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https://github.com/jriecken/sat-js

A simple JavaScript library for performing 2D collision detection
https://github.com/jriecken/sat-js

collision-test javascript

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A simple JavaScript library for performing 2D collision detection

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README 

        
# SAT.js



 - [Classes](#classes)

 - [Collision Tests](#collision-tests)

 - [Examples](#examples)



## About



SAT.js is a simple JavaScript library for performing collision detection (and projection-based collision response) of simple 2D shapes.  It uses the [Separating Axis Theorem](http://en.wikipedia.org/wiki/Hyperplane_separation_theorem) (hence the name)



It supports detecting collisions between:

 - Circles (using Voronoi Regions.)

 - Convex Polygons (and simple Axis-Aligned Boxes, which are of course, convex polygons.)



It also supports checking whether a point is inside a circle or polygon.



It's released under the [MIT](http://en.wikipedia.org/wiki/MIT_License) license.



Current version: `0.9.0`.



Nicely compresses with the [Google Closure Compiler](https://developers.google.com/closure/compiler/) in **Advanced** mode to about 6KB (2KB gzipped)



To use it in node.js, you can run `npm install sat` and then use it with `var SAT = require('sat');`



## Classes



SAT.js contains the following JavaScript classes:



### SAT.Vector (aliased as SAT.V)



This is a simple 2D vector/point class.  It is created by calling:

```javascript

// Create the vector (10,10) - If (x,y) not specified, defaults to (0,0).

var v = new SAT.Vector(10, 10)

```



It has the following properties:



 - `x` - The x-coordinate of the Vector.

 - `y` - The y-coordinate of the Vector.



It contains the following methods:



 - `copy(other)` - Copy the value of another Vector to this one.

 - `clone()` - Return a new vector with the same coordinates as this one.

 - `perp()` - Change this vector to be perpendicular to what it was before.

 - `rotate(angle)` - Rotate this vector counter-clockwise by the specified number of radians.

 - `reverse()` - Reverse this Vector.

 - `normalize()` - Make the Vector unit-lengthed.

 - `add(other)` - Add another Vector to this one.

 - `sub(other)` - Subtract another Vector from this one.

 - `scale(x,y)` - Scale this Vector in the X and Y directions.

 - `project(other)` - Project this Vector onto another one.

 - `projectN(other)` - Project this Vector onto a unit Vector.

 - `reflect(axis)` - Reflect this Vector on an arbitrary axis Vector.

 - `reflectN(axis)` - Reflect this Vector on an arbitrary axis unit Vector.

 - `dot(other)` - Get the dot product of this Vector and another.

 - `len2()` - Get the length squared of this Vector.

 - `len()` - Get the length of this Vector



### SAT.Circle



This is a simple circle with a center position and a radius.  It is created by calling:

```javascript

// Create a circle whose center is (10,10) with radius of 20

var c = new SAT.Circle(new SAT.Vector(10,10), 20);

```



It has the following properties:



 - `pos` - A Vector representing the center of the circle.

 - `r` - The radius of the circle

 - `offset` - Offset of center of circle from `pos`.



 It has the following methods:



 - `setOffset(offset)` - Set the current offset

 - `getAABB()` - Compute the axis-aligned bounding box. Returns a new Polygon every time it is called.

 - `getAABBAsBox()` - Compute the axis-aligned bounding box. Returns a new Box every time it is called.



### SAT.Polygon



This is a **convex** polygon, whose points are specified in a counter-clockwise fashion.  It is created by calling:

```javascript

// Create a triangle at (0,0)

var p = new SAT.Polygon(new SAT.Vector(), [

  new SAT.Vector(),

  new SAT.Vector(100,0),

  new SAT.Vector(50,75)

]);

```



Note: The points are counter-clockwise *with respect to the coordinate system*. If you directly draw the points on a screen that has the origin at the top-left corner it will _appear_ visually that the points are being specified clockwise. This is just because of the inversion of the Y-axis when being displayed.



You can create a line segment by creating a `Polygon` that contains only 2 points.



Any identical consecutive points will be combined. (this can happen if you convert a `Box` with zero width or height into a `Polygon`)



It has the following properties:



 - `pos` - The position of the polygon (all points are relative to this).

 - `points` - Array of vectors representing the original points of the polygon.

 - `angle` - Angle to rotate the polgon (affects `calcPoints`)

 - `offset` - Translation to apply to the polygon before the `angle` rotation (affects `calcPoints`)

 - `calcPoints` - (Calculated) The collision polygon - effectively `points` with `angle` and `offset` applied.

 - `edges` - (Calculated) Array of Vectors representing the edges of the calculated polygon

 - `normals` - (Calculated) Array of Vectors representing the edge normals of the calculated polygon (perpendiculars)



You should _not_ manually change any of the properties except `pos` - use the `setPoints`, `setAngle`, and `setOffset` methods to ensure that the calculated properties are updated correctly.



It has the following methods:



 - `setPoints(points)` - Set the original points

 - `setAngle(angle)` - Set the current rotation angle (in radians)

 - `setOffset(offset)` - Set the current offset

 - `rotate(angle)` - Rotate the original points of this polygon counter-clockwise (around its local coordinate system) by the specified number of radians. The `angle` rotation will be applied on top of this rotation.

 - `translate(x, y)` - Translate the original points of this polygon (relative to the local coordinate system) by the specified amounts. The `offset` translation will be applied on top of this translation.

 - `getAABB()` - Compute the axis-aligned bounding box. Returns a new Polygon every time it is called. Is performed based on the `calcPoints`.

 - `getAABBAsBox()` - Compute the axis-aligned bounding box. Returns a new Box every time it is called. Is performed based on the `calcPoints`.

 - `getCentroid()` - Compute the [Centroid](https://en.wikipedia.org/wiki/Centroid#Centroid_of_a_polygon) of the polygon. Is performed based on the `calcPoints`.



### SAT.Box



This is a simple Box with a position, width, and height.  It is created by calling:

```javascript

// Create a box at (10,10) with width 20 and height 40.

var b = new SAT.Box(new SAT.Vector(10,10), 20, 40);

```



It has the following properties:



 - `pos` - The bottom-left coordinate of the box (i.e the smallest `x` value and the smallest `y` value).

 - `w` - The width of the box.

 - `h` - The height of the box.



It has the following methods:



 - `toPolygon()` - Returns a new Polygon whose edges are the edges of the box.



### SAT.Response



This is the object representing the result of a collision between two objects.  It just has a simple `new Response()` constructor.



It has the following properties:



 - `a` - The first object in the collision.

 - `b` - The second object in the collison.

 - `overlap` - Magnitude of the overlap on the shortest colliding axis.

 - `overlapN` - The shortest colliding axis (unit-vector)

 - `overlapV` - The overlap vector (i.e. `overlapN.scale(overlap, overlap)`).  If this vector is subtracted from the position of `a`, `a` and `b` will no longer be colliding.

 - `aInB` - Whether the first object is completely inside the second.

 - `bInA` - Whether the second object is completely inside the first.



It has the following methods:



- `clear()` - Clear the response so that it is ready to be reused for another collision test.



Note: The `clear`ed value for a `Response` has what may seem to be strange looking values:



```javascript

{

  a: null,

  b: null,

  overlap: 1.7976931348623157e+308,

  overlapV: Vector(0, 0),

  overlapN: Vector(0, 0),

  aInB: true,

  bInA: true

}

```



These just make calculating the response simpler in the collision tests. If the collision test functions return `false` the values that are in the response should not be examined, and `clear()` should be called before using it for another collision test.



## Collision Tests



SAT.js contains the following collision tests:



### `SAT.pointInCircle(p, c)`



Checks whether a given point is inside the specified circle.



### `SAT.pointInPolygon(p, poly)`



Checks whether a given point is inside a specified convex polygon.



### `SAT.testCircleCircle(a, b, response)`



Tests for a collision between two `Circle`s, `a`, and `b`.  If a response is to be calculated in the event of collision, pass in a `clear`ed `Response` object.



Returns `true` if the circles collide, `false` otherwise.



If it returns `false` you should not use any values that are in the `response` (if one is passed in)



### `SAT.testPolygonCircle(polygon, circle, response)`



Tests for a collision between a `Polygon` and a `Circle`.  If a response is to be calculated in the event of a collision, pass in a `clear`ed `Response` object.



Returns `true` if there is a collision, `false` otherwise.



If it returns `false` you should not use any values that are in the `response` (if one is passed in)



### `SAT.testCirclePolygon(circle, polygon, response)`



The same thing as `SAT.testPolygonCircle`, but in the other direction.



Returns `true` if there is a collision, `false` otherwise.



If it returns `false` you should not use any values that are in the `response` (if one is passed in)



*Note: This is slightly slower than `SAT.testPolygonCircle` as it just calls that and reverses the result*



### `SAT.testPolygonPolygon(a, b, response)`



Tests whether two polygons `a` and `b` collide. If a response is to be calculated in the event of collision, pass in a `clear`ed `Response` object.



Returns `true` if there is a collision, `false` otherwise.



If it returns `false` you should not use any values that are in the `response` (if one is passed in)



*Note: If you want to detect a collision between `Box`es, use the `toPolygon()` method*



## Examples



Test two circles

```javascript

var V = SAT.Vector;

var C = SAT.Circle;



var circle1 = new C(new V(0,0), 20);

var circle2 = new C(new V(30,0), 20);

var response = new SAT.Response();

var collided = SAT.testCircleCircle(circle1, circle2, response);



// collided => true

// response.overlap => 10

// response.overlapV => (10, 0)

```



Test a circle and a polygon

```javascript

var V = SAT.Vector;

var C = SAT.Circle;

var P = SAT.Polygon;



var circle = new C(new V(50,50), 20);

// A square

var polygon = new P(new V(0,0), [

  new V(0,0), new V(40,0), new V(40,40), new V(0,40)

]);

var response = new SAT.Response();

var collided = SAT.testPolygonCircle(polygon, circle, response);



// collided => true

// response.overlap ~> 5.86

// response.overlapV ~> (4.14, 4.14) - i.e. on a diagonal

```



Test two polygons

```javascript

var V = SAT.Vector;

var P = SAT.Polygon;



// A square

var polygon1 = new P(new V(0,0), [

  new V(0,0), new V(40,0), new V(40,40), new V(0,40)

]);

// A triangle

var polygon2 = new P(new V(30,0), [

  new V(0,0), new V(30, 0), new V(0, 30)

]);

var response = new SAT.Response();

var collided = SAT.testPolygonPolygon(polygon1, polygon2, response);



// collided => true

// response.overlap => 10

// response.overlapV => (10, 0)

```



No collision between two Boxes

```javascript

var V = SAT.Vector;

var B = SAT.Box;



var box1 = new B(new V(0,0), 20, 20).toPolygon();

var box2 = new B(new V(100,100), 20, 20).toPolygon();

var collided = SAT.testPolygonPolygon(box1, box2);



// collided => false

```



Hit testing a circle and polygon

```javascript

var V = SAT.Vector;

var C = SAT.Circle;

var P = SAT.Polygon;



var triangle = new P(new V(30,0), [

  new V(0,0), new V(30, 0), new V(0, 30)

]);

var circle = new C(new V(100,100), 20);



SAT.pointInPolygon(new V(0,0), triangle); // false

SAT.pointInPolygon(new V(35, 5), triangle); // true

SAT.pointInCircle(new V(0,0), circle); // false

SAT.pointInCircle(new V(110,110), circle); // true

```



## Tests



To run the tests from your console:



```

npm install

npm run test

```