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flock.js
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flock.js
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/*global define*/
define(function() {
'use strict';
var sn;
/**
* @module plugins/sprite/flock
*/
/**
* This plugin tracks groups of sprites and moves them together using the boids flocking
* algorithm.
* <p>
* This plugin supports phasers and will flock more efficiently, but with less
* accuracy with phased updates.
* <p>
* Note that this plugin will not move the sprites, it only calculates velocity. To move the
* sprites you should add the {@link module:plugins/sprite/apply-velocity.ApplyVelocity|apply-velocity}
* plugin after this one as a commit update. In this way the sprites accurately update based on
* their positions at the same moment in time.
* <p>
* Note that this should not be constructed directly, but rather via the updates or commit
* property in your spawnSprite data, e.g. <code>update:[{name:'flock'}]</code>.
* <p>
* See The <code>opts<code> parameter in the {@link module:sprites/sprite.Sprite|Sprite constructor}
* <p>
* Alongside the name, you can pass the following options
* <dl>
* <dt>tracker</dt><dd>Pass a tracker object here. See ProximityTracker. Sprites that flock
* with the same tracker will belong to the same flock. You should also apply the
* {@link module:plugins/sprite/track.Track|track plugin} to track the sprite in the
* {@link module:ai/proximity-tracker.ProximityTracker|proximity tracker}.</dd>
* <dt>flock_speed</dt><dd>In pixels/second. This is the maximum speed for any flockmate.</dd>
* <dt>flock_neighborhood</dt><dd>The radius that defines the influential
* flockmates, in pixels. Larger is generally better but slower, dependant on the tracker.</dd>
* <dt>flock_separation</dt><dd>This is the desired distance between flockmates. Flock pressure
* may force them closer together, but you can increase this to try to force them further apart.</dd>
* <dt>flock_neighbor_limit</dt><dd>If you're experiencing slow performance, try setting a neighbor
* limit. This limits the flockmates that can influence a sprite to a set number of closest neighbors.
* This degrades the quality of the flocking behavior. To include all flockmates, set this to a very
* high number.</dd>
* <dt>flock_steering</dt><dd>Pass a function here to control the flock. The function should be of the form
* <pre>
* flock_steering: function(sprite, out) {
* out[0]=1;
* out[1]=0;
* }
* </pre>
* And should steer each flockmate accordingly by populating the passed in spanned 2-length array with x,y
* values. In the above example, the values 1,0 will guide the sprite eastwards. In a real example, your code
* might determine the map tile that a sprite is on and guide it along a path, or simply move it on a
* vector towards some known point.
* </dd>
* </dl>
* @constructor module:plugins/sprite/flock.Flock
*/
function Flock() {
/* TODO: Docs - Show an example of a complete flocked sprite with all required plugins. */
/* TODO: Add support for phased updates */
/* TODO: Try making a flock of 1. It just spins round and acts weird. Work out if that's expected
* or indicative of some bug. */
this.xy = [0,0];
this.xy2 = [0,0];
}
/** Called with the update options as the function context, one of which
* is this.sprite, which refers to the sprite being updated.
* @method module:plugins/sprite/flock.Flock#update
* @private
* @param {Number} now The time of the current frame
* @param {Boolean} phaseOn If the update is controlled by a phaser,
* this will be true to hint that we do a full batch of work, or false
* to hint that we try to exit as trivially as possible. Ignored on this
* plugin.
* @return true normally, or false to prevent any further
* plugins being called on this sprite for this frame.
*/
Flock.prototype.update = function(now, phaseOn) {
var dt;
if (this.lastTime===undefined) {
dt = 16;
} else {
dt = now - this.lastTime;
}
this.lastTime = now;
var x = 0, y = 0, i, dx, dy, d2, n;
var s = this.sprite;
var neighbors = this.tracker.find(s.x, s.y, this.flock_neighborhood, true);
/* TODO: Maintain current direction.
*
* TODO: Should phasing alter weights?
*/
var weightSeparation = 1;
var weightAlignment = 1;
var weightCohesion = 1.5;
var weightSteering = 4;
var weightInertia = 1.5;
/* TODO: I have a vague suspicion that not all the vertical components are being
* halved correctly. */
/* steering */
this.flock_steering(s, this.xy);
this.xy[0] = this.xy[0] * weightSteering;
this.xy[1] = this.xy[1] * weightSteering;
/* cohesion: Find average location of neighbours for cohesion vector */
var count = Math.min(this.flock_neighbor_limit, neighbors.length);
if (count>0) {
for (i = count - 1; i >= 0; i--) {
n = neighbors[i];
x+=n.x;
y+=n.y;
}
x/=count;
y/=count;
s.vectorTo(x, y, this.xy2);
this.xy[0] = this.xy[0] + weightCohesion * this.xy2[0];
this.xy[1] = this.xy[1] + weightCohesion * this.xy2[1];
}
/* alignment: average vector of neighbours */
if (count>0) {
for (x = 0, y = 0, i = count - 1; i >= 0; i--) {
n = neighbors[i];
s.vector(this.xy2);
x+=this.xy2[0];
y+=this.xy2[1];
}
this.xy[0] = this.xy[0] + weightAlignment * x/count;
this.xy[1] = this.xy[1] + weightAlignment * y/(count/2); /* /2 count because we assume isometric, so this converts from screen to world-space */
}
/* separation: Any flockmates that are too close should repel the sprite. */
count = 0;
for (x = 0, y = 0, i = 0; i < neighbors.length; i++) {
n = neighbors[i];
dx = s.x - n.x;
dy = 2*(s.y - n.y);
d2 = (dx*dx)+(dy+dy);
if (d2>this.flock_separation2) {
break;
}
count++;
var prop = 1-Math.sqrt(d2/this.flock_separation2);
x+=prop*dx;
y+=prop*dy;
}
if (count>0) {
x/=count;
count/=2; /* /2 count because we assume isometric, so this converts from screen to world-space */
y/=count;
this.xy[0] = this.xy[0] + weightSeparation*x;
this.xy[1] = this.xy[1] + weightSeparation*y;
}
/* update velocity */
s.velocityx = weightInertia * s.velocityx + this.xy[0];
s.velocityy = weightInertia * s.velocityy + this.xy[1];
var maxSpeed = this.flock_speed * dt/1000;
var mag = (s.velocityx*s.velocityx)+(s.velocityy*s.velocityy);
if (mag>(maxSpeed*maxSpeed)) {
mag = Math.sqrt(mag);
s.velocityx = maxSpeed * s.velocityx/mag;
s.velocityy = maxSpeed * s.velocityy/mag;
}
return true;
};
/**
* @method module:plugins/sprite/flock.Flock#init
* @private
*/
Flock.prototype.onSpriteRemoved = function() {
};
/**
* @method module:plugins/sprite/flock.Flock#init
* @private
*/
Flock.prototype.init = function(s) {
this.sprite = s;
/* Some sensible defaults */
if (this.flock_speed===undefined) {
this.flock_speed = 120;
}
if (this.flock_neighborhood===undefined) {
this.flock_neighborhood = 50;
}
if (this.flock_separation===undefined) {
this.flock_separation = Math.min(20, this.flock_neighborhood / 2);
}
this.flock_separation2 = this.flock_separation*this.flock_separation;
if (this.flock_neighbor_limit===undefined) {
this.flock_neighbor_limit = 5;
}
};
return function(snaps) {
sn = snaps;
sn.registerSpriteUpdater('flock', Flock);
};
});