Deferred image generator subsetting

src/image/SkImage_Generator.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImage_Base.h"
 #include "SkBitmap.h"
-#include "SkCanvas.h"
 #include "SkData.h"
 #include "SkImageCacherator.h"
 #include "SkImagePriv.h"
 #include "SkPixelRef.h"
-#include "SkSurface.h"
 
 class SkImage_Generator : public SkImage_Base {
 public:
     SkImage_Generator(SkImageCacherator::Validator* validator)
         : INHERITED(validator->fInfo.width(), validator->fInfo.height(), validator->fUniqueID)
         , fCache(validator)
     {}
 
     virtual SkImageInfo onImageInfo() const override {
         return fCache.info();
@@ skipping 49 matching lines @@
 bool SkImage_Generator::getROPixels(SkBitmap* bitmap, CachingHint chint) const {
     return fCache.lockAsBitmap(bitmap, this, chint);
 }
 
 GrTexture* SkImage_Generator::asTextureRef(GrContext* ctx, const GrTextureParams& params,
                                            SkSourceGammaTreatment gammaTreatment) const {
     return fCache.lockAsTexture(ctx, params, gammaTreatment, this);
 }
 
 sk_sp<SkImage> SkImage_Generator::onMakeSubset(const SkIRect& subset) const {
-    // TODO: make this lazy, by wrapping the subset inside a new generator or something
-    // For now, we do effectively what we did before, make it a raster
+    SkASSERT(fCache.info().bounds().contains(subset));
+    SkASSERT(fCache.info().bounds() != subset);
 
-    const SkImageInfo info = SkImageInfo::MakeN32(subset.width(), subset.height(),
-                                                  this->alphaType());
-    auto surface(SkSurface::MakeRaster(info));
-    if (!surface) {
-        return nullptr;
-    }
-    surface->getCanvas()->clear(0);
-    surface->getCanvas()->drawImage(this, SkIntToScalar(-subset.x()), SkIntToScalar(-subset.y()),
-                                    nullptr);
-    return surface->makeImageSnapshot();
+    const SkIRect generatorSubset = subset.makeOffset(fCache.fOrigin.x(), fCache.fOrigin.y());
+    SkImageCacherator::Validator validator(fCache.fSharedGenerator, &generatorSubset);
+    return validator ? sk_sp<SkImage>(new SkImage_Generator(&validator)) : nullptr;
 }
 
 sk_sp<SkImage> SkImage::MakeFromGenerator(SkImageGenerator* generator, const SkIRect* subset) {
-    SkImageCacherator::Validator validator(generator, subset);
+    SkImageCacherator::Validator validator(SkImageCacherator::SharedGenerator::Make(generator),
+                                           subset);
 
     return validator ? sk_make_sp<SkImage_Generator>(&validator) : nullptr;
 }