[css3-images] `image-resolution: span` and transformations.

Hi,

The snap keyword for image-resolution is defined as:

> If the "snap" keyword is provided, the computed ‘<resolution>’ (if
> any) is the specified resolution rounded to the nearest value that
> would map one image pixel to an integer number of device pixels. If
> the resolution is taken from the image, then the used intrinsic
> resolution is the image's native resolution similarly adjusted.

<resolution> values of image-resolution count image pixels per CSS 
pixels. snap is about image pixel per device pixels. CSS transforms can 
change the ratio between CSS pixels and device pixels[1].

Therefore, should `snap` be affected by transforms? If this is done at 
computed value time, do implementations need to have accumulated 
transformation matrices that early?


[1] Although I’m not sure that ratio still makes sense if the 
transformation has any skew component, a rotation component that is not 
a multiple of 90° around the Z axis, or a scale component that does not 
preserve aspect ratios.


-- 
Simon Sapin