Question

I’m working on a project where I port my CUDA code for usage
as a module in a big application which maintains its own
OpenGL state. My module basically is a volume renderer.
I am now facing the problem that I have to setup the rays
of the volume renderer to exactly mimic the OpenGL camera,
so that my volume renderering fits with the rest of the rendered scene.

At the point where my CUDA code is called there is a viewing matrix
(no model-view matrix) and a projection matrix set.
I already extracted the frustum parameters and the camera position
in world space.

u *= -c_pp.right;
v *= -c_pp.top;

Ray eyeRay;
eyeRay.o = make_float3(c_camPosition); //origin
eyeRay.d = normalize(make_float3(u, v, -c_pp.near)); //direction

u and v are normalized screen coordinates running from -1 to 1.
c_pp describes the view frustum using top, right and near.
I’m now looking for the appropriate matrix I have to multiply with
so that eyeRay.d shows in the right direction. So far using the
viewing matrix or its transposed or inverted version failed.

Update:

Changed u *= -c_pp.right to u *= c_pp.right and everything works
by multiplying eyeRay.d with the inverse viewing matrix.

Complete fixed code:

u *= c_pp.right;
v *= -c_pp.top;

Ray eyeRay;
eyeRay.o = make_float3(c_camPosition); //origin
eyeRay.d = make_float3(u, v, -c_pp.near)); //direction
eyeRay.d = mul(c_invViewMatrix, eyeRay.d);

with c_inViewMatrix being the inverse view matrix.

Answer 1

This question has been answered by the original poster inline. The answer is to change u *= -c_pp.right to u *= c_pp.right (sign change). See above.

I’ve added this answer to reduce the number of unanswered questions in the CUDA tag to help make it more useful.