[cairo] GL backend progress report

[Carl Worth]

On Dec 5, David Reveman wrote:
 > If you're wondering how the GL backend is coming along, here is some
 > info.

David, thanks for the update.

 > Cairo and gradients
 > Are there any plans on adding built in gradient functions to cairo?
 > Like:=20
 > cairo_gradient_linear (cr, x_from, y_from, x_to, y_to,=20
 >                        x_dst, y_dst, width, height)
 > 
 > cairo_gradient_radial (cr, ...)

Yes, I do want to add something to cairo to address this need. As
usual, I'm first investigating what support is provided by
PostScript. It allows for the following shading types:

	Function-based shadings
	Axial shadings
	Radial shadings
	Free-form Gouraud-shaded triangle meshes
	Lattice-form Gouraud-shaded triangle meshes
	Coons patch meshes
	Tensor-product patch meshes

I'd like to decide the simplest subset of those that would be
sufficient.

The function-based shading is initially the most appealing as it
provides the most generality. I started playing with an API for
function-based shading some time ago, and I've been hoping to get more
time to play with that again.

If we get that working we can then see how efficiently we can
implement it with the GL backend and then decide which other shading
types we might also want to add.

 > In the nearest future time will be spent on tackling the anti-aliasing
 > problem, making sure libglc works as well as possible on different
 > hardware and performance optimizations.

Sounds great! Keep up the good work. I haven't had a chance to bring
up a GLX-enabled server yet, but I hope to be able to play with this
code soon.

 > The bits can be found at http://www.cs.umu.se/~c99pnn/thesis/

Thanks. And please feel free to add whatever information you would
like to the wiki pages at http://cairographics.org It would be fine
with me if you wanted to host all of your current content there.

-Carl