Squashed commit of the following:

commit 421e56d37d738c8a97dcd01fcee858de54954efc
Merge: 9c5325b 4eb61c0
Author: liabru <liabru@brm.io>
Date:   Tue Jan 12 23:33:43 2021 +0000

    Merge branch 'removeDuplicatePoints' of https://github.com/tumult/matter-js into tumult-removeDuplicatePoints

    # Conflicts:
    #	src/factory/Bodies.js

commit 4eb61c0
Author: Jonathan Deutsch <jonathan@tumult.com>
Date:   Thu Jul 26 15:37:00 2018 -0700

    change removeDuplicatePoints precision to default in docs

commit 6c5d406
Author: Jonathan Deutsch <jonathan@tumult.com>
Date:   Thu Jul 26 14:33:39 2018 -0700

    Add removeDuplicatePoints option from polygon-decomp 0.3.0 to Bodies.fromVertices()

demo/lib/decomp.js

@@ -4,6 +4,7 @@ module.exports = {
     quickDecomp: polygonQuickDecomp,
     isSimple: polygonIsSimple,
     removeCollinearPoints: polygonRemoveCollinearPoints,
+    removeDuplicatePoints: polygonRemoveDuplicatePoints,
     makeCCW: polygonMakeCCW
 };
 
@@ -179,6 +180,9 @@ function polygonMakeCCW(polygon){
     // reverse poly if clockwise
     if (!isLeft(polygonAt(polygon, br - 1), polygonAt(polygon, br), polygonAt(polygon, br + 1))) {
         polygonReverse(polygon);
+        return true;
+    } else {
+        return false;
     }
 }
 
@@ -243,6 +247,27 @@ function polygonCanSee(polygon, a,b) {
     return true;
 }
 
+/**
+ * Check if two vertices in the polygon can see each other
+ * @method canSee2
+ * @param  {Number} a Vertex index 1
+ * @param  {Number} b Vertex index 2
+ * @return {Boolean}
+ */
+function polygonCanSee2(polygon, a,b) {
+    // for each edge
+    for (var i = 0; i !== polygon.length; ++i) {
+        // ignore incident edges
+        if (i === a || i === b || (i + 1) % polygon.length === a || (i + 1) % polygon.length === b){
+            continue;
+        }
+        if( lineSegmentsIntersect(polygonAt(polygon, a), polygonAt(polygon, b), polygonAt(polygon, i), polygonAt(polygon, i+1)) ){
+            return false;
+        }
+    }
+    return true;
+}
+
 /**
  * Copy the polygon from vertex i to vertex j.
  * @method copy
@@ -526,9 +551,12 @@ function polygonQuickDecomp(polygon, result,reflexVertices,steinerPoints,delta,m
                 }
 
                 for (var j = lowerIndex; j <= upperIndex; ++j) {
-                    if (isLeftOn(polygonAt(poly, i - 1), polygonAt(poly, i), polygonAt(poly, j)) && isRightOn(polygonAt(poly, i + 1), polygonAt(poly, i), polygonAt(poly, j))) {
+                    if (
+                        isLeftOn(polygonAt(poly, i - 1), polygonAt(poly, i), polygonAt(poly, j)) &&
+                        isRightOn(polygonAt(poly, i + 1), polygonAt(poly, i), polygonAt(poly, j))
+                    ) {
                         d = sqdist(polygonAt(poly, i), polygonAt(poly, j));
-                        if (d < closestDist) {
+                        if (d < closestDist && polygonCanSee2(poly, i, j)) {
                             closestDist = d;
                             closestIndex = j % polygon.length;
                         }
@@ -585,6 +613,23 @@ function polygonRemoveCollinearPoints(polygon, precision){
     return num;
 }
 
+/**
+ * Remove duplicate points in the polygon.
+ * @method removeDuplicatePoints
+ * @param  {Number} [precision] The threshold to use when determining whether two points are the same. Use zero for best precision.
+ */
+function polygonRemoveDuplicatePoints(polygon, precision){
+    for(var i=polygon.length-1; i>=1; --i){
+        var pi = polygon[i];
+        for(var j=i-1; j>=0; --j){
+            if(points_eq(pi, polygon[j], precision)){
+                polygon.splice(i,1);
+                continue;
+            }
+        }
+    }
+}
+
 /**
  * Check if two scalars are equal
  * @static
@@ -596,9 +641,22 @@ function polygonRemoveCollinearPoints(polygon, precision){
  */
 function scalar_eq(a,b,precision){
     precision = precision || 0;
-    return Math.abs(a-b) < precision;
+    return Math.abs(a-b) <= precision;
+}
+
+/**
+ * Check if two points are equal
+ * @static
+ * @method points_eq
+ * @param  {Array} a
+ * @param  {Array} b
+ * @param  {Number} [precision]
+ * @return {Boolean}
+ */
+function points_eq(a,b,precision){
+    return scalar_eq(a[0],b[0],precision) && scalar_eq(a[1],b[1],precision);
 }
 
 },{}]},{},[1])
 (1)
-});
+});

src/factory/Bodies.js

@@ -193,9 +193,10 @@ var Vector = require('../geometry/Vector');
      * @param {bool} [flagInternal=false]
      * @param {number} [removeCollinear=0.01]
      * @param {number} [minimumArea=10]
+     * @param {number} [removeDuplicatePoints=0.01]
      * @return {body}
      */
-    Bodies.fromVertices = function(x, y, vertexSets, options, flagInternal, removeCollinear, minimumArea) {
+    Bodies.fromVertices = function(x, y, vertexSets, options, flagInternal, removeCollinear, minimumArea, removeDuplicatePoints) {
         var globals = typeof global !== 'undefined' ? global : window,
             decomp,
             body,
@@ -220,6 +221,7 @@ var Vector = require('../geometry/Vector');
         flagInternal = typeof flagInternal !== 'undefined' ? flagInternal : false;
         removeCollinear = typeof removeCollinear !== 'undefined' ? removeCollinear : 0.01;
         minimumArea = typeof minimumArea !== 'undefined' ? minimumArea : 10;
+        removeDuplicatePoints = typeof removeDuplicatePoints !== 'undefined' ? removeDuplicatePoints : 0.01;
 
         if (!decomp) {
             Common.warn('Bodies.fromVertices: poly-decomp.js required. Could not decompose vertices. Fallback to convex hull.');
@@ -256,6 +258,8 @@ var Vector = require('../geometry/Vector');
                 decomp.makeCCW(concave);
                 if (removeCollinear !== false)
                     decomp.removeCollinearPoints(concave, removeCollinear);
+                if (removeDuplicatePoints !== false)
+                    decomp.removeDuplicatePoints(concave, removeDuplicatePoints);
 
                 // use the quick decomposition algorithm (Bayazit)
                 var decomposed = decomp.quickDecomp(concave);