Add dest type hint to SkShader::ContextRec

Let SkBlitter decide which dst type is optimal (PMColor vs PM4f), and
pass that info to shaders.

R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1724503002

Review URL: https://codereview.chromium.org/1724503002

3 files changed, 18 insertions, 3 deletions

diff --git a/src/core/SkBlitter.cpp b/src/core/SkBlitter.cpp
index 804bc813d6..c7c903dc6b 100644
--- a/src/core/SkBlitter.cpp
+++ b/src/core/SkBlitter.cpp
@@ -789,6 +789,16 @@ private:
 
 #include "SkCoreBlitters.h"
 
+SkShader::ContextRec::DstType SkBlitter::PreferredShaderDest(const SkImageInfo& dstInfo) {
+#ifdef SK_FORCE_PM4f_FOR_L32_BLITS
+    return SkShader::ContextRec::kPM4f_DstType;
+#else
+    return (dstInfo.isSRGB() || dstInfo.colorType() == kRGBA_F16_SkColorType)
+            ? SkShader::ContextRec::kPM4f_DstType
+            : SkShader::ContextRec::kPMColor_DstType;
+#endif
+}
+
 SkBlitter* SkBlitter::Choose(const SkPixmap& device,
                              const SkMatrix& matrix,
                              const SkPaint& origPaint,
@@ -875,7 +885,8 @@ SkBlitter* SkBlitter::Choose(const SkPixmap& device,
      */
     SkShader::Context* shaderContext = nullptr;
     if (shader) {
-        SkShader::ContextRec rec(*paint, matrix, nullptr);
+        const SkShader::ContextRec rec(*paint, matrix, nullptr,
+                                       PreferredShaderDest(device.info()));
         size_t contextSize = shader->contextSize(rec);
         if (contextSize) {
             // Try to create the ShaderContext
@@ -961,7 +972,8 @@ class SkZeroShaderContext : public SkShader::Context {
 public:
     SkZeroShaderContext(const SkShader& shader, const SkShader::ContextRec& rec)
         // Override rec with the identity matrix, so it is guaranteed to be invertible.
-        : INHERITED(shader, SkShader::ContextRec(*rec.fPaint, SkMatrix::I(), nullptr)) {}
+        : INHERITED(shader, SkShader::ContextRec(*rec.fPaint, SkMatrix::I(), nullptr,
+                                                 rec.fPreferredDstType)) {}
 
     void shadeSpan(int x, int y, SkPMColor colors[], int count) override {
         sk_bzero(colors, count * sizeof(SkPMColor));
diff --git a/src/core/SkBlitter.h b/src/core/SkBlitter.h
index 5740a5eaed..8711f1a10f 100644
--- a/src/core/SkBlitter.h
+++ b/src/core/SkBlitter.h
@@ -137,6 +137,8 @@ public:
                                    SkTBlitterAllocator*);
     ///@}
 
+    static SkShader::ContextRec::DstType PreferredShaderDest(const SkImageInfo&);
+
 protected:
     SkAutoMalloc fBlitMemory;
 };
diff --git a/src/core/SkDraw.cpp b/src/core/SkDraw.cpp
index b041df8f7a..0c17c94884 100644
--- a/src/core/SkDraw.cpp
+++ b/src/core/SkDraw.cpp
@@ -1896,7 +1896,8 @@ void SkDraw::drawVertices(SkCanvas::VertexMode vmode, int count,
             if (textures) {
                 SkMatrix tempM;
                 if (texture_to_matrix(state, vertices, textures, &tempM)) {
-                    SkShader::ContextRec rec(p, *fMatrix, &tempM);
+                    SkShader::ContextRec rec(p, *fMatrix, &tempM,
+                                             SkBlitter::PreferredShaderDest(fDst.info()));
                     if (!blitter->resetShaderContext(rec)) {
                         continue;
                     }