On Feb 12, 2009, at 4:22 PM, David Hyatt wrote: > On Feb 12, 2009, at 4:15 PM, Robert O'Callahan wrote: > >> On Fri, Feb 13, 2009 at 10:52 AM, Brad Kemper >> <brad.kemper@gmail.com> wrote: >> On Thu, Feb 12, 2009 at 12:22 PM, Robert O'Callahan <robert@ocallahan.org >> > wrote: >> On Fri, Feb 13, 2009 at 8:43 AM, Brad Kemper >> <brad.kemper@gmail.com> wrote: >> 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. >> >> That's the way to go. What you would do is construct a mask the >> size of the border-box whose alpha values in the border are the >> border-image's alpha values, and whose alpha values in the padding- >> box are 1. Then you apply blur to that mask (or not) >> >> ..and then clip out the padding-box from that, which ordinarily >> would not have a shadow from the border cast onto it (or does this >> shadow still get drawn behind the padding box?)... >> >> You build the element's mask, then you build the shadow, then you >> cut the mask out of the shadow by painting alpha=0 with the >> "source" Porter-Duff operator using the element's mask as the mask. >> The alpha values of the cut-out shadow will be the shadow alpha >> value multiplied by (1 - the mask alpha value). So no shadow will >> draw under the padding-box. > > It's a given that the shadow itself when offset will contain only > transparent pixels in its own offset padding are "Pre-blur" that is. Obviously blurring it could result in pixels in the offset padding area. ;) dave
Received on Thursday, 12 February 2009 22:25:38 UTC