This technique for shadow mapping does the reverse when comparing depths. Instead of the normal case of comparing depths in light space, this method suggest that the comparison should be done in eye space. This requires the depth buffer from the lights’ view and from the camera’s view at the time of the comparison. This method is probably most useful when doing deferred lightning.

Link to the paper “Forward Shadow Mapping”
http://www.cs.unc.edu/~zhangh/shadow.html