[cairo] Projective transformations
Behdad Esfahbod
behdad at behdad.org
Wed Mar 21 06:42:59 PDT 2007
On Wed, 2007-03-21 at 07:00 -0400, Bill Spitzak wrote:
> Carl Worth wrote:
>
> > One problematic aspect is that a projective transformation would
> > destroy the current algorithm implementing path stroking, (which
> > currently pre-computes a pen that is assumed to be stable throughout
> > the stroke). So there's at least one unsolved problem there.
>
> It would not be a problem if the pen and font were fixed to the ctm at
> the moment they were specified, rather than changing with the ctm. This
> is in fact one of the primary reasons I want this change.
>
> The result you are suggesting is not very useful, as it can be
> duplicated by drawing on a flat surface and then perspective
> transforming that image, and in fact that is probably the only practical
> way to implement it. Far more interesting is to be able to draw with a
> pen and font that does not change size with distance and remains
> parallel to the screen, which has the added benefit that it is quite
> easy to make the existing Cairo do this.
>
> PS: Choosing a font or line width when a perspective transform is in
> effect should choose the affine transform that would happen for x==y==0.
Good points. Maybe we can start up the lock-pen-width thread again.
Anyone volunteering to update the patch to current master?
Speaking of projective transformations, they make
cairo_transform_distance() obsolete.
--
behdad
http://behdad.org/
"Those who would give up Essential Liberty to purchase a little
Temporary Safety, deserve neither Liberty nor Safety."
-- Benjamin Franklin, 1759
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