Comments on: Instance Cloud Reduction reloaded

By: Daniel Rákos

Daniel Rákos — Mon, 28 Feb 2011 18:10:26 +0000

Yeah, you’ve understood the functionality of DrawTransformFeedback correctly, however in this case we don’t use transform feedback in the classical way as we capture only transformation data and not the whole mesh that’s why it is not appropriate in our situation.
The ARB_draw_indirect2 extension proposed by me would allow the algorithm to handle arbitrary heterogeneous set of objects, not just instances of the same mesh, that’s why I mentioned that in the first case.

By: dchristopherfennell

dchristopherfennell — Mon, 28 Feb 2011 14:46:06 +0000

You mentioned above that glDrawTransformFeedback captures data from the previous feedback step, which is how I understood it. I was just looking for a way to get the number of ‘objects’ written without the use of a query. I’ll read up on atomic counters and ARB_draw_indirect. Thanks for pointing that out too.

By: Daniel Rákos

Daniel Rákos — Mon, 28 Feb 2011 12:26:10 +0000

Sorry, actually I was wrong. You don’t necessarily need ARB_draw_indirect2 to accomplish that, but you need ARB_draw_indirect and atomic counters which are currently not available in OpenGL but will be exposed via the ARB_shader_atomic_counters extension in the near future.

By: Daniel Rákos

Daniel Rákos — Thu, 24 Feb 2011 08:15:26 +0000

You either misunderstood the way how glDrawTransformFeedback works or how my demo works. While it would be possible to use transform feedback obejcts (i.e. glGenTransformFeedbacks), glDrawTransformFeedback would draw only the captured data from the previous feedback step, that is in our case just the transformation data of the objects, not the object meshes themselves, so in our case the AutoDraw feature is not really usable. Actually there is my Mountains Demo that takes advantage of the presented technique using transform feedback objects: OpenGL 4.0 - Mountains Demo released Also please read my suggestions for OpenGL 4.2 as there I mention a feature called ARB_draw_indirect2 that could make it possible to accomplish the ICR technique without a query: Suggestions for OpenGL 4.2 and beyond

By: dchristopherfennell

dchristopherfennell — Wed, 23 Feb 2011 22:36:55 +0000

Hello,

I enjoyed learning from your nature example on culling additional geometry through the use of geometry shaders. Is there any chance you could modify this example to use glGenTransformFeedbacks && glDrawTransformFeedback with instancing? The new GL features avoids the expense of using a query.

Thanks.

By: Daniel Rákos

Daniel Rákos — Mon, 09 Aug 2010 15:52:50 +0000

It’s good to see that at least a slight performance increase of about 20% is observed both on NVIDIA and AMD cards.

I will update the demo in the future to take advantage of the new features in OpenGL 4 in order to further improve the performance of the algorithm.

By: Rachan

Rachan — Sun, 08 Aug 2010 10:04:04 +0000

5 visible trees and 113 visible grass

NVIDIA 260 GTX can produce 100 FPS for old version and 124 FPS for new version.

By: Heady

Heady — Fri, 09 Jul 2010 09:13:27 +0000

My good old NVIDIA 8800 GTS 640 MB has an increase of about 64 FPS to 80 FPS.
The lack of an benchmark mode makes comparison quite painfull