Add SkRasterPipeline support to SkModeColorFilter.

The shader leaves its color in r,g,b,a, so to implement this color filter, we move {r,g,b,a} into {dr,dg,db,da}, then load the filter's color in {r,g,b,a}, then apply the xfermode as usual.

I've left a note about how we could sometimes cut a stage for some xfermodes.  Similarly we really only need to move_src_dst instead of swap_src_dst, but it seemed handy and less error prone to do a full two way swap.  As usual, we can always circle back and fine-tune these things if we want.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3243
CQ_INCLUDE_TRYBOTS=master.client.skia:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD-Trybot

Change-Id: I928c0fb25236eb75cf238134c6bebb53af5ddf07
Reviewed-on: https://skia-review.googlesource.com/3243
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Matt Sarett <msarett@google.com>

1 files changed, 17 insertions, 2 deletions

diff --git a/src/core/SkModeColorFilter.cpp b/src/core/SkModeColorFilter.cpp
index ba3b50d763..e165f69bcd 100644
--- a/src/core/SkModeColorFilter.cpp
+++ b/src/core/SkModeColorFilter.cpp
@@ -9,6 +9,7 @@
 #include "SkColorFilter.h"
 #include "SkColorPriv.h"
 #include "SkModeColorFilter.h"
+#include "SkRasterPipeline.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 #include "SkUtils.h"
@@ -59,11 +60,10 @@ void SkModeColorFilter::filterSpan(const SkPMColor shader[], int count, SkPMColo
 }
 
 void SkModeColorFilter::filterSpan4f(const SkPM4f shader[], int count, SkPM4f result[]) const {
-    SkPM4f            color = SkPM4f::FromPMColor(fPMColor);
     SkXfermodeProc4f  proc = SkXfermode::GetProc4f(fMode);
 
     for (int i = 0; i < count; i++) {
-        result[i] = proc(color, shader[i]);
+        result[i] = proc(fPM4f, shader[i]);
     }
 }
 
@@ -75,6 +75,7 @@ void SkModeColorFilter::flatten(SkWriteBuffer& buffer) const {
 void SkModeColorFilter::updateCache() {
     fPMColor = SkPreMultiplyColor(fColor);
     fProc = SkXfermode::GetProc(fMode);
+    fPM4f = SkPM4f::FromPMColor(fPMColor);
 }
 
 sk_sp<SkFlattenable> SkModeColorFilter::CreateProc(SkReadBuffer& buffer) {
@@ -83,6 +84,20 @@ sk_sp<SkFlattenable> SkModeColorFilter::CreateProc(SkReadBuffer& buffer) {
     return SkColorFilter::MakeModeFilter(color, mode);
 }
 
+bool SkModeColorFilter::onAppendStages(SkRasterPipeline* p) const {
+    // TODO: For some modes we can cut a stage by loading the fPM4f into dr,dg,db,da
+    // and applying the opposite xfermode, e.g. dst-in instead of src-in.
+    p->append(SkRasterPipeline::swap_src_dst);
+    p->append(SkRasterPipeline::constant_color, &fPM4f);
+
+    // TODO: This is ugly.  I think we want static SkXfermode::AppendStages(Mode).
+    if (auto xfermode = SkXfermode::Make(fMode)) {
+        return xfermode->appendStages(p);
+    }
+    p->append(SkRasterPipeline::srcover);
+    return true;
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 #if SK_SUPPORT_GPU
 #include "GrBlend.h"