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Re: Gradient syntax proposal

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Fri, 14 Aug 2009 16:54:39 -0500
Message-ID: <dd0fbad0908141454q217d5217ie1e7152ac8da86ae@mail.gmail.com>
To: Brad Kemper <brad.kemper@gmail.com>
Cc: www-style list <www-style@w3.org>
On Fri, Aug 14, 2009 at 4:27 PM, Brad Kemper<brad.kemper@gmail.com> wrote:
> On Aug 14, 2009, at 1:33 PM, "Tab Atkins Jr." <jackalmage@gmail.com> wrote:
>> On Fri, Aug 14, 2009 at 3:01 PM, Brad Kemper<brad.kemper@gmail.com> wrote:
>>> On Aug 14, 2009, at 11:03 AM, "Tab Atkins Jr." <jackalmage@gmail.com>
>>> wrote:
>>>> I don't see why the color *has* to come first, still.  Leaving it as
>>>> it is, where you can specify them in either order.
>>> If you keep the ability to specify the starting point as a coordinate
>>> that
>>> could contain percentages or lengths, then it can be very confusing to
>>> have
>>> the first thing after be a percentage (or a length). Making the color as
>>> the
>>> first item of the pair prevents that. If we get rid of the coordinate
>>> stops
>>> then it's not s problem.
>> Alternate idea: bring back the functional syntax for this.  ^_^
>> "point(<bg-position) point(bg-position)" would work.  That way we're
>> not introducing a sometimes-comma, and the complex lengths/percentages
>> are clearly separated from the color-stops.
> Using xy points is really not neccesary when 0% is always a corner or side,
> and 100% is always it's opposite corner.

Indeed, but the whole purpose of the <bg-position> construction is to
allow gradients that start/end at points *not* on a corner or
side-center.  (Example 7 in my draft.)

>> I'm really not averse to requiring [<color> <percentage>?], I just
>> don't feel like restricting it unless necessary.
> It's not neccesary if we get rid of the measurements before the first stop,
> as I've suggested.

Not convinced yet that that's desirable.  The additional comma has
been removed at this point, though, and I've changed the separator
between the direction and color-stops to be / rather than a comma.
That should completely disambiguate things.

>>>> Also, leaving out <distance>.  Mixing percentages and distances brings
>>>> up the possibility (in fact, the certainty) of color-stops swapping
>>>> their order based on box size.  I don't think that's desirable.  The
>>>> only way around it would be to force the color-stops to be specified
>>>> in order, and say that out-of-order stops are treated the same as
>>>> same-position stops (they produce an instant transition from the first
>>>> specified to the last).  Would this be okay?
>>> I think it would be OK to have the starting and ending points as
>>> distances
>>> or percentages, and have either percentages-only or distances-only in
>>> between.
>> I thought about allowing distances for the start/end points, but this
>> produces an ambiguity.  Is 0%/100% defined by the first and last
>> color-stop, or by <direction>?  If the former, how does this work when
>> first/last color-stops have a %?
> Usually, 0% would always be a corner or side, and 100% would always be it's
> opposite. But... I think that maybe if the first and last are both fixed
> lengths with percentages between them, then they could become the new 0% and
> 100%. But only in that case and no others. If that's too complicated then
> just don't mix at all.


>>> Any distance that went beyond 100% would be clipped (unless we are
>>> seriously going to define "running into a side" as being 100%.
>> I can seriously see myself wanting to do "background:
>> linear-gradient(-45deg inner, silver, white)" on a long article, as a
>> little visual flourish that only affects the top of the block.
> It seems kind of unpredictable or difficult to imagine where that would
> stop. I think you'd want more control. Like this:
> background: linear-gradient(-45deg, silver 0, white 200px)
>> [snip]
>> You're trying
>> instead indicate how far from the *original ending-point* the new
>> ending-point should be.
> No I'm not. I'm measuring from the starting point to say where the ending
> point should be.

I'm not sure that it's useful to be able to say "push the starting
point this many pixels from the original location", but then "set the
ending-point to this new distance from the starting point".  The two
things aren't symmetrical now.  Better if we can specify someway that
the start should be x distance from the edge/corner, and the end
should be y distance from the edge/corner.

In other words, I want a gradient that goes left-to-right, but leaving
100px free on each edge.  I'm not sure how wide the box would be.  I
can't do this in your proposal - something like "linear-gradient(left
/ white 100px, silver 50%, white 100px)" would instead either do
nothing, or make an image with 100px of white, then 50px of
white->silver and 50px of silver->white, with white filling the rest.

I can do this with the <bg-position> construction, as
"linear-gradient(100px top to calc(100% - 100px) top / white, silver,

Received on Friday, 14 August 2009 21:55:35 UTC

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