75 lines
2.4 KiB
Markdown
75 lines
2.4 KiB
Markdown
---
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title: "SpatialHash<T>"
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date: 2019-09-15T11:28:40-07:00
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weight: 10
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---
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*SpatialHash<T>* is used for broad-phase collision detection. It can quickly return a set of potential collisions of a transformed shape. *SpatialHash<T>* takes an ID type that is used to avoid comparing certain shape-transforms.
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## Methods
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##### **public SpatialHash(int cellSize)**
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Constructor method. Takes an integer representing the width of a cell in the spatial hash.
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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.
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A good rule of thumb is picking a cell width that is roughly twice the size of the most common objects in your game.
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**Example:**
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```cs
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var hash = new SpatialHash<int>(16);
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```
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---
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##### **public void Insert(T id, IShape2D shape, Transform2D Transform2D)**
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Given an ID, a shape, and corresponding transform, inserts into the spatial hash. Uses the shape's AABB to insert into appropriate hash cells.
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**Example:**
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```cs
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var hash = new SpatialHash<int>(16);
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var circle = new MoonTools.Core.Bonk.Circle(8);
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var circleTransform = new Transform2D(new Vector2(16, 16));
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var rect = new Rectangle(-2, -2, 2, 2);
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var rectTransform = new Transform2D(new Vector2(8, 8));
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hash.Insert(0, circle, circleTransform);
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hash.Insert(1, rect, rectTransform);
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```
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---
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##### **public IEnumerable<(T, IShape2D, Transform2D)> Retrieve(T id, IShape2D shape, Transform2D Transform2D)**
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Given an ID, a shape, and corresponding transform, retrieves a set of potential collisions from the spatial hash.
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**Example:**
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```cs
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var hash = new SpatialHash<int>(16);
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var circle = new MoonTools.Core.Bonk.Circle(8);
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var circleTransform = new Transform2D(new Vector2(16, 16));
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var rect = new Rectangle(-2, -2, 2, 2);
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var rectTransform = new Transform2D(new Vector2(8, 8));
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hash.Insert(0, circle, circleTransform);
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hash.Insert(1, rect, rectTransform);
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hash.Retrieve(1, rect, rectTransform);
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```
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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.
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---
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##### **public void Clear()**
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Empties the spatial hash. Useful when the spatial hash contains dynamic data that needs to be updated. |