adding new GM to demostrate new shadows

src/core/SkShadowShader.cpp

Index: src/core/SkShadowShader.cpp
diff --git a/src/core/SkShadowShader.cpp b/src/core/SkShadowShader.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..e9ff4fd950b60a34322dc6eee26c599493e3564a
--- /dev/null
+++ b/src/core/SkShadowShader.cpp
@@ -0,0 +1,558 @@
+/*

[robertphillips, 2016/07/26 16:15:05]

2016

[vjiaoblack, 2016/07/27 15:26:27]

Done.

+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkBitmapProcShader.h"
+#include "SkBitmapProcState.h"
+#include "SkColor.h"
+#include "SkEmptyShader.h"
+#include "SkErrorInternals.h"
+#include "SkShadowShader.h"
+#include "SkMathPriv.h"

[robertphillips, 2016/07/26 16:15:05]

Do we need SkNormalSource.h ?

[vjiaoblack, 2016/07/27 15:26:27]

Done.

+#include "SkNormalSource.h"
+#include "SkPoint3.h"
+#include "SkReadBuffer.h"
+#include "SkWriteBuffer.h"
+
+////////////////////////////////////////////////////////////////////////////
+
+/** \class SkShadowShaderImpl
+    This subclass of shader applies shadowing
+*/
+class SkShadowShaderImpl : public SkShader {
+public:
+    /** Create a new shadowing shader that shadows
+        @param to do        to do
+    */
+    SkShadowShaderImpl(sk_sp<SkShader> povDepthShader,
+                       sk_sp<SkShader> diffuseShader,
+                       sk_sp<SkLights> lights)
+            : povDepthShader(std::move(povDepthShader))
+            , diffuseShader(std::move(diffuseShader))
+            , fLights(std::move(lights)) { }
+
+    bool isOpaque() const override;
+
+#if SK_SUPPORT_GPU
+    sk_sp<GrFragmentProcessor> asFragmentProcessor(GrContext*,
+                                                   const SkMatrix& viewM,
+                                                   const SkMatrix* localMatrix,
+                                                   SkFilterQuality,
+                                                   SkSourceGammaTreatment) const override;
+#endif
+
+    class ShadowShaderContext : public SkShader::Context {
+    public:
+        // The context takes ownership of the states. It will call their destructors
+        // but will NOT free the memory.
+        ShadowShaderContext(const SkShadowShaderImpl&, const ContextRec&,
+                            SkShader::Context* povDepthContext,
+                            SkShader::Context* diffuseContext,
+                            void* heapAllocated);
+
+        ~ShadowShaderContext() override;
+
+        void shadeSpan(int x, int y, SkPMColor[], int count) override;
+
+        uint32_t getFlags() const override { return fFlags; }
+
+    private:
+        SkShader::Context*        fDiffuseContext1;
+        SkShader::Context*        fDiffuseContext2;
+        uint32_t                  fFlags;
+
+        void* fHeapAllocated;
+
+        typedef SkShader::Context INHERITED;
+    };
+
+    SK_TO_STRING_OVERRIDE()

[robertphillips, 2016/07/26 16:15:05]

Tab this over ?

[vjiaoblack, 2016/07/27 15:26:27]

Done.

+SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkShadowShaderImpl)
+
+protected:
+    void flatten(SkWriteBuffer&) const override;
+    size_t onContextSize(const ContextRec&) const override;
+    Context* onCreateContext(const ContextRec&, void*) const override;
+
+private:
+    sk_sp<SkShader> povDepthShader;
+    sk_sp<SkShader> diffuseShader;
+    sk_sp<SkLights> fLights;
+
+    friend class SkShadowShader;
+
+    typedef SkShader INHERITED;
+};
+
+////////////////////////////////////////////////////////////////////////////
+
+#if SK_SUPPORT_GPU
+
+#include "GrCoordTransform.h"
+#include "GrFragmentProcessor.h"
+#include "GrInvariantOutput.h"
+#include "GrTextureAccess.h"
+#include "glsl/GrGLSLFragmentProcessor.h"
+#include "glsl/GrGLSLFragmentShaderBuilder.h"
+#include "glsl/GrGLSLProgramDataManager.h"
+#include "glsl/GrGLSLUniformHandler.h"
+#include "SkGr.h"
+#include "SkGrPriv.h"
+#include "SkSpecialImage.h"
+#include "SkImage_Base.h"
+#include "SkImageInfo.h"
+#include "GrContext.h"
+#include "GrContextOptions.h"
+
+class ShadowFP : public GrFragmentProcessor {
+public:
+    ShadowFP(sk_sp<GrFragmentProcessor> povDepth,
+             sk_sp<GrFragmentProcessor> diffuse,
+             sk_sp<SkLights> lights) {
+
+        // fuse all ambient lights into a single one
+        // TODO do we support 4 directional lights, or just 4 lights?

[robertphillips, 2016/07/26 16:15:05]

Probably any number of ambient + 4 "real" ones.

Maybe replace 4 everywhere with kMaxNumNonAmbientLights ?

[vjiaoblack, 2016/07/27 15:26:27]

Done.

+        fAmbientColor.set(0.0f, 0.0f, 0.0f);
+

[robertphillips, 2016/07/26 16:15:05]

This doesn't seem quite right. fNumLights needs to factor into account that all
the ambient lights are collapsed together.

[vjiaoblack, 2016/07/27 15:26:28]

I'll change fNumLights to fNumDirLights.

+        fNumLights = lights->numLights(); // refers to directional lights.

[robertphillips, 2016/07/26 16:15:05]

You probably can't have this assert but keep a separate counter for the number
of non-ambient lights encountered and then just drop the extras on the floor
(asserting if there are any extras)

[vjiaoblack, 2016/07/27 15:26:27]

Done.

+        SkASSERT(fNumLights <= 4 && fNumLights >= 0);
+        for (int i = 0; i < lights->numLights(); ++i) {
+            if (SkLights::Light::kAmbient_LightType == lights->light(i).type()) {
+                fAmbientColor += lights->light(i).color();
+            } else {
+                fLightColor[i] = lights->light(i).color();
+                fLightDir[i] = lights->light(i).dir();
+                fDepthMapAccess[i].reset(((SkImage_Base*)lights->light(i).getShadowMap().get())->

[jvanverth1, 2016/07/26 15:01:25]

You might want to break this line up -- it's a little confusing as to what's
going on here.

[vjiaoblack, 2016/07/27 15:26:28]

Done.

+                        asTextureRef(GrContext::Create(kOpenGL_GrBackend, (GrBackendContext) nullptr, GrContextOptions()),

[jvanverth1, 2016/07/26 15:01:24]

Lines too long (must be <= 100 chars)

[vjiaoblack, 2016/07/27 15:26:28]

Done.

+                                     GrTextureParams::ClampNoFilter(), SkSourceGammaTreatment::kIgnore));
+                this->addTextureAccess(&fDepthMapAccess[i]);
+//                        // TODO: Call unref on the GrTexture somewhere.

[jvanverth1, 2016/07/26 15:01:25]

Is this still needed? Otherwise you have a memory leak.

[vjiaoblack, 2016/07/27 15:26:28]

Hm. I'm trying to fix this (and it seems like a pretty bad memory leak), but it
might take a while - I'll continue on to fix the other comments and come back to
this.

edit: fixed! thanks for the tips

+            }
+        }
+
+        this->registerChildProcessor(std::move(povDepth));
+        this->registerChildProcessor(std::move(diffuse));
+        this->initClassID<ShadowFP>();
+    }
+
+    class GLSLShadowFP : public GrGLSLFragmentProcessor {
+    public:
+        GLSLShadowFP() { }
+
+        void emitCode(EmitArgs& args) override {
+
+            GrGLSLFragmentBuilder* fragBuilder = args.fFragBuilder;
+            GrGLSLUniformHandler* uniformHandler = args.fUniformHandler;
+
+            // add uniforms
+            int32_t numLights = args.fFp.cast<ShadowFP>().fNumLights;
+
+            const char* lightDirUniName[4] = {nullptr};
+            const char* lightColorUniName[4] = {nullptr};
+
+            for (int i = 0; i < numLights; i++) {
+                lightDirUniName[i] = nullptr;
+                fLightDirUni[i] = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                           kVec3f_GrSLType, kDefault_GrSLPrecision,

[jvanverth1, 2016/07/26 15:01:25]

Line up indents next to parens.

[vjiaoblack, 2016/07/27 15:26:28]

Done.

+                                                           "LightDir" + (i+1), &lightDirUniName[i]);
+
+                lightColorUniName[i] = nullptr;
+                fLightColorUni[i] = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                             kVec3f_GrSLType, kDefault_GrSLPrecision,

[jvanverth1, 2016/07/26 15:01:24]

Lines too long.

[vjiaoblack, 2016/07/27 15:26:28]

Done.

+                                                             "LightColor" + (i+1), &lightColorUniName[i]);
+            }
+
+            SkString povDepth("povDepth");
+            this->emitChild(0, nullptr, &povDepth, args);
+
+            SkString diffuseColor("inDiffuseColor");
+            this->emitChild(1, nullptr, &diffuseColor, args);
+
+            SkString depthMaps[4];
+
+            for (int i = 0; i < numLights; i++) {
+                const char* povCoord = "povCoord" + i;
+
+                fragBuilder->codeAppendf("vec2 %s = vMatrixCoord_0_1_Stage0 + (vec2(%s) * povDepth.b * 255 / 400);",

[jvanverth1, 2016/07/26 15:01:25]

Line too long. Also, it's not clear to me what this math is doing. Why divide by
400?

[vjiaoblack, 2016/07/27 15:26:28]

Done.

+                                         povCoord, lightDirUniName[i]);
+
+                fragBuilder->appendTextureLookup(&depthMaps[i], args.fTexSamplers[i],
+                                                 povCoord,
+                                                 kVec2f_GrSLType);
+            }
+
+            const char* ambientColorUniName = nullptr;
+            fAmbientColorUni = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                          kVec3f_GrSLType, kDefault_GrSLPrecision,
+                                                          "AmbientColor", &ambientColorUniName);
+
+            fragBuilder->codeAppendf("vec4 resultDiffuseColor = %s;", diffuseColor.c_str());
+
+            // all the normal vectors point straight up
+            SkString totalLightColor("totalLightColor");
+            fragBuilder->codeAppendf("vec3 %s = vec3(0,0,0);", totalLightColor.c_str());
+
+            for (int i = 0; i < numLights; i++) {
+                fragBuilder->codeAppendf("if (%s.b >= %s.b) {",
+                                         povDepth.c_str(), depthMaps[i].c_str());
+                fragBuilder->codeAppendf("%s += dot(vec3(0,0,1), %s) * %s;", totalLightColor.c_str(),

[jvanverth1, 2016/07/26 15:01:24]

Line too long.

[vjiaoblack, 2016/07/27 15:26:28]

Done.

+                                         lightDirUniName[i], lightColorUniName[i]);
+                fragBuilder->codeAppendf("}");
+            }
+
+
+            fragBuilder->codeAppendf("%s += %s;", totalLightColor.c_str(), ambientColorUniName);
+            fragBuilder->codeAppendf("resultDiffuseColor *= vec4(%s, 1);", totalLightColor.c_str());
+
+            fragBuilder->codeAppendf("%s = resultDiffuseColor;", args.fOutputColor);
+        }
+
+        static void GenKey(const GrProcessor& proc, const GrGLSLCaps&,
+                           GrProcessorKeyBuilder* b) {
+            const ShadowFP& shadowFP = proc.cast<ShadowFP>();
+            b->add32(shadowFP.fNumLights);
+        }
+
+    protected:
+        void onSetData(const GrGLSLProgramDataManager& pdman, const GrProcessor& proc) override {
+            const ShadowFP &shadowFP = proc.cast<ShadowFP>();
+

[robertphillips, 2016/07/26 16:15:05]

We set fNumLights in the ctor. Is it correct to reset it here ?

[vjiaoblack, 2016/07/27 15:26:28]

We set fNumLights in the ShadowFP constructor. We are currently in the
GLSLShadowFP, which isn't done with the same constructor.

We need to pass in fNumLights in from the ShadowFP.

+            fNumLights = shadowFP.numLights();
+
+            SkASSERT(fNumLights <= 4);
+
+            for (int i = 0; i < fNumLights; i++) {

[robertphillips, 2016/07/26 16:15:05]

Do we need the "1" suffixes?

[vjiaoblack, 2016/07/27 15:26:28]

Done.

+                const SkVector3 &lightDir1 = shadowFP.lightDir(i);
+                if (lightDir1 != fLightDir[i]) {
+                    pdman.set3fv(fLightDirUni[i], 1, &lightDir1.fX);
+                    fLightDir[i] = lightDir1;
+                }
+                const SkColor3f &lightColor1 = shadowFP.lightColor(i);
+                if (lightColor1 != fLightColor[i]) {
+                    pdman.set3fv(fLightColorUni[i], 1, &lightColor1.fX);
+                    fLightColor[i] = lightColor1;
+                }
+            }
+
+            const SkColor3f& ambientColor = shadowFP.ambientColor();
+            if (ambientColor != fAmbientColor) {
+                pdman.set3fv(fAmbientColorUni, 1, &ambientColor.fX);
+                fAmbientColor = ambientColor;
+            }
+        }
+
+    private:
+        SkVector3 fLightDir[4];
+        GrGLSLProgramDataManager::UniformHandle fLightDirUni[4];
+        SkColor3f fLightColor[4];
+        GrGLSLProgramDataManager::UniformHandle fLightColorUni[4];
+
+        SkColor3f fAmbientColor;
+        GrGLSLProgramDataManager::UniformHandle fAmbientColorUni;
+

[robertphillips, 2016/07/26 16:15:05]

can this just be an int? 

[vjiaoblack, 2016/07/27 15:26:27]

Done.

+        int32_t fNumLights;
+    };
+
+    void onGetGLSLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override {
+        GLSLShadowFP::GenKey(*this, caps, b);
+    }
+
+    const char* name() const override { return "shadowFP"; }
+
+    void onComputeInvariantOutput(GrInvariantOutput* inout) const override {
+        inout->mulByUnknownFourComponents();
+    }
+    int32_t numLights() const { return fNumLights; }
+    const SkColor3f& ambientColor() const { return fAmbientColor; }
+    const SkVector3& lightDir(int i) const {
+        SkASSERT(i < fNumLights);
+        return fLightDir[i];
+    }
+    const SkVector3& lightColor(int i) const {
+        SkASSERT(i < fNumLights);
+        return fLightColor[i];
+    }
+
+private:
+    GrGLSLFragmentProcessor* onCreateGLSLInstance() const override { return new GLSLShadowFP; }
+
+    bool onIsEqual(const GrFragmentProcessor& proc) const override {
+        const ShadowFP& shadowFP = proc.cast<ShadowFP>();

[robertphillips, 2016/07/26 16:15:05]

Shouldn't we check if the number of lights is the same first ?
Since we're comparing possible empty slots at the end, have we guaranteed that
all the slots are initialized?

[vjiaoblack, 2016/07/27 15:26:27]

Done.

+        return fLightDir[0] == shadowFP.fLightDir[0] &&
+               fLightColor[0] == shadowFP.fLightColor[0] &&
+               fLightDir[1] == shadowFP.fLightDir[1] &&
+               fLightColor[1] == shadowFP.fLightColor[1] &&
+               fLightDir[2] == shadowFP.fLightDir[2] &&
+               fLightColor[2] == shadowFP.fLightColor[2] &&
+               fLightDir[3] == shadowFP.fLightDir[3] &&
+               fLightColor[3] == shadowFP.fLightColor[3] &&
+               fAmbientColor == shadowFP.fAmbientColor;
+    }
+

[robertphillips, 2016/07/26 16:15:05]

line this guy up with the rest ?

[vjiaoblack, 2016/07/27 15:26:27]

Done.

+    int          fNumLights;
+
+    SkVector3        fLightDir[4];
+    SkColor3f        fLightColor[4];
+    GrTextureAccess  fDepthMapAccess[4];
+
+    SkColor3f        fAmbientColor;
+};
+
+////////////////////////////////////////////////////////////////////////////
+
+sk_sp<GrFragmentProcessor> SkShadowShaderImpl::asFragmentProcessor(
+        GrContext* context,
+        const SkMatrix& viewM,
+        const SkMatrix* localMatrix,
+        SkFilterQuality filterQuality,
+        SkSourceGammaTreatment gammaTreatment) const {
+

[robertphillips, 2016/07/26 16:15:05]

I'm not in love with the D_FP* names

[vjiaoblack, 2016/07/27 15:26:28]

Done.

+    sk_sp<GrFragmentProcessor> D_FP1 = povDepthShader->asFragmentProcessor(context, viewM,
+                                                                    localMatrix, filterQuality,
+                                                                    gammaTreatment);
+
+    sk_sp<GrFragmentProcessor> D_FP2 = diffuseShader->asFragmentProcessor(context, viewM,
+                                                                            localMatrix, filterQuality,

[jvanverth1, 2016/07/26 15:01:25]

Line too long.

[vjiaoblack, 2016/07/27 15:26:27]

Done.

+                                                                            gammaTreatment);
+
+    sk_sp<GrFragmentProcessor> shadowfp = sk_make_sp<ShadowFP>(D_FP1, D_FP2, fLights);
+    return shadowfp;
+}
+
+
+#endif
+
+////////////////////////////////////////////////////////////////////////////
+
+bool SkShadowShaderImpl::isOpaque() const {
+    return povDepthShader->isOpaque() || diffuseShader->isOpaque();
+}
+
+SkShadowShaderImpl::ShadowShaderContext::ShadowShaderContext(
+        const SkShadowShaderImpl& shader, const ContextRec& rec,
+        SkShader::Context* povDepthContext,
+        SkShader::Context* diffuseContext,
+        void* heapAllocated)
+        : INHERITED(shader, rec)
+        , fDiffuseContext1(povDepthContext)
+        , fDiffuseContext2(diffuseContext)
+        , fHeapAllocated(heapAllocated) {
+    bool isOpaque = shader.isOpaque();
+
+    // update fFlags
+    uint32_t flags = 0;
+    if (isOpaque && (255 == this->getPaintAlpha())) {
+        flags |= kOpaqueAlpha_Flag;
+    }
+
+    fFlags = flags;
+}
+
+SkShadowShaderImpl::ShadowShaderContext::~ShadowShaderContext() {
+    // The dependencies have been created outside of the context on memory that was allocated by
+    // the onCreateContext() method. Call the destructors and free the memory.
+    fDiffuseContext1->~Context();
+    fDiffuseContext2->~Context();
+
+    sk_free(fHeapAllocated);
+}
+
+static inline SkPMColor convert(SkColor3f color, U8CPU a) {
+    if (color.fX <= 0.0f) {
+        color.fX = 0.0f;
+    } else if (color.fX >= 255.0f) {
+        color.fX = 255.0f;
+    }
+
+    if (color.fY <= 0.0f) {
+        color.fY = 0.0f;
+    } else if (color.fY >= 255.0f) {
+        color.fY = 255.0f;
+    }
+
+    if (color.fZ <= 0.0f) {
+        color.fZ = 0.0f;
+    } else if (color.fZ >= 255.0f) {
+        color.fZ = 255.0f;
+    }
+//    printf();
+    return SkPreMultiplyARGB(a, (int) color.fX,  (int) color.fY, (int) color.fZ);
+}
+
+// larger is better (fewer times we have to loop), but we shouldn't
+// take up too much stack-space (each one here costs 16 bytes)
+#define BUFFER_MAX 16
+void SkShadowShaderImpl::ShadowShaderContext::shadeSpan(int x, int y,
+                                                        SkPMColor result[], int count) {
+    const SkShadowShaderImpl& lightShader = static_cast<const SkShadowShaderImpl&>(fShader);
+
+    SkPMColor diffuse[BUFFER_MAX];
+    SkPoint3 normals[BUFFER_MAX];
+
+    do {
+        int n = SkTMin(count, BUFFER_MAX);
+
+        fDiffuseContext1->shadeSpan(x, y, diffuse, n);
+        fDiffuseContext2->shadeSpan(x, y, diffuse, n);
+
+        for (int i = 0; i < n; ++i) {
+
+            SkColor diffColor = SkUnPreMultiply::PMColorToColor(diffuse[i]);
+
+            SkColor3f accum = SkColor3f::Make(0.0f, 0.0f, 0.0f);
+            // This is all done in linear unpremul color space (each component 0..255.0f though)
+            for (int l = 0; l < lightShader.fLights->numLights(); ++l) {
+                const SkLights::Light& light = lightShader.fLights->light(l);
+
+                if (SkLights::Light::kAmbient_LightType == light.type()) {
+                    accum += light.color().makeScale(255.0f);
+                } else {
+                    SkScalar NdotL = normals[i].dot(light.dir());
+                    if (NdotL < 0.0f) {
+                        NdotL = 0.0f;
+                    }
+
+                    NdotL = 1.0f;
+
+                    accum.fX += light.color().fX * SkColorGetR(diffColor) * NdotL;
+                    accum.fY += light.color().fY * SkColorGetG(diffColor) * NdotL;
+                    accum.fZ += light.color().fZ * SkColorGetB(diffColor) * NdotL;
+                }
+            }
+
+            result[i] = convert(accum, SkColorGetA(diffColor));
+        }
+
+        result += n;
+        x += n;
+        count -= n;
+    } while (count > 0);
+}
+
+////////////////////////////////////////////////////////////////////////////
+
+#ifndef SK_IGNORE_TO_STRING
+void SkShadowShaderImpl::toString(SkString* str) const {
+    str->appendf("ShadowShader: ()");
+}
+#endif
+
+sk_sp<SkFlattenable> SkShadowShaderImpl::CreateProc(SkReadBuffer& buf) {
+
+    // Discarding SkShader flattenable params
+    bool hasLocalMatrix = buf.readBool();
+    SkAssertResult(!hasLocalMatrix);
+
+    int numLights = buf.readInt();
+
+    SkLights::Builder builder;
+
+    for (int l = 0; l < numLights; ++l) {
+        bool isAmbient = buf.readBool();
+
+        SkColor3f color;
+        if (!buf.readScalarArray(&color.fX, 3)) {
+            return nullptr;
+        }
+
+        if (isAmbient) {
+            builder.add(SkLights::Light(color));
+        } else {
+            SkVector3 dir;
+            if (!buf.readScalarArray(&dir.fX, 3)) {
+                return nullptr;
+            }
+            builder.add(SkLights::Light(color, dir));
+        }
+    }
+
+    sk_sp<SkLights> lights(builder.finish());
+
+    sk_sp<SkShader> povDepthShader(buf.readFlattenable<SkShader>());
+    sk_sp<SkShader> diffuseShader(buf.readFlattenable<SkShader>());
+
+    return sk_make_sp<SkShadowShaderImpl>(std::move(povDepthShader),
+                                          std::move(diffuseShader),
+                                          std::move(lights));
+}
+
+void SkShadowShaderImpl::flatten(SkWriteBuffer& buf) const {
+    this->INHERITED::flatten(buf);
+
+    buf.writeInt(fLights->numLights());
+    for (int l = 0; l < fLights->numLights(); ++l) {
+        const SkLights::Light& light = fLights->light(l);
+
+        bool isAmbient = SkLights::Light::kAmbient_LightType == light.type();
+
+        buf.writeBool(isAmbient);
+        buf.writeScalarArray(&light.color().fX, 3);
+        if (!isAmbient) {
+            buf.writeScalarArray(&light.dir().fX, 3);
+        }
+    }
+
+    buf.writeFlattenable(povDepthShader.get());
+    buf.writeFlattenable(diffuseShader.get());
+}
+
+size_t SkShadowShaderImpl::onContextSize(const ContextRec& rec) const {
+    return sizeof(ShadowShaderContext);
+}
+
+SkShader::Context* SkShadowShaderImpl::onCreateContext(const ContextRec& rec,
+                                                       void* storage) const {
+    size_t heapRequired = povDepthShader->contextSize(rec) +
+                           diffuseShader->contextSize(rec);
+
+    void* heapAllocated = sk_malloc_throw(heapRequired);
+
+    void* povDepthContextStorage = heapAllocated;
+
+    SkShader::Context* povDepthContext = povDepthShader->createContext(rec, povDepthContextStorage);
+    if (!povDepthContext) {
+        sk_free(heapAllocated);
+        return nullptr;
+    }
+
+    void* diffuseContextStorage = (char*)heapAllocated + povDepthShader->contextSize(rec);
+
+    SkShader::Context* diffuseContext2 = diffuseShader->createContext(rec, diffuseContextStorage);
+    if (!diffuseContext2) {
+        sk_free(heapAllocated);
+        return nullptr;
+    }
+
+
+    return new (storage) ShadowShaderContext(*this, rec, povDepthContext, diffuseContext2,
+                                             heapAllocated);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+sk_sp<SkShader> SkShadowShader::Make(sk_sp<SkShader> povDepthShader,
+                                     sk_sp<SkShader> diffuseShader,
+                                     sk_sp<SkLights> lights) {
+    if (!povDepthShader || !diffuseShader) {
+        // TODO: Use paint's color in absence of a diffuseShader
+        // TODO: Use a default implementation of normalSource instead
+        return nullptr;
+    }
+
+    SkASSERT(lights->numLights() <= 4);
+
+    return sk_make_sp<SkShadowShaderImpl>(std::move(povDepthShader),
+                                          std::move(diffuseShader),
+                                          std::move(lights));
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkShadowShader)
+    SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkShadowShaderImpl)
+SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END
+
+///////////////////////////////////////////////////////////////////////////////