title: calculate depth of the points lying in a plane? depth buffer
body: <p>Currently i am working on the Z-buffer.I have the idea of original plane(in the world), and i process out screen vertices through: 
  <em>world to camera transformation,</em> 
  <em>x_projection = x(world) / -z(world)</em>
  <em>(similar for y)</em>
  now i am unable to find out, how i am supposed to get all the z values within the projected triangular plane on the screen.</p>
  
  <p>information i have : coordinates in world space, normals in the world space, coordinates in camera space, coordinates on the 2d plane</p>