }
+    if (l2 > r2) { SkTSwap(l2, r2); }
+    return (SkTMax(l1, l2) + SkTMin(r1, r2)) >> 1;
+}
+
+// Here we always send in l < SK_Fixed1, and the first alpha we want to compute is alphas[0]
+static inline void computeAlphaAboveLine(SkAlpha* alphas, SkFixed l, SkFixed r,
+                                         SkFixed dY, SkAlpha fullAlpha) {
+    SkASSERT(l <= r);
+    SkASSERT(l >> 16 == 0);
+    int R = SkFixedCeilToInt(r);
+    if (R == 0) {
+        return;
+    } else if (R == 1) {
+        alphas[0] = getPartialAlpha(((R << 17) - l - r) >> 9, fullAlpha);
+    } else {
+        SkFixed first = SK_Fixed1 - l; // horizontal edge length of the left-most triangle
+        SkFixed last = r - ((R - 1) << 16); // horizontal edge length of the right-most triangle
+        SkFixed firstH = SkFixedMul_lowprec(first, dY); // vertical edge of the left-most triangle
+        alphas[0] = SkFixedMul_lowprec(first, firstH) >> 9; // triangle alpha
+        SkFixed alpha16 = firstH + (dY >> 1); // rectangle plus triangle
+        for (int i = 1; i < R - 1; i++) {
+            alphas[i] = alpha16 >> 8;
+            alpha16 += dY;
+        }
+        alphas[R - 1] = fullAlpha - partialTriangleToAlpha(last, dY);
+    }
+}
+
+// Here we always send in l < SK_Fixed1, and the first alpha we want to compute is alphas[0]
+static inline void computeAlphaBelowLine(SkAlpha* alphas, SkFixed l, SkFixed r, SkFixed dY, SkAlpha fullAlpha) {
+    SkASSERT(l <= r);
+    SkASSERT(l >> 16 == 0);
+    int R = SkFixedCeilToInt(r);
+    if (R == 0) {
+        return;
+    } else if (R == 1) {
+        alphas[0] = getPartialAlpha(trapezoidToAlpha(l, r), fullAlpha);
+    } else {
+        SkFixed first = SK_Fixed1 - l; // horizontal edge length of the left-most triangle
+        SkFixed last = r - ((R - 1) << 16); // horizontal edge length of the right-most triangle
+        SkFixed lastH = SkFixedMul_lowprec(last, dY); // vertical edge of the right-most triangle
+        alphas[R-1] = SkFixedMul_lowprec(last, lastH) >> 9; // triangle alpha
+        SkFixed alpha16 = lastH + (dY >> 1); // rectangle plus triangle
+        for (int i = R - 2; i > 0; i--) {
+            alphas[i] = alpha16 >> 8;
+            alpha16 += dY;
+        }
+        alphas[0] = fullAlpha - partialTriangleToAlpha(first, dY);
+    }
+}
+
+// Note that if fullAlpha != 0xFF, we'll multiply alpha by fullAlpha
+static inline void blit_single_alpha(AdditiveBlitter* blitter, int y, int x,
+                              SkAlpha alpha, SkAlpha fullAlpha, SkAlpha* maskRow,
+                              bool isUsingMask) {
+    if (isUsingMask) {
+        if (fullAlpha == 0xFF) {
+            maskRow[x] = alpha;
+        } else {
+            addAlpha(maskRow[x], getPartialAlpha(alpha, fullAlpha));
+        }
+    } else {
+        if (fullAlpha == 0xFF) {
+            blitter->getRealBlitter()->blitV(x, y, 1, alpha);
+        } else {
+            blitter->blitAntiH(x, y, getPartialAlpha(alpha, fullAlpha));
+        }
+    }
+}
+
+static inline void blit_two_alphas(AdditiveBlitter* blitter, int y, int x,
+                            SkAlpha a1, SkAlpha a2, SkAlpha fullAlpha, SkAlpha* maskRow,
+                            bool isUsingMask) {
+    if (isUsingMask) {
+        addAlpha(maskRow[x], a1);
+        addAlpha(maskRow[x + 1], a2);
+    } else {
+        if (fullAlpha == 0xFF) {
+            blitter->getRealBlitter()->blitV(x, y, 1, a1);
+            blitter->getRealBlitter()->blitV(x + 1, y, 1, a2);
+        } else {
+            blitter->blitAntiH(x, y, a1);
+            blitter->blitAntiH(x + 1, y, a2);
+        }
+    }
+}
+
+// It's important that this is inline. Otherwise it'll be much slower.
+static SK_ALWAYS_INLINE void blit_full_alpha(AdditiveBlitter* blitter, int y, int x, int len,
+                            SkAlpha fullAlpha, SkAlpha* maskRow, bool isUsingMask) {
+    if (isUsingMask) {
+        for (int i=0; i<len; i++) {
+            addAlpha(maskRow[x + i], fullAlpha);
+        }
+    } else {
+        if (fullAlpha == 0xFF) {
+            blitter->getRealBlitter()->blitH(x, y, len);
+        } else {
+            blitter->blitAntiH(x, y, len, fullAlpha);
+        }
+    }
+}
+
+static void blit_aaa_trapezoid_row(AdditiveBlitter* blitter, int y,
+                                   SkFixed ul, SkFixed ur, SkFixed ll, SkFixed lr,
+                                   SkFixed lDY, SkFixed rDY, SkAlpha fullAlpha, SkAlpha* maskRow,
+                                   bool isUsingMask) {
+    int L = SkFixedFloorToInt(ul), R = SkFixedCeilToInt(lr);
+    int len = R - L;
+
+    if (len == 1) {
+        SkAlpha alpha = trapezoidToAlpha(ur - ul, lr - ll);
+        blit_single_alpha(blitter, y, L, alpha, fullAlpha, maskRow, isUsingMask);
+        return;
+    }
+
+    // SkDebugf("y = %d, len = %d, ul = %f, ur = %f, ll = %f, lr = %f\n", y, len,
+    //         SkFixedToFloat(ul), SkFixedToFloat(ur), SkFixedToFloat(ll), SkFixedToFloat(lr));
+
+    const int kQuickLen = 31;
+    // This is faster than SkAutoSMalloc<1024>
+    char quickMemory[(sizeof(SkAlpha) * 2 + sizeof(int16_t)) * (kQuickLen + 1)];
+    SkAlpha* alphas;
+
+    if (len <= kQuickLen) {
+        alphas = (SkAlpha*)quickMemory;
+    } else {
+        alphas = new SkAlpha[(len + 1) * (sizeof(SkAlpha) * 2 + sizeof(int16_t))];
+    }
+
+    SkAlpha* tempAlphas = alphas + len + 1;
+    int16_t* runs = (int16_t*)(alphas + (len + 1) * 2);
+
+    for (int i = 0; i < len; i++) {
+        runs[i] = 1;
+        alphas[i] = fullAlpha;
+    }
+    runs[len] = 0;
+
+    int uL = SkFixedFloorToInt(ul);
+    int lL = SkFixedCeilToInt(ll);
+    if (uL + 2 == lL) { // We only need to compute two triangles, accelerate this special case
+        SkFixed first = (uL << 16) + SK_Fixed1 - ul;
+        SkFixed second = ll - ul - first;
+        SkAlpha a1 = fullAlpha - partialTriangleToAlpha(first, lDY);
+        SkAlpha a2 = partialTriangleToAlpha(second, lDY);
+        alphas[0] = alphas[0] > a1 ? alphas[0] - a1 : 0;
+        alphas[1] = alphas[1] > a2 ? alphas[1] - a2 : 0;
+    } else {
+        computeAlphaBelowLine(tempAlphas + uL - L, ul - (uL << 16), ll - (uL << 16),
+                lDY, fullAlpha);
+        for (int i = uL; i < lL; i++) {
+            if (alphas[i - L] > tempAlphas[i - L]) {
+                alphas[i - L] -= tempAlphas[i - L];
+            } else {
+                alphas[i - L] = 0;
+            }
+        }
+    }
+
+    int uR = SkFixedFloorToInt(ur);
+    int lR = SkFixedCeilToInt(lr);
+    if (uR + 2 == lR) { // We only need to compute two triangles, accelerate this special case
+        SkFixed first = (uR << 16) + SK_Fixed1 - ur;
+        SkFixed second = lr - ur - first;
+        SkAlpha a1 = partialTriangleToAlpha(first, rDY);
+        SkAlpha a2 = fullAlpha - partialTriangleToAlpha(second, rDY);
+        alphas[len-2] = alphas[len-2] > a1 ? alphas[len-2] - a1 : 0;
+        alphas[len-1] = alphas[len-1] > a2 ? alphas[len-1] - a2 : 0;
+    } else {
+        computeAlphaAboveLine(tempAlphas + uR - L, ur - (uR << 16), lr - (uR << 16),
+                rDY, fullAlpha);
+        for (int i = uR; i < lR; i++) {
+            if (alphas[i - L] > tempAlphas[i - L]) {
+                alphas[i - L] -= tempAlphas[i - L];
+            } else {
+                alphas[i - L] = 0;
+            }
+        }
+    }
+
+    if (isUsingMask) {
+        for (int i=0; i<len; i++) {
+            addAlpha(maskRow[L + i], alphas[i]);
+        }
+    } else {
+        if (fullAlpha == 0xFF) { // Real blitter is faster than RunBasedAdditiveBlitter
+            blitter->getRealBlitter()->blitAntiH(L, y, alphas, runs);
+        } else {
+            blitter->blitAntiH(L, y, alphas, len);
+        }
+    }
+
+    if (len > kQuickLen) {
+        delete [] alphas;
+    }
+}
+
+static inline void blit_trapezoid_row(AdditiveBlitter* blitter, int y,
+                               SkFixed ul, SkFixed ur, SkFixed ll, SkFixed lr,
+                               SkFixed lDY, SkFixed rDY, SkAlpha fullAlpha,
+                               SkAlpha* maskRow, bool isUsingMask) {
+    SkASSERT(lDY >= 0 && rDY >= 0); // We should only send in the absolte value
+
+    if (ul > ur) {
+#ifdef SK_DEBUG
+        SkDebugf("ul = %f > ur = %f!\n", SkFixedToFloat(ul), SkFixedToFloat(ur));
+#endif
+        return;
+    }
+
+    // Edge crosses. Approximate it. This should only happend due to precision limit,
+    // so the approximation could be very coarse.
+    if (ll > lr) {
+#ifdef SK_DEBUG
+        SkDebugf("approximate intersection: %d %f %f\n", y,
+                 SkFixedToFloat(ll), SkFixedToFloat(lr));
+#endif
+        ll = lr = approximateIntersection(ul, ll, ur, lr);
+    }
+
+    if (ul == ur && ll == lr) {
+        return; // empty trapzoid
+    }
+
+    // We're going to use the left line ul-ll and the rite line ur-lr
+    // to exclude the area that's not covered by the path.
+    // Swapping (ul, ll) or (ur, lr) won't affect that exclusion
+    // so we'll do that for simplicity.
+    if (ul > ll) { SkTSwap(ul, ll); }
+    if (ur > lr) { SkTSwap(ur, lr); }
+
+    SkFixed joinLeft = SkFixedCeilToFixed(ll);
+    SkFixed joinRite = SkFixedFloorToFixed(ur);
+    if (joinLeft <= joinRite) { // There's a rect from joinLeft to joinRite that we can blit
+        if (joinLeft < joinRite) {
+            blit_full_alpha(blitter, y, joinLeft >> 16, (joinRite - joinLeft) >> 16, fullAlpha,
+                            maskRow, isUsingMask);
+        }
+        if (ul < joinLeft) {
+            int len = SkFixedCeilToInt(joinLeft - ul);
+            if (len == 1) {
+                SkAlpha alpha = trapezoidToAlpha(joinLeft - ul, joinLeft - ll);
+                blit_single_alpha(blitter, y, ul >> 16, alpha, fullAlpha, maskRow, isUsingMask);
+            } else if (len == 2) {
+                SkFixed first = joinLeft - SK_Fixed1 - ul;
+                SkFixed second = ll - ul - first;
+                SkAlpha a1 = partialTriangleToAlpha(first, lDY);
+                SkAlpha a2 = fullAlpha - partialTriangleToAlpha(second, lDY);
+                blit_two_alphas(blitter, y, ul >> 16, a1, a2, fullAlpha, maskRow, isUsingMask);
+            } else {
+                blit_aaa_trapezoid_row(blitter, y, ul, joinLeft, ll, joinLeft, lDY, SK_MaxS32,
+                                       fullAlpha, maskRow, isUsingMask);
+            }
+        }
+        if (lr > joinRite) {
+            int len = SkFixedCeilToInt(lr - joinRite);
+            if (len == 1) {
+                SkAlpha alpha = trapezoidToAlpha(ur - joinRite, lr - joinRite);
+                blit_single_alpha(blitter, y, joinRite >> 16, alpha, fullAlpha, maskRow,
+                                  isUsingMask);
+            } else if (len == 2) {
+                SkFixed first = joinRite + SK_Fixed1 - ur;
+                SkFixed second = lr - ur - first;
+                SkAlpha a1 = fullAlpha - partialTriangleToAlpha(first, rDY);
+                SkAlpha a2 = partialTriangleToAlpha(second, rDY);
+                blit_two_alphas(blitter, y, joinRite >> 16, a1, a2, fullAlpha, maskRow,
+                                isUsingMask);
+            } else {
+                blit_aaa_trapezoid_row(blitter, y, joinRite, ur, joinRite, lr, SK_MaxS32, rDY,
+                                       fullAlpha, maskRow, isUsingMask);
+            }
+        }
+    } else {
+        blit_aaa_trapezoid_row(blitter, y, ul, ur, ll, lr, lDY, rDY, fullAlpha, maskRow,
+                               isUsingMask);
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+static bool operator<(const SkAnalyticEdge& a, const SkAnalyticEdge& b) {
+    int valuea = a.fUpperY;
+    int valueb = b.fUpperY;
+
+    if (valuea == valueb) {
+        valuea = a.fX;
+        valueb = b.fX;
+    }
+
+    if (valuea == valueb) {
+        valuea = a.fDX;
+        valueb = b.fDX;
+    }
+
+    return valuea < valueb;
+}
+
+static SkAnalyticEdge* sort_edges(SkAnalyticEdge* list[], int count, SkAnalyticEdge** last) {
+    SkTQSort(list, list + count - 1);
+
+    // now make the edges linked in sorted order
+    for (int i = 1; i < count; i++) {
+        list[i - 1]->fNext = list[i];
+        list[i]->fPrev = list[i - 1];
+    }
+
+    *last = list[count - 1];
+    return list[0];
+}
+
+#ifdef SK_DEBUG
+    static void validate_sort(const SkAnalyticEdge* edge) {
+        SkFixed y = SkIntToFixed(-32768);
+
+        while (edge->fUpperY != SK_MaxS32) {
+            edge->validate();
+            SkASSERT(y <= edge->fUpperY);
+
+            y = edge->fUpperY;
+            edge = (SkAnalyticEdge*)edge->fNext;
+        }
+    }
+#else
+    #define validate_sort(edge)
+#endif
+
+// return true if we're done with this edge
+static bool update_edge(SkAnalyticEdge* edge, SkFixed last_y) {
+    if (last_y >= edge->fLowerY) {
+        if (edge->fCurveCount < 0) {
+            if (static_cast<SkAnalyticCubicEdge*>(edge)->updateCubic()) {
+                return false;
+            }
+        } else if (edge->fCurveCount > 0) {
+            if (static_cast<SkAnalyticQuadraticEdge*>(edge)->updateQuadratic()) {
+                return false;
+            }
+        }
+        return true;
+    }
+    SkASSERT(false);
+    return false;
+}
+
+// For an edge, we consider it smooth if the Dx doesn't change much, and Dy is large enough
+// For curves that are updating, the Dx is not changing much if fQDx/fCDx and fQDy/fCDy are
+// relatively large compared to fQDDx/QCDDx and fQDDy/fCDDy
+static inline bool isSmoothEnough(SkAnalyticEdge* thisEdge, SkAnalyticEdge* nextEdge, int stop_y) {
+    if (thisEdge->fCurveCount < 0) {
+        const SkCubicEdge& cEdge = static_cast<SkAnalyticCubicEdge*>(thisEdge)->fCEdge;
+        int ddshift = cEdge.fCurveShift;
+        return SkAbs32(cEdge.fCDx) >> 1 >= SkAbs32(cEdge.fCDDx) >> ddshift &&
+                SkAbs32(cEdge.fCDy) >> 1 >= SkAbs32(cEdge.fCDDy) >> ddshift &&
+                // current Dy is (fCDy - (fCDDy >> ddshift)) >> dshift
+                (cEdge.fCDy - (cEdge.fCDDy >> ddshift)) >> cEdge.fCubicDShift >= SK_Fixed1;
+    } else if (thisEdge->fCurveCount > 0) {
+        const SkQuadraticEdge& qEdge = static_cast<SkAnalyticQuadraticEdge*>(thisEdge)->fQEdge;
+        return SkAbs32(qEdge.fQDx) >> 1 >= SkAbs32(qEdge.fQDDx) &&
+                SkAbs32(qEdge.fQDy) >> 1 >= SkAbs32(qEdge.fQDDy) &&
+                // current Dy is (fQDy - fQDDy) >> shift
+                (qEdge.fQDy - qEdge.fQDDy) >> qEdge.fCurveShift
+                >= SK_Fixed1;
+    }
+    return SkAbs32(nextEdge->fDX - thisEdge->fDX) <= SK_Fixed1 && // DDx should be small
+            nextEdge->fLowerY - nextEdge->fUpperY >= SK_Fixed1; // Dy should be large
+}
+
+// Check if the leftE and riteE are changing smoothly in terms of fDX.
+// If yes, we can later skip the fractional y and directly jump to integer y.
+static inline bool isSmoothEnough(SkAnalyticEdge* leftE, SkAnalyticEdge* riteE,
+                           SkAnalyticEdge* currE, int stop_y) {
+    if (currE->fUpperY >= stop_y << 16) {
+        return false; // We're at the end so we won't skip anything
+    }
+    if (leftE->fLowerY + SK_Fixed1 < riteE->fLowerY) {
+        return isSmoothEnough(leftE, currE, stop_y); // Only leftE is changing
+    } else if (leftE->fLowerY > riteE->fLowerY + SK_Fixed1) {
+        return isSmoothEnough(riteE, currE, stop_y); // Only riteE is changing
+    }
+
+    // Now both edges are changing, find the second next edge
+    SkAnalyticEdge* nextCurrE = currE->fNext;
+    if (nextCurrE->fUpperY >= stop_y << 16) { // Check if we're at the end
+        return false;
+    }
+    if (*nextCurrE < *currE) {
+        SkTSwap(currE, nextCurrE);
+    }
+    return isSmoothEnough(leftE, currE, stop_y) && isSmoothEnough(riteE, nextCurrE, stop_y);
+}
+
+static inline void aaa_walk_convex_edges(SkAnalyticEdge* prevHead, AdditiveBlitter* blitter,
+                           int start_y, int stop_y, SkFixed leftBound, SkFixed riteBound,
+                           bool isUsingMask) {
+    validate_sort((SkAnalyticEdge*)prevHead->fNext);
+
+    SkAnalyticEdge* leftE = (SkAnalyticEdge*) prevHead->fNext;
+    SkAnalyticEdge* riteE = (SkAnalyticEdge*) leftE->fNext;
+    SkAnalyticEdge* currE = (SkAnalyticEdge*) riteE->fNext;
+
+    SkFixed y = SkTMax(leftE->fUpperY, riteE->fUpperY);
+
+    #ifdef SK_DEBUG
+    int frac_y_cnt = 0;
+    int total_y_cnt = 0;
+    #endif
+
+    for (;;) {
+        // We have to check fLowerY first because some edges might be alone (e.g., there's only
+        // a left edge but no right edge in a given y scan line) due to precision limit.
+        while (leftE->fLowerY <= y) { // Due to smooth jump, we may pass multiple short edges
+            if (update_edge(leftE, y)) {
+                if (SkFixedFloorToInt(currE->fUpperY) >= stop_y) {
+                    goto END_WALK;
+                }
+                leftE = currE;
+                currE = (SkAnalyticEdge*)currE->fNext;
+            }
+        }
+        while (riteE->fLowerY <= y) { // Due to smooth jump, we may pass multiple short edges
+            if (update_edge(riteE, y)) {
+                if (SkFixedFloorToInt(currE->fUpperY) >= stop_y) {
+                    goto END_WALK;
+                }
+                riteE = currE;
+                currE = (SkAnalyticEdge*)currE->fNext;
+            }
+        }
+
+        SkASSERT(leftE);
+        SkASSERT(riteE);
+
+        // check our bottom clip
+        if (SkFixedFloorToInt(y) >= stop_y) {
+            break;
+        }
+
+        SkASSERT(SkFixedFloorToInt(leftE->fUpperY) <= stop_y);
+        SkASSERT(SkFixedFloorToInt(riteE->fUpperY) <= stop_y);
+
+        leftE->goY(y);
+        riteE->goY(y);
+
+        if (leftE->fX > riteE->fX || (leftE->fX == riteE->fX &&
+                                      leftE->fDX > riteE->fDX)) {
+            SkTSwap(leftE, riteE);
+        }
+
+        SkFixed local_bot_fixed = SkMin32(leftE->fLowerY, riteE->fLowerY);
+        // Skip the fractional y if edges are changing smoothly
+        if (isSmoothEnough(leftE, riteE, currE, stop_y)) {
+            local_bot_fixed = SkFixedCeilToFixed(local_bot_fixed);
+        }
+        local_bot_fixed = SkMin32(local_bot_fixed, SkIntToFixed(stop_y + 1));
+
+        SkFixed left = leftE->fX;
+        SkFixed dLeft = leftE->fDX;
+        SkFixed rite = riteE->fX;
+        SkFixed dRite = riteE->fDX;
+        if (0 == (dLeft | dRite)) {
+            int     fullLeft    = SkFixedCeilToInt(left);
+            int     fullRite    = SkFixedFloorToInt(rite);
+            SkFixed partialLeft = SkIntToFixed(fullLeft) - left;
+            SkFixed partialRite = rite - SkIntToFixed(fullRite);
+            int     fullTop     = SkFixedCeilToInt(y);
+            int     fullBot     = SkFixedFloorToInt(local_bot_fixed);
+            SkFixed partialTop  = SkIntToFixed(fullTop) - y;
+            SkFixed partialBot  = local_bot_fixed - SkIntToFixed(fullBot);
+            if (fullTop > fullBot) { // The rectangle is within one pixel height...
+                partialTop -= (SK_Fixed1 - partialBot);
+                partialBot = 0;
+            }
+
+            if (fullRite >= fullLeft) {
+                // Blit all full-height rows from fullTop to fullBot
+                if (fullBot > fullTop) {
+                    blitter->getRealBlitter()->blitAntiRect(fullLeft - 1, fullTop,
+                                                            fullRite - fullLeft, fullBot - fullTop,
+                                                            f2a(partialLeft), f2a(partialRite));
+                }
+
+                if (partialTop > 0) { // blit first partial row
+                    if (partialLeft > 0) {
+                        blitter->blitAntiH(fullLeft - 1, fullTop - 1,
+                                f2a(SkFixedMul_lowprec(partialTop, partialLeft)));
+                    }
+                    if (partialRite > 0) {
+                        blitter->blitAntiH(fullRite, fullTop - 1,
+                                f2a(SkFixedMul_lowprec(partialTop, partialRite)));
+                    }
+                    blitter->blitAntiH(fullLeft, fullTop - 1, fullRite - fullLeft,
+                                       f2a(partialTop));
+                }
+
+                if (partialBot > 0) { // blit last partial row
+                    if (partialLeft > 0) {
+                        blitter->blitAntiH(fullLeft - 1, fullBot,
+                                           f2a(SkFixedMul_lowprec(partialBot, partialLeft)));
+                    }
+                    if (partialRite > 0) {
+                        blitter->blitAntiH(fullRite, fullBot,
+                                           f2a(SkFixedMul_lowprec(partialBot, partialRite)));
+                    }
+                    blitter->blitAntiH(fullLeft, fullBot, fullRite - fullLeft, f2a(partialBot));
+                }
+            } else { // left and rite are within the same pixel
+                if (partialTop > 0) {
+                    blitter->getRealBlitter()->blitV(fullLeft - 1, fullTop - 1, 1,
+                            f2a(SkFixedMul_lowprec(partialTop, rite - left)));
+                }
+                if (partialBot > 0) {
+                    blitter->getRealBlitter()->blitV(fullLeft - 1, fullBot, 1,
+                            f2a(SkFixedMul_lowprec(partialBot, rite - left)));
+                }
+                if (fullBot >= fullTop) {
+                    blitter->getRealBlitter()->blitV(fullLeft - 1, fullTop, fullBot - fullTop,
+                            f2a(rite - left));
+                }
+            }
+
+            y = local_bot_fixed;
+        } else {
+            // The following constant are used to snap X
+            // We snap X mainly for speedup (no tiny triangle) and
+            // avoiding edge cases caused by precision errors
+            const SkFixed kSnapDigit = SK_Fixed1 >> 4;
+            const SkFixed kSnapHalf = kSnapDigit >> 1;
+            const SkFixed kSnapMask = (-1 ^ (kSnapDigit - 1));
+            left += kSnapHalf; rite += kSnapHalf; // For fast rounding
+
+            // Number of blit_trapezoid_row calls we'll have
+            int count = SkFixedCeilToInt(local_bot_fixed) - SkFixedFloorToInt(y);
+            #ifdef SK_DEBUG
+            total_y_cnt += count;
+            frac_y_cnt += ((int)(y & 0xFFFF0000) != y);
+            if ((int)(y & 0xFFFF0000) != y) {
+                SkDebugf("frac_y = %f\n", SkFixedToFloat(y));
+            }
+            #endif
+
+            // If we're using mask blitter, we advance the mask row in this function
+            // to save some "if" condition checks.
+            SkAlpha* maskRow = nullptr;
+            if (isUsingMask) {
+                maskRow = static_cast<MaskAdditiveBlitter*>(blitter)->getRow(y >> 16);
+            }
+
+            // Instead of writing one loop that handles both partial-row blit_trapezoid_row
+            // and full-row trapezoid_row together, we use the following 3-stage flow to
+            // handle partial-row blit and full-row blit separately. It will save us much time
+            // on changing y, left, and rite.
+            if (count > 1) {
+                if ((int)(y & 0xFFFF0000) != y) { // There's a partial-row on the top
+                    count--;
+                    SkFixed nextY = SkFixedCeilToFixed(y + 1);
+                    SkFixed dY = nextY - y;
+                    SkFixed nextLeft = left + SkFixedMul_lowprec(dLeft, dY);
+                    SkFixed nextRite = rite + SkFixedMul_lowprec(dRite, dY);
+                    blit_trapezoid_row(blitter, y >> 16, left & kSnapMask, rite & kSnapMask,
+                            nextLeft & kSnapMask, nextRite & kSnapMask, leftE->fDY, riteE->fDY,
+                            getPartialAlpha(0xFF, dY), maskRow, isUsingMask);
+                    left = nextLeft; rite = nextRite; y = nextY;
+                }
+
+                while (count > 1) { // Full rows in the middle
+                    count--;
+                    if (isUsingMask) {
+                        maskRow = static_cast<MaskAdditiveBlitter*>(blitter)->getRow(y >> 16);
+                    }
+                    SkFixed nextY = y + SK_Fixed1, nextLeft = left + dLeft, nextRite = rite + dRite;
+                    blit_trapezoid_row(blitter, y >> 16, left & kSnapMask, rite & kSnapMask,
+                            nextLeft & kSnapMask, nextRite & kSnapMask,
+                            leftE->fDY, riteE->fDY, 0xFF, maskRow, isUsingMask);
+                    left = nextLeft; rite = nextRite; y = nextY;
+                }
+            }
+
+            if (isUsingMask) {
+                maskRow = static_cast<MaskAdditiveBlitter*>(blitter)->getRow(y >> 16);
+            }
+
+            SkFixed dY = local_bot_fixed - y; // partial-row on the bottom
+            SkASSERT(dY <= SK_Fixed1);
+            // Smooth jumping to integer y may make the last nextLeft/nextRite out of bound.
+            // Take them back into the bound here.
+            SkFixed nextLeft = SkTMax(left + SkFixedMul_lowprec(dLeft, dY), leftBound);
+            SkFixed nextRite = SkTMin(rite + SkFixedMul_lowprec(dRite, dY), riteBound);
+            blit_trapezoid_row(blitter, y >> 16, left & kSnapMask, rite & kSnapMask,
+                    nextLeft & kSnapMask, nextRite & kSnapMask, leftE->fDY, riteE->fDY,
+                    getPartialAlpha(0xFF, dY), maskRow, isUsingMask);
+            left = nextLeft; rite = nextRite; y = local_bot_fixed;
+            left -= kSnapHalf; rite -= kSnapHalf;
+        }
+
+        leftE->fX = left;
+        riteE->fX = rite;
+        leftE->fY = riteE->fY = y;
+    }
+
+END_WALK:
+    ;
+    #ifdef SK_DEBUG
+    SkDebugf("frac_y_cnt = %d, total_y_cnt = %d\n", frac_y_cnt, total_y_cnt);
+    #endif
+}
+
+void SkScan::aaa_fill_path(const SkPath& path, const SkIRect* clipRect, AdditiveBlitter* blitter,
+                   int start_y, int stop_y, const SkRegion& clipRgn, bool isUsingMask) {
+    SkASSERT(blitter);
+
+    if (path.isInverseFillType() || !path.isConvex()) {
+        // fall back to supersampling AA
+        SkScan::AntiFillPath(path, clipRgn, blitter->getRealBlitter(true), false);
+        return;
+    }
+
+    SkEdgeBuilder   builder;
+
+    // If we're convex, then we need both edges, even the right edge is past the clip
+    const bool canCullToTheRight = !path.isConvex();
+
+    SkASSERT(GlobalAAConfig::getInstance().fUseAnalyticAA);
+    int count = builder.build(path, clipRect, 0, canCullToTheRight, true);
+    SkASSERT(count >= 0);
+
+    SkAnalyticEdge** list = (SkAnalyticEdge**)builder.analyticEdgeList();
+
+    SkIRect rect = clipRgn.getBounds();
+    if (0 == count) {
+        if (path.isInverseFillType()) {
+            /*
+             *  Since we are in inverse-fill, our caller has already drawn above
+             *  our top (start_y) and will draw below our bottom (stop_y). Thus
+             *  we need to restrict our drawing to the intersection of the clip
+             *  and those two limits.
+             */
+            if (rect.fTop < start_y) {
+                rect.fTop = start_y;
+            }
+            if (rect.fBottom > stop_y) {
+                rect.fBottom = stop_y;
+            }
+            if (!rect.isEmpty()) {
+                blitter->blitRect(rect.fLeft, rect.fTop, rect.width(), rect.height());
+            }
+        }
+        return;
+    }
+
+    SkAnalyticEdge headEdge, tailEdge, *last;
+    // this returns the first and last edge after they're sorted into a dlink list
+    SkAnalyticEdge* edge = sort_edges(list, count, &last);
+
+    headEdge.fPrev = nullptr;
+    headEdge.fNext = edge;
+    headEdge.fUpperY = headEdge.fLowerY = SK_MinS32;
+    headEdge.fX = SK_MinS32;
+    headEdge.fDX = 0;
+    headEdge.fDY = SK_MaxS32;
+    headEdge.fUpperX = SK_MinS32;
+    edge->fPrev = &headEdge;
+
+    tailEdge.fPrev = last;
+    tailEdge.fNext = nullptr;
+    tailEdge.fUpperY = tailEdge.fLowerY = SK_MaxS32;
+    headEdge.fX = SK_MaxS32;
+    headEdge.fDX = 0;
+    headEdge.fDY = SK_MaxS32;
+    headEdge.fUpperX = SK_MaxS32;
+    last->fNext = &tailEdge;
+
+    // now edge is the head of the sorted linklist
+
+    if (clipRect && start_y < clipRect->fTop) {
+        start_y = clipRect->fTop;
+    }
+    if (clipRect && stop_y > clipRect->fBottom) {
+        stop_y = clipRect->fBottom;
+    }
+
+    if (!path.isInverseFillType() && path.isConvex()) {
+        SkASSERT(count >= 2);   // convex walker does not handle missing right edges
+        aaa_walk_convex_edges(&headEdge, blitter, start_y, stop_y,
+                              rect.fLeft << 16, rect.fRight << 16, isUsingMask);
+    } else {
+        SkFAIL("Concave AAA is not yet implemented!");
+    }
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+void SkScan::AAAFillPath(const SkPath& path, const SkRegion& origClip, SkBlitter* blitter) {
+    if (origClip.isEmpty()) {
+        return;
+    }
+
+    const bool isInverse = path.isInverseFillType();
+    SkIRect ir;
+    path.getBounds().roundOut(&ir);
+    if (ir.isEmpty()) {
+        if (isInverse) {
+            blitter->blitRegion(origClip);
+        }
+        return;
+    }
+
+    SkIRect clippedIR;
+    if (isInverse) {
+       // If the path is an inverse fill, it's going to fill the entire
+       // clip, and we care whether the entire clip exceeds our limits.
+       clippedIR = origClip.getBounds();
+    } else {
+       if (!clippedIR.intersect(ir, origClip.getBounds())) {
+           return;
+       }
+    }
+
+    // Our antialiasing can't handle a clip larger than 32767, so we restrict
+    // the clip to that limit here. (the runs[] uses int16_t for its index).
+    //
+    // A more general solution (one that could also eliminate the need to
+    // disable aa based on ir bounds (see overflows_short_shift) would be
+    // to tile the clip/target...
+    SkRegion tmpClipStorage;
+    const SkRegion* clipRgn = &origClip;
+    {
+        static const int32_t kMaxClipCoord = 32767;
+        const SkIRect& bounds = origClip.getBounds();
+        if (bounds.fRight > kMaxClipCoord || bounds.fBottom > kMaxClipCoord) {
+            SkIRect limit = { 0, 0, kMaxClipCoord, kMaxClipCoord };
+            tmpClipStorage.op(origClip, limit, SkRegion::kIntersect_Op);
+            clipRgn = &tmpClipStorage;
+        }
+    }
+    // for here down, use clipRgn, not origClip
+
+    SkScanClipper   clipper(blitter, clipRgn, ir);
+    const SkIRect*  clipRect = clipper.getClipRect();
+
+    if (clipper.getBlitter() == nullptr) { // clipped out
+        if (isInverse) {
+            blitter->blitRegion(*clipRgn);
+        }
+        return;
+    }
+
+    // now use the (possibly wrapped) blitter
+    blitter = clipper.getBlitter();
+
+    if (isInverse) {
+        // Currently, we use the old path to render the inverse path,
+        // so we don't need this.
+        // sk_blit_above(blitter, ir, *clipRgn);
+    }
+
+    SkASSERT(SkIntToScalar(ir.fTop) <= path.getBounds().fTop);
+
+    if (MaskAdditiveBlitter::canHandleRect(ir) && !isInverse) {
+        MaskAdditiveBlitter additiveBlitter(blitter, ir, *clipRgn, isInverse);
+        aaa_fill_path(path, clipRect, &additiveBlitter, ir.fTop, ir.fBottom, *clipRgn, true);
+    } else {
+        RunBasedAdditiveBlitter additiveBlitter(blitter, ir, *clipRgn, isInverse);
+        aaa_fill_path(path, clipRect, &additiveBlitter, ir.fTop, ir.fBottom, *clipRgn, false);
+    }
+
+    if (isInverse) {
+        // Currently, we use the old path to render the inverse path,
+        // so we don't need this.
+        // sk_blit_below(blitter, ir, *clipRgn);
+    }
+}
+
+// This almost copies SkScan::AntiFillPath
+void SkScan::AAAFillPath(const SkPath& path, const SkRasterClip& clip, SkBlitter* blitter) {
+    if (clip.isEmpty()) {
+        return;
+    }
+
+    if (clip.isBW()) {
+        AAAFillPath(path, clip.bwRgn(), blitter);
+    } else {
+        SkRegion        tmp;
+        SkAAClipBlitter aaBlitter;
+
+        tmp.setRect(clip.getBounds());
+        aaBlitter.init(blitter, &clip.aaRgn());
+        AAAFillPath(path, tmp, &aaBlitter);
+    }
+}