---
title: "NarrowPhase"
date: 2019-09-15T11:19:13-07:00
weight: 20
---

*NarrowPhase* is a static class containing methods for narrow-phase collision detection.

Note that all the **TestCollision** overloads automatically employ fast path checks.

## Methods

##### **public static bool TestCollision(IShape2D shapeA, Transform2D transformA, IShape2D shapeB, Transform2D transformB)**

Tests if the two shape-transform pairs are overlapping.

**Example:**
```cs
var circleA = new Circle(2);
var transformA = new Transform2D(new Vector2(-1, -1));
var circleB = new Circle(2);
var transformB = new Transform2D(new Vector2(1, 1));

var result = GJK2D.TestCollision(circleA, transformA, circleB, transformB);
```

In this example, these transformed circles are indeed overlapping, so *result* will be true.

---

##### **public static bool TestCollision(IHasAABB2D hasBoundingBoxA, Transform2D transformA, IHasAABB2D hasBoundingBoxB, Transform2D transformB)**

Detects whether two AABB-transform pairs are overlapping.

---

##### **public static bool TestCollision(MultiShape multiShape, Transform2D multiShapeTransform, IShape2D shape, Transform2D shapeTransform)**

Tests if a multishape-transform and shape-transform pair are overlapping.

---

##### **public static bool TestCollision(IShape2D shape, Transform2D shapeTransform, MultiShape multiShape, Transform2D multiShapeTransform)**

Tests if a multishape-transform and shape-transform pair are overlapping.

---

##### **public static bool TestCollision(MultiShape multiShapeA, Transform2D transformA, MultiShape multiShapeB, Transform2D transformB)**

Tests if two multishape-transform pairs are overlapping.

---

##### **public static bool TestRectangleOverlap(Rectangle rectangleA, Transform2D transformA, Rectangle rectangleB, Transform2D transformB)**

Fast path for axis-aligned rectangles. Assumes that the transforms have zero rotation. If the transforms have non-zero rotation this will be inaccurate.

---

##### **public static bool TestPointRectangleOverlap(Point point, Transform2D pointTransform, Rectangle rectangle, Transform2D rectangleTransform)**

Fast path for overlapping point and axis-aligned rectangle. The rectangle transform must have non-zero rotation.

---

##### **public static bool TestCircleOverlap(Circle circleA, Transform2D transformA, Circle circleB, Transform2D transformB)**

Fast path for overlapping circles. The circles must have uniform scaling.

---

##### **public static (bool, Simplex) FindCollisionSimplex(IShape2D shapeA, Transform2D transformA, IShape2D shapeB, Transform2D transformB)**

Tests if the two shape-transform pairs are overlapping, and if so returns a Simplex that can be used by the EPA algorithm to determine a minimum separating vector.

**Example:**
```cs
var circleA = new Circle(2);
var transformA = new Transform2D(new Vector2(-1, -1));
var circleB = new Circle(2);
var transformB = new Transform2D(new Vector2(1, 1));

var (result, simplex) = GJK2D.TestCollision(circleA, transformA, circleB, transformB);
```

In this example, these transformed circles are indeed overlapping, so *result* will be true and *simplex* will contain the Simplex that can be used by EPA to determine a minimum separating vector.

---

##### **public unsafe static Vector2 Intersect(IShape2D shapeA, Transform2D Transform2DA, IShape2D shapeB, Transform2D Transform2DB, Simplex2D simplex)**

Returns a minimum separating vector in the direction from A to B. This information can be used to push two overlapping shape-transforms apart.