How to draw a line between two sprites

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:bust_in_silhouette: Asked By curioussavage

Hi I am trying to use a line2D to draw a line between two sprites for a second to indicate a laser being fired. My problem is that the “lasers” show up positioned wrong. The target in the example below is a KinematicBody2D (same as the parent of this Line2D node. Its the same scene). I have some other logic around setting destinations for these ships and selecting them that uses global_position too and it works fine.

I think I’m stuck because I’m still getting the hang of thinking in terms of these different coordinate systems.

extends Line2D

var damage = 0
var laser_time = 1

var timer = null
var gun_target = null

func _ready():
    timer = get_node("gun_timer")

func _physics_process(delta):
    if timer.is_stopped():
        gun_target = null

func shoot(target):
    gun_target = target

game screenshot

:bust_in_silhouette: Reply From: bitwes

I do something similar, I have a simple "chain lightning effect that makes a line move between objects. This is the draw method (3.0). I move the object towards the object. This draws a line from where the object is to the other object.

func _draw():
	var from = _origin_pos - get_global_position()
	var to = Vector2(0, 0)

	from = from.normalized() * 100
	to = to.normalized() * 100

	# blue
	draw_line(from, to , Color(0, 0, 1), 5)
	# white
	draw_line(from, to, Color(1, 1, 1), 1)

And this is how I move the object toward its destination. I call this from _process() but should be fine in _process_physics…actually maybe that’s where it SHOULD be.

func _move_towards_target(delta):
  # _wr_target_obj is a weak reference to the object I'm trying to 
  # move towards.
	var target_obj = _wr_target_obj.get_ref()
	var _target_pos = target_obj.get_global_position()
	var pos = get_global_position()

	var dist_to = get_global_position().distance_to(_target_pos)

    var movement = _target_pos - pos
	movement = movement.normalized()
	movement = movement * delta *  CHAIN_SPEED

I’m glad you posted this because making sure I don’t keep around refs to nodes is one thing I have been meaning to fix. Didn’t know about get_ref. I don’t think this solves my root problem though - that the coordinates I am using for my line are wrong. If I were to follow this I would still be using the same positions. I am using global_position but It doesn’t seem like that is working. It does work for the movement of ships ( they move to where I click on the screen. Even when the camera is scrolled.)

I suspect I am not accounting for how the camera affects positions. Or it could be something else.

curioussavage | 2018-03-08 05:33

Have you tried tacking on the normalized()? I remember knowing how this all worked when I made that method. It has since left me.

bitwes | 2018-03-08 06:50

:bust_in_silhouette: Reply From: curioussavage

Looks like the solution was to call to_local on both Vector2 before adding the points. This, sort of, makes sense to me. Probably need to review the docs about the coordinate system etc.

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