G'day, I have 4 vertices ( x1 y1 z1, x2 y2 z2 etc..) which make up a quad. I then want to tessellate that quad into smaller quads so i need to calculate the vertices for each of the smaller quads. I'm doing this for lighting purposes because opengl calculates light on a per-vertex basis so to get accurate lighting i need to spit my quad up into smaller quads. I'm a little stumped on this one, any ideas?

Take the average of all four vertices, and the average of each pair of adjacent corners:

X----0----X|         ||         |0    0    0|         ||         |X----0----XX -> original vertices0 -> averaged points

then connect the old and new points to make four quads

X----0----X|    |    ||    |    |0----0----0|    |    ||    |    |X----0----XX -> original vertices0 -> averaged points