opengl - 3D linear surface -

i need make interpolation , build linear surface using opengl, have problem algorithm. in book(rodgers computer graphics) said equation of linear surface q(u,w) = p(u,0)(1-w) + p(u,1) * w. can`t find way use it. how can this?

make grid , approximate quads.

pseudo-code

density = 0.01; (a = 0.0; <= 1.0; += density) {     (b = 0.0; b <= 1.0; b += density) {          draw-quad(                   q(a,           b),                    q(a + density, b),                   q(a + density, b + density),                   q(a,           b + density));     } }