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Scaled Vector Graphics on the Web for Fun and ?

jacoby profile image Dave Jacoby Originally published at jacoby.github.io on ・2 min read

This is an image.

Clock

I enjoy playing with clocks, and this is from that tool.

This is done with Scaled Vector Graphics , or SVGs. SVGs are a text-based XML format, and they look like this.

<svg xmlns="http://www.w3.org/2000/svg" id="neck" viewBox="0 0 900 900">
    <style>
        .loop {
            stroke: #666;
            stroke-width: 20;
            fill-opacity: 0;
            }
        #cen, #day, #hor, #min, #sec {
            stroke: #666;
            stroke-width: 10;
            }
        #cen { fill: lightblue; }
        #day { fill: yellowgreen; }
        #hor { fill: yellow; }
        #min { fill: orange; }
        #sec { fill: red; }
    </style>

    <circle id="d_loop" cx="450" cy="450" r="100" class="loop"/>
    <circle id="h_loop" cx="450" cy="450" r="200" class="loop"/>
    <circle id="m_loop" cx="450" cy="450" r="300" class="loop"/>
    <circle id="s_loop" cx="450" cy="450" r="400" class="loop"/>

    <circle id="sec" cx="450" cy="050" r="30" class="dot"/>
    <circle id="min" cx="450" cy="150" r="30" class="dot"/>
    <circle id="hor" cx="450" cy="250" r="30" class="dot"/>
    <circle id="day" cx="450" cy="350" r="30" class="dot"/>
    <circle id="cen" cx="450" cy="450" r="30" class="dot"/>
</svg>

What do we see? We see things with ID tags, so they can be uniquely identified and with CLASS tags so they can be grouped.

This means, in a web context, you can uniquely address those things and change them.

function draw_second(seconds) {
  let deg = seconds * 6;
  let deg2 = (deg - 90) % 360;
  let sec = document.getElementById("sec");
  let xy = circleCoords(400, deg2);
  let x = 450 + xy.x;
  let y = 450 + xy.y;
  sec.setAttribute("cx", x);
  sec.setAttribute("cy", y);
}

function circleCoords(radius, degFromTop) {
  const rads = degToRad(degFromTop);
  return {
    x: radius * Math.cos(rads),
    y: radius * Math.sin(rads)
  };
}

function degToRad(deg) {
  return (deg / 360) * (Math.PI * 2);
}

There is more, of course, but each circle has a center, which is defined by the x and y coordinates, and so the cx is the x coordinate of that circle and cy is the y coordinate. The base image is 900x900, so this is placed in relation to 450,450 and the radius is 400, so we set that with setAttribute, just like we’re messing with the DOM in other contexts.

There are two other uses I know for SVGs. Logos are great in SVG, because they scale, still looking sharp when blown up to poster and side-of-truck sizes. They are also useful for laser cutters, where different colors are used for different laser intensity, so that a thick black section is made darker, but a thin red line will be cut through.

But remember that, in a web context, the parts of the image are as addressable and modifiable as anything else on a web page.

If you have any questions or comments, I would be glad to hear it. Ask me on Twitter or make an issue on my blog repo.

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jacoby profile

Dave Jacoby

@jacoby

Long time computer user. Long time programmer.

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