Update 2pt conical gradient in raster pipeline

The updated algorithm matches our new GPU algorithm
(https://skia.org/dev/design/conical) and it brings
about 7%-26% speedup. In the next CL, I'll simplify
the GPU code by reusing the CPU code in this CL.

    7.20% faster in gradient_conical_clamp_hicolor
    8.94% faster in gradient_conicalZero_clamp_hicolor
   10.00% faster in gradient_conicalOut_clamp_hicolor
   11.72% faster in gradient_conicalOutZero_clamp_hicolor
   13.62% faster in gradient_conical_clamp_3color
   16.52% faster in gradient_conicalZero_clamp_3color
   17.48% faster in gradient_conical_clamp
   17.70% faster in gradient_conical_clamp_shallow
   20.60% faster in gradient_conicalOut_clamp_3color
   20.98% faster in gradient_conicalOutZero_clamp_3color
   21.79% faster in gradient_conicalZero_clamp
   22.48% faster in gradient_conicalOut_clamp
   26.13% faster in gradient_conicalOutZero_clamp

Bug: skia:
Change-Id: Ia159495e1c77658cb28e48c9edf84938464e501c
Reviewed-on: https://skia-review.googlesource.com/90262
Commit-Queue: Yuqian Li <liyuqian@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>

1 files changed, 29 insertions, 2 deletions

diff --git a/src/shaders/gradients/SkTwoPointConicalGradient.h b/src/shaders/gradients/SkTwoPointConicalGradient.h
index 96039e4771..623e69f95a 100644
--- a/src/shaders/gradients/SkTwoPointConicalGradient.h
+++ b/src/shaders/gradients/SkTwoPointConicalGradient.h
@@ -13,6 +13,30 @@
 
 class SkTwoPointConicalGradient final : public SkGradientShaderBase {
 public:
+    // See https://skia.org/dev/design/conical for what focal data means and how our shader works.
+    // We make it public so the GPU shader can also use it.
+    struct FocalData {
+        SkScalar    fR1;        // r1 after mapping focal point to (0, 0)
+        SkScalar    fFocalX;    // f
+        bool        fIsSwapped; // whether we swapped r0, r1
+
+        // The input r0, r1 are the radii when we map centers to {(0, 0), (1, 0)}.
+        // We'll post concat matrix with our transformation matrix that maps focal point to (0, 0).
+        void set(SkScalar r0, SkScalar r1, SkMatrix& matrix);
+
+        // Whether the focal point (0, 0) is on the end circle with center (1, 0) and radius r1. If
+        // this is true, it's as if an aircraft is flying at Mach 1 and all circles (soundwaves)
+        // will go through the focal point (aircraft). In our previous implementations, this was
+        // known as the edge case where the inside circle touches the outside circle (on the focal
+        // point). If we were to solve for t bruteforcely using a quadratic equation, this case
+        // implies that the quadratic equation degenerates to a linear equation.
+        bool isFocalOnCircle() const { return SkScalarNearlyZero(1 - fR1); }
+
+        bool isSwapped() const { return fIsSwapped; }
+        bool isWellBehaved() const { return !this->isFocalOnCircle() && fR1 > 1; }
+        bool isNativelyFocal() const { return SkScalarNearlyZero(fFocalX); }
+    };
+
     static sk_sp<SkShader> Create(const SkPoint& start, SkScalar startRadius,
                                   const SkPoint& end, SkScalar endRadius,
                                   const Descriptor&);
@@ -45,12 +69,13 @@ protected:
 private:
     enum class Type {
         kRadial,
-        kTwoPoint,
+        kStrip,
+        kFocal
     };
 
     SkTwoPointConicalGradient(const SkPoint& c0, SkScalar r0,
                               const SkPoint& c1, SkScalar r1,
-                              const Descriptor&, Type, const SkMatrix&);
+                              const Descriptor&, Type, const SkMatrix&, const FocalData&);
 
     SkPoint  fCenter1;
     SkPoint  fCenter2;
@@ -58,6 +83,8 @@ private:
     SkScalar fRadius2;
     Type     fType;
 
+    FocalData fFocalData;
+
     friend class SkGradientShader;
     typedef SkGradientShaderBase INHERITED;
 };