Help With Grenade Throwing (Almost Implemented)

Questions
1

Hello all,

Any physics guys/gals out there? I need some help implementing throwing a grenade…I have it almost figured out. Basically I have a scene successfully set up with CannonJS physics working via:

let gravityVector: Vector3 = new Vector3(0, -500, 0);
let physicsPlugin: CannonJSPlugin = new CannonJSPlugin(undefined, undefined, CANNON);
this.scene.enablePhysics(gravityVector, physicsPlugin);

And on G key pressed i create a sphere that will spawn at the current position of the camera with the appropriate aim vector (NOTE: The line of code I need help with is commented out):

document.addEventListener('keydown', event => { 
      if (this.isSceneLocked && event.code == 'KeyG') {

        let wm = this.camera.getWorldMatrix();
        let aimVector = Vector3.TransformNormal(Vector3.Forward(), wm).normalize();

        let sphere = Mesh.CreateSphere("sphere", 16, 10, this.scene);
        sphere.physicsImpostor = new PhysicsImpostor(sphere, PhysicsImpostor.SphereImpostor, { mass: 1, restitution: 0.9 }, this.scene);
        sphere.position = this.camera.position.add(aimVector);

        // NEED HELP WITH THIS ---> sphere.physicsImpostor.applyImpulse(this.camera.position.add(aimVector), this.camera.position);


      } 

});

which produces this result:

My goal is to be able to apply an impulse or force so that the “grenade” flies off towards the direction I am aiming with the crosshairs. But I cant seem to get the applyImpulse() code correct. And I want to be able to control the distance and arc of the grenade a bit.

As for the landing of the grenade I already know to add some linearDamping and angularDamping but I left that part out of my code snippet for brevity.

2

Check out the Holiday demo from 2020. That has the same idea but with snowballs!

You should be able to borrow right from that!

3

Thanks man Ill take a look now!

4

If you just need a bit of juice, scaling the impulse should do the trick
sphere.physicsImpostor.applyImpulse(aimVector.scale(20), sphere.position);

1 Like
5

So scaling it does make it launch nicely. However…no matter where I am facing it seems to launch in the Z direction (from the position of the camera) but not the direction i am facing

6

Make sure you try the edited code, and not the one I posted at first

7

Just tried the updated code… and it is producing this result:

The ball spins like crazy lol. Its fire from the correct vector it seems though. I tried scaling more but it just produced more spinning. The video may be a bit laggy but they are spinning super fast

It does seem to be working pretty well tho if i scale up to 500. Just lots of spin lol

8

UPDATE: This is the cleanest solution for me. Added some linearDamping to simulate friction and angularDamping to prevent the infinite spinning after contact with the ground. Also i changed the contactPoint to be new Vector3(0, .5, 0) to produce just a little bit of spin on impulse. On G Press:

    let wm = this.camera.getWorldMatrix();
    let aimVector = Vector3.TransformNormal(Vector3.Forward(), wm).normalize();

    let sphere = Mesh.CreateSphere("sphere", 16, 10, this.scene);
    sphere.physicsImpostor = new PhysicsImpostor(sphere, PhysicsImpostor.SphereImpostor, { mass: 1, restitution: 0.9 }, this.scene);
    sphere.position = this.camera.position.add(aimVector);

    sphere.physicsImpostor.physicsBody.linearDamping = .5; //friction
    sphere.physicsImpostor.physicsBody.angularDamping = .4; // prevent infinite spinning
    sphere.position = this.camera.position.add(aimVector);

    sphere.physicsImpostor.applyImpulse(aimVector.scale(1000), new Vector3(0, .5, 0))

Thanks @PirateJC and @Raggar for the help!

Final Result:

1 Like