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[css-shapes] Positioning <basic-shapes> summary, v2

From: Alan Stearns <stearns@adobe.com>
Date: Tue, 29 Oct 2013 13:50:07 -0700
To: www-style list <www-style@w3.org>
CC: fantasai <fantasai.lists@inkedblade.net>
Message-ID: <CE956D8F.32853%stearns@adobe.com>
Hey all,

I'm still looking for a resolution on how <basic-shape> syntax will be
handled. Fantasai and I have staked out our positions, and I don't think
either of us is moving. So it will probably help to get others' opinions.

The remaining issue is that the current draft uses x and y arguments for
positioning rectangles, circles and ellipses lifted from SVG Basic Shapes.
Fantasai would rather have these shapes use a <new-position> syntax, which
would be an improved version of the <position> syntax we use for
backgrounds and gradients.

One complication is that percentage values for SVG-style x and y are
interpreted differently than percentage values in the corresponding
components of the <new-position> syntax.

For background, the <basic-shape> syntax is used by both CSS and SVG in
the clip-path property of CSS Masking that just went to Last Call. This is
one of the reasons behind my stubbornness about keeping SVG-style syntax.

So my proposal (A) is to stay with the SVG-style syntax in the draft
today, and have that syntax use SVG interpretation of percentages:

rectangle ( x y w h [round <border-radius>] )
circle ( x y r )

Then at the next level of CSS Shapes, define a CSS-style syntax using a
new shape() function. This function would use the CSS interpretation of
percentages. Most of the arguments to this function would be rearrangable
and optional, but I'm omitting that here for brevity.

shape ( rectangle w h at <new-position> round <border-radius> )
shape ( circle r at <new-position> )

Fantasai's proposal (B) is to take what we would define for the shape()
function arguments, and use that for the <basic-shape> functions in the
current draft. These functions would use CSS interpretation of percentages.

rectangle ( w h at <new-position> round <border-radius> )
circle ( r at <new-position> )

The main drawback of A is duplication. The percentage issue only applies
to rectangles, not circles. So while rectangle() and shape(rectangle)
provide different functionality, circle() and shape(circle) are really
just two ways of saying the same thing.

The main drawback of B is that we lose SVG interpretation of percentages.

An additional drawback that applies somewhat to both approaches is that we
haven't yet defined <new-position> or exactly what the CSS-style rectangle
syntax should be. So I expect there will be some rounds of bikeshedding on
these topics. For A, I believe that results in the shape() function moving
to the next module level. For B, I believe that results in holding up the
current level until we reach agreement on these two items.

If you have an opinion on which approach to take, please reply.

Thanks,

Alan
Received on Tuesday, 29 October 2013 20:50:39 UTC

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