We currently do not special-case images in composited rasterization,
except for "directly composited images". These are composited <img> elements
that have no box decoration. In such cases we raster tiles at the intrinsic
scale of the image, and then scale those tiles as appropriate to the desired
scale. This has better-quality output, because images can look quite bad
when rastered at a smaller scale than the display scale.
This bug tracks plumbing and utilizing a raster scale setting for
cc::PictureLayer's that represent bare images, with no box decoration,
either via <img> or CSS background-image. This expands the use cases for
raster optimization to background-image, which is a very common way to
put images on web pages, especially involving sprites. It will also allow
us to remove PictureImageLayer.
Comment 1 by greensoc...@gmail.com
, Oct 4 2016