FBO object and measuring performance....

OpenGL OpenGL: Basic Coding
1

Hello,

I need some help understanding the following:

I have some scene which is heavily dependent on the fragment processor, ie: lots of fragments to process, using a custom shader program.

The rendering is setup as following:

  1. create an FBO of size NxN.
  2. render the scene into the FBO.
  3. display the FBO on a texmapped quad.

Now I would like to be able to see the effect of the FBO resolution (NxN) on my fps. To my understanding, the smaller the FBO is the more fragments i dont process, so the higher the framerate.

But how can I measure this?

thanks in advance,
ut.

2

Yes a smaller FBO does result in fewer fragments to render, just like the framebuffer.
Check if you can use a extension called GL_EXT_timer_query, it allows you to make measure the time between different tasks on the gpu.

3

thank you very much…
will try that out, i think its exactly what I’m after…

since i always seem to ask and not contribute here is the specs for the extension…
http://www.nvidia.com/dev_content/nvopenglspecs/GL_EXT_timer_query.txt

ut.