Leading Projectiles

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1

Godot Version

4.3

Question

Hey all, if the answer to this is “study vectors some more” that’s fair enough.
However, if anybody has a mind for these things and how to explain them I would gladly have your advice.

I’ve got a 3D game, where stationary turrets shoot at the player.
For that I’ve got a simple marker I point towards the player to which the meshes are attached

cannon_marker.look_at(player.global_position, Vector3(0, 1, 0), true)

Easy enough.

However, my player is on a PathFollow3D and is continuously pulled forward, which means the turrets are forever aiming at a point the player isn’t at anymore.

How would I lead these shots, so they fly towards where the player will be?
This is a level of vectors that is making my head spin.

Thanks in advance.

2

You need to know how far the player can travel over the course of time it takes for the bullet to reach them

var distance: float = cannon_marker.global_position.distance_to(player.global_position)
var bullet_travel_time: float = distance / BULLET_SPEED

var player_travel_distance: float = PLAYER_SPEED * bullet_travel_time
var lead_position: Vector3 = player.move_direction * player_travel_distance

cannon_marker.look_at(lead_position, Vector3.UP, true)

The trickiest part will be determining which direction the player is moving by a path3D. If you want perfect accuracy you will sample the path3D by the player’s current offset plus travel distance. If you want a realistic (and pretty good) accuracy you will store the player’s last position and calculate the direction from their last position.

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3

Hey Gert, apologies for the late reply, but thank you for taking the time!

This code makes more sense than I thought it would, so thank you for that. I’ll need to mull over the direction part however.

I’ve tried to input a few different things into the “player.move_direction” and at best I have these turrets shooting where the player will be in ten minutes or ignoring the player’s position entirely.

I did make a mistake for a little while with the PLAYER_SPEED, which on this occasion would just be the incremental value I add to the Progress of the PathFollow.
I only use the player speed for sideways motion (imagine going down a tunnel, where going down the tunnel happens at a fixed rate.)
I think I still need a lot to do a bit of learning in regards to Vectors in 3D haha.

4

Figured out how to get the player’s direction following along the path3D.

Took a lot of faffing about with velocities before realising they were always wrong.

Thank you so much for the help, I wouldn’t have known where to begin otherwise.

var distance : float = cannon_marker.global_position.distance_to(player.global_position)
			var forward_direction = player.transform.basis.z.normalized()
			var player_fwd_speed = 5.0 # arbitrary testing value as this doesn't match the follow speed
			var bullet_travel_time : float = distance / 20.0 # replace by bullet speed
			
			# Inverted direction, based on the PathFollow heading South rather than North
			predicted_position = player.global_position + (-forward_direction * player_fwd_speed * bullet_travel_time)
			cannon_marker.look_at(predicted_position, Vector3.UP, true)
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