scrawl-canvas
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<h1 id="net-factory">Net 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>
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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>
<li><a href="../../demo/particles-012.html">particles-012</a> - Use Net entity particles as reference coordinates for other artefacts</li>
</ul>
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<h4 id="imports">Imports</h4>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">import</span> { constructors, artefact, artefactnames, entity, world, particle } <span class="hljs-keyword">from</span> <span class="hljs-string">'../core/library.js'</span>;
<span class="hljs-keyword">import</span> { pushUnique, mergeOver, λ<span class="hljs-literal">null</span>, isa_fn, isa_obj, xt, xta, Ωempty } <span class="hljs-keyword">from</span> <span class="hljs-string">'../core/utilities.js'</span>;
<span class="hljs-keyword">import</span> { currentGroup } <span class="hljs-keyword">from</span> <span class="hljs-string">'../core/document.js'</span>;
<span class="hljs-keyword">import</span> { makeParticle } <span class="hljs-keyword">from</span> <span class="hljs-string">'./particle.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> { makeSpring } <span class="hljs-keyword">from</span> <span class="hljs-string">'./particleSpring.js'</span>;
<span class="hljs-keyword">import</span> baseMix <span class="hljs-keyword">from</span> <span class="hljs-string">'../mixin/base.js'</span>;
<span class="hljs-keyword">import</span> entityMix <span class="hljs-keyword">from</span> <span class="hljs-string">'../mixin/entity.js'</span>;</pre></div></div>
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<h4 id="net-constructor">Net constructor</h4>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> <span class="hljs-title class_">Net</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_">initializePositions</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>);</pre></div></div>
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<p>The entity places a <code>hitRadius</code> around each of its particles - effectively a distributed hit zone which can be used for drag-and-drop, and other user interactions..</p>
</div>
<div class="content"><div class='highlight'><pre> <span class="hljs-variable language_">this</span>.<span class="hljs-property">onEnter</span> = λ<span class="hljs-literal">null</span>;
<span class="hljs-variable language_">this</span>.<span class="hljs-property">onLeave</span> = λ<span class="hljs-literal">null</span>;
<span class="hljs-variable language_">this</span>.<span class="hljs-property">onDown</span> = λ<span class="hljs-literal">null</span>;
<span class="hljs-variable language_">this</span>.<span class="hljs-property">onUp</span> = λ<span class="hljs-literal">null</span>;</pre></div></div>
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<p>Net entitys generate their Particles once, on initialization, in line with the <code>generate</code> function’s instructions. Scrawl-canvas includes a number of pre-built generator functions, which we can reference by their String names: <code>weak-net</code>, <code>strong-net</code>, <code>weak-shape</code>, <code>strong-shape</code></p>
</div>
<div class="content"><div class='highlight'><pre> <span class="hljs-variable language_">this</span>.<span class="hljs-property">generate</span> = λ<span class="hljs-literal">null</span>;</pre></div></div>
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<p>The <code>postGenerate</code> function runs imediately after the <code>generate</code> function. We can use it to amend the attributes of selected Particles, for instance to make them static.</p>
</div>
<div class="content"><div class='highlight'><pre> <span class="hljs-variable language_">this</span>.<span class="hljs-property">postGenerate</span> = λ<span class="hljs-literal">null</span>;</pre></div></div>
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<p>As part of its <code>stamp</code> functionality the Net entity will invoke the <code>stampAction</code> function. If not supplied, the entity will not display anything on the canvas.</p>
</div>
<div class="content"><div class='highlight'><pre> <span class="hljs-variable language_">this</span>.<span class="hljs-property">stampAction</span> = λ<span class="hljs-literal">null</span>;</pre></div></div>
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<p>Setup the particle store, and the entity’s <code>springs</code> Array</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-variable language_">this</span>.<span class="hljs-property">particleStore</span> = [];
<span class="hljs-variable language_">this</span>.<span class="hljs-property">springs</span> = [];
<span class="hljs-keyword">if</span> (!items.<span class="hljs-property">group</span>) items.<span class="hljs-property">group</span> = currentGroup;
<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">purge</span>) <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">purgeArtefact</span>(<span class="hljs-variable language_">this</span>.<span class="hljs-property">purge</span>);
<span class="hljs-keyword">return</span> <span class="hljs-variable language_">this</span>;
};</pre></div></div>
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<h4 id="net-prototype">Net 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_">Net</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">'Net'</span>;
P.<span class="hljs-property">lib</span> = <span class="hljs-string">'entity'</span>;
P.<span class="hljs-property">isArtefact</span> = <span class="hljs-literal">true</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);
P = <span class="hljs-title function_">entityMix</span>(P);</pre></div></div>
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<h4 id="net-attributes">Net attributes</h4>
<ul>
<li>Attributes defined in the <a href="../mixin/base.html">base mixin</a>: <strong>name</strong>.</li>
<li>Attributes defined in the <a href="../mixin/position.html">position mixin</a>: <strong>group, visibility, order, calculateOrder, stampOrder, start, <em>startX</em>, <em>startY</em>, handle, <em>handleX</em>, <em>handleY</em>, offset, <em>offsetX</em>, <em>offsetY</em>, dimensions, <em>width</em>, <em>height</em>, pivoted, mimicked, lockTo, <em>lockXTo</em>, <em>lockYTo</em>, scale, roll, noUserInteraction, noPositionDependencies, noCanvasEngineUpdates, noFilters, noPathUpdates, purge, bringToFrontOnDrag</strong>.</li>
<li>Attributes defined in the <a href="../mixin/delta.html">delta mixin</a>: <strong>delta, noDeltaUpdates</strong>.</li>
<li>Attributes defined in the <a href="../mixin/pivot.html">pivot mixin</a>: <strong>pivot, pivotCorner, addPivotHandle, addPivotOffset, addPivotRotation</strong>.</li>
<li>Attributes defined in the <a href="../mixin/mimic.html">mimic mixin</a>: <strong>mimic, useMimicDimensions, useMimicScale, useMimicStart, useMimicHandle, useMimicOffset, useMimicRotation, useMimicFlip, addOwnDimensionsToMimic, addOwnScaleToMimic, addOwnStartToMimic, addOwnHandleToMimic, addOwnOffsetToMimic, addOwnRotationToMimic</strong>.</li>
<li>Attributes defined in the <a href="../mixin/path.html">path mixin</a>: <strong>path, pathPosition, addPathHandle, addPathOffset, addPathRotation, constantPathSpeed</strong>.</li>
<li>Attributes defined in the <a href="../mixin/entity.html">entity mixin</a>: <strong>method, pathObject, winding, flipReverse, flipUpend, scaleOutline, lockFillStyleToEntity, lockStrokeStyleToEntity, onEnter, onLeave, onDown, onUp, <em>fillStyle, strokeStyle, globalAlpha, globalCompositeOperation, lineWidth, lineCap, lineJoin, lineDash, lineDashOffset, miterLimit, shadowOffsetX, shadowOffsetY, shadowBlur, shadowColor, filter</em></strong>.</li>
<li>Attributes defined in the <a href="../mixin/anchor.html">anchor mixin</a>: <strong>anchor</strong>.</li>
<li>Attributes defined in the <a href="../mixin/filter.html">filter mixin</a>: <strong>filters, isStencil</strong>.</li>
</ul>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">let</span> defaultAttributes = {</pre></div></div>
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<p><strong>world</strong> - World object; can be set using the String name of a World object, or the World object itself.</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">world</span>: <span class="hljs-literal">null</span>,</pre></div></div>
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<p><strong>artefact</strong> - In theory, any Scrawl-canvas object whose <code>isArtefact</code> flag is set to <code>true</code> can be assigned to this attribute. However this has not been tested on non-entity artefacts. For now, stick to Scrawl-canvas entity objects.</p>
<ul>
<li>Can be set using the String name of an artefact object, or the artefact object itself.</li>
</ul>
</div>
<div class="content"><div class='highlight'><pre> <span class="hljs-attr">artefact</span>: <span class="hljs-literal">null</span>,</pre></div></div>
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<p><strong>historyLength</strong> - positive integer Number - every Particle will keep a record of its recent state, in a set of ParticleHistory arrays stored in the Particle’s <code>history</code> Array. The Net entity will set the maximum permitted length of the history array whenever it generates a new Particle. </p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">historyLength</span>: <span class="hljs-number">1</span>,</pre></div></div>
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<p>Net entitys will, as part of the Display cycle, apply any force objects assigned to a Particle. The initial forces assigned to every new Particle will be in line with the Force objects included in the Net’s <strong>forces</strong> Array.</p>
<ul>
<li>To set the Array, supply a new Array containing Force objects, and/or the name Strings of those Force objects, to the <code>forces</code> attribute.</li>
</ul>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">forces</span>: <span class="hljs-literal">null</span>,</pre></div></div>
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<p><strong>mass</strong> - positive float Number - the initial mass assigned to each Particle when it is generated. Note that, unlike Net entitys, a Net entity will generate all its Particles with the same mass value</p>
<ul>
<li>The <code>mass</code> attribute is used by the pre-defined <em><strong>gravity Force</strong></em></li>
</ul>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">mass</span>: <span class="hljs-number">1</span>,</pre></div></div>
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<p>Physics calculations are handled by the Net entity’s physics <strong>engine</strong> which must be a String value of either <code>euler</code> (the default engine), <code>improved-euler</code> or <code>runge-kutta</code>.</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">engine</span>: <span class="hljs-string">'euler'</span>,</pre></div></div>
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<p><strong>springConstant</strong>, <strong>damperConstant</strong> - positive float Numbers - used for the initial values for any Spring objects generated to connect two Particles</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">springConstant</span>: <span class="hljs-number">50</span>,
<span class="hljs-attr">damperConstant</span>: <span class="hljs-number">10</span>,</pre></div></div>
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<p>This is a ratio figure, not the actual rest length. If <code>== 1</code>, spring restLength will equal the initial distance between the two particles. <code>< 1</code> and the length will be proportionately smaller; <code>> 1</code> gives results in a longer length</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">restLength</span>: <span class="hljs-number">1</span>,</pre></div></div>
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<p><strong>showSprings</strong> - Boolean flag - when set, Scrawl-canvas will display the Spring connections between Particle pairs</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">showSprings</span>: <span class="hljs-literal">false</span>,</pre></div></div>
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<p><strong>showSpringColor</strong> - CSS color String - the strokeStyle color used to display the Spring objects</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">showSpringsColor</span>: <span class="hljs-string">'#000000'</span>,</pre></div></div>
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<h5 id="weak-net-strong-net">weak-net, strong-net</h5>
<p><strong>rows</strong>, <strong>columns</strong> - positive integer Numbers</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">rows</span>: <span class="hljs-number">0</span>,
<span class="hljs-attr">columns</span>: <span class="hljs-number">0</span>,</pre></div></div>
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<p><strong>rowDistance</strong>, <strong>columnDistance</strong> - positive float Numbers, representing the absolute pixel distance between rows and columns, or percentage String values representing the distance as measured relative to the host Cell’s dimensions</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">rowDistance</span>: <span class="hljs-number">0</span>,
<span class="hljs-attr">columnDistance</span>: <span class="hljs-number">0</span>,</pre></div></div>
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<h5 id="weak-shape-strong-shape">weak-shape, strong-shape</h5>
<p><strong>shapeTemplate</strong> - String name of a shape-based entity, or the entity object itself - used as the template along which particles will be generated</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">shapeTemplate</span>: <span class="hljs-literal">null</span>,</pre></div></div>
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<p><strong>precision</strong> - positive integer Number - the number of particles to generate along the template path</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">precision</span>: <span class="hljs-number">20</span>,</pre></div></div>
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<p><strong>joinTemplateEnds</strong> - Boolean flag - when set, springs will be generated to connect the start and the end particles on the template path</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">joinTemplateEnds</span>: <span class="hljs-literal">false</span>,
<span class="hljs-attr">particlesAreDraggable</span>: <span class="hljs-literal">false</span>,</pre></div></div>
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<p>Note that the <strong>hitRadius</strong> attribute - a positive float Number - is absolute, and has nothing to do with the entity’s dimensions. Net entity hit zones are tied to its Particles, not its start coordinate.</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">hitRadius</span>: <span class="hljs-number">10</span>,</pre></div></div>
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<p><strong>showHitRadius</strong> - Boolean flag - when set, Scrawl-canvas will display appropriate circles around each of the Net entity’s Particles (in addition to any artefact stamped at the Particle’s position)</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">showHitRadius</span>: <span class="hljs-literal">false</span>,</pre></div></div>
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<p><strong>hitRadiusColor</strong> - CSS color String - the strokeStyle color used to display the hit radius</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">hitRadiusColor</span>: <span class="hljs-string">'#000000'</span>,</pre></div></div>
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<p><strong>resetAfterBlur</strong> - positive float Number (measuring seconds) - physics simulations can be brittle, particularly if they are forced to calculate Particle loads (accelerations), velocities and speeds over a large time step. Rather than manage that time step in cases where the user may neglect or navigate away from the browser tab containing the physics animation, Scrawl-canvas will stop, clear, and recreate the scene if the time it takes the user to return to (re-focus on) the web page is greater than the value set in this attribute.</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">resetAfterBlur</span>: <span class="hljs-number">3</span>,</pre></div></div>
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<h5 id="not-defined-in-the-defs-object-but-set-up-in-the-constructor-and-setters">Not defined in the defs object, but set up in the constructor and setters</h5>
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<p><strong>particleStore</strong> - an Array where all the Net’s current particles will be stored. To render the entity, we need to iterate through these particles and use them to repeatedly stamp the Net’s artefact - or perform equivalent <canvas> context engine instructions - onto the host Cell. These actions will be defined in the <code>stampAction</code> function.</p>
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<p><strong>stampAction</strong> - define all major rendering actions in this function. The function receives the following arguments: <code>(artefact, particle, host)</code> - where <code>artefact</code> is the Net entity’s artefact object (if any has been defined/set); <code>particle</code> is the current Particle object whose history needs to be rendered onto the canvas; and <code>host</code> is the Cell wrapper on which we will draw our graphics</p>
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<p><strong>springs</strong> - Array - holds all the entity’s Spring objects</p>
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<div class="content"><div class='highlight'><pre>};
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">packetExclusions</span> = <span class="hljs-title function_">pushUnique</span>(P.<span class="hljs-property">packetExclusions</span>, [<span class="hljs-string">'forces'</span>, <span class="hljs-string">'springs'</span>, <span class="hljs-string">'particleStore'</span>]);
P.<span class="hljs-property">packetExclusionsByRegex</span> = <span class="hljs-title function_">pushUnique</span>(P.<span class="hljs-property">packetExclusionsByRegex</span>, []);
P.<span class="hljs-property">packetCoordinates</span> = <span class="hljs-title function_">pushUnique</span>(P.<span class="hljs-property">packetCoordinates</span>, []);
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">'world'</span>, <span class="hljs-string">'artefact'</span>, <span class="hljs-string">'shapeTemplate'</span>]);
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">'generate'</span>, <span class="hljs-string">'postGenerate'</span>, <span class="hljs-string">'stampAction'</span>]);
P.<span class="hljs-property">finalizePacketOut</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params">copy, items</span>) {
<span class="hljs-keyword">let</span> forces = items.<span class="hljs-property">forces</span> || <span class="hljs-variable language_">this</span>.<span class="hljs-property">forces</span> || <span class="hljs-literal">false</span>;
<span class="hljs-keyword">if</span> (forces) {
<span class="hljs-keyword">let</span> tempForces = [];
forces.<span class="hljs-title function_">forEach</span>(<span class="hljs-function"><span class="hljs-params">f</span> =></span> {
<span class="hljs-keyword">if</span> (f.<span class="hljs-property">substring</span>) tempForces.<span class="hljs-title function_">push</span>(f);
<span class="hljs-keyword">else</span> <span class="hljs-keyword">if</span> (<span class="hljs-title function_">isa_obj</span>(f) && f.<span class="hljs-property">name</span>) tempForces.<span class="hljs-title function_">push</span>(f.<span class="hljs-property">name</span>);
});
copy.<span class="hljs-property">forces</span> = tempForces;
}
<span class="hljs-keyword">let</span> tempParticles = [];
<span class="hljs-variable language_">this</span>.<span class="hljs-property">particleStore</span>.<span class="hljs-title function_">forEach</span>(<span class="hljs-function"><span class="hljs-params">p</span> =></span> tempParticles.<s