[PDF] Add support for xfermodes / blend modes.

[PDF] Add support for xfermodes / blend modes.

- Change SkGraphicState to track and set the blend mode (xfermode) for modes built in to PDF (non porter duff modes + src over).
- Add SkXfermode::asMode() to retrieve xfermode as an enum for non porter duff modes.
- Move SkXfermode.cpp around a bit to support asMode() -- Generally move utility functions toward the top of the file.
- Make SkPDFFormXObject an isolated transparency group, as it used for saveLayer, which draws on transparent, not the device background.
- Set the graphic state in drawDevice and drawBitmap in order to get the right xfermode and alpha.

Committed: http://code.google.com/p/skia/source/detail?r=774

[reed1, 2011-02-04 11:12:47]

1. Lets discuss separately reorganizing SkXfermode.cpp, and just add the new
virtuals in this CL. Combining the two makes it very hard to see what changes
are cosmetic, and what changes are part of the new feature. Also, the current
organization is somewhat deliberate, as it separates functionality of Xfermode
and SkProcCoeffXfermode (which perhaps should be in a separate impl file).

2. Lets add a unittest (skia/trunk/tests) for the new method.

[Steve VanDeBogart, 2011-02-04 18:27:09]

On 2011/02/04 11:12:47, reed1 wrote:
> 1. Lets discuss separately reorganizing SkXfermode.cpp, and just add the new
> virtuals in this CL. Combining the two makes it very hard to see what changes
> are cosmetic, and what changes are part of the new feature. Also, the current
> organization is somewhat deliberate, as it separates functionality of Xfermode
> and SkProcCoeffXfermode (which perhaps should be in a separate impl file).

I didn't just move the file around for fun :-).  asMode() uses gProcCoeffs.  In
order to keep SkProcXfermode::asMode with the other SkProcXfermode methods,
gProcCoeffs needs to be declared or defined first.  I could add declarations for
all the stuff I moved, but it seemed better to move it.

Everything in the diff is just lines moving within the file (no other changes)
except for the two new instances of the asMode method.

> 2. Lets add a unittest (skia/trunk/tests) for the new method.

Done.

[reed1, 2011-02-05 21:46:37]

I should have studied your changes more closely. Sorry for the delay.

LGTM