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import { System } from '@serpentity/serpentity';
import { Body, Constraint, SAT, World } from 'matter-js';
import GrabberNode from '../nodes/grabber';
import GrabbableNode from '../nodes/grabbable';
import Config from '../config';
const internals = {
kGrabRadius: 50,
kNoEngine: 'No matter js physics engine found. Make sure you set the `engine` key in the config object when initializing.'
};
/**
* Handles grabbing between entities
*
* @extends {external:Serpentity.System}
* @class GrabSystem
* @param {object} config a configuration object to extend.
*/
export default class GrabSystem extends System {
constructor(config = {}) {
super();
/**
* The node collection of grabbers
*
* @property {external:Serpentity.NodeCollection} grabbers
* @instance
* @memberof GrabSystem
*/
this.grabbers = null;
/**
* The node collection of grabbables
*
* @property {external:Serpentity.NodeCollection} grabbables
* @instance
* @memberof GrabSystem
*/
this.grabbables = null;
/**
* The matter-js engine we will use to add and remove constraints
*
* @property {external:MatterJs.Engine} engine
* @instance
* @memberof GrabSystem
*/
this.engine = config.engine;
if (!this.engine) {
throw new Error(internals.kNoEngine);
}
}
/**
* Initializes system when added. Requests grabber and grabbable nodes
*
* @function added
* @memberof GrabSystem
* @instance
* @param {external:Serpentity.Engine} engine the serpentity engine to
* which we are getting added
*/
added(engine) {
this.grabbers = engine.getNodes(GrabberNode);
this.grabbables = engine.getNodes(GrabbableNode);
}
/**
* Clears system resources when removed.
*
* @function removed
* @instance
* @memberof GrabSystem
*/
removed() {
this.grabbers = null;
this.grabbables = null;
}
/**
* Runs on every update of the loop. Triggers grab and manages cooldown
*
* @function update
* @instance
* @param {Number} currentFrameDuration the duration of the current
* frame
* @memberof GrabSystem
*/
update(currentFrameDuration) {
for (const grabber of this.grabbers) {
const grab = grabber.grab;
if (grab.grabbing && !grab.locked) {
this._grab(grabber);
}
const isGrabReleased = !grab.grabbing || grab.currentCooldown >= grab.cooldown;
if (grab.constraint && isGrabReleased) {
this._release(grabber);
}
if (!grab.grabbing && grab.locked && grab.currentCooldown >= grab.cooldown) {
this._unlock(grabber);
}
if (grab.locked) {
grab.currentCooldown += currentFrameDuration;
}
grab.grabbing = 0;
}
}
// Executes the dash action
_grab(grabber) {
const grab = grabber.grab;
grab.locked = true;
grab.currentCooldown = 0;
Body.setPosition(grabber.grabArea.area, grabber.body.body.position);
for (const grabbable of this.grabbables) {
if (grabbable.entity === grabber.entity) {
continue;
}
const collision = SAT.collides(grabber.grabArea.area, grabbable.body.body);
if (collision.collided) {
grab.constraint = this._createConstraint(grabber.body.body, grabbable.body.body);
}
}
}
// Executes the unlock action
_unlock(grabber) {
grabber.grab.locked = false;
}
// Releases a constraint
_release(grabber) {
World.remove(this.engine.world, grabber.grab.constraint);
grabber.grab.currentCooldown = 0;
grabber.grab.constraint = null;
}
// Performs a grab between two entities
_createConstraint(grabber, grabbable) {
const constraint = Constraint.create({ // Attach the sensor to the body
bodyA: grabber,
bodyB: grabbable,
damping: 0,
length: internals.kGrabRadius / Config.meterSize,
stiffness: 1
});
World.add(this.engine.world, [constraint]);
return constraint;
}
}
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