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HTML - How to draw a 'target'  / concentric circles on a canvas

Posted on 2014-07-20
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Last Modified: 2014-07-20
How can use  JS  to draw a 'target'  (Like the Target icon ) or concentric circles when a  canvas is click on a an specific point?

 var ctx = canvas.getContext('2d');
????
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Question by:JElster
2 Comments
 
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Robert Schutt earned 2000 total points
ID: 40207638
maybe something like this? http://jsfiddle.net/robert_schutt/8usRk/
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext('2d');

var C_RADIUS = 20, C_NUM = 3, C_WIDTH = 10;

$('#canvas').click(function(e){
    var offset = $(this).offset();
    ctx.clearRect(0, 0, canvas.width, canvas.height);
    var x = e.pageX - offset.left - C_WIDTH / 2;
    var y = e.pageY - offset.top - C_WIDTH / 2;
    ctx.lineWidth = C_WIDTH;
    ctx.strokeStyle = 'black';
    ctx.beginPath();
    ctx.moveTo(x - C_NUM * C_RADIUS, y);
    ctx.lineTo(x + C_NUM * C_RADIUS, y);
    ctx.closePath();
    ctx.stroke();
    ctx.beginPath();
    ctx.moveTo(x, y - C_NUM * C_RADIUS);
    ctx.lineTo(x, y + C_NUM * C_RADIUS);
    ctx.closePath();
    ctx.stroke();
    ctx.strokeStyle = 'red';
    for (var c = 0; c <= C_NUM; c++) {
        ctx.beginPath();
        ctx.arc(x, y, C_WIDTH / 2 + c * C_RADIUS, 0, 2 * Math.PI, true);
        ctx.closePath();
        ctx.stroke();
    }
});

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by:JElster
ID: 40207923
thx again!
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