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[css3-images] radial-gradient issue raised by Brad

From: Brian Manthos <brianman@microsoft.com>
Date: Fri, 12 Aug 2011 23:28:43 +0000
To: "www-style@w3.org" <www-style@w3.org>
Message-ID: <9710FCC2E88860489239BE0308AC5D1711DB0B@TK5EX14MBXC264.redmond.corp.microsoft.com>
http://dev.w3.org/csswg/css3-images/#radial-gradients
# Brad suggests that we could drop the position/sizing arguments
# and just use background-position and background-size. This
# would force all non-background uses of radial gradient to be
# centered and box-filling. Is this acceptable or not?

The current grammar is:

<radial-gradient> = radial-gradient(
	[<'background-position'>,]? 
	[[
		[<shape> || <size>]
		|
		[<length> | <percentage>]{2}
	],]? 
	<color-stop>[, <color-stop>]+
)
<shape> = circle | ellipse
<size> = closest-side | closest-corner | farthest-side | farthest-corner | contain | cover


For a moment, let's ignore the first parameter and the stops.  Thus we have the following combinations:
1	circle closest-side = circle contain
2	circle closest-corner
3	circle farthest-side
4	circle farthest-corner = circle cover
5	ellipse closest-side = ellipse contain
6	ellipse closest-corner
7	ellipse farthest-side
8	ellipse farthest-corner = ellipse cover
9	<length> <length>
10	<length> <percentage>
11	<percentage> <length>
12	<percentage> <percentage>

As I understand it, the proposed grammar is:

<radial-gradient> = radial-gradient(
	[<bg-position>,]? 
	[<bg-size>,]?
	<color-stop>[, <color-stop>]+
)
<bg-size> = [ <length> | <percentage> | auto ]{1,2} | cover | contain

Again, ignoring the first parameter and the stops, the following combinations are available:
i	<length>
ii	<length> <length>
iii	<length> <percentage>
iv	<length> auto
v	<percentage>
vi	<percentage> <length>
vii	<percentage> <percentage>
viii	<percentage> auto
ix	auto
x	auto <length>
xi	auto <percentage>
xii	auto auto
xiii	cover
xiv	contain

My initial thoughts of new syntax vs. old:
A. [+1] Old has 16, new has 14. 
B. [+2] Syntaxes 'i' and 'v' are added functionality, and potentially convenient.
C. [-6] I'm unclear on the meaning or value of having the auto parameter (iv, viii, ix, x, xi, xii).
D. [-1] No ability to distinguish ellipse vs. circle in cover (xiii vs 4, 8).
E. [-1] No ability to distinguish ellipse vs. circle in contain (xiv vs 1, 5).
F. [-2] Lost functionality for closest-corner (2, 6).
G. [-2] Lost functionality for farthest-side (3, 7).

Tally that up: -9.

I strongly prefer the current syntax to the proposal.
Received on Friday, 12 August 2011 23:29:12 GMT

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