gEDA-user: )(

[Peter Clifton <pcjc2@xxxxxxxxx>]

On Thu, 2009-10-01 at 22:21 +0000, Frank Bergmann wrote:
> On Thu, 01 Oct 2009 23:22:14 +0200, Stefan Salewski wrote:
> 
> > Hope not annoying you, but if you followed this list very carefully the
> > last years (I did not
> 
> Me too. I am pretty new to this project.
> 
> > ) you may know that Peter C. is a very smart
> > software developer who has contributed much to gEDA and PCB project.
> 
> But I realized that already.
> 
> > So there will be good reasons for using OpenGL -- I can imagine
> > transparency and maybe 3D view.

Transparency, and a _huge_ win in rendering speed are the reasons for GL
over plain X rendering. cairo is pretty but slower than our old X
rendering.

> 3D view is pretty difficult for a 2D library...but its an "high level"
> abstraction providing basic graphic shapes and could be easier (?) to
> use as native OpenGL.

3D is a long way off - mainly due to lack of models. The GL stuff I'm
using is all projected flat, and used to accelerate drawing of objects
using triangles. (Although for round line-ends, having only triangles as
a primitive is no fun!)

The GL stencil buffer is used for fast sub-compositing (allowing
translucent layers without each line drawn showing).

This is an old screen-shot before I'd figured out how to get the
sub-compositing to work:

http://www2.eng.cam.ac.uk/~pcjc2/geda/pcb+gl.png

This shows it working (in the background to PCB's new DRC window).

http://www2.eng.cam.ac.uk/~pcjc2/geda/drc_for_real.png

For completeness.. the DRC window now has graphics:

http://www2.eng.cam.ac.uk/~pcjc2/geda/drc_for_real2.png

As an older (code no longer in existence) example, perspective like this
is not hard to achieve:

http://www2.eng.cam.ac.uk/~pcjc2/geda/gerbv_GL.png

(That IIRC, is cairo-rendered onto a texture, then stretched onto a
quad). I had that manoeverable on a 3D joystick. It was novel to play
with, but probably of limited practical use until we have more 3D models
to add to the scene.

(And models would be much harder than simple texture+quad+view matrix).

Best regards,

Peter C.




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