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[whatwg] Canvas line styles comments

From: Philip Taylor <excors+whatwg@gmail.com>
Date: Sat, 2 Feb 2008 22:20:45 +0000
Message-ID: <ea09c0d10802021420i289fa879md341f606a934d8dc@mail.gmail.com>
On 02/02/2008, Kristof Zelechovski <giecrilj at stegny.2a.pl> wrote:
> You considered the convex hull of the original lines to get that paradox;
> I had the stroke path segments in mind.
> (Stroke path segments are the path equivalent of the stroked curve
> when the stroke operator is not allowed and must be replaced by the fill
> operator).
> Each line corresponds to two parallel stroke path segments;
> two of them intersect and the other two get joint with an arc.
> One of the possible arcs is in the convex hull of those stroke path
> segments.

If the two lines are very short, their stroke paths will (if I
understand correctly) look like

           .-.
           | |
           | |
           | |
     .-----|-*-------.
     '-----|-|-------'
           | |
           | |
           '-'

where the * is the join point and the short lines are the two parallel
stroke path segments of each line. Then the convex hull is nearly a
square rotated by 45 degrees, like

           .-.
          /| |'-
        /  | |  '-
      /    | |    '-.
     .-----|-*-------.
     '-----|-|-------'
      '.   | |    .-'
        '-.| |_.-'
           '-'

and so an arc with radius lineWidth/2 from the rightmost point going
clockwise to the upmost point will not be contained entirely within
that nearly-square. So neither arc is within the convex hull.

-- 
Philip Taylor
excors at gmail.com
Received on Saturday, 2 February 2008 14:20:45 UTC

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