optimised contacts and supports memory and gc use

src/collision/Collision.js

@@ -47,7 +47,8 @@ var Pair = require('./Pair');
             normal: { x: 0, y: 0 },
             tangent: { x: 0, y: 0 },
             penetration: { x: 0, y: 0 },
-            supports: []
+            supports: [null, null],
+            supportCount: 0
         };
     };
 
@@ -152,10 +153,8 @@ var Pair = require('./Pair');
             supports[supportCount++] = supportsB[0];
         }
 
-        // update supports array size if changed
-        if (supports.length !== supportCount) {
-            supports.length = supportCount;
-        }
+        // update support count
+        collision.supportCount = supportCount;
 
         return collision;
     };
@@ -374,11 +373,26 @@ var Pair = require('./Pair');
 
     /**
      * An array of body vertices that represent the support points in the collision.
+     * 
+     * _Note:_ Only the first `collision.supportCount` items of `collision.supports` are active.
+     * Therefore use `collision.supportCount` instead of `collision.supports.length` when iterating the active supports.
+     * 
      * These are the deepest vertices (along the collision normal) of each body that are contained by the other body's vertices.
      *
      * @property supports
      * @type vector[]
      * @default []
      */
 
+    /**
+     * The number of active supports for this collision found in `collision.supports`.
+     * 
+     * _Note:_ Only the first `collision.supportCount` items of `collision.supports` are active.
+     * Therefore use `collision.supportCount` instead of `collision.supports.length` when iterating the active supports.
+     *
+     * @property supportCount
+     * @type number
+     * @default 0
+     */
+
 })();

src/collision/Contact.js

@@ -13,7 +13,7 @@ module.exports = Contact;
     /**
      * Creates a new contact.
      * @method create
-     * @param {vertex} vertex
+     * @param {vertex} [vertex]
      * @return {contact} A new contact
      */
     Contact.create = function(vertex) {

src/collision/Pair.js

@@ -28,8 +28,8 @@ var Contact = require('./Contact');
             bodyA: bodyA,
             bodyB: bodyB,
             collision: collision,
-            contacts: [],
-            activeContacts: [],
+            contacts: [Contact.create(), Contact.create()],
+            contactCount: 0,
             separation: 0,
             isActive: true,
             confirmedActive: true,
@@ -56,12 +56,11 @@ var Contact = require('./Contact');
      * @param {number} timestamp
      */
     Pair.update = function(pair, collision, timestamp) {
-        var contacts = pair.contacts,
-            supports = collision.supports,
-            activeContacts = pair.activeContacts,
+        var supports = collision.supports,
+            supportCount = collision.supportCount,
+            contacts = pair.contacts,
             parentA = collision.parentA,
-            parentB = collision.parentB,
-            parentAVerticesLength = parentA.vertices.length;
+            parentB = collision.parentB;
 
         pair.isActive = true;
         pair.timeUpdated = timestamp;
@@ -73,27 +72,31 @@ var Contact = require('./Contact');
         pair.restitution = parentA.restitution > parentB.restitution ? parentA.restitution : parentB.restitution;
         pair.slop = parentA.slop > parentB.slop ? parentA.slop : parentB.slop;
 
+        pair.contactCount = supportCount;
         collision.pair = pair;
 
-        var activeContactIndex = 0,
-            supportsLength = supports.length;
-
-        for (var i = 0; i < supportsLength; i++) {
-            var support = supports[i],
-                contactId = support.body === parentA ? support.index : parentAVerticesLength + support.index,
-                contact = contacts[contactId];
-
-            if (contact) {
-                activeContacts[activeContactIndex++] = contact;
-            } else {
-                contact = Contact.create(support);
-                activeContacts[activeContactIndex++] = contact;
-                contacts[contactId] = contact;
-            }
+        var support = supports[0],
+        contact = contacts[0];
+
+        // reset first contact if support changed
+        if (contact.vertex !== support) {
+            contact.vertex = support;
+            contact.normalImpulse = 0;
+            contact.tangentImpulse = 0;
         }
 
-        if (activeContacts.length !== activeContactIndex) {
-            activeContacts.length = activeContactIndex;
+        if (supportCount < 2) {
+            return;
+        }
+
+        support = supports[1];
+        contact = contacts[1];
+
+        // reset second contact if support changed
+        if (contact.vertex !== support) {
+            contact.vertex = support;
+            contact.normalImpulse = 0;
+            contact.tangentImpulse = 0;
         }
     };
 
@@ -110,7 +113,7 @@ var Contact = require('./Contact');
             pair.timeUpdated = timestamp;
         } else {
             pair.isActive = false;
-            pair.activeContacts.length = 0;
+            pair.contactCount = 0;
         }
     };
 

src/collision/Resolver.js

@@ -29,7 +29,7 @@ var Bounds = require('../geometry/Bounds');
     Resolver.preSolvePosition = function(pairs) {
         var i,
             pair,
-            activeCount,
+            contactCount,
             pairsLength = pairs.length;
 
         // find total contacts on each body
@@ -39,9 +39,9 @@ var Bounds = require('../geometry/Bounds');
             if (!pair.isActive)
                 continue;
 
-            activeCount = pair.activeContacts.length;
-            pair.collision.parentA.totalContacts += activeCount;
-            pair.collision.parentB.totalContacts += activeCount;
+            contactCount = pair.contactCount;
+            pair.collision.parentA.totalContacts += contactCount;
+            pair.collision.parentB.totalContacts += contactCount;
         }
     };
 
@@ -176,16 +176,16 @@ var Bounds = require('../geometry/Bounds');
             if (!pair.isActive || pair.isSensor)
                 continue;
 
-            var contacts = pair.activeContacts,
-                contactsLength = contacts.length,
+            var contacts = pair.contacts,
+                contactCount = pair.contactCount,
                 collision = pair.collision,
                 bodyA = collision.parentA,
                 bodyB = collision.parentB,
                 normal = collision.normal,
                 tangent = collision.tangent;
 
             // resolve each contact
-            for (j = 0; j < contactsLength; j++) {
+            for (j = 0; j < contactCount; j++) {
                 var contact = contacts[j],
                     contactVertex = contact.vertex,
                     normalImpulse = contact.normalImpulse,
@@ -254,9 +254,9 @@ var Bounds = require('../geometry/Bounds');
                 normalY = collision.normal.y,
                 tangentX = collision.tangent.x,
                 tangentY = collision.tangent.y,
-                contacts = pair.activeContacts,
-                contactsLength = contacts.length,
-                contactShare = 1 / contactsLength,
+                contacts = pair.contacts,
+                contactCount = pair.contactCount,
+                contactShare = 1 / contactCount,
                 inverseMassTotal = bodyA.inverseMass + bodyB.inverseMass,
                 friction = pair.friction * pair.frictionStatic * frictionNormalMultiplier;
 
@@ -269,7 +269,7 @@ var Bounds = require('../geometry/Bounds');
             bodyB.angularVelocity = bodyB.angle - bodyB.anglePrev;
 
             // resolve each contact
-            for (j = 0; j < contactsLength; j++) {
+            for (j = 0; j < contactCount; j++) {
                 var contact = contacts[j],
                     contactVertex = contact.vertex;
 

src/render/Render.js

@@ -1205,8 +1205,8 @@ var Mouse = require('../core/Mouse');
                 continue;
 
             collision = pair.collision;
-            for (j = 0; j < pair.activeContacts.length; j++) {
-                var contact = pair.activeContacts[j],
+            for (j = 0; j < pair.contactCount; j++) {
+                var contact = pair.contacts[j],
                     vertex = contact.vertex;
                 c.rect(vertex.x - 1.5, vertex.y - 1.5, 3.5, 3.5);
             }
@@ -1230,13 +1230,13 @@ var Mouse = require('../core/Mouse');
 
             collision = pair.collision;
 
-            if (pair.activeContacts.length > 0) {
-                var normalPosX = pair.activeContacts[0].vertex.x,
-                    normalPosY = pair.activeContacts[0].vertex.y;
+            if (pair.contactCount > 0) {
+                var normalPosX = pair.contacts[0].vertex.x,
+                    normalPosY = pair.contacts[0].vertex.y;
 
-                if (pair.activeContacts.length === 2) {
-                    normalPosX = (pair.activeContacts[0].vertex.x + pair.activeContacts[1].vertex.x) / 2;
-                    normalPosY = (pair.activeContacts[0].vertex.y + pair.activeContacts[1].vertex.y) / 2;
+                if (pair.contactCount === 2) {
+                    normalPosX = (pair.contacts[0].vertex.x + pair.contacts[1].vertex.x) / 2;
+                    normalPosY = (pair.contacts[0].vertex.y + pair.contacts[1].vertex.y) / 2;
                 }
 
                 if (collision.bodyB === collision.supports[0].body || collision.bodyA.isStatic === true) {