Arithmetic xfermode stage.

src/effects/SkArithmeticMode.cpp

Index: src/effects/SkArithmeticMode.cpp
diff --git a/src/effects/SkArithmeticMode.cpp b/src/effects/SkArithmeticMode.cpp
index bf17bb833dac5989b426d27eb0d2a71aef34f427..b8aa36853a52d33a2fe7718eb6eb39bfb637a98a 100644
--- a/src/effects/SkArithmeticMode.cpp
+++ b/src/effects/SkArithmeticMode.cpp
@@ -8,6 +8,7 @@
 #include "SkArithmeticMode.h"
 #include "SkColorPriv.h"
 #include "SkNx.h"
+#include "SkRasterPipeline.h"
 #include "SkReadBuffer.h"
 #include "SkString.h"
 #include "SkUnPreMultiply.h"
@@ -29,6 +30,11 @@ public:
 
     void xfer32(SkPMColor[], const SkPMColor[], int count, const SkAlpha[]) const override;
 
+    bool onAppendStages(SkRasterPipeline* p) const override {
+        p->append(&Stage, this);
+        return true;
+    }
+
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkArithmeticMode_scalar)
 
@@ -39,6 +45,10 @@ public:
 #endif
 
 private:
+    static void SK_VECTORCALL Stage(SkRasterPipeline::Stage* st, size_t x,
+                                    Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                    Sk4f dr, Sk4f dg, Sk4f db, Sk4f da);
+
     void flatten(SkWriteBuffer& buffer) const override {
         buffer.writeScalar(fK[0]);
         buffer.writeScalar(fK[1]);
@@ -64,6 +74,26 @@ sk_sp<SkFlattenable> SkArithmeticMode_scalar::CreateProc(SkReadBuffer& buffer) {
     return SkArithmeticMode::Make(k1, k2, k3, k4, enforcePMColor);
 }
 
+void SK_VECTORCALL SkArithmeticMode_scalar::Stage(SkRasterPipeline::Stage* st, size_t x,
+                                                  Sk4f  r, Sk4f  g, Sk4f  b, Sk4f  a,
+                                                  Sk4f dr, Sk4f dg, Sk4f db, Sk4f da) {
+    auto self = st->ctx<const SkArithmeticMode_scalar*>();
+
+    const Sk4f k1 = self->fK[0],
+               k2 = self->fK[1],
+               k3 = self->fK[2],
+               k4 = self->fK[3];
+
+    r = k1*r*dr + k2*r + k3*dr + k4;
+    g = k1*g*dg + k2*g + k3*dg + k4;
+    b = k1*b*db + k2*b + k3*db + k4;
+    a = k1*a*da + k2*a + k3*da + k4;
+
+    // A later stage (clamp_01_premul) will pin and fEnforcePMColor for us.
+
+    st->next(x, r,g,b,a, dr,dg,db,da);
+}
+
 void SkArithmeticMode_scalar::xfer32(SkPMColor dst[], const SkPMColor src[],
                                  int count, const SkAlpha aaCoverage[]) const {
     const Sk4f k1 = fK[0] * (1/255.0f),