Render to Far Plane (gl_Position.z = 1)

Gaming and Visualization Technologies APIs OpenGL
1

Hi,

this is a basic question but requires some in depth knowledge that I am missing.

I want to render a texture on the far plane, that is gl_Position.z = 1 & gl_Position.w = 1. Hard Coded and without Matrices.

It appears that GL clips including the far plane.

Can I modify the clipping comparison?
Is there a standard way to place geometry on the far plane?

Also:
The largest possible depth value appears to be: 0.99999991059303297

Interestingly, the largest value provided by <math.h> and nextafter(1.0f, 0.0f) is 0.99999994039535522

I would have thought that the precision would be the same by now, can anyone elaborate on this? Or point to some documentation.

Best Regards.

2

Are you rendering said texture first?

If you are, you can clear the depth buffer, disable depth test & write, render it at an arbitrary distance (e.g. 0), and re-enable depth test & write. That’ll give you an image on the far plane.

3

I think you can also use glDepthFunc() to change comparison function; however, its a bit slower than DarkUranium’s method.

https://www.khronos.org/opengl/wiki/GLAPI/glDepthFunc
https://www.khronos.org/opengl/wiki/Depth_Test#Depth_buffer