add backdrop option to SaveLayerRec

src/core/SkCanvas.cpp

Index: src/core/SkCanvas.cpp
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 1d37e584193e83fa0979117b964cc6195ba15d77..f35ebf3230dc781b63b8a6278d773d723d4ea4d1 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -480,7 +480,7 @@ public:
                 rawBounds = &apply_paint_to_bounds_sans_imagefilter(*fPaint, *rawBounds, &storage);
             }
             (void)canvas->internalSaveLayer(rawBounds, &tmp, SkCanvas::kARGB_ClipLayer_SaveFlag,
-                                            SkCanvas::kFullLayer_SaveLayerStrategy);
+                                            SkCanvas::kFullLayer_SaveLayerStrategy, nullptr);
             fTempLayerForImageFilter = true;
             // we remove the imagefilter/xfermode inside doNext()
         }
@@ -1121,12 +1121,18 @@ bool SkCanvas::clipRectBounds(const SkRect* bounds, SaveFlags flags,
 }
 
 int SkCanvas::saveLayer(const SkRect* bounds, const SkPaint* paint) {
+    return this->saveLayerWithPickup(bounds, paint, nullptr);
+}
+
+int SkCanvas::saveLayerWithPickup(const SkRect* bounds, const SkPaint* paint,
+                                  SkImageFilter* pickup) {
     if (gIgnoreSaveLayerBounds) {
         bounds = nullptr;
     }
-    SaveLayerStrategy strategy = this->willSaveLayer(bounds, paint, kARGB_ClipLayer_SaveFlag);
+    SaveFlags flags = kARGB_ClipLayer_SaveFlag;
+    SaveLayerStrategy strategy = this->willSaveLayer(bounds, paint, flags);
     fSaveCount += 1;
-    this->internalSaveLayer(bounds, paint, kARGB_ClipLayer_SaveFlag, strategy);
+    this->internalSaveLayer(bounds, paint, flags, strategy, pickup);
     return this->getSaveCount() - 1;
 }
 
@@ -1136,7 +1142,7 @@ int SkCanvas::saveLayer(const SkRect* bounds, const SkPaint* paint, SaveFlags fl
     }
     SaveLayerStrategy strategy = this->willSaveLayer(bounds, paint, flags);
     fSaveCount += 1;
-    this->internalSaveLayer(bounds, paint, flags, strategy);
+    this->internalSaveLayer(bounds, paint, flags, strategy, nullptr);
     return this->getSaveCount() - 1;
 }
 
@@ -1145,9 +1151,17 @@ int SkCanvas::saveLayerPreserveLCDTextRequests(const SkRect* bounds, const SkPai
     return this->saveLayer(bounds, paint, (SaveFlags)flags);
 }
 
+static void draw_filter_into_device(SkBaseDevice* src, SkImageFilter* filter, SkBaseDevice* dst) {
+    SkCanvas c(dst);
+
+    const SkBitmap& srcBM = src->accessBitmap(false);
+    SkPaint p;
+    p.setImageFilter(filter);
+    c.drawBitmap(srcBM, 0, 0, &p);
+}
 
 void SkCanvas::internalSaveLayer(const SkRect* bounds, const SkPaint* paint, SaveFlags flags,
-                                 SaveLayerStrategy strategy) {
+                                 SaveLayerStrategy strategy, SkImageFilter* pickup) {
 #ifndef SK_SUPPORT_LEGACY_CLIPTOLAYERFLAG
     flags |= kClipToLayer_SaveFlag;
 #endif
@@ -1208,8 +1222,12 @@ void SkCanvas::internalSaveLayer(const SkRect* bounds, const SkPaint* paint, Sav
         }
         device = newDev;
     }
-
     device->setOrigin(ir.fLeft, ir.fTop);
+
+    if (pickup) {
+        draw_filter_into_device(fMCRec->fTopLayer->fDevice, pickup, device);
+    }
+
     DeviceCM* layer =
             new DeviceCM(device, paint, this, fConservativeRasterClip, forceSpriteOnRestore);
     device->unref();