scrawl-canvas
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Version 8.9.4 - 19 Nov 2022
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<ul class="sections">
<li id="section-1">
<div class="annotation">
<div class="sswrap ">
<a class="ss" href="#section-1">§</a>
</div>
<h1 id="demo-particles-001">Demo Particles 001</h1>
<p>Emitter entity, and Particle World, basic functionality</p>
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<li id="section-2">
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<p><a href="../../demo/particles-001.html">Run code</a></p>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">import</span> {
addNativeListener,
library <span class="hljs-keyword">as</span> L,
makeEmitter,
makeRender,
makeWorld,
observeAndUpdate,
} <span class="hljs-keyword">from</span> <span class="hljs-string">'../source/scrawl.js'</span>
<span class="hljs-keyword">import</span> { reportSpeed } <span class="hljs-keyword">from</span> <span class="hljs-string">'./utilities.js'</span>;</pre></div></div>
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<li id="section-3">
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<h4 id="scene-setup">Scene setup</h4>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">let</span> canvas = L.<span class="hljs-property">artefact</span>.<span class="hljs-property">mycanvas</span>;</pre></div></div>
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<li id="section-4">
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<p>Initial canvas background color - we will also allow the user to control this attribute’s value</p>
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<div class="content"><div class='highlight'><pre>canvas.<span class="hljs-title function_">setBase</span>({
<span class="hljs-attr">backgroundColor</span>: <span class="hljs-string">'#000040'</span>,
});</pre></div></div>
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<li id="section-5">
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<h4 id="particle-physics-animation-scene">Particle physics animation scene</h4>
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<p>Create a World object which we can then assign to the Emitter entity</p>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">let</span> myWorld = <span class="hljs-title function_">makeWorld</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">'demo-world'</span>,</pre></div></div>
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<p><code>tickMultiplier</code> controls the speed of the Emitter’s animation</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">tickMultiplier</span>: <span class="hljs-number">2</span>,</pre></div></div>
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<p>We can define additional attributes for the World object, including their setter and getter functions (if required). We can also initialize the attribute as a Scrawl-canvas Coordinate, Vector or Quaternion object.</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">userAttributes</span>: [</pre></div></div>
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<p>These first two new attributes are purely for testing - we will get their values and log them to the console</p>
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<div class="content"><div class='highlight'><pre> {
<span class="hljs-attr">key</span>: <span class="hljs-string">'hello'</span>,
<span class="hljs-attr">defaultValue</span>: <span class="hljs-string">'Hello World'</span>,
<span class="hljs-attr">setter</span>: <span class="hljs-keyword">function</span> (<span class="hljs-params">item</span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-property">hello</span> = <span class="hljs-string">`Hello <span class="hljs-subst">${item}</span>!`</span>},
},
{
<span class="hljs-attr">key</span>: <span class="hljs-string">'testCoordinate'</span>,
<span class="hljs-attr">type</span>: <span class="hljs-string">'Coordinate'</span>,</pre></div></div>
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<p>@ts-expect-error</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">getter</span>: <span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) { <span class="hljs-keyword">return</span> [].<span class="hljs-title function_">concat</span>(<span class="hljs-variable language_">this</span>.<span class="hljs-property">testCoordinate</span>) },</pre></div></div>
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<p>@ts-expect-error</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">setter</span>: <span class="hljs-keyword">function</span> (<span class="hljs-params">item</span>) { <span class="hljs-variable language_">this</span>.<span class="hljs-property">testCoordinate</span>.<span class="hljs-title function_">set</span>(item) },
},</pre></div></div>
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<p>We will store a user-updatable Number value - <code>alphaDecay</code> - which we will use in the <code>stampAction</code> function to tweak the particle effect that we are trying to achieve</p>
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<div class="content"><div class='highlight'><pre> {
<span class="hljs-attr">key</span>: <span class="hljs-string">'alphaDecay'</span>,
<span class="hljs-attr">defaultValue</span>: <span class="hljs-number">6</span>,
},
],</pre></div></div>
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<p>Overwrite our user-defined attributes’ default values with new data, for testing.
@ts-expect-error</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">hello</span>: <span class="hljs-string">'Wonderful Person'</span>,
<span class="hljs-attr">testCoordinate</span>: [<span class="hljs-number">100</span>, <span class="hljs-number">100</span>],
});</pre></div></div>
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<p>Test the World object’s user-defined attributes</p>
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<div class="content"><div class='highlight'><pre>myWorld.<span class="hljs-title function_">set</span>({ <span class="hljs-attr">testCoordinate</span>: [<span class="hljs-string">'center'</span>, <span class="hljs-string">'center'</span>] });
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myWorld.<span class="hljs-title function_">get</span>(<span class="hljs-string">'testCoordinate'</span>));</pre></div></div>
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<p>Define an Emitter entity</p>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> myEmitter = <span class="hljs-title function_">makeEmitter</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">'use-raw-2d-context'</span>,</pre></div></div>
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<p>Every emitter <strong>must</strong> be associated with a World object. The attribute’s value can be the World object’s String name value, or the object itself</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">world</span>: myWorld,</pre></div></div>
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<p>The Emitter is a normal Scrawl-canvas entity. It can be positioned absolutely/relatively - as here, by setting the <code>start</code> (<code>startX</code>, <code>startY</code>) coordinates. Or it can be positioned by reference to other Scrawl-canvas artefacts using the <code>pivot</code>, <code>mimic</code>, <code>path</code>, <code>mouse</code> and/or Net <code>particle</code> functionality.</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">start</span>: [<span class="hljs-string">'center'</span>, <span class="hljs-string">'center'</span>],</pre></div></div>
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<p>Emitter entitys use <em><strong>ephemeral particles</strong></em> to produce their visual effects, generating a steady stream of particles over time and then killing them off in various ways. The <code>generationRate</code> attribute <em>sets the number of particles that the Emitter will generate every second</em>.</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">generationRate</span>: <span class="hljs-number">60</span>,</pre></div></div>
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<p>A common way to kill off generated particles is to give them a lifetime limit (measured in seconds). We can set that value using the <code>killAfterTime</code> attribute. We can also add in a measure of variability using the <code>killAfterTimeVariation</code> attribute.</p>
<ul>
<li>The Emitter being defined here, for instance, will generate a regular stream of 60 particles every second, with each of the particles having a lifetime limit of between 4.9 and 5.1 seconds</li>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">killAfterTime</span>: <span class="hljs-number">5</span>,
<span class="hljs-attr">killAfterTimeVariation</span>: <span class="hljs-number">0.1</span>,</pre></div></div>
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<p>For every Display cycle tick (which in optimal conditions will be around 17 milliseconds after the previous tick), a particle will update its position and record the new position using a ParticleHistory array. This data is then added to the entity’s <code>history</code> array. We can limit the number of ParticleHistory arrays stored in the history array by setting the <code>historyLength</code> attribute to a suitable integer Number value.</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">historyLength</span>: <span class="hljs-number">100</span>,</pre></div></div>
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<p>The key functionality of a particle is that it moves. </p>
<ul>
<li>Particles will move as a consequence of the forces and spring constraints applied to them. </li>
<li>When the particle is generated, we can give it an initial <em><strong>velocity</strong></em>; with no other force or spring applied to the particle, it will move at a constant speed over time to match this initial velocity value.</li>
<li>We set the particle’s initial velocity using a set of six <strong>range</strong> attributes, which represent the distance travelled in the x, y and z directions, as measured in pixels-per-second.</li>
<li>The <code>rangeFrom</code> attributes represent the lowest value in that dimension that will be generated. This value is <em><strong>local to the particle</strong></em> thus negative values are to the left (x) or above (y) or behind (z) the particles initial position.</li>
<li>The <code>range</code> attribute is the maximum random value which will be added to the rangeFrom value. </li>
<li>All particles are assigned a (constrained) random velocity in this manner when they are generated. The values given below will ensure that every particle generated by this Emitter will have a vector velocity of somewhere between -20 to +20 pixels/second in both the x (left-right) and ‘y’ (above-below) directions, and between -0.2 and -1.2 pixels/second in the z (behind-infront) direction.</li>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">rangeX</span>: <span class="hljs-number">40</span>,
<span class="hljs-attr">rangeFromX</span>: -<span class="hljs-number">20</span>,
<span class="hljs-attr">rangeY</span>: <span class="hljs-number">40</span>,
<span class="hljs-attr">rangeFromY</span>: -<span class="hljs-number">20</span>,
<span class="hljs-attr">rangeZ</span>: -<span class="hljs-number">1</span>,
<span class="hljs-attr">rangeFromZ</span>: -<span class="hljs-number">0.2</span>,</pre></div></div>
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<p>We can assign a range of colors to our particle - we’ll start the demo with the minimum and maximum fillStyle colors set to the same color</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-attr">fillMinimumColor</span>: <span class="hljs-string