# uniform z slices in clip-space [closed]

1) Context I'm using a regular OpenGL perspective projection matrix created with GLM (glm::perspective) and taking the inverse (glm::inverse) to transform clip-space back into view space (and world space ultimately). Now with z-values at the near and far plane it's easy to choose the x,y,z,w components of the clip-space cube corners and get the world space point of the frustum volume.

2) Question Now, I want to harness the fact that clip space is a cube and generate a grid over the frustum. for x,y this works with the regular inverse projection matrix. For z, if I take uniform subdivisions of the range [-1.0, 1.0] with w=1.0, the view space z values will not be linear. I haven't got enough sleep recently to convince myself to do the math. What would be an inverse projection matrix to do this?

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## closed as unclear what you're asking by Josh Petrie♦Dec 22 '14 at 19:50

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question.If this question can be reworded to fit the rules in the help center, please edit the question.

"I want to harness the fact that clip space is a cube" Clip-space is not a cube. It's not even three dimensional; it's a four-dimensional homogeneous coordinate system. And what kind of grid are you trying to overlay? A grid is 2-dimensional, so what do you need the Z coordinate for? – Nicol Bolas Apr 24 '13 at 4:39
Q = Proj*P, Q = Q/Q.w the frustum will be a cube. So in that space it'll be easy to do any subdivision and map it back to the frustum. in world space... – FHoenig Apr 24 '13 at 5:32
technically, I'm actually talking about NDC space. – FHoenig Apr 24 '13 at 5:59