Display voxels using shaders in openGL

Question

I am working on voxelisation using the rendering pipeline and now I successfully voxelise the scene using vertex+geometry+fragment shaders. Now my voxels are stored in a 3D texture which has size, for example, 128x128x128.

My original model of the scene is centered at (0,0,0) and it extends in both positive and negative axis. The texure, however, is centered at (63,63,63) in tex coordinates.

I implemented a simple ray marcing for visualizing but it doesn't take into account the camera movements (I can render only from very fixed positions because my ray have to be generated taking into account the different coordinates of the 3D texture).

My question is: how can I map my rays so that they are generated at point Po with direction D in the coordinates of my 3D model but intersect the voxels at the corresponding position in texture coordinates and every movement of the camera in the 3D world is remapped in the voxel coordinates?

Right now I generate the rays in this way: create a quad in front of the camera at position (63,63,-20) cast rays in direction towards (63,63,3)

Answer 1

I think you should store your entire view transform matrix in your shader uniform params. Then for each shader execution you can use its screen coords and view transform to compute the view ray direction for your particular pixel. Having the ray direction and camera position you just use them the same as currently.

There's also another way to do this that you can try:

Let's say you have a cube (0,0,0)->(1,1,1) and for each corner you assign a color based on its position, like (1,0,0) is red, etc.

Now for every frame you draw your cube front faces to the texture, and cube back faces to the second texture.

In the final rendering you can use both textures to get enter and exit 3D vectors, already in the texture space, which makes your final shader much simpler.

You can read better descriptions here:

http://graphicsrunner.blogspot.com/2009/01/volume-rendering-101.html

http://web.cse.ohio-state.edu/~tong/vr/