collision detection

This application demonstrates a simple technique for determining when a physical object of interest has collided with another object. Ideally, one can receive this information directly from the physics engine. However, in many contexts, the only situation in which an object has high acceleration is when collisions have occured. Therefore, one can simply get an empirical estimate of acceleration from successive velocity vectors, and use the magnitude of the result to guess when there has been a collision.

1-2-three
example 24: collision detection

<!DOCTYPE html>
<html>
<head>
<title>example 24: collision detection</title>

var overlay = null;

function b2three(trans,mat) {
  var basis = trans.getBasis();
  var origin = trans.getOrigin();
  var m = mat.elements;
  var v = basis.getRow(0);
  m[0] = v.x(); m[4+0] = v.y(); m[8+0] = v.z(); m[12+0] = origin.x();
  v = basis.getRow(1);
  m[1] = v.x(); m[4+1] = v.y(); m[8+1] = v.z(); m[12+1] = origin.y();
  v = basis.getRow(2);
  m[2] = v.x(); m[4+2] = v.y(); m[8+2] = v.z(); m[12+2] = origin.z();
  m[3] = 0.0; m[4+3] = 0.0; m[8+3] = 0.0; m[12+3] = 1.0;
}

function initPhysics() {
  var collision_config = new Ammo.btDefaultCollisionConfiguration();
  var dispatcher = new Ammo.btCollisionDispatcher( collision_config );
  var overlappingPairCache =  new Ammo.btDbvtBroadphase();
  var solver = new Ammo.btSequentialImpulseConstraintSolver();
  dynamicsWorld = new Ammo.btDiscreteDynamicsWorld( dispatcher, overlappingPairCache, solver, collision_config );
  dynamicsWorld.setGravity(new Ammo.btVector3(0, -12, 0));
  return dynamicsWorld;
}

// body2world storage
var trans=new Ammo.btTransform();

function body2world(body,v3B) {
  var trans = body.getWorldTransform();
  var result = trans.op_mul(v3B);
  return result;
}

function init() {
  var mycanvas = document.getElementsByTagName("canvas")[0];
  var w = mycanvas.clientWidth;
  var h = mycanvas.clientHeight;
  
  if (!overlay)
    overlay = createOverlay(mycanvas);

renderer = new THREE.WebGLRenderer({canvas:mycanvas});
  renderer.setSize( w, h );

scene = new THREE.Scene();
  scene.matrixAutoUpdate = false;

camera = new THREE.PerspectiveCamera(
      35,     // Field of view
      w / h,  // Aspect ratio
      0.1,    // Near
      10000   // Far
  );
  camera.position.set( -30, 0, 50 );
  scene.add(camera);
  camera.lookAt( new THREE.Vector3(0,-15,0) );

var light = new THREE.PointLight( 0xFFFF33 );
  light.position.set( 10, 0, 10 );
  scene.add( light );
  
  light = new THREE.AmbientLight( 0xCCCCBB );
  scene.add( light );
  
  dynamicsWorld = initPhysics();
  
  // ground physics
  var groundShape=new Ammo.btBoxShape(new Ammo.btVector3(20,10,20));
  var groundTransform=new Ammo.btTransform();
  groundTransform.setIdentity();
  groundTransform.setOrigin(new Ammo.btVector3(0,-25,0));
  var localInertia=new Ammo.btVector3(0,0,0);
  var motionState = new Ammo.btDefaultMotionState( groundTransform );
  var cInfo = new Ammo.btRigidBodyConstructionInfo(0, motionState, groundShape, localInertia);
  var body=new Ammo.btRigidBody(cInfo);
  dynamicsWorld.addRigidBody(body);
  
  // ground visualization
  var groundCube = new THREE.Mesh(
    new THREE.CubeGeometry( 2*20, 2*10, 2*20 ),
    new THREE.MeshLambertMaterial( { color: 0x0000FF } )
  );
  scene.add( groundCube );
  groundCube.position.set(0,-25,0);
  
  var lander = new Lander(scene,dynamicsWorld);
  
  var isFirstFrame = true;
  var lastVel = new Ammo.btVector3();
  var clock = new THREE.Clock();
  
  function animate() {
    var dt = clock.getDelta();
    // cap dt to avoid instability
    var minSecPerFrame = 1.0 / 60;
    if (dt > minSecPerFrame) 
      dt = minSecPerFrame;
      
    dynamicsWorld.stepSimulation(dt,1);

function onKeyUp(evt) {
    switch (evt.keyCode) {
      case 65: // 'a'
        index = 0;
        lander.thrustCubeA[index].visible = false;
        lander.trimOnA[index] = false;
        break;
      case 68: // 'd'
        index = 1;
        lander.thrustCubeA[index].visible = false;
        lander.trimOnA[index] = false;
        break;
      case 87: // 'w'
        index = 3;
        lander.thrustCubeA[index].visible = false;
        lander.trimOnA[index] = false;
        break;
      case 83: // 's'
        index = 2;
        lander.thrustCubeA[index].visible = false;
        lander.trimOnA[index] = false;
        break;
      case 32: // spacebar
        lander.mainThrustCube.visible = false;
        lander.mainOn = false; 
        break;
    }
  }
  
  window.onkeydown = onKeyDown;
  window.onkeyup = onKeyUp;	
}

window.onload = init;
window.onresize = init;

</script>
 </head>
 <body>
  <div id="container">
   <canvas id="canvas" style="width:100%;height:95%;border:1px gray solid;"></canvas>
  </div>
 </body>
</html>

collision detection

1-2-threeexample 24: collision detection

1-2-three
example 24: collision detection