85 lines
3.1 KiB
Markdown
85 lines
3.1 KiB
Markdown
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## Exercise 1: Projectiles
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There are several ways we can create projectiles in Godot. To choose the right one we need to think about how the projectiles should behave. Consider the following:
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* Should there be a limited number of projectiles?
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* What happens to projectiles that leave the viewing area?
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* Should shots ricochet?
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* Do projectiles need momentum, acceleration, deceleration?
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Depending on what we need the projectiles to do, we could choose a body type for them.
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### Area Node Bullet
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The area node is probably the simplest way to achieve a projectile. Areas can receive signals when a child collision shape intersects another collision shape (so they know when they have hit something).
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An area node also inherits a Transform, with a position property that can be written to.
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```
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extends Area2D
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var speed = 750
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func setSpeed(speedVal):
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speed = speedVal
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func _physics_process(delta):
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position += transform.x * speed * delta
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func _on_body_entered(body):
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# blast the body?
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if body.is_in_group("boxes"):
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body.queue_free()
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queue_free()
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```
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Now to use our bullet we need to be able to create the bullet and position it with code. This is called instantiation.
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To be able to instantiate a scene in Godot we must pre-load it.
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`var bullet = preload("res://scenes/bullet.tscn")`
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We can now create as many isntances of the bullet as we wish!
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But be careful! When we add our bullet to the world, we want to add it at the global scope - not at the scope of the character. Otherwise, when the character moves the bullet will move with them.
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```
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if Input.is_action_just_pressed("blast"):
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var mybullet = bullet.instantiate()
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mybullet.setSpeed(-BLAST_SPEED if faceLeft else BLAST_SPEED)
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owner.add_child(mybullet)
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mybullet.transform = markerLeft.global_transform if faceLeft else markerRight.global_transform
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```
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### RigidBody Missile
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For our next example, we will create our projectile from a RigidBody so that it can react via physics to the environment.
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One thing to note about RigidBodies is that they do not by default hear collision signals. This is a performance consideration, and usually this is a good thing, but in the case of our missile we want the RigidBody to know about the collision.
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For this reason in the inspector we will need to turn on collision_monitor and set a value in max_collision_objects. After this, we will be able to detect collisions.
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```
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extends RigidBody2D
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func _on_body_entered(body):
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# check here to see if the thing should explode
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print("missile hit something")
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if body.is_in_group("boxes"):
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body.queue_free()
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if not body.is_in_group("player"):
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queue_free()
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```
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As before, we need to think about instantiation of the missile. Depending on the direction the player is facing, we could either apply a negative or a positive impulse to the RigidBody.
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```
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if Input.is_action_just_pressed("blast"):
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var myMissile = missile.instantiate()
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owner.add_child(myMissile)
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myMissile.transform = markerLeft.global_transform if faceLeft else markerRight.global_transform
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var missileForce = -600 if faceLeft else 600
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myMissile.apply_impulse(Vector2(missileForce,10), Vector2(0, 0))
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```
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