adding new GM to demostrate new shadows

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2118553002

Review-Url: https://codereview.chromium.org/2118553002

2 files changed, 751 insertions, 0 deletions

diff --git a/src/core/SkShadowShader.cpp b/src/core/SkShadowShader.cpp
new file mode 100644
index 0000000000..c5a99e9e91
--- /dev/null
+++ b/src/core/SkShadowShader.cpp
@@ -0,0 +1,719 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+#include "SkLights.h"
+#include "SkReadBuffer.h"
+#include "SkShadowShader.h"
+#include "SkPoint3.h"
+
+////////////////////////////////////////////////////////////////////////////
+#ifdef SK_EXPERIMENTAL_SHADOWING
+
+#define SK_MAX_NON_AMBIENT_LIGHTS 4
+
+/** \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,
+                       int diffuseWidth, int diffuseHeight)
+            : fPovDepthShader(std::move(povDepthShader))
+            , fDiffuseShader(std::move(diffuseShader))
+            , fLights(std::move(lights))
+            , fDiffuseWidth(diffuseWidth)
+            , fDiffuseHeight(diffuseHeight) { }
+
+    bool isOpaque() const override;
+
+#if SK_SUPPORT_GPU
+    sk_sp<GrFragmentProcessor> asFragmentProcessor(const AsFPArgs&) 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*        fPovDepthContext;
+        SkShader::Context*        fDiffuseContext;
+        uint32_t                  fFlags;
+
+        void* fHeapAllocated;
+
+        typedef SkShader::Context INHERITED;
+    };
+
+    SK_TO_STRING_OVERRIDE()
+    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> fPovDepthShader;
+    sk_sp<SkShader> fDiffuseShader;
+    sk_sp<SkLights> fLights;
+
+    int fDiffuseWidth;
+    int fDiffuseHeight;
+
+    friend class SkShadowShader;
+
+    typedef SkShader INHERITED;
+};
+
+////////////////////////////////////////////////////////////////////////////
+
+#if SK_SUPPORT_GPU
+
+#include "GrCoordTransform.h"
+#include "GrFragmentProcessor.h"
+#include "GrInvariantOutput.h"
+#include "glsl/GrGLSLFragmentProcessor.h"
+#include "glsl/GrGLSLFragmentShaderBuilder.h"
+#include "SkGr.h"
+#include "SkGrPriv.h"
+#include "SkSpecialImage.h"
+#include "SkImage_Base.h"
+#include "GrContext.h"
+
+class ShadowFP : public GrFragmentProcessor {
+public:
+    ShadowFP(sk_sp<GrFragmentProcessor> povDepth,
+             sk_sp<GrFragmentProcessor> diffuse,
+             sk_sp<SkLights> lights,
+             int diffuseWidth, int diffuseHeight,
+             GrContext* context) {
+
+        // fuse all ambient lights into a single one
+        fAmbientColor.set(0.0f, 0.0f, 0.0f);
+
+        fNumDirLights = 0; // refers to directional lights.
+        for (int i = 0; i < lights->numLights(); ++i) {
+            if (SkLights::Light::kAmbient_LightType == lights->light(i).type()) {
+                fAmbientColor += lights->light(i).color();
+            } else if (fNumDirLights < SK_MAX_NON_AMBIENT_LIGHTS){
+                fLightColor[fNumDirLights] = lights->light(i).color();
+                fLightDir[fNumDirLights] = lights->light(i).dir();
+                SkImage_Base* shadowMap = ((SkImage_Base*)lights->light(i).getShadowMap().get());
+
+                // this sk_sp gets deleted when the ShadowFP is destroyed, and frees the GrTexture*
+                fTexture[fNumDirLights] = sk_sp<GrTexture>(shadowMap->asTextureRef(context,
+                                                           GrTextureParams::ClampNoFilter(),
+                                                           SkSourceGammaTreatment::kIgnore));
+                fDepthMapAccess[fNumDirLights].reset(fTexture[fNumDirLights].get());
+                this->addTextureAccess(&fDepthMapAccess[fNumDirLights]);
+
+                fDepthMapHeight[fNumDirLights] = shadowMap->height();
+                fDepthMapWidth[fNumDirLights] = shadowMap->width();
+
+                fNumDirLights++;
+            }
+        }
+
+        fWidth = diffuseWidth;
+        fHeight = diffuseHeight;
+
+        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>().fNumDirLights;
+            SkASSERT(numLights <= SK_MAX_NON_AMBIENT_LIGHTS);
+
+            const char* lightDirUniName[SK_MAX_NON_AMBIENT_LIGHTS] = {nullptr};
+            const char* lightColorUniName[SK_MAX_NON_AMBIENT_LIGHTS] = {nullptr};
+
+            const char* depthMapWidthUniName[SK_MAX_NON_AMBIENT_LIGHTS] = {nullptr};
+            const char* depthMapHeightUniName[SK_MAX_NON_AMBIENT_LIGHTS] = {nullptr};
+
+            SkString lightDirUniNameBase("lightDir");
+            SkString lightColorUniNameBase("lightColor");
+
+            SkString depthMapWidthUniNameBase("dmapWidth");
+            SkString depthMapHeightUniNameBase("dmapHeight");
+
+            for (int i = 0; i < numLights; i++) {
+                SkString lightDirUniNameStr(lightDirUniNameBase);
+                lightDirUniNameStr.appendf("%d", i);
+                SkString lightColorUniNameStr(lightColorUniNameBase);
+                lightColorUniNameStr.appendf("%d", i);
+
+                SkString depthMapWidthUniNameStr(depthMapWidthUniNameBase);
+                depthMapWidthUniNameStr.appendf("%d", i);
+                SkString depthMapHeightUniNameStr(depthMapHeightUniNameBase);
+                depthMapHeightUniNameStr.appendf("%d", i);
+
+                fLightDirUni[i] = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                             kVec3f_GrSLType,
+                                                             kDefault_GrSLPrecision,
+                                                             lightDirUniNameStr.c_str(),
+                                                             &lightDirUniName[i]);
+                fLightColorUni[i] = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                               kVec3f_GrSLType,
+                                                               kDefault_GrSLPrecision,
+                                                               lightColorUniNameStr.c_str(),
+                                                               &lightColorUniName[i]);
+
+                fDepthMapWidthUni[i]  = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                   kInt_GrSLType,
+                                                   kDefault_GrSLPrecision,
+                                                   depthMapWidthUniNameStr.c_str(),
+                                                   &depthMapWidthUniName[i]);
+                fDepthMapHeightUni[i] = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                   kInt_GrSLType,
+                                                   kDefault_GrSLPrecision,
+                                                   depthMapHeightUniNameStr.c_str(),
+                                                   &depthMapHeightUniName[i]);
+            }
+
+
+            const char* widthUniName = nullptr;
+            const char* heightUniName = nullptr;
+
+            fWidthUni = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                   kInt_GrSLType,
+                                                   kDefault_GrSLPrecision,
+                                                   "width", &widthUniName);
+            fHeightUni = uniformHandler->addUniform(kFragment_GrShaderFlag,
+                                                    kInt_GrSLType,
+                                                    kDefault_GrSLPrecision,
+                                                    "height", &heightUniName);
+
+
+            SkString povDepth("povDepth");
+            this->emitChild(0, nullptr, &povDepth, args);
+
+            SkString diffuseColor("inDiffuseColor");
+            this->emitChild(1, nullptr, &diffuseColor, args);
+
+            SkString depthMaps[SK_MAX_NON_AMBIENT_LIGHTS];
+
+            for (int i = 0; i < numLights; i++) {
+                SkString povCoord("povCoord");
+                povCoord.appendf("%d", i);
+
+                // vMatrixCoord_0_1_Stage0 is the texture sampler coordinates.
+                // povDepth.b * 255 scales it to 0 - 255, bringing it to world space,
+                // and the / 400 brings it back to a sampler coordinate, 0 - 1
+                // The 400 comes from the shadowmaps GM.
+                // TODO use real shadowmaps size
+                SkString offset("offset");
+                offset.appendf("%d", i);
+
+                SkString scaleVec("scaleVec");
+                scaleVec.appendf("%d", i);
+
+                SkString scaleOffsetVec("scaleOffsetVec");
+                scaleOffsetVec.appendf("%d", i);
+
+                fragBuilder->codeAppendf("vec2 %s = vec2(%s) * povDepth.b * 255 / 400;\n",
+                                         offset.c_str(), lightDirUniName[i]);
+
+                fragBuilder->codeAppendf("vec2 %s = (vec2(%s, %s) / vec2(%s, %s));\n",
+                                         scaleVec.c_str(),
+                                         widthUniName, heightUniName,
+                                         depthMapWidthUniName[i], depthMapHeightUniName[i]);
+
+                fragBuilder->codeAppendf("vec2 %s = 1 - %s;\n",
+                                         scaleOffsetVec.c_str(), scaleVec.c_str());
+
+
+                fragBuilder->codeAppendf("vec2 %s = (vMatrixCoord_0_1_Stage0 + "
+                                                    "vec2(%s.x, 0 - %s.y)) "
+                                                   " * %s + vec2(0,1) * %s;\n",
+
+                                         povCoord.c_str(), offset.c_str(), offset.c_str(),
+                                         scaleVec.c_str(), scaleOffsetVec.c_str());
+
+                fragBuilder->appendTextureLookup(&depthMaps[i], args.fTexSamplers[i],
+                                                 povCoord.c_str(),
+                                                 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());
+
+            // Essentially,
+            // diffColor * (ambientLightTot + foreachDirLight(lightColor * (N . L)))
+            SkString totalLightColor("totalLightColor");
+            fragBuilder->codeAppendf("vec3 %s = vec3(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());
+                // Note that dot(vec3(0,0,1), %s) == %s.z * %s
+                fragBuilder->codeAppendf("%s += %s.z * %s;",
+                                         totalLightColor.c_str(),
+                                         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.fNumDirLights);
+        }
+
+    protected:
+        void onSetData(const GrGLSLProgramDataManager& pdman, const GrProcessor& proc) override {
+            const ShadowFP &shadowFP = proc.cast<ShadowFP>();
+
+            fNumDirLights = shadowFP.numLights();
+
+            for (int i = 0; i < fNumDirLights; i++) {
+                const SkVector3& lightDir = shadowFP.lightDir(i);
+                if (lightDir != fLightDir[i]) {
+                    pdman.set3fv(fLightDirUni[i], 1, &lightDir.fX);
+                    fLightDir[i] = lightDir;
+                }
+                const SkColor3f& lightColor = shadowFP.lightColor(i);
+                if (lightColor != fLightColor[i]) {
+                    pdman.set3fv(fLightColorUni[i], 1, &lightColor.fX);
+                    fLightColor[i] = lightColor;
+                }
+
+                int depthMapWidth = shadowFP.depthMapWidth(i);
+                if (depthMapWidth != fDepthMapWidth[i]) {
+                    pdman.set1i(fDepthMapWidthUni[i], depthMapWidth);
+                    fDepthMapWidth[i] = depthMapWidth;
+                }
+                int depthMapHeight = shadowFP.depthMapHeight(i);
+                if (depthMapHeight != fDepthMapHeight[i]) {
+                    pdman.set1i(fDepthMapHeightUni[i], depthMapHeight);
+                    fDepthMapHeight[i] = depthMapHeight;
+                }
+            }
+
+            int width = shadowFP.width();
+            if (width != fWidth) {
+                pdman.set1i(fWidthUni, width);
+                fWidth = width;
+            }
+            int height = shadowFP.height();
+            if (height != fHeight) {
+                pdman.set1i(fHeightUni, height);
+                fHeight = height;
+            }
+
+            const SkColor3f& ambientColor = shadowFP.ambientColor();
+            if (ambientColor != fAmbientColor) {
+                pdman.set3fv(fAmbientColorUni, 1, &ambientColor.fX);
+                fAmbientColor = ambientColor;
+            }
+        }
+
+    private:
+        SkVector3 fLightDir[SK_MAX_NON_AMBIENT_LIGHTS];
+        GrGLSLProgramDataManager::UniformHandle fLightDirUni[SK_MAX_NON_AMBIENT_LIGHTS];
+        SkColor3f fLightColor[SK_MAX_NON_AMBIENT_LIGHTS];
+        GrGLSLProgramDataManager::UniformHandle fLightColorUni[SK_MAX_NON_AMBIENT_LIGHTS];
+
+        int fDepthMapWidth[SK_MAX_NON_AMBIENT_LIGHTS];
+        GrGLSLProgramDataManager::UniformHandle fDepthMapWidthUni[SK_MAX_NON_AMBIENT_LIGHTS];
+        int fDepthMapHeight[SK_MAX_NON_AMBIENT_LIGHTS];
+        GrGLSLProgramDataManager::UniformHandle fDepthMapHeightUni[SK_MAX_NON_AMBIENT_LIGHTS];
+
+        int fWidth;
+        GrGLSLProgramDataManager::UniformHandle fWidthUni;
+        int fHeight;
+        GrGLSLProgramDataManager::UniformHandle fHeightUni;
+
+        SkColor3f fAmbientColor;
+        GrGLSLProgramDataManager::UniformHandle fAmbientColorUni;
+
+        int fNumDirLights;
+    };
+
+    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 fNumDirLights; }
+    const SkColor3f& ambientColor() const { return fAmbientColor; }
+    const SkVector3& lightDir(int i) const {
+        SkASSERT(i < fNumDirLights);
+        return fLightDir[i];
+    }
+    const SkVector3& lightColor(int i) const {
+        SkASSERT(i < fNumDirLights);
+        return fLightColor[i];
+    }
+
+    int depthMapWidth(int i) const {
+        SkASSERT(i < fNumDirLights);
+        return fDepthMapWidth[i];
+    }
+    int depthMapHeight(int i) const {
+        SkASSERT(i < fNumDirLights);
+        return fDepthMapHeight[i];
+    }
+    int width() const {return fWidth; }
+    int height() const {return fHeight; }
+
+private:
+    GrGLSLFragmentProcessor* onCreateGLSLInstance() const override { return new GLSLShadowFP; }
+
+    bool onIsEqual(const GrFragmentProcessor& proc) const override {
+        const ShadowFP& shadowFP = proc.cast<ShadowFP>();
+        if (fAmbientColor != shadowFP.fAmbientColor || fNumDirLights != shadowFP.fNumDirLights) {
+            return false;
+        }
+
+        if (fWidth != shadowFP.fWidth || fHeight != shadowFP.fHeight) {
+            return false;
+        }
+
+        for (int i = 0; i < fNumDirLights; i++) {
+            if (fLightDir[i] != shadowFP.fLightDir[i] ||
+                fLightColor[i] != shadowFP.fLightColor[i]) {
+                return false;
+            }
+
+            if (fDepthMapWidth[i] != shadowFP.fDepthMapWidth[i] ||
+                fDepthMapHeight[i] != shadowFP.fDepthMapHeight[i]) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    int              fNumDirLights;
+
+    SkVector3        fLightDir[SK_MAX_NON_AMBIENT_LIGHTS];
+    SkColor3f        fLightColor[SK_MAX_NON_AMBIENT_LIGHTS];
+    GrTextureAccess  fDepthMapAccess[SK_MAX_NON_AMBIENT_LIGHTS];
+    sk_sp<GrTexture> fTexture[SK_MAX_NON_AMBIENT_LIGHTS];
+
+    int              fDepthMapWidth[SK_MAX_NON_AMBIENT_LIGHTS];
+    int              fDepthMapHeight[SK_MAX_NON_AMBIENT_LIGHTS];
+
+    int              fHeight;
+    int              fWidth;
+
+    SkColor3f        fAmbientColor;
+};
+
+////////////////////////////////////////////////////////////////////////////
+
+sk_sp<GrFragmentProcessor> SkShadowShaderImpl::asFragmentProcessor(const AsFPArgs& fpargs) const {
+
+    sk_sp<GrFragmentProcessor> povDepthFP = fPovDepthShader->asFragmentProcessor(fpargs);
+
+    sk_sp<GrFragmentProcessor> diffuseFP = fDiffuseShader->asFragmentProcessor(fpargs);
+
+    sk_sp<GrFragmentProcessor> shadowfp = sk_make_sp<ShadowFP>(std::move(povDepthFP),
+                                                               std::move(diffuseFP),
+                                                               std::move(fLights),
+                                                               fDiffuseWidth, fDiffuseHeight,
+                                                               fpargs.fContext);
+    return shadowfp;
+}
+
+
+#endif
+
+////////////////////////////////////////////////////////////////////////////
+
+bool SkShadowShaderImpl::isOpaque() const {
+    return fDiffuseShader->isOpaque();
+}
+
+SkShadowShaderImpl::ShadowShaderContext::ShadowShaderContext(
+        const SkShadowShaderImpl& shader, const ContextRec& rec,
+        SkShader::Context* povDepthContext,
+        SkShader::Context* diffuseContext,
+        void* heapAllocated)
+        : INHERITED(shader, rec)
+        , fPovDepthContext(povDepthContext)
+        , fDiffuseContext(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.
+    fPovDepthContext->~Context();
+    fDiffuseContext->~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;
+    }
+
+    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];
+
+    do {
+        int n = SkTMin(count, BUFFER_MAX);
+
+        fPovDepthContext->shadeSpan(x, y, diffuse, n);
+        fDiffuseContext->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.fX += light.color().fX * SkColorGetR(diffColor);
+                    accum.fY += light.color().fY * SkColorGetG(diffColor);
+                    accum.fZ += light.color().fZ * SkColorGetB(diffColor);
+                } else {
+                    // scaling by fZ accounts for lighting direction
+                    accum.fX += light.color().makeScale(light.dir().fZ).fX * SkColorGetR(diffColor);
+                    accum.fY += light.color().makeScale(light.dir().fZ).fY * SkColorGetG(diffColor);
+                    accum.fZ += light.color().makeScale(light.dir().fZ).fZ * SkColorGetB(diffColor);
+                }
+            }
+
+            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;
+            }
+
+            sk_sp<SkImage> depthMap;
+            if (!(depthMap = sk_ref_sp<SkImage>(buf.readImage()))) {
+                return nullptr;
+            }
+
+            SkLights::Light light = SkLights::Light(color, dir);
+            light.setShadowMap(depthMap);
+
+            builder.add(light);
+        }
+    }
+
+    sk_sp<SkLights> lights(builder.finish());
+
+    int diffuseWidth = buf.readInt();
+    int diffuseHeight = buf.readInt();
+
+    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),
+                                          diffuseWidth, diffuseHeight);
+}
+
+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.writeImage(light.getShadowMap().get());
+    }
+
+    buf.writeInt(fDiffuseWidth);
+    buf.writeInt(fDiffuseHeight);
+
+    buf.writeFlattenable(fPovDepthShader.get());
+    buf.writeFlattenable(fDiffuseShader.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 = fPovDepthShader->contextSize(rec) +
+                          fDiffuseShader->contextSize(rec);
+
+    void* heapAllocated = sk_malloc_throw(heapRequired);
+
+    void* povDepthContextStorage = heapAllocated;
+
+    SkShader::Context* povDepthContext =
+            fPovDepthShader->createContext(rec, povDepthContextStorage);
+
+    if (!povDepthContext) {
+        sk_free(heapAllocated);
+        return nullptr;
+    }
+
+    void* diffuseContextStorage = (char*)heapAllocated + fPovDepthShader->contextSize(rec);
+
+    SkShader::Context* diffuseContext = fDiffuseShader->createContext(rec, diffuseContextStorage);
+    if (!diffuseContext) {
+        sk_free(heapAllocated);
+        return nullptr;
+    }
+
+    return new (storage) ShadowShaderContext(*this, rec, povDepthContext, diffuseContext,
+                                             heapAllocated);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+sk_sp<SkShader> SkShadowShader::Make(sk_sp<SkShader> povDepthShader,
+                                     sk_sp<SkShader> diffuseShader,
+                                     sk_sp<SkLights> lights,
+                                     int diffuseWidth, int diffuseHeight) {
+    if (!povDepthShader || !diffuseShader) {
+        // TODO: Use paint's color in absence of a diffuseShader
+        // TODO: Use a default implementation of normalSource instead
+        return nullptr;
+    }
+
+    return sk_make_sp<SkShadowShaderImpl>(std::move(povDepthShader),
+                                          std::move(diffuseShader),
+                                          std::move(lights),
+                                          diffuseWidth, diffuseHeight);
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkShadowShader)
+    SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkShadowShaderImpl)
+SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END
+
+///////////////////////////////////////////////////////////////////////////////
+
+#endif
diff --git a/src/core/SkShadowShader.h b/src/core/SkShadowShader.h
new file mode 100644
index 0000000000..7cbcbca224
--- /dev/null
+++ b/src/core/SkShadowShader.h
@@ -0,0 +1,32 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+
+#ifndef SkShadowShader_DEFINED
+#define SkShadowShader_DEFINED
+
+#ifdef SK_EXPERIMENTAL_SHADOWING
+
+class SkLights;
+class SkShader;
+
+class SK_API SkShadowShader {
+public:
+    /** This shader combines the diffuse color in 'diffuseShader' with the shadows
+     *  determined by the 'povDepthShader' and the shadow maps stored in each of the
+     *  lights in 'lights'
+     */
+    static sk_sp<SkShader> Make(sk_sp<SkShader> povDepthShader,
+                                sk_sp<SkShader> diffuseShader,
+                                sk_sp<SkLights> lights,
+                                int diffuseWidth, int diffuseHeight);
+
+    SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()
+};
+
+#endif
+#endif