How to implement bullet knockback?

Question

I'm trying to make a clone of Super Crate Box (simple 2D platformer with shooting mechanics; just to learn Godot). I'm not sure how to implement the knockback effect when enemy gets hit by a bullet.

In order to check for collisions I use Area2D. The bullets checks for collision with the script like so:

# BULLET
func _on_Area2D_body_enter( body ):
if body.get_meta("type") == "enemy":
    set_process(false)
    body.get_hit(5, (get_global_pos() - body.get_global_pos()).normalized() * 100)
    queue_free()
else:
    pass

On the enemy the get_hit() function looks as follows:

# ENEMY
func get_hit(dmg, force):
# print("Got hit with dmg: " + str(dmg) + "and force of: " + str(force))
health -= dmg
move(force)

In this code the idea was to compute the difference in positions between the bullet and the enemy at the moment the bullet hits. I could then use this vector (or just it's horizontal part) to move the enemy back a bit. Unfortunately the computed vector is unreliable. Sometimes its horizontal (x) part is has opposite sign than expected.

To be honest I'm not sure I should be using Area2D and checking for its entering and leaving. The enemy and the bullet are KinematicBody2D. I don't need any elaborate physics in this game. Simple knockback seems like a job for a force impulse but that would require RigidBody2D... am I right?

How should I go about it? Should I stick to Area2D for collision checking?

Also I'm new so I hope I made this question as concise and as clear as possible and I did everything according to the rules. If not please let me know.

Comments

You could use the vector of the bullet's flying direction to calculate the knockback angle and the bullet's speed for the force.

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Heavy btw, you know, getting hit by bullet does NOT knock you back, thats 110% hollywood ;D

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Using the bullets velocity vector makes a lot of sense actually... Thank you.

Answer 1

You can use RigidBody2D's impulse, but you may not ever get it behaving quite the way you like.

With Kinematic2D you just need to calculate some force to be applied to the box, then every frame add it to the target and reduce it, until it ceases to exist. Maybe at some threshold value you clamp it or remove it. Then you would fine tune the force and the reduction factor as you like. Maybe even take into account the mass of the object too.

The normal direction should just be the (B - A).normalized(). Where B is your point of contact for the bullet, and A is your point of origin of the bullet.

Comments

I used the point of origin and the point of collision (only x part of difference of those two). I also used move_to() function. Seems to work good for now. Thank you.

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You're welcome. ^_^ Glad it worked out.