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2D Collider

Create Collider

The engine currently supports three different colliders: BoxCollider2D, CircleCollider2D and PolygonCollider2D. Click the Add Component button on the Inspector panel and enter the name of the collider to add it.

colliders

Properties

The different colliders have the following properties in common:

inspector

PropertiesDescription
EditingWhether to edit the collider. Check this option to edit the position, style and size of the collider in the scene. For details, please refer to Editing Collider below
TagTag. When a collision occurs, you can distinguish different colliders according to Tag.
GroupCollider group. By Collision Matrix, you can set the possibility of collision between different groups.
SensorSpecify whether the collider is of sensor type, the collider of sensor type will generate a collision callback, but no physical collision effect will occur
DensityThe density of the collider, used to calculate the mass of the rigid body.
FrictionThe friction factor of the collider, the motion of the collider will be affected by the friction when it touches.
RestitutionThe elasticity coefficient of the collider, specifying whether the collider will be affected by the elasticity when it collides.
OffsetThe offset of the collider with respect to the center of the node.

BoxCollider

The Box Collider component is a common collider used to simulate a rectangle-like collider. It can be added by clicking Add Component -> BoxCollider2D on the Inspector panel of the 2D node.

box-collider-2d

Properties

PropertiesDescription
SizeThe size of the box collider component

Please refer to BoxCollider2D API for details.

Editing Collider

For all colliders, check Editing to edit them within the scene.

editing

Press the left mouse button and drag within the collider to adjust the offset of the collider, and on gizmo and drag the left mouse button to adjust the shape and size of the collider.

edit-box-collider

Holding down the Alt button while dragging will keep the rectangle center position unchanged during the dragging process.

alt

Entering on the Inspector panel also refines the size and offset of the collider.

input

CircleCollider2D

Click Add Component on the Inspector panel and enter CircleCollider2D to add a circle collider.

circle-collider

Properties

PropertiesDescription
Radiusradius of the circle

Please refer to CircleCollider2D API for details.

Editing Collider

When holding down the Alt button to drag, the circle center position will be maintained during the dragging process.

edit-circle-collider

PolygonCollider2D

The Polygon Collider component allows you to edit more detailed physics shapes for more accurate physics simulation of objects.

Click Add Component on the Inspector panel and enter PolygonCollider2D to add a polygon collider.

polygon

Properties

PropertiesDescription
ThresholdSpecifies the minimum distance between the vertices of the generated map outline, the larger the value, the fewer points will be generated, adjustable according to requirements
PointsThe vertices of the polygon can be edited within the scene by checking Editing, and can also be adjusted by entering values on the Inspector panel

Please refer to PolygonCollider2D API for details.

Edit Collider

In the case of Sprite components, the engine generates outlines based on the Sprite.

default

By dragging the mouse gizmo you can adjust the position of the outline points.

edit

By adjusting the Threshold and clicking the points button, you can adjust the shape of the outline and the number of points.

threshold-1

When you mouse over a line segment of a polygon, the line segment will be highlighted and the mouse will change to add style, then click the left mouse button to insert a new point in the line segment.

add-point

Details

Box2D physics colliders are internally composed of Box2D b2Fixture. Due to some limitations inside Box2D, a polygon physics collider may be composed of more than one b2Fixture.

These cases are as follows:

  1. when the shape of the vertices of a polygon physics collider is a concave polygon, the physics system automatically splits these vertices into multiple convex polygon. However, it should be noted that the algorithm cannot handle the problem of self-intersection of concave polygons.
  2. When the polygon physics collider has more vertices than b2.maxPolygonVertices (typically 8), the physics system automatically splits these vertices into multiple convex polygon.

Normally these details are of no concern, but when ray detection is used and the detection type is ERaycast2DType.All, a collider may detect multiple collision points because multiple b2Fixtures are detected.