read back depth buffer

Scripting Issues
1

Hi

I’m unable to find a method to read back a single depth value, given a 2D screen coordinate. Just blind? Or is there no such a method.

Thanks

2

Attach a render-texture to bitplane RTPDepthStencil of base.win with RTMCopyRam - this will copy the texture from GPU to system RAM every frame (slow) allowing you to store that texture into a PNMImage and reading the values.

3

Something like: (untested)

texDepth = Texture()
base.win.addRenderTexture(texDepth, GraphicsOutput.RTMCopyRam, GraphicsOutput.RTPDepthStencil)
img = PNMImage()

# Then, when you want to read it out:
texDepth.store(img)
4

Thanks, but that is a bit overkill. One pixel would be enough (more glReadPixel style). Based on the scene, it sometimes possible to avoid an expensive (glReadPixel has its own drawbacks, I know) collision detection and just (un-)project the mouse coordinates and the depth value back into 3D space.

5

I’m not sure that glReadPixel would be any faster than the proposed solution, actually. But if you really want it, you could try using the new OpenGL callback mechanism.

David

6

if i remember right glReadPixel is not be implemented in hardware at all but hacked in there for compatibility sake. I think its suuuper slow on modern cards.

7

Yeah, glReadPixel will not be too much faster than the code I showed.
First google result for glReadPixel:
gamedev.net/community/forums … _id=473794

It’s probably better to only sample the center pixel and sending that to CPU. Or, a separate 1px*1px render.