Re: Not rendering the buffer...

Edgar B wrote:

Sorry, at the end I got lost :S

Can you tell me what is the most basic solution I need to
implement to speed up the process? I know that if the window is
minimised then my program runs faster so I assumed that if I
implemented off screen rendering I would exploit that solution
because the problem of minimising the window is that I get
errors in the data collected with glReadPixels(). So someone
kindly suggested to use pbuffers and not using glReadPixels. Is
that a simple solution?

It rendering faster, because it renders nothing at all. The
vertices are processed, yes. But since the window is not visible
no fragments are rasterized, since the driver only lets
rasterize, what has the chance to get displayed. Rendering into
a minimized/hidden window is a waste of time, sine no pixel will
be there.


I am starting to read now about pbuffers, but is that the
simplest solution? the image processing operation i want to do
with the data obtained is just simple filtering operations
(Derivatives of gaussianas, etc)... I read that I could benefit
from pbuffers by performing operations in the GPU (like DoG
filters) which I assume is faster. Is that correct?

PBuffers are just a form of framebuffer. They are off screen
buffers, which means, the driver cannot make assumptions about
visibility. They will just render, what you deliver to them.
Other than the fact that they're offscreen they're pretty the
same like a normal framebuffer. The PBuffer itself will bring no
speedup, the performance is about the same like in a normal
window.

glReadPixels is the actual bottleneck: It forces the GPU to
syncronize out of order and to perform data conversion. Pixel
Buffer Objects are one way, another is to use simple
glCopyTexSubImage and glGetTexImage.

Wolfgang Draxinger
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