OpenSCAD file with an irregular pattern

uncacheable_pattern.scad

// Context: ochafik@'s attempts to speed up OpenSCAD
// fast-union feature: https://github.com/openscad/openscad/pull/3636
// lazier union features: https://github.com/openscad/openscad/pull/3637
//
// (and parallelization attempts, not sent as PRs yet)
//
// fast-union, lazy-union, push-transforms-down-unions, lazy-module and flatten-children all help here!
// openscad --enable=fast-union cube-with-half-spheres-dents.scad -o cube-with-half-spheres-dents.stl

top_transform = true;
top_union = true;
N = 5;
size = 2;
$fn=12;

module grid(N)
{
  for (i=[0:N-1], j=[0:N-1]) translate([i * size, j * size, 0])
    {
        sphere(d=1, $fn=16);

        difference() {
            h = 1 + (i + N * j) / pow(N, 2);
            
            // Explicit union here as difference isn't optimized by fast-union yet.
            // (to be done soon)
            union() {
              hull() {
                cube(h, center=true);
                cylinder(h / 2 - 0.01, d=h * 1.3);
              }

              cylinder(h, r=0.45);
              translate([0, 0.5, 0])
                cylinder(h, r=0.2);
            }
        }
    }
}

if (top_union)
  union() {
    if (top_transform)
      translate([0, 0, 1])
        grid(N);
    else
      grid(N);
  }
else if (top_transform)
  translate([0, 0, 1])
    grid(N);
else
  grid(N);