Fix bug with very large round rects with large radii

src/core/SkRRect.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkRRect.h"
 #include "SkMatrix.h"
 
@@ skipping 110 matching lines @@
  *  We need all combinations of predicates to be true to have a "safe" radius value.
  */
 static SkScalar clamp_radius_check_predicates(SkScalar rad, SkScalar min, SkScalar max) {
     SkASSERT(min < max);
     if (rad > max - min || min + rad > max || max - rad < min) {
         rad = SkScalarDecULP(rad);
     }
     return rad;
 }
 
+// These parameters intentionally double. Apropos crbug.com/463920, if one of the
+// radii is huge while the other is small, single precision math can completely
+// miss the fact that a scale is required.
+static double compute_min_scale(double rad1, double rad2, double limit, double curMin) {
+    if ((rad1 + rad2) > limit) {
+        return SkTMin(curMin, limit / (rad1 + rad2));
+    }
+    return curMin;
+}
+
 void SkRRect::setRectRadii(const SkRect& rect, const SkVector radii[4]) {
     if (rect.isEmpty() || !rect.isFinite()) {
         this->setEmpty();
         return;
     }
 
     if (!SkScalarsAreFinite(&radii[0].fX, 8)) {
         this->setRect(rect);    // devolve into a simple rect
         return;
     }
@@ skipping 25 matching lines @@
     // Proportionally scale down all radii to fit. Find the minimum ratio
     // of a side and the radii on that side (for all four sides) and use
     // that to scale down _all_ the radii. This algorithm is from the
     // W3 spec (http://www.w3.org/TR/css3-background/) section 5.5 - Overlapping
     // Curves:
     // "Let f = min(Li/Si), where i is one of { top, right, bottom, left },
     //   Si is the sum of the two corresponding radii of the corners on side i,
     //   and Ltop = Lbottom = the width of the box,
     //   and Lleft = Lright = the height of the box.
     // If f < 1, then all corner radii are reduced by multiplying them by f."
-    SkScalar scale = SK_Scalar1;
+    double scale = 1.0;
 
-    if (fRadii[0].fX + fRadii[1].fX > rect.width()) {
-        scale = SkMinScalar(scale,
-                            SkScalarDiv(rect.width(), fRadii[0].fX + fRadii[1].fX));
-    }
-    if (fRadii[1].fY + fRadii[2].fY > rect.height()) {
-        scale = SkMinScalar(scale,
-                            SkScalarDiv(rect.height(), fRadii[1].fY + fRadii[2].fY));
-    }
-    if (fRadii[2].fX + fRadii[3].fX > rect.width()) {
-        scale = SkMinScalar(scale,
-                            SkScalarDiv(rect.width(), fRadii[2].fX + fRadii[3].fX));
-    }
-    if (fRadii[3].fY + fRadii[0].fY > rect.height()) {
-        scale = SkMinScalar(scale,
-                            SkScalarDiv(rect.height(), fRadii[3].fY + fRadii[0].fY));
-    }
+    scale = compute_min_scale(fRadii[0].fX, fRadii[1].fX, rect.width(),  scale);
+    scale = compute_min_scale(fRadii[1].fY, fRadii[2].fY, rect.height(), scale);
+    scale = compute_min_scale(fRadii[2].fX, fRadii[3].fX, rect.width(),  scale);
+    scale = compute_min_scale(fRadii[3].fY, fRadii[0].fY, rect.height(), scale);
 
-    if (scale < SK_Scalar1) {
+    if (scale < 1.0) {
         for (int i = 0; i < 4; ++i) {
             fRadii[i].fX *= scale;
             fRadii[i].fY *= scale;
         }
     }
 
     // skbug.com/3239 -- its possible that we can hit the following inconsistency:
     //     rad == bounds.bottom - bounds.top
     //     bounds.bottom - radius < bounds.top
     //     YIKES
@@ skipping 384 matching lines @@
     }
 
     for (int i = 0; i < 4; ++i) {
         validate_radius_check_predicates(fRadii[i].fX, fRect.fLeft, fRect.fRight);
         validate_radius_check_predicates(fRadii[i].fY, fRect.fTop, fRect.fBottom);
     }
 }
 #endif // SK_DEBUG
 
 ///////////////////////////////////////////////////////////////////////////////