scrawl-canvas
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<h1 id="gradient-factory">Gradient factory</h1>
<p>Scrawl-canvas Gradient objects implement the Canvas API’s <a href="https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/createLinearGradient">createLinearGradient</a> method. The resulting <a href="https://developer.mozilla.org/en-US/docs/Web/API/CanvasGradient">CanvasGradient</a> object can be used by any Scrawl-canvas entity as its <code>fillStyle</code> or <code>strokeStyle</code>.</p>
<ul>
<li>Most gradient-related functionality has been coded up in the <a href="../mixin/styles.html">styles mixin</a>, and is documented there.</li>
<li>Gradients fully participate in the Scrawl-canvas packet system, thus can be saved, restored, cloned, killed, etc.</li>
<li>Gradients can be animated in a variety of ways; the can act as target objects for Scrawl-canvas Tweens.</li>
</ul>
<p>Gradients can be applied to an entity in two different ways, depending on the entity’s <code>lockFillStyleToEntity</code> and <code>lockStrokeStyleToEntity</code> attribute flags:</p>
<ul>
<li><strong>Cell-locked</strong> Gradients will cover the entire Cell; an entity moved from one part of the display to another will show different parts of the gradient</li>
<li><strong>Entity-locked</strong> Gradients display their entire color range on the entity, move with the entity and even rotate with the entity.</li>
</ul>
</div>
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<h4 id="demos">Demos:</h4>
<ul>
<li><a href="../../demo/canvas-003.html">Canvas-003</a> - Linear gradients</li>
<li><a href="../../demo/canvas-005.html">Canvas-005</a> - Cell-locked, and Entity-locked, gradients; animating gradients by delta, and by tween</li>
<li><a href="../../demo/canvas-022.html">Canvas-022</a> - Grid entity - basic functionality (color, gradients)</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 } <span class="hljs-keyword">from</span> <span class="hljs-string">'../core/library.js'</span>;
<span class="hljs-keyword">import</span> { pushUnique, Ωempty } <span class="hljs-keyword">from</span> <span class="hljs-string">'../core/utilities.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> stylesMix <span class="hljs-keyword">from</span> <span class="hljs-string">'../mixin/styles.js'</span>;</pre></div></div>
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<h4 id="gradient-constructor">Gradient constructor</h4>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> <span class="hljs-title class_">Gradient</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_">stylesInit</span>(items);
<span class="hljs-keyword">return</span> <span class="hljs-variable language_">this</span>;
};</pre></div></div>
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<h4 id="gradient-prototype">Gradient prototype</h4>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">let</span> P = <span class="hljs-title class_">Gradient</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">'Gradient'</span>;
P.<span class="hljs-property">lib</span> = <span class="hljs-string">'styles'</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);
P = <span class="hljs-title function_">stylesMix</span>(P);</pre></div></div>
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<h4 id="gradient-attributes">Gradient 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/styles.html">styles mixin</a>: <strong>start, end, palette, paletteStart, paletteEnd, cyclePalette</strong>.</li>
<li>Attributes defined in the <a href="./palette.html">Palette factory</a>: <strong>colors, cyclic</strong>.</li>
</ul>
<p>No additional attributes are defined in this file.</p>
</div>
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<h4 id="packet-management">Packet management</h4>
</div>
<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">'palette'</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>
<p>No additional kill functionality required</p>
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<h4 id="get-set-deltaset">Get, Set, deltaSet</h4>
<p>No additional functionality required</p>
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<h4 id="prototype-functions">Prototype functions</h4>
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<p><code>buildStyle</code> - internal function: creates the linear gradient on the Cell’s CanvasRenderingContext2D engine, and then adds the color stops to it.</p>
</div>
<div class="content"><div class='highlight'><pre>P.<span class="hljs-property">buildStyle</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params">cell</span>) {
<span class="hljs-keyword">if</span> (cell) {
<span class="hljs-keyword">let</span> engine = cell.<span class="hljs-property">engine</span>;
<span class="hljs-keyword">if</span> (engine) {
<span class="hljs-keyword">let</span> gradient = engine.<span class="hljs-title function_">createLinearGradient</span>(...<span class="hljs-variable language_">this</span>.<span class="hljs-property">gradientArgs</span>);
<span class="hljs-keyword">return</span> <span class="hljs-variable language_">this</span>.<span class="hljs-title function_">addStopsToGradient</span>(gradient, <span class="hljs-variable language_">this</span>.<span class="hljs-property">paletteStart</span>, <span class="hljs-variable language_">this</span>.<span class="hljs-property">paletteEnd</span>, <span class="hljs-variable language_">this</span>.<span class="hljs-property">cyclePalette</span>);
}
}
<span class="hljs-keyword">return</span> <span class="hljs-string">'rgba(0,0,0,0)'</span>;
};</pre></div></div>
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<p><code>updateGradientArgs</code> - internal function</p>
</div>
<div class="content"><div class='highlight'><pre>P.<span class="hljs-property">updateGradientArgs</span> = <span class="hljs-keyword">function</span> (<span class="hljs-params">x, y</span>) {
<span class="hljs-keyword">let</span> gradientArgs = <span class="hljs-variable language_">this</span>.<span class="hljs-property">gradientArgs</span>,
currentStart = <span class="hljs-variable language_">this</span>.<span class="hljs-property">currentStart</span>,
currentEnd = <span class="hljs-variable language_">this</span>.<span class="hljs-property">currentEnd</span>;
<span class="hljs-keyword">let</span> sx = currentStart[<span class="hljs-number">0</span>] + x,
sy = currentStart[<span class="hljs-number">1</span>] + y,
ex = currentEnd[<span class="hljs-number">0</span>] + x,
ey = currentEnd[<span class="hljs-number">1</span>] + y;</pre></div></div>
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<p>check to correct situation where coordinates represent a ‘0 x 0’ box - which will cause errors in some browsers</p>
</div>
<div class="content"><div class='highlight'><pre> <span class="hljs-keyword">if</span> (sx === ex && sy === ey) ex++;
gradientArgs.<span class="hljs-property">length</span> = <span class="hljs-number">0</span>;
gradientArgs.<span class="hljs-title function_">push</span>(sx, sy, ex, ey);
};</pre></div></div>
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<h4 id="factory">Factory</h4>
<pre><code>scrawl.<span class="hljs-title function_">makeGradient</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">'colored-pipes'</span>,
<span class="hljs-attr">endX</span>: <span class="hljs-string">'100%'</span>,
<span class="hljs-attr">cyclePalette</span>: <span class="hljs-literal">true</span>,
<span class="hljs-attr">colors</span>: [
[<span class="hljs-number">0</span>, <span class="hljs-string">'black'</span>],
[<span class="hljs-number">99</span>, <span class="hljs-string">'red'</span>],
[<span class="hljs-number">199</span>, <span class="hljs-string">'black'</span>],
[<span class="hljs-number">299</span>, <span class="hljs-string">'blue'</span>],
[<span class="hljs-number">399</span>, <span class="hljs-string">'black'</span>],
[<span class="hljs-number">499</span>, <span class="hljs-string">'gold'</span>],
[<span class="hljs-number">599</span>, <span class="hljs-string">'black'</span>],
[<span class="hljs-number">699</span>, <span class="hljs-string">'green'</span>],
[<span class="hljs-number">799</span>, <span class="hljs-string">'black'</span>],
[<span class="hljs-number">899</span>, <span class="hljs-string">'lavender'</span>],
[<span class="hljs-number">999</span>, <span class="hljs-string">'black'</span>]
],
})
scrawl.<span class="hljs-title function_">makeBlock</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">'animated-block'</span>,
<span class="hljs-attr">width</span>: <span class="hljs-number">150</span>,
<span class="hljs-attr">height</span>: <span class="hljs-number">150</span>,
<span class="hljs-attr">startX</span>: <span class="hljs-number">180</span>,
<span class="hljs-attr">startY</span>: <span class="hljs-number">120</span>,
<span class="hljs-attr">handleX</span>: <span class="hljs-string">'center'</span>,
<span class="hljs-attr">handleY</span>: <span class="hljs-string">'center'</span>,
<span class="hljs-attr">strokeStyle</span>: <span class="hljs-string">'coral'</span>,
<span class="hljs-attr">fillStyle</span>: <span class="hljs-string">'colored-pipes'</span>,
<span class="hljs-attr">lineWidth</span>: <span class="hljs-number">2</span>,
<span class="hljs-attr">method</span>: <span class="hljs-string">'fillAndDraw'</span>,
});
</code></pre>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> makeGradient = <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_">Gradient</span>(items);
};
constructors.<span class="hljs-property">Gradient</span> = <span class="hljs-title class_">Gradient</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> {
makeGradient,
};</pre></div></div>
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