cc: Stretch textures by .5 texels to prevent out of bounds sampling

cc: Stretch textures by .5 texels to prevent out of bounds sampling

This will allow us to revert texture clamping logic that reduces
the fill rate on some devices.

Instead of requiring us to clamp texture sampling, this patch
stretches textures by .5 texels past quad bounds to avoid
blending in invalid texels when GL_LINEAR filtering is used.

BUG=173480
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=182116

[brianderson, 2013-02-13 00:10:19]

https://codereview.chromium.org/12220133/diff/2015/cc/picture_layer_impl.cc
File cc/picture_layer_impl.cc (right):

https://codereview.chromium.org/12220133/diff/2015/cc/picture_layer_impl.cc#n...
cc/picture_layer_impl.cc:99: bool isPixelAligned = isAxisAlignedInTarget &&
drawTransform().IsIdentityOrIntegerTranslation();
Note: the logic here reflects the logic used to determine when to use GL_NEAREST
in gl_renderer.cc.

The scale is taken into account at a per-tiling level inside the
PictureLayerTiling::Iterator constructor.

https://codereview.chromium.org/12220133/diff/2015/cc/picture_layer_tiling.cc
File cc/picture_layer_tiling.cc (right):

https://codereview.chromium.org/12220133/diff/2015/cc/picture_layer_tiling.cc...
cc/picture_layer_tiling.cc:222: if (layerDeviceAlignment ==
LayerAlignedToDevice){
This is where the scale is taken into account.

Although we use GL_LINEAR when dest_to_content_scale > 1, we don't risk sampling
outside of texels bounds when texel:pixel ration > 1.

[enne (OOO), 2013-02-13 00:22:32]

lgtm

[commit-bot: I haz the power, 2013-02-13 00:29:48]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/brianderson@chromium.org/12220133/2015

[commit-bot: I haz the power, 2013-02-13 04:31:18]

Change committed as 182116