Introduce chop_off(), generic flat chopping module

planter.scad

@@ -29,6 +29,25 @@ module half_sphere(d) {
     }
 }
 
+module chop_off(x, thickness) {
+    assert($children == 1);
+
+    difference() {
+        children(0);
+
+        translate([-500 - x, -500, -500])
+        cube([500, 1000, 1000]);
+    }
+
+    hull()
+    intersection() {
+        children(0);
+
+        translate([-x, -500, -500])
+        cube([thickness, 1000, 1000]);
+    }
+}
+
 // The body, a full cylinder with ridges
 //
 // Its diameter is calculated from `diameter` (for the hollow inside), `thickness`, and `cut_depth`.
@@ -99,14 +118,9 @@ if(wall_mount_percent > 0) {
 
     wall_depth = full_diameter * sqrt(1 - (1 - wall_mount_percent / 100)^2);
 
-    difference() {
+    chop_off(wall_x, thickness) {
         planter();
-        translate([-wall_x - full_diameter, -wall_depth / 2, -full_diameter - 1])
-        cube([full_diameter, wall_depth, height + full_diameter + 2]);
     }
-
-    translate([-wall_x, -wall_depth / 2, 0])
-    cube([thickness, wall_depth, height]);
 } else {
     planter();
 }