External SkImageGenerator API

Introduce an SkImageGenerator API to support the implementation of
externally-managed image decode and scale caches.

BUG=skia:5806
R=reed@google.com

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4720

Change-Id: Ibfe37af5471f78f28f88f9d5e80938882be1a344
Reviewed-on: https://skia-review.googlesource.com/4720
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Mike Reed <reed@google.com>

2 files changed, 44 insertions, 1 deletions

diff --git a/include/core/SkDevice.h b/include/core/SkDevice.h
index d521fec5ca..b0aac41d0b 100644
--- a/include/core/SkDevice.h
+++ b/include/core/SkDevice.h
@@ -255,7 +255,6 @@ protected:
 
     virtual GrContext* context() const { return nullptr; }
 
-protected:
     virtual sk_sp<SkSurface> makeSurface(const SkImageInfo&, const SkSurfaceProps&);
     virtual bool onPeekPixels(SkPixmap*) { return false; }
 
@@ -359,6 +358,10 @@ private:
         *const_cast<SkImageInfo*>(&fInfo) = fInfo.makeWH(w, h);
     }
 
+    bool drawExternallyScaledImage(const SkDraw& draw, const SkImage* image, const SkRect* src,
+                                   const SkRect& dst, const SkPaint& paint,
+                                   SkCanvas::SrcRectConstraint constraint);
+
     SkIPoint    fOrigin;
     SkMetaData* fMetaData;
     const SkImageInfo    fInfo;
diff --git a/include/core/SkImageGenerator.h b/include/core/SkImageGenerator.h
index 5e7214c7d1..2e34bfe2ce 100644
--- a/include/core/SkImageGenerator.h
+++ b/include/core/SkImageGenerator.h
@@ -19,6 +19,7 @@ class GrTexture;
 class GrTextureParams;
 class SkBitmap;
 class SkData;
+class SkImage;
 class SkImageGenerator;
 class SkMatrix;
 class SkPaint;
@@ -199,6 +200,40 @@ public:
     }
 
     /**
+     *  External generator API: provides efficient access to externally-managed image data.
+     *
+     *  Skia calls accessScaledPixels() during rasterization, to gain temporary access to
+     *  the external pixel data, packaged as a raster SkImage.
+     *
+     *  @param srcRect     the source rect in use for the current draw
+     *  @param totalMatrix full matrix in effect (mapping srcRect -> device space)
+     *  @param quality     the SkFilterQuality requested for rasterization.
+     *  @param rec         out param, expected to be set when the call succeeds:
+     *
+     *                       - fImage wraps the external pixel data
+     *                       - fSrcRect is an adjusted srcRect
+     *                       - fQuality is the adjusted filter quality
+     *
+     *  @return            true on success, false otherwise (error or if this API is not supported;
+     *                     in this case Skia will fall back to its internal scaling and caching
+     *                     heuristics)
+     *
+     *  Implementors can return pixmaps with a different size than requested, by adjusting the
+     *  src rect.  The contract is that Skia will observe the adjusted src rect, and will map it
+     *  to the same dest as the original draw (the impl doesn't get to control the destination).
+     *
+     */
+
+    struct ScaledImageRec {
+        sk_sp<SkImage>  fImage;
+        SkRect          fSrcRect;
+        SkFilterQuality fQuality;
+    };
+
+    bool accessScaledImage(const SkRect& srcRect, const SkMatrix& totalMatrix,
+                           SkFilterQuality quality, ScaledImageRec* rec);
+
+    /**
      *  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.
@@ -263,6 +298,11 @@ protected:
         return false;
     }
 
+    virtual bool onAccessScaledImage(const SkRect&, const SkMatrix&, SkFilterQuality,
+                                     ScaledImageRec*) {
+        return false;
+    }
+
     bool tryGenerateBitmap(SkBitmap* bm, const SkImageInfo* optionalInfo, SkBitmap::Allocator*);
 
 private: