add doc

README.md

@@ -357,7 +357,7 @@ These examples incubate dotSCAD and dotSCAD refactors these examples. See [examp
 --|--
 [**triangle/tri_circumcenter**(shape_pts)](https://openhome.cc/eGossip/OpenSCAD/lib3x-tri_circumcenter.html) | return the circumcenter of a triangle.
 [**triangle/tri_incenter**(shape_pts)](https://openhome.cc/eGossip/OpenSCAD/lib3x-tri_incenter.html) | return the incenter of a triangle.
-**triangle/tri_ear_clipping**(shape_pts,  ret = "TRI_INDICES", ...) |  triangulation by [ear clipping](https://en.wikipedia.org/wiki/Polygon_triangulation#Ear_clipping_method).
+[**triangle/tri_ear_clipping**(shape_pts,  ret = "TRI_INDICES", ...)](https://openhome.cc/eGossip/OpenSCAD/lib3x-tri_ear_clipping.html) | triangulation by [ear clipping](https://en.wikipedia.org/wiki/Polygon_triangulation#Ear_clipping_method).
 **triangle/tri_delaunay**(points, ret = "TRI_INDICES") | return the [Delaunay triangulation](https://en.wikipedia.org/wiki/Delaunay_triangulation) of the points.
 **triangle/tri_delaunay_indices**(d) | return triangle indices from a delaunay object.
 **triangle/tri_delaunay_shapes**(d) | return triangle shapes from a delaunay object.

docs/lib3x-tri_ear_clipping.md

@@ -0,0 +1,59 @@
+# tri_ear_clipping
+
+Given a 2D shape. This function performs a polygon triangulation based on [Ear clipping](https://en.wikipedia.org/wiki/Polygon_triangulation#Ear_clipping_method).
+
+**Since:** 3.0
+
+## Parameters
+
+- `shape_pts` : The shape points.
+- `ret` : The type of returned data. Default to `"TRI_INDICES"` which returns the indices of the `shape_pts`. If `"TRI_SHAPES"` is given, return triangle shapes.
+- `epsilon` : An upper bound on the relative error due to rounding in floating point arithmetic. Default to 0.0001.
+
+## Examples
+
+    use <triangle/tri_ear_clipping.scad>; 
+
+    shape = [
+        [0, 0],
+        [10, 0],
+        [12, 5],
+        [5, 10],
+        [10, 15],
+        [0, 20],
+        [-5, 18],
+        [-18, 3],
+        [-4, 10]
+    ];
+
+    all_indices = tri_ear_clipping(shape);
+
+    for(tri_indices = all_indices) {
+        offset(-.1)
+            polygon([for(i = tri_indices) shape[i]]);
+    }
+
+![tri_ear_clipping](images/lib3x-tri_ear_clipping-1.JPG)
+
+    use <triangle/tri_ear_clipping.scad>; 
+
+    shape = [
+        [0, 0],
+        [10, 0],
+        [12, 5],
+        [5, 10],
+        [10, 15],
+        [0, 20],
+        [-5, 18],
+        [-18, 3],
+        [-4, 10]
+    ];
+
+    tris = tri_ear_clipping(shape, ret = "TRI_SHAPES");
+
+    for(tri = tris) {
+        offset(-.1)
+            polygon(tri);
+    }
+
+![tri_ear_clipping](images/lib3x-tri_ear_clipping-1.JPG)

src/triangle/tri_ear_clipping.scad

@@ -1,10 +1,15 @@
 /**
-   copy from triangulate.scad, would move into triangle category
+* tri_circumcenter.scad
+*
+* @copyright Justin Lin, 2021
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib3x-tri_ear_clipping.html
+*
 **/
 
 use <_impl/_tri_ear_clipping_impl.scad>;
 
-// ret: "TRI_SHAPES", "TRI_INDICES"
 function tri_ear_clipping(shape_pts,  ret = "TRI_INDICES", epsilon = 0.0001) = 
     let(tris = _tri_ear_clipping_impl(shape_pts,  epsilon))
     ret == "TRI_INDICES" ? tris : [for(tri = tris) [for(idx = tri) shape_pts[idx]]];