bonk-docs/content/api/SpatialHash.md

title	date	weight
SpatialHash<T>	2019-09-15T11:28:40-07:00	10

SpatialHash is used for broad-phase collision detection. It can quickly return a set of potential collisions of a transformed shape. SpatialHash takes an ID type that is used to avoid comparing certain shape-transforms.

Methods

public SpatialHash(int cellSize)

Constructor method. Takes an integer representing the width of a cell in the spatial hash.

The cell width must not be too large or too small. If the cell width is too small, then shape-transforms will occupy many cells, and the hash check will have to check all of those cells for potential collisions. If the cell width is too large, then many shape-transforms will be contained in each cell and many expensive collision tests will have to be made.

A good rule of thumb is picking a cell width that is roughly twice the size of the most common objects in your game.

Example:

var hash = new SpatialHash<int>(16);

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public void Insert(T id, IShape2D shape, Transform2D Transform2D)

Given an ID, a shape, and corresponding transform, inserts into the spatial hash. Uses the shape's AABB to insert into appropriate hash cells.

Example:

var hash = new SpatialHash<int>(16);

var circle = new MoonTools.Bonk.Circle(8);
var circleTransform = new Transform2D(new Vector2(16, 16));

var rect = new Rectangle(-2, -2, 2, 2);
var rectTransform = new Transform2D(new Vector2(8, 8));

hash.Insert(0, circle, circleTransform);
hash.Insert(1, rect, rectTransform);

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public IEnumerable<(T, IShape2D, Transform2D)> Retrieve(T id, IShape2D shape, Transform2D Transform2D)

Given an ID, a shape, and corresponding transform, retrieves a set of potential collisions from the spatial hash.

Example:

var hash = new SpatialHash<int>(16);

var circle = new MoonTools.Bonk.Circle(8);
var circleTransform = new Transform2D(new Vector2(16, 16));

var rect = new Rectangle(-2, -2, 2, 2);
var rectTransform = new Transform2D(new Vector2(8, 8));

hash.Insert(0, circle, circleTransform);
hash.Insert(1, rect, rectTransform);

hash.Retrieve(1, rect, rectTransform);

In this example, the circle we inserted will be in the IEnumerable returned by the Retrieve call because they both exist in the same hash cell.

If a potential colliding shape-transform has the same ID as the one passed into the method, it will not be returned in the IEnumerable.

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public void Clear()

Empties the spatial hash. Useful when the spatial hash contains dynamic data that needs to be updated.