File: src/collision/Collision.js
/**
* The `Matter.Collision` module contains methods for detecting collisions between a given pair of bodies.
*
* For efficient detection between a list of bodies, see `Matter.Detector` and `Matter.Query`.
*
* See `Matter.Engine` for collision events.
*
* @class Collision
*/
var Collision = {};
module.exports = Collision;
var Vertices = require('../geometry/Vertices');
var Pair = require('./Pair');
(function() {
var _supports = [];
var _overlapAB = {
overlap: 0,
axis: null
};
var _overlapBA = {
overlap: 0,
axis: null
};
/**
* Creates a new collision record.
* @method create
* @param {body} bodyA The first body part represented by the collision record
* @param {body} bodyB The second body part represented by the collision record
* @return {collision} A new collision record
*/
Collision.create = function(bodyA, bodyB) {
return {
pair: null,
collided: false,
bodyA: bodyA,
bodyB: bodyB,
parentA: bodyA.parent,
parentB: bodyB.parent,
depth: 0,
normal: { x: 0, y: 0 },
tangent: { x: 0, y: 0 },
penetration: { x: 0, y: 0 },
supports: [null, null],
supportCount: 0
};
};
/**
* Detect collision between two bodies.
* @method collides
* @param {body} bodyA
* @param {body} bodyB
* @param {pairs} [pairs] Optionally reuse collision records from existing pairs.
* @return {collision|null} A collision record if detected, otherwise null
*/
Collision.collides = function(bodyA, bodyB, pairs) {
Collision._overlapAxes(_overlapAB, bodyA.vertices, bodyB.vertices, bodyA.axes);
if (_overlapAB.overlap <= 0) {
return null;
}
Collision._overlapAxes(_overlapBA, bodyB.vertices, bodyA.vertices, bodyB.axes);
if (_overlapBA.overlap <= 0) {
return null;
}
// reuse collision records for gc efficiency
var pair = pairs && pairs.table[Pair.id(bodyA, bodyB)],
collision;
if (!pair) {
collision = Collision.create(bodyA, bodyB);
collision.collided = true;
collision.bodyA = bodyA.id < bodyB.id ? bodyA : bodyB;
collision.bodyB = bodyA.id < bodyB.id ? bodyB : bodyA;
collision.parentA = collision.bodyA.parent;
collision.parentB = collision.bodyB.parent;
} else {
collision = pair.collision;
}
bodyA = collision.bodyA;
bodyB = collision.bodyB;
var minOverlap;
if (_overlapAB.overlap < _overlapBA.overlap) {
minOverlap = _overlapAB;
} else {
minOverlap = _overlapBA;
}
var normal = collision.normal,
tangent = collision.tangent,
penetration = collision.penetration,
supports = collision.supports,
depth = minOverlap.overlap,
minAxis = minOverlap.axis,
normalX = minAxis.x,
normalY = minAxis.y,
deltaX = bodyB.position.x - bodyA.position.x,
deltaY = bodyB.position.y - bodyA.position.y;
// ensure normal is facing away from bodyA
if (normalX * deltaX + normalY * deltaY >= 0) {
normalX = -normalX;
normalY = -normalY;
}
normal.x = normalX;
normal.y = normalY;
tangent.x = -normalY;
tangent.y = normalX;
penetration.x = normalX * depth;
penetration.y = normalY * depth;
collision.depth = depth;
// find support points, there is always either exactly one or two
var supportsB = Collision._findSupports(bodyA, bodyB, normal, 1),
supportCount = 0;
// find the supports from bodyB that are inside bodyA
if (Vertices.contains(bodyA.vertices, supportsB[0])) {
supports[supportCount++] = supportsB[0];
}
if (Vertices.contains(bodyA.vertices, supportsB[1])) {
supports[supportCount++] = supportsB[1];
}
// find the supports from bodyA that are inside bodyB
if (supportCount < 2) {
var supportsA = Collision._findSupports(bodyB, bodyA, normal, -1);
if (Vertices.contains(bodyB.vertices, supportsA[0])) {
supports[supportCount++] = supportsA[0];
}
if (supportCount < 2 && Vertices.contains(bodyB.vertices, supportsA[1])) {
supports[supportCount++] = supportsA[1];
}
}
// account for the edge case of overlapping but no vertex containment
if (supportCount === 0) {
supports[supportCount++] = supportsB[0];
}
// update support count
collision.supportCount = supportCount;
return collision;
};
/**
* Find the overlap between two sets of vertices.
* @method _overlapAxes
* @private
* @param {object} result
* @param {vertices} verticesA
* @param {vertices} verticesB
* @param {axes} axes
*/
Collision._overlapAxes = function(result, verticesA, verticesB, axes) {
var verticesALength = verticesA.length,
verticesBLength = verticesB.length,
verticesAX = verticesA[0].x,
verticesAY = verticesA[0].y,
verticesBX = verticesB[0].x,
verticesBY = verticesB[0].y,
axesLength = axes.length,
overlapMin = Number.MAX_VALUE,
overlapAxisNumber = 0,
overlap,
overlapAB,
overlapBA,
dot,
i,
j;
for (i = 0; i < axesLength; i++) {
var axis = axes[i],
axisX = axis.x,
axisY = axis.y,
minA = verticesAX * axisX + verticesAY * axisY,
minB = verticesBX * axisX + verticesBY * axisY,
maxA = minA,
maxB = minB;
for (j = 1; j < verticesALength; j += 1) {
dot = verticesA[j].x * axisX + verticesA[j].y * axisY;
if (dot > maxA) {
maxA = dot;
} else if (dot < minA) {
minA = dot;
}
}
for (j = 1; j < verticesBLength; j += 1) {
dot = verticesB[j].x * axisX + verticesB[j].y * axisY;
if (dot > maxB) {
maxB = dot;
} else if (dot < minB) {
minB = dot;
}
}
overlapAB = maxA - minB;
overlapBA = maxB - minA;
overlap = overlapAB < overlapBA ? overlapAB : overlapBA;
if (overlap < overlapMin) {
overlapMin = overlap;
overlapAxisNumber = i;
if (overlap <= 0) {
// can not be intersecting
break;
}
}
}
result.axis = axes[overlapAxisNumber];
result.overlap = overlapMin;
};
/**
* Finds supporting vertices given two bodies along a given direction using hill-climbing.
* @method _findSupports
* @private
* @param {body} bodyA
* @param {body} bodyB
* @param {vector} normal
* @param {number} direction
* @return [vector]
*/
Collision._findSupports = function(bodyA, bodyB, normal, direction) {
var vertices = bodyB.vertices,
verticesLength = vertices.length,
bodyAPositionX = bodyA.position.x,
bodyAPositionY = bodyA.position.y,
normalX = normal.x * direction,
normalY = normal.y * direction,
vertexA = vertices[0],
vertexB = vertexA,
nearestDistance = normalX * (bodyAPositionX - vertexB.x) + normalY * (bodyAPositionY - vertexB.y),
vertexC,
distance,
j;
// find deepest vertex relative to the axis
for (j = 1; j < verticesLength; j += 1) {
vertexB = vertices[j];
distance = normalX * (bodyAPositionX - vertexB.x) + normalY * (bodyAPositionY - vertexB.y);
// convex hill-climbing
if (distance < nearestDistance) {
nearestDistance = distance;
vertexA = vertexB;
}
}
// measure next vertex
vertexC = vertices[(verticesLength + vertexA.index - 1) % verticesLength];
nearestDistance = normalX * (bodyAPositionX - vertexC.x) + normalY * (bodyAPositionY - vertexC.y);
// compare with previous vertex
vertexB = vertices[(vertexA.index + 1) % verticesLength];
if (normalX * (bodyAPositionX - vertexB.x) + normalY * (bodyAPositionY - vertexB.y) < nearestDistance) {
_supports[0] = vertexA;
_supports[1] = vertexB;
return _supports;
}
_supports[0] = vertexA;
_supports[1] = vertexC;
return _supports;
};
/*
*
* Properties Documentation
*
*/
/**
* A reference to the pair using this collision record, if there is one.
*
* @property pair
* @type {pair|null}
* @default null
*/
/**
* A flag that indicates if the bodies were colliding when the collision was last updated.
*
* @property collided
* @type boolean
* @default false
*/
/**
* The first body part represented by the collision (see also `collision.parentA`).
*
* @property bodyA
* @type body
*/
/**
* The second body part represented by the collision (see also `collision.parentB`).
*
* @property bodyB
* @type body
*/
/**
* The first body represented by the collision (i.e. `collision.bodyA.parent`).
*
* @property parentA
* @type body
*/
/**
* The second body represented by the collision (i.e. `collision.bodyB.parent`).
*
* @property parentB
* @type body
*/
/**
* A `Number` that represents the minimum separating distance between the bodies along the collision normal.
*
* @readOnly
* @property depth
* @type number
* @default 0
*/
/**
* A normalised `Vector` that represents the direction between the bodies that provides the minimum separating distance.
*
* @property normal
* @type vector
* @default { x: 0, y: 0 }
*/
/**
* A normalised `Vector` that is the tangent direction to the collision normal.
*
* @property tangent
* @type vector
* @default { x: 0, y: 0 }
*/
/**
* A `Vector` that represents the direction and depth of the collision.
*
* @property penetration
* @type vector
* @default { x: 0, y: 0 }
*/
/**
* An array of body vertices that represent the support points in the collision.
*
* _Note:_ Only the first `collision.supportCount` items of `collision.supports` are active.
* Therefore use `collision.supportCount` instead of `collision.supports.length` when iterating the active supports.
*
* These are the deepest vertices (along the collision normal) of each body that are contained by the other body's vertices.
*
* @property supports
* @type vector[]
* @default []
*/
/**
* The number of active supports for this collision found in `collision.supports`.
*
* _Note:_ Only the first `collision.supportCount` items of `collision.supports` are active.
* Therefore use `collision.supportCount` instead of `collision.supports.length` when iterating the active supports.
*
* @property supportCount
* @type number
* @default 0
*/
})();