Use a more advanced chamfer algorithm for stacking_lip

Removes the need for "h_lip" within that function.

Significantly reduces the number of operations.
Which is helpful when importing to FreeCAD.

Future Work:
* Convert chamfer calculations to functions.
* Use those functions to replace "h_lip" with a calculated value.
* Genericize chamfer code to a module.

gridfinity-rebuilt-utility.scad

@@ -5,6 +5,7 @@
  */
 
 include <standard.scad>
+include <gridfinity-stacking-lip-constants.scad>
 
 // ===== User Modules ===== //
 
@@ -361,49 +362,53 @@ module refined_hole() {
 }
 
 /**
- * @brief Stacking lip based on https://gridfinity.xyz/specification/
- * @details Also includes a support base.
+ * @brief Stacking lip with a chamfered top.
+ * @details Based on https://gridfinity.xyz/specification/
+ *          Also includes a support base.
  */
-module stacking_lip() {
-    // Technique: Descriptive constant names are useful, but can be unweildy.
-    // Use abbreviations if they are going to be re-used repeatedly in a small piece of code.
-    inner_slope = stacking_lip_inner_slope_height_mm;
-    wall_height = stacking_lip_wall_height_mm;
+module stacking_lip_chamfered() {
+    // Replace 2D edge with a radius.
+    // Method used: tangent, tangent, radius algorithm
+    // See:  https://math.stackexchange.com/questions/797828/calculate-center-of-circle-tangent-to-two-lines-in-space
+    before_chamfer = stacking_lip_points[2];
+    to_chamfer = stacking_lip_points[3]; // tip, Point to Chamfer
+    after_chamfer = stacking_lip_points[4];
 
-    support_wall = stacking_lip_support_wall_height_mm;
-    s_total = stacking_lip_support_height_mm;
+    chamfer_vectors = [
+        to_chamfer - before_chamfer,
+        after_chamfer - to_chamfer,
+        ];
 
-    polygon([
-        [0, 0], // Inner tip
-        [inner_slope, inner_slope], // Go out 45 degrees
-        [inner_slope, inner_slope+wall_height], // Vertical increase
-        [stacking_lip_depth, stacking_lip_height], // Go out 45 degrees
-        [stacking_lip_depth, -s_total], // Down to support bottom
-        [0, -support_wall], // Up and in
-        [0, 0] // Close the shape. Tehcnically not needed.
-    ]);
-}
+    to_chamfer_angle = 180 +
+        atan2(
+            cross(chamfer_vectors[0], chamfer_vectors[1]),
+            chamfer_vectors[0] * chamfer_vectors[1]
+        );
+    half_angle = to_chamfer_angle / 2;
 
-/**
- * @brief Stacking lip with a rounded top.
- */
-module stacking_lip_rounded_top() {
-    radius_center_y = h_lip - r_f1;
+    // Distance from tip to the center point of the circle.
+    distance_from_edge = r_f1 / sin(half_angle);
+
+    // Circle's center point
+    chamfer_center_vector = [
+        distance_from_edge * sin(half_angle),
+        distance_from_edge * cos(half_angle)
+    ];
+    chamfer_center_point = to_chamfer - chamfer_center_vector;
+
+    // Exact point edges intersect the circle
+    intersection_distance = distance_from_edge * cos(half_angle);
 
     union() {
-        // Create rounded top
-        intersection() {
-            translate([0, radius_center_y, 0])
-            square([stacking_lip_depth, stacking_lip_height]);
-            offset(r = r_f1)
-            offset(delta = -r_f1)
-            stacking_lip();
-        }
-        // Remove pointed top
+        // Rounded top chamfer
+        translate(concat(chamfer_center_point, [0]))
+        circle(r = r_f1);
+
+        // Stacking lip with cutout for circle to fit in
         difference(){
-            stacking_lip();
-            translate([0, radius_center_y, 0])
-            square([stacking_lip_depth*2, stacking_lip_height*2]);
+            polygon(stacking_lip_points);
+            translate([to_chamfer.x, to_chamfer.y, 0])
+            circle(r = intersection_distance);
         }
     }
 }
@@ -416,7 +421,7 @@ module profile_wall(height_mm) {
     assert(is_num(height_mm))
     translate([1.4, 0, 0]){
         translate([0, height_mm, 0])
-        stacking_lip_rounded_top();
+        stacking_lip_chamfered();
         translate([stacking_lip_depth-d_wall/2, 0, 0])
         square([d_wall/2, height_mm]);
     }

gridfinity-stacking-lip-constants.scad

@@ -0,0 +1,47 @@
+/**
+ * @file gridfinity-stacking-lip-constants.scad
+ * @brief Constants which define the stacking lip.
+ * @copyright MIT License, Arthur Moore 2024.
+ *            See LICENSE for more information.
+ */
+
+ include <standard.scad>
+
+//Based on https://gridfinity.xyz/specification/
+stacking_lip_inner_slope_height_mm = 0.7;
+stacking_lip_wall_height_mm = 1.8;
+stacking_lip_outer_slope_height_mm = 1.9;
+
+stacking_lip_depth =
+    stacking_lip_inner_slope_height_mm +
+    stacking_lip_outer_slope_height_mm;
+stacking_lip_height =
+    stacking_lip_inner_slope_height_mm +
+    stacking_lip_wall_height_mm +
+    stacking_lip_outer_slope_height_mm;
+
+// Extracted from `profile_wall_sub_sub`.
+stacking_lip_support_wall_height_mm = 1.2;
+stacking_lip_support_height_mm =
+    stacking_lip_support_wall_height_mm + d_wall2;
+
+
+
+// Technique: Descriptive constant names are useful, but can be unweildy.
+// Use abbreviations if they are going to be re-used repeatedly in a small piece of code.
+// Python style _ to indicate this is an internal variable.
+_slishmm = stacking_lip_inner_slope_height_mm;
+
+/**
+ * @brief Points used to make a stacking lip polygon.
+ * @details Also includes a support base.
+ */
+stacking_lip_points = [
+    [0, 0], // Inner tip
+    [_slishmm, _slishmm], // Go out 45 degrees
+    [_slishmm, _slishmm + stacking_lip_wall_height_mm], // Vertical increase
+    [stacking_lip_depth, stacking_lip_height], // Go out 45 degrees
+    [stacking_lip_depth, -stacking_lip_support_height_mm], // Down to support bottom
+    [0, -stacking_lip_support_wall_height_mm], // Up and in
+    [0, 0] // Close the shape. Tehcnically not needed.
+];

standard.scad

@@ -55,24 +55,6 @@ h_lip = 3.548;
 d_wall2 = r_base-r_c1-d_clear*sqrt(2);
 d_magic = -2*d_clear-2*d_wall+d_div;
 
-// Stacking Lip
-// Based on https://gridfinity.xyz/specification/
-stacking_lip_inner_slope_height_mm = 0.7;
-stacking_lip_wall_height_mm = 1.8;
-stacking_lip_outer_slope_height_mm = 1.9;
-stacking_lip_depth =
-    stacking_lip_inner_slope_height_mm +
-    stacking_lip_outer_slope_height_mm;
-stacking_lip_height =
-    stacking_lip_inner_slope_height_mm +
-    stacking_lip_wall_height_mm +
-    stacking_lip_outer_slope_height_mm;
-
-// Extracted from `profile_wall_sub_sub`.
-stacking_lip_support_wall_height_mm = 1.2;
-stacking_lip_support_height_mm =
-    stacking_lip_support_wall_height_mm + d_wall2;
-
 
 // Baseplate constants