PDA

View Full Version : How to force to write in the framebuffer? (on AMD)



Groovounet
09-13-2010, 02:37 AM
Hi,

I was playing with this very interesting tool Froggy FragSnipper (http://www.icare3d.org/blog_techno/gpu/the_froggy_fragsniffer.html) which allows to see how the GPU rasterizes.

However this tool only works with Windows XP as Windows 7 doesn't allows to write to the framebuffer and display a texture.

I try it on a GeForce 470 and it works perfectly. However, it since that AMD writes on a texture even on WindowsXP... Is anyone know if we can force to write to the framebuffer on AMD?

ZbuffeR
09-13-2010, 03:14 AM
If I sum up, it works only on XP and nvidia ?
Sound more like a bug in the tool, or relying too much on single-buffered rendering.
Did you try to contact the author ?
What says GLIntercept ?

Groovounet
09-13-2010, 03:47 AM
Yes it only works on nVidia and XP.

Are you aware of some issues or specific behaviours with single buffered rendering on AMD?

The author didn't tried on AMD.
I don't think that GLIntercept is any help here. The rendering is correct, it just displays everything all at once instead of showing the rasterization pattern. This is the behaviour expected on Windows 7 which doesn't allow to write to the framebuffer and that why I think AMD drivers behave the same way on XP...

ZbuffeR
09-13-2010, 04:57 AM
I recall front buffer rendering done in the Blender UI for example caused a few problems (slowness or garbage results) on ATI, never had problems on nvidia.
By reading the Froggy FragSniper page, it looks like a tool developed specifically for G80 hardware. The ideas are very interesting, but depend a lot on how frontbuffer rendering is implemented.
For ATI, maybe the front buffer is only accessible when the card is done drawing its current primitive, so you can't see "part of triangle".

Groovounet
09-13-2010, 06:41 AM
Yes maybe. :p

It's possible that AMD uses the render to texture even for the rendering into the framebuffer and then blit this texture...