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133 lines
4.8 KiB
Markdown
133 lines
4.8 KiB
Markdown
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Using Area2D
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============
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Introduction
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------------
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Godot offers a number of collision objects to provide both collision detection
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and response. Trying to decide which one to use for your project can be confusing.
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You can avoid problems and simplify development if you understand how each of them
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works and what their pros and cons are. In this tutorial, we'll look at the
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`Area2D` node and show some examples of how it can be used.
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Note:
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This document assumes you're familiar with Godot's various physics
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bodies. Please read `doc_physics_introduction` first.
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What is an area?
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----------------
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An Area2D defines a region of 2D space. In this space you can detect other
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`CollisionObject2D` nodes overlapping, entering,
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and exiting. Areas also allow for overriding local physics properties. We'll
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explore each of these functions below.
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Area properties
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---------------
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Areas have many properties you can use to customize their behavior.
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The first eight properties are used to configure the area's physics override
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behavior. We'll look at how to use those in the section below.
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*Monitoring* and *Monitorable* are used to enable and disable the area.
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The "Collision" section is where you configure the area's collision layer(s)
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and mask(s).
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The "Audio Bus" section allows you to override audio in the area, for example to
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apply an audio effect when the player moves through.
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Note that Area2D extends `CollisionObject2D`, so it
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also provides properties inherited from that class, such as `input_pickable`.
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Overlap detection
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-----------------
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Perhaps the most common use of Area2D nodes is for contact and overlap detection.
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When you need to know that two objects have touched, but don't need physical
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collision, you can use an area to notify you of the contact.
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For example, let's say we're making a coin for the player to pick up. The coin is
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not a solid object - the player can't stand on it or push it - we just want it
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to disappear when the player touches it.
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Here's the node setup for the coin:
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To detect the overlap, we'll connect the appropriate signal on the Area2d. Which
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signal to use depends on the player's node type. If the player is another area,
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use `area_entered`. However, let's assume our player is a `KinematicBody2D`
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(and therefore a `CollisionObject2D` type), so we'll connect the
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`body_entered` signal.
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Note:
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If you're not familiar with using signals, see `doc_signals` for
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an introduction.
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gdscript GDScript
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```
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extends Area2D
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func _on_Coin_body_entered(body):
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queue_free()
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```
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Now our player can collect the coins!
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Some other usage examples:
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- Areas are great for bullets and other projectiles that hit and deal damage, but don't need any other physics such as bouncing.
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- Use a large circular area around an enemy to define its "detect" radius. When the player is outside the area, the enemy can't "see" it.
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- "Security cameras" - In a large level with multiple cameras, attach areas to each camera and activate them when the player enters.
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See the `doc_your_first_2d_game` for an example of using Area2D in a game.
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Area influence
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--------------
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The second major use for area nodes is to alter physics. By default, the area
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won't do this, but you can enable this with the *Space Override* property. When
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areas overlap, they are processed in *Priority* order (higher priority areas are
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processed first). There are four options for override:
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- *Combine* - The area adds its values to what has been calculated so far.
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- *Replace* - The area replaces physics properties, and lower priority areas are ignored.
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- *Combine-Replace* - The area adds its gravity/damping values to whatever has been calculated so far (in priority order), ignoring any lower priority areas.
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- *Replace-Combine* - The area replaces any gravity/damping calculated so far, but keeps calculating the rest of the areas.
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Using these properties, you can create very complex behavior with multiple
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overlapping areas.
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The physics properties that can be overridden are:
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- *Gravity* - Gravity's strength inside the area.
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- *Gravity Vec* - Gravity's direction. This vector does not need to be normalized.
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- *Linear Damp* - How quickly objects stop moving - linear velocity lost per second.
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- *Angular Damp* - How quickly objects stop spinning - angular velocity lost per second.
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Point gravity
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~~~~~~~~~~~~~
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The *Gravity Point* property allows you to create an "attractor". Gravity in the
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area will be calculated towards a point, given by the *Gravity Vec* property.
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Values are relative to the Area2D, so for example using `(0, 0)` will attract
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objects to the center of the area.
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Examples
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~~~~~~~~
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The example project attached below has three areas demonstrating physics
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override.
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You can download this project here:
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:download:`using_area_2d.zip <files/using_area_2d.zip )`
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