Re: [Lib2geom-devel] Impossible to correctly scale LPE stitch subcurves?

[<Jea...@ma...>]

Hi!
I think that when trying to apply transform to an object having a path
effect, the transform should go into a "tranform" attribute.

Maybe the result of a path effect could be a group containing the output.
I think this would "solve" the problem, but this would also open the way
to more sophisticated outputs (?)

This also means that the transform attribute should be applied to the path
before the effect is computed, and removed from the output...

A better fix would be as follows: in the future, we can dream of multiple
effects applied one after the other. A transform is then simply a "linear
effect". Applying a new transform would simply mean insert a new
"transform effect" at the end of the list. You could navigate the list (or
even better, the tree as we might want to breaks things into components),
and the transformation would go at the current level...


> Please ignore my earlier mail because it was sent too soon. :-(
>
>
> Hello all,
>
> I am trying to fix transformation behavior for LPE (translation,
> scaling, rotation). I think I found a fundamental problem.
>
> Take Stitch Subcurves. Let's say we are stitching between a straight
> horizontal line, and a line with a horizontal and angled part:
> Because stitching is equidistant, the stitch start points would be:
>
>     ____o_____________o
>    /
>   /
>  /
> o
>
> o__________o___________o
>
> Note that the distance between stitch points is constant *along* the
> length of the line (not just the distance in the x-direction as this
> would not work in general)
>
> Now, after scaling in the Y direction:
>
>     __________________o
>    /
>    |
>    |
>    o
>    |
>    |
>    |
>   /
>  |
>  |
>  |
>  |
>  |
>  |
>  /
> o
>
> o__________o___________o
>
> Can you spot the problem? The 2nd line has shifted position along the
> line, because the distance along the angled part of the topline changed
> dramatically.
> For 'correct visual scaling' the result should have been:
>
>     ____o_____________o
>    /
>    |
>    |
>    |
>    |
>    |
>    |
>   /
>  |
>  |
>  |
>  |
>  |
>  |
>  /
> o
>
> o__________o___________o
>
> This however can never be the result of any stitch subpath, because the
> stitch start points are not equidistant (unless using the variance
> parameters and being very very lucky).
>
> I have attached an SVG for you to try with the latest inkscape SVN.
> Note that this problem exists regardless of the "scale width relative"
> setting.
>
> Thanks for any comment on how to "fix" this.
>
> kind regards,
> Johan
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