Use first/second instead of min/max in 2pt conical gradient

Here's the tiny performance gain:

$python tools/calmbench/calmbench.py firstsecond --extraarg "-m conic"

firstsecond (compared to master) is likely
    4.23% faster in gradient_conicalOut_clamp_3color
    4.23% faster in gradient_conicalOutZero_clamp_3color
    4.79% faster in gradient_conical_clamp_shallow_dither
    6.04% faster in gradient_conical_clamp_3color
    6.04% faster in gradient_conicalZero_clamp_3color
    6.42% faster in gradient_conicalOut_clamp
    6.43% faster in gradient_conicalOutZero_clamp
    6.74% faster in gradient_conical_clamp
    6.98% faster in gradient_conical_clamp_shallow
    6.98% faster in gradient_conicalZero_clamp

Bug: skia:
Change-Id: Id74866908b99753ed8b16a657d3f67c9255d0043
Reviewed-on: https://skia-review.googlesource.com/76561
Commit-Queue: Yuqian Li <liyuqian@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/shaders/gradients/SkTwoPointConicalGradient.cpp b/src/shaders/gradients/SkTwoPointConicalGradient.cpp
index cd7bbb1252..8cf6409afe 100644
--- a/src/shaders/gradients/SkTwoPointConicalGradient.cpp
+++ b/src/shaders/gradients/SkTwoPointConicalGradient.cpp
@@ -210,6 +210,7 @@ void SkTwoPointConicalGradient::appendGradientStages(SkArenaAlloc* alloc, SkRast
     } else {
         isWellBehaved = SkScalarAbs(dRadius) >= dCenter;
         bool isFlipped = isWellBehaved && dRadius < 0;
+        bool isFirst = (coeffA > 0) != isFlipped;
 
         // We want the larger root, per spec:
         //   "For all values of ω where r(ω) > 0, starting with the value of ω nearest
@@ -221,8 +222,11 @@ void SkTwoPointConicalGradient::appendGradientStages(SkArenaAlloc* alloc, SkRast
         // (https://html.spec.whatwg.org/multipage/canvas.html#dom-context-2d-createradialgradient)
         //
         // ... except when the gradient is flipped.
-        p->append(isFlipped ? SkRasterPipeline::xy_to_2pt_conical_quadratic_min
-                            : SkRasterPipeline::xy_to_2pt_conical_quadratic_max, ctx);
+        //
+        // The first root (-b + sqrt(...)) / 2a is larger if a (i.e. coeffA) > 0 and the second
+        // root (-b - sqrt(...)) / 2a is larger if a < 0.
+        p->append(isFirst ? SkRasterPipeline::xy_to_2pt_conical_quadratic_first
+                          : SkRasterPipeline::xy_to_2pt_conical_quadratic_second, ctx);
     }
 
     if (!isWellBehaved) {