1 files changed, 26 insertions, 0 deletions
diff --git a/src/jumper/SkJumper_stages.cpp b/src/jumper/SkJumper_stages.cpp
index 61ef73a46d..83c806026f 100644
--- a/src/jumper/SkJumper_stages.cpp
+++ b/src/jumper/SkJumper_stages.cpp
@@ -945,6 +945,32 @@ STAGE(linear_gradient_2stops) {
     a = mad(t, c->f[3], c->b[3]);
 }
 
+STAGE(xy_to_polar_unit) {
+    F X = r,
+      Y = g;
+    F xabs = abs_(X),
+      yabs = abs_(Y);
+
+    F slope = min(xabs, yabs)/max(xabs, yabs);
+    F s = slope * slope;
+
+    // Use a 7th degree polynomial to approximate atan.
+    // This was generated using sollya.gforge.inria.fr.
+    // A float optimized polynomial was generated using the following command.
+    // P1 = fpminimax((1/(2*Pi))*atan(x),[|1,3,5,7|],[|24...|],[2^(-40),1],relative);
+    F phi = slope
+             * (0.15912117063999176025390625f     + s
+             * (-5.185396969318389892578125e-2f   + s
+             * (2.476101927459239959716796875e-2f + s
+             * (-7.0547382347285747528076171875e-3f))));
+
+    phi = if_then_else(xabs < yabs, 1.0f/4.0f - phi, phi);
+    phi = if_then_else(X < 0.0f   , 1.0f/2.0f - phi, phi);
+    phi = if_then_else(Y < 0.0f   , 1.0f - phi     , phi);
+    phi = if_then_else(phi != phi , 0              , phi);  // Check for NaN.
+    r = phi;
+}
+
 STAGE(save_xy) {
     auto c = (SkJumper_SamplerCtx*)ctx;