image-orientation feature set and grammar tweaks

Hi all,

I'm working on implementing the 'image-orientation' property at Mozilla, for inclusion in some future version of Firefox. The initial implementation is nearly done at this point. What I've implemented so far is the CSS Level 4 version of 'image-orientation', plus the 'flip' feature that Tab Atkins describes in this email:

http://lists.w3.org/Archives/Public/www-style/2011Dec/0003.html

I felt that it made sense to support this since 'from-image' requires that we be able to display any EXIF orientation anyway.

The grammar in that email is as follows:

> image-orientation: from-image | [ <angle>? flip? ]

The grammar I've used in the implementation is this:

> image-orientation: from-image | flip | <angle> flip?

The meaning is that 'flip' on its own is equivalent to '0deg flip'. I require the angle to always appear before the 'flip' since the rotation always happens before the flip; this makes the syntax nicely mirror the semantics.

In my implementation, flipping is always done horizontally, rather than in the inline direction. I felt this made more sense; I know there are uses for flipping an image according to the inline direction, but that feels like a different feature to me.

I'd love to hear any feedback you may have. Also, are there any other implementations of this in the works so far? From what I can tell this feature was only partially completed in WebKit and was removed from Blink.

Thanks,
- Seth Fowler