I have created a line inside a canvas element. I am looking for the easiest way to detect if the position of the mouse is inside the line, which is inside the canvas.
I have used this function to see the position of the mouse inside the canvas, but I am very confused on how I should proceed.
function getMousePos(c, evt) {
var rect = c.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
I have also looked at this topic Fabricjs detect mouse over object path , but it detects if the mouse is inside the canvas, not inside the object.
The line that I create is a part of smaller lines, connected to each other.
for (var i = 0; i < 140 ; i++) {
ctx.beginPath();
ctx.moveTo(x[i],y[i]);
ctx.quadraticCurveTo(x[i],50,x[i+1],y[i+1]);
ctx.lineWidth = 40;
ctx.strokeStyle = 'white';
ctx.lineCap = 'round';
ctx.stroke();
}
where x[i] and y[i] are the arrays with the coordinates that I want.
I hope my question is clear, although I am not very familiar with javascript.
Thanks Dimitra
A Demo: http://jsfiddle.net/m1erickson/Cw4ZN/
You need these concepts to check if the mouse is inside a line:
Define the starting & ending points of a line
Listen for mouse events
On mousemove, check if the mouse is within a specified distance of the line
Here's annotated example code for you to learn from.
$(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>
About hit-testing Paths:
If you create Paths using path commands you can use context.isPointInPath(mouseX,mouseY) to check if the mouse is inside a path. context.isPointInPath does not work well with lines however because lines theoretically have zero width to "hit".
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