mousemove - Web API 接口参考 | MDN (mozilla.org)
动画.gif
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
canvas {
border: 1px solid black;
width: 560px;
height: 360px;
}
</style>
</head>
<body>
<canvas id="myPics" width="560" height="360"></canvas>
<script>
// When true, moving the mouse draws on the canvas
let isDrawing = false;
let x = 0;
let y = 0;
const myPics = document.getElementById('myPics');
const context = myPics.getContext('2d');
// The x and y offset of the canvas from the edge of the page
const rect = myPics.getBoundingClientRect();
// Add the event listeners for mousedown, mousemove, and mouseup
myPics.addEventListener('mousedown', e => {
x = e.clientX - rect.left;
y = e.clientY - rect.top;
isDrawing = true;
});
myPics.addEventListener('mousemove', e => {
if (isDrawing === true) {
drawLine(context, x, y, e.clientX - rect.left, e.clientY - rect.top);
x = e.clientX - rect.left;
y = e.clientY - rect.top;
}
});
window.addEventListener('mouseup', e => {
if (isDrawing === true) {
drawLine(context, x, y, e.clientX - rect.left, e.clientY - rect.top);
x = 0;
y = 0;
isDrawing = false;
}
});
function drawLine(context, x1, y1, x2, y2) {
context.beginPath();
context.strokeStyle = 'black';
context.lineWidth = 1;
context.moveTo(x1, y1);
context.lineTo(x2, y2);
context.stroke();
context.closePath();
}
</script>
</body>
</html>
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