don't overclamp cubics (see skbug.com/1316)

src/core/SkEdgeClipper.cpp

 
 /*
  * Copyright 2009 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 "SkEdgeClipper.h"
@@ skipping 265 matching lines @@
 // Modify pts[] in place so that it is clipped in Y to the clip rect
 static void chop_cubic_in_Y(SkPoint pts[4], const SkRect& clip) {
 
     // are we partially above
     if (pts[0].fY < clip.fTop) {
         SkScalar t;
         if (chopMonoCubicAtY(pts, clip.fTop, &t)) {
             SkPoint tmp[7];
             SkChopCubicAt(pts, tmp, t);
 
-            // tmp[3, 4, 5].fY should all be to the below clip.fTop, and
-            // still be monotonic in Y. Since we can't trust the numerics of
+            // tmp[3, 4, 5].fY should all be to the below clip.fTop.
+            // Since we can't trust the numerics of
             // the chopper, we force those conditions now
             tmp[3].fY = clip.fTop;
             clamp_ge(tmp[4].fY, clip.fTop);
-            clamp_ge(tmp[5].fY, tmp[4].fY);
+            clamp_ge(tmp[5].fY, clip.fTop);
 
             pts[0] = tmp[3];
             pts[1] = tmp[4];
             pts[2] = tmp[5];
         } else {
             // if chopMonoCubicAtY failed, then we may have hit inexact numerics
             // so we just clamp against the top
             for (int i = 0; i < 4; i++) {
                 clamp_ge(pts[i].fY, clip.fTop);
             }
@@ skipping 53 matching lines @@
     }
 
     // are we partially to the left
     if (pts[0].fX < clip.fLeft) {
         SkScalar t;
         if (chopMonoCubicAtX(pts, clip.fLeft, &t)) {
             SkPoint tmp[7];
             SkChopCubicAt(pts, tmp, t);
             this->appendVLine(clip.fLeft, tmp[0].fY, tmp[3].fY, reverse);
 
-            // tmp[3, 4, 5].fX should all be to the right of clip.fLeft, and
-            // still be monotonic in X. Since we can't trust the numerics of
+            // tmp[3, 4, 5].fX should all be to the right of clip.fLeft.
+            // Since we can't trust the numerics of
             // the chopper, we force those conditions now
             tmp[3].fX = clip.fLeft;
             clamp_ge(tmp[4].fX, clip.fLeft);
-            clamp_ge(tmp[5].fX, tmp[4].fX);
+            clamp_ge(tmp[5].fX, clip.fLeft);
 
             pts[0] = tmp[3];
             pts[1] = tmp[4];
             pts[2] = tmp[5];
         } else {
             // if chopMonocubicAtY failed, then we may have hit inexact numerics
             // so we just clamp against the left
             this->appendVLine(clip.fLeft, pts[0].fY, pts[3].fY, reverse);
             return;
         }
     }
 
     // are we partially to the right
     if (pts[3].fX > clip.fRight) {
         SkScalar t;
         if (chopMonoCubicAtX(pts, clip.fRight, &t)) {
             SkPoint tmp[7];
             SkChopCubicAt(pts, tmp, t);
             tmp[3].fX = clip.fRight;
             clamp_le(tmp[2].fX, clip.fRight);
-            clamp_le(tmp[1].fX, tmp[2].fX);
+            clamp_le(tmp[1].fX, clip.fRight);
 
             this->appendCubic(tmp, reverse);
             this->appendVLine(clip.fRight, tmp[3].fY, tmp[6].fY, reverse);
         } else {
             // if chopMonoCubicAtX failed, then we may have hit inexact numerics
             // so we just clamp against the right
             this->appendVLine(clip.fRight, pts[0].fY, pts[3].fY, reverse);
         }
     } else {    // wholly inside the clip
         this->appendCubic(pts, reverse);
     }
 }
 
 bool SkEdgeClipper::clipCubic(const SkPoint srcPts[4], const SkRect& clip) {
     fCurrPoint = fPoints;
     fCurrVerb = fVerbs;
 
     SkRect  bounds;
     bounds.set(srcPts, 4);
 
     if (!quick_reject(bounds, clip)) {
         SkPoint monoY[10];
         int countY = SkChopCubicAtYExtrema(srcPts, monoY);
         for (int y = 0; y <= countY; y++) {
-        //    sk_assert_monotonic_y(&monoY[y * 3], 4);
             SkPoint monoX[10];
             int countX = SkChopCubicAtXExtrema(&monoY[y * 3], monoX);
             for (int x = 0; x <= countX; x++) {
-            //    sk_assert_monotonic_y(&monoX[x * 3], 4);
-            //    sk_assert_monotonic_x(&monoX[x * 3], 4);
                 this->clipMonoCubic(&monoX[x * 3], clip);
                 SkASSERT(fCurrVerb - fVerbs < kMaxVerbs);
                 SkASSERT(fCurrPoint - fPoints <= kMaxPoints);
             }
         }
     }
 
     *fCurrVerb = SkPath::kDone_Verb;
     fCurrPoint = fPoints;
     fCurrVerb = fVerbs;
@@ skipping 93 matching lines @@
         assert_monotonic(&pts[0].fY, count);
     }
 }
 
 void sk_assert_monotonic_x(const SkPoint pts[], int count) {
     if (count > 1) {
         assert_monotonic(&pts[0].fX, count);
     }
 }
 #endif