More Interesting Collisions? [SOLVED]

[Ethan-Taylor]

Hey guys,
I'm using Hardon Collider for my project. At the moment I'm using it for everything including bullets that the player shoots.

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function ammo.update(dt)
	for i,v in ipairs(ammo) do
		if v.id == nil then
			v.id = ammo.id
			ammo.id = ammo.id + 1
		end

		v.bullet.type = v.id
		v.xvel = v.xvel + 12000 * dt * math.cos(v.angle)
		v.yvel = v.yvel + 12000 * dt * math.sin(v.angle)
		if v.reverse == 1 then
			v.x = v.x - (v.xvel + 1) * dt
			v.y = v.y - (v.yvel + 1) * dt
		else
			v.x = v.x + v.xvel * dt
			v.y = v.y + v.yvel * dt
		end

-- Continued

So basically when the bullet hits something v.reverse = 1
But is there a more realistic approach, rather than just reversing the bullet direction?
If so could you give me some code that will make the velocity do that?

Oh, and explain it too!

Cheerus

[ivan]

Hello Ethan,
It depends if you're going for 'realistic' physics,
in which case you can't just reverse the velocity during a collision.
For example, imagine a bullet hitting a wall.
If the wall is perpendicular to the bullet's path, then you can reverse its velocity:

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        |
------> |
        |

Now imagine a bullet hitting an inclined/slope tile.
It would look kind of strange if you reversed the velocity in the latter case:

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         /
------> /
       /

Usually you would want to 'deflect' the bullet based on the collision normal (axis of shortest separation).
One approach is:
collision_normal = separation / len(separation)
relative_velocity = bullet.velocity - wall.velocity
pen_speed = dot (relative_velocity, collision_normal)
pen_component = (normal * pen_speed)
restitution = [0-1] (0 restitution means non-elastic, 1 means perfectly elastic)
dt_velocity = pen_component*restitution

bullet.velocity = bullet.velocity - dt_velocity

Unfortunately, it gets more complicated if you want to have 'friction'.
Take a look at my short tutorial on game physics.

[Ethan-Taylor]

Hello Ethan,
It depends if you're going for 'realistic' physics,
in which case you can't just reverse the velocity during a collision.
For example, imagine a bullet hitting a wall.
If the wall is perpendicular to the bullet's path, then you can reverse its velocity:

How can the wall have velocity?!

[davisdude]

May just be me, but I think he means the bullet's velocity. Plus a wall does have velocity. It just has a magnitude of 0 and a direction of 0 degrees.

[ivan]

Yea, I didn't word it properly, I meant reversing the bullet's velocity.

And yes, as davis mentioned, stationary objects have velocity of 0, where 0 doesn't affect the equation:
relative_velocity = object1_velocity - object2_velocity

[Ethan-Taylor]

Yea, I didn't word it properly, I meant reversing the bullet's velocity.

And yes, as davis mentioned, stationary objects have velocity of 0, where 0 doesn't affect the equation:
relative_velocity = object1_velocity - object2_velocity

How do we convert the original code into v.xvel and v.yvel?
Sorry If I'm being a bit of a noob XD

[Ethan-Taylor]

Nvm.
I've got it up and running now.
Thanks for the support!