Adding option to SkTileGrid for specifying border pixels.

Adding option to SkTileGrid for specifying border pixels.

The purpose of this patch is to make it possible for the chromium compositor to
generate a TileGrid structure that is better suited for scaled playback.
Committed: https://code.google.com/p/skia/source/detail?r=7680

[reed1, 2013-02-08 20:44:01]

I'm still not clear, by reading the comments in the public header, what
borderPixels is for, but perhaps thats fine for now.

lgtm

https://codereview.appspot.com/7300072/diff/3001/src/core/SkTileGrid.cpp
File src/core/SkTileGrid.cpp (right):

https://codereview.appspot.com/7300072/diff/3001/src/core/SkTileGrid.cpp#newc...
src/core/SkTileGrid.cpp:58: void SkTileGrid::search(const SkIRect& query,
SkTDArray<void*>* results) {
Unrelated to this CL, but how is it correct to do these truncating divides?

https://codereview.appspot.com/7300072/diff/3001/src/core/SkTileGridPicture.cpp
File src/core/SkTileGridPicture.cpp (right):

https://codereview.appspot.com/7300072/diff/3001/src/core/SkTileGridPicture.c...
src/core/SkTileGridPicture.cpp:19: fYTileCount = (height + tileHeight - 1) /
tileHeight;
SkASSERT(borderPixels >= 0) ?

[junov1, 2013-02-08 20:53:10]

On 2013/02/08 20:44:01, reed1 wrote:
> I'm still not clear, by reading the comments in the public header, what
> borderPixels is for, but perhaps thats fine for now.

I'm not sure how to explain it clearer without getting into the details of how
the chromium compositor works. Basically, tile size and tile stride do not match
in the compositor because it makes its tiles overlap by a certain number of
"border pixels".  The overlap is to avoid filtering artifacts when compositing
the tiles with transforms that break texel-to-pixel alignment.


> SkTDArray<void*>* results) {
> Unrelated to this CL, but how is it correct to do these truncating divides?

It is intended. The offsets are designed to make the truncation land in the
right spot. Limit conditions are validated by the unit test.

[reed1, 2013-02-08 21:12:13]

On 2013/02/08 20:53:10, junov1 wrote:
> On 2013/02/08 20:44:01, reed1 wrote:
> > I'm still not clear, by reading the comments in the public header, what
> > borderPixels is for, but perhaps thats fine for now.
> 
> I'm not sure how to explain it clearer without getting into the details of how
> the chromium compositor works. Basically, tile size and tile stride do not
match
> in the compositor because it makes its tiles overlap by a certain number of
> "border pixels".  The overlap is to avoid filtering artifacts when compositing
> the tiles with transforms that break texel-to-pixel alignment.

That description helped. Can you include part of that?

> 
> 
> > SkTDArray<void*>* results) {
> > Unrelated to this CL, but how is it correct to do these truncating divides?
> 
> It is intended. The offsets are designed to make the truncation land in the
> right spot. Limit conditions are validated by the unit test.

Perhaps a comment to this effect (whatever "right spot" means). I guess I want
it to be clear to the next person who edits this class what the intent of those
calculations is.