- From: Simon Fraser <smfr@me.com>
- Date: Tue, 27 Apr 2010 20:07:53 -0700
- To: fantasai <fantasai.lists@inkedblade.net>
- Cc: Sylvain Galineau <sylvaing@microsoft.com>, "www-style@w3.org" <www-style@w3.org>, Brian Manthos <brianman@microsoft.com>, Prabs Chawla <pchawla@microsoft.com>, Bert Bos <bert@w3.org>
On Apr 27, 2010, at 6:32 PM, fantasai wrote: > On 04/27/2010 05:31 PM, Sylvain Galineau wrote: >> Note: the WG has resolved to add box-shadow back to CSS3 Background& Borders [1] but as the >> editor's draft has not yet been updated, the following refers to the last document version for which >> it was defined [2]. >> >> According to the spec: >> >> # The fourth length is a spread radius. Positive values cause the shadow to grow in all directions by the >> # specified radius. Negative values cause the shadow to shrink. The shadow should not change shape >> # when a spread radius is applied: sharp corners should remain sharp. >> >> The requirement to not change the shape of the shadow seems very desirable from an author standpoint >> e.g. the large spread shadow of an oval-shaped box should be oval as well. >> >> This in turn implies scaling border-radii. One could. for instance, adjust the border-radii of the spread >> shadow by multiplying them by (1+((2 *spread-radius)/max(width, height)). Alternatively, one >> could attempt to obtain better fidelity by adjusting horizontal and vertical border radii independently. >> >> Given that preserving the overall shape is desirable and that the number of alternatives to achieve it should >> be fairly small, is this something implementors are interested in defining interoperably as part of this edit ? > > Hm, I didn't realize this was ambiguous. > > The simplest definition would be: > * When border-radius is zero, the shadow's radius is also zero. > * When border-radius is nonzero, the shadow's radii are increased (or decreased) > by the spread value. For circular curves, this effectively moves all points on > the curve outward by the same amount the sides move outward. > > However, that might not give a correct "spread" effect for ellipses: I suspect the > concept of pushing the curve "outward" does not work for elliptical curves because, > IIRC, elliptical tangents are not perpendicular to radii. (I suspect pushing the > curve outward--in the direction perpendicular to the curve at each point on the > curve--would result in something that is not an ellipse.) I don't understand what the 'spread' value is trying to do. Can someone post links to some pictures? Simon
Received on Wednesday, 28 April 2010 03:08:29 UTC