More fine-grained collision filtering in the style of Box2D

demo/dev.html

@@ -61,6 +61,7 @@
                     <option value="beachBalls">Beach Balls</option>
                     <option value="stress">Stress 1</option>
                     <option value="stress2">Stress 2</option>
+                    <option value="collisionFiltering">Collision Filtering</option>
                 </select>
                 <input id="demo-reset" value="Reset" type="submit">
             </div>

demo/js/Demo.js

@@ -448,12 +448,12 @@
     
     Demo.chains = function() {
         var _world = _engine.world,
-            groupId = Body.nextGroupId();
+            groupId = Body.nextNonCollidingGroupId();
         
         Demo.reset();
          
         var ropeA = Composites.stack(200, 100, 5, 2, 10, 10, function(x, y, column, row) {
-            return Bodies.rectangle(x, y, 50, 20, { groupId: groupId });
+            return Bodies.rectangle(x, y, 50, 20, { collisionFilter: {group: groupId} });
         });
         
         Composites.chain(ropeA, 0.5, 0, -0.5, 0, { stiffness: 0.8, length: 2 });
@@ -466,10 +466,10 @@
         
         World.add(_world, ropeA);
         
-        groupId = Body.nextGroupId();
+        groupId = Body.nextNonCollidingGroupId();
         
         var ropeB = Composites.stack(500, 100, 5, 2, 10, 10, function(x, y, column, row) {
-            return Bodies.circle(x, y, 20, { groupId: groupId });
+            return Bodies.circle(x, y, 20, { collisionFilter: {group: groupId} });
         });
         
         Composites.chain(ropeB, 0.5, 0, -0.5, 0, { stiffness: 0.8, length: 2 });
@@ -485,12 +485,12 @@
 
     Demo.bridge = function() {
         var _world = _engine.world,
-            groupId = Body.nextGroupId();
+            groupId = Body.nextNonCollidingGroupId();
         
         Demo.reset();
          
         var bridge = Composites.stack(150, 300, 9, 1, 10, 10, function(x, y, column, row) {
-            return Bodies.rectangle(x, y, 50, 20, { groupId: groupId });
+            return Bodies.rectangle(x, y, 50, 20, { collisionFilter: {group: groupId} });
         });
         
         Composites.chain(bridge, 0.5, 0, -0.5, 0, { stiffness: 0.9 });
@@ -937,8 +937,8 @@
         
         Demo.reset();
 
-        var groupId = Body.nextGroupId(),
+        var groupId = Body.nextNonCollidingGroupId(),
-            particleOptions = { friction: 0.00001, groupId: groupId, render: { visible: false }},
+            particleOptions = { friction: 0.00001, collisionFilter: { group: groupId }, render: { visible: false }},
             cloth = Composites.softBody(200, 200, 20, 12, 5, 5, false, 8, particleOptions);
 
         for (var i = 0; i < 20; i++) {
@@ -1231,6 +1231,44 @@
         var renderOptions = _engine.render.options;
     };
 
+    Demo.collisionFiltering = function() {
+        var _world = _engine.world;
+
+        Demo.reset();
+
+        var i;
+
+        World.add(_world,
+            Composites.stack(275, 150, 5, 10, 10, 10, function(x, y, column, row) {
+                return Bodies.circle(x, y, 20, {
+                    collisionFilter: {
+                        category: row < 7 ? 2 : 4
+                    },
+                    render: {
+                        strokeStyle: row < 7 ? 'red' : 'green',
+                        fillStyle: 'transparent'
+                    }
+                });
+            })
+        );
+
+        World.add(_world,
+            Bodies.circle(400, 40, 30, {
+                collisionFilter: {
+                    mask: 5
+                },
+                render: {
+                    fillStyle: 'blue'
+                }
+            })
+        );
+
+        var renderOptions = _engine.render.options;
+        renderOptions.wireframes = false;
+        renderOptions.background = '#111';
+        renderOptions.showCollisions = true;
+    };
+
     // the functions for the demo interface and controls below
 
     Demo.initControls = function() {

src/body/Body.js

@@ -15,7 +15,8 @@ var Body = {};
 
     Body._inertiaScale = 4;
 
-    var _nextGroupId = 1;
+    var _nextCollidingGroupId = 1,
+        _nextNonCollidingGroupId = -1;
 
     /**
      * Creates a new rigid body model. The options parameter is an object that specifies any properties you wish to override the defaults.
@@ -49,7 +50,11 @@ var Body = {};
             restitution: 0,
             friction: 0.1,
             frictionAir: 0.01,
-            groupId: 0,
+            collisionFilter: {
+                category: 1,
+                mask: 0xFFFFFFFF,
+                group: 0
+            },
             slop: 0.05,
             timeScale: 1,
             render: {
@@ -70,12 +75,21 @@ var Body = {};
     };
 
     /**
-     * Returns the next unique groupID number.
+     * Returns the next unique groupID number for which bodies will collide.
-     * @method nextGroupId
+     * @method nextCollidingGroupId
      * @return {Number} Unique groupID
      */
-    Body.nextGroupId = function() {
+    Body.nextCollidingGroupId = function() {
-        return _nextGroupId++;
+        return _nextCollidingGroupId++;
+    };
+
+    /**
+     * Returns the next collisionFilter.group value for which bodies will not collide.
+     * @method nextNonCollidingGroupId
+     * @return {Number} Unique groupID
+     */
+    Body.nextNonCollidingGroupId = function() {
+        return _nextNonCollidingGroupId--;
     };
 
     /**
@@ -673,18 +687,56 @@ var Body = {};
      */
 
     /**
-     * An integer `Number` that specifies the collision group the body belongs to. 
+     * An `Object` that specifies the collision filtering properties of this body.
-     * Bodies with the same `groupId` are considered _as-one_ body and therefore do not interact.
-     * This allows for creation of segmented bodies that can self-intersect, such as a rope.
-     * The default value 0 means the body does not belong to a group, and can interact with all other bodies.
      *
-     * @property groupId
+     * Collisions between two bodies will obey the following rules:
-     * @type number
+     * - If the two bodies have the same non-zero value of `collisionFilter.group`,
+     *   they will always collide if the value is positive, and they will never collide
+     *   if the value is negative.
+     * - If the two bodies have different values of `collisionFilter.group` or if one
+     *   (or both) of the bodies has a value of 0, then the category/mask rules apply as follows:
+     *
+     * Each body belongs to a collision category, given by `collisionFilter.category`. This
+     * value is used as a bit field and the category should have only one bit set, meaning that
+     * the value of this property is a power of two in the range [1, 2^31]. Thus, there are 32
+     * different collision categories available.
+     * Each body also defines a collision bitmask, given by `collisionFilter.mask` which specifies
+     * the categories it collides with (the value is the bitwise AND value of all these categories).
+     *
+     * Using the category/mask rules, two bodies `A` and `B` collide if each includes the other's
+     * category in its mask, i.e. `(categoryA & maskB) !== 0` and `(categoryB & maskA) !== 0`
+     * are both true.
+     *
+     * @property collisionFilter
+     * @type object
+     */
+
+    /**
+     * An Integer `Number`, see `collisionFilter`
+     *
+     * @property collisionFilter.group
+     * @type object
      * @default 0
      */
 
     /**
-     * A `Number` that specifies a tollerance on how far a body is allowed to 'sink' or rotate into other bodies.
+     * An Integer `Number`, see `collisionFilter`
+     *
+     * @property collisionFilter.category
+     * @type object
+     * @default 1
+     */
+
+    /**
+     * An Integer `Number`, see `collisionFilter`
+     *
+     * @property collisionFilter.mask
+     * @type object
+     * @default -1
+     */
+
+    /**
+     * A `Number` that specifies a tolerance on how far a body is allowed to 'sink' or rotate into other bodies.
      * Avoid changing this value unless you understand the purpose of `slop` in physics engines.
      * The default should generally suffice, although very large bodies may require larger values for stable stacking.
      *

src/collision/Detector.js

@@ -26,14 +26,15 @@ var Detector = {};
             var bodyA = broadphasePairs[i][0], 
                 bodyB = broadphasePairs[i][1];
 
-            // NOTE: could share a function for the below, but may drop performance?
+            var collisionFilterA = bodyA.collisionFilter,
-
+                collisionFilterB = bodyB.collisionFilter;
-            if (bodyA.groupId && bodyB.groupId && bodyA.groupId === bodyB.groupId)
-                continue;
 
             if ((bodyA.isStatic || bodyA.isSleeping) && (bodyB.isStatic || bodyB.isSleeping))
                 continue;
             
+            if (!_pairCollides(collisionFilterA, collisionFilterB))
+                continue;
+
             metrics.midphaseTests += 1;
 
             // mid phase
@@ -128,4 +129,11 @@ var Detector = {};
         return collisions;
     };
     
+    var _pairCollides = function(filterA, filterB) {
+        if (filterA.group === filterB.group && filterA.group !== 0)
+            return filterA.group > 0;
+
+        return ((filterA.mask & filterB.category) !== 0 && (filterB.mask & filterA.category) !== 0);
+    };
+
 })();

src/factory/Composites.js

@@ -226,7 +226,7 @@ var Composites = {};
      * @return {composite} A new composite car body
      */
     Composites.car = function(xx, yy, width, height, wheelSize) {
-        var groupId = Body.nextGroupId(),
+        var collisionFilterGroup = Body.nextNonCollidingGroupId(),
             wheelBase = -20,
             wheelAOffset = -width * 0.5 + wheelBase,
             wheelBOffset = width * 0.5 - wheelBase,
@@ -234,7 +234,9 @@ var Composites = {};
     
         var car = Composite.create({ label: 'Car' }),
             body = Bodies.trapezoid(xx, yy, width, height, 0.3, { 
-                groupId: groupId, 
+                collisionFilter: {
+                    group: collisionFilterGroup
+                },
                 friction: 0.01,
                 chamfer: {
                     radius: 10
@@ -242,14 +244,18 @@ var Composites = {};
             });
     
         var wheelA = Bodies.circle(xx + wheelAOffset, yy + wheelYOffset, wheelSize, { 
-            groupId: groupId, 
+            collisionFilter: {
+                group: collisionFilterGroup
+            },
             restitution: 0.5, 
             friction: 0.9,
             density: 0.01
         });
                     
         var wheelB = Bodies.circle(xx + wheelBOffset, yy + wheelYOffset, wheelSize, { 
-            groupId: groupId, 
+            collisionFilter: {
+                group: collisionFilterGroup
+            },
             restitution: 0.5, 
             friction: 0.9,
             density: 0.01