How to visualize a depth texture in OpenGL?

Question

I'm working on a shadow mapping algorithm, and I'd like to debug the depth map that it's generating on its first pass. However, depth textures don't seem to render properly to the viewport. Is there any easy way to display a depth texture as a greyscale image, preferably without using a shader?

Answer 1

You may need to change the depth texture parameters to display it as greyscale levels :

glTexParameteri( GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_NONE )
glTexParameteri( GL_TEXTURE_2D, GL_DEPTH_TEXTURE_MODE, GL_LUMINANCE )

You can then normally use the texture as a 'normal' greyscale 2d texture, either via fixed function, or a 'sampler2d' shader uniform.

Answer 2

Sure, just bind your depth texture to your favourite texture unit, enable texturing, and draw a 2D quad! You could also size the quad to only fill part of the screen so that you can view the shadowmap in realtime.

OpenGL also has functions which can copy the texture into an array for you. You could save this as an image and use an image viewer to view it.

Answer 3

Depth textures (2D) can be used just like any regular grayscale texture. The only problem might be that the values inside it are all too high and you only see a white texture. If that's the case play around with the z-near and -far planes that are used when creating the depth texture (or scale the values with a shader or maybe glTexEnv).