perpendicular round rects; fuzzy convexity

src/core/SkPath.cpp

Index: src/core/SkPath.cpp
diff --git a/src/core/SkPath.cpp b/src/core/SkPath.cpp
index 9df62850fd2eb5bc9cf442dc4675b7091cded8c1..d49a964492f483cc10b7063fe18a091511466d0a 100644
--- a/src/core/SkPath.cpp
+++ b/src/core/SkPath.cpp
@@ -2283,8 +2283,20 @@ void SkPath::validate() const {
 static int sign(SkScalar x) { return x < 0; }
 #define kValueNeverReturnedBySign   2
 
-static int CrossProductSign(const SkVector& a, const SkVector& b) {
-    return SkScalarSignAsInt(SkPoint::CrossProduct(a, b));
+static bool AlmostEqual(SkScalar compA, SkScalar compB) {
+    // The error epsilon was empirically derived; worse case round rects
+    // with a mid point outset by 2x float epsilon in tests had an error
+    // of 12.
+    const int epsilon = 16;
+    if (!SkScalarIsFinite(compA) || !SkScalarIsFinite(compB)) {
+        return false;
+    }
+    if (sk_float_abs(compA) <= FLT_EPSILON && sk_float_abs(compB) <= FLT_EPSILON) {
+        return true;
+    }
+    int aBits = SkFloatAs2sCompliment(compA);
+    int bBits = SkFloatAs2sCompliment(compB);
+    return aBits < bBits + epsilon && bBits < aBits + epsilon;
 }
 
 // only valid for a single contour
@@ -2295,6 +2307,7 @@ struct Convexicator {
     , fDirection(SkPath::kUnknown_Direction) {
         fSign = 0;
         // warnings
+        fLastPt.set(0, 0);
         fCurrPt.set(0, 0);
         fVec0.set(0, 0);
         fVec1.set(0, 0);
@@ -2320,6 +2333,7 @@ struct Convexicator {
         } else {
             SkVector vec = pt - fCurrPt;
             if (vec.fX || vec.fY) {
+                fLastPt = fCurrPt;
                 fCurrPt = pt;
                 if (++fPtCount == 2) {
                     fFirstVec = fVec1 = vec;
@@ -2353,7 +2367,11 @@ private:
         SkASSERT(vec.fX || vec.fY);
         fVec0 = fVec1;
         fVec1 = vec;
-        int sign = CrossProductSign(fVec0, fVec1);
+        SkScalar cross = SkPoint::CrossProduct(fVec0, fVec1);

[reed1, 2013/10/29 20:50:06]

I need some comment block or other way to know what we're doing now.

+        SkScalar smallest = SkTMin(fCurrPt.fX, SkTMin(fCurrPt.fY, SkTMin(fLastPt.fX, fLastPt.fY)));
+        SkScalar largest = SkTMax(fCurrPt.fX, SkTMax(fCurrPt.fY, SkTMax(fLastPt.fX, fLastPt.fY)));
+        largest = SkTMax(largest, -smallest);
+        int sign = AlmostEqual(largest, largest + cross) ? 0 : SkScalarSignAsInt(cross);
         if (0 == fSign) {
             fSign = sign;
             if (1 == sign) {
@@ -2369,6 +2387,7 @@ private:
         }
     }
 
+    SkPoint             fLastPt;
     SkPoint             fCurrPt;
     SkVector            fVec0, fVec1, fFirstVec;
     int                 fPtCount;   // non-degenerate points