Extract most of the mutable state of SkShader into a separate Context object.

src/core/SkDraw.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDraw.h"
 #include "SkBlitter.h"
 #include "SkBounder.h"
@@ skipping 2337 matching lines @@
 
     src[0] = texs[state.f0];
     src[1] = texs[state.f1];
     src[2] = texs[state.f2];
     dst[0] = verts[state.f0];
     dst[1] = verts[state.f1];
     dst[2] = verts[state.f2];
     return matrix->setPolyToPoly(src, dst, 3);
 }
 
+/**
+ *  This class is NOT immutable due to the setup() method being called repeatedly after

[scroggo, 2014/04/02 20:16:53]

Now that setup is on the context, isn't this comment no longer needed?

[Dominik Grewe, 2014/04/03 12:12:59]

You're right. Thanks for spotting.

+ *  the shader has been associated with a paint. This is okay because we only ever
+ *  associate this shader with temporary paints.
+ */
 class SkTriColorShader : public SkShader {
 public:
     SkTriColorShader() {}
 
-    bool setup(const SkPoint pts[], const SkColor colors[], int, int, int);
+    virtual SkShader::Context* createContext(
+            const SkBitmap&, const SkPaint&, const SkMatrix&, void*) const SK_OVERRIDE;
+    virtual size_t contextSize() const SK_OVERRIDE;
 
-    virtual void shadeSpan(int x, int y, SkPMColor dstC[], int count) SK_OVERRIDE;
+    class TriColorShaderContext : public SkShader::Context {
+    public:
+        TriColorShaderContext(const SkTriColorShader& shader, const SkBitmap& device,
+                              const SkPaint& paint, const SkMatrix& matrix);
+        virtual ~TriColorShaderContext();
+
+        bool setup(const SkPoint pts[], const SkColor colors[], int, int, int);
+
+        virtual void shadeSpan(int x, int y, SkPMColor dstC[], int count) SK_OVERRIDE;
+
+    private:
+        SkMatrix    fDstToUnit;
+        SkPMColor   fColors[3];
+
+        typedef SkShader::Context INHERITED;
+    };
 
     SK_DEVELOPER_TO_STRING()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkTriColorShader)
 
 protected:
     SkTriColorShader(SkReadBuffer& buffer) : SkShader(buffer) {}
 
-private:
-    SkMatrix    fDstToUnit;
-    SkPMColor   fColors[3];
-
     typedef SkShader INHERITED;
 };
 
-bool SkTriColorShader::setup(const SkPoint pts[], const SkColor colors[],
-                             int index0, int index1, int index2) {
+SkShader::Context* SkTriColorShader::createContext(const SkBitmap& device, const SkPaint& paint,
+                                                   const SkMatrix& matrix, void* storage) const {
+    if (!this->validContext(device, paint, matrix)) {
+        return NULL;
+    }
+
+    return SkNEW_PLACEMENT_ARGS(storage, TriColorShaderContext, (*this, device, paint, matrix));
+}
+
+bool SkTriColorShader::TriColorShaderContext::setup(const SkPoint pts[], const SkColor colors[],
+                                                    int index0, int index1, int index2) {
 
     fColors[0] = SkPreMultiplyColor(colors[index0]);
     fColors[1] = SkPreMultiplyColor(colors[index1]);
     fColors[2] = SkPreMultiplyColor(colors[index2]);
 
     SkMatrix m, im;
     m.reset();
     m.set(0, pts[index1].fX - pts[index0].fX);
     m.set(1, pts[index2].fX - pts[index0].fX);
     m.set(2, pts[index0].fX);
@@ skipping 13 matching lines @@
     int scale = SkScalarToFixed(v) >> 8;
     if (scale < 0) {
         scale = 0;
     }
     if (scale > 255) {
         scale = 255;
     }
     return SkAlpha255To256(scale);
 }
 
-void SkTriColorShader::shadeSpan(int x, int y, SkPMColor dstC[], int count) {
+
+SkTriColorShader::TriColorShaderContext::TriColorShaderContext(
+        const SkTriColorShader& shader, const SkBitmap& device,
+        const SkPaint& paint, const SkMatrix& matrix)
+    : INHERITED(shader, device, paint, matrix) {}
+
+SkTriColorShader::TriColorShaderContext::~TriColorShaderContext() {}
+
+size_t SkTriColorShader::contextSize() const {
+    return sizeof(TriColorShaderContext);
+}
+void SkTriColorShader::TriColorShaderContext::shadeSpan(int x, int y, SkPMColor dstC[], int count) {
     SkPoint src;
 
     for (int i = 0; i < count; i++) {
         fDstToUnit.mapXY(SkIntToScalar(x), SkIntToScalar(y), &src);
         x += 1;
 
         int scale1 = ScalarTo256(src.fX);
         int scale2 = ScalarTo256(src.fY);
         int scale0 = 256 - scale1 - scale2;
         if (scale0 < 0) {
@@ skipping 86 matching lines @@
             SkShader* compose = SkNEW_ARGS(SkComposeShader,
                                            (&triShader, shader, xmode));
             p.setShader(compose)->unref();
             if (releaseMode) {
                 xmode->unref();
             }
         }
     }
 
     SkAutoBlitterChoose blitter(*fBitmap, *fMatrix, p);
-    // important that we abort early, as below we may manipulate the shader
-    // and that is only valid if the shader returned true from setContext.
-    // If it returned false, then our blitter will be the NullBlitter.
+    // Abort early if we failed to create a shader context.
     if (blitter->isNullBlitter()) {
         return;
     }
 
     // setup our state and function pointer for iterating triangles
     VertState       state(count, indices, indexCount);
     VertState::Proc vertProc = state.chooseProc(vmode);
 
     if (NULL != textures || NULL != colors) {
         SkMatrix  tempM;
         SkMatrix  savedLocalM;
         if (shader) {
             savedLocalM = shader->getLocalMatrix();
         }
 
-        // setContext has already been called and verified to return true
-        // by the constructor of SkAutoBlitterChoose
-        bool prevContextSuccess = true;
         while (vertProc(&state)) {
             if (NULL != textures) {
                 if (texture_to_matrix(state, vertices, textures, &tempM)) {
                     tempM.postConcat(savedLocalM);
                     shader->setLocalMatrix(tempM);
-                    // Need to recall setContext since we changed the local matrix.
-                    // However, we also need to balance the calls this with a
-                    // call to endContext which requires tracking the result of
-                    // the previous call to setContext.
-                    if (prevContextSuccess) {
-                        shader->endContext();
-                    }
-                    prevContextSuccess = shader->setContext(*fBitmap, p, *fMatrix);
-                    if (!prevContextSuccess) {
+                    if (!blitter->resetShaderContext(*fBitmap, p, *fMatrix)) {
                         continue;
                     }
                 }
             }
             if (NULL != colors) {
-                if (!triShader.setup(vertices, colors,
-                                     state.f0, state.f1, state.f2)) {
+                // Find the context for triShader.
+                SkTriColorShader::TriColorShaderContext* triColorShaderContext;
+
+                SkShader::Context* shaderContext = blitter->getShaderContext();
+                SkASSERT(shaderContext);
+                if (p.getShader() == &triShader) {
+                    triColorShaderContext =
+                            static_cast<SkTriColorShader::TriColorShaderContext*>(shaderContext);
+                } else {
+                    // The shader is a compose shader and triShader is its first shader.
+                    SkComposeShader::ComposeShaderContext* composeShaderContext =
+                            static_cast<SkComposeShader::ComposeShaderContext*>(shaderContext);

[scroggo, 2014/04/02 20:16:53]

This code makes a lot of assumptions about the code above it. It'd be nice if we
could add some asserts to verify that all these static casts are valid.

For example, we could add in some debug code to assert that p.getShader() == the
compose shader you created up above.

It might be nice to also assert that the compose shader's shaderA is the
triColorShader (although admittedly, there is not an API on SkComposeShader to
get shaderA - perhaps add a debug only getter?).

[Dominik Grewe, 2014/04/03 12:12:59]

Good point. I've added the asserts.

+                    SkShader::Context* shaderContextA = composeShaderContext->getShaderContextA();
+                    triColorShaderContext =
+                            static_cast<SkTriColorShader::TriColorShaderContext*>(shaderContextA);
+                }
+
+                if (!triColorShaderContext->setup(vertices, colors,
+                                                  state.f0, state.f1, state.f2)) {
                     continue;
                 }
             }
 
             SkPoint tmp[] = {
                 devVerts[state.f0], devVerts[state.f1], devVerts[state.f2]
             };
             SkScan::FillTriangle(tmp, *fRC, blitter.get());
         }
 
         // now restore the shader's original local matrix
         if (NULL != shader) {
             shader->setLocalMatrix(savedLocalM);
         }
-
-        // If the final call to setContext fails we must make it suceed so that the
-        // call to endContext in the destructor for SkAutoBlitterChoose is balanced.
-        if (!prevContextSuccess) {
-            prevContextSuccess = shader->setContext(*fBitmap, paint, SkMatrix::I());
-            SkASSERT(prevContextSuccess);
-        }
     } else {
         // no colors[] and no texture
         HairProc hairProc = ChooseHairProc(paint.isAntiAlias());
         const SkRasterClip& clip = *fRC;
         while (vertProc(&state)) {
             hairProc(devVerts[state.f0], devVerts[state.f1], clip, blitter.get());
             hairProc(devVerts[state.f1], devVerts[state.f2], clip, blitter.get());
             hairProc(devVerts[state.f2], devVerts[state.f0], clip, blitter.get());
         }
     }
@@ skipping 211 matching lines @@
         mask->fImage = SkMask::AllocImage(size);
         memset(mask->fImage, 0, mask->computeImageSize());
     }
 
     if (SkMask::kJustComputeBounds_CreateMode != mode) {
         draw_into_mask(*mask, devPath, style);
     }
 
     return true;
 }