Add SaveLayer-Draw-Restore optimization.

This is like SkPictureRecord's remove_save_layer1 but works with all draw calls.

Interesting patterns removed:
  SaveLayer-DrawRect-Restore: Silk SKPs, desk_weather
  SaveLayer-DrawPath-Restore: desk_carsvg, desk_wowwiki, tabl_androidpolice
  SaveLayer-DrawPosTextH-Restore: tabl_android_police
There may be others, but I stopped looking.


BUG=skia:2378
R=robertphillips@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/269813010

git-svn-id: http://skia.googlecode.com/svn/trunk@14610 2bbb7eff-a529-9590-31e7-b0007b416f81

2 files changed, 72 insertions, 0 deletions

diff --git a/src/record/SkRecordOpts.cpp b/src/record/SkRecordOpts.cpp
index aaa611cf39..5b648f4215 100644
--- a/src/record/SkRecordOpts.cpp
+++ b/src/record/SkRecordOpts.cpp
@@ -16,6 +16,7 @@ using namespace SkRecords;
 void SkRecordOptimize(SkRecord* record) {
     // TODO(mtklein): fuse independent optimizations to reduce number of passes?
     SkRecordNoopSaveRestores(record);
+    SkRecordNoopSaveLayerDrawRestores(record);
     SkRecordAnnotateCullingPairs(record);
     SkRecordReduceDrawPosTextStrength(record);  // Helpful to run this before BoundDrawPosTextH.
     SkRecordBoundDrawPosTextH(record);
@@ -69,6 +70,73 @@ void SkRecordNoopSaveRestores(SkRecord* record) {
     while (apply(&pass, record));  // Run until it stops changing things.
 }
 
+// For some SaveLayer-[drawing command]-Restore patterns, merge the SaveLayer's alpha into the
+// draw, and no-op the SaveLayer and Restore.
+struct SaveLayerDrawRestoreNooper {
+    typedef Pattern3<Is<SaveLayer>, IsDraw, Is<Restore> > Pattern;
+
+    bool onMatch(SkRecord* record, Pattern* pattern, unsigned begin, unsigned end) {
+        SaveLayer* saveLayer = pattern->first<SaveLayer>();
+        if (saveLayer->bounds != NULL) {
+            // SaveLayer with bounds is too tricky for us.
+            return false;
+        }
+
+        SkPaint* layerPaint = saveLayer->paint;
+        if (NULL == layerPaint) {
+            // There wasn't really any point to this SaveLayer at all.
+            return KillSaveLayerAndRestore(record, begin);
+        }
+
+        SkPaint* drawPaint = pattern->second<SkPaint>();
+        if (drawPaint == NULL) {
+            // We can just give the draw the SaveLayer's paint.
+            // TODO(mtklein): figure out how to do this clearly
+            return false;
+        }
+
+        const uint32_t layerColor = layerPaint->getColor();
+        const uint32_t  drawColor =  drawPaint->getColor();
+        if (!IsOnlyAlpha(layerColor) || !IsOpaque(drawColor) || HasAnyEffect(*layerPaint)) {
+            // Too fancy for us.  Actually, as long as layerColor is just an alpha
+            // we can blend it into drawColor's alpha; drawColor doesn't strictly have to be opaque.
+            return false;
+        }
+
+        drawPaint->setColor(SkColorSetA(drawColor, SkColorGetA(layerColor)));
+        return KillSaveLayerAndRestore(record, begin);
+    }
+
+    static bool KillSaveLayerAndRestore(SkRecord* record, unsigned saveLayerIndex) {
+        record->replace<NoOp>(saveLayerIndex);    // SaveLayer
+        record->replace<NoOp>(saveLayerIndex+2);  // Restore
+        return true;
+    }
+
+    static bool HasAnyEffect(const SkPaint& paint) {
+        return paint.getPathEffect()  ||
+               paint.getShader()      ||
+               paint.getXfermode()    ||
+               paint.getMaskFilter()  ||
+               paint.getColorFilter() ||
+               paint.getRasterizer()  ||
+               paint.getLooper()      ||
+               paint.getImageFilter();
+    }
+
+    static bool IsOpaque(SkColor color) {
+        return SkColorGetA(color) == SK_AlphaOPAQUE;
+    }
+    static bool IsOnlyAlpha(SkColor color) {
+        return SK_ColorTRANSPARENT == SkColorSetA(color, SK_AlphaTRANSPARENT);
+    }
+};
+void SkRecordNoopSaveLayerDrawRestores(SkRecord* record) {
+    SaveLayerDrawRestoreNooper pass;
+    apply(&pass, record);
+}
+
+
 // Replaces DrawPosText with DrawPosTextH when all Y coordinates are equal.
 struct StrengthReducer {
     typedef Pattern1<Is<DrawPosText> > Pattern;
diff --git a/src/record/SkRecordOpts.h b/src/record/SkRecordOpts.h
index 6db7abca61..ad8c3bcfc7 100644
--- a/src/record/SkRecordOpts.h
+++ b/src/record/SkRecordOpts.h
@@ -17,6 +17,10 @@ void SkRecordOptimize(SkRecord*);
 // Turns logical no-op Save-[non-drawing command]*-Restore patterns into actual no-ops.
 void SkRecordNoopSaveRestores(SkRecord*);
 
+// For some SaveLayer-[drawing command]-Restore patterns, merge the SaveLayer's alpha into the
+// draw, and no-op the SaveLayer and Restore.
+void SkRecordNoopSaveLayerDrawRestores(SkRecord*);
+
 // Annotates PushCull commands with the relative offset of their paired PopCull.
 void SkRecordAnnotateCullingPairs(SkRecord*);