This function calculates the color for a single pixel. This function uses the Back To Front Levoy Algorithm.
First, a view ray is calculated and clipped to the 6 bounding planes. Then the clipping points are sorted by the distance to the viewer.
Then a ray From the farthest to the nearest clipping point is shot and the voxel array is sampled with a specified step size.
With every step along the ray the color is recalculated by adding the color of a new voxel to the accumulated color.