Bug 1297427 - Use calculate curve origin instead of reusing center curve origin in DottedCornerFinder. r=bas

gfx/2d/BezierUtils.cpp

@@ -329,6 +329,9 @@ CalculateDistanceToEllipticArc(const Point& P, const Point& normal,
   Float n1 = (- B + S) / A;
   Float n2 = (- B - S) / A;
 
+  MOZ_ASSERT(n1 >= 0);
+  MOZ_ASSERT(n2 >= 0);
+
   return n1 < n2 ? n1 : n2;
 }
 

layout/base/DottedCornerFinder.cpp

@@ -57,7 +57,8 @@ DottedCornerFinder::DottedCornerFinder(const Bezier& aOuterBezier,
    mNormalSign((aCorner == C_TL || aCorner == C_BR) ? -1.0f : 1.0f),
    mC0(aC0), mCn(aCn),
    mR0(aR0), mRn(aRn), mMaxR(std::max(aR0, aRn)),
-   mCurveOrigin(mC0.x, mCn.y),
+   mCenterCurveOrigin(mC0.x, mCn.y),
+   mInnerCurveOrigin(mInnerBezier.mPoints[0].x, mInnerBezier.mPoints[3].y),
    mBestOverlap(0.0f),
    mHasZeroBorderWidth(false), mHasMore(true),
    mMaxCount(aCornerDim.width + aCornerDim.height),
@@ -185,8 +186,8 @@ DottedCornerFinder::Next(void)
       phi = M_PI / 2.0f + phi;
     }
 
-    Point C(mCurveOrigin.x + mCenterCurveR * cos(phi),
-            mCurveOrigin.y + mCenterCurveR * sin(phi));
+    Point C(mCenterCurveOrigin.x + mCenterCurveR * cos(phi),
+            mCenterCurveOrigin.y + mCenterCurveR * sin(phi));
     return DottedCornerFinder::Result(C, mR0);
   }
 
@@ -288,7 +289,7 @@ DottedCornerFinder::FindNext(Float overlap)
       }
 
       Point normal = PointRotateCCW90(Diff / DiffLength) * (-mNormalSign);
-      r = CalculateDistanceToEllipticArc(C, normal, mCurveOrigin,
+      r = CalculateDistanceToEllipticArc(C, normal, mInnerCurveOrigin,
                                          mInnerWidth, mInnerHeight);
 
       // Check overlap along arc.

layout/base/DottedCornerFinder.h

@@ -57,7 +57,9 @@ public:
 
     Result(const Point& aC, Float aR)
      : C(aC), r(aR)
-    {}
+    {
+      MOZ_ASSERT(aR >= 0);
+    }
   };
 
   //                        aBorderRadiusX
@@ -189,11 +191,12 @@ private:
   Float mMaxR;
 
   // Parameters for the center curve with perfect circle and the inner curve.
+  // The center curve doesn't necessarily share the origin with others.
   //
   //               ___---+
   //           __--      |
   //         _-          |
-  //       /        __---+
+  //       /        __-+ |
   //     /      __--     |
   //    |     /          |
   //   |    /        __--+--
@@ -203,18 +206,39 @@ private:
   // |    |     |        | |
   // |    |     |        | | mInnerHeight
   // |    |    |         | |
-  // |    |    |         | |
-  // |    |    |         | v
-  // +----+----+---------+
-  //      |    |         | mCurveOrigin
-  //      |    |<------->|
-  //      |  mInnerWidth |
-  //      |              |
-  //      |<------------>|
-  //        mCenterCurveR
+  // |    +    |         | |
+  // |         |         | v
+  // +---------+---------+
+  //           |         | mInnerCurveOrigin
+  //           |<------->|
+  //           mInnerWidth
   //
-  Point mCurveOrigin;
+  //               ___---+
+  //           __--
+  //         _-
+  //       /        __-+
+  //     /      __--   |
+  //    |     /        |
+  //   |    /        __--+
+  //  |    |       _-  |
+  //  |    |      /    |
+  // |     |     /     |
+  // |    |     |      |
+  // |    |     |      |
+  // |    |    |       |
+  // |    +--- | ------+
+  // |    |    |       | mCenterCurveOrigin
+  // +    |    +       |
+  //      |            |
+  //      |            |
+  //      |            |
+  //      |            |
+  //      |<---------->|
+  //       mCenterCurveR
+  //
+  Point mCenterCurveOrigin;
   Float mCenterCurveR;
+  Point mInnerCurveOrigin;
   Float mInnerWidth;
   Float mInnerHeight;