The equation I use for 3D projection is X2D=X/Z*ZOOM:Y2D=Y/Z*ZOOM Using algebra, assuming a constant Y you can easily derive the equations Z=Y/Y2D*ZOOM:X=Z*X2D/ZOOM Which should get you 3D coordinates from 2D coordinates and a constant Y value. Using this you can easily use the X and Z coordinates as X and Y coordinates and place pixels accurately on the screen for the mode 7 effect.