Re: Issues with box-shadow spread

On Nov 30, 2010, at 9:15 PM, Behdad Esfahbod wrote:

> Hi all,
> Re:

I do have to update that picture, because the blur doesn't match the spec any more.

> In reading the CSS Backgrounds and Borders Module Level 3 W3C Working Draft 12
> June 2010 it occurred to me that the spread distance value of a box-shadow
> property is not correctly specified.
> Currently, the spec says that:
> """The fourth length is a spread distance. Positive values cause the shadow
> shape to expand in all directions by the specified radius."""
> However, in the Example XXVIII case, the "Spread Applied" contour does not
> follow the word of the spec.  If you check the lower left, if one was to
> follow the word of the spec, one would get a round corner, but what we see is
> a acute corner.  Ie. the lower-left corner of the Spread Applied contour is
> simply farther away from the lower-left corner of the box than the specified
> box-shadow spread value.

You must have missed this line:

"For corners with a zero border-radius, however, the corner must remain sharp—the operation is equivalent to scaling the shadow shape."

> What seems to be the *intent* of the spec is that, in Postscript terms, the
> spread box is the union of the box and the result of the stroke operation,
> with line-join=miter and an infinite miter-limit.  I can't describe it in a
> simpler way.  Negative values of the spread can be prescribed as the box with
> the stroke area removed instead of added.

That is more or less accurate in PostScript terms.

Received on Wednesday, 1 December 2010 05:35:54 UTC