scrawl-canvas
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<h1 id="spring-factory">Spring 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>Spring</strong> object connects together two Particle objects, linking them together with a set of constraints which together exert a spring force on the Particles.</p>
<ul>
<li>Currently Scrawl-canvas offers only the spring constraint for connecting Particles; it does not (yet) define joint or other types of constraint.</li>
<li>The <a href="./net.html">Net</a> entity is, at the moment, the only entity which makes use of Spring objects.</li>
</ul>
<p>The Spring factory uses the Base mixin, thus Spring objects can be cloned and killed like other Scrawl-canvas objects. Spring objects are stored in the <code>scrawl.library.spring</code> section of the Scrawl-canvas library object.</p>
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<h4 id="demos">Demos:</h4>
<ul>
<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-010.html">particles-010</a> - Net entity: using a shape path as a net template</li>
</ul>
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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, particle } <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>, 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>
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<h4 id="spring-constructor">Spring constructor</h4>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> <span class="hljs-title class_">Spring</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>
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<h4 id="spring-prototype">Spring 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_">Spring</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">'Spring'</span>;
P.<span class="hljs-property">lib</span> = <span class="hljs-string">'spring'</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>
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<h4 id="mixins">Mixins</h4>
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<div class="content"><div class='highlight'><pre>P = <span class="hljs-title function_">baseMix</span>(P);</pre></div></div>
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<h4 id="spring-attributes">Spring attributes</h4>
<ul>
<li>Attributes defined in the <a href="../mixin/base.html">base mixin</a>: <strong>name</strong>.</li>
</ul>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">let</span> defaultAttributes = {</pre></div></div>
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<p><strong>particleFrom</strong>, <strong>particleTo</strong> - String name of a Particle, or the Particle object itself. These attributes hold references to the Particle objects involved in this constraint.</p>
</div>
<div class="content"><div class='highlight'><pre> <span class="hljs-attr">particleFrom</span>: <span class="hljs-literal">null</span>,
<span class="hljs-attr">particleFromIsStatic</span>: <span class="hljs-literal">false</span>,
<span class="hljs-attr">particleTo</span>: <span class="hljs-literal">null</span>,
<span class="hljs-attr">particleToIsStatic</span>: <span class="hljs-literal">false</span>,</pre></div></div>
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<p><code>springConstant</code> - float Number. Larger values make the spring stiffer. Suggested values: 5 - 300</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">springConstant</span>: <span class="hljs-number">50</span>,</pre></div></div>
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<p><code>damperConstant</code> - float Number. Larger values forces the spring to take a longer time to come to equilibrium. Suggested values: 5 - 50</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">damperConstant</span>: <span class="hljs-number">10</span>,</pre></div></div>
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<p><code>restLength</code> - The spring’s ideal length - the further away from its ideal, the more force the spring will apply to its connected body objects to get them back to their optimal distance </p>
</div>
<div class="content"><div class='highlight'><pre> <span class="hljs-attr">restLength</span>: <span class="hljs-number">1</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>
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<h4 id="packet-management">Packet management</h4>
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<div class="content"><div class='highlight'><pre>P.<span class="hljs-property">packetObjects</span> = <span class="hljs-title function_">pushUnique</span>(P.<span class="hljs-property">packetObjects</span>, [<span class="hljs-string">'particleFrom'</span>, <span class="hljs-string">'particleTo'</span>]);</pre></div></div>
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<h4 id="clone-management">Clone management</h4>
<p>No additional clone functionality required</p>
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<h4 id="kill-management">Kill management</h4>
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<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>
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<h4 id="get-set-deltaset">Get, Set, deltaSet</h4>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">let</span> S = P.<span class="hljs-property">setters</span>;</pre></div></div>
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<p><code>particleFrom</code>, <code>particleTo</code></p>
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<div class="content"><div class='highlight'><pre>S.<span class="hljs-property">particleFrom</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params">item</span>) {
<span class="hljs-keyword">if</span> (item.<span class="hljs-property">substring</span>) item = particle[item];
<span class="hljs-keyword">if</span> (item && item.<span class="hljs-property">type</span> === <span class="hljs-string">'Particle'</span>) <span class="hljs-variable language_">this</span>.<span class="hljs-property">particleFrom</span> = item;
};
S.<span class="hljs-property">particleTo</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params">item</span>) {
<span class="hljs-keyword">if</span> (item.<span class="hljs-property">substring</span>) item = particle[item];
<span class="hljs-keyword">if</span> (item && item.<span class="hljs-property">type</span> === <span class="hljs-string">'Particle'</span>) <span class="hljs-variable language_">this</span>.<span class="hljs-property">particleTo</span> = item;
};</pre></div></div>
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<h4 id="prototype-functions">Prototype functions</h4>
<p><code>applySpring</code> - internal function</p>
</div>
<div class="content"><div class='highlight'><pre>P.<span class="hljs-property">applySpring</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) {
<span class="hljs-keyword">let</span> {particleFrom, particleTo, particleFromIsStatic, particleToIsStatic, springConstant, damperConstant, restLength} = <span class="hljs-variable language_">this</span>;
<span class="hljs-keyword">if</span> (particleFrom && particleTo) {
<span class="hljs-keyword">let</span> {<span class="hljs-attr">position</span>: fromPosition, <span class="hljs-attr">velocity</span>: fromVelocity, <span class="hljs-attr">load</span>: fromLoad} = particleFrom;
<span class="hljs-keyword">let</span> {<span class="hljs-attr">position</span>: toPosition, <span class="hljs-attr">velocity</span>: toVelocity, <span class="hljs-attr">load</span>: toLoad} = particleTo;
<span class="hljs-keyword">let</span> dVelocity = <span class="hljs-title function_">requestVector</span>(toVelocity).<span class="hljs-title function_">vectorSubtract</span>(fromVelocity),
dPosition = <span class="hljs-title function_">requestVector</span>(toPosition).<span class="hljs-title function_">vectorSubtract</span>(fromPosition);
<span class="hljs-keyword">let</span> firstNorm = <span class="hljs-title function_">requestVector</span>(dPosition).<span class="hljs-title function_">normalize</span>(),
secondNorm = <span class="hljs-title function_">requestVector</span>(firstNorm);
firstNorm.<span class="hljs-title function_">scalarMultiply</span>(springConstant * (dPosition.<span class="hljs-title function_">getMagnitude</span>() - restLength));
dVelocity.<span class="hljs-title function_">vectorMultiply</span>(secondNorm).<span class="hljs-title function_">scalarMultiply</span>(damperConstant).<span class="hljs-title function_">vectorMultiply</span>(secondNorm);
<span class="hljs-keyword">let</span> force = <span class="hljs-title function_">requestVector</span>(firstNorm).<span class="hljs-title function_">vectorAdd</span>(dVelocity);
<span class="hljs-keyword">if</span> (!particleFromIsStatic) fromLoad.<span class="hljs-title function_">vectorAdd</span>(force);
<span class="hljs-keyword">if</span> (!particleToIsStatic) toLoad.<span class="hljs-title function_">vectorSubtract</span>(force);
<span class="hljs-title function_">releaseVector</span>(dVelocity, dPosition, firstNorm, secondNorm, force);
}
};</pre></div></div>
</li>
<li id="section-18">
<div class="annotation">
<div class="sswrap ">
<a class="ss" href="#section-18">§</a>
</div>
<h4 id="factory">Factory</h4>
<pre><code>scrawl.<span class="hljs-title function_">makeNet</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">'test-net'</span>,
<span class="hljs-attr">generate</span>: <span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) {
<span class="hljs-keyword">let</span> { name, particleStore, springs, springConstant, damperConstant } = <span class="hljs-variable language_">this</span>;
<span class="hljs-keyword">let</span> leftParticle, rightParticle;
<span class="hljs-comment">// generate particles</span>
leftParticle = <span class="hljs-title function_">makeParticle</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">`<span class="hljs-subst">${name}</span>-left`</span>,
<span class="hljs-attr">positionX</span>: <span class="hljs-number">0</span>,
<span class="hljs-attr">positionY</span>: <span class="hljs-number">0</span>,
});
rightParticle = leftParticle.<span class="hljs-title function_">clone</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">`<span class="hljs-subst">${name}</span>-right`</span>,
<span class="hljs-attr">positionX</span>: <span class="hljs-number">100</span>,
});
leftParticle.<span class="hljs-title function_">run</span>(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-literal">false</span>);
rightParticle.<span class="hljs-title function_">run</span>(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-literal">false</span>);
particleStore.<span class="hljs-title function_">push</span>(leftParticle, rightParticle);
<span class="hljs-comment">// generate spring</span>
<span class="hljs-keyword">let</span> mySpring = <span class="hljs-title function_">makeSpring</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">`<span class="hljs-subst">${name}</span>-link-<span class="hljs-subst">${i}</span>-<span class="hljs-subst">${i+<span class="hljs-number">1</span>}</span>`</span>,
<span class="hljs-attr">particleFrom</span>: leftParticle,
<span class="hljs-attr">particleTo</span>: rightParticle,
springConstant,
damperConstant,
<span class="hljs-attr">restLength</span>: <span class="hljs-number">100</span>,
});
springs.<span class="hljs-title function_">push</span>(mySpring);
},
...
}).<span class="hljs-title function_">run</span>();
</code></pre>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> makeSpring = <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_">Spring</span>(items);
};
constructors.<span class="hljs-property">Spring</span> = <span class="hljs-title class_">Spring</span>;</pre></div></div>
</li>
<li id="section-19">
<div class="annotation">
<div class="sswrap ">
<a class="ss" href="#section-19">§</a>
</div>
<h4 id="exports">Exports</h4>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">export</span> {
makeSpring,
};</pre></div></div>
</li>
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