add special-case for chopping at exactly half for rational-quads (2-3x faster)

git-svn-id: http://skia.googlecode.com/svn/trunk@8672 2bbb7eff-a529-9590-31e7-b0007b416f81

3 files changed, 87 insertions, 0 deletions

diff --git a/bench/PathBench.cpp b/bench/PathBench.cpp
index 658ee96f63..016bf4e0c5 100644
--- a/bench/PathBench.cpp
+++ b/bench/PathBench.cpp
@@ -864,6 +864,68 @@ private:
     typedef SkBenchmark INHERITED;
 };
 
+///////////////////////////////////////////////////////////////////////////////
+
+#include "SkGeometry.h"
+
+class RationalQuadBench_Chop5 : public SkBenchmark {
+    enum {
+        N = 100000
+    };
+    SkRationalQuad fRQ;
+public:
+    RationalQuadBench_Chop5(void* param) : INHERITED(param) {
+        fRQ.fPts[0].set(0, 0);
+        fRQ.fPts[1].set(100, 0);
+        fRQ.fPts[2].set(100, 100);
+        fRQ.fW = SkScalarCos(SK_ScalarPI/4);
+    }
+    
+private:
+    virtual const char* onGetName() SK_OVERRIDE {
+        return "ratquad-chop-0.5";
+    }
+    
+    virtual void onDraw(SkCanvas*) SK_OVERRIDE {
+        SkRationalQuad dst[2];
+        for (int i = 0; i < N; ++i) {
+            fRQ.chopAt(0.5f, dst);
+        }
+    }
+    
+    typedef SkBenchmark INHERITED;
+};
+
+class RationalQuadBench_ChopHalf : public SkBenchmark {
+    enum {
+        N = 100000
+    };
+    SkRationalQuad fRQ;
+public:
+    RationalQuadBench_ChopHalf(void* param) : INHERITED(param) {
+        fRQ.fPts[0].set(0, 0);
+        fRQ.fPts[1].set(100, 0);
+        fRQ.fPts[2].set(100, 100);
+        fRQ.fW = SkScalarCos(SK_ScalarPI/4);
+    }
+    
+private:
+    virtual const char* onGetName() SK_OVERRIDE {
+        return "ratquad-chop-half";
+    }
+    
+    virtual void onDraw(SkCanvas*) SK_OVERRIDE {
+        SkRationalQuad dst[2];
+        for (int i = 0; i < N; ++i) {
+            fRQ.chop(dst);
+        }
+    }
+    
+    typedef SkBenchmark INHERITED;
+};
+
+///////////////////////////////////////////////////////////////////////////////
+
 const SkRect ConservativelyContainsBench::kBounds = SkRect::MakeWH(SkIntToScalar(100), SkIntToScalar(100));
 const SkSize ConservativelyContainsBench::kQueryMin = SkSize::Make(SkIntToScalar(1), SkIntToScalar(1));
 const SkSize ConservativelyContainsBench::kQueryMax = SkSize::Make(SkIntToScalar(40), SkIntToScalar(40));
@@ -918,3 +980,6 @@ DEF_BENCH( return new ArbRoundRectBench(p, true); )
 DEF_BENCH( return new ConservativelyContainsBench(p, ConservativelyContainsBench::kRect_Type); )
 DEF_BENCH( return new ConservativelyContainsBench(p, ConservativelyContainsBench::kRoundRect_Type); )
 DEF_BENCH( return new ConservativelyContainsBench(p, ConservativelyContainsBench::kOval_Type); )
+
+DEF_BENCH( return new RationalQuadBench_Chop5(p) )
+DEF_BENCH( return new RationalQuadBench_ChopHalf(p) )
diff --git a/include/core/SkGeometry.h b/include/core/SkGeometry.h
index 0d1081fb2d..8bdbbe09e0 100644
--- a/include/core/SkGeometry.h
+++ b/include/core/SkGeometry.h
@@ -218,6 +218,7 @@ struct SkRationalQuad {
 
     void evalAt(SkScalar t, SkPoint* pt) const;
     void chopAt(SkScalar t, SkRationalQuad dst[2]) const;
+    void chop(SkRationalQuad dst[2]) const;
 };
 
 #endif
diff --git a/src/core/SkGeometry.cpp b/src/core/SkGeometry.cpp
index 511c34e1aa..a440d039de 100644
--- a/src/core/SkGeometry.cpp
+++ b/src/core/SkGeometry.cpp
@@ -1464,3 +1464,24 @@ void SkRationalQuad::chopAt(SkScalar t, SkRationalQuad dst[2]) const {
     dst[0].fW = tmp2[0].fZ / root;
     dst[1].fW = tmp2[2].fZ / root;
 }
+
+void SkRationalQuad::chop(SkRationalQuad dst[2]) const {
+    SkScalar scale = SkScalarInvert(SK_Scalar1 + fW);
+    SkScalar p1x = fW * fPts[1].fX;
+    SkScalar p1y = fW * fPts[1].fY;
+    SkScalar mx = (fPts[0].fX + 2 * p1x + fPts[2].fX) * scale * SK_ScalarHalf;
+    SkScalar my = (fPts[0].fY + 2 * p1y + fPts[2].fY) * scale * SK_ScalarHalf;
+
+    dst[0].fPts[0] = fPts[0];
+    dst[0].fPts[1].set((fPts[0].fX + p1x) * scale,
+                       (fPts[0].fY + p1y) * scale);
+    dst[0].fPts[2].set(mx, my);
+
+    dst[1].fPts[0].set(mx, my);
+    dst[1].fPts[1].set((p1x + fPts[2].fX) * scale,
+                       (p1y + fPts[2].fY) * scale);
+    dst[1].fPts[2] = fPts[2];
+
+    dst[0].fW = dst[1].fW = SkScalarSqrt((1 + fW) * SK_ScalarHalf);
+}
+