Fix LPE Powerstroke unintuitive / unstable / scale-dependent behavior

(visible for example with Catmul-Rom interpolation)
The instability happens when the width-value of adjacent control knots are the same.
It's technical, but here goes quickly. Knots are treated as [offset along path, width] points.
The offset along path is the segment number + the location along that segment.
The width is (may not be true, but for ease of discussion) in canvas coordinates.
This means that the interpolation is performed in a *very* compressed coordinate system, 
where the x-coords may range from, say, 0 to 5, and the y-coords from 0 to 2000. 
This is also scale dependent; changing the scale of your path and scaling all widths accordingly will change the look of your path.

The fix now does the interpolation in a scaled coordinate system. It stretches the x-coordinates to the arclength of the path.
After interpolation, the inverse scaling is applied to the interpolation result.

(bzr r13627)

0 files changed, 0 insertions, 0 deletions