Depth Buffer and deferred rendering

dingojohn · 2010-07-30T13:30:19

Hi,I'm currently working on a deferred renderer and now trying to optimize the lighting calculation. The way I have done it so far is the a color attachment to store depth value linearly, which I then use to reconstruct position. Then, I figured that I need to do depth testing for more efficient lighting calculation - or rather not to do the calculations. However, early z does only work with the default depth buffer as far as I understand, and thus I have to duplicate depth information, stored in two different ways. How do you normally solve this? Use the default depth buffer and letting opengl write to that itself (possibly flipping far and near for more precision), or are you simply saving the info in a dedicated color attachment? If you save it in a depth attachment, do you do it as a texture or as a renderbuffer? Can you do depth testing on a MRT with an attached texture as depth attachment, and is there a performance penalty for this?(The way I currently store depth is the negated view-space z value divided by zfar, and I figure I need to fetch it much differently if I get it as z/w after perspective transformation from the standard depth buffer)Thanks in advance.Tell me if I need to elaborate anything.

Graphics and GPU Programming Programming OpenGL

Started by dingojohn July 28, 2010 11:24 AM

12 comments, last by dingojohn 13 years, 8 months ago

allingm

539

July 30, 2010 11:37 AM

I forgot to say a couple things.

1) Turn off color writes for stencil volumes.
2) Turn off depth writes for stencil volumes and lights.
3) Turn on depth reads for stencil volumes.
4) Turn off depth reads for lights. (doesn't really matter here)

dingojohn

159

Author

July 30, 2010 12:41 PM

Yeah, that was what I was thinking. However, "solved" my depth problems is not exactly right, as I still have no clue as to how I am going to utilize the texture as the depth buffer for the second pass, as I am not using MRT for that, due to the fact that I render to the window. Depth testing that I have to use for the stencil generation works with the current depthbuffer unless I am mistaken. In this case as I do not use MRT that would be the window's own depth buffer, and not my custom texture that I just rendered to in order to use the info to reconstruct position.

I might be missing something quite simple, but I'm still not getting anywhere.

venzon

256

July 30, 2010 12:55 PM

Quote:Original post by dingojohn
For this I need to utilize the depth that is written to the texture to do depth testing against backfaces of the light volume (and perhaps also front faces), but I'm not sure how I can do that, as for the second pass I draw directly to the window's default framebuffer.

To do depth testing using a depth texture that you've previously written to, you need to attach it to your FBO. As far as I know, you can't attach depth textures to the special framebuffer FBO 0. Your options are:
1) draw your second pass to an FBO with your depth texture attached (which will make opengl use it for depth testing) and also a new color texture attached, then do a third full-screen pass to simply write the color texture to the framebuffer. This is what I do, and it's when I apply my tonemapping.
2) insert a full screen pass before your second pass. In this new pass, draw to the special framebuffer FBO 0 and you read from your depth texture and in your fragment shader set the fragment's depth to what you read from your depth texture.

I'd strongly recommend option 1 because then you have you scene's color in a texture, which is useful for all kinds of post-processing.