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Re: gEDA-user: pcjc2 tessellation

On Mon, 2011-05-16 at 21:38 +1000, Russell Shaw wrote:

> Hi,
> I've looked in cairo before but never much got the hang of it
> in detail.

Its complex code implementing some hard to understand algorithms!

> One thing i'm eternally conflicted with is relying on video-card
> hardware that is closed source.

PCB+GL works very nicely on Intel graphics HW, with completely a open
source driver stack. It works even better on Nvidia ;)

> If you just generate pixels from scanline rendering in software,
> this can be done directly from a list of arbitrarily intersecting
> lines without requiring the bentley-ottmann polygon generator step.
> You generate the whole window pixmap yourself and send that to the
> screen.
> Using this, i could avoid openGL. However, if an open hardware
> accelerated openGL came along i was happy with, then i would need
> to use the bentley-ottmann step to generate polygons, but i don't
> understand that bit of code in detail, even though i've read the
> paper. If i understood it in detail, then i could look closer at
> how pcjc2 works and maybe improve something.

I don't throw GL polygons, I still use the Bentley-Ottman step, as you
can see. GL polygon primitives require convex, hole free polygons only,
and our are not guaranteed to be.

Some clever people are doing more complex polygon rasterisation in GL
shaders I believe.

Best wishes,

Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,

Tel: +44 (0)7729 980173 - (No signal in the lab!)
Tel: +44 (0)1223 748328 - (Shared lab phone, ask for me)

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