Multiple motions to affect parent node

Pechvogel

Hello,

I am still a rookie with Godot but made some great progress the last few days. Finished all my tutorials on Youtube/UAcademy and decided to start trying stuff on my own which brought me here.

Following guides online, I learned to work with a motion for my character. When pressing a button, I would increase x/y of that motion and call move_and_slide().

But now I want my character to be affected from different motions. My character node has for example 3 child nodes which could affect the character his motion. One on the left of the character and two on the right. If I press the left arrow, the one child node responsible for that direction should move the character. The same applies for the other two nodes that have to be activated when pressing the right arrow.

But here comes the thing I cannot get past yet without some help:

When pressing the left and right buttons together, my character should ONLY move to the right but with less force since the left is also applying force.

Any ideas how to get started with this? Is the Vector2 motion a good way to implement this or should I look at other alternatives?

Thanks a lot and have a great evening!

Cheers! Tom

Pechvogel

As final result I would like to have something like this: If I press the A key, the character should move to the right If I press the B key, the character should move up with DOUBLE force If I press the C key, the character should move in a skew motion

And ofcourse, the motions should cancel each other out.

Sorry for the tough question, thanks for the help!

Pechvogel

Maybe I can try to use Rigidbodies. Is it bad practise to let the colliders touch each other the whole time? Since they are pushing the character... Any performance issues?

TwistedTwigleg

You can just add multiple different vectors to the motion variable, which should get you something close to what I think you are looking for. For example, I think the following code should do something similar to what you are looking for:

extends KinematicBody2D
# The velocity/motion of the KinematicBody2D node
var motion = Vector2(0, 0)
# The strength of the force applied by each key
const A_KEY_FORCE = 10
const B_KEY_FORCE = 20
const C_KEY_FORCE = 10
func _ready():
	pass
func _physics_process(delta):
	# Make a vector to store the direction the input will cause the character to move in
	var input_motion = Vector2(0, 0)
	if (Input.is_action_pressed("A_Key"):
		# Add right movement to input_motion
		input_motion += Vector2(1, 0) * A_KEY_FORCE
	if (Input.is_action_pressed("B_Key"):
		# Add Upwards motion to input_motion
		input_motion += Vector2(0, -1) * B_KEY_FORCE
	if (Input.is_action_pressed("C_Key"):
		# Add a slanted left-up motion to input_motion
		input_motion += Vector2(-0.5, -0.5) * C_KEY_FORCE
	# Optional: clamp the motion within a maximum speed of 40 units
	if (input_motion.length() > 40):
		input_motion = input_motion.normalized() * 40
	# Set motion to input_motion
	# (you can also add input_motion to motion, depending on how you want the character to move)
	motion = input_motion
	# Move the player using move_and_slide
	motion = move_and_slide(motion)

I have not tested the code and it is very bare bones, but that is one way you could implement the code where it changes the motion variable based on the input(s) pressed. If you are adding input_motion to motion, you'll probably want to add some form of drag so when no keys are pressed the character slows down, as otherwise the character will never decelerate.

Hopefully the code above makes sense. The main idea is to add different values to motion (or input_motion in this case) so the movement effects are combined together when the character moves using move_and_slide.

@Pechvogel said: Maybe I can try to use Rigidbodies. Is it bad practise to let the colliders touch each other the whole time? Since they are pushing the character... Any performance issues?

You could do it that way, though if you can help it I would not recommend using RigidBody2D nodes to move a character, if nothing else because of the complexities it would bring.

One of the biggest issues I can see is the RigidBody2D nodes moving out of alignment and therefor no longer pushing the character. Because RigidBody2D nodes can can be effected by other RigidBody2D nodes (and KinematicBody2D nodes if I recall correctly), you will need to write code to keep them in the correct relative positions while pushing the character in the indented direction, which may be tricky to get working.

Another issue is having the KinematicBody2D node effected by the RigidBody2D nodes movement. Last I knew, KinematicBody2D nodes can push RigidBody2D nodes, but not the other way around. If this is the case, the having the RigidBody2D nodes move the character might require writing code that transfers the velocity of the impact with a RigidBody2D node to the KinematicBody2D node. That said, I might be mistaken and/or things have changed, in which case this would not be nearly as much of an issue.

I'm not sure if there would be performance issues or not. For a few RigidBody2D nodes, it probably will not be an issue even if there is collision every frame, so long as there are not too many collisions going on in the physics world. It will almost certainly have some performance implications, but how much I have no idea. I mostly do 3D game development with Godot, so I'm not as familiar with the technicalities of the 2D side. On the 3D side, a few dozen RigidBody nodes colliding at the same time does not impact performance too much, especially if the collision shapes are relatively simple. I imagine this holds for RigidBody2D nodes as well. The best way to know for sure would be to test and see what the performance looks like.

Hopefully this helps! (Side note: Welcome to the forums!)

Pechvogel

This helps a lot!

Thank you for your detailed explanation and code example! The information about KinematicBody2D and collisions are also very helpfull. I will roll with the first part of your answer since in my case there will be too much collisions which will impact performance in the long run.

Pechvogel

I have been playing around a little bit the last few days but I still need some help with what I am trying to achieve.

How to apply force to a specific part of a parent? I have added a small image to clarify. When pressing A, I would like the player to go up in a straight line. If I press B I would like the player go up but also a bit to the left since we are applying force to the right side of the player. Or that is what I am trying to achieve. Can someone tell me if this is possible and how to do it? Also how would my nodes be structured?

TwistedTwigleg

Initially I thought they were supposed to just represent the motion the player was taking, but looking at the most recent picture, I realized that this might not be the case. My apologizes if I misunderstood what you are wanting to achieve!

If possible, can you explain what you are trying to achieve, what the end result is supposed to look like. For example, are the blocks moving the player? Or are they representations of the motion the player is should take if certain conditions are met.

For example, if you are wanting something like this catapult demo from the Matter JS physics library? Or are you wanting something akin to the movement in the Super Mario Bros games?

How to apply force to a specific part of a parent?

With a KinematicBody2D node, there is no way to apply a force to a point relative to the parent, as the velocity/motion is always relative to the center of the KinematicBody2D node.

The reason behind this is that it gives exactly the same result with less computing power. KinematicBody nodes are not really designed to be moved by the world around them, but instead to move through how the code tells it to move, while still being constrained by the physics of the game world. This gives finer control over how the object moves through the physics world, but this means there is less done automatically.

If you want to apply a force to a point relative to the player, you probably want to use a RigidBody2D node for your player.

Both add_force and apply_impulse take both a direction and a position to apply the force, similar to the move_and_slide function in the KinematicBody2D node. The difference is they also take a relative position, so it can calculate the amount of rotation force would be applied to the RigidBody2D node.

This is because Godot's physics engine handles the collision responses, movement, and applying angular velocity (rotation) with RigidBody2D nodes, while all this has to be done manually with KinematicBody2D nodes. The reason the add_force and apply_impulse functions also take a position along with the force to be applied, because this information can help Godot's physics engine know how much force to add, and how much it would effect the rotation.

side note: If you need something similar to move_and_slide, you can either adjust the linear_velocity variable of the RigidBody2D node, or use the add_force/apply_impulse functions to control where the player moves. The Godot Demo repository has a RigidBody2D based character that might serve as a good reference.

Hopefully this helps a bit, and again my apologizes if I misunderstood the situation.

Megalomaniak

I'm guessing that @Pechvogel (and correct me if I'm wrong) is after something more along the lines of I am Bread or perhaps Happy Wheels.

Pechvogel

@TwistedTwigleg Please do not apologize! You did a great job helping me since all of this is kinda new to me and it is hard for me to say exactly what I am looking for since I do not know how things are called. I already learned a lot thanks to you and your examples!

I am want to achieve the same movement like nimbatus (@Megalomaniak). The player can add "engines" to himself and binding keys to those engines. If the user presses a key, one or more engines should move or push the player to a specific direction. But those engines should apply force at their location and not at the center of our player. I hope this make more sense.

After a lot of searching the internet I think I should roll with the rigidbody2d and applying force at a specific point. But I really have no clue how to implement this since the engines are "child nodes" of the parent and where should the force be applied? The child should pull or push the parent from its location. Maybe working with "joints" (something I used in Unity) should solve this?

Thanks a lot and have a great evening!

Pechvogel

Small update: I got it to work using Rigidbody2d and a joint. I also noticed the "no collisions" option in the joint which is a life saver :)

The only thing I need to fix is that they are fixed and not getting dragged behind.

Edit: fixed by adding joints on top and bottom which makes sense

TwistedTwigleg

Sorry about the delay @Pechvogel, and thank you for explaining what you were wanting to achieve. Now I have a much better grasp of the situation.

It is awesome that you were able to get it working with RigidBody2D nodes and Joints! Using joints to move the RigidBody2D node is a good idea. I'll need to remember it for future reference, as I often forget the joint nodes exist :sweat_smile:

Thanks again for the explanation, and my apologizes for the incorrect assumption.