javascript - HTML canvas art, generate coordinates data from sketch

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javascript - HTML canvas art, generate coordinates data from sketch

asked Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

javascript - HTML canvas art, generate coordinates data from sketch

I use HTML5 canvas to draw a heart shape:

<!DOCTYPE HTML>
<html>
  <head>
    <style>
      body {
        margin: 0px;
        padding: 0px;
      }
    </style>
  </head>
  <body>
    <canvas id="myCanvas" width="1366" height="600"></canvas>
    <script>
     var heart = [
        [707,359],[707,359],[707,359],[707,359],[708,358],[711,354],[713,352],[714,348],[716,345],[720,335],
        [721,334],[722,333],[724,332],[725,330],[727,327],[731,322],[734,320],[737,318],[740,314],[743,312],
        [745,311],[749,309],[753,308],[757,306],[761,303],[764,302],[767,302],[771,301],[774,301],[778,301],
        [783,301],[786,301],[790,300],[796,300],[801,300],[805,300],[809,300],[811,300],[815,302],[817,303],
        [820,305],[822,306],[824,307],[827,309],[830,311],[834,313],[836,314],[838,316],[841,318],[844,321],
        [845,324],[847,326],[849,328],[852,332],[853,334],[855,336],[857,337],[858,339],[860,341],[862,345],
        [863,349],[863,352],[864,356],[864,359],[865,362],[866,364],[868,368],[869,372],[870,377],[871,381],
        [872,384],[872,388],[872,392],[872,395],[872,399],[872,401],[872,405],[872,409],[871,412],[870,417],
        [869,419],[869,422],[867,427],[866,429],[865,434],[863,438],[862,442],[861,443],[860,445],[857,448],
        [854,451],[852,454],[849,456],[846,459],[843,460],[836,466],[835,466],[833,467],[821,475],[820,477],
        [819,478],[817,481],[815,483],[811,486],[808,487],[803,491],[802,491],[800,492],[795,493],[791,497],
        [789,498],[786,498],[780,502],[772,507],[770,510],[767,511],[762,516],[758,520],[756,524],[753,527],
        [750,529],[746,532],[741,534],[736,537],[732,538],[731,539],[735,537],[735,537],[735,537],[730,543],
        [729,546],[727,551],[726,553],[723,555],[721,558],[715,568],[714,570],[714,572],[713,575],[708,585],
        [708,586],[707,586],[704,583],[704,359],[704,359],[700,356],[698,352],[697,350],[696,345],[694,343],
        [693,340],[690,335],[688,335],[687,334],[683,332],[681,329],[677,326],[675,323],[672,319],[669,314],
        [668,312],[663,310],[660,310],[656,310],[653,309],[647,309],[644,308],[642,308],[637,307],[632,303],
        [628,301],[624,297],[621,297],[619,297],[616,297],[616,298],[616,299],[614,300],[620,302],[620,302],
        [620,302],[618,302],[612,302],[605,302],[598,302],[596,303],[594,305],[592,307],[590,309],[586,310],
        [583,313],[582,315],[579,319],[576,320],[573,323],[571,325],[569,327],[563,329],[560,333],[558,336],
        [557,338],[556,341],[555,343],[551,346],[549,349],[549,354],[549,357],[547,361],[546,367],[543,372],
        [542,375],[541,380],[540,381],[540,382],[540,382],[540,382],[540,382],[540,384],[540,386],[540,389],
        [539,391],[539,394],[539,398],[539,404],[539,408],[539,412],[539,416],[540,423],[542,428],[544,433],
        [549,436],[552,439],[555,442],[557,445],[560,448],[562,452],[564,459],[565,461],[560,449],[560,449],
        [561,450],[571,458],[580,466],[584,469],[587,473],[589,476],[591,477],[575,466],[575,466],[575,466],
        [576,466],[582,471],[587,475],[590,477],[594,481],[598,484],[601,489],[604,491],[607,495],[611,496],
        [617,498],[622,500],[626,501],[629,504],[633,508],[636,510],[642,515],[650,522],[651,525],[655,528],
        [657,529],[660,530],[663,530],[667,533],[671,534],[676,536],[679,537],[681,539],[683,540],[676,536],
        [676,536],[676,536],[679,539],[684,546],[687,548],[689,551],[692,554],[696,558],[698,563],[701,567],
        [702,571],[704,574],[705,577],[706,579],[707,580],[708,582],[709,586]
    ];
    var canvas = document.getElementById('myCanvas');
    var context = canvas.getContext('2d');

    context.beginPath();
    context.moveTo(707, 359);
    for(var i = 1; i < (heart.length - 1) ; i++){
        context.lineTo(heart[i][0], heart[i][1])

    }
    // line 1


    context.lineWidth = 2;
    context.strokeStyle = 'blue';
    context.stroke();
    </script>
  </body>
</html>

It looks like this:

enter image description here

Is there easier way to generate the coordinates data for other shapes? I hope there is some tool let me draw a shape sketch and generate coordinates data for me.

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1 Answer

深蓝 · Answer 1 · 2021-10-23T20:07:09+0000

Recorder

Fiddle demo

You need a way to record your points so you can reproduce them as a string, array etc.

This will record anything you draw onto the canvas:

var points = [],    /// holds strokes and points
    isDown = false, /// for draw mode
    prevX, prevY;   /// for draw mode

At the first click, record the first point:

canvas.onmousedown = function(e) {

    /// adjust mouse position (see below)
    var pos = getXY(e);

    /// this is used to draw a line
    prevX = pos.x;
    prevY = pos.y;

    /// add new stroke
    points.push([]);

    /// record point in this stroke
    points[points.length - 1].push([pos.x, pos.y]);

    /// we are in draw mode   
    isDown = true;
}

Then it's simply a matter of pushing all the points drawn to the current stroke:

canvas.onmousemove = function(e) {

    if (!isDown) return;

    var pos = getXY(e);

    /// draw a line from previous point to this        
    ctx.beginPath();
    ctx.moveTo(prevX, prevY);
    ctx.lineTo(pos.x, pos.y);
    ctx.stroke();

    /// set previous to this point
    prevX = pos.x;
    prevY = pos.y;

    /// record to current stroke
    points[points.length - 1].push([pos.x, pos.y]);
}

And on mouse up; in the demo it produces the points as string which can be copied directly into your JS code:

canvas.onmouseup = function() {
    isDown = false;
    coords.innerHTML = JSON.stringify(points);
}

We adjust the mouse position so it becomes relative to canvas:

function getXY(e) {
    var r = canvas.getBoundingClientRect();
    return {x: e.clientX - r.left, y: e.clientY - r.top}
}

Render

Now that we have the points recorded we need a way to reproduce them.

This snippet is able to render the strokes and points we just recorded - for the demo I set red color to differentiate between rendered strokes and drawn:

function renderPoints(points) {

    ctx.clearRect(0, 0, canvas.width, canvas.height);
    ctx.strokeStyle = '#f00';

    /// get a stroke
    for(var i = 0, t, p, pts; pts = points[i]; i++) {

        /// render stroke
        ctx.beginPath();
        ctx.moveTo(pts[0][0], pts[0][2]);
        for(t = 1; p =pts[t]; t++) {
            ctx.lineTo(p[0], p[1]);
        }
        ctx.stroke();
    }
    ctx.strokeStyle = '#000';
}

Conclusion

This heart (?!):

snapshot

produces these points for you:

[[[103,99],[103,100],[103,98],[105,93],[115,79],[129,61],[139,52],[145,49],[149,49],[152,51],[154,54],[155,57],[156,65],[154,79],[152,89],[149,99],[145,110],[139,124],[131,142],[118,163],[108,176],[101,184],[97,185],[94,187],[87,187],[76,180],[65,166],[60,156],[54,145],[46,119],[41,98],[39,84],[39,81],[39,79],[39,77],[39,76],[40,75],[42,74],[43,72],[46,69],[47,67],[48,67],[49,67],[50,67],[51,68],[52,69],[54,70],[61,75],[71,87],[82,101],[84,105],[87,108],[89,111],[89,112],[89,113],[89,114],[89,115],[89,116],[90,118]]]

They can be given directly to the render method, or the stroke/point array can be made more sophisticated by that you prefix it with some code to allow you to copy-and-paste the produced string directly, for example:

var code = '    var points = ' + JSON.stringify(points) + ';';

Fiddle demo

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javascript - HTML canvas art, generate coordinates data from sketch

javascript - HTML canvas art, generate coordinates data from sketch

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1 Answer

Recorder

Render

Conclusion

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