Physics and Terrains - WebGL Game Development - page 261

Cheating in the bullet action
In this section, we will talk about cheating in the physics world. For simplicity, the
code of the bullet should be similar to the grenade because all we need to do is to
change the direction vector of the impulse/force. The following code demonstrates
the application of impulse on our bullet object:
var impulse=jigLib.GLMatrix.multiplyVec3(this.initialModelMatrix,
[0,0,-2000]);
this.rigidBody.applyWorldImpulse(jigLib.Vector3DUtil.create
(impulse[0],impulse[1],impulse[2]),jigLib.Vector3DUtil.
create(pos.x,pos.y,pos.z));
We needed a strong impulse in the -Z direction, and that is it. However, most of the
time in games, we do want physics collisions detection but do not want the physics
engine to control the trajectory. So, let's visit a similar case. Open the Bullet.js ile
from primitive/game in your text editor.
The initialize function of the Bullet class is absolutely the same, except we check
if the rigid body is initialized. We initialize its position and add the body to the
physics system as follows:
Bullet.prototype.initialize=function() {
...
this.positions=[];
for(vari=0;i<count;++i){
this.positions.push(this.calculatePosition(i*this.steps));
}
if(this.rigidBody){
this.initializePosition();
this.system.addBody(this.rigidBody);
}
}
The initializePosition function takes an element from the positions array at
the this.counter value, transforms that value using initialModelMatrix from
the camera, and moves rigidBody to the new calculated position. This is where the
cheating happened. This function is also invoked from the update function. It simply
moves the rigidBody parameter to a predefined value; we did not let physics control
its motion/trajectory. Initially the counter is 0 to set the initial bullet location.
Bullet.prototype.initializePosition=function(){
var mat=mat4.create();
mat4.translate(mat,this.initialModelMatrix,this.
positions[this.counter]);
var newPos=jigLib.GLMatrix.multiplyVec3(mat,[0,0,-1]);
this.rigidBody.moveTo(jigLib.Vector3DUtil.create(newPos[0],
newPos[1],newPos[2]));
}