Adding an option to render only the shadow in SkDropShadowImageFilter

src/effects/SkDropShadowImageFilter.cpp

Index: src/effects/SkDropShadowImageFilter.cpp
diff --git a/src/effects/SkDropShadowImageFilter.cpp b/src/effects/SkDropShadowImageFilter.cpp
index 339e9557ad0a807db6183b6109abc892049941ab..0ba8b234b7977f2ed18823c5e6e68b9c43f40fed 100644
--- a/src/effects/SkDropShadowImageFilter.cpp
+++ b/src/effects/SkDropShadowImageFilter.cpp
@@ -17,14 +17,15 @@
 
 SkDropShadowImageFilter::SkDropShadowImageFilter(SkScalar dx, SkScalar dy,
                                                  SkScalar sigmaX, SkScalar sigmaY, SkColor color,
-                                                 SkImageFilter* input, const CropRect* cropRect,
-                                                 uint32_t uniqueID)
+                                                 ShadowMode shadowMode, SkImageFilter* input,
+                                                 const CropRect* cropRect, uint32_t uniqueID)
     : INHERITED(1, &input, cropRect, uniqueID)
     , fDx(dx)
     , fDy(dy)
     , fSigmaX(sigmaX)
     , fSigmaY(sigmaY)
     , fColor(color)
+    , fShadowMode(shadowMode)
 {
 }
 
@@ -36,6 +37,9 @@ SkDropShadowImageFilter::SkDropShadowImageFilter(SkReadBuffer& buffer)
     fSigmaX = buffer.readScalar();
     fSigmaY = buffer.readScalar();
     fColor = buffer.readColor();
+    fShadowMode = buffer.isVersionLT(SkReadBuffer::kDropShadowMode_Version) ?
+                  kDrawShadowAndForeground_ShadowMode :
+                  static_cast<ShadowMode>(buffer.readInt());
     buffer.validate(SkScalarIsFinite(fDx) &&
                     SkScalarIsFinite(fDy) &&
                     SkScalarIsFinite(fSigmaX) &&
@@ -50,7 +54,11 @@ SkFlattenable* SkDropShadowImageFilter::CreateProc(SkReadBuffer& buffer) {
     SkScalar sigmaX = buffer.readScalar();
     SkScalar sigmaY = buffer.readScalar();
     SkColor color = buffer.readColor();
-    return Create(dx, dy, sigmaX, sigmaY, color, common.getInput(0), &common.cropRect(), common.uniqueID());
+    ShadowMode shadowMode = buffer.isVersionLT(SkReadBuffer::kDropShadowMode_Version) ?
+                            kDrawShadowAndForeground_ShadowMode :
+                            static_cast<ShadowMode>(buffer.readInt());
+    return Create(dx, dy, sigmaX, sigmaY, color, shadowMode, common.getInput(0),
+                  &common.cropRect(), common.uniqueID());
 }
 
 void SkDropShadowImageFilter::flatten(SkWriteBuffer& buffer) const {
@@ -60,6 +68,7 @@ void SkDropShadowImageFilter::flatten(SkWriteBuffer& buffer) const {
     buffer.writeScalar(fSigmaX);
     buffer.writeScalar(fSigmaY);
     buffer.writeColor(fColor);
+    buffer.writeInt(static_cast<int>(fShadowMode));
 }
 
 bool SkDropShadowImageFilter::onFilterImage(Proxy* proxy, const SkBitmap& source,
@@ -98,7 +107,9 @@ bool SkDropShadowImageFilter::onFilterImage(Proxy* proxy, const SkBitmap& source
     canvas.translate(SkIntToScalar(srcOffset.fX - bounds.fLeft),
                      SkIntToScalar(srcOffset.fY - bounds.fTop));
     canvas.drawBitmap(src, offsetVec.fX, offsetVec.fY, &paint);
-    canvas.drawBitmap(src, 0, 0);
+    if (fShadowMode == kDrawShadowAndForeground_ShadowMode) {
+        canvas.drawBitmap(src, 0, 0);
+    }
     *result = device->accessBitmap(false);
     offset->fX = bounds.fLeft;
     offset->fY = bounds.fTop;
@@ -116,7 +127,11 @@ void SkDropShadowImageFilter::computeFastBounds(const SkRect& src, SkRect* dst)
     shadowBounds.offset(fDx, fDy);
     shadowBounds.outset(SkScalarMul(fSigmaX, SkIntToScalar(3)),
                         SkScalarMul(fSigmaY, SkIntToScalar(3)));
-    dst->join(shadowBounds);
+    if (fShadowMode == kDrawShadowAndForeground_ShadowMode) {
+        dst->join(shadowBounds);
+    } else {
+        *dst = shadowBounds;
+    }
 }
 
 bool SkDropShadowImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
@@ -130,7 +145,9 @@ bool SkDropShadowImageFilter::onFilterBounds(const SkIRect& src, const SkMatrix&
     ctm.mapVectors(&sigma, 1);
     bounds.outset(SkScalarCeilToInt(SkScalarMul(sigma.x(), SkIntToScalar(3))),
                   SkScalarCeilToInt(SkScalarMul(sigma.y(), SkIntToScalar(3))));
-    bounds.join(src);
+    if (fShadowMode == kDrawShadowAndForeground_ShadowMode) {
+        bounds.join(src);
+    }
     if (getInput(0) && !getInput(0)->filterBounds(bounds, ctm, &bounds)) {
         return false;
     }