@deltasnare/physics2d-collision

Polygon-to-polygon collision calculator for Deltasnare's physics engine

Usage

const collision = require('@deltasnare/physics2d-collision')
const { mat2d } = require('gl-matrix')

// create some collider models
const target = collision.create([[0, 5], [-2, 0], [0, -5], [2, 0]])
const near = collision.create([[1, 3], [1, -3], [4, -3], [4, 3]])
const far = collision.create([[3, 3], [3, -3], [6, -3], [6, 3]])

// transform models
const transformed = collision.transform(target, mat2d.fromTranslation([], [-1, -5]))

// test for collisions
const nearCollision = collision.check(target, near) // { depth: 1, normal: [1, 0] }
const farCollision = collision.check(target, far) // null

The collision module exports three functions:

collision.create(vertices)

Creates a collider model. The argument is an array of vertices in vec2 format ([x, y]). The vertices must define a convex mesh in counter-clockwise order. Failing to comply with this assumption may lead to undefiend behavior and/or the physics engine blowing up. For the structure of the returned collider model, see below.

collision.transform(model, transform)

Transforms a collider model with a 2D matrix, returning the resulting model. The model argument must be a collider model created by collision.create() or compatible with it, and transform is a mat2d, a 3x2 2D transformation matrix.

collision.check(first, second)

Checks if two models collide. Both arguments must be collider models created by collision.create() or compatible with it. Returns null if the objects do not collide. If they do, it returns a collision in the following format:

{ depth: 1, normal: [1, 0] }

Where

• depth is the penetration depth (how far the objects overlap)
• normal is the collision normal, the direction of the penetration. This vector is normalized.

Collider Models

Collider models are the basic models that can be collided with this module. Here is an example:

{ vertices: [ [ 0, 5 ], [ -2, 0 ], [ 0, -5 ], [ 2, 0 ] ],
  normals:
   [ [ -0.9284766908852593, 0.3713906763541037 ],
     [ -0.9284766908852593, -0.3713906763541037 ],
     [ 0.9284766908852593, -0.3713906763541037 ],
     [ 0.9284766908852593, 0.3713906763541037 ] ],
  boundingBox: { min: [ -2, -5 ], max: [ 2, 5 ] } }

Collider models are objects, with the following layout:

• vertices is an array of vec2 which define a convex polygon in counter-clockwise order
• normals is an array of vec2 where each member normals[i] corresponds to the outer normal of the edge between vertices[i] and vertices[i + 1]
• boundingBox defines an axis-aligned bounding box of the mesh using an object, where:
  • min is a vec2, containing the lowest coordinates of the box in each axis, and
  • max is a vec2, containing the highest coordinates of the box in each axis