Re: gEDA-user: Building the PCB+GL branch [WAS: Re: Open GL survey (for PCB)]

[Peter Clifton <pcjc2@xxxxxxxxx>]

On Wed, 2009-01-28 at 19:59 -0500, Dan McMahill wrote:

> without looking at the code, is it feasible without major pain to have 
> GL be a runtime selection?

I was thinking I'd split out the HID vtable callbacks into GTK / GL
versions, and #ifdef the HID setup.

Since the HID vtable can (I think) modified at run-time, I don't see why
we couldn't swap the rendering functions.

The main difficulty would be ensuring that the GC state for both the GDK
and GL drawing are kept set up.

GDK / X11 needs GC setting up. GL needs fbconfigs / GLXVisuals
selecting. We'd of course need to make having failed picking up the
correct GLX visual non-fatal.

> Here's why I ask.  I *routinely* run the 
> same binary on the same computer but with drastically different 
> displays.  On one day I might be at the computer running the program and 
> have access to the modern display hardware that gave 1300 FPS for that 
> glxgears demo but then I might use vnc to connect to that same machine 
> later and have not GLX support.

I tried it from my laptop (albeit on a fast university network), remote
X11 forwarded. I had to force the GL library to pick an indirect
rendering mode (sends commands via the wire to the X server, rather than
talking to the hardware), but I was _amazed_ at how fast it ran.

It wasn't noticeably slower than on my local PC. (Same for gschem,
including vicious dragging of entire schematics). The only parts which
were slow.. were the GTK dialogs.

(Testing gschem on a different computer via X11 gave really poor panning
performance though.. I guess it might have been falling back on some of
the cairo rendering (possibly via the network, right to the client app).

> Should I expect a speed improvement with GLX or just cool stuff like 
> layer transparency?  I suspect that's a feature that won't take much use 
> before I say "how did I live without this?".

It is faster, and transparent ;)

Ok.. I got the feeling it wasn't as snappy (dare I say slower?) than GDK
rendering for small designs, but for big complex stuff, you're looking
at say, 2-3fps -> 20fps speed change (plucking some vaguely remembered
numbers out of my head).

DJ tested it, and IIRC got similar speed-ups over Lesstif.


Go on.. take it for a test-drive, you know you want to ;)

-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)



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