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Re: [css3-images] Linear gradients feedback

From: Dave Singer <singer@apple.com>
Date: Tue, 7 Sep 2010 20:27:03 -0700
Cc: "Tab Atkins Jr." <jackalmage@gmail.com>, Simon Fraser <smfr@me.com>, www-style list <www-style@w3.org>
Message-Id: <B3B854AA-1428-4DFB-A375-5FD0D16DBAED@apple.com>
To: fantasai <fantasai.lists@inkedblade.net>
actually I think I can be vastly clearer and also merge a whole load  
of suggestions/solutions.  and (the devil of people who used to be in  
research departments) generalize!  Try this:

Linear gradients.  These are drawn between two parallel lines (the  
'from' and 'to' lines), which are perpendicular to the gradient  
vector.  The intersection of the 'from' line and the gradient vector  
is less far along the vector than the intersection of the 'to' line.  
Each of these lines intersects the shape to be filled at the furthest  
possible extremity in the negative ('from') and positive ('to')  
directions along the gradient vector. (Which means we don't need to  
care about what the colors are before 'from' or after 'to' since they  
are not visible).

This generalizes your diagram for the 'to' line and uses it for the  
'from' line.  It also covers the degenerate cases where the furthest  
extremity is a line (0, 90, 180, and 270).  It fills from any corner  
or edge in any stable direction.

So, what fill cases does this *not* cover?  Well, those whose  
direction is determined by the geometry of the box that they are  
filling.  Since the box edges are vertical and horizontal (known  
directions), that leaves us with diagonals.

So, the next more general syntax is where the first argument is  
*either* a vector direction (number), or one of the four vectors bl- 
tr, tl-br, tr-bl, br-tl (t[op], b[ottom], l[eft], r[ight],  
obviously).  We only need the diagonals as a special case.

Ah, but we can deal with some of Elika's incisive question about the  
axis system in use, if we go for two arguments; then the gradient  
vector is defined by an angle relative to a base vector.  So, then we  
have a syntax with two arguments;
a base direction, specifying two corners
plus an angle relative to that base direction

the first argument is one of the possibilities: b-t, t-b, l-r, r-l, bl- 
tr, tl-br, tr-bl, br-tl
the second is an angle relative to that base vector
      the two combined give a computed gradient vector, and after  
that, everything falls out.

Transitions are then defined as interpolating between the computed  
gradient vectors, of course.

Now we only need one syntax and we can interpolate, and so on.

linear-gradient( base-direction, relative-angle, from-color, to-color,  
{stop%, stop-color}* )  where from-color is defined as from 0% and to- 
color is defined as to 100%.

cleaner? clearer?

Dave Singer
Multimedia and Software Standards, Apple

singer@apple.com
Received on Wednesday, 8 September 2010 03:27:52 GMT

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