Fix highcontrastfilter on ANGLE D3D9

On NVIDIA and Intel GPUs, running the angle_d3d9_es2 config, we were
getting the wrong result from the HSL conversion. From debugging the
shader, it seems that max(x, y) is not necessarily equal to either x
or y. Tried several ways to fix it, but the only reasonably one that
worked was to alter our conditionals. This is slower, but the filter
is already doing a large amount of work.

Bug: skia:7273
Change-Id: I9724285a0d5834cf98189df9efbdc02b5e1de4a7
Reviewed-on: https://skia-review.googlesource.com/68213
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/src/effects/SkHighContrastFilter.cpp b/src/effects/SkHighContrastFilter.cpp
index b1900f0567..9df04c110b 100644
--- a/src/effects/SkHighContrastFilter.cpp
+++ b/src/effects/SkHighContrastFilter.cpp
@@ -298,10 +298,13 @@ void GLHighContrastFilterEffect::emitCode(EmitArgs& args) {
         fragBuilder->codeAppendf("  s = l > 0.5 ?");
         fragBuilder->codeAppendf("      d / (2 - fmax - fmin) :");
         fragBuilder->codeAppendf("      d / (fmax + fmin);");
-        fragBuilder->codeAppendf("  if (fmax == color.r) {");
+        // We'd like to just write "if (color.r == fmax) { ... }". On many GPUs, running the
+        // angle_d3d9_es2 config, that failed. It seems that max(x, y) is not necessarily equal
+        // to either x or y. Tried several ways to fix it, but this was the only reasonable fix.
+        fragBuilder->codeAppendf("  if (color.r >= color.g && color.r >= color.b) {");
         fragBuilder->codeAppendf("    h = (color.g - color.b) / d + ");
         fragBuilder->codeAppendf("        (color.g < color.b ? 6 : 0);");
-        fragBuilder->codeAppendf("  } else if (fmax == color.g) {");
+        fragBuilder->codeAppendf("  } else if (color.g >= color.b) {");
         fragBuilder->codeAppendf("    h = (color.b - color.r) / d + 2;");
         fragBuilder->codeAppendf("  } else {");
         fragBuilder->codeAppendf("    h = (color.r - color.g) / d + 4;");