added shape_glued2circles

README.md

@@ -88,6 +88,7 @@ Too many dependencies? Because OpenSCAD doesn't provide namespace management, I
 	- [shape_cyclicpolygon](https://openhome.cc/eGossip/OpenSCAD/lib-shape_cyclicpolygon.html)
     - [shape_pentagram](https://openhome.cc/eGossip/OpenSCAD/lib-shape_pentagram.html)	
 	- [shape_superformula](https://openhome.cc/eGossip/OpenSCAD/lib-shape_superformula.html)
+	- [shape_glued2circles](https://openhome.cc/eGossip/OpenSCAD/lib-shape_glued2circles.html)
 	- [shape_path_extend](https://openhome.cc/eGossip/OpenSCAD/lib-shape_path_extend.html)		
 
 - 2D Shape Extrusion

docs/lib-shape_glued2circles.md

@@ -0,0 +1,75 @@
+# shape_glued2circles
+
+Returns shape points of two glued circles. They can be used with xxx_extrude modules of dotSCAD. The shape points can be also used with the built-in polygon module. 
+
+Dependencies: `rotate_p`, `bezier_curve`, `shape_pie`.
+
+## Parameters
+
+- `radius` : The radius of two circles.
+- `centre_dist` : The distance between centres of two circles.
+- `tangent_angle` : The angle of a tangent line. It defaults to 30 degrees. See examples below.
+- `t_step` : It defaults to 0.1. See [bezier_curve](https://openhome.cc/eGossip/OpenSCAD/lib-bezier_curve.html) for details.
+- `$fa`, `$fs`, `$fn` : Check [the circle module](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#circle) for more details.
+
+## Examples
+
+    include <rotate_p.scad>;
+    include <bezier_curve.scad>;
+    include <shape_pie.scad>;
+    include <shape_glued2circles.scad>;
+
+    $fn = 36;
+
+    radius = 10;
+    centre_dist = 30;
+
+    shape_pts = shape_glued2circles(radius, centre_dist);
+    polygon(shape_pts); 
+
+![shape_glued2circles](images/lib-shape_glued2circles-1.JPG)
+
+    include <rotate_p.scad>;
+    include <bezier_curve.scad>;
+    include <shape_pie.scad>;
+    include <shape_glued2circles.scad>;
+
+    $fn = 36;
+
+    radius = 10;
+    centre_dist = 30;
+
+    shape_pts = shape_glued2circles(radius, centre_dist);
+    width = centre_dist / 2 + radius;
+
+    rotate_extrude() difference() {    
+        polygon(shape_pts);    
+
+        translate([-width, -radius]) 
+            square([width, radius * 2]);
+    }
+
+![shape_glued2circles](images/lib-shape_glued2circles-2.JPG)
+
+    include <rotate_p.scad>;
+    include <bezier_curve.scad>;
+    include <shape_pie.scad>;
+    include <shape_glued2circles.scad>;
+
+    $fn = 36;
+
+    radius = 10;
+    centre_dist = 30;
+
+    shape_pts = shape_glued2circles(radius, centre_dist);
+    width = centre_dist + radius * 2;
+
+    rotate_extrude() translate([0.00001, 0, 0]) 
+        rotate(-90) difference() { 
+            polygon(shape_pts);    
+
+            translate([0, -radius / 2]) 
+                square([width, radius], center = true);
+        }
+
+![shape_glued2circles](images/lib-shape_glued2circles-3.JPG)

src/shape_glued2circles.scad

@@ -0,0 +1,79 @@
+
+/**
+* shape_glued2circles.scad
+*
+* Returns shape points of two glued circles. 
+* They can be used with xxx_extrude modules of dotSCAD.
+* The shape points can be also used with the built-in polygon module. 
+* 
+* @copyright Justin Lin, 2017
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib-shape_glued2circles.html
+*
+**/ 
+
+function _glued2circles_pie_curve(radius, centre_dist, tangent_angle) =
+    let(
+        begin_ang = 90 + tangent_angle,
+        shape_pts = shape_pie(radius, [-begin_ang, begin_ang])
+    )
+    [
+        for(i = [1:len(shape_pts) - 1])
+            shape_pts[i] + [centre_dist / 2, 0]
+    ];
+    
+function _glued2circles_bezier(radius, centre_dist, tangent_angle, t_step, ctrl_p1) = 
+    let(
+        ctrl_p = rotate_p([radius * tan(tangent_angle), -radius], tangent_angle),
+        ctrl_p2 = [-ctrl_p[0], ctrl_p[1]] + [centre_dist / 2, 0],
+        ctrl_p3 = [-ctrl_p2[0], ctrl_p2[1]],
+        ctrl_p4 = [-ctrl_p1[0], ctrl_p1[1]]            
+    )
+    bezier_curve(
+        t_step,
+        [
+            ctrl_p1,
+            ctrl_p2,
+            ctrl_p3,
+            ctrl_p4        
+        ]
+    );    
+
+function _glued2circles_lower_half_curve(curve_pts, leng, i = 0) =
+    i < leng ? (
+        curve_pts[leng - 1 - i][0] >= 0 ? 
+            concat(
+                [curve_pts[leng - 1 - i]], 
+                _glued2circles_lower_half_curve(curve_pts, leng, i + 1)
+            ) : 
+            _glued2circles_lower_half_curve(curve_pts, leng, i + 1)
+    ) : [];    
+    
+function _glued2circles_half_glued_circle(radius, centre_dist, tangent_angle, t_step) =
+    let(
+        pie_curve_pts = _glued2circles_pie_curve(radius, centre_dist, tangent_angle),
+        curve_pts = _glued2circles_bezier(radius, centre_dist, tangent_angle, t_step, pie_curve_pts[0]),
+        lower_curve_pts = _glued2circles_lower_half_curve(curve_pts, len(curve_pts)),
+        leng_half_curve_pts = len(lower_curve_pts),
+        upper_curve_pts = [
+            for(i = [0:leng_half_curve_pts - 1])
+                let(pt = lower_curve_pts[leng_half_curve_pts - 1 - i])
+                [pt[0], -pt[1]]
+        ]
+    ) concat(
+        lower_curve_pts,
+        pie_curve_pts,        
+        upper_curve_pts
+    );
+    
+function shape_glued2circles(radius, centre_dist, tangent_angle = 30, t_step = 0.1) =
+    let(
+        half_glued_circles = _glued2circles_half_glued_circle(radius, centre_dist, tangent_angle, t_step),
+        leng_half_glued_circles = len(half_glued_circles),
+        left_half_glued_circles = [
+            for(i = [0:leng_half_glued_circles - 1])
+                let(pt = half_glued_circles[leng_half_glued_circles - 1 - i])
+                [-pt[0], pt[1]]
+        ]    
+    ) concat(half_glued_circles, left_half_glued_circles);