可以做一个画笔了

图片

<

    let ctx = canvas.getContext('2d');
    let painting = false

    ctx.fillStyle = 'green';
    canvas.onmousedown = () => {
        painting = true
    }
    canvas.onmousemove = (e) => {
        if (painting === true) {
            ctx.fillRect(e.clientX - 5, e.clientY - 25, 10, 10);
        } else {
            console.log(什么都不做)
        }

    }
    canvas.onmouseup = () => {
        painting = false

    }

</script>
</body>