[cairo] [PATCH 0/6 v0] RFC: Projective transformation

[Bryce Harrington]

On Fri, Nov 28, 2014 at 08:31:18PM -0800, Bryce Harrington wrote:
> This resurrects a patch proposed some years back for adding 2d
> projective transformation support to Cairo.  I've reviewed and updated
> the patch for the current codebase, and made a test demo to try it out.
> There's a bug that occurs on rotational transformations that I haven't
> figured out -- suggestions appreciated.
> 
> You might recall that this time last year there was a discussion here
> about 4x4 matrices in Cairo for doing more advanced 3d transformations.
> There were doubts expressed about whether that would stretch Cairo's
> focus too far.  However, 2d projective transformation requires only 2
> elements to added to Cairo's matrix support so perhaps is more
> in-scope.
> 
> I'll follow up with the demo program code.  This displays a simple
> geometry transformed using each of the different basic matrix operations
> along with the same including projective components for comparison.
> 
> In the demo program you can see the bug in the rotation transformation.
> Even without any projective transformation applied the rotation is
> behaving weirdly.  If the demo program is built against vanilla cairo,
> this bug does not occur.

Derek spotted the error and found a fix, and it all seems to be working
nicely now.  I'm not sure what to do about the ABI breakage, but I've
pushed the current projective transform work here if anyone wishes to
continue following the work:

  http://cgit.freedesktop.org/~bryce/cairo/log/?h=perspective-transform

Bryce