Help with collisions in space

Help Programming
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1

Godot Version

4.5

Question

I am making a space game with momentum based movement and I am trying to make collisions where you bounce off of things. Right now, when I hit something light, I think it mostly works, but when I hit a planet(20000kg), I just stop.
Here’s my movement and collision code:

    var target_acceleration = Vector3.ZERO
	var relative_acceleration = Vector3.ZERO
	if Input.is_key_pressed(KEY_W):
		target_acceleration.z += (-acceleration*delta) #Applying axial acceleration, compensated for time since last tick
	if Input.is_key_pressed(KEY_S):
		target_acceleration.z += (acceleration*delta)#Applying axial acceleration, compensated for time since last tick
	if Input.is_key_pressed(KEY_A):
		target_acceleration.x += (-acceleration*delta)#Applying axial acceleration, compensated for time since last tick
	if Input.is_key_pressed(KEY_D):
		target_acceleration.x += (acceleration*delta)#Applying axial acceleration, compensated for time since last tick
	if Input.is_key_pressed(KEY_CTRL):
		target_acceleration.y += (-acceleration*delta)#Applying axial acceleration, compensated for time since last tick
	if Input.is_key_pressed(KEY_SPACE):
		target_acceleration.y += (acceleration*delta)#Applying axial acceleration, compensated for time since last tick
	
	relative_acceleration = transform.basis * target_acceleration #Rotate movement to be relative to ship's orientation
	target_velocity += relative_acceleration #Apply acceleration
	
	target_velocity *= natural_deceleration #Natural deceleration
	
	velocity = target_velocity
	velocity += get_gravity() #Apply gravity

	bounces = 0
	remaining = velocity * delta
	
	impact = move_and_collide(remaining) #Built in function to have nice movement, velocity, and collision
	
	if impact != null:
		velocity = velocity.bounce(impact.get_normal())
		remaining = impact.get_remainder()
		
		impact = null
		impact = move_and_collide(remaining)

Thanks to pizza_delivery_man and hyvernox, here is fixed code:

	var target_acceleration = Vector3.ZERO
	var relative_acceleration = Vector3.ZERO
	if Input.is_key_pressed(KEY_W):
		target_acceleration.z += (-acceleration*delta) #Applying axial acceleration, compensated for time since last tick
	if Input.is_key_pressed(KEY_S):
		target_acceleration.z += (acceleration*delta)#Applying axial acceleration, compensated for time since last tick
	if Input.is_key_pressed(KEY_A):
		target_acceleration.x += (-acceleration*delta)#Applying axial acceleration, compensated for time since last tick
	if Input.is_key_pressed(KEY_D):
		target_acceleration.x += (acceleration*delta)#Applying axial acceleration, compensated for time since last tick
	if Input.is_key_pressed(KEY_CTRL):
		target_acceleration.y += (-acceleration*delta)#Applying axial acceleration, compensated for time since last tick
	if Input.is_key_pressed(KEY_SPACE):
		target_acceleration.y += (acceleration*delta)#Applying axial acceleration, compensated for time since last tick
	
	relative_acceleration = transform.basis * target_acceleration #Rotate movement to be relative to ship's orientation
	target_velocity += relative_acceleration #Apply acceleration
	
	target_velocity *= natural_deceleration #Natural deceleration
	
	velocity = target_velocity
	velocity += get_gravity() * delta #Apply gravity

	
	impact = move_and_collide(velocity*delta) #Built in function to have nice movement, velocity, and collision
	
	if impact != null:
		var collider = impact.get_collider()
		var bounce = collider.physics_material_override.bounce
		
		var impact_normal = impact.get_normal()
		#impact_normal *= bounce
		#impact_normal = impact_normal.normalized()
				
		velocity = velocity.bounce(impact_normal)
		velocity *= bounce
		target_velocity = velocity
		
		impact = null
		impact = move_and_collide(velocity*delta)
2

Are you sure the remainder goes into move_and_collide() ?
I would expect the velocity should.
Also with momentum transfer all momentum is conserved … m1v1 + m2v2 =[const] and its the same before and after the collision.

its possible that the spaceship would not bounce much. (Especially if theres no angle). The planet should weigh (edit: have greater mass than…) more than 20 metric tons.

If we are talking cartoon physics, then im not sure … if that isnt cartoony anyway. In real life there could be energy dissipated as heat, dust, derbris taking some energy as momentum etc.

1 Like
3

I’ve got the bounce actually working, the trouble I have now is that when I pull the bounce from the RididBody(planet) I bounce with more velocity than I started. What did I do wrong?

	if impact != null:
		var collider = impact.get_collider()
		var bounce = collider.physics_material_override.bounce
		
		var impact_normal = impact.get_normal()
		impact_normal *= bounce
		impact_normal = impact_normal.normalized()
				
		velocity = velocity.bounce(impact_normal)
		target_velocity = velocity
		
		impact = null
		impact = move_and_collide(velocity*delta)
4

The planet is moving? I cant tell without running the code to be honest.

The planets momentum m2×v2 is greater … so when the objects collide the [const] is preserved and the ships momentum m1×v1 grabs some velocity (or energy) from the planet in the collision, so the planet slows and the ship goes much faster …

v1 =( [const] - m2× v2)/m1

So you would have to replace [const] with initial momentum of the system and compute the new v1 if you knew v2 … or the change in v2 … then it would make sense.

5

First you take the collision normal, then you multiply it by bounce just to normalize it afterwards?

Shouldn’t you mutliply the velocity by bounce instead?

6

Yes that was me being stupid. That seems to work as intended now, thanks for the help.

7

No, I just worded poorly. Sorry!
Thanks for the help, I think I’ve got it solved now.