square funnel

module square_funnel(steps, thickness, height, 
                     s_dim, s_oRadius, s_iRadius, 
                     e_dim, e_oRadius, e_iRadius)
{
  // Calculate interpolation steps.
  extrude_length = height / steps;
  w_s = (e_dim[0] - s_dim[0]) / steps;
  l_s = (e_dim[1] - s_dim[1]) / steps;
  ir_s = (e_iRadius - s_iRadius) / steps;
  or_s = (e_oRadius - s_oRadius) / steps;

  // Starting stuff
  w = s_dim[0];
  l = s_dim[1];
  ir = s_iRadius;
  or = s_oRadius;

  // Join together a whole bunch of extrusions
  union()
  {
    for (i=[0:steps])
    {
      // Move up to the next step
      translate([0,0,i*extrude_length])

      // Extrude one section
      linear_extrude(
        height = extrude_length, 
        center = true)

      // Create a hollow rounded rect
      // Add the interpolation to each variable
      difference() {
        rounded_square(
          [w + (w_s*i), l + (l_s*i)],
          [or + (or_s*i),or + (or_s*i),or + (or_s*i),or + (or_s*i)],
          true);
        rounded_square(
          [w + (w_s*i) - (thickness*2), l + (l_s*i) - (thickness*2)],
          [ir + (ir_s*i),ir + (ir_s*i),ir + (ir_s*i),ir + (ir_s*i)],
          true);
      }
    }
  }
}