API to support native scaling by image-generator

include/core/SkImageGenerator.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageGenerator_DEFINED
 #define SkImageGenerator_DEFINED
 
@@ skipping 134 matching lines @@
      *
      *  Regarding the GrTextureParams parameter:
      *
      *  If the context (the provided one or the generator's intrinsic one) determines that to
      *  support the specified usage, it must return a different sized texture it may,
      *  so the caller must inspect the texture's width/height and compare them to the generator's
      *  getInfo() width/height. For readback usage use GrTextureParams::ClampNoFilter()
      */
     GrTexture* generateTexture(GrContext*, const SkIRect* subset = nullptr);
 
+    struct SupportedSizes {
+        SkISize fSizes[2];
+    };
+
+    /**
+     *  Some generators can efficiently scale their contents. If this is supported, the generator
+     *  may only support certain scaled dimensions. Call this with the desired scale factor,
+     *  and it will return true if scaling is supported, and in supportedSizes[] it will return
+     *  the nearest supported dimensions.
+     *
+     *  If no native scaling is supported, or scale is invalid (e.g. scale <= 0 || scale > 1)
+     *  this will return false, and the supportedsizes will be undefined.
+     */
+    bool computeScaledDimensions(SkScalar scale, SupportedSizes*);

[msarett, 2015/11/30 21:24:26]

I remember that we wanted fSizes[0] to be smaller if possible and fSizes[1] to
be larger if possible?

It's probably fine not to mention this in the comments since I don't think the
initial implementations will behave this way anyway.

[reed1, 2015/11/30 21:29:19]

I'm not sure what "smaller" means anymore, since there are two values. I removed
that language on purpose, though happy to rethink about it.

+
+    /**
+     *  Scale the generator's pixels to fit into scaledSize.
+     *  This routine also support retrieving only a subset of the pixels. That subset is specified
+     *  by the following rectangle (in the scaled space):
+     *
+     *      subset = SkIRect::MakeXYWH(subsetOrigin.x(), subsetOrigin.y(),
+     *                                 subsetPixels.width(), subsetPixels.height())
+     *
+     *  If subset is not contained inside the scaledSize, this returns false.
+     *
+     *      whole = SkIRect::MakeWH(scaledSize.width(), scaledSize.height())
+     *      if (!whole.contains(subset)) {
+     *          return false;
+     *      }
+     *
+     *  If the requested colortype/alphatype in pixels is not supported,
+     *  or the requested scaledSize is not supported, or the generator encounters an error,
+     *  this returns false.
+     */
+    bool generateScaledPixels(const SkISize& scaledSize, const SkIPoint& subsetOrigin,
+                              const SkPixmap& subsetPixels);
+
+    bool generateScaledPixels(const SkPixmap& scaledPixels) {
+        return this->generateScaledPixels(SkISize::Make(scaledPixels.width(),
+                                                        scaledPixels.height()),
+                                          SkIPoint::Make(0, 0), scaledPixels);
+    }
+
     /**
      *  If the default image decoder system can interpret the specified (encoded) data, then
      *  this returns a new ImageGenerator for it. Otherwise this returns NULL. Either way
      *  the caller is still responsible for managing their ownership of the data.
      */
     static SkImageGenerator* NewFromEncoded(SkData*);
 
     /** Return a new image generator backed by the specified picture.  If the size is empty or
      *  the picture is NULL, this returns NULL.
      *  The optional matrix and paint arguments are passed to drawPicture() at rasterization
@@ skipping 27 matching lines @@
     virtual bool onGetPixels(const SkImageInfo& info, void* pixels, size_t rowBytes,
                              SkPMColor ctable[], int* ctableCount);
     virtual bool onGetYUV8Planes(SkISize sizes[3], void* planes[3], size_t rowBytes[3]);
     virtual bool onGetYUV8Planes(SkISize sizes[3], void* planes[3], size_t rowBytes[3],
                                  SkYUVColorSpace* colorSpace);
 
     virtual GrTexture* onGenerateTexture(GrContext*, const SkIRect*) {
         return nullptr;
     }
 
+    virtual bool onComputeScaledDimensions(SkScalar, SupportedSizes*) {
+        return false;
+    }
+    virtual bool onGenerateScaledPixels(const SkISize&, const SkIPoint&, const SkPixmap&) {
+        return false;
+    }
+
     bool tryGenerateBitmap(SkBitmap* bm, const SkImageInfo* optionalInfo, SkBitmap::Allocator*);
 
 private:
     const SkImageInfo fInfo;
     const uint32_t fUniqueID;
 
     // This is our default impl, which may be different on different platforms.
     // It is called from NewFromEncoded() after it has checked for any runtime factory.
     // The SkData will never be NULL, as that will have been checked by NewFromEncoded.
     static SkImageGenerator* NewFromEncodedImpl(SkData*);
 };
 
 #endif  // SkImageGenerator_DEFINED