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

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