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Re: [css3-background] box-shadow spread Multiple Choice Question

From: Brad Kemper <brad.kemper@gmail.com>
Date: Thu, 3 Jun 2010 17:05:29 -0700
Message-Id: <0FB0128E-838F-4A49-BA92-E8BF330B3460@gmail.com>
To: fantasai <fantasai.lists@inkedblade.net>
Cc: "www-style@w3.org" <www-style@w3.org>
Thank you, fantasai. This looks like an accurate list if the options,  
well explained. My order of preference is:

3a. In my tests, it actually looked better than 2a's truer offset, and  
if it is better for performance, so much the better.

2a. What I originally proposed.

3. I could live without the square corner requirement, even though I  
think it is pretty nice to have.

2. This one could actually be a raster effect, which may (?) make it  
mote acceleratable using a graphics card. It is also more likely what  
we'd have to do to bring spread to text-shadow (which I really hope we  
do, as it really proves it's worth even moreso for defining shadows  
for small finicky shapes).

1. Better than nothing, but it is not just distortion of elipses that  
suffers. It is scaling of elipses, too, because the scaling is not  
nearly enough. Consider the difference between the inside and outside  
radii of a border whose 'border-radius' measurement is close to its  
'border-width'. It is a big difference, with the inside at or near  
zero radius. Now consider how little you have to scale a typical  
element to get offsets of a few (or even several) pixels. Hardly any  
at all, so that the corners look very odd, not much at all like a real  


By the way, one other issue I have is that I don't think we need the  
word 'radius' in 'spread-radius' or even 'blur-radius'. It is kind of  
confusing, like saying 'offset-radius'. For blur, it is actually more  
like a diameter (of the blur brush being swept around the perimeter).

On Jun 3, 2010, at 3:56 PM, fantasai <fantasai.lists@inkedblade.net>  

> Given that
>  a) We made some very significant changes to CSS3 Backgrounds and  
> Borders
>     at the last F2F in March
>  b) We have not yet published a new official draft of the changes
>  c) The spec is already in CR, and therefore under Call for  
> Implementations
> I think it is imperative that we publish a new official Last Call  
> Working
> Draft asap.
> However! We still have an open issue, which is the behavior of box- 
> shadow's
> spread radius. There are a fixed number of options that have been  
> proposed.
> I will attempt to list them all:
>  1. Change spread to scale. The border-box shape is scaled up or down
>     in each dimension independently as necessary to increase its width
>     and height by the spread radius.
>     Note: If the width and height are not equal, this will distort the
>           shape.
>  2. Define spread as an outward outset normal to the original shadow
>     perimeter. (This is equivalent to a blur operation with a  
> threshold
>     operation that makes all non-transparent areas solid, and to  
> stroking
>     the perimeter of the border-box with a spread-radius-sized brush,
>     and is the strictest interpretation of a "spread" concept.)
>     Note: If the corner curves are not circular, the curves will no
>           longer be elliptical.
>     Note: If the shadow shape is contracted by more than the border- 
> radius,
>           round corners will become sharp.
>  2a. As for 2, but special-case border-radius: 0; to be a sharp- 
> cornered
>      rectangle.
>  3. Define spread as an outward outset of the box sides and a  
> corresponding
>     increase in the border-radii.
>     Note: If the corner curves are not circular, the distance  
> between the
>           original edge and the altered edge will not be constant.
>     Note: If the shadow shape is contracted by more than the border- 
> radius,
>           round corners will become sharp.
>  3a. As for 3, but special-case border-radius: 0; to be a sharp- 
> cornered
>      rectangle.
>  4. Define spread radius as outward normal outset, but allow  
> implementations
>     to approximate as per 3.
>  4a. As for 4, but special-case border-radius: 0; to be a sharp- 
> cornered
>      rectangle.
>  5. Drop spread radius from box-shadow.
> If I am missing your preferred option, please respond to this email  
> with an
> explanation of your preferred option.
> For details on concepts 2, 2a, 3, 3a, 4, and 4a, see the editor's  
> draft,
> which defines 4a, and thus has definitions for all the rest.
>  http://dev.w3.org/csswg/css3-background/#the-box-shadow
> If you think the above definitions are missing details... They are  
> missing
> details! Check the spec before complaining that they are missing.  
> I've added
> Brad's diagram and rearranged the text. If there are any outstanding  
> editorial
> or clarificational comments, let me know, preferably *before* we  
> discuss the
> topic on a telecon.
> Finally, I respectfully request that the chairs schedule ten minutes  
> of an
> upcoming telecon to conduct a straw poll, hopefully resolve the  
> issue, and
> approve publication of a css3-background LCWD. I also request that  
> if the
> discussion takes more than 8 minutes that we take option 5 and  
> publish. I
> understand that CSS2.1 is the top priority, but it is also urgent  
> that we
> officially publish the major changes we made to background-clip.
> Thanks~
> ~fantasai
Received on Friday, 4 June 2010 00:06:17 UTC

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