Use a simpler method for calculating atan

Change-Id: I675851350c02c85f3f212c214766b3e8a6761dc9
Reviewed-on: https://skia-review.googlesource.com/13402
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Herb Derby <herb@google.com>

diff --git a/src/effects/gradients/SkSweepGradient.cpp b/src/effects/gradients/SkSweepGradient.cpp
index 79013b3..06b9f21 100644 (file)
--- a/src/effects/gradients/SkSweepGradient.cpp
+++ b/src/effects/gradients/SkSweepGradient.cpp
@@ -7,6 +7,8 @@
 
 #include "SkSweepGradient.h"
 
+#include <algorithm>
+
 static SkMatrix translate(SkScalar dx, SkScalar dy) {
     SkMatrix matrix;
     matrix.setTranslate(dx, dy);
@@ -56,6 +58,7 @@ SkSweepGradient::SweepGradientContext::SweepGradientContext(
     : INHERITED(shader, rec) {}
 
 //  returns angle in a circle [0..2PI) -> [0..255]
+#ifdef SK_LEGACY_SWEEP_GRADIENT
 static unsigned SkATan2_255(float y, float x) {
     //    static const float g255Over2PI = 255 / (2 * SK_ScalarPI);
     static const float g255Over2PI = 40.584510488433314f;
@@ -74,6 +77,26 @@ static unsigned SkATan2_255(float y, float x) {
     SkASSERT(ir >= 0 && ir <= 255);
     return ir;
 }
+#else
+static unsigned SkATan2_255(float y, float x) {
+    if (y == 0 && x == 0) return 0;
+    float yabs = sk_float_abs(y),
+        xabs = sk_float_abs(x);
+    float little, big;
+    std::tie(little, big) = std::minmax(yabs, xabs);
+    float a = little/big;
+    float s = a * a;
+    float r = a*(40.57589784014689f
+                 + s*(-13.222755844396332f + s*(6.314046289038564f - s*1.7989502668982151f)));
+    r = xabs < yabs ? 255/4.0f - r : r;
+    r = x < 0.0f    ? 255/2.0f - r : r;
+    r = y < 0.0f    ? 255      - r : r;
+
+    int ir = (int)r;
+    SkASSERT(ir >= 0 && ir <= 255);
+    return ir;
+}
+#endif
 
 void SkSweepGradient::SweepGradientContext::shadeSpan(int x, int y, SkPMColor* SK_RESTRICT dstC,
                                                       int count) {