#### Culling frustum becoming narrow when looking up or down

I have a problem implementing frustum culling in OpenGL.
I implemented plane extraction in world space, using this Lighthouse3d tutorial (the rest of the engine comes from learnopengl.com).
It works well, but only when the camera points towards the horizon. If the camera points up or down, the frustum becomes progressively narrow.

Indeed, far frustum plane size is 1023 * 828 when pointing to horizon, but only 17 * 14 when pointing up or down. The same problem occurs for the near frustum plane.

Here is the code that updates the frustum each frame (C++):

``````  tang = (float) tan(glm::radians(45.0f) * 0.5f);
ratio = SCR_WIDTH * 1.0 / SCR_HEIGHT;

// Direction vectors
cameraZ = cameraFront * -1.0f;
cameraRight = glm::cross(glm::vec3(0.0f, 1.0f,  0.0f), cameraZ);
cameraUp = glm::cross(cameraZ, cameraRight);

// Dimensions of near and far frustum planes
Hnear = nearDist * tang; // Hnear = near plane height
Wnear = Hnear * ratio; // Wnear = near plane width
Hfar = farDist  * tang; // Hfar = far plane height
Wfar = Hfar * ratio; // Wfar = far plane width

// Distance of near and far planes
fc = cameraPos - cameraZ * farDist; // fc = far center
nc = cameraPos - cameraZ * nearDist; // nc = near center

// Extraction of frustum points
ntl = nc + (cameraUp * Hnear) - (cameraRight * Wnear);
ntr = nc + (cameraUp * Hnear) + (cameraRight * Wnear);
nbl = nc - (cameraUp * Hnear) - (cameraRight * Wnear);
nbr = nc - (cameraUp * Hnear) + (cameraRight * Wnear);

ftl = fc + (cameraUp * Hfar) - (cameraRight * Wfar);
ftr = fc + (cameraUp * Hfar) + (cameraRight * Wfar);
fbl = fc - (cameraUp * Hfar) - (cameraRight * Wfar);
fbr = fc - (cameraUp * Hfar) + (cameraRight * Wfar);

// Computation of the 6 frustum planes
topPlane = {ntr,ntl,ftl};
bottomPlane = {nbl,nbr,fbr};
leftPlane = {ntl,nbl,fbl};
rightPlane = {nbr,ntr,fbr};
nearPlane = {ntl,ntr,nbr};
farPlane = {ftr,ftl,fbl};
``````

Here is the result:

Source: Windows Questions C++