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<!DOCTYPE html> <html> <head> <title>Force factory</title> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <meta name="viewport" content="width=device-width, target-densitydpi=160dpi, initial-scale=1.0; maximum-scale=1.0; user-scalable=0;"> <link rel="stylesheet" media="all" href="../../docco.css" /> </head> <body> <div id="container"> <div id="background"></div> <ul id="jump_to"> <li> <a class="large" href="javascript:void(0);">Jump To …</a> <a class="small" href="javascript:void(0);">+</a> <div id="jump_wrapper"> <div id="jump_page_wrapper"> <div id="jump_page"> <a class="source" href="../core/animationloop.html"> ./source/core/animationloop.js </a> <a class="source" href="../core/document.html"> ./source/core/document.js </a> <a class="source" href="../core/events.html"> ./source/core/events.js </a> <a class="source" href="../core/init.html"> ./source/core/init.js </a> <a class="source" href="../core/library.html"> ./source/core/library.js </a> <a class="source" 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href="../mixin/pattern.html"> ./source/mixin/pattern.js </a> <a class="source" href="../mixin/pivot.html"> ./source/mixin/pivot.js </a> <a class="source" href="../mixin/position.html"> ./source/mixin/position.js </a> <a class="source" href="../mixin/shapeBasic.html"> ./source/mixin/shapeBasic.js </a> <a class="source" href="../mixin/shapeCurve.html"> ./source/mixin/shapeCurve.js </a> <a class="source" href="../mixin/shapePathCalculation.html"> ./source/mixin/shapePathCalculation.js </a> <a class="source" href="../mixin/styles.html"> ./source/mixin/styles.js </a> <a class="source" href="../mixin/tween.html"> ./source/mixin/tween.js </a> </div> </div> </li> </ul> <ul class="sections"> <li id="section-1"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-1">§</a> </div> <h1 id="force-factory">Force factory</h1> <p>The Scrawl-canvas particle physics engine is a simple system designed to allow developers a way to add particle-based effects to their canvas animation scenes. The physics engine is built on top of the following components:</p> <ul> <li><a href="./particle.html">Particle objects</a>, which represent a 3-dimensional coordinate - based on a Scrawl-canvas <a href="./vector.html">Vector object</a> - and include a history of recent positions which we can use to determine how to display that particle on screen.</li> <li><a href="./particleHistory.html">History arrays</a> which can be pooled (reused) to cut down on Array creation and distruction during the animation.</li> <li><a href="./particleForce.html">Force objects</a> which define the general and occasional forces to be applied to each particle in the system as the animation progresses - a <strong>gravity</strong> force object is pre-defined by Scrawl-canvas.</li> <li><a href="./particleSpring.html">Spring objects</a> used to define a constraint (connection) between two particles in a system.</li> <li><a href="./particleWorld.html">World objects</a> where we can store attributes and values used by various objects; these attributes can be set up so that they will be inherited by clones of the World object. We can also influence the speed of the physics animation here.</li> </ul> <p>We do not have to handle particle generation and manipulation ourselves. Instead, Scrawl-canvas gives us three dedicated <strong>entitys</strong> which we use to add particle animation effects to the canvas scene. These entitys are:</p> <ul> <li><a href="./tracer.html">Tracer</a> - this entity generates a single non-recycled (in other words: long lasting) particle with a history, which we can use to display trace effects in the animation.</li> <li><a href="./emitter.html">Emitter</a> - an entity which generates a stream of short-lived, recycled particles, each with its own history. Emitters are highly versatile entitys which can generate a wide range of effects.</li> <li><a href="./net.html">Net</a> - a (generally) larger entity which uses both forces and springs to manage the animation of its non-recycled particles. Note that other artefacts can use Net particles as a reference for their own positioning.</li> </ul> <h4 id="particle-physics">Particle physics</h4> <p>The Scrawl-canvas particle physics engine system is based on a fairly classical understanding of particle <em><strong>kinetics</strong></em> (applying forces and constraints to a small, spherical object in 3D space) and <em><strong>kinematics</strong></em> (the movement of the small object in response to the forces and constraints applied to it).</p> <p>A Scrawl-canvas <strong>Force</strong> object is, essentially, a wrapper around an <code>action</code> function which calculates a force operating on a particle. The force object <strong>must</strong> have a unique name. Also …</p> <p>The action function <strong>must</strong> accept three arguments, in the following order:</p> <ul> <li>a Particle object</li> <li>a World object</li> <li>a Cell object</li> </ul> <p>The function <strong>must add</strong> the result of its calculation to the Particle object’s <code>load</code> Vector.</p> <p>… See the <strong>gravity force</strong>, below, for an example of how to construct a Force object.</p> <p>The Force factory uses the Base mixin, thus Force objects can be cloned and killed like other Scrawl-canvas objects. Force objects are stored in the <code>scrawl.library.force</code> section of the Scrawl-canvas library object.</p> </div> </li> <li id="section-2"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-2">§</a> </div> <h4 id="demos">Demos:</h4> <ul> <li><a href="../../demo/particles-001.html">particles-001</a> - Emitter entity, and Particle World, basic functionality</li> <li><a href="../../demo/particles-007.html">particles-007</a> - Particle Force objects: generation and functionality</li> <li><a href="../../demo/particles-008.html">particles-008</a> - Net entity: generation and basic functionality, including Spring objects</li> <li><a href="../../demo/particles-009.html">particles-009</a> - Net particles: drag-and-drop functionality</li> <li><a href="../../demo/particles-012.html">particles-012</a> - Use Net entity particles as reference coordinates for other artefacts</li> </ul> </div> </li> <li id="section-3"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-3">§</a> </div> <h4 id="imports">Imports</h4> </div> <div class="content"><div class='highlight'><pre><span class="hljs-keyword">import</span> { constructors } <span class="hljs-keyword">from</span> <span class="hljs-string">'../core/library.js'</span>; <span class="hljs-keyword">import</span> { mergeOver, pushUnique, λ<span class="hljs-literal">null</span>, isa_fn, Ωempty } <span class="hljs-keyword">from</span> <span class="hljs-string">'../core/utilities.js'</span>; <span class="hljs-keyword">import</span> { requestVector, releaseVector } <span class="hljs-keyword">from</span> <span class="hljs-string">'./vector.js'</span>; <span class="hljs-keyword">import</span> baseMix <span class="hljs-keyword">from</span> <span class="hljs-string">'../mixin/base.js'</span>;</pre></div></div> </li> <li id="section-4"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-4">§</a> </div> <h4 id="force-constructor">Force constructor</h4> </div> <div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> <span class="hljs-title class_">Force</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params">items = Ωempty</span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">makeName</span>(items.<span class="hljs-property">name</span>); <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">register</span>(); <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">set</span>(<span class="hljs-variable language_">this</span>.<span class="hljs-property">defs</span>); <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">set</span>(items); <span class="hljs-keyword">if</span> (!<span class="hljs-variable language_">this</span>.<span class="hljs-property">action</span>) <span class="hljs-variable language_">this</span>.<span class="hljs-property">action</span> = λ<span class="hljs-literal">null</span>; <span class="hljs-keyword">return</span> <span class="hljs-variable language_">this</span>; };</pre></div></div> </li> <li id="section-5"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-5">§</a> </div> <h4 id="force-prototype">Force prototype</h4> </div> <div class="content"><div class='highlight'><pre><span class="hljs-keyword">let</span> P = <span class="hljs-title class_">Force</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span> = <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">create</span>(<span class="hljs-title class_">Object</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>); P.<span class="hljs-property">type</span> = <span class="hljs-string">'Force'</span>; P.<span class="hljs-property">lib</span> = <span class="hljs-string">'force'</span>; P.<span class="hljs-property">isArtefact</span> = <span class="hljs-literal">false</span>; P.<span class="hljs-property">isAsset</span> = <span class="hljs-literal">false</span>;</pre></div></div> </li> <li id="section-6"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-6">§</a> </div> <h4 id="mixins">Mixins</h4> </div> <div class="content"><div class='highlight'><pre>P = <span class="hljs-title function_">baseMix</span>(P);</pre></div></div> </li> <li id="section-7"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-7">§</a> </div> <h4 id="force-attributes">Force attributes</h4> <ul> <li>Attributes defined in the <a href="../mixin/base.html">base mixin</a>: <strong>name</strong>.</li> </ul> </div> <div class="content"><div class='highlight'><pre><span class="hljs-keyword">let</span> defaultAttributes = { <span class="hljs-attr">action</span>: <span class="hljs-literal">null</span>, }; P.<span class="hljs-property">defs</span> = <span class="hljs-title function_">mergeOver</span>(P.<span class="hljs-property">defs</span>, defaultAttributes);</pre></div></div> </li> <li id="section-8"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-8">§</a> </div> <h4 id="packet-management">Packet management</h4> </div> <div class="content"><div class='highlight'><pre>P.<span class="hljs-property">packetFunctions</span> = <span class="hljs-title function_">pushUnique</span>(P.<span class="hljs-property">packetFunctions</span>, [<span class="hljs-string">'action'</span>]);</pre></div></div> </li> <li id="section-9"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-9">§</a> </div> <h4 id="clone-management">Clone management</h4> <p>No additional clone functionality required</p> </div> </li> <li id="section-10"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-10">§</a> </div> <h4 id="kill-management">Kill management</h4> </div> <div class="content"><div class='highlight'><pre>P.<span class="hljs-property">kill</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">deregister</span>(); <span class="hljs-keyword">return</span> <span class="hljs-literal">true</span>; };</pre></div></div> </li> <li id="section-11"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-11">§</a> </div> <h4 id="get-set-deltaset">Get, Set, deltaSet</h4> </div> <div class="content"><div class='highlight'><pre><span class="hljs-keyword">let</span> S = P.<span class="hljs-property">setters</span>; S.<span class="hljs-property">action</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params">item</span>) { <span class="hljs-keyword">if</span> (<span class="hljs-title function_">isa_fn</span>(item)) <span class="hljs-variable language_">this</span>.<span class="hljs-property">action</span> = item; <span class="hljs-keyword">else</span> <span class="hljs-variable language_">this</span>.<span class="hljs-property">action</span> = λ<span class="hljs-literal">null</span>; }</pre></div></div> </li> <li id="section-12"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-12">§</a> </div> <h4 id="factory">Factory</h4> <pre><code><span class="hljs-keyword">let</span> myRepellorBall = scrawl.<span class="hljs-title function_">makeWheel</span>({ <span class="hljs-attr">name</span>: <span class="hljs-string">'big-ball'</span>, <span class="hljs-attr">radius</span>: <span class="hljs-number">30</span>, }); scrawl.<span class="hljs-title function_">makeForce</span>({ <span class="hljs-attr">name</span>: <span class="hljs-string">'example-repellor'</span>, <span class="hljs-attr">action</span>: <span class="hljs-function">(<span class="hljs-params">particle, world, host</span>) =></span> { <span class="hljs-keyword">let</span> {load, position} = particle; <span class="hljs-keyword">let</span> ballPosition = myRepellorBall.<span class="hljs-title function_">get</span>(<span class="hljs-string">'position'</span>); <span class="hljs-keyword">let</span> tempVector = scrawl.<span class="hljs-title function_">requestVector</span>(ballPosition).<span class="hljs-title function_">vectorSubtract</span>(position); <span class="hljs-keyword">let</span> magnitude = tempVector.<span class="hljs-title function_">getMagnitude</span>(); <span class="hljs-keyword">if</span> (magnitude && magnitude < myRepellorBall.<span class="hljs-title function_">get</span>(<span class="hljs-string">'radius'</span>)) { tempVector.<span class="hljs-title function_">scalarMultiply</span>(<span class="hljs-number">1</span> / (magnitude / <span class="hljs-number">1000</span>)); load.<span class="hljs-title function_">vectorSubtract</span>(tempVector) } scrawl.<span class="hljs-title function_">releaseVector</span>(tempVector); }, }); </code></pre> </div> <div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> makeForce = <span class="hljs-keyword">function</span> (<span class="hljs-params">items</span>) { <span class="hljs-keyword">if</span> (!items) <span class="hljs-keyword">return</span> <span class="hljs-literal">false</span>; <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Force</span>(items); }; constructors.<span class="hljs-property">Force</span> = <span class="hljs-title class_">Force</span>; <span class="hljs-title function_">makeForce</span>({ <span class="hljs-attr">name</span>: <span class="hljs-string">'gravity'</span>, <span class="hljs-attr">action</span>: <span class="hljs-function">(<span class="hljs-params">particle, world, host</span>) =></span> { <span class="hljs-keyword">let</span> {mass, load} = particle; <span class="hljs-keyword">let</span> c = <span class="hljs-title function_">requestVector</span>(); c.<span class="hljs-title function_">setFromVector</span>(world.<span class="hljs-property">gravity</span>).<span class="hljs-title function_">scalarMultiply</span>(mass); load.<span class="hljs-title function_">vectorAdd</span>(c); <span class="hljs-title function_">releaseVector</span>(c); }, });</pre></div></div> </li> <li id="section-13"> <div class="annotation"> <div class="sswrap "> <a class="ss" href="#section-13">§</a> </div> <h4 id="exports">Exports</h4> </div> <div class="content"><div class='highlight'><pre><span class="hljs-keyword">export</span> { makeForce, };</pre></div></div> </li> </ul> </div> </body> </html>