add backdrop option to SaveLayerRec

src/core/SkCanvas.cpp

 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapDevice.h"
 #include "SkCanvas.h"
 #include "SkCanvasPriv.h"
@@ skipping 462 matching lines @@
              */
             SkPaint tmp;
             tmp.setImageFilter(fPaint->getImageFilter());
             tmp.setXfermode(fPaint->getXfermode());
             SkRect storage;
             if (rawBounds) {
                 // Make rawBounds include all paint outsets except for those due to image filters.
                 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()
         }
 
         if (SkDrawLooper* looper = paint.getLooper()) {
             void* buffer = fLooperContextAllocator.reserveT<SkDrawLooper::Context>(
                     looper->contextSize());
             fLooperContext = looper->createContext(canvas, buffer);
             fIsSimple = false;
         } else {
@@ skipping 620 matching lines @@
         fMCRec->fRasterClip.setRect(ir);
     }
 
     if (intersection) {
         *intersection = ir;
     }
     return true;
 }
 
 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;
 }
 
 int SkCanvas::saveLayer(const SkRect* bounds, const SkPaint* paint, SaveFlags flags) {
     if (gIgnoreSaveLayerBounds) {
         bounds = nullptr;
     }
     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;
 }
 
 int SkCanvas::saveLayerPreserveLCDTextRequests(const SkRect* bounds, const SkPaint* paint) {
     unsigned flags = kARGB_ClipLayer_SaveFlag | kPreserveLCDText_PrivateSaveFlag;
     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
 
     // do this before we create the layer. We don't call the public save() since
     // that would invoke a possibly overridden virtual
     this->internalSave();
 
     fDeviceCMDirty = true;
 
@@ skipping 40 matching lines @@
             newDev = SkBitmapDevice::Create(createInfo.fInfo, surfaceProps);
             if (nullptr == newDev) {
                 SkErrorInternals::SetError(kInternalError_SkError,
                                            "Unable to create device for layer.");
                 return;
             }
             forceSpriteOnRestore = true;
         }
         device = newDev;
     }
+    device->setOrigin(ir.fLeft, ir.fTop);
 
-    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();
 
     layer->fNext = fMCRec->fTopLayer;
     fMCRec->fLayer = layer;
     fMCRec->fTopLayer = layer;    // this field is NOT an owner of layer
 }
 
 int SkCanvas::saveLayerAlpha(const SkRect* bounds, U8CPU alpha) {
@@ skipping 1790 matching lines @@
     }
 
     if (matrix) {
         canvas->concat(*matrix);
     }
 }
 
 SkAutoCanvasMatrixPaint::~SkAutoCanvasMatrixPaint() {
     fCanvas->restoreToCount(fSaveCount);
 }