scrawl-canvas
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<h1 id="particlehistory-factory">ParticleHistory 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>
<p><strong>ParticleHistory</strong> objects are Arrays in which Scrawl-canvas records history data for a given particle at a specified time. The array holds data in the following format:</p>
<pre><code>[
<span class="hljs-title class_">Number</span>:particle-life-time-remaining,
<span class="hljs-title class_">Number</span>:particle-z-position,
<span class="hljs-title class_">Number</span>:particle-x-position,
<span class="hljs-title class_">Number</span>:particle-y-position
]
</code></pre>
<p>Because of the number of ParticleHistory arrays that can be generated and discarded in even a simple particle physics animation, Scrawl-canvas includes functionality to pool and reuse ParticleHistory arrays. The exported functions <code>requestParticleHistoryObject</code> and <code>releaseParticleHistoryObject</code> give us access to the pool mechanism.</p>
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<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-002.html">particles-002</a> - Emitter using artefacts</li>
<li><a href="../../demo/particles-005.html">particles-005</a> - Emit particles from inside an artefact’s area</li>
<li><a href="../../demo/particles-011.html">particles-011</a> - Tracer entity: basic functionality</li>
<li><a href="../../demo/particles-012.html">particles-012</a> - Use Net entity particles as reference coordinates for other artefacts</li>
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<h4 id="imports">Imports</h4>
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<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> { λ<span class="hljs-literal">null</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'../core/utilities.js'</span>;</pre></div></div>
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<h4 id="particlehistory-constructor">ParticleHistory constructor</h4>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> <span class="hljs-title class_">ParticleHistory</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params">items</span>) {
<span class="hljs-keyword">let</span> history = [];
<span class="hljs-title class_">Object</span>.<span class="hljs-title function_">setPrototypeOf</span>(history, <span class="hljs-title class_">ParticleHistory</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>);
<span class="hljs-keyword">if</span> (items) history.<span class="hljs-title function_">set</span>(items);
<span class="hljs-keyword">return</span> history;
};</pre></div></div>
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<h4 id="particlehistory-prototype">ParticleHistory prototype</h4>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">let</span> P = <span class="hljs-title class_">ParticleHistory</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_">Array</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>);
P.<span class="hljs-property">constructor</span> = <span class="hljs-title class_">ParticleHistory</span>;
P.<span class="hljs-property">type</span> = <span class="hljs-string">'ParticleHistory'</span>;</pre></div></div>
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<h4 id="mixins">Mixins</h4>
<p>ParticleHistory Arrays do not use mixins - they are regular Javascript Arrays. As such, they do not possess packet, clone or kill functionality.</p>
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<h4 id="particlehistory-attributes">ParticleHistory attributes</h4>
<p>There are no attributes. The constructor returns an Array containing two members, whose prototype object includes functions for manipulating those members in various ways.</p>
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<h4 id="get-set-deltaset">Get, Set, deltaSet</h4>
<p>There are no getter or setter functions.</p>
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<h4 id="prototype-functions">Prototype functions</h4>
<p>There are no additional prototype functions.</p>
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<h4 id="particlehistory-pool">ParticleHistory pool</h4>
<p>An attempt to reuse history arrays rather than constantly creating and deleting them</p>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> particleHistoryPool = [];</pre></div></div>
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<p><code>exported function</code> - retrieve a ParticleHistory from the history pool</p>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> requestParticleHistoryObject = <span class="hljs-keyword">function</span> (<span class="hljs-params">items, y</span>) {
<span class="hljs-keyword">if</span> (!particleHistoryPool.<span class="hljs-property">length</span>) particleHistoryPool.<span class="hljs-title function_">push</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ParticleHistory</span>());
<span class="hljs-keyword">let</span> c = particleHistoryPool.<span class="hljs-title function_">shift</span>();
<span class="hljs-keyword">return</span> c
};</pre></div></div>
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<p><code>exported function</code> - return a ParticleHistory array to the history pool. Failing to return arrays to the pool may lead to more inefficient code and possible memory leaks.</p>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> releaseParticleHistoryObject = <span class="hljs-keyword">function</span> (<span class="hljs-params">h</span>) {
<span class="hljs-keyword">if</span> (h && h.<span class="hljs-property">type</span> === <span class="hljs-string">'ParticleHistory'</span>) {
h.<span class="hljs-property">length</span> = <span class="hljs-number">0</span>;
particleHistoryPool.<span class="hljs-title function_">push</span>(h);</pre></div></div>
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<p>Do not keep excessive numbers of under-utilised arrays in the pool</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-keyword">if</span> (particleHistoryPool.<span class="hljs-property">length</span> > <span class="hljs-number">100</span>) particleHistoryPool.<span class="hljs-property">length</span> = <span class="hljs-number">0</span>;
}
};</pre></div></div>
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<h4 id="factory">Factory</h4>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> makeParticleHistory = <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_">ParticleHistory</span>(items);
};
constructors.<span class="hljs-property">ParticleHistory</span> = <span class="hljs-title class_">ParticleHistory</span>;</pre></div></div>
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<h4 id="exports">Exports</h4>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">export</span> {
makeParticleHistory,
requestParticleHistoryObject,
releaseParticleHistoryObject,
};</pre></div></div>
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