add newImage API

src/image/SkImage.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkImagePriv.h"
@@ skipping 60 matching lines @@
     return NULL;
 }
 
 SkSurface* SkImage::newSurface(const SkImageInfo& info, const SkSurfaceProps* props) const {
     if (NULL == props) {
         props = &as_IB(this)->props();
     }
     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) {
     switch (info.colorType()) {
         case kN32_SkColorType:
             return kUnpremul_SkAlphaType != info.alphaType();
         case kRGB_565_SkColorType:
             return true;
         case kAlpha_8_SkColorType:
             return true;
@@ skipping 12 matching lines @@
     SkBitmap bm;
     bm.installPixels(dstInfo, dstPixels, dstRowBytes);
     SkCanvas canvas(bm);
 
     SkPaint paint;
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);
     canvas.drawImage(this, -SkIntToScalar(srcX), -SkIntToScalar(srcY), &paint);
 
     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();
+}
+
+