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Re: [gradients] basics

From: Simon Fraser <smfr@me.com>
Date: Sat, 07 Nov 2009 17:41:34 -0800
Cc: www-style <www-style@w3.org>
Message-id: <835D99AE-71E4-467B-90E4-8F39984B361C@me.com>
To: news@terrainformatica.com
On Nov 7, 2009, at 3:36 pm, Andrew Fedoniouk wrote:

> Reading this:
> http://dev.w3.org/csswg/css3-images/#gradients-
>
> The very first phrase:
>
> "A gradient is a browser-generated image specified entirely in CSS,  
> which consists of smooth fades between several colors."
>
> appears as technically incorrect.
>
> Common interpretation of the gradient in graphics: rule that defines  
> color progression or distribution of colors inside some figure.
>
> Filling of some image by gradient is just one of possible cases.
>
> This for example:
> http://www.terrainformatica.com/w3/ed-gradient.png
> is an example of equidistant gradient.
>
> I mean that insisting on gradient as such a "generated image" cuts  
> many
> useful cases upfront.
>
> As I said couple of times already:
> gradients belong to the value of 'background-color' attribute more  
> than to 'background-image'.

The current gradient proposals address the application of gradients to  
CSS images. This is not to say that these are the only types of  
gradients we would ever want in CSS; you could imagine border  
gradients, outline gradients, and perhaps even shadow gradients. But  
these would be separate properties, or new values for existing  
properties, which I don't believe would conflict with the current  
proposal.

In addition, starting with gradients in CSS images is more likely to  
result in implementations, since WebKit and Gecko already have support  
for image gradients.

Also, gradients are only one kind of generated image. You could also  
imagine solid-color images, image generators (e.g. checkerboard,  
perlin noise etc), and generating images by applying effects to one or  
more input images. "Generated images" are a powerful concept, so I  
think it makes sense to start there with gradients.

> If to think that gradient is such a background-image then we need to
> define how such an image is affected by say:
>
> background-size: ...;
> background-attachment: ... | fixed | local;
> background-repeat: ...;

You are correct. Gradient images have no intrinsic size, so the  
behavior of these properties needs to be specified. At one point Gecko  
used background-repeat as an indication that it should paint a  
repeating gradient, but that is not in Tab's current proposal.

> And second paragraph:
> "In many places this specification references a box, such ...."
> definitely requires more formal specification. E.g. "would be filled
> by an SVG image" is just sort of guess or appellation to
> reader's intuition.

Agreed, this could be improved.

Simon
Received on Sunday, 8 November 2009 01:42:20 GMT

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