Re: [CSSWG] Minutes and Resolutions 2009-02-04: box-shadow and border-image

On Thu, Feb 12, 2009 at 9:54 AM, David Hyatt <hyatt@apple.com> wrote:

>
> Rather than suppressing the shadow, what about using the border-image as a
> mask when deciding how to draw the shadow?  In theory it should be possible
> to intelligently draw a more complex shadow for a border-image object.
>
> dave
>

This would be my second choice, if a compromise is really needed. Why?
Because it creates new questions about the author's intent that could
otherwise be dealt with directly by the author when he crafts the shadows
himself in an image editor. So, if you generated dynamically generated the
shadow based on the image, in order to have a viable fallback, then you have
these issues:

1. How to deal with soft image edges, where there is variable opacity?
Currently, WebKit seems to clip shadows to the vector edge of the border
box, and not draw them behind areas of variable opacity (such as
backgrounds). It seems like for a raster image that was 50% opaque, it would
have draw the shadow behind the whole image at 50% of its normal opacity. Or
do you set some sort of threshold on images of varying opacity, and just
draw a hard inner edge at 50% and not draw shadows for any pixels more
transparent than that? Any of those choices may or may not be what the
author wants. Setting the shadow in the image himself provides more options.

2. If I am crafting the image and shadows myself, I can create parts of the
image that glow like lights and don't cast any shadow, and other parts that
do cast a shadow. Dynamically generated images don't give me that option.

3. Currently, box-shadows without the 'inset' keyword do not cast shadows
upon the padding box. Would this still be the case when an image abutted the
padding box? For consistency, I would say it shouldn't, and for many designs
I would not want it to, but it's a question to be answered, and may
complicate the implementation.

By the way, I am more ambivelant about how inset shadows should work in
regard to image-shadow. They are much less an edge/border effect, and more
of padding-box effect against the background. Putting an inset shadow on a
complex border is much different than putting an inset shadow on a padding
box. I am inclined to think that  inset shadows should not be supressed and
should not be dynamically drawn inside the images of the image-border.