Re: [gradients] basics

On Nov 8, 2009, at 8:50 AM, Simon Fraser wrote:

>>> 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.
>>
>> I don't understand how this is unclear.  If these properties have
>> undefined interactions with images lacking intrinsic sizes, then the
>> problem lies in CSS2.1.  It is not appropriate to define that
>> treatment here.
>
> I see that <http://www.w3.org/TR/css3-background/#the-background- 
> size> etc. describe behavior when lacking intrinsic size. I stand  
> corrected.
>
> Making gradients always have no intrinsic size does prevent one  
> possible effect an author may desire: generating a gradient image of  
> a particular size, and then having that tiled over the background.

Right. I think this is a fairly essential assumption of the proposal,  
and not one that I would change either. Because there is no intrinsic  
size or aspect ratio, the default interaction with 'background-image'  
is that the gradient is scaled to the dimensions of the background  
positioning area.

If you actually want the gradient scaled to some other dimensions, you  
can use 'background-size' to do so. Then you can use 'background- 
repeat' to tile the gradient. Which is why you don't need the gradient  
function itself to have a way to repeat the gradient inside itself.

Any UA that supports 'background-repeat', 'background-size', and Tab's  
'linear-gradient()' should support tiling a properly sized gradient  
with 'background-repeat'. What Gecko does that goes beyond this is to  
adjust the tiling so that the gradients in each tile line up with each  
other. Thus, if you had a 30deg gradient, the tiles of 'background- 
repeat' are not in rows and columns as they normally are, but  
presumably shift each column (or row?) so that the colors of the  
gradient in each tile will line up with its neighbor. Although, that  
doesn't precisely describe how something like 'repeat-x' would work  
with a gradient that includes, say, a 10deg gradient or even a top- 
left to lower-right gradient.

That is kind of nice behavior, even though it seems like a somewhat  
uncommon need. Perhaps we could eventually add a note to 'background- 
repeat' to explain how to tile generated images like gradients that  
can have a more seamless joining of tiles as with Gecko.