Analytic AntiAlias for Convex Shapes

src/core/SkEdge.h

 /*
  * 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 SkEdge_DEFINED
 #define SkEdge_DEFINED
@@ skipping 112 matching lines @@
     fX          = SkFDot6ToFixed(x0 + SkFixedMul(slope, dy));   // + SK_Fixed1/2
     fDX         = slope;
     fFirstY     = top;
     fLastY      = bot - 1;
     fCurveCount = 0;
     fWinding    = SkToS8(winding);
     fCurveShift = 0;
     return 1;
 }
 
+//////////////Analytic Edges////////////////////////////////
+
+struct SkAnalyticEdge {
+    enum Type {
+        kLine_Type,
+        kQuad_Type,

[caryclark, 2016/08/10 13:08:10]

could you add a comment about how conic is supported?

[liyuqian, 2016/08/16 13:22:05]

Done.

+        kCubic_Type
+    };
+
+    SkAnalyticEdge* fNext;
+    SkAnalyticEdge* fPrev;
+
+    SkFixed fX;
+    SkFixed fDX;
+    SkFixed fUpperX;

[caryclark, 2016/08/10 13:08:10]

Could you add comments on what these fields mean and/or how they are used?

[liyuqian, 2016/08/16 13:22:05]

Done.

+    SkFixed fY;
+    SkFixed fUpperY;
+    SkFixed fLowerY;
+    SkFixed fDY;            // abs of the inverse of fDX; may be SK_MaxS32 when fDX is close to 0

[caryclark, 2016/08/10 13:08:10]

is this comment on the right line?

[liyuqian, 2016/08/16 13:22:05]

Yes, I'm adding an extra newline to make it more clear.

+                            // fDY is only used for blitting trapezoids
+    int8_t  fCurveCount;    // only used by kQuad(+) and kCubic(-)
+    uint8_t fCurveShift;    // appled to all Dx/DDx/DDDx except for fCubicDShift exception
+    uint8_t fCubicDShift;   // applied to fCDx and fCDy only in cubic
+    int8_t  fWinding;       // 1 or -1
+
+    static const int kDefaultAccuracy = 4; // default accuracy for snapping y
+
+    static inline SkFixed snapY(SkFixed y, int accuracy = kDefaultAccuracy) {
+        // We do ceiling to ensure that y is increasing
+        return SkFixedCeilToFixed(y << accuracy) >> accuracy;
+    }
+
+    static inline SkFixed snapX(SkFixed x, int accuracy = kDefaultAccuracy) {
+        return SkFixedRoundToFixed(x << accuracy) >> accuracy;
+    }
+
+    inline void goY(SkFixed y) {
+        if (y == fY + SK_Fixed1) {
+            fX = fX + fDX;
+            return;
+        } else if (y != fY) {
+            // Drop lower digits as our alpha only has 8 bits
+            // (fDX and y - fUpperY may be greater than SK_Fixed1)
+            fX = fUpperX + SkFixedMul_lowprec(fDX, y - fUpperY);
+        }
+        fY = y;
+    }
+
+    int setLine(const SkPoint& p0, const SkPoint& p1, const SkIRect* clip);

[caryclark, 2016/08/10 13:08:10]

what does the return result mean? If it is always 1 or 0, can it return a bool
instead?

[liyuqian, 2016/08/16 13:22:05]

I've changed it to bool. I don't know why the original code (which I copied
from) has return type int.

+    // call this version if you know you don't have a clip
+    inline int setLine(const SkPoint& p0, const SkPoint& p1);

[caryclark, 2016/08/10 13:08:10]

ditto

[liyuqian, 2016/08/16 13:22:05]

Done.

+    inline int updateLine(SkFixed ax, SkFixed ay, SkFixed bx, SkFixed by);
+    void chopLineWithClip(const SkIRect& clip);
+
+    inline bool intersectsClip(const SkIRect& clip) const {
+        SkASSERT(SkFixedFloorToInt(fUpperY) < clip.fBottom);
+        return SkFixedCeilToInt(fLowerY) > clip.fTop;
+    }
+
+#ifdef SK_DEBUG
+    void dump() const {
+        SkDebugf("edge: upperY:%d lowerY:%d y:%g x:%g dx:%g w:%d\n",
+                 fUpperY, fLowerY, SkFixedToFloat(fY), SkFixedToFloat(fX),
+                 SkFixedToFloat(fDX), fWinding);
+    }
+
+    void validate() const {
+         SkASSERT(fPrev && fNext);
+         SkASSERT(fPrev->fNext == this);
+         SkASSERT(fNext->fPrev == this);
+
+         SkASSERT(fUpperY < fLowerY);
+         SkASSERT(SkAbs32(fWinding) == 1);
+    }
+#endif
+};
+
+struct SkAnalyticQuadraticEdge : public SkAnalyticEdge {
+    SkFixed fQx, fQy;
+    SkFixed fQDx, fQDy;
+    SkFixed fQDDx, fQDDy;
+    SkFixed fQLastX, fQLastY;
+
+    // snap y to integer points in the middle of the curve to accelerate AAA path filling
+    SkFixed fSnappedX, fSnappedY;
+
+    int setQuadratic(const SkPoint pts[3]);
+    int updateQuadratic();
+};
+
+struct SkAnalyticCubicEdge : public SkAnalyticEdge {
+    SkFixed fCx, fCy;
+    SkFixed fCDx, fCDy;
+    SkFixed fCDDx, fCDDy;
+    SkFixed fCDDDx, fCDDDy;
+    SkFixed fCLastX, fCLastY;
+
+    int setCubic(const SkPoint pts[4]);
+    int updateCubic();
+};
+
+int SkAnalyticEdge::setLine(const SkPoint& p0, const SkPoint& p1) {
+    SkFixed x0, y0, x1, y1;
+
+    x0 = SkScalarToFixed(p0.fX);
+    y0 = snapY(SkScalarToFixed(p0.fY));
+    x1 = SkScalarToFixed(p1.fX);
+    y1 = snapY(SkScalarToFixed(p1.fY));
+
+    int winding = 1;
+
+    if (y0 > y1) {
+        SkTSwap(x0, x1);
+        SkTSwap(y0, y1);
+        winding = -1;
+    }
+
+    // are we a zero-height line?
+    if (y0 == y1) {
+        return 0;
+    }
+
+    SkFixed slope = SkFixedDiv(x1 - x0, y1 - y0);
+
+    fX          = x0;
+    fDX         = slope;
+    fUpperX     = x0;
+    fY          = y0;
+    fUpperY     = y0;
+    fLowerY     = y1;
+    fDY         = x1 - x0 != 0 ? SkAbs32(SkFixedDiv(y1 - y0, x1 - x0)) : SK_MaxS32;

[caryclark, 2016/08/10 13:08:10]

x1 == x0 ?

[liyuqian, 2016/08/16 13:22:05]

Done.

+    fCurveCount = 0;
+    fWinding    = SkToS8(winding);
+    fCurveShift = 0;
+    return 1;
+}
+
+////////////////////////////////////////////////////////////
+
 
 #endif