scrawl-canvas
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Version 8.9.4 - 19 Nov 2022
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<h1 id="demo-canvas-019a">Demo Canvas 019a</h1>
<p>Gradient and Color factories - transparency - alternative approach using Cells instead of images</p>
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<p><a href="../../demo/canvas-019a.html">Run code</a></p>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">import</span> {
library <span class="hljs-keyword">as</span> L,
importDomImage,
makeFilter,
makePicture,
createImageFromEntity,
makeRadialGradient,
makeBlock,
makeRender,
addNativeListener,
} <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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</div>
<h4 id="scene-setup">Scene setup</h4>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> canvases = L.<span class="hljs-property">canvas</span>;</pre></div></div>
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<p>Import the images we defined in the DOM (in <img> elements)</p>
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<div class="content"><div class='highlight'><pre><span class="hljs-title function_">importDomImage</span>(<span class="hljs-string">'.places'</span>);</pre></div></div>
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<p>For this scene, we’ll build a data structure which we can iterate over, to build the entitys, assets and gradients required by the scene</p>
</div>
<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> data = [
{
<span class="hljs-attr">canvas</span>: canvases[<span class="hljs-string">'hackney'</span>],
<span class="hljs-attr">image</span>: <span class="hljs-string">'hackney-bg'</span>,
<span class="hljs-attr">transparency</span>: <span class="hljs-string">'transparent'</span>,
},
{
<span class="hljs-attr">canvas</span>: canvases[<span class="hljs-string">'heathrow'</span>],
<span class="hljs-attr">image</span>: <span class="hljs-string">'heathrow-bg'</span>,
<span class="hljs-attr">transparency</span>: <span class="hljs-string">'rgba(0,0,0,0)'</span>,
},
{
<span class="hljs-attr">canvas</span>: canvases[<span class="hljs-string">'kingston'</span>],
<span class="hljs-attr">image</span>: <span class="hljs-string">'kingston-bg'</span>,
<span class="hljs-attr">transparency</span>: <span class="hljs-string">'#00000000'</span>,
},
{
<span class="hljs-attr">canvas</span>: canvases[<span class="hljs-string">'burglary'</span>],
<span class="hljs-attr">image</span>: <span class="hljs-string">'burglary-bg'</span>,
<span class="hljs-attr">transparency</span>: <span class="hljs-string">'#0000'</span>,
},
];</pre></div></div>
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<p>This array will hold a set of functions which we will invoke in turn at the start of each Display cycle</p>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> checkFunctions = [];</pre></div></div>
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<p>The blur filter is temporary - we use it once on each image to generate a blurred version of that image</p>
<ul>
<li>We do it this way because the blur filter is computationally very expensive - capturing a blurred version of the image is a lot better for end user power consumption</li>
</ul>
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<div class="content"><div class='highlight'><pre><span class="hljs-title function_">makeFilter</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">'blur'</span>,
<span class="hljs-attr">method</span>: <span class="hljs-string">'gaussianBlur'</span>,
<span class="hljs-attr">radius</span>: <span class="hljs-number">20</span>,
});</pre></div></div>
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<p>Iterate through our data array to create Scrawl-canvas objects</p>
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<div class="content"><div class='highlight'><pre>data.<span class="hljs-title function_">forEach</span>(<span class="hljs-function"><span class="hljs-params">scene</span> =></span> {</pre></div></div>
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<p>Firstly, build the blurred image in its own cell</p>
<ul>
<li>We only need to compile this once, thus don’t include the cell in any part of the Display cycle</li>
</ul>
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<div class="content"><div class='highlight'><pre> <span class="hljs-keyword">let</span> mycell = scene.<span class="hljs-property">canvas</span>.<span class="hljs-title function_">buildCell</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">`<span class="hljs-subst">${scene.image}</span>-blurred-cell`</span>,
<span class="hljs-attr">dimensions</span>: [<span class="hljs-string">'100%'</span>, <span class="hljs-string">'100%'</span>],
<span class="hljs-attr">cleared</span>: <span class="hljs-literal">false</span>,
<span class="hljs-attr">compiled</span>: <span class="hljs-literal">false</span>,
<span class="hljs-attr">shown</span>: <span class="hljs-literal">false</span>,
});
<span class="hljs-title function_">makePicture</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">`<span class="hljs-subst">${scene.image}</span>-blurred-image`</span>,
<span class="hljs-attr">group</span>: <span class="hljs-string">`<span class="hljs-subst">${scene.image}</span>-blurred-cell`</span>,
<span class="hljs-attr">asset</span>: scene.<span class="hljs-property">image</span>,
<span class="hljs-attr">dimensions</span>: [<span class="hljs-string">'100%'</span>, <span class="hljs-string">'100%'</span>],
<span class="hljs-attr">copyDimensions</span>: [<span class="hljs-string">'100%'</span>, <span class="hljs-string">'100%'</span>],
<span class="hljs-attr">filters</span>: [<span class="hljs-string">'blur'</span>],
<span class="hljs-attr">method</span>: <span class="hljs-string">'fill'</span>,
});</pre></div></div>
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<p>The new Cell’s compile action is blocking, because the blur filter takes a long time to complete. To get something up on the screen we can defer the compile action until after the current RAF completes by putting it in a setTimeout invocation.</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-built_in">setTimeout</span>(<span class="hljs-function">() =></span> mycell.<span class="hljs-title function_">compile</span>(), <span class="hljs-number">0</span>);</pre></div></div>
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<p>Next, build a gradient using transparency and apply it in a second Block which displays in the original canvas</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-title function_">makeRadialGradient</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">`<span class="hljs-subst">${scene.image}</span>-gradient`</span>,
<span class="hljs-attr">start</span>: [<span class="hljs-string">'50%'</span>, <span class="hljs-string">'50%'</span>],
<span class="hljs-attr">end</span>: [<span class="hljs-string">'50%'</span>, <span class="hljs-string">'50%'</span>],
<span class="hljs-attr">startRadius</span>: <span class="hljs-string">'5%'</span>,
<span class="hljs-attr">endRadius</span>: <span class="hljs-string">'20%'</span>,
<span class="hljs-attr">colors</span>: [
[<span class="hljs-number">0</span>, scene.<span class="hljs-property">transparency</span>],
[<span class="hljs-number">999</span>, <span class="hljs-string">'lightgray'</span>]
],
});
<span class="hljs-keyword">const</span> gradientBlock = <span class="hljs-title function_">makeBlock</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">`<span class="hljs-subst">${scene.image}</span>-gradient-block`</span>,
<span class="hljs-attr">group</span>: scene.<span class="hljs-property">canvas</span>.<span class="hljs-property">base</span>.<span class="hljs-property">name</span>,
<span class="hljs-attr">start</span>: [<span class="hljs-string">'center'</span>, <span class="hljs-string">'center'</span>],
<span class="hljs-attr">handle</span>: [<span class="hljs-string">'center'</span>, <span class="hljs-string">'center'</span>],
<span class="hljs-attr">dimensions</span>: [<span class="hljs-string">'200%'</span>, <span class="hljs-string">'200%'</span>],
<span class="hljs-attr">fillStyle</span>: <span class="hljs-string">`<span class="hljs-subst">${scene.image}</span>-gradient`</span>,
<span class="hljs-attr">lockFillStyleToEntity</span>: <span class="hljs-literal">true</span>,
});</pre></div></div>
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<p>Now we can draw our blurred image into the scene </p>
<ul>
<li>We use some compositing magic so it only appears where the gradient is not transparent</li>
</ul>
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<div class="content"><div class='highlight'><pre> <span class="hljs-title function_">makePicture</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">`<span class="hljs-subst">${scene.image}</span>-blurred-block`</span>,
<span class="hljs-attr">group</span>: scene.<span class="hljs-property">canvas</span>.<span class="hljs-property">base</span>.<span class="hljs-property">name</span>,
<span class="hljs-attr">asset</span>: <span class="hljs-string">`<span class="hljs-subst">${scene.image}</span>-blurred-cell`</span>,
<span class="hljs-attr">dimensions</span>: [<span class="hljs-string">'100%'</span>, <span class="hljs-string">'100%'</span>],
<span class="hljs-attr">copyDimensions</span>: [<span class="hljs-string">'100%'</span>, <span class="hljs-string">'100%'</span>],
<span class="hljs-attr">method</span>: <span class="hljs-string">'fill'</span>,
<span class="hljs-attr">globalCompositeOperation</span>: <span class="hljs-string">'source-atop'</span>,
});</pre></div></div>
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<p>Lastly, display the original image in the canvas</p>
<ul>
<li>Again, we use compositing magic to draw on the bits missed by the blurred image</li>
</ul>
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<div class="content"><div class='highlight'><pre> <span class="hljs-title function_">makePicture</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">`<span class="hljs-subst">${scene.image}</span>-original-image`</span>,
<span class="hljs-attr">group</span>: scene.<span class="hljs-property">canvas</span>.<span class="hljs-property">base</span>.<span class="hljs-property">name</span>,
<span class="hljs-attr">asset</span>: scene.<span class="hljs-property">image</span>,
<span class="hljs-attr">dimensions</span>: [<span class="hljs-string">'100%'</span>, <span class="hljs-string">'100%'</span>],
<span class="hljs-attr">copyDimensions</span>: [<span class="hljs-string">'100%'</span>, <span class="hljs-string">'100%'</span>],
<span class="hljs-attr">method</span>: <span class="hljs-string">'fill'</span>,
<span class="hljs-attr">globalCompositeOperation</span>: <span class="hljs-string">'destination-over'</span>,
});</pre></div></div>
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<p>Check whether the mouse cursor is hovering over this canvas, and update the filter Block entity’s positioning accordingly</p>
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<div class="content"><div class='highlight'><pre> <span class="hljs-keyword">const</span> <span class="hljs-title function_">f</span> = (<span class="hljs-params"></span>) => {
<span class="hljs-keyword">const</span> here = scene.<span class="hljs-property">canvas</span>.<span class="hljs-property">here</span>;
<span class="hljs-keyword">return</span> <span class="hljs-keyword">function</span> (<span class="hljs-params"></span>) {
gradientBlock.<span class="hljs-title function_">set</span>({
<span class="hljs-attr">lockTo</span>: (here.<span class="hljs-property">active</span>) ? <span class="hljs-string">'mouse'</span> : <span class="hljs-string">'start'</span>,
});
}
};
checkFunctions.<span class="hljs-title function_">push</span>(<span class="hljs-title function_">f</span>());
});</pre></div></div>
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<h4 id="scene-animation">Scene animation</h4>
<p>Function to display frames-per-second data, and other information relevant to the demo</p>
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<div class="content"><div class='highlight'><pre><span class="hljs-keyword">const</span> report = <span class="hljs-title function_">reportSpeed</span>(<span class="hljs-string">'#reportmessage'</span>);</pre></div></div>
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<p>Create the Display cycle animation</p>
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<div class="content"><div class='highlight'><pre><span class="hljs-title function_">makeRender</span>({
<span class="hljs-attr">name</span>: <span class="hljs-string">'demo-animation'</span>,
<span class="hljs-attr">target</span>: [canvases[<span class="hljs-string">'hackney'</span>], canvases[<span class="hljs-string">'heathrow&#x