Chart.js chart clipped or masked by a custom vector path

Julian Dimitrov · July 7, 2020

For the past few days, I'm struggling with one Chart.js chart that I want to clip or mask with custom vector path. I was able to do something like what I want, but I think I'm missing something.

The approach that I took is to create the chart in html (the traditional way, with html canvas ..etc) and then create a svg with the shape I want to cut off and then overlay the <canvas> and <svg> elements. This is what I was able to accomplish:

js:

var config = {
            type: 'line',
            data: {
                labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
                datasets: [{
                    label: 'My First dataset',
                    fill: false,
                    borderColor: "red",
                    backgroundColor: "red",
                    data: [
                        {x:23,y:57},
                        {x:43,y:67},
                        {x:143,y:167}
                    ]
                }, {
                    label: 'My Second dataset ',
                    fill: false,
                    borderColor: "blue",
                    backgroundColor: "blue",
                    data: [
                        {x:12,y:76},
                        {x:23,y:89},
                        {x:143,y:167}
                    ]
                }]
            },
            options: {
                title: {
                    display: false,
                    text: 'Chart.js Line Chart'
                }
            }
        };

        window.onload = function () {
            var ctx = document.getElementById('canvas').getContext('2d');
            window.myLine = new Chart(ctx, config);
        };

css:

canvas {
            position: absolute;
            z-index: 0;
        }
    
        svg {
            position: absolute;
            z-index: 1;
        }
        body {
            background-color: white;
        }

html:

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.9.3/Chart.min.js"></script>
<head>
    <title> My cutoff chart </title>
</head>
<body>
  <canvas id="canvas"></canvas>
  <svg viewBox="0 0 200 100" xmlns="http://www.w3.org/2000/svg"
        xmlns:xlink="http://www.w3.org/1999/xlink">
        <defs>
            <style>
                #clickHandler {
                    pointer-events: all;
                }
            </style>
            <path id="ship" 
                d="m 100.09542,69.20104 h -83.5475 v -0.41351 -0.41351 l -0.595313,0.0828 -0.595312,0.0828 -0.01659,-0.66146 -0.01659,-0.66146 -0.380288,0.12526 -0.380288,0.12526 -1.890519,0.007 -1.890518,0.007 -0.556877,-0.50403 -0.556878,-0.50403 v -0.38141 -0.38142 l 1.06532,-1.21026 1.065319,-1.21027 -0.09501,-0.28554 -0.09501,-0.28554 -1.433331,-0.20539 -1.433331,-0.20539 -0.859896,-0.13733 -0.859896,-0.13733 v -0.38353 -0.38353 l -1.220114,-0.57352 -1.220114,-0.57352 -0.737049,-1.01747 -0.73705,-1.01747 -0.8116695,-2.57755 -0.8116695,-2.57756 -0.3901093,-1.98437 -0.3901092,-1.98438 -0.1825245,-1.65364 -0.1825245,-1.65365 h 1.5141537 1.5141538 l 0.132161,-0.50538 0.132161,-0.50539 2.753486,-0.18768 2.753485,-0.18767 v -0.35283 -0.35282 l 0.307053,-0.6739 0.307053,-0.67391 h 1.904977 1.904977 l 1.193236,-0.16355 1.193236,-0.16355 0.365047,-0.8067 0.365045,-0.8067 1.190625,-0.37783 1.190625,-0.37784 4.034896,-0.1393 4.034896,-0.13929 v -0.30579 -0.30578 l 0.849273,-0.74523 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2.513542,-0.17857 2.513541,-0.17856 3.79988,-0.51512 3.799877,-0.51511 0.180554,-0.29215 0.180555,-0.29214 0.606329,-3.31745 0.606333,-3.31746 0.393073,-0.39307 0.393073,-0.39308 h 0.852265 0.852268 l 0.317889,-1.18854 0.317886,-1.18855 3.459062,0.10402 3.459061,0.10403 0.169617,0.16961 0.169614,0.16962 0.143208,5.34668 0.142968,5.34667 1.717418,0.1323 1.717416,0.13229 0.08401,0.52916 0.08401,0.52917 0.1346,0.39688 0.13459,0.39687 0.25994,-0.46302 0.25993,-0.46302 h 3.9273 3.92729 l 0.1523,0.39687 0.1523,0.39688 h 1.63278 1.63278 l 0.35148,-0.46302 0.35148,-0.46302 0.008,-0.46302 0.008,-0.46302 h 3.28946 3.28947 l 0.16795,0.52916 0.16795,0.52917 h 6.59675 6.59676 v -0.52917 -0.52916 h 3.30729 3.30729 v -0.75275 -0.75274 l 0.48385,-0.43788 0.48386,-0.43788 h 0.40118 0.40118 l 0.46944,0.51872 0.46945,0.51874 -0.12644,0.73804 -0.12643,0.73804 -0.19802,0.46302 -0.19802,0.46302 4.72466,-0.003 4.72466,-0.003 0.99752,-0.16487 0.99752,-0.16486 -0.1725,-0.91953 -0.17251,-0.91953 0.35298,-0.21815 0.35298,-0.21815 0.21107,0.13044 0.21107,0.13045 v 1.04272 1.04272 h 1.29052 1.29052 l 0.28495,-0.34335 0.28495,-0.34335 0.14065,-2.7655 0.14064,-2.76551 0.1645,-2.11667 0.16451,-2.11666 0.91522,-1.12448 0.91522,-1.12448 h 0.24687 0.24687 v 1.98437 1.98438 h 1.05833 1.05833 v 0.26458 0.26459 h -0.24701 -0.24701 l -0.0837,0.71713 -0.0837,0.71715 -0.66145,0.18252 -0.66146,0.18253 1.24115,0.0264 1.24116,0.0264 0.17453,0.28239 0.17452,0.28239 -0.55578,0.14534 -0.55579,0.14535 v 0.74612 0.74613 l -0.8599,0.0829 -0.85989,0.0829 v 1.19063 1.19062 l 0.85989,0.0829 0.8599,0.0829 v -0.66891 -0.66892 l -0.53658,-0.28716 -0.53658,-0.28717 0.15532,-0.25131 0.15532,-0.25132 h 1.0271 1.02711 l 0.15347,0.24832 0.15347,0.24832 -0.46859,0.28798 -0.46858,0.28797 0.66146,-0.0733 0.66145,-0.0733 0.0677,-1.71979 0.0677,-1.71979 0.14895,-0.64766 0.14894,-0.64766 0.24235,0.38307 0.24235,0.38308 0.004,2.26219 0.004,2.26219 0.3175,0.3175 0.3175,0.3175 h 0.47625 0.47625 v 0.64362 0.64363 l 0.5268,0.1672 0.52679,0.1672 0.26696,-0.16498 0.26695,-0.16499 v -0.52916 -0.52917 l 0.26458,0.16352 0.26458,0.16352 v 0.51 0.51 l 0.8599,0.35945 0.8599,0.35943 0.36113,0.43546 0.36113,0.43546 -0.18881,1.25917 -0.18881,1.25918 -0.23314,0.43567 -0.23314,0.43568 0.65613,0.16468 0.65613,0.16467 2.1e-4,0.45798 2.1e-4,0.45798 0.75188,1.5875 0.75189,1.5875 1.23054,1.91823 1.23055,1.91823 0.33246,0.037 0.33247,0.037 0.97177,-0.0577 0.97177,-0.0577 0.29431,0.54992 0.29431,0.54992 h 0.63653 0.63654 l 0.18667,-0.30203 0.18667,-0.30204 0.15967,-2.1242 0.15967,-2.1242 0.33073,-0.10935 0.33073,-0.10936 5.3e-4,2.20487 5.3e-4,2.20486 3.0196,0.0151 3.0196,0.0151 0.4194,0.34806 0.41939,0.34807 1.4e-4,0.16604 1.3e-4,0.16604 -2.40702,-0.0934 -2.40701,-0.0934 -0.29187,0.29186 -0.29174,0.29187 2.23573,0.0403 2.23573,0.0403 0.26458,0.0615 0.26458,0.0615 1.91823,0.0305 1.91823,0.0305 v 0.42473 0.42473 l 4.16719,-0.17789 4.16719,-0.17789 1.51081,-0.27919 1.51082,-0.27919 0.40741,0.15633 0.40741,0.15634 v 0.48438 0.48438 l -2.40439,2.50049 -2.4044,2.50049 -1.84101,2.24895 -1.841,2.24896 -1.31085,2.60364 -1.31085,2.60364 v 0.63751 0.6375 l 0.8599,0.0355 0.8599,0.0355 1.05833,-0.0538 1.05833,-0.0538 0.92604,0.63314 0.92605,0.63314 -0.0719,0.87537 -0.0719,0.87537 -0.45725,0.7761 -0.45726,0.77609 -1.35008,0.89689 -1.35008,0.89688 -1.9519,0.5409 -1.95188,0.5409 z m 33.00145,-39.6875 h 0.1323 v -0.13229 -0.13229 h -0.1323 -0.13229 v 0.13229 0.13229 z m 20.54212,-7.82802 0.22768,-0.14071 v -0.24897 -0.24897 h -0.39688 -0.39687 v 0.22049 0.22049 l 0.16919,0.16919 0.1692,0.1692 z"
                 />
            <rect id="bg" x="-1%" y="-1%" width="102%" height="102%"/>
            <mask id="myMask">
                <use xlink:href="#bg" fill="white"/>
                <use xlink:href="#ship" fill="black" />
            </mask>
        </defs>
        <use xlink:href="#bg" mask="url(#myMask)" fill="chocolate" fill-opacity="0.5"/>
        <use xlink:href="#ship" fill="none" id="clickHandler" style="fill:none; stroke-width:0.264583;stroke:black;"/>
        </svg>
</body>

Here is a working code pen.

So far so good, but I wasn't able to align the chart and the cutout properly. The desired position of the visible part of the chart is inside the blue rectangle:

As I said, I'm not sure that I took the best approach for achieving this effect. And to be honest, my knowledge in front-end development and graphical design (using .svg files) are very basic.

Any help will be greatly appreciated

Thanks in advance,

Julian

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Chart.js chart clipped or masked by a custom vector path

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