Analytic AntiAlias for Convex Shapes

src/core/SkEdge.cpp

 /*
  * 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.
  */
 
 
 #include "SkEdge.h"
 #include "SkFDot6.h"
@@ skipping 154 matching lines @@
     // shift down dist (it is currently in dot6)
     // down by 5 should give us 1/2 pixel accuracy (assuming our dist is accurate...)
     // this is chosen by heuristic: make it as big as possible (to minimize segments)
     // ... but small enough so that our curves still look smooth
     dist = (dist + (1 << 4)) >> 5;
 
     // each subdivision (shift value) cuts this dist (error) by 1/4
     return (32 - SkCLZ(dist)) >> 1;
 }
 
-int SkQuadraticEdge::setQuadratic(const SkPoint pts[3], int shift)
-{
+bool SkQuadraticEdge::setQuadraticWithoutUpdate(const SkPoint pts[3], int shift) {
     SkFDot6 x0, y0, x1, y1, x2, y2;
 
     {
 #ifdef SK_RASTERIZE_EVEN_ROUNDING
         x0 = SkScalarRoundToFDot6(pts[0].fX, shift);
         y0 = SkScalarRoundToFDot6(pts[0].fY, shift);
         x1 = SkScalarRoundToFDot6(pts[1].fX, shift);
         y1 = SkScalarRoundToFDot6(pts[1].fY, shift);
         x2 = SkScalarRoundToFDot6(pts[2].fX, shift);
         y2 = SkScalarRoundToFDot6(pts[2].fY, shift);
@@ skipping 72 matching lines @@
     A = SkFDot6ToFixedDiv2(y0 - y1 - y1 + y2);  // 1/2 the real value
     B = SkFDot6ToFixed(y1 - y0);                // 1/2 the real value
 
     fQy     = SkFDot6ToFixed(y0);
     fQDy    = B + (A >> shift);     // biased by shift
     fQDDy   = A >> (shift - 1);     // biased by shift
 
     fQLastX = SkFDot6ToFixed(x2);
     fQLastY = SkFDot6ToFixed(y2);
 
+    return true;
+}
+
+int SkQuadraticEdge::setQuadratic(const SkPoint pts[3], int shift) {
+    if (!setQuadraticWithoutUpdate(pts, shift)) {
+        return 0;
+    }
     return this->updateQuadratic();
 }
 
 int SkQuadraticEdge::updateQuadratic()
 {
     int     success;
     int     count = fCurveCount;
     SkFixed oldx = fQx;
     SkFixed oldy = fQy;
     SkFixed dx = fQDx;
@@ skipping 46 matching lines @@
 */
 static SkFDot6 cubic_delta_from_line(SkFDot6 a, SkFDot6 b, SkFDot6 c, SkFDot6 d)
 {
     // since our parameters may be negative, we don't use << to avoid ASAN warnings
     SkFDot6 oneThird = (a*8 - b*15 + 6*c + d) * 19 >> 9;
     SkFDot6 twoThird = (a + 6*b - c*15 + d*8) * 19 >> 9;
 
     return SkMax32(SkAbs32(oneThird), SkAbs32(twoThird));
 }
 
-int SkCubicEdge::setCubic(const SkPoint pts[4], int shift) {
+bool SkCubicEdge::setCubicWithoutUpdate(const SkPoint pts[4], int shift) {
     SkFDot6 x0, y0, x1, y1, x2, y2, x3, y3;
 
     {
 #ifdef SK_RASTERIZE_EVEN_ROUNDING
         x0 = SkScalarRoundToFDot6(pts[0].fX, shift);
         y0 = SkScalarRoundToFDot6(pts[0].fY, shift);
         x1 = SkScalarRoundToFDot6(pts[1].fX, shift);
         y1 = SkScalarRoundToFDot6(pts[1].fY, shift);
         x2 = SkScalarRoundToFDot6(pts[2].fX, shift);
         y2 = SkScalarRoundToFDot6(pts[2].fY, shift);
@@ skipping 75 matching lines @@
     D = SkFDot6UpShift(y3 + 3 * (y1 - y2) - y0, upShift);
 
     fCy     = SkFDot6ToFixed(y0);
     fCDy    = B + (C >> shift) + (D >> 2*shift);    // biased by shift
     fCDDy   = 2*C + (3*D >> (shift - 1));           // biased by 2*shift
     fCDDDy  = 3*D >> (shift - 1);                   // biased by 2*shift
 
     fCLastX = SkFDot6ToFixed(x3);
     fCLastY = SkFDot6ToFixed(y3);
 
+    return true;
+}
+
+int SkCubicEdge::setCubic(const SkPoint pts[4], int shift) {
+    if (!this->setCubicWithoutUpdate(pts, shift)) {
+        return 0;
+    }
     return this->updateCubic();
 }
 
 int SkCubicEdge::updateCubic()
 {
     int     success;
     int     count = fCurveCount;
     SkFixed oldx = fCx;
     SkFixed oldy = fCy;
     SkFixed newx, newy;
@@ skipping 29 matching lines @@
         success = this->updateLine(oldx, oldy, newx, newy);
         oldx = newx;
         oldy = newy;
     } while (count < 0 && !success);
 
     fCx         = newx;
     fCy         = newy;
     fCurveCount = SkToS8(count);
     return success;
 }