Re: [filter-effects] drop-shadow inset shadow

On Sat, Mar 30, 2013 at 7:28 AM, Dirk Schulze <dschulze@adobe.com> wrote:
> Hi,
>
> Currently the drop-shadow shorthand filter does not support inset shadows and the inset keyword (in comparison to box-shadow for instance). I wonder if this could be added to the spec and would like to hear implementers input.
>
> Most shorthands have the advantage that they can easily be HW accelerated. This already seems not always be the case for drop-shadow on some platforms. However,  I do not think that it is harder to implement inset shadow, even if it will be of course slower than other filters.
>
> Here is a short example how to use inset shadows with SVG Filters today[1]:
>
>                 <filter id="innershadow" x0="-50%" y0="-50%" width="200%" height="200%">
>                         <feGaussianBlur in="SourceAlpha" stdDeviation="2" result="blur"/>
>                         <feOffset dy="3" dx="3"/>
>                         <feComposite in2="SourceAlpha" operator="arithmetic"
>                                         k2="-1" k3="1" result="shadowDiff"/>
>                         <feFlood flood-color="black" flood-opacity="1"/>
>                         <feComposite in2="shadowDiff" operator="in"/>
>                         <feComposite in2="SourceGraphic" operator="over"/>
>                 </filter>
>
> Implementations could replace the inset shadow in the CSS string with an equivalent filter chain as above.
>
> Greetings,
> Dirk
>
> [1] http://ledrug.wordpress.com/2010/09/30/learning-svg-lesson-2/

+1, and it would also be nice to support spread, if that's possible to
do in filters.

~TJ