$(function() {
// canvas related variables
var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
var $canvas = $("#canvas");
var canvasOffset = $canvas.offset();
var offsetX = canvasOffset.left;
var offsetY = canvasOffset.top;
// dom element to indicate if mouse is inside/outside line
var $hit = $("#hit");
// determine how close the mouse must be to the line
// for the mouse to be inside the line
var tolerance = 5;
// define the starting & ending points of the line
var line = {
x0: 50,
y0: 50,
x1: 100,
y1: 100
};
// set the fillstyle of the canvas
ctx.fillStyle = "red";
// draw the line for the first time
draw(line);
// function to draw the line
// and optionally draw a dot when the mouse is inside
function draw(line, mouseX, mouseY, lineX, lineY) {
ctx.clearRect(0, 0, canvas.width, canvas.height);
ctx.beginPath();
ctx.moveTo(line.x0, line.y0);
ctx.lineTo(line.x1, line.y1);
ctx.stroke();
if (mouseX && lineX) {
ctx.beginPath();
ctx.arc(lineX, lineY, tolerance, 0, Math.PI * 2);
ctx.closePath();
ctx.fill();
}
}
// calculate the point on the line that's
// nearest to the mouse position
function linepointNearestMouse(line, x, y) {
//
lerp = function(a, b, x) {
return (a + x * (b - a));
};
var dx = line.x1 - line.x0;
var dy = line.y1 - line.y0;
var t = ((x - line.x0) * dx + (y - line.y0) * dy) / (dx * dx + dy * dy);
var lineX = lerp(line.x0, line.x1, t);
var lineY = lerp(line.y0, line.y1, t);
return ({
x: lineX,
y: lineY
});
};
// handle mousemove events
// calculate how close the mouse is to the line
// if that distance is less than tolerance then
// display a dot on the line
function handleMousemove(e) {
e.preventDefault();
e.stopPropagation();
mouseX = parseInt(e.clientX - offsetX);
mouseY = parseInt(e.clientY - offsetY);
if (mouseX < line.x0 || mouseX > line.x1) {
$hit.text("Outside");
draw(line);
return;
}
var linepoint = linepointNearestMouse(line, mouseX, mouseY);
var dx = mouseX - linepoint.x;
var dy = mouseY - linepoint.y;
var distance = Math.abs(Math.sqrt(dx * dx + dy * dy));
if (distance < tolerance) {
$hit.text("Inside the line");
draw(line, mouseX, mouseY, linepoint.x, linepoint.y);
} else {
$hit.text("Outside");
draw(line);
}
}
// tell the browser to call handleMousedown
// whenever the mouse moves
$("#canvas").mousemove(function(e) {
handleMousemove(e);
});
}); // end $(function(){});
body {
background-color: ivory;
}
canvas {
border: 1px solid red;
}
<!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.com/jquery.min.js"></script>
</head>
<body>
<h2 id="hit">Move mouse near line</h2>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>