pythonopenglpyopenglperspectivecamera

Why gluPerspective gives a result that does not match the formula in the documentation?

Return of gluPerspective differ from formula in documentation

Formula for gluPerspective described in IBM-doc and Khronos doc is
f/aspect 0 0 0
0 f 0 0
0 0 (far + near) / (near - far) (2 * far + near) / (near-far)
0 0 -1 0

but when I check gluPerspective matrix with python:

glMatrixMode(GL_PROJECTION)
glLoadIdentity()
gluPerspective(fov_h, aspect_ratio, near, far)
projection_matrix = glGetFloatv(GL_PROJECTION_MATRIX)

result seems too look like:
f/aspect 0 0 0
0 f 0 0
0 0 (far + near) / (near - far) -1
0 0 (2 * far + near) / (near-far) 0

For e.g. parameters gluPerspective(45.0, 4/3, 0.1, 100) returns:

[[ 1.8106601 0. 0. 0. ]

[ 0. 2.4142137 0. 0. ]

[ 0. 0. -1.002002 -1. ]

[ 0. 0. -0.2002002 0. ]]

So:

Solution

  • I think the formula is correct and the problem here is your interpretation of the output. My guess is that the output is shown in so-called column major order. You are assuming that the output is row major order, but that isn't the case. See this wikepedia article for an explanation of the difference.