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I'm trying to implement zooming and panning a canvas which contains a picture. I found this example .html, but the transformations are applied on the picture withing the canvas, not on the canvas itself. I don't understand the code pletely, so I didn't manage to customize it for my needs. Can someone help me with that?

Or, if you could remend me some good library suitable for my needs, that would be great. Thanks.

I'm trying to implement zooming and panning a canvas which contains a picture. I found this example http://phrogz/tmp/canvas_zoom_to_cursor.html, but the transformations are applied on the picture withing the canvas, not on the canvas itself. I don't understand the code pletely, so I didn't manage to customize it for my needs. Can someone help me with that?

Or, if you could remend me some good library suitable for my needs, that would be great. Thanks.

  • javascript
  • jquery
  • html
  • canvas
  • zooming
Share Improve this question asked Jul 23, 2014 at 9:54 nenanena 1471 gold badge3 silver badges11 bronze badges 2
  • 3 why do you need to move the canvas itself rather than an image inside the canvas? – Timothy Groote Commented Jul 23, 2014 at 9:56
  • 1 Because I have two overlaying canvas elements, one for holding the picture and the other one for drawing on it. So when the picture is moved/zoomed, the other canvas should follow. – nena Commented Jul 23, 2014 at 9:59
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1 Answer 1

Reset to default 12

Check out the transformation methods available on the context object.

Context.scale will allow you to scale your content.

Context.translate will allow you to offset the drawing of your content to create your panning effect.

If you want 2 overlaying canvases to maintain their aspect ratio then you would scale & translate both canvases by the same amount.

Here's example code and a Demo: http://jsfiddle/m1erickson/H6UMN/

<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery./jquery.min.js"></script>
<style>
    body{ background-color: ivory; }
    #wrapper{position:relative;}
    canvas{position:absolute; border:1px solid red;}
</style>
<script>
$(function(){

    var canvas=document.getElementById("canvas");
    var ctx=canvas.getContext("2d");
    var canvas1=document.getElementById("canvas1");
    var ctx1=canvas1.getContext("2d");

    var $canvas=$("#canvas");
    var canvasOffset=$canvas.offset();
    var offsetX=canvasOffset.left;
    var offsetY=canvasOffset.top;
    var scrollX=$canvas.scrollLeft();
    var scrollY=$canvas.scrollTop();
    var cw=canvas.width;
    var ch=canvas.height;

    var scaleFactor=1.00;
    var panX=0;
    var panY=0;

    var circleX=150;
    var circleY=150;
    var radius=15;

    drawTranslated();

    $("#canvas").mousemove(function(e){handleMouseMove(e);});
    $("#scaledown").click(function(){ scaleFactor/=1.1; drawTranslated(); });
    $("#scaleup").click(function(){ scaleFactor*=1.1; drawTranslated(); });
    $("#panleft").click(function(){ panX-=10; drawTranslated(); });
    $("#panright").click(function(){ panX+=10; drawTranslated(); });

    function drawTranslated(){

        ctx.clearRect(0,0,cw,ch);
        ctx.save();
        ctx.translate(panX,panY);
        ctx.scale(scaleFactor,scaleFactor);
        ctx.beginPath();
        ctx.rect(circleX-radius,circleY-radius,radius*2,radius*2);
        ctx.closePath();
        ctx.fillStyle="blue";
        ctx.fill();
        ctx.restore();

        ctx1.clearRect(0,0,cw,ch);
        ctx1.save();
        ctx1.translate(panX,panY);
        ctx1.scale(scaleFactor,scaleFactor);
        ctx1.beginPath();
        ctx1.arc(circleX,circleY,radius,0,Math.PI*2);
        ctx1.closePath();
        ctx1.fillStyle="red";
        ctx1.fill();
        ctx1.restore();
    }

}); // end $(function(){});
</script>
</head>
<body>
    <button id=scaledown>Scale Down</button>
    <button id=scaleup>Scale Up</button>
    <button id=panleft>Pan Left</button>
    <button id=panright>Pan Right</button><br>
    <div id=wrapper>
        <canvas id="canvas" width=350 height=300></canvas>
        <canvas id="canvas1" width=350 height=300></canvas>
    </div>
</body>
</html>

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