Implement support for non-scale/translate CTM in image filters.

src/core/SkCanvas.cpp

Index: src/core/SkCanvas.cpp
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 8426f090ec5949653ab516ffca3f7d33a317c338..3a9b4ed39dfed6bf52a4f6cfe6898dab72ac4cba 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -113,11 +113,13 @@ struct DeviceCM {
     SkRasterClip        fClip;
     const SkMatrix*     fMatrix;
     SkPaint*            fPaint; // may be null (in the future)
+    SkMatrix            fStashedMatrix; // Original CTM; used by imageFilter at saveLayer time
 
     DeviceCM(SkBaseDevice* device, const SkPaint* paint, SkCanvas* canvas,
-             bool conservativeRasterClip)
+             bool conservativeRasterClip, const SkMatrix& stashedMatrix)
         : fNext(NULL)
         , fClip(conservativeRasterClip)
+        , fStashedMatrix(stashedMatrix)
     {
         if (NULL != device) {
             device->ref();
@@ -438,7 +440,8 @@ SkBaseDevice* SkCanvas::init(SkBaseDevice* device, InitFlags flags) {
     fMCRec = (MCRec*)fMCStack.push_back();
     new (fMCRec) MCRec(fConservativeRasterClip);
 
-    fMCRec->fLayer = SkNEW_ARGS(DeviceCM, (NULL, NULL, NULL, fConservativeRasterClip));
+    fMCRec->fLayer = SkNEW_ARGS(DeviceCM, (NULL, NULL, NULL, fConservativeRasterClip,
+                                fMCRec->fMatrix));
     fMCRec->fTopLayer = fMCRec->fLayer;
 
     fSurfaceBase = NULL;
@@ -899,6 +902,20 @@ void SkCanvas::internalSaveLayer(const SkRect* bounds, const SkPaint* paint, Sav
 #ifndef SK_SUPPORT_LEGACY_CLIPTOLAYERFLAG
     flags |= kClipToLayer_SaveFlag;
 #endif
+    SkLazyPaint lazyP;
+    SkImageFilter* imageFilter = paint ? paint->getImageFilter() : NULL;
+    SkMatrix matrix = fMCRec->fMatrix;
+    SkMatrix remainder;
+    SkSize scale;
+    if (imageFilter && !matrix.isScaleTranslate() && matrix.decomposeScale(&scale, &remainder)) {
+        this->resetMatrix();

[reed1, 2015/03/26 15:54:03]

these two calls for matrix changes are virtual, which we don't want to make
(esp. if we're in a picture-recorder).

[Stephen White, 2015/03/26 16:18:34]

Hmm -- they don't seem to be virtual on SkCanvas? At any rate, I was messing the
fMCRec->fMatrix directly before, and you asked me to change it. I must've
misunderstood -- what should I change it to?

+        this->scale(scale.width(), scale.height());
+        SkAutoTUnref<SkImageFilter> matrixFilter(SkImageFilter::CreateMatrixFilter(remainder, SkFilterQuality::kHigh_SkFilterQuality, imageFilter));

[reed1, 2015/03/26 15:54:03]

kLow might be more honest, since by definition remainder has rotation/skew which
we always leave to kLow (bilerp).

[Stephen White, 2015/03/26 16:18:34]

Done.

+        imageFilter = matrixFilter.get();
+        SkPaint* p = lazyP.set(*paint);
+        p->setImageFilter(imageFilter);
+        paint = p;
+    }
 
     // do this before we create the layer. We don't call the public save() since
     // that would invoke a possibly overridden virtual
@@ -907,7 +924,7 @@ void SkCanvas::internalSaveLayer(const SkRect* bounds, const SkPaint* paint, Sav
     fDeviceCMDirty = true;
 
     SkIRect ir;
-    if (!this->clipRectBounds(bounds, flags, &ir, paint ? paint->getImageFilter() : NULL)) {
+    if (!this->clipRectBounds(bounds, flags, &ir, imageFilter)) {
         return;
     }
 
@@ -952,7 +969,7 @@ void SkCanvas::internalSaveLayer(const SkRect* bounds, const SkPaint* paint, Sav
     }
 
     device->setOrigin(ir.fLeft, ir.fTop);
-    DeviceCM* layer = SkNEW_ARGS(DeviceCM, (device, paint, this, fConservativeRasterClip));
+    DeviceCM* layer = SkNEW_ARGS(DeviceCM, (device, paint, this, fConservativeRasterClip, matrix));
     device->unref();
 
     layer->fNext = fMCRec->fTopLayer;
@@ -1005,6 +1022,9 @@ void SkCanvas::internalRestore() {
             // reset this, since internalDrawDevice will have set it to true
             fDeviceCMDirty = true;
         }
+        if (layer->fPaint && layer->fPaint->fImageFilter) {

[reed1, 2015/03/26 15:54:03]

the check seems a little fragile, since it somehow knows the predicate being
used in internalSave. I think an explicit flag in the layer, or just always
copying it, would be clearer.

[Stephen White, 2015/03/26 16:18:34]

Done.

+            fMCRec->fMatrix = layer->fStashedMatrix;
+        }
         SkDELETE(layer);
     }
 }