<div id="toc" class="toc">
<div id="toctitle">Table of Contents</div>
<ul class="sectlevel1">
<li><a href="#_introduction">Introduction</a>
<ul class="sectlevel2">
<li><a href="#_one_sentence_summary">One-Sentence Summary</a></li>
<li><a href="#_rationale">Rationale</a></li>
</ul>
</li>
<li><a href="#_using_collagen">Using Collagen</a>
<ul class="sectlevel2">
<li><a href="#_a_basic_example">A Basic Example</a></li>
<li><a href="#_a_more_complicated_example">A More Complicated Example</a></li>
<li><a href="#_memes">Memes</a></li>
</ul>
</li>
<li><a href="#_faq">FAQ</a></li>
</ul>
</div>
<div id="preamble">
<div class="sectionbody">
<div class="admonitionblock note">
<table>
<tr>
<td class="icon">
<i class="fa icon-note" title="Note"></i>
</td>
<td class="content">
<div class="paragraph">
<p>This project is a work in progress, but it’s coming along well!
Testing and documentation definitely need to be beefed up, but the functionality is nearly all there.</p>
</div>
</td>
</tr>
</table>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_introduction">Introduction</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_one_sentence_summary">One-Sentence Summary</h3>
<div class="paragraph">
<p>Collagen is a program that takes as input a folder containing zero or more image files
(<code>.jpeg</code>, <code>.png</code>, etc.) and a JSON manifest file describing the layout of these images
along with SVG components such as shapes and text, and produces as output a single SVG
file with all assets embedded.</p>
</div>
</div>
<div class="sect2">
<h3 id="_rationale">Rationale</h3>
<div class="paragraph">
<p>There are several widely used image formats, perhaps the three best known of which are JPEG, PNG, and SVG.
JPEG and PNG are <a href="https://en.wikipedia.org/wiki/Raster_graphics" target="_blank" rel="noopener">raster formats</a>, which means they correspond to a rectangular grid of pixels.
On the other hand, SVG is a <a href="https://en.wikipedia.org/wiki/Vector_graphics" target="_blank" rel="noopener">vector format</a>, which means it describes perfectly precise curves that can be displayed with arbitrarily high precision.
These three formats are each optimized for a different use case:</p>
</div>
<div class="ulist">
<ul>
<li>
<p><a href="https://en.wikipedia.org/wiki/Jpeg" target="_blank" rel="noopener">JPEG</a> uses lossy compression that preserves visual quality on most "real-life" images — images that contain smoothly-varying gradients — but which produces <a href="https://en.wikipedia.org/wiki/Compression_artifact#Images" target="_blank" rel="noopener">visible artifacts</a> when used on other kinds of images, especially ones containing hard edges and/or text.</p>
</li>
<li>
<p><a href="https://en.wikipedia.org/wiki/Portable_Network_Graphics" target="_blank" rel="noopener">PNG</a> uses lossless compression that handles images with few distinct colors well, but requires an inordinate amount of space for storing images with many colors.</p>
</li>
<li>
<p><a href="https://en.wikipedia.org/wiki/Scalable_Vector_Graphics" target="_blank" rel="noopener">SVG</a> is a vector graphics format which can nevertheless contain embedded raster images; however, doing so requires base64 encoding the raster image.</p>
</li>
</ul>
</div>
<div class="paragraph">
<p>Because each of these image formats is optimized for only a single use case, they cannot be easily combined.
For instance, overlaying text on a JPEG image will introduce compression artifacts that were not present in the original text, while overlaying a JPEG image on a PNG will cause the file size to balloon.</p>
</div>
<div class="paragraph">
<p><em>Collagen</em> — from "collage" and "generate"<sup class="footnote">[<a id="_footnoteref_1" class="footnote" href="#_footnotedef_1" title="View footnote.">1</a>]</sup> — aims to fix this problem by packing all types of images, as well as vector shapes and text, into a single SVG file, the actual rendering of which is left to an SVG viewer application (which includes most web browsers).
This allows a user to combine several graphics into a single file that can be displayed as an image without compromising on visual quality or file size.<sup class="footnote">[<a id="_footnoteref_2" class="footnote" href="#_footnotedef_2" title="View footnote.">2</a>]</sup></p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_using_collagen">Using Collagen</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The input to Collagen is a folder containing at the very least a <code>collagen.json</code> manifest file describing the layout of the resulting SVG.
If the manifest specifies any image files (by their path relative to the folder), then those image files must also be present at the expected path in the folder.
An input folder satisfying these criteria will be referred to as a <em>skeleton</em>.</p>
</div>
<div class="sect2">
<h3 id="_a_basic_example">A Basic Example</h3>
<div class="paragraph">
<p>An example of a simple input-output pair is below.
Suppose you have the following simple skeleton at directory <code>example-01</code>:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight"><code data-lang="text">example-01
├── collagen.json
└── images
└── smiley.jpg</code></pre>
</div>
</div>
<div class="paragraph">
<p>Where <a href="/tests/examples/kitty-nesting-smiley/skeleton/smiley/skeleton/images/smiley.jpg" target="_blank" rel="noopener"><code>images/smiley.jpg</code></a> is the following image (whose native size is 380×380 pixels):</p>
</div>
<div class="imageblock">
<div class="content">
<img src="/tests/examples/kitty-nesting-smiley/skeleton/smiley/skeleton/images/smiley.jpg" alt="smiley" width="200px">
</div>
</div>
<div class="paragraph">
<p>And where <a href="/tests/examples/kitty-nesting-smiley/skeleton/smiley/skeleton/collagen.json" target="_blank" rel="noopener"><code>collagen.json</code></a> contains the following:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight"><code data-lang="json">{
<span class="key"><span class="delimiter">"</span><span class="content">vars</span><span class="delimiter">"</span></span>: { <i class="conum" data-value="1"></i><b>(1)</b>
<span class="key"><span class="delimiter">"</span><span class="content">bubble_text</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">Collagen!!</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">nose_color</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">#f00</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text_color</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">#000</span><span class="delimiter">"</span></span>
},
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: { <span class="key"><span class="delimiter">"</span><span class="content">viewBox</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">0 0 500 400</span><span class="delimiter">"</span></span> },
<span class="key"><span class="delimiter">"</span><span class="content">children</span><span class="delimiter">"</span></span>: [
{
<span class="key"><span class="delimiter">"</span><span class="content">image_path</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">images/smiley.jpg</span><span class="delimiter">"</span></span>, <i class="conum" data-value="2"></i><b>(2)</b>
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: { <span class="key"><span class="delimiter">"</span><span class="content">transform</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">translate(0 100) scale(1.3)</span><span class="delimiter">"</span></span> }
},
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">circle</span><span class="delimiter">"</span></span>, <i class="conum" data-value="3"></i><b>(3)</b>
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">cx</span><span class="delimiter">"</span></span>: <span class="integer">123</span>,
<span class="key"><span class="delimiter">"</span><span class="content">cy</span><span class="delimiter">"</span></span>: <span class="integer">240</span>,
<span class="key"><span class="delimiter">"</span><span class="content">r</span><span class="delimiter">"</span></span>: <span class="integer">15</span>,
<span class="key"><span class="delimiter">"</span><span class="content">fill</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{nose_color}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">stroke</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">#000</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">stroke-width</span><span class="delimiter">"</span></span>: <span class="integer">3</span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">path</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">d</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">M 230 140 L 265 120 A 100 40 0 1 0 235 110 Z</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">stroke</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">#000</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">stroke-width</span><span class="delimiter">"</span></span>: <span class="integer">3</span>,
<span class="key"><span class="delimiter">"</span><span class="content">fill</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">#fff</span><span class="delimiter">"</span></span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{bubble_text}</span><span class="delimiter">"</span></span>, <i class="conum" data-value="4"></i><b>(4)</b>
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="integer">250</span>,
<span class="key"><span class="delimiter">"</span><span class="content">y</span><span class="delimiter">"</span></span>: <span class="integer">97</span>,
<span class="key"><span class="delimiter">"</span><span class="content">text-anchor</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">start</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">dominant-baseline</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">top</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">font-family</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">Impact</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">font-size</span><span class="delimiter">"</span></span>: <span class="integer">30</span>,
<span class="key"><span class="delimiter">"</span><span class="content">fill</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{text_color}</span><span class="delimiter">"</span></span>
}
}
]
}</code></pre>
</div>
</div>
<div class="colist arabic">
<table>
<tr>
<td><i class="conum" data-value="1"></i><b>1</b></td>
<td>A dictionary of variables. In <code>text</code> and <code>attrs</code> values, variables enclosed in curly brackets will have their value substituted.
For example, if <code>vars</code> contains values for <code>dx</code> and <code>dy</code>, then a translation could be applied with <code>transform: translate({dx} {dy})</code>.
If a child’s <code>vars</code> doesn’t contain a variable that the child needs the value of, the variable’s value will be looked up by walking up the list of ancestors until the root is reached (i.e., variable scopes are nested).</td>
</tr>
<tr>
<td><i class="conum" data-value="2"></i><b>2</b></td>
<td>To include an image, just give its relative path.</td>
</tr>
<tr>
<td><i class="conum" data-value="3"></i><b>3</b></td>
<td>Most other tags are specified with the <code>tag</code> field, which contains the name of the SVG tag to use.</td>
</tr>
<tr>
<td><i class="conum" data-value="4"></i><b>4</b></td>
<td>If a tag has a <code>text</code> field, the given text will be the content of the tag, as in <code><text>your text here</text></code>.</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Then, running the following command:<sup class="footnote">[<a id="_footnoteref_3" class="footnote" href="#_footnotedef_3" title="View footnote.">3</a>]</sup></p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight"><code data-lang="bash">cargo run -- -i example-01 -o example-01.svg</code></pre>
</div>
</div>
<div class="paragraph">
<p>Will produce the following file, <a href="/tests/examples/kitty-nesting-smiley/skeleton/smiley/out.svg" target="_blank" rel="noopener"><code>examples-01.svg</code></a>:</p>
</div>
<div class="imageblock">
<div class="content">
<img src="/tests/examples/kitty-nesting-smiley/skeleton/smiley/out.svg" alt="out" width="500">
</div>
</div>
<div class="paragraph">
<p>If you zoom in, you’ll see the smiley face’s pixels.
But because the nose and speech bubble are SVG elements (i.e., vector graphics, not raster) they look nice and smooth and crisp even when zoomed in.
That’s the whole point!
Perfectly precise vector graphics can coexist alongside raster graphics.
(This simple example shows just one image, but of course we could include arbitrarily many by simply adding more children of the form <code>{"image_path": <path>}</code>.)</p>
</div>
</div>
<div class="sect2">
<h3 id="_a_more_complicated_example">A More Complicated Example</h3>
<div class="paragraph">
<p>As we’ve seen, we can include raster images in skeletons; it would be silly if we couldn’t also include other skeletons!
Nested skeletons can be included by adding a child of the form <code>{"clgn_path": <path>}</code>.
(Whereas a standalone skeleton gets turned into a <code><svg></code> tag, a nested skeleton will reside in a <code><g></code> tag.)
Let’s include the above skeleton in another (and just for fun, let’s add a photo of a kitten (<a href="https://commons.wikimedia.org/w/index.php?title=File:Cute_grey_kitten.jpg&oldid=479136954" target="_blank" rel="noopener">source</a>) too, because why not):</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight"><code data-lang="text">example-02
├── collagen.json
├── example-01
│  ├── collagen.json
│  └── images
│  └── smiley.jpg
└── kitty.jpg</code></pre>
</div>
</div>
<div class="paragraph">
<p>Where <a href="/tests/examples/kitty-nesting-smiley/skeleton/collagen.json" target="_blank" rel="noopener"><code>example-02/collagen.json</code></a> is below:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="CodeRay highlight"><code data-lang="json">{
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: { <span class="key"><span class="delimiter">"</span><span class="content">viewBox</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">0 0 300 250</span><span class="delimiter">"</span></span> },
<span class="key"><span class="delimiter">"</span><span class="content">children</span><span class="delimiter">"</span></span>: [
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">rect</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">10</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">y</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">10</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">width</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">275</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">height</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">225</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">fill</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">#ddd</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">stroke</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">#00f</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">stroke-width</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">10</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">stroke-dasharray</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">10 10</span><span class="delimiter">"</span></span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">g</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: { <span class="key"><span class="delimiter">"</span><span class="content">transform</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">translate(50 25) scale(.5)</span><span class="delimiter">"</span></span> },
<span class="key"><span class="delimiter">"</span><span class="content">children</span><span class="delimiter">"</span></span>: [
{
<span class="key"><span class="delimiter">"</span><span class="content">clgn_path</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">./example-01</span><span class="delimiter">"</span></span>
}
]
},
{
<span class="key"><span class="delimiter">"</span><span class="content">image_path</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">./kitty.jpg</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: { <span class="key"><span class="delimiter">"</span><span class="content">transform</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">translate(180 150) scale(.15)</span><span class="delimiter">"</span></span> }
}
]
}</code></pre>
</div>
</div>
<div class="paragraph">
<p>Here’s <a href="/tests/examples/kitty-nesting-smiley/out.svg" target="_blank" rel="noopener">the result</a> when you run <code>cargo run -- -i example-02 -o example-02.svg</code>:</p>
</div>
<div class="imageblock">
<div class="content">
<img src="/tests/examples/kitty-nesting-smiley/out.svg" alt="out" width="600">
</div>
</div>
<div class="paragraph">
<p>So, as far as Collagen is concerned, skeletons act more or less the same as raster images, in the sense that the path is sufficient to include them.
The only difference is that the path to a skeleton child is given by the key <code>clgn_path</code> instead of <code>image_path</code>.</p>
</div>
</div>
<div class="sect2">
<h3 id="_memes">Memes</h3>
<div class="paragraph">
<p>A format that makes it easy to place text on images?
Sounds like it would be perfect for memes.</p>
</div>
<div class="listingblock">
<div class="title"><a href="/tests/examples/drake-user-specified-font/skeleton/collagen.json" target="_blank" rel="noopener"><code>example-03/collagen.json</code></a></div>
<div class="content">
<pre class="CodeRay highlight"><code data-lang="json">{
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: { <span class="key"><span class="delimiter">"</span><span class="content">viewBox</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">0 0 800 650</span><span class="delimiter">"</span></span> },
<span class="key"><span class="delimiter">"</span><span class="content">children</span><span class="delimiter">"</span></span>: [
{
<span class="key"><span class="delimiter">"</span><span class="content">fonts</span><span class="delimiter">"</span></span>: [
{
<span class="key"><span class="delimiter">"</span><span class="content">name</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">Impact</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">path</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">./impact.woff2</span><span class="delimiter">"</span></span> <i class="conum" data-value="1"></i><b>(1)</b>
}
]
},
{
<span class="key"><span class="delimiter">"</span><span class="content">image_path</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">./drake-small.jpg</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">width</span><span class="delimiter">"</span></span>: <span class="integer">800</span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">vars</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="integer">550</span>,
<span class="key"><span class="delimiter">"</span><span class="content">dy</span><span class="delimiter">"</span></span>: <span class="integer">50</span>
},
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">font-family</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">Impact</span><span class="delimiter">"</span></span>, <i class="conum" data-value="2"></i><b>(2)</b>
<span class="key"><span class="delimiter">"</span><span class="content">font-size</span><span class="delimiter">"</span></span>: <span class="integer">50</span>,
<span class="key"><span class="delimiter">"</span><span class="content">color</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">black</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text-anchor</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">middle</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">vertical-align</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">top</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{x}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">y</span><span class="delimiter">"</span></span>: <span class="integer">420</span>
},
<span class="key"><span class="delimiter">"</span><span class="content">children</span><span class="delimiter">"</span></span>: [
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">tspan</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">Using SVG-based text,</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{x}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">dy</span><span class="delimiter">"</span></span>: <span class="integer">0</span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">tspan</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">which is infinitely</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{x}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">dy</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{dy}</span><span class="delimiter">"</span></span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">tspan</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">zoomable and has</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{x}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">dy</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{dy}</span><span class="delimiter">"</span></span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">tspan</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">no artifacts</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{x}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">dy</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{dy}</span><span class="delimiter">"</span></span>
}
}
]
}
]
}</code></pre>
</div>
</div>
<div class="colist arabic">
<table>
<tr>
<td><i class="conum" data-value="1"></i><b>1</b></td>
<td>Hmm, why might we need the path to a <code>woff2</code> file?</td>
</tr>
<tr>
<td><i class="conum" data-value="2"></i><b>2</b></td>
<td>It’s not a meme unless it uses the <a href="https://en.wikipedia.org/wiki/Impact_(typeface)" target="_blank" rel="noopener">Impact font</a>.
But what if our device doesn’t have Impact on it?
(iPhones don’t, for instance.)</td>
</tr>
</table>
</div>
<div class="paragraph">
<p><a href="/tests/examples/drake-user-specified-font/skeleton/collagen.json" target="_blank" rel="noopener"><code>example-03/collagen.json</code></a> produces the following meme:</p>
</div>
<div class="imageblock">
<div class="content">
<img src="/tests/examples/drake-user-specified-font/out.svg" alt="out" width="600">
</div>
</div>
<div class="paragraph">
<p>If you’re on a device that doesn’t include the <a href="https://en.wikipedia.org/wiki/Impact_(typeface)" target="_blank" rel="noopener">Impact font</a> (which includes iPhones, for one), you might wonder what magic occurred that made the bottom pane’s font show up correctly — as Impact and not, say, Times New Roman.
After all, if the specified <code>font-face</code> is not available — and Impact is not available on iPhones — the browser will fall back to another font.
So, for maximum portability, Collagen allows <em>embedding</em> fonts in SVGs — that’s how we got Impact to show up on devices that don’t have the font natively.
Of course, if you stick to web-safe fonts or you <em>know</em> that the recipient has all the fonts you want to use, then you can just refer to the fonts by name and they’ll show up correctly.
But if you want to use fonts that aren’t on the receiving device, then you can still get a portable file by embedding the font in the SVG.</p>
</div>
<div class="paragraph">
<p>For reference, here’s the file above but without the font embedded.</p>
</div>
<div class="listingblock">
<div class="title"><a href="/tests/examples/drake-no-font/skeleton/collagen.json" target="_blank" rel="noopener"><code>example-04/collagen.json</code></a></div>
<div class="content">
<pre class="CodeRay highlight"><code data-lang="json">{
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: { <span class="key"><span class="delimiter">"</span><span class="content">viewBox</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">0 0 800 650</span><span class="delimiter">"</span></span> },
<span class="key"><span class="delimiter">"</span><span class="content">children</span><span class="delimiter">"</span></span>: [ <i class="conum" data-value="1"></i><b>(1)</b>
{
<span class="key"><span class="delimiter">"</span><span class="content">image_path</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">./drake-small.jpg</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">width</span><span class="delimiter">"</span></span>: <span class="integer">800</span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">vars</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="integer">550</span>,
<span class="key"><span class="delimiter">"</span><span class="content">dy</span><span class="delimiter">"</span></span>: <span class="integer">50</span>
},
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">font-family</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">Impact</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">font-size</span><span class="delimiter">"</span></span>: <span class="integer">50</span>,
<span class="key"><span class="delimiter">"</span><span class="content">color</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">black</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text-anchor</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">middle</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">vertical-align</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">top</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{x}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">y</span><span class="delimiter">"</span></span>: <span class="integer">420</span>
},
<span class="key"><span class="delimiter">"</span><span class="content">children</span><span class="delimiter">"</span></span>: [
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">tspan</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">Using SVG-based text,</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{x}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">dy</span><span class="delimiter">"</span></span>: <span class="integer">0</span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">tspan</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">which is infinitely</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{x}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">dy</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{dy}</span><span class="delimiter">"</span></span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">tspan</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">zoomable and has</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{x}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">dy</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{dy}</span><span class="delimiter">"</span></span>
}
},
{
<span class="key"><span class="delimiter">"</span><span class="content">tag</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">tspan</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">text</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">no artifacts</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">attrs</span><span class="delimiter">"</span></span>: {
<span class="key"><span class="delimiter">"</span><span class="content">x</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{x}</span><span class="delimiter">"</span></span>,
<span class="key"><span class="delimiter">"</span><span class="content">dy</span><span class="delimiter">"</span></span>: <span class="string"><span class="delimiter">"</span><span class="content">{dy}</span><span class="delimiter">"</span></span>
}
}
]
}
]
}</code></pre>
</div>
</div>
<div class="colist arabic">
<table>
<tr>
<td><i class="conum" data-value="1"></i><b>1</b></td>
<td>This time, we didn’t embed Impact.</td>
</tr>
</table>
</div>
<div class="paragraph">
<p>Now, if you view the result in a desktop browser, it should look the same as above, but on a mobile device the font in the bottom pane might be Times New Roman (or some other fallback font) instead of Impact.</p>
</div>
<div class="imageblock">
<div class="content">
<img src="/tests/examples/drake-no-font/out.svg" alt="out" width="600">
</div>
</div>
<div class="paragraph">
<p>So it’s nice to be able to embed fonts (although it’s not great for the resulting file size…).</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_faq">FAQ</h2>
<div class="sectionbody">
<div class="qlist qanda">
<ol>
<li>
<p><em>Wait, so all this does is base64 encode assets and put them in an SVG with other SVG elements?</em></p>
<p>It adds some additional features, such as nesting of skeletons and the use of tag-wide variables and interpolation of these variables in attributes.
But yes, for the most part, all this project does is allow raster images to coexist with each other and with vector graphics.
If you need to embed fonts in an SVG, Collagen lets you do that, too.</p>
</li>
<li>
<p><em>Couldn’t I just do the base64 encoding and create the SVG myself?</em></p>
<p>Yes.
All Collagen does it automate this.</p>
</li>
<li>
<p><em>I want to put some text on a JPEG. What’s so bad about just opening an image editor, adding the text, and pressing save?</em></p>
<p>The text will look bad because</p>
<div class="olist arabic">
<ol class="arabic">
<li>
<p>It will no be longer an infinitely zoomable vector entity, but instead will have been rasterized, i.e., rendered onto a fixed pixel grid that is only finitely zoomable.</p>
</li>
<li>
<p>JPEG in particular is not optimized for text, so artifacts will be visible (see <a href="https://commons.wikimedia.org/w/index.php?title=File:Jpeg-text-artifacts.gif&oldid=453916290" target="_blank" rel="noopener">here</a> or the Drake meme above).</p>
</li>
</ol>
</div>
</li>
<li>
<p><em>I’m ok with text being rasterized. This means I can convert my JPEG to PNG and avoid #2 above, right?</em></p>
<p>Yes and no. While the text will look sort of ok (when not zoomed in), you now have the problem that your JPEG is being stored as a PNG.
Chances are that this will cause the resulting file size to explode because PNG is simply not meant to store the kind of images that JPEG is meant to store.
For instance, the JPEG below (<a href="https://commons.wikimedia.org/w/index.php?title=File:Planta62.jpg&oldid=424889773" target="_blank" rel="noopener">source</a>) is 57KB, whereas the PNG is 434KB.</p>
<div class="openblock">
<div class="content">
<div class="dlist">
<dl>
<dt class="hdlist1">This JPEG weighs in at 57KB</dt>
<dd>
<div class="imageblock">
<div class="content">
<img src="/assets/pics/Planta62.jpg" alt="Planta62" width="300">
</div>
</div>
</dd>
<dt class="hdlist1">The equivalent PNG weighs in at 434KB</dt>
<dd>
<div class="imageblock">
<div class="content">
<img src="/assets/pics/Planta62.png" alt="Planta62" width="300">
</div>
</div>
</dd>
</dl>
</div>
</div>
</div>
</li>
<li>
<p><em>But surely just placing black text on top of an all-white PNG is fine? Because it’s stored losslessly?</em></p>
<p>Sure, <em>if</em> you don’t mind your text being rasterized, i.e., not perfectly precise and infinitely zoomable.
The image below is black text on a white background.</p>
<div class="imageblock">
<div class="content">
<img src="/assets/pics/text_png.png" alt="text png">
</div>
</div>
<div class="paragraph">
<p>You don’t have to zoom in very far to see the text get fuzzy.
And if this image undergoes additional rounds of editing and compression, this problem will only get worse.
In contrast, the text in the smiley-face image above (and, naturally, the text on this webpage) is perfectly precise and will retain all of its detail at arbitrary magnification.</p>
</div>
</li>
</ol>
</div>
</div>
</div>
<div id="footnotes">
<hr>
<div class="footnote" id="_footnotedef_1">
<a href="#_footnoteref_1">1</a>. And because <a href="https://en.wikipedia.org/wiki/Collagen">collagen</a> is the protein that holds your body together. <code>s/protein/tool/;s/body/images/</code>
</div>
<div class="footnote" id="_footnotedef_2">
<a href="#_footnoteref_2">2</a>. Technically base64 encoding data does increase its size by about a third. However, you don’t need to pay this cost when transmitting the file; you can transmit the raw components and then use Collagen to encode them into an SVG on the receiving end. In other words, Collagen is akin to compression such as gunzip: it allows a smaller payload to be transmitted as long as the receiving end can turn it back into something useful.
</div>
<div class="footnote" id="_footnotedef_3">
<a href="#_footnoteref_3">3</a>. At some point <code>cargo run --</code> will be replaced with an actual standalone executable <code>clgn</code>.
</div>
</div>