Question

我试图在画布中绘制并改变div大小但是我无法从鼠标点精确绘制，鼠标和线之间有一定的距离，实际绘图就在这里。

CSS

canvas {
    border: 1px solid #ccc;
    transform: scale(0.5)
}

JS

var el = document.getElementById('c');
var ctx = el.getContext('2d');
var isDrawing;

el.onmousedown = function (e) {
    isDrawing = true;
    ctx.moveTo(e.clientX, e.clientY);
};
el.onmousemove = function (e) {
    if (isDrawing) {
        ctx.lineTo(e.clientX, e.clientY);
        ctx.stroke();
    }
};

el.onmouseup = function () {
    isDrawing = false;
};

HTML

<canvas id="c" width="500" height="300"></canvas>

Demo fiddle

Answer 1

您需要从鼠标位置减去画布的左侧和顶部，并将所有内容乘以2（或任何比例的倒数）。

var rect = el.getBoundingClientRect();

// code here
ctx.moveTo((e.clientX - rect.left) * 2, (e.clientY - rect.top) * 2);

// code here
ctx.lineTo((e.clientX - rect.left) * 2, (e.clientY - rect.top) * 2);

此处更新了jsfiddle - ＆gt; http://jsfiddle.net/Lqbeqjzb/7/

编辑：根据评论改变你的小提琴 - ＆gt; https://jsfiddle.net/pb5ckhjm/4/

Answer 2

尝试使用鼠标悬停

el.onmouseover = function (e) {
isDrawing = true;
ctx.moveTo(e.clientX, e.clientY);
 };

让我知道这就是你想要的

css变换缩放鼠标不能正常工作

2 个答案: