koobas.hobune.stream
Rigidbody magnitude comparison is not working correctlly?
i want to compare the magnitudes of two rigidbodies and destroy the one that is moving slower when they collide. I do this by comparing the magnitudes of the 2 rigidbodies. It works fine most of the time but sometimes the wrong object gets destroyed, and when this happens one of the objects is completely at rest and the other is moving, so there is no way that the magnitudes would be equal. The code looks likes this:
function OnCollisionEnter(collision : Collision) {
if(collision.gameObject.tag == "projectile") {
if(collision.rigidbody.velocity.magnitude < rigidbody.velocity.magnitude) {
collision.gameObject.GetComponent(ProjectileScript).destroyMe(player);
}
}
any ideas??
Can you show us the code for the destroy$$anonymous$$e method?
Also, not related but small perofrmance improvement, use sqr$$anonymous$$agnitude when you just want to check a difference:
if(collision.rigidbody.velocity.sqr$$anonymous$$agnitude < rigidbody.velocity.sqr$$anonymous$$agnitude)
start with a Debug Log. As in :
Debug.Log(collision.rigidbody.velocity.magnitude); Debug.Log(rigidbody.velocity.magnitude);
that may provide a clue. also, the mass will affect magnitude along with speed, so if the objects have different masses, that could affect it.
Also might not be working as expected because they've already collided when it checks the velocity ; so the velocity has already changed, and isn't what it was before impact.
e.g.
before Impact : Obj01 speed = 100.0 , and Obj02 speed = 500.0 ; ... you want Obj01 to die here
... but...
After Impact : Obj01 got a kickstart from highspeed Obj02 and it's speed now = 50 heading in the other direction, and Obj02 bounced off the other one fairly hard and it's speed ended up decreasing to 35 so it dies ins$$anonymous$$d.
Not sure if that's what's going on here, but that's the first thing that came to $$anonymous$$d. Need the speeds of them from right BEFORE they hit each other, not afterward ; and not sure if OnCollisionEnter would call and calculate quite fast enough all the time to catch the speed before it changed. $$anonymous$$ight be why it works for you most of the time, but not always.
$$anonymous$$ass doesn't affect magnitude or speed at all, and it would be really wrong if it did. Velocity is speed/direction only, magnitude is simply how much speed there is. The only affect mass has is how much force it takes to get to a given speed.
duh, my mistake, of course. Thinking of the wrong thing
The magnitude inside OnCollisionXXX is the magnitude after the collision has been processed by the physics engine.
If you want the magnitude before the collision, you will have to save it in a variable and update it each FixedUpdate (in both scripts):
var prevSqrMagnitude : float;
void FixedUpdate()
{
prevSqrMagnitude = rigidbody.velocity.sqrMagnitude;
}
Then, in the script with the OnCollisionEnter function:
function OnCollisionEnter(collision : Collision) {
if(collision.gameObject.tag == "projectile") {
var projectile : ProjectileScript = collision.gameObject.GetComponent(ProjectileScript);
if(projectile.prevSqrMagnitude < prevSqrMagnitude ) {
projectile.destroyMe(player);
}
}
}
@Lo0NuhtiK may be right: the velocities may have been changed by the collision. You could store the velocities in FixedUpdate in both objects and compare them:
var lastVel: float = 0;
function FixedUpdate(){ // this function must exist in both scripts! lastVel = rigidbody.velocity.magnitude; }
function OnCollisionEnter(collision : Collision) { if (collision.gameObject.tag == "projectile") { var otherScript = collision.gameObject.GetComponent(ProjectileScript); if (otherScript.lastVel < lastVel){ // compare the velocities prior collision otherScript.destroyMe(player); } } }
