How to shoot a particle at my mouse pointer in 3D

itgiawa

I'm trying to fire a projectile from my 3D character to my mouse pointer using ray casting.

When I press my input this code is called:

	var z = 0
	var position2D = get_viewport().get_mouse_position()
	var dropPlane  = Plane(Vector3(0, 1, 0), z)
	var mouse_position3D = dropPlane.intersects_ray($Spatial/Camera.project_ray_origin(position2D),$Spatial/Camera.project_ray_normal(position2D))
	

	var mouse_direction = mouse_position3D.normalized()
	spell_instance.look_at(mouse_direction, Vector3.UP)
	add_child(spell_instance)

Inside my projectile object I have this:

	func _physics_process(delta):
		apply_impulse(transform.basis.z, -transform.basis.z)

It kinda works, but it doesnt hit my pointer exactly and I'm not sure why. I don't understand what z is supposed to do. How is it possible to describe a plane in 3D space with a vector and a float? Wouldn't you need two vectors to describe a plane? I cant visualize how the ray casting is supposed to work so its really hard for me to fix...

newmodels

Ray casting! a Ray is a line in 3d space. You have the starting point, then the ending point. Godot scans along the line looking for a collision. With some math, it can find a collision without scanning each segment. It tests against the physics body to see if it collides with it.

So it like poking it with a stick.

newmodels

Here I found this for Plane. https://docs.godotengine.org/en/stable/classes/class_plane.html

Your passing the wrong argument into I think for the second. You might dry using intersects_segment().

newmodels

Looking at the code, you might try just using Camera.project_ray_normal(); This assumes the Plane has a physics body, or an Area.

TwistedTwigleg

@itgiawa said: I'm trying to fire a projectile from my 3D character to my mouse pointer using ray casting.

When I press my input this code is called:
	var z = 0
	var position2D = get_viewport().get_mouse_position()
	var dropPlane  = Plane(Vector3(0, 1, 0), z)
	var mouse_position3D = dropPlane.intersects_ray($Spatial/Camera.project_ray_origin(position2D),$Spatial/Camera.project_ray_normal(position2D))
	

	var mouse_direction = mouse_position3D.normalized()
	spell_instance.look_at(mouse_direction, Vector3.UP)
	add_child(spell_instance)
Inside my projectile object I have this:
	func _physics_process(delta):
		apply_impulse(transform.basis.z, -transform.basis.z)
It kinda works, but it doesnt hit my pointer exactly and I'm not sure why. I don't understand what z is supposed to do. How is it possible to describe a plane in 3D space with a vector and a float? Wouldn't you need two vectors to describe a plane? I cant visualize how the ray casting is supposed to work so its really hard for me to fix...

The Vector is the normal, and then the Z is how far that plane is from origin. For example, if you have a plane defined like Plane(Vector3.UP, 20), then the plane will have a normal facing (0, 1, 0) and will be positioned at (0, 20, 0), which is 20 units from the center.

With the pointer, how is it off? Is the height off, or is there an offset on the X or Z axes?

Something you may be able to try is using the project function to get the mouse position on the plane, using code something like this:

var position2D = get_viewport().get_mouse_position()
var dropPlane = Plane(Vector3.UP, z)
var mouse_depth_distance = 1
var position_in_3D = $Spatial/Camera.project_ray_origin(position2D) + ($Spatial/Camera.project_ray_normal(position2D) * mouse_depth_distance)
var mouse_position3D = dropPlane.project(position_in_3D)

# I think this code may make the instance look at the mouse position a little more reliably, but not totally sure
spell_instance.look_at(spell_instance.global_transform.origin.direction_to(mouse_position3D), Vector3.UP)
add_child(spell_instance)

I have not tested it though, so I'm not sure it will work.

newmodels

I remember in godot 3.2.3, I always had to add the it has a child to the scene, before I could change any transforms or locations. It might need be child before telling it to look at.

itgiawa

edit i think the problem is my camera is orthographic / isometric. ill look into how to do ray tracing w that type of camera....

@newmodels Thanks! I dont think I can make the plane have a collision shape since then it would block holes in the ground. I think lookat is working since changing z has an effect. I'm think my plane is at a weird angle. I think what would really help me is to be able to visualize the plane that I'm creating. Do you know if its possible to easily, programaticly drop a mesh on it?

My game looks like this:

@TwistedTwigleg In my head I picture the Vector.UP plane as being perpendicular to the ground in my screenshot and I picture z as being the offset along one of the axies (I assume the z axis, but in TwistedTwigleg's example the z is the offset along the y axis). But changing my z value causes the projectile to shoot in really weird places that are not perpendicular to any axis. So I think I can conclude that my plane is not perpendicular to any axis?

With the pointer, how is it off? Is the height off, or is there an offset on the X or Z axes? The height and offset to axes is off to different degrees based on where I click. Its as if the plane I'm creating is at some strange angle. There is also a case where if I fire directly to the right of the character the projectile fires left, but if I extend my mouse farther right it corrects itself to fire right .

@TwistedTwigleg your code makes it so that projectiles only fire down and slightly to the left or right depending on if the pointer is more left or right.

TwistedTwigleg

@itgiawa said: @TwistedTwigleg In my head I picture the Vector.UP plane as being perpendicular to the ground in my screenshot and I picture z as being the offset along one of the axies (I assume the z axis, but in TwistedTwigleg's example the z is the offset along the y axis). But changing my z value causes the projectile to shoot in really weird places that are not perpendicular to any axis. So I think I can conclude that my plane is not perpendicular to any axis?

Ah, okay. Maybe the issue is that the axis origin itself is also off-axis, in which case that could be contributing to the issue. One potential way around this is to not offset the plane, but instead offset the positions to the plane, do the calculation, and then apply the offset on the result. I'm not 100% sure that would work though, nor if the origin offset is the issue...

The height and offset to axes is off to different degrees based on where I click. Its as if the plane I'm creating is at some strange angle. There is also a case where if I fire directly to the right of the character the projectile fires left, but if I extend my mouse farther right it corrects itself to fire right .

@TwistedTwigleg your code makes it so that projectiles only fire down and slightly to the left or right depending on if the pointer is more left or right.

Hmm, strange, not what I would have expected. Maybe visualizing the plane would help? Can you add a MeshInstance node (as a child of the root of the scene) with a Plane or Quad mesh (not sure which would be better here) and then add something like the following code:

extends MeshInstance
# set this to the normal passed to the plane for raycasting
export (Vector3) var plane_normal = Vector3(0, 1, 0)
func _ready():
	# rotate to look at the normal position:
	look_at(global_transform.origin + plane_normal.normalized(), Vector3.UP)

You may want to give the MeshInstance an unshaded material with the depth pass disabled or position it above the ground a bit, so its easier to see the rotation.

TwistedTwigleg

Just thought of something else: Does your scene have collision setup on the individual tiles? If so, you could potentially just raycast into the scene using either a Raycast node or DirectSpaceState and then make the Y position of the result the same as the Y position of the character, so it only rotates on the Y axis when passed to look_at.

itgiawa

@TwistedTwigleg Thanks! I got it working. In case anyone is interested heres what I did:

	var spell_instance = spell.instance()
	
	add_child(spell_instance)
	var mouse_position = get_viewport().get_mouse_position()
	var ray_origin = $Spatial/Camera.project_ray_origin(mouse_position)

	var ray_target = ray_origin + $Spatial/Camera.project_ray_normal(mouse_position) * 1000

	var space_state = get_world().direct_space_state
	var intersection = space_state.intersect_ray(ray_origin, ray_target)

	if not intersection.empty():
		var ground_position = intersection.position
		spell_instance.look_at(ground_position, Vector3.UP)

I think one mistake I was making was I was adding the spell_instance as a child AFTER I made the spell_instance look at the target. I think when you add something as a child to something else it adopts the direction of its parent which was undoing my look_at()

TwistedTwigleg

Awesome! I’m glad you got it working =)