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

On Sat, Mar 30, 2013 at 8:28 AM, Brad Kemper <brad.kemper@gmail.com> wrote:

> On Mar 30, 2013, at 8:05 AM, "Tab Atkins Jr." <jackalmage@gmail.com>
> wrote:
>
> 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.
>
>
> I agree. I haven't tried Dirk's code, but I do hope filters can gain the
> ability to do inner shadows and spread. I don't know what primitives can be
> used to create the spread effect, though. It seems like it needs something
> like PhotoShop's 'maximize' and 'minimize' filters:
>
>
> http://help.adobe.com/en_US/photoshop/cs/using/WSfd1234e1c4b69f30ea53e41001031ab64-7970a.html#WSfd1234e1c4b69f30ea53e41001031ab64-795da
>

I think spread could be implemented by adding a circular input option to
feMorphology (currently it uses a square as its input area and produces
blocky results).