add newImage API

src/image/SkImage.cpp

Index: src/image/SkImage.cpp
diff --git a/src/image/SkImage.cpp b/src/image/SkImage.cpp
index 1acff3e4ed5ff7bad77e7bc63643c5bda0f39974..9af9727cc32c884a4f94de8a913a902559884bf8 100644
--- a/src/image/SkImage.cpp
+++ b/src/image/SkImage.cpp
@@ -78,6 +78,22 @@ SkSurface* SkImage::newSurface(const SkImageInfo& info, const SkSurfaceProps* pr
     return as_IB(this)->onNewSurface(info, *props);
 }
 
+SkImage* SkImage::newImage(int newWidth, int newHeight, const SkIRect* subset,
+                           SkFilterQuality quality) const {
+    if (newWidth < 0 || newHeight < 0) {
+        return NULL;
+    }
+    if (subset && !SkIRect::MakeWH(this->width(), this->height()).contains(*subset)) {
+        return NULL;
+    }
+
+    if (NULL == subset && this->width() == newWidth && this->height() == newHeight) {
+        return SkRef(const_cast<SkImage*>(this));
+    }
+
+    return as_IB(this)->onNewImage(newWidth, newHeight, subset, quality);
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 
 static bool raster_canvas_supports(const SkImageInfo& info) {
@@ -110,3 +126,32 @@ bool SkImage_Base::onReadPixels(const SkImageInfo& dstInfo, void* dstPixels, siz
 
     return true;
 }
+
+SkImage* SkImage_Base::onNewImage(int newWidth, int newHeight, const SkIRect* subset,
+                                  SkFilterQuality quality) const {
+    const bool opaque = this->isOpaque();
+    const SkImageInfo info = SkImageInfo::Make(newWidth, newHeight, kN32_SkColorType,
+                                               opaque ? kOpaque_SkAlphaType : kPremul_SkAlphaType);

[scroggo, 2015/01/05 16:15:33]

If this image is unpremul, does this work properly? And is it deliberate that
the new SkImage is premul rather than unpremul?

[reed1, 2015/01/05 21:58:14]

This is the "base" implementation, which may change the alphatype (but in theory
now how the image actually draws). Future CLs (I hope) will be more optimal for
specific subclasses, where we can avoid "drawing" to create the subset.

[scroggo, 2015/01/05 22:12:02]

+1 to the more optimal subclass overrides.

In the meantime, won't this break for an unpremul image? (Or did you already add
drawing unpremul sources?)

[reed1, 2015/01/20 22:23:08]

unpremul : good point, have to think about that case...

+    SkAutoTUnref<SkSurface> surface(this->newSurface(info, NULL));
+    if (!surface.get()) {
+        return NULL;
+    }
+
+    SkRect src;
+    if (subset) {
+        src.set(*subset);
+    } else {
+        src = SkRect::MakeWH(SkIntToScalar(this->width()), SkIntToScalar(this->height()));
+    }
+
+    surface->getCanvas()->scale(newWidth / src.width(), newHeight / src.height());
+    surface->getCanvas()->translate(-src.x(), -src.y());
+
+    SkPaint paint;
+    paint.setXfermodeMode(SkXfermode::kSrc_Mode);
+    paint.setFilterQuality(quality);
+    surface->getCanvas()->drawImage(this, 0, 0, &paint);
+    return surface->newImageSnapshot();
+}
+
+