[xlib] howto create screenshots?

[Tomas Carnecky]

Tomas Carnecky wrote:
> I've seen that when my application runs as the only opengl application 
> on the system, I could get 20-30 fps, but as soon as I've started 
> another opengl app (cedega/wine World of Warcraft or even glxgears at 
> 300x300px), the framerate dropped down to 2-8 fps.

I've just done some tests and this came out:

with just glReadPixels into a 'GL_PIXEL_PACK_BUFFER_EXT', I can easily 
get ~500MiB/s which makes ~100fps.

If I add a memcpy(), to copy the image pixels into a (static) local 
buffer, the framerate drops down to ~60fps (300MiB/s).

if I start glxgears, the framerate drops down to 6-8 fps (30-40MiB/s), 
depending on how large the glxgears window is (300x300 up to fullscreen).

When I move the windows around (and both opengl apps are running) I can 
feel lags of about 0.5 sec, but the mouse stays always responsive as 
usual. If only the capture app is running, There are no lags.

I can post the source code of the application I've used to make these 
tests if anyone wants.

so far
tom