I want to make a number of cones (as a hacky way of doing a voronoi tiling), and then mask what we see with an image. Here's the snippit of code I'm using, from my draw routine. col[i] is the color for the ith cone and outline is an image file used as the mask.

I'm using size(640, 480, OPENGL); as my render mode.



 // draw the 'cones'
 pushMatrix();
 // -10 means the cones are below the surface
 // (so we can draw on top of them later)
 translate(0,0,-10);
 for (int i = 0; i < numpop; i++) {

   noStroke();
   
   r=brightness(col[i]);
   b=1-brightness(col[i]);
   g=0;
   
   fill(r,g,b);
   
   cone((xx[i]),(yy[i]),600.0,10.0);

 }
 popMatrix();

 outline.mask(outline);    
 image(outline,0,0);



Now, when I have the cones translated by (0,0,-10), the mask shows up, but all the cones are a uniform solid blue. When I use (0,0,0) translation the cones appear in the proper colours, but the mask vanishes.

Any ideas?