Tweak SkPictureShader's tile semantics.

Tweak SkPictureShader's tile semantics.

Currently, the tile offset is added when drawing the picture. This might
have made a tiny bit of sense when the picture was always positioned at
origin, but with a picture cull rect offset things looks really strange.

For example, to specify a tile == the picture cull rect we have to pass
in [-cullrect.x, -cullrect.y, cullrect.width, cullrect.height]. Yikes.

(there's also a bug when not passing a tile, as we use a default tile
== cullrect but don't compensate for the above oddity)

This changes the semantics of the tile offset: it is now subtracted when
drawing the picture tile. As a consequence, one can pass in a tile equal
to the cull rect and get the expected behavior (same when not passing
a tile).

This will require a minor Blink change with the roll, as one client
works around the current behavior:
https://codereview.chromium.org/789503003

R=reed@google.com,robertphillips@google.com
BUG=440046
Committed: https://skia.googlesource.com/skia/+/a2bd24fd15378d0a25d79b4aa2d76dddc4cf564c

[reed1, 2014-12-08 18:12:32]

lgtm

[f(malita), 2014-12-08 19:10:20]

The CQ bit was checked by fmalita@chromium.org

[commit-bot: I haz the power, 2014-12-08 19:11:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/733203005/1

[commit-bot: I haz the power, 2014-12-08 19:13:31]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/a2bd24fd15378d0a25d79b4aa2d76dddc4cf564c

[robertphillips, 2014-12-08 20:01:31]

after the fact nits - ignore at will.

https://codereview.chromium.org/733203005/diff/1/gm/pictureshadertile.cpp
File gm/pictureshadertile.cpp (right):

https://codereview.chromium.org/733203005/diff/1/gm/pictureshadertile.cpp#new...
gm/pictureshadertile.cpp:61: protected:
rm these virtual keywords?

https://codereview.chromium.org/733203005/diff/1/gm/pictureshadertile.cpp#new...
gm/pictureshadertile.cpp:107:
fShaders[i].reset(SkShader::CreatePictureShader(picturePtr,
tab these guys over?

https://codereview.chromium.org/733203005/diff/1/gm/pictureshadertile.cpp#new...
gm/pictureshadertile.cpp:132: private:
can this be: static void draw_scene ?
Otherwise the call sites should be: this->drawScene.

[f(malita), 2014-12-08 20:11:37]

On 2014/12/08 20:01:31, robertphillips wrote:
> after the fact nits - ignore at will.
> 
> https://codereview.chromium.org/733203005/diff/1/gm/pictureshadertile.cpp
> File gm/pictureshadertile.cpp (right):
> 
>
https://codereview.chromium.org/733203005/diff/1/gm/pictureshadertile.cpp#new...
> gm/pictureshadertile.cpp:61: protected:
> rm these virtual keywords?
> 
>
https://codereview.chromium.org/733203005/diff/1/gm/pictureshadertile.cpp#new...
> gm/pictureshadertile.cpp:107:
> fShaders[i].reset(SkShader::CreatePictureShader(picturePtr,
> tab these guys over?
> 
>
https://codereview.chromium.org/733203005/diff/1/gm/pictureshadertile.cpp#new...
> gm/pictureshadertile.cpp:132: private:
> can this be: static void draw_scene ?
> Otherwise the call sites should be: this->drawScene.

Thanks & sorry for rushing the CL in. Will land a followup.