post apply non-scale transforms after imagefilters have run

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 178 matching lines @@
     values: they reflect the top of the save stack, but translated and clipped
     by the device's XY offset and bitmap-bounds.
 */
 struct DeviceCM {
     DeviceCM*           fNext;
     SkBaseDevice*       fDevice;
     SkRasterClip        fClip;
     SkPaint*            fPaint; // may be null (in the future)
     const SkMatrix*     fMatrix;
     SkMatrix            fMatrixStorage;
+    SkMatrix            fStashedMatrix; // original CTM; used by imagefilter in saveLayer
     const bool          fDeviceIsBitmapDevice;
 
     DeviceCM(SkBaseDevice* device, const SkPaint* paint, SkCanvas* canvas,
-             bool conservativeRasterClip, bool deviceIsBitmapDevice)
+             bool conservativeRasterClip, bool deviceIsBitmapDevice, const SkMatrix& stashed)
         : fNext(nullptr)
         , fClip(conservativeRasterClip)
+        , fStashedMatrix(stashed)
         , fDeviceIsBitmapDevice(deviceIsBitmapDevice)
     {
         if (nullptr != device) {
             device->ref();
             device->onAttachToCanvas(canvas);
         }
         fDevice = device;
         fPaint = paint ? new SkPaint(*paint) : nullptr;
     }
 
@@ skipping 442 matching lines @@
     fSaveCount = 1;
     fMetaData = nullptr;
 
     fClipStack.reset(new SkClipStack);
 
     fMCRec = (MCRec*)fMCStack.push_back();
     new (fMCRec) MCRec(fConservativeRasterClip);
 
     SkASSERT(sizeof(DeviceCM) <= sizeof(fDeviceCMStorage));
     fMCRec->fLayer = (DeviceCM*)fDeviceCMStorage;
-    new (fDeviceCMStorage) DeviceCM(nullptr, nullptr, nullptr, fConservativeRasterClip, false);
+    new (fDeviceCMStorage) DeviceCM(nullptr, nullptr, nullptr, fConservativeRasterClip, false,
+                                    fMCRec->fMatrix);
 
     fMCRec->fTopLayer = fMCRec->fLayer;
 
     fSurfaceBase = nullptr;
 
     if (device) {
         // The root device and the canvas should always have the same pixel geometry
         SkASSERT(fProps.pixelGeometry() == device->surfaceProps().pixelGeometry());
         device->onAttachToCanvas(this);
         fMCRec->fLayer->fDevice = SkRef(device);
@@ skipping 508 matching lines @@
 
 void SkCanvas::internalSaveLayer(const SaveLayerRec& rec, SaveLayerStrategy strategy) {
     const SkRect* bounds = rec.fBounds;
     const SkPaint* paint = rec.fPaint;
     SaveLayerFlags saveLayerFlags = rec.fSaveLayerFlags;
 
 #ifndef SK_SUPPORT_LEGACY_CLIPTOLAYERFLAG
     saveLayerFlags &= ~kDontClipToLayer_PrivateSaveLayerFlag;
 #endif
 
+    SkLazyPaint lazyP;
+    SkImageFilter* imageFilter = paint ? paint->getImageFilter() : NULL;
+    SkMatrix stashedMatrix = fMCRec->fMatrix;
+#ifndef SK_SUPPORT_LEGACY_IMAGEFILTER_CTM
+    SkMatrix remainder;
+    SkSize scale;
+    /*
+     *  ImageFilters (so far) do not correctly handle matrices (CTM) that contain rotation/skew/etc.
+     *  but they do handle scaling. To accommodate this, we do the following:
+     *
+     *  1. Stash off the current CTM
+     *  2. Decompose the CTM into SCALE and REMAINDER
+     *  3. Wack the CTM to be just SCALE, and wrap the imagefilter with a MatrixImageFilter that
+     *     contains the REMAINDER
+     *  4. Proceed as usual, allowing the client to draw into the layer (now with a scale-only CTM)
+     *  5. During restore, we process the MatrixImageFilter, which applies REMAINDER to the output
+     *     of the original imagefilter, and draw that (via drawSprite)
+     *  6. Unwack the CTM to its original state (i.e. stashedMatrix)
+     *
+     *  Perhaps in the future we could augment #5 to apply REMAINDER as part of the draw (no longer
+     *  a sprite operation) to avoid the extra buffer/overhead of MatrixImageFilter.
+     */
+    if (imageFilter &&
+        !stashedMatrix.isScaleTranslate() &&
+        stashedMatrix.decomposeScale(&scale, &remainder))
+    {
+        // We will restore the matrix (which we are overwriting here) in restore via fStashedMatrix
+        this->internalSetMatrix(SkMatrix::MakeScale(scale.width(), scale.height()));
+        SkPaint* p = lazyP.set(*paint);
+        p->setImageFilter(SkImageFilter::MakeMatrixFilter(remainder,
+                                                          SkFilterQuality::kLow_SkFilterQuality,

[Stephen White, 2016/04/20 18:39:34]

Blink currently uses High quality in SkiaImageFilterBuilder::buildTransform().
Won't using Low here cause a quality loss?

[reed1, 2016/04/20 19:42:50]

My thinking was that since we decompose the scale, the filter should just see
rotations etc, meaning that there should be minimal advantage to using something
fancier than bilerp (e.g. High or Medium). Additionally, those latter two cache
their labors, which will have zero value here, since we don't have a reliable
key for a saveLayer as src.

Are you ok if we try with Low, and examine the layout results, and see if they
are acceptable?

[Stephen White, 2016/04/20 21:19:32]

OK, let's give it a try.

+                                                          sk_ref_sp(imageFilter)));
+        imageFilter = p->getImageFilter();
+        paint = p;
+    }
+#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;
 
     SkIRect ir;
-    if (!this->clipRectBounds(bounds, saveLayerFlags, &ir, paint ? paint->getImageFilter() : nullptr)) {
+    if (!this->clipRectBounds(bounds, saveLayerFlags, &ir, imageFilter)) {
         return;
     }
 
     // FIXME: do willSaveLayer() overriders returning kNoLayer_SaveLayerStrategy really care about
     // the clipRectBounds() call above?
     if (kNoLayer_SaveLayerStrategy == strategy) {
         return;
     }
 
     bool isOpaque = SkToBool(saveLayerFlags & kIsOpaque_SaveLayerFlag);
@@ skipping 35 matching lines @@
             forceSpriteOnRestore = true;
         }
         device = newDev;
     }
     device->setOrigin(ir.fLeft, ir.fTop);
 
     if (rec.fBackdrop) {
         draw_filter_into_device(fMCRec->fTopLayer->fDevice, rec.fBackdrop, device, fMCRec->fMatrix);
     }
 
-    DeviceCM* layer =
-            new DeviceCM(device, paint, this, fConservativeRasterClip, forceSpriteOnRestore);
+    DeviceCM* layer = new DeviceCM(device, paint, this, fConservativeRasterClip,
+                                   forceSpriteOnRestore, stashedMatrix);
     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) {
     if (0xFF == alpha) {
         return this->saveLayer(bounds, nullptr);
@@ skipping 24 matching lines @@
 
     /*  Time to draw the layer's offscreen. We can't call the public drawSprite,
         since if we're being recorded, we don't want to record this (the
         recorder will have already recorded the restore).
     */
     if (layer) {
         if (layer->fNext) {
             const SkIPoint& origin = layer->fDevice->getOrigin();
             this->internalDrawDevice(layer->fDevice, origin.x(), origin.y(),
                                      layer->fPaint, layer->fDeviceIsBitmapDevice);
+            // restore what we smashed in internalSaveLayer
+            fMCRec->fMatrix = layer->fStashedMatrix;
             // reset this, since internalDrawDevice will have set it to true
             fDeviceCMDirty = true;
             delete layer;
         } else {
             // we're at the root
             SkASSERT(layer == (void*)fDeviceCMStorage);
             layer->~DeviceCM();
+            // no need to update fMCRec, 'cause we're killing the canvas
         }
     }
 }
 
 sk_sp<SkSurface> SkCanvas::makeSurface(const SkImageInfo& info, const SkSurfaceProps* props) {
     if (nullptr == props) {
         props = &fProps;
     }
     return this->onNewSurface(info, *props);
 }
@@ skipping 155 matching lines @@
     }
 
     this->checkForDeferredSave();
     fDeviceCMDirty = true;
     fCachedLocalClipBoundsDirty = true;
     fMCRec->fMatrix.preConcat(matrix);
 
     this->didConcat(matrix);
 }
 
+void SkCanvas::internalSetMatrix(const SkMatrix& matrix) {
+    fDeviceCMDirty = true;
+    fCachedLocalClipBoundsDirty = true;
+    fMCRec->fMatrix = matrix;
+}
+
 void SkCanvas::setMatrix(const SkMatrix& matrix) {
     this->checkForDeferredSave();
-    fDeviceCMDirty = true;
-    fCachedLocalClipBoundsDirty = true;
-    fMCRec->fMatrix = matrix;
+    this->internalSetMatrix(matrix);
     this->didSetMatrix(matrix);
 }
 
 void SkCanvas::resetMatrix() {
-    SkMatrix matrix;
-
-    matrix.reset();
-    this->setMatrix(matrix);
+    this->setMatrix(SkMatrix::I());
 }
 
 //////////////////////////////////////////////////////////////////////////////
 
 void SkCanvas::clipRect(const SkRect& rect, SkRegion::Op op, bool doAA) {
     this->checkForDeferredSave();
     ClipEdgeStyle edgeStyle = doAA ? kSoft_ClipEdgeStyle : kHard_ClipEdgeStyle;
     this->onClipRect(rect, op, edgeStyle);
 }
 
@@ skipping 1543 matching lines @@
 
 SkAutoCanvasMatrixPaint::~SkAutoCanvasMatrixPaint() {
     fCanvas->restoreToCount(fSaveCount);
 }
 
 #ifdef SK_SUPPORT_LEGACY_NEW_SURFACE_API
 SkSurface* SkCanvas::newSurface(const SkImageInfo& info, const SkSurfaceProps* props) {
     return this->makeSurface(info, props).release();
 }
 #endif