I need to model a source pattern shift on a mesh grid( when light source is tilted by some angle theta)

Situation: when light rays falls vertically (i.e zero degree tilt) , lets say the pattern formed on a grid is at location (x,y). Now, i tilt the light source so now rays fall at an angle of 20 degres, so the orignal source pattern on the grid will shift to new location (x',y').

I need to model this in terms of equations. Is there any equation or concepts that deal with modelling shifts in terms of incedent angle.

Any Insight is highly appreciated!!