Add subsets to SkImageGenerator and SkImageCacherator .

src/core/SkPictureImageGenerator.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 "SkImageGenerator.h"
 #include "SkCanvas.h"
 #include "SkMatrix.h"
 #include "SkPaint.h"
 #include "SkPicture.h"
 #include "SkSurface.h"
 #include "SkTLazy.h"
 
 class SkPictureImageGenerator : SkImageGenerator {
 public:
     static SkImageGenerator* Create(const SkISize&, const SkPicture*, const SkMatrix*,
                                     const SkPaint*);
 
 protected:
     bool onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes, SkPMColor ctable[],
                      int* ctableCount) override;
 #if SK_SUPPORT_GPU
-    GrTexture* onGenerateTexture(GrContext*, SkImageUsageType) override;
+    GrTexture* onGenerateTexture(GrContext*, SkImageUsageType, const SkIRect*) override;
 #endif
 
 private:
     SkPictureImageGenerator(const SkISize&, const SkPicture*, const SkMatrix*, const SkPaint*);
 
     SkAutoTUnref<const SkPicture> fPicture;
     SkMatrix                      fMatrix;
     SkTLazy<SkPaint>              fPaint;
 
     typedef SkImageGenerator INHERITED;
@@ skipping 45 matching lines @@
 SkImageGenerator* SkImageGenerator::NewFromPicture(const SkISize& size, const SkPicture* picture,
                                                    const SkMatrix* matrix, const SkPaint* paint) {
     return SkPictureImageGenerator::Create(size, picture, matrix, paint);
 }
 
 ///////////////////////////////////////////////////////////////////////////////////////////////////
 
 #if SK_SUPPORT_GPU
 #include "GrTexture.h"
 
-GrTexture* SkPictureImageGenerator::onGenerateTexture(GrContext* ctx, SkImageUsageType usage) {
+GrTexture* SkPictureImageGenerator::onGenerateTexture(GrContext* ctx, SkImageUsageType usage,
+                                                      const SkIRect* subset) {
+    const SkImageInfo& info = this->getInfo();
+    SkImageInfo surfaceInfo = subset ? info.makeWH(subset->width(), subset->height()) : info;
+
     //
     // TODO: respect the usage, by possibly creating a different (pow2) surface
     //
     SkAutoTUnref<SkSurface> surface(SkSurface::NewRenderTarget(ctx,
                                                                SkSurface::kYes_Budgeted,
-                                                               this->getInfo()));
+                                                               surfaceInfo));
     if (!surface.get()) {
         return nullptr;
     }
+
+    SkMatrix matrix = fMatrix;
+    if (subset) {
+        matrix.postTranslate(-subset->x(), -subset->y());
+    }
     surface->getCanvas()->clear(0); // does NewRenderTarget promise to do this for us?
-    surface->getCanvas()->drawPicture(fPicture, &fMatrix, fPaint.getMaybeNull());
+    surface->getCanvas()->drawPicture(fPicture, &matrix, fPaint.getMaybeNull());
     SkAutoTUnref<SkImage> image(surface->newImageSnapshot());
     if (!image.get()) {
         return nullptr;
     }
     return SkSafeRef(image->getTexture());
 }
 #endif