W3C home > Mailing lists > Public > www-style@w3.org > September 2009

Re: Drop-Shadow proposal

From: Andrew Fedoniouk <news@terrainformatica.com>
Date: Sat, 12 Sep 2009 21:47:22 -0700
Message-ID: <4AAC795A.3060500@terrainformatica.com>
To: Brad Kemper <brad.kemper@gmail.com>
CC: www-style list <www-style@w3.org>
Brad Kemper wrote:
> On Sep 12, 2009, at 1:47 PM, Andrew Fedoniouk wrote:
>> Brad Kemper wrote:
>>> On Sep 9, 2009, at 12:57 PM, fantasai wrote:
>>>> ACTION: Brad to come up with full shadow proposal (not finalized, 
>>>> but to
>>>>         see where we're going)
>>> OK, and here it is:
>>> http://www.bradclicks.com/cssplay/drop-shadow/Drop-Shadow.html
>> Beautiful proposal :)
> Thank you.
>> But while reading it I've got a question about this image:
>> http://www.bradclicks.com/cssplay/drop-shadow/inner-shadow_example2.png
>> I see a [lighter] halo around "W3C" logo image. Question is: what kind 
>> of shadow is that?
> It's not really a halo, because it is only to the bottom right of the 
> logo...
> It gets a little tricky to try to explain the inner shadow through 
> semi-opaque openings, but I'll try: Notice how the 100% opaque dots 

> around the edge are actually completely cut-out holes that let all the 
> light in through them at an angle that is down and to the right? The 
> same thing is happening with the 100% opaque logo. It is a completely 
> cut-out hole, whereas the rest of the orange background is more like 
> looking through translucent paper which casts a shadow too. The logo is 
> cut completely out of that paper, so it lets light through at the same 
> angle as the shadow.
> I think the light from the dots looks even lighter because of the 
> contrast, but it is actually the same color of orange as what you see 
> near the logo.

I am not sure I understand physics here. See:
1) For shadow purposes that logo is treated as if it is transparent 
(punched) so it does not cast the shadow.
2) But at the same time it is rendered as if it is non-transparent.

Seems like contradictory for me.

And yet for practical purposes different UA will probably choose 
different non-Gaussian filters for producing such effects. I mean that 
you as an artist cannot rely on quality of the shadow. So in most cases 
you will end up drawing such complex effects in you favorite image 
editor. I am yet silent about computational complexity of producing such 
layers and rendering many of them with alpha... And animation on top of 

Is such effect so appealing/popular?

And yet yet about inner shadows versus just shadows ...

Inner (inset) shadow is different from just shadow only on
in borders area. Having things like border-image it is very easy
to produce image that can be used as such inset shadow.
Usefulness of inner shadows on text are a bit doubtful.
So I just do not understand why inset shadows are so needed.

I've mentioned once that it is just enough to extend @outline by
additional value 'glow' (which is needed by itself) and pair of
offsets (lengths) to achieve simple shadow effects.
DOM element is rendered off-screen and all non-transparent pixels are 
used to generate shadows.
So you can have shadowed text, etc. If the element has solid
background then it will be rendered as box with shadow.
In any case shadows has to be drawn on the same layer as outlines.

Andrew Fedoniouk.

Received on Sunday, 13 September 2009 04:47:51 UTC

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