per-material friction and restitution

TomDDH · Jan 5, 2015 · 09c91fd · 09c91fd
1 parent ccb78bf
commit 09c91fd
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Showing 3 changed files with 99 additions and 4 deletions.
diff --git a/demos/simpleFriction.html b/demos/simpleFriction.html
@@ -0,0 +1,71 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>cannon.js - friction demo</title>
+    <meta charset="utf-8">
+    <link rel="stylesheet" href="css/style.css" type="text/css"/>
+    <meta name="viewport" content="width=device-width, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0">
+  </head>
+  <body>
+    <script src="../build/cannon.js"></script>
+    <script src="../build/cannon.demo.js"></script>
+    <script src="../libs/dat.gui.js"></script>
+    <script src="../libs/Three.js"></script>
+    <script src="../libs/TrackballControls.js"></script>
+    <script src="../libs/Detector.js"></script>
+    <script src="../libs/Stats.js"></script>
+    <script src="../libs/smoothie.js"></script>
+    <script>
+
+    /**
+     * How to set friction per material.
+     */
+
+    var demo = new CANNON.Demo(), size = 1.0;
+
+    demo.addScene("Friction", function(){
+        var shape = new CANNON.Box(new CANNON.Vec3(size,size,size));
+
+        // Create world
+        var world = demo.getWorld();
+        world.broadphase = new CANNON.NaiveBroadphase();
+        world.iterations = 10;
+
+        // Materials
+        var groundMaterial = new CANNON.Material();
+        groundMaterial.friction = 0.3;
+
+        // ground plane
+        var groundShape = new CANNON.Plane();
+        var groundBody = new CANNON.Body({ mass: 0, material: groundMaterial });
+        groundBody.addShape(groundShape);
+        world.add(groundBody);
+        demo.addVisual(groundBody);
+
+        // Create a slippery material (friction coefficient = 0.0)
+        var slipperyMaterial = new CANNON.Material();
+        slipperyMaterial.friction = 0;
+
+        // Create slippery box
+        var boxBody = new CANNON.Body({ mass: 1, material: slipperyMaterial });
+        boxBody.addShape(shape);
+        boxBody.position.set(0,0,5);
+        world.add(boxBody);
+        demo.addVisual(boxBody);
+
+        // Create box made of groundMaterial
+        var boxBody2 = new CANNON.Body({ mass: 10, material: groundMaterial });
+        boxBody2.addShape(shape);
+        boxBody2.position.set(size*4,0,5);
+        world.add(boxBody2);
+        demo.addVisual(boxBody2);
+
+        // Change gravity so the boxes will slide along x axis
+        world.gravity.set(-3,0,-60);
+      });
+
+      demo.start();
+
+    </script>
+  </body>
+</html>
diff --git a/src/material/Material.js b/src/material/Material.js
@@ -13,12 +13,24 @@ function Material(name){
      * @type {String}
      */
     this.name = name;
-    
+
     /**
      * material id.
      * @property id
      */
     this.id = Material.idCounter++;
+
+    /**
+     * Friction for this material.
+     * @property {number} friction
+     */
+    this.friction = -1;
+
+    /**
+     * Restitution for this material.
+     * @property {number} restitution
+     */
+    this.restitution = -1;
 }
 
 Material.idCounter = 0;
diff --git a/src/world/World.js b/src/world/World.js
@@ -588,7 +588,6 @@ World.prototype.internalStep = function(dt){
         } else {
             cm = this.defaultContactMaterial;
         }
-        var mu = cm.friction;
 
         // g = ( xj + rj - xi - ri ) .dot ( ni )
         var gvec = World_step_gvec;
@@ -602,7 +601,20 @@ World.prototype.internalStep = function(dt){
 
             c.enabled = bi.collisionResponse && bj.collisionResponse && si.collisionResponse && sj.collisionResponse;
 
-			c.restitution = cm.restitution;
+            var mu = cm.friction;
+            c.restitution = cm.restitution;
+
+            // If friction or restitution were specified in the material, use them
+            if(bi.material && bj.material){
+                if(bi.material.friction >= 0 && bj.material.friction >= 0){
+                    mu = bi.material.friction * bj.material.friction;
+                }
+
+                if(bi.material.restitution >= 0 && bj.material.restitution >= 0){
+                    c.restitution = bi.material.restitution * bj.material.restitution;
+                }
+            }
+
 			c.penetration = g;
 			c.setSpookParams(cm.contactEquationStiffness,
                              cm.contactEquationRelaxation,
@@ -614,7 +626,7 @@ World.prototype.internalStep = function(dt){
 			if(mu > 0){
 
 				// Create 2 tangent equations
-				var mug = mu*gnorm;
+				var mug = mu * gnorm;
 				var reducedMass = (bi.invMass + bj.invMass);
 				if(reducedMass > 0){
 					reducedMass = 1/reducedMass;