allow imagefilter to manage CTM decomposition

src/core/SkImageFilter.cpp

 /*
  * Copyright 2012 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 "SkImageFilter.h"
 #include "SkImageFilterCacheKey.h"
 
@@ skipping 312 matching lines @@
     if (!this->isColorFilterNode(filterPtr)) {
         return false;
     }
     if (nullptr != this->getInput(0) || (*filterPtr)->affectsTransparentBlack()) {
         (*filterPtr)->unref();
         return false;
     }
     return true;
 }
 
+bool SkImageFilter::onCanHandleAffine() const {

[Stephen White, 2016/04/25 14:09:34]

Wouldn't it be simpler to have (non-virtual) canHandleAffine do the recursion,
and make onCanHandleAffine non-recursive? That would keep the subclasses
simpler. Is there a node which needs to control the recursion beyond "I can't
handle affine transforms; abort"?

[reed1, 2016/04/25 14:13:35]

Good idea! See follow-on CL https://codereview.chromium.org/1915943002/

+    bool hasInputs = false;
+
+    const int count = this->countInputs();
+    for (int i = 0; i < count; ++i) {
+        SkImageFilter* input = this->getInput(i);
+        if (input) {
+            if (!input->canHandleAffine()) {
+                return false;
+            }
+            hasInputs = true;
+        }
+    }
+    // We return true iff we had 1 or more inputs, and all of them can handle affine.
+    // If we have no inputs, or 1 or more of them do not handle affine, then we return false.

[Stephen White, 2016/04/25 14:09:34]

Why would a null input imply we can't handle affine transforms? This just means
we're using the input primitive, which is pretty common.

+    return hasInputs;
+}
+
 bool SkImageFilter::applyCropRect(const Context& ctx, const SkIRect& srcBounds,
                                   SkIRect* dstBounds) const {
     SkIRect temp = this->onFilterNodeBounds(srcBounds, ctx.ctm(), kForward_MapDirection);
     fCropRect.applyTo(temp, ctx.ctm(), this->affectsTransparentBlack(), dstBounds);
     // Intersect against the clip bounds, in case the crop rect has
     // grown the bounds beyond the original clip. This can happen for
     // example in tiling, where the clip is much smaller than the filtered
     // primitive. If we didn't do this, we would be processing the filter
     // at the full crop rect size in every tile.
     return dstBounds->intersect(ctx.clipBounds());
@@ skipping 211 matching lines @@
 
 SK_DECLARE_STATIC_ONCE_PTR(SkImageFilter::Cache, cache);
 SkImageFilter::Cache* SkImageFilter::Cache::Get() {
     return cache.get([]{ return SkImageFilter::Cache::Create(kDefaultCacheSize); });
 }
 
 void SkImageFilter::PurgeCache() {
     Cache::Get()->purge();
 }