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Re: [css3-images] linear-gradient keywords and angles are opposite

From: Brad Kemper <brad.kemper@gmail.com>
Date: Wed, 8 Jun 2011 11:02:30 -0700
Message-Id: <80310836-FEB3-4519-ACA0-C8D12512E0F0@gmail.com>
Cc: "Tab Atkins Jr." <jackalmage@gmail.com>, Brian Manthos <brianman@microsoft.com>, "www-style@w3.org" <www-style@w3.org>
To: Sylvain Galineau <sylvaing@microsoft.com>

On Jun 8, 2011, at 9:59 AM, Sylvain Galineau <sylvaing@microsoft.com> wrote:

> [Tab Atkins:] 
>> On Wed, Jun 8, 2011 at 4:27 AM, Brad Kemper <brad.kemper@gmail.com> wrote:
>>> On Jun 7, 2011, at 11:34 AM, Brian Manthos <brianman@microsoft.com>
>> wrote:
>>>> Paraphrasing [1]:
>>>> When specified via angle, the angle can be understood as both the
>>>> direction ("toward the <angle>") and the ending point ("ends at
>> <angle>").
>>>> Paraphrasing [2] and [3]:
>>>> When specified via keyword, the keyword can be understood as both
>>>> opposite direction ("away from the <keyword(s)>") and the starting
>>>> point ("starts at
>>>>  <keyword>").
>>>> Is it intentional that these two ways of specifying gradient-line are
>>>> opposite?
>>> I don't think they are. In [1], the angle determines the starting AND
>>> ending points. In [2] and [3], the ending point (and thus the
>>> direction) is determined by the starting point. I see no inconsistency.
>> This was brought up during the ftf, and I think it's a valid point.
>> In my head (and I expect in others'), when I think of what angle to use
>> for a gradient I do so by imagining a compass rose, with 0deg at the top,
>> 90deg to the right, etc.  I then set the gradient angle by choosing which
>> angle I want the gradient to point toward.
>> Similarly, if I imagine keywords, I do so with 'top' at the top, 'right'
>> at the right, etc.  Now, though, I have to reverse how I deal with my
>> mental image - if I want the gradient to point up, I don't choose 'top', I
>> choose 'bottom'.
>> I'm not sure if this is an important enough disconnect to justify changing
>> the keywords, but we brainstormed it a bit at the ftf.  I don't think we
>> came up with any set of directional keywords that was sufficiently decent
>> to work as replacements, though.  If anyone has any suggestions, please
>> speak up!  The current front-runner is 'upward'/'rightward'/etc, which
>> isn't very good.
> Right; to expand on some of the feedback given at the f2f, it helps to think
> of animating or transitioning gradients in order to understand the disconnect.
> A safe - I think - working assumption is that CSS authors are very familiar
> with top/right/bottom/left and the spatial relationship between them.

Agree, and also the words used by border-radius to describe corners (top-right, top-left, bottom-right, bottom-left).

> The 
> question is whether the following would be natural to web authors: that 
> transitioning a linear gradient from 0deg to 90deg is equivalent on the keyword 
> side to going from bottom to left. 

Would it be? Or would 'bottom left' (not necessarily 45deg) be the halfway point of that transition?

> In other words, given North==0deg and East==90deg,

Is that a given now? Was it decided in Kyoto, without me there to voice my opposition? I haven't seen the transcripts yet. I still find it counter-intuitive. It also means I can't use the prefixed gradients with degrees in live style sheets, even experimentally to gain author experience, because there will be no graceful degradation for those using slightly older browsers. And old versions only go away very slowly. 

Likewise, all of the many CSS gradient editors out there which produce a style sheet full of prefixed 'linear-gradient' and '-webkit-gradient' with degrees will have to be changed, and include a note about how the gradients will be completely different in slightly older browsers. And if we change the meaning of the keywords, then even more editors will need changing (including those with -ms-filter support, which only use keyword direction). In that case, IE6 would be supported, but existing versions of Firefox would not. 

> should transitioning from
> North to East be doable by transitioning from top to right ? I think many would 
> answer this question in the affirmative. (And would love to see a poll on the
> question similar to the one done for the bearing angle issue).

Maybe that would be a good question if we were using the keywords 'North' and 'East'. But we are not. Transitioning from 90deg (straight up) to left (meaning "from left to right") is perfectly reasonable. 

> That top is a starting point but 0deg an end point is inconsistent; the inconsistency
> is hard to justify and even more confusing once animations are involved.

Why is 0deg only an end point? The angle is the same along the entire path. 
Received on Wednesday, 8 June 2011 18:03:15 UTC

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