Using <window>.screenToWorld within vizcave powerwall

[VizMars]

I want to calculate depth information for each screen pixel in a way that for given 2d screen coordinates (x,y) I get the distance from the user's head to the point in the 3d scene that corresponds to the given 2d screen coordinates. Ultimately, the goal is to construct a "depth map" for a scene given the user's head position and gaze direction.