Add downsample from 8888 to 4444.

Add downsample from 8888 to 4444.

Extend SkBitmap::copyTo to copy from a source with
SkARGB_8888_Config to a destination bitmap with
SkARGB_4444_Config.

BUG=http://code.google.com/p/chromium/issues/detail?id=245774
R=reed@google.com

Committed: https://code.google.com/p/skia/source/detail?r=10621

[reed1, 2013-08-07 18:30:03]

Can we create a simple gm for this?

https://codereview.chromium.org/22350003/diff/1/src/core/SkBitmap.cpp
File src/core/SkBitmap.cpp (right):

https://codereview.chromium.org/22350003/diff/1/src/core/SkBitmap.cpp#newcode...
src/core/SkBitmap.cpp:1122: SkColor c =
SkUnPreMultiply::PMColorToColor(srcRow[x]);
Why the unpremultiply step? I think you can call this guy directly:

static inline SkPMColor16 SkDitherARGB32To4444(SkPMColor c, unsigned dither)

[scroggo, 2013-08-07 19:04:19]

> Can we create a simple gm for this?

Done.

https://codereview.chromium.org/22350003/diff/1/src/core/SkBitmap.cpp
File src/core/SkBitmap.cpp (right):

https://codereview.chromium.org/22350003/diff/1/src/core/SkBitmap.cpp#newcode...
src/core/SkBitmap.cpp:1122: SkColor c =
SkUnPreMultiply::PMColorToColor(srcRow[x]);
On 2013/08/07 18:30:03, reed1 wrote:
> Why the unpremultiply step? I think you can call this guy directly:
> 
> static inline SkPMColor16 SkDitherARGB32To4444(SkPMColor c, unsigned dither)

Overlooked that one. New patch calls the version that takes an SkPMColor.

[reed1, 2013-08-07 19:12:03]

lgtm

[scroggo, 2013-08-07 19:17:18]

Committed patchset #3 manually as r10621 (presubmit successful).