Add SkRasterPipeline blitter.

This is now pixel-exact with the existing sRGB SW impl as far as I've tested.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2146413002
CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Review-Url: https://codereview.chromium.org/2146413002

10 files changed, 383 insertions, 7 deletions

diff --git a/gyp/core.gypi b/gyp/core.gypi
index 2e1c88a1d2..736e47d115 100644
--- a/gyp/core.gypi
+++ b/gyp/core.gypi
@@ -231,6 +231,7 @@
         '<(skia_src_path)/core/SkQuadClipper.h',
         '<(skia_src_path)/core/SkRasterClip.cpp',
         '<(skia_src_path)/core/SkRasterPipeline.cpp',
+        '<(skia_src_path)/core/SkRasterPipelineBlitter.cpp',
         '<(skia_src_path)/core/SkRasterizer.cpp',
         '<(skia_src_path)/core/SkReadBuffer.h',
         '<(skia_src_path)/core/SkReadBuffer.cpp',
diff --git a/include/core/SkColorFilter.h b/include/core/SkColorFilter.h
index 7b2ee7845e..609550f676 100644
--- a/include/core/SkColorFilter.h
+++ b/include/core/SkColorFilter.h
@@ -16,6 +16,7 @@
 class GrContext;
 class GrFragmentProcessor;
 class SkBitmap;
+class SkRasterPipeline;
 
 /**
  *  ColorFilters are optional objects in the drawing pipeline. When present in
@@ -70,6 +71,8 @@ public:
 
     virtual void filterSpan4f(const SkPM4f src[], int count, SkPM4f result[]) const;
 
+    bool appendStages(SkRasterPipeline*) const;
+
     enum Flags {
         /** If set the filter methods will not change the alpha channel of the colors.
         */
@@ -168,6 +171,8 @@ public:
 protected:
     SkColorFilter() {}
 
+    virtual bool onAppendStages(SkRasterPipeline*) const;
+
 private:
     /*
      *  Returns 1 if this is a single filter (not a composition of other filters), otherwise it
diff --git a/include/core/SkXfermode.h b/include/core/SkXfermode.h
index 6215315576..2d12b3c931 100644
--- a/include/core/SkXfermode.h
+++ b/include/core/SkXfermode.h
@@ -14,6 +14,7 @@
 class GrFragmentProcessor;
 class GrTexture;
 class GrXPFactory;
+class SkRasterPipeline;
 class SkString;
 
 struct SkPM4f;
@@ -164,6 +165,8 @@ public:
 
     virtual SkXfermodeProc4f getProc4f() const;
 
+    bool appendStages(SkRasterPipeline*) const;
+
     /**
      *  If the specified mode can be represented by a pair of Coeff, then return
      *  true and set (if not NULL) the corresponding coeffs. If the mode is
@@ -216,15 +219,15 @@ public:
 #if SK_SUPPORT_GPU
     /** Used by the SkXfermodeImageFilter to blend two colors via a GrFragmentProcessor.
         The input to the returned FP is the src color. The dst color is
-        provided by the dst param which becomes a child FP of the returned FP. 
+        provided by the dst param which becomes a child FP of the returned FP.
         It is legal for the function to return a null output. This indicates that
         the output of the blend is simply the src color.
      */
     virtual sk_sp<GrFragmentProcessor> makeFragmentProcessorForImageFilter(
                                                             sk_sp<GrFragmentProcessor> dst) const;
 
-    /** A subclass must implement this factory function to work with the GPU backend. 
-        The xfermode will return a factory for which the caller will get a ref. It is up 
+    /** A subclass must implement this factory function to work with the GPU backend.
+        The xfermode will return a factory for which the caller will get a ref. It is up
         to the caller to install it. XferProcessors cannot use a background texture.
       */
     virtual sk_sp<GrXPFactory> asXPFactory() const;
@@ -281,6 +284,7 @@ protected:
 
     virtual D32Proc onGetD32Proc(uint32_t flags) const;
     virtual F16Proc onGetF16Proc(uint32_t flags) const;
+    virtual bool onAppendStages(SkRasterPipeline*) const;
 
 private:
     enum {
diff --git a/src/core/SkBlitter.cpp b/src/core/SkBlitter.cpp
index f5d13dc5f1..a6ab29157f 100644
--- a/src/core/SkBlitter.cpp
+++ b/src/core/SkBlitter.cpp
@@ -853,6 +853,10 @@ SkBlitter* SkBlitter::Choose(const SkPixmap& device,
         p->setColor(0);
     }
 
+    if (auto blitter = SkCreateRasterPipelineBlitter(device, *paint)) {
+        return blitter.release();
+    }
+
     if (nullptr == shader) {
         if (mode) {
             // xfermodes (and filters) require shaders for our current blitters
diff --git a/src/core/SkColorFilter.cpp b/src/core/SkColorFilter.cpp
index 167a668380..31c0ddb06b 100644
--- a/src/core/SkColorFilter.cpp
+++ b/src/core/SkColorFilter.cpp
@@ -37,6 +37,14 @@ sk_sp<GrFragmentProcessor> SkColorFilter::asFragmentProcessor(GrContext*) const
 }
 #endif
 
+bool SkColorFilter::appendStages(SkRasterPipeline* pipeline) const {
+    return this->onAppendStages(pipeline);
+}
+
+bool SkColorFilter::onAppendStages(SkRasterPipeline*) const {
+    return false;
+}
+
 void SkColorFilter::filterSpan4f(const SkPM4f src[], int count, SkPM4f result[]) const {
     const int N = 128;
     SkPMColor tmp[N];
diff --git a/src/core/SkCoreBlitters.h b/src/core/SkCoreBlitters.h
index 8fcfde6f76..a784d4714a 100644
--- a/src/core/SkCoreBlitters.h
+++ b/src/core/SkCoreBlitters.h
@@ -13,6 +13,7 @@
 #include "SkBlitRow.h"
 #include "SkShader.h"
 #include "SkSmallAllocator.h"
+#include <memory>
 
 class SkRasterBlitter : public SkBlitter {
 public:
@@ -210,4 +211,8 @@ SkBlitter* SkBlitter_ChooseD565(const SkPixmap& device, const SkPaint& paint,
                                 SkShader::Context* shaderContext,
                                 SkTBlitterAllocator* allocator);
 
+
+// Returns nullptr if no SkRasterPipeline blitter can be constructed for this paint.
+std::unique_ptr<SkBlitter> SkCreateRasterPipelineBlitter(const SkPixmap&, const SkPaint&);
+
 #endif
diff --git a/src/core/SkRasterPipeline.cpp b/src/core/SkRasterPipeline.cpp
index 899142886c..c50383af01 100644
--- a/src/core/SkRasterPipeline.cpp
+++ b/src/core/SkRasterPipeline.cpp
@@ -22,11 +22,23 @@ void SkRasterPipeline::append(SkRasterPipeline::Fn body_fn, const void* body_ctx
     fTail.push_back({ &JustReturn, const_cast<void*>(tail_ctx) });
 }
 
-void SkRasterPipeline::run(size_t n) {
+void SkRasterPipeline::extend(const SkRasterPipeline& src) {
+    SkASSERT(src.fBody.count() == src.fTail.count());
+
+    Fn body_fn = src.fBodyStart,
+       tail_fn = src.fTailStart;
+    for (int i = 0; i < src.fBody.count(); i++) {
+        this->append(body_fn, src.fBody[i].fCtx,
+                     tail_fn, src.fTail[i].fCtx);
+        body_fn = src.fBody[i].fNext;
+        tail_fn = src.fTail[i].fNext;
+    }
+}
+
+void SkRasterPipeline::run(size_t x, size_t n) {
     // It's fastest to start uninitialized if the compilers all let us.  If not, next fastest is 0.
     Sk4f v;
 
-    size_t x = 0;
     while (n >= 4) {
         fBodyStart(fBody.begin(), x, v,v,v,v, v,v,v,v);
         x += 4;
diff --git a/src/core/SkRasterPipeline.h b/src/core/SkRasterPipeline.h
index 186ee654c2..acbabcbadc 100644
--- a/src/core/SkRasterPipeline.h
+++ b/src/core/SkRasterPipeline.h
@@ -72,9 +72,10 @@ public:
 
     SkRasterPipeline();
 
-    // Run the pipeline constructed with append(), walking x through [0,n),
+    // Run the pipeline constructed with append(), walking x through [x,x+n),
     // generally in 4 pixel steps, but sometimes 1 pixel at a time.
-    void run(size_t n);
+    void run(size_t x, size_t n);
+    void run(size_t n) { this->run(0, n); }
 
     // Use this append() if your stage is sensitive to the number of pixels you're working with:
     //   - body will always be called for a full 4 pixels
@@ -93,6 +94,9 @@ public:
         this->append(body, ctx, tail, ctx);
     }
 
+    // Append all stages to this pipeline.
+    void extend(const SkRasterPipeline&);
+
 private:
     using Stages = SkSTArray<10, Stage, /*MEM_COPY=*/true>;
 
diff --git a/src/core/SkRasterPipelineBlitter.cpp b/src/core/SkRasterPipelineBlitter.cpp
new file mode 100644
index 0000000000..c4870d33bc
--- /dev/null
+++ b/src/core/SkRasterPipelineBlitter.cpp
@@ -0,0 +1,325 @@
+/*
+ * 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 "SkBlitter.h"
+#include "SkColor.h"
+#include "SkColorFilter.h"
+#include "SkPM4f.h"
+#include "SkPM4fPriv.h"
+#include "SkRasterPipeline.h"
+#include "SkShader.h"
+#include "SkSRGB.h"
+#include "SkXfermode.h"
+
+
+class SkRasterPipelineBlitter : public SkBlitter {
+public:
+    static std::unique_ptr<SkBlitter> Create(const SkPixmap&, const SkPaint&);
+
+    void blitH    (int x, int y, int w)                            override;
+    void blitAntiH(int x, int y, const SkAlpha[], const int16_t[]) override;
+    void blitMask (const SkMask&, const SkIRect& clip)             override;
+
+    // TODO: The default implementations of the other blits look fine,
+    // but some of them like blitV could probably benefit from custom
+    // blits using something like a SkRasterPipeline::runFew() method.
+
+private:
+    SkRasterPipelineBlitter(SkPixmap dst,
+                            SkRasterPipeline shader,
+                            SkRasterPipeline colorFilter,
+                            SkRasterPipeline xfermode,
+                            SkPM4f paintColor)
+        : fDst(dst)
+        , fShader(shader)
+        , fColorFilter(colorFilter)
+        , fXfermode(xfermode)
+        , fPaintColor(paintColor)
+    {}
+
+    SkPixmap         fDst;
+    SkRasterPipeline fShader, fColorFilter, fXfermode;
+    SkPM4f           fPaintColor;
+
+    typedef SkBlitter INHERITED;
+};
+
+std::unique_ptr<SkBlitter> SkCreateRasterPipelineBlitter(const SkPixmap& dst,
+                                                         const SkPaint& paint) {
+    return SkRasterPipelineBlitter::Create(dst, paint);
+}
+
+
+// The default shader produces a constant color (from the SkPaint).
+static void SK_VECTORCALL constant_color(SkRasterPipeline::Stage* st, size_t x,
+                                         Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                         Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto color = st->ctx<const SkPM4f*>();
+    r = color->r();
+    g = color->g();
+    b = color->b();
+    a = color->a();
+    st->next(x, r,g,b,a, dr,dg,db,da);
+}
+
+// The default transfer mode is srcover, s' = s + d*(1-sa).
+static void SK_VECTORCALL srcover(SkRasterPipeline::Stage* st, size_t x,
+                                  Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                  Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto A = 1.0f - a;
+    r += dr*A;
+    g += dg*A;
+    b += db*A;
+    a += da*A;
+    st->next(x, r,g,b,a, dr,dg,db,da);
+}
+
+static Sk4f lerp(const Sk4f& from, const Sk4f& to, const Sk4f& cov) {
+    return from + (to-from)*cov;
+}
+
+// s' = d(1-c) + sc, for a constant c.
+static void SK_VECTORCALL lerp_constant_float(SkRasterPipeline::Stage* st, size_t x,
+                                              Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                              Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    Sk4f c = *st->ctx<const float*>();
+
+    r = lerp(dr, r, c);
+    g = lerp(dg, g, c);
+    b = lerp(db, b, c);
+    a = lerp(da, a, c);
+    st->next(x, r,g,b,a, dr,dg,db,da);
+}
+
+// s' = d(1-c) + sc, 4 pixels at a time for 8-bit coverage.
+static void SK_VECTORCALL lerp_a8(SkRasterPipeline::Stage* st, size_t x,
+                                  Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                  Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto ptr = st->ctx<const uint8_t*>() + x;
+    Sk4f c = SkNx_cast<float>(Sk4b::Load(ptr)) * (1/255.0f);
+
+    r = lerp(dr, r, c);
+    g = lerp(dg, g, c);
+    b = lerp(db, b, c);
+    a = lerp(da, a, c);
+    st->next(x, r,g,b,a, dr,dg,db,da);
+}
+
+// Tail variant of lerp_a8() handling 1 pixel at a time.
+static void SK_VECTORCALL lerp_a8_1(SkRasterPipeline::Stage* st, size_t x,
+                                    Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                    Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto ptr = st->ctx<const uint8_t*>() + x;
+    Sk4f c = *ptr * (1/255.0f);
+
+    r = lerp(dr, r, c);
+    g = lerp(dg, g, c);
+    b = lerp(db, b, c);
+    a = lerp(da, a, c);
+    st->next(x, r,g,b,a, dr,dg,db,da);
+}
+
+static void upscale_lcd16(const Sk4h& lcd16, Sk4f* r, Sk4f* g, Sk4f* b) {
+    Sk4i _32_bit = SkNx_cast<int>(lcd16);
+
+    *r = SkNx_cast<float>(_32_bit & SK_R16_MASK_IN_PLACE) * (1.0f / SK_R16_MASK_IN_PLACE);
+    *g = SkNx_cast<float>(_32_bit & SK_G16_MASK_IN_PLACE) * (1.0f / SK_G16_MASK_IN_PLACE);
+    *b = SkNx_cast<float>(_32_bit & SK_B16_MASK_IN_PLACE) * (1.0f / SK_B16_MASK_IN_PLACE);
+}
+
+// s' = d(1-c) + sc, 4 pixels at a time for 565 coverage.
+static void SK_VECTORCALL lerp_lcd16(SkRasterPipeline::Stage* st, size_t x,
+                                     Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                     Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto ptr = st->ctx<const uint16_t*>() + x;
+    Sk4f cr, cg, cb;
+    upscale_lcd16(Sk4h::Load(ptr), &cr, &cg, &cb);
+
+    r = lerp(dr, r, cr);
+    g = lerp(dg, g, cg);
+    b = lerp(db, b, cb);
+    a = 1.0f;
+    st->next(x, r,g,b,a, dr,dg,db,da);
+}
+
+// Tail variant of lerp_lcd16() handling 1 pixel at a time.
+static void SK_VECTORCALL lerp_lcd16_1(SkRasterPipeline::Stage* st, size_t x,
+                                       Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                       Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto ptr = st->ctx<const uint16_t*>() + x;
+    Sk4f cr, cg, cb;
+    upscale_lcd16({*ptr,0,0,0}, &cr, &cg, &cb);
+
+    r = lerp(dr, r, cr);
+    g = lerp(dg, g, cg);
+    b = lerp(db, b, cb);
+    a = 1.0f;
+    st->next(x, r,g,b,a, dr,dg,db,da);
+}
+
+// Load 4 8-bit sRGB pixels from SkPMColor order to RGBA.
+static void SK_VECTORCALL load_d_srgb(SkRasterPipeline::Stage* st, size_t x,
+                                      Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                      Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto ptr = st->ctx<const uint32_t*>() + x;
+
+    dr = { sk_linear_from_srgb[(ptr[0] >> SK_R32_SHIFT) & 0xff],
+           sk_linear_from_srgb[(ptr[1] >> SK_R32_SHIFT) & 0xff],
+           sk_linear_from_srgb[(ptr[2] >> SK_R32_SHIFT) & 0xff],
+           sk_linear_from_srgb[(ptr[3] >> SK_R32_SHIFT) & 0xff] };
+
+    dg = { sk_linear_from_srgb[(ptr[0] >> SK_G32_SHIFT) & 0xff],
+           sk_linear_from_srgb[(ptr[1] >> SK_G32_SHIFT) & 0xff],
+           sk_linear_from_srgb[(ptr[2] >> SK_G32_SHIFT) & 0xff],
+           sk_linear_from_srgb[(ptr[3] >> SK_G32_SHIFT) & 0xff] };
+
+    db = { sk_linear_from_srgb[(ptr[0] >> SK_B32_SHIFT) & 0xff],
+           sk_linear_from_srgb[(ptr[1] >> SK_B32_SHIFT) & 0xff],
+           sk_linear_from_srgb[(ptr[2] >> SK_B32_SHIFT) & 0xff],
+           sk_linear_from_srgb[(ptr[3] >> SK_B32_SHIFT) & 0xff] };
+
+    // TODO: this >> doesn't really need mask if we make it logical instead of arithmetic.
+    da = SkNx_cast<float>((Sk4i::Load(ptr) >> SK_A32_SHIFT) & 0xff) * (1/255.0f);
+
+    st->next(x, r,g,b,a, dr,dg,db,da);
+}
+
+// Tail variant of load_d_srgb() handling 1 pixel at a time.
+static void SK_VECTORCALL load_d_srgb_1(SkRasterPipeline::Stage* st, size_t x,
+                                        Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                        Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto ptr = st->ctx<const uint32_t*>() + x;
+
+    dr = { sk_linear_from_srgb[(*ptr >> SK_R32_SHIFT) & 0xff], 0,0,0 };
+    dg = { sk_linear_from_srgb[(*ptr >> SK_G32_SHIFT) & 0xff], 0,0,0 };
+    db = { sk_linear_from_srgb[(*ptr >> SK_B32_SHIFT) & 0xff], 0,0,0 };
+    da = {        (1/255.0f) * (*ptr >> SK_A32_SHIFT)        , 0,0,0 };
+
+    st->next(x, r,g,b,a, dr,dg,db,da);
+}
+
+// Write out 4 pixels as 8-bit SkPMColor-order sRGB.
+static void SK_VECTORCALL store_srgb(SkRasterPipeline::Stage* st, size_t x,
+                                     Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                     Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto dst = st->ctx<uint32_t*>() + x;
+    ( sk_linear_to_srgb(r) << SK_R32_SHIFT
+    | sk_linear_to_srgb(g) << SK_G32_SHIFT
+    | sk_linear_to_srgb(b) << SK_B32_SHIFT
+    | Sk4f_round(255.0f*a) << SK_A32_SHIFT).store(dst);
+}
+
+// Tail variant of store_srgb() handling 1 pixel at a time.
+static void SK_VECTORCALL store_srgb_1(SkRasterPipeline::Stage* st, size_t x,
+                                       Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                       Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto dst = st->ctx<uint32_t*>() + x;
+    *dst = Sk4f_toS32(swizzle_rb_if_bgra({ r[0], g[0], b[0], a[0] }));
+}
+
+
+template <typename Effect>
+static bool append_effect_stages(const Effect* effect, SkRasterPipeline* pipeline) {
+    return !effect || effect->appendStages(pipeline);
+}
+
+
+std::unique_ptr<SkBlitter> SkRasterPipelineBlitter::Create(const SkPixmap& dst,
+                                                           const SkPaint& paint) {
+    if (!dst.info().gammaCloseToSRGB()) {
+        return nullptr;  // TODO: f16, etc.
+    }
+    if (paint.getShader()) {
+        return nullptr;  // TODO: need to work out how shaders and their contexts work
+    }
+
+    SkRasterPipeline shader, colorFilter, xfermode;
+    if (!append_effect_stages(paint.getColorFilter(), &colorFilter) ||
+        !append_effect_stages(paint.getXfermode(),    &xfermode   )) {
+        return nullptr;
+    }
+
+    std::unique_ptr<SkRasterPipelineBlitter> blitter(new SkRasterPipelineBlitter{
+        dst,
+        shader, colorFilter, xfermode,
+        SkColor4f::FromColor(paint.getColor()).premul(),
+    });
+
+    if (!paint.getShader()) {
+        blitter->fShader.append(constant_color, &blitter->fPaintColor);
+    }
+    if (!paint.getXfermode()) {
+        blitter->fXfermode.append(srcover);
+    }
+
+    return std::move(blitter);
+}
+
+void SkRasterPipelineBlitter::blitH(int x, int y, int w) {
+    auto dst = fDst.writable_addr(0,y);
+
+    SkRasterPipeline p;
+    p.extend(fShader);
+    p.extend(fColorFilter);
+    p.append(load_d_srgb, load_d_srgb_1, dst);
+    p.extend(fXfermode);
+    p.append(store_srgb, store_srgb_1, dst);
+
+    p.run(x, w);
+}
+
+void SkRasterPipelineBlitter::blitAntiH(int x, int y, const SkAlpha aa[], const int16_t runs[]) {
+    auto dst = fDst.writable_addr(0,y);
+    float coverage;
+
+    SkRasterPipeline p;
+    p.extend(fShader);
+    p.extend(fColorFilter);
+    p.append(load_d_srgb, load_d_srgb_1, dst);
+    p.extend(fXfermode);
+    p.append(lerp_constant_float, &coverage);
+    p.append(store_srgb, store_srgb_1, dst);
+
+    for (int16_t run = *runs; run > 0; run = *runs) {
+        coverage = *aa * (1/255.0f);
+        p.run(x, run);
+
+        x    += run;
+        runs += run;
+        aa   += run;
+    }
+}
+
+void SkRasterPipelineBlitter::blitMask(const SkMask& mask, const SkIRect& clip) {
+    if (mask.fFormat == SkMask::kBW_Format) {
+        // TODO: native BW masks?
+        return INHERITED::blitMask(mask, clip);
+    }
+
+    int x = clip.left();
+    for (int y = clip.top(); y < clip.bottom(); y++) {
+        auto dst = fDst.writable_addr(0,y);
+
+        SkRasterPipeline p;
+        p.extend(fShader);
+        p.extend(fColorFilter);
+        p.append(load_d_srgb, load_d_srgb_1, dst);
+        p.extend(fXfermode);
+        switch (mask.fFormat) {
+            case SkMask::kA8_Format:
+                p.append(lerp_a8, lerp_a8_1, mask.getAddr8(x,y)-x);
+                break;
+            case SkMask::kLCD16_Format:
+                p.append(lerp_lcd16, lerp_lcd16_1, mask.getAddrLCD16(x,y)-x);
+                break;
+            default: break;
+        }
+        p.append(store_srgb, store_srgb_1, dst);
+
+        p.run(x, clip.width());
+    }
+}
diff --git a/src/core/SkXfermode.cpp b/src/core/SkXfermode.cpp
index e91f53a6cc..9246568699 100644
--- a/src/core/SkXfermode.cpp
+++ b/src/core/SkXfermode.cpp
@@ -1420,6 +1420,14 @@ bool SkXfermode::IsOpaque(const SkXfermode* xfer, SrcColorOpacity opacityType) {
     return xfer->isOpaque(opacityType);
 }
 
+bool SkXfermode::appendStages(SkRasterPipeline* pipeline) const {
+    return this->onAppendStages(pipeline);
+}
+
+bool SkXfermode::onAppendStages(SkRasterPipeline*) const {
+    return false;
+}
+
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkXfermode)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkProcCoeffXfermode)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END