Writing the correct value in the depth buffer when using ray-casting
- by hidayat
I am doing a ray-casting in a 3d texture until I hit a correct value. I am doing the ray-casting in a cube and the cube corners are already in world coordinates so I don't have to multiply the vertices with the modelviewmatrix to get the correct position.
Vertex shader
world_coordinate_ = gl_Vertex;
Fragment shader
vec3 direction = (world_coordinate_.xyz - cameraPosition_);
direction = normalize(direction);
for (float k = 0.0; k < steps; k += 1.0) {
....
pos += direction*delta_step;
float thisLum = texture3D(texture3_, pos).r;
if(thisLum > surface_)
...
}
Everything works as expected, what I now want is to sample the correct value to the depth buffer. The value that is now written to the depth buffer is the cube coordinate. But I want the value of pos in the 3d texture to be written.
So lets say the cube is placed 10 away from origin in -z and the size is 10*10*10. My solution that does not work correctly is this:
pos *= 10;
pos.z += 10;
pos.z *= -1;
vec4 depth_vec = gl_ProjectionMatrix * vec4(pos.xyz, 1.0);
float depth = ((depth_vec.z / depth_vec.w) + 1.0) * 0.5;
gl_FragDepth = depth;
