0
votes

Changing viewport's coordinate system height changes user's coordinate system starting origin point on X axis and I can't understand why. What is a relationship here? Shouldn't it impact Y axis of user coordinate system because we are changing the height (Y axis) of viewport?

Viewport coordinate system: 1250x1250. User coordinate system: 500x500. When the aspect ratio is such, no mater what width and height I give to viewBox property (viewBox = <min-x> <min-y> <width> <height>) min-x of viewbox always starts from 0 which is left side corner of the screen. But if I change viewport coordinate system to 1250x329, for example, then min-x at 0 value will start somewhere from the middle of the screen and not from the left side as it should. Why is that?

Here is a live codepen https://codepen.io/Limpuls/pen/LYNXQPK with CSS for SVG element's height set to 100% giving perfect centering and origin starting point from left corner because then viewport is 1250x1250. Change it to 100vh instead (commented out code in CSS) then the viewport becomes 1250x329 and throws off the starting point of viewBox breaking my Javascript logic for centering SVG paths.

What is causing this behaviour and how can I modify my calculations in JS to adopt to any viewport height, not just when it's a perfect number like 1250x1250 or 700x700?

Code:

<div class="container-fluid">
        <section class="row first">
            <div class="col-lg-12">
                <div class="svg">
                    <svg viewBox="0 0 500 500" fill="none" xmlns="http://www.w3.org/2000/svg">
                        <path d="M26 2V30H19.52V18.52H6.80001V30H0.320007V2H6.80001V13.04H19.52V2H26Z" fill="black"/>
                        <path d="M53.2647 19.32C53.2647 19.4 53.2247 19.96 53.1447 21H36.8647C37.158 22.3333 37.8514 23.3867 38.9447 24.16C40.038 24.9333 41.398 25.32 43.0247 25.32C44.1447 25.32 45.1314 25.16 45.9847 24.84C46.8647 24.4933 47.678 23.96 48.4247 23.24L51.7447 26.84C49.718 29.16 46.758 30.32 42.8647 30.32C40.438 30.32 38.2914 29.8533 36.4247 28.92C34.558 27.96 33.118 26.64 32.1047 24.96C31.0914 23.28 30.5847 21.3733 30.5847 19.24C30.5847 17.1333 31.078 15.24 32.0647 13.56C33.078 11.8533 34.4514 10.5333 36.1847 9.6C37.9447 8.64 39.9047 8.16 42.0647 8.16C44.1714 8.16 46.078 8.61333 47.7847 9.52C49.4914 10.4267 50.8247 11.7333 51.7847 13.44C52.7714 15.12 53.2647 17.08 53.2647 19.32ZM42.1047 12.88C40.6914 12.88 39.5047 13.28 38.5447 14.08C37.5847 14.88 36.998 15.9733 36.7847 17.36H47.3847C47.1714 16 46.5847 14.92 45.6247 14.12C44.6647 13.2933 43.4914 12.88 42.1047 12.88Z" fill="black"/>
                        <path d="M57.4191 0.319998H63.6591V30H57.4191V0.319998Z" fill="black"/>
                        <path d="M69.4503 0.319998H75.6903V30H69.4503V0.319998Z" fill="black"/>
                        <path d="M91.7216 30.32C89.4549 30.32 87.4149 29.8533 85.6016 28.92C83.8149 27.96 82.4149 26.64 81.4016 24.96C80.3882 23.28 79.8816 21.3733 79.8816 19.24C79.8816 17.1067 80.3882 15.2 81.4016 13.52C82.4149 11.84 83.8149 10.5333 85.6016 9.6C87.4149 8.64 89.4549 8.16 91.7216 8.16C93.9882 8.16 96.0149 8.64 97.8016 9.6C99.5882 10.5333 100.988 11.84 102.002 13.52C103.015 15.2 103.522 17.1067 103.522 19.24C103.522 21.3733 103.015 23.28 102.002 24.96C100.988 26.64 99.5882 27.96 97.8016 28.92C96.0149 29.8533 93.9882 30.32 91.7216 30.32ZM91.7216 25.2C93.3216 25.2 94.6282 24.6667 95.6416 23.6C96.6816 22.5067 97.2016 21.0533 97.2016 19.24C97.2016 17.4267 96.6816 15.9867 95.6416 14.92C94.6282 13.8267 93.3216 13.28 91.7216 13.28C90.1216 13.28 88.8016 13.8267 87.7616 14.92C86.7216 15.9867 86.2016 17.4267 86.2016 19.24C86.2016 21.0533 86.7216 22.5067 87.7616 23.6C88.8016 24.6667 90.1216 25.2 91.7216 25.2Z" fill="black"/>
                        <path d="M109.819 22.56C110.939 22.56 111.859 22.92 112.579 23.64C113.299 24.3333 113.659 25.2533 113.659 26.4C113.659 26.9333 113.592 27.4667 113.459 28C113.326 28.5333 113.032 29.3333 112.579 30.4L110.299 36.16H106.339L108.099 29.8C107.432 29.5333 106.899 29.1067 106.499 28.52C106.126 27.9067 105.939 27.2 105.939 26.4C105.939 25.2533 106.299 24.3333 107.019 23.64C107.766 22.92 108.699 22.56 109.819 22.56Z" fill="black"/>
                        <path d="M171.976 2L162.816 30H155.856L149.696 11.04L143.336 30H136.416L127.216 2H133.936L140.256 21.68L146.856 2H152.856L159.256 21.84L165.776 2H171.976Z" fill="black"/>
                        <path d="M183.792 30.32C181.525 30.32 179.485 29.8533 177.672 28.92C175.885 27.96 174.485 26.64 173.472 24.96C172.459 23.28 171.952 21.3733 171.952 19.24C171.952 17.1067 172.459 15.2 173.472 13.52C174.485 11.84 175.885 10.5333 177.672 9.6C179.485 8.64 181.525 8.16 183.792 8.16C186.059 8.16 188.085 8.64 189.872 9.6C191.659 10.5333 193.059 11.84 194.072 13.52C195.085 15.2 195.592 17.1067 195.592 19.24C195.592 21.3733 195.085 23.28 194.072 24.96C193.059 26.64 191.659 27.96 189.872 28.92C188.085 29.8533 186.059 30.32 183.792 30.32ZM183.792 25.2C185.392 25.2 186.699 24.6667 187.712 23.6C188.752 22.5067 189.272 21.0533 189.272 19.24C189.272 17.4267 188.752 15.9867 187.712 14.92C186.699 13.8267 185.392 13.28 183.792 13.28C182.192 13.28 180.872 13.8267 179.832 14.92C178.792 15.9867 178.272 17.4267 178.272 19.24C178.272 21.0533 178.792 22.5067 179.832 23.6C180.872 24.6667 182.192 25.2 183.792 25.2Z" fill="black"/>
                        <path d="M205.723 11.32C206.469 10.28 207.469 9.49333 208.723 8.96C210.003 8.42667 211.469 8.16 213.123 8.16V13.92C212.429 13.8667 211.963 13.84 211.723 13.84C209.936 13.84 208.536 14.3467 207.523 15.36C206.509 16.3467 206.003 17.84 206.003 19.84V30H199.763V8.48H205.723V11.32Z" fill="black"/>
                        <path d="M216.833 0.319998H223.073V30H216.833V0.319998Z" fill="black"/>
                        <path d="M250.784 0.319998V30H244.824V27.52C243.278 29.3867 241.038 30.32 238.104 30.32C236.078 30.32 234.238 29.8667 232.584 28.96C230.958 28.0533 229.678 26.76 228.744 25.08C227.811 23.4 227.344 21.4533 227.344 19.24C227.344 17.0267 227.811 15.08 228.744 13.4C229.678 11.72 230.958 10.4267 232.584 9.52C234.238 8.61333 236.078 8.16 238.104 8.16C240.851 8.16 242.998 9.02667 244.544 10.76V0.319998H250.784ZM239.184 25.2C240.758 25.2 242.064 24.6667 243.104 23.6C244.144 22.5067 244.664 21.0533 244.664 19.24C244.664 17.4267 244.144 15.9867 243.104 14.92C242.064 13.8267 240.758 13.28 239.184 13.28C237.584 13.28 236.264 13.8267 235.224 14.92C234.184 15.9867 233.664 17.4267 233.664 19.24C233.664 21.0533 234.184 22.5067 235.224 23.6C236.264 24.6667 237.584 25.2 239.184 25.2Z" fill="black"/>
                        </svg>                       
                </div>               
            </div>
        </section>
</div>

CSS

section {
    height: 100vh;
    width: 100vw;
}

svg {
    height: 100%;
    //height: 100vh;
    width: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
}

Javascript excerpt for dynamically centering SVG <path> by calculating viewBox <min-x> using formula: ((Viewport width - total SVG <path> width) / 2) / Viewport to viewBox width ratio

let totalSVGwidth = 0;
let totalSVGheight = 0;
let totalSpacingBetweenLetters = 0;
let viewBoxScaleX = 500;
let winViewportSVGwidthDiff = 0;
let svgViewportWidth = document.querySelector(".svg").offsetWidth;
let totalSVGwidthWithSpaces = 0;
let viewportCoordSpaceUserCoordSpaceRatio = document.querySelector(".svg").offsetWidth / viewBoxScaleX;

document.querySelectorAll("path").forEach((path, index) => {
    totalSVGwidth = totalSVGwidth + path.getBoundingClientRect().width;
        if ((index + 1) < document.querySelectorAll("path").length) {
            totalSpacingBetweenLetters += (document.querySelectorAll("path")[index + 1].getBoundingClientRect().x - path.getBoundingClientRect().x) - path.getBoundingClientRect().width;
        }

    totalSVGwidthWithSpaces += totalSpacingBetweenLetters + totalSVGwidth;
    // formula
    document.querySelectorAll("svg")[0].setAttribute("viewBox", (0 - ((svgViewportWidth - (totalSpacingBetweenLetters + totalSVGwidth)) / 2) / viewportCoordSpaceUserCoordSpaceRatio) + " " + 0 + " " + viewBoxScaleX + " " + viewBoxScaleX);
});
1

1 Answers

3
votes

You need to read up on how viewBox works.

But in summary, if the viewport (ie the <svg> width and height) has a different aspect ratio to the viewBox width and height, then by default, the area represented by the viewBox will be centred in the viewport.

The snippet below attempt to represent that behaviour.

<svg width="1250" height="329" viewBox="0 0 500 500">
   <rect x="-700" width="1898" height="500" fill="none" stroke="green" stroke-width="2"/>
   <text x="-600" y="100" fill="green" font-size="20">1250 x 329 viewport</text>
   
   <rect width="500" height="500" fill="red" fill-opacity="0.05" stroke="red" stroke-width="2"/>
   <text x="10" y="20" fill="red" font-size="20">(0,0)</text>
   <text x="250" y="250" fill="red" font-size="20" text-anchor="middle">500 x 500 viewBox area</text>
</svg>

(0,0) remains at the top left of the viewBox area. Not the viewport.

You can control what happens, when the aspect ratios don't match, by way of the preserveAspectRatio attribute. If you want the viewBox area to always be stuck to the top left of the viewport, then use preserveAspectRatio="xMinYMin meet".

<svg width="1250" height="329" viewBox="0 0 500 500" preserveAspectRatio="xMinYMin meet">
   <rect x="0" width="1898" height="500" fill="none" stroke="green" stroke-width="2"/>
   <text x="-600" y="100" fill="green" font-size="20">1250 x 329 viewport</text>
   
   <rect width="500" height="500" fill="red" fill-opacity="0.05" stroke="red" stroke-width="2"/>
   <text x="10" y="20" fill="red" font-size="20">(0,0)</text>
   <text x="250" y="250" fill="red" font-size="20" text-anchor="middle">500 x 500 viewBox area</text>
</svg>