// loop over u and v to define per-vertex attributes
var maxindex = 0;
for(var i=0; i<=uSegments; i++) {
    for(var j=0; j<=vSegments; j++) {

        // current position (u,v) on the surface
        var u = uMin + i * (uMax-uMin) / uSegments;
        var v = vMin + j * (vMax-vMin) / vSegments;

        // current index into the vertex buffers
        var vindex = i*(vSegments+1) + j;

        var p = definition.position(u,v);
        vposition[vindex*3]   = p[0];
        vposition[vindex*3+1] = p[1];
        vposition[vindex*3+2] = p[2];

        // index inside the
        var iindex = i*vSegments + j;

        // indices for drawing two triangles per patch
        if(i<uSegments && j<vSegments) {
            var ii = iindex*6;
            triangles[ii++] = vindex;
            triangles[ii++] = vindex+(vSegments+1);
            triangles[ii++] = vindex+(vSegments+1)+1;
            triangles[ii++] = vindex+(vSegments+1)+1;
            triangles[ii++] = vindex+1;
            triangles[ii++] = vindex;
        };
    }
}