Incorrect depth buffer check in depth buffer test

[icoderaven]

The current depth buffer test compares the linear depth for a particular pixel with the raybox intersection distance along the ray.

This is incorrect, and should be comparing the linear depth against the distance along the ray projected to the camera z axis (assuming that scene depth buffer is equivalent to a depth image transformed by the projection matrix to normalized 0..1 values)

i.e., instead of

if (t.x > getLinearDepth(SCN_DBUF) )

it should be something along the lines of

if (t.x * dot(scn.dir_vec, dir) > getLinearDepth(SCN_DBUF) )

where for convenience I have exposed the camera z in world frame as scn.dir_vec
Of possible relevance to @drmateo and #44

[icoderaven]

Also, the ray direction should be normalized within the rayCast() method.

[NBickford-NV]

Hi icoderaven,

I've just pushed commit 9ffc6b7, which should fix this by adding a new function, getRayDepthBufferMax, to cuda_gvdb_raycast.cuh. Essentially, this function computes getLinearDepth(SCN_DBUF)/dot(scn.dir_vec, dir), except it turns out we can use the transformation matrix to avoid having to store dir_vec. However, I might add something like dir_vec in the future to avoid the matrix-vector multiplication in getRayDepthBufferMax as an optimization.

Thanks!