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Collider
========
A collider, or collision object, is used to detect collisions. There are different types of colliders, each with a different shape. They are usually centered on the hot spot of sprites, but that can be changed by altering their *anchor*.
Colliders must be spawned as children of [entities](/engine/entity). To detect collisions, you may implement function `onCollision()` on the entity (see the example below), or use the colliders directly. Additionally, a single entity may have multiple colliders attached to it. This allows users to work with more complex shapes than simple primitives.
A collider is an abstract concept, and hence can't be spawned directly. Rather, you can spawn colliders of specific shapes, such as [CollisionBox](/engine/collisionbox) and [CollisionBall](/engine/collisionball). All Colliders share some functionalities (detailed in this page), but there are functionalities tied to specific shapes.
*Example*
```
using SurgeEngine.Actor;
using SurgeEngine.Player;
using SurgeEngine.Collisions.CollisionBall;
object "CollisionDoll" is "entity"
{
actor = Actor("CollisionDoll");
collider = CollisionBall(25); // ball with radius = 25px
// The player has a built-in collider
// Let's make it visible for debugging
state "main"
{
player = Player.active;
player.collider.visible = true;
collider.visible = true;
}
// Detect collisions between a collider that is a child
// of this object and any other collider in the game
fun onCollision(otherCollider)
{
// A collision has occurred.
Console.print("Collided with something");
// Collided with a player?
if(otherCollider.entity.hasTag("player")) {
player = otherCollider.entity;
Console.print("Touched " + player.name);
}
}
// While onCollision() catches the moment a collision
// first occurs, onOverlap() is called every frame
// this collider collides with other collider
fun onOverlap(otherCollider)
{
// This function is optional.
}
}
```
Properties
----------
#### entity
`entity`: object, read-only.
The [Entity](/engine/entity) associated with this collider.
#### enabled
`enabled`: boolean.
Is the collider enabled? A collider that is not enabled will not notify the parent object if a collision occurs. The default value is `true`, i.e., colliders are enabled by default.
#### visible
`visible`: boolean.
Is the collider visible? This is useful for debugging. The default value is `false`.
Functions
---------
#### collidesWith
`collidesWith(collider)`
Checks if this collider is colliding with some other collider.
*Arguments*
* `collider`: [Collider](/engine/collider) object. The other collider.
*Returns*
Returns `true` if there is a collision (the colliders overlap), or `false` otherwise.
#### contains
`contains(point)`
Checks if the collider contains the given point, given in world coordinates.
*Arguments*
* `point`: [Vector2](/engine/vector2) object. The point to be tested.
*Returns*
Returns `true` if the point is contained in the collider, or `false` otherwise.
#### setAnchor
`setAnchor(x, y)`
Defines the anchor of the collider to be (`x`, `y`), where these values are (usually) numbers between 0.0 and 1.0. Imagine a bounding box of the collider. Point (0.5, 0.5) is the default, representing its center. Point (0.0, 0.0) is the top-left and (1,0, 1.0), the bottom-right. The anchor of the collider will be aligned to the hot spot of the sprite of the entity.
*Arguments*
* `x`: number. Usually a value between 0.0 and 1.0.
* `y`: number. Usually a value between 0.0 and 1.0.
*Returns*
Returns the collider itself.
*Example*
```
// ...
using SurgeEngine.Collisions.CollisionBox;
object "CollisionTestObject" is "entity"
{
// see that the following collision box
// has its anchor on pixel (16, 64)
collider = CollisionBox(32, 64).setAnchor(0.5, 1.0);
// ...
}
```
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