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

7 files changed, 41 insertions, 11 deletions

diff --git a/bench/SkLinearBitmapPipelineBench.cpp b/bench/SkLinearBitmapPipelineBench.cpp
index 8a4ba2cef9..8c44fa8511 100644
--- a/bench/SkLinearBitmapPipelineBench.cpp
+++ b/bench/SkLinearBitmapPipelineBench.cpp
@@ -196,7 +196,8 @@ struct SkBitmapFPOrigShader : public CommonBitmapFPBenchmark {
         SkAutoTMalloc<SkPMColor> buffer4b(width*height);
 
         uint32_t storage[200];
-        const SkShader::ContextRec rec(fPaint, fM, nullptr);
+        const SkShader::ContextRec rec(fPaint, fM, nullptr,
+                                       SkShader::ContextRec::kPMColor_DstType);
         SkASSERT(fPaint.getShader()->contextSize(rec) <= sizeof(storage));
         SkShader::Context* ctx = fPaint.getShader()->createContext(rec, storage);
 
diff --git a/gm/SkLinearBitmapPipelineGM.cpp b/gm/SkLinearBitmapPipelineGM.cpp
index fea095239a..c8fcfc9efe 100644
--- a/gm/SkLinearBitmapPipelineGM.cpp
+++ b/gm/SkLinearBitmapPipelineGM.cpp
@@ -6,6 +6,7 @@
  */
 
 #include "gm.h"
+#include "SkBlitter.h"
 #include "SkCanvas.h"
 #include "SkColor.h"
 #include "SkImage.h"
@@ -67,7 +68,8 @@ static void draw_rect_orig(SkCanvas* canvas, const SkRect& r, SkColor c, const S
         paint.setFilterQuality(SkFilterQuality::kNone_SkFilterQuality);
     }
     paint.setShader(shader)->unref();
-    const SkShader::ContextRec rec(paint, *mat, nullptr);
+    const SkShader::ContextRec rec(paint, *mat, nullptr,
+                                   SkBlitter::PreferredShaderDest(pmsrc.info()));
     SkASSERT(paint.getShader()->contextSize(rec) <= sizeof(storage));
 
     SkShader::Context* ctx = paint.getShader()->createContext(rec, storage);
diff --git a/include/core/SkShader.h b/include/core/SkShader.h
index 8e69fafa78..72cd4a2dbe 100644
--- a/include/core/SkShader.h
+++ b/include/core/SkShader.h
@@ -10,6 +10,7 @@
 
 #include "SkBitmap.h"
 #include "SkFlattenable.h"
+#include "SkImageInfo.h"
 #include "SkMask.h"
 #include "SkMatrix.h"
 #include "SkPaint.h"
@@ -96,14 +97,22 @@ public:
      *  ContextRec acts as a parameter bundle for creating Contexts.
      */
     struct ContextRec {
-        ContextRec(const SkPaint& paint, const SkMatrix& matrix, const SkMatrix* localM)
+        enum DstType {
+            kPMColor_DstType, // clients prefer shading into PMColor dest
+            kPM4f_DstType,    // clients prefer shading into PM4f dest
+        };
+
+        ContextRec(const SkPaint& paint, const SkMatrix& matrix, const SkMatrix* localM,
+                   DstType dstType)
             : fPaint(&paint)
             , fMatrix(&matrix)
-            , fLocalMatrix(localM) {}
+            , fLocalMatrix(localM)
+            , fPreferredDstType(dstType) {}
 
-        const SkPaint*  fPaint;         // the current paint associated with the draw
-        const SkMatrix* fMatrix;        // the current matrix in the canvas
-        const SkMatrix* fLocalMatrix;   // optional local matrix
+        const SkPaint*  fPaint;            // the current paint associated with the draw
+        const SkMatrix* fMatrix;           // the current matrix in the canvas
+        const SkMatrix* fLocalMatrix;      // optional local matrix
+        const DstType   fPreferredDstType; // the "natural" client dest type
     };
 
     class Context : public ::SkNoncopyable {
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;
                     }
diff --git a/tests/SkColor4fTest.cpp b/tests/SkColor4fTest.cpp
index 97ae5e3d5b..00581cc1e6 100644
--- a/tests/SkColor4fTest.cpp
+++ b/tests/SkColor4fTest.cpp
@@ -148,7 +148,10 @@ DEF_TEST(Color4f_shader, reporter) {
     for (const auto& rec : recs) {
         uint32_t storage[200];
         paint.setShader(rec.fFact())->unref();
-        const SkShader::ContextRec contextRec(paint, SkMatrix::I(), nullptr);
+        // Encourage 4f context selection. At some point we may need
+        // to instantiate two separate contexts for optimal 4b/4f selection.
+        const SkShader::ContextRec contextRec(paint, SkMatrix::I(), nullptr,
+                                              SkShader::ContextRec::kPM4f_DstType);
         SkASSERT(paint.getShader()->contextSize(contextRec) <= sizeof(storage));
         SkShader::Context* ctx = paint.getShader()->createContext(contextRec, storage);
         REPORTER_ASSERT(reporter, ctx->supports4f() == rec.fSupports4f);