我有以下 Javascript、HTML 和 CSS 代码
function distanceBetween(point1, point2) {
return Math.sqrt(Math.pow(point2.x - point1.x, 2) + Math.pow(point2.y - point1.y, 2));
}
function angleBetween(point1, point2) {
return Math.atan2(point2.x - point1.x, point2.y - point1.y);
}
function draw() {
var img = new Image();
img.src = 'http://www.tricedesigns.com/wp-content/uploads/2012/01/brush2.png';
var el = document.getElementById('DrawingPattern');
var ctx = el.getContext('2d');
ctx.lineJoin = ctx.lineCap = 'round';
var isDrawing, lastPoint;
el.onmousedown = function (e) {
isDrawing = true;
lastPoint = {x: e.clientX, y: e.clientY};
};
el.onmousemove = function (e) {
if (!isDrawing) return;
var currentPoint = {x: e.clientX, y: e.clientY};
var dist = distanceBetween(lastPoint, currentPoint);
var angle = angleBetween(lastPoint, currentPoint);
for (var i = 0; i < dist; i++) {
x = lastPoint.x + (Math.sin(angle) * i) - 25;
y = lastPoint.y + (Math.cos(angle) * i) - 25;
ctx.drawImage(img, x, y);
}
lastPoint = currentPoint;
};
el.onmouseup = function () {
isDrawing = false;
};
}html, body {
color: #fff;
background: #000;
font-family: "Lucida Grande";
}
canvas{
position: static;
cursor: move;
margin: auto;
width: 70%;
border: 3px solid #73AD21;
background: white;
overflow: visible;
}<body onload=draw()>
<canvas width="1024" height="649" id="DrawingPattern">
<!-- add fallback content-->
</canvas>
</body>整个代码都有效，我遇到的唯一问题是当我开始在 Canvas 上绘图时，光标与光标的有效位置不对齐。因此，当我绘制它时，线条会位于另一个位置，高于或低于光标的实际位置。我尝试了不同的方法，但我猜是某种缩放问题，但我无法解决它。
最佳答案
这是一个缩放问题。即使您通过按百分比设置 CSS 宽度来缩放 Canvas 元素，绘图区域的大小也不会改变。你在屏幕空间中获取鼠标坐标，但在绘制时需要转换到 Canvas 空间。
为此，通过考虑 el.width( Canvas 宽度)和 el.offsetWidth(元素宽度)之间的差异来计算比例。由于通过保持纵横比按比例缩放 Canvas ，因此可以对 X 和 Y 坐标使用相同的缩放比例。
我添加了一个 elementScale() 函数并更新了代码以将 clientX 和 clientY 与返回值相乘。
function distanceBetween(point1, point2) {
return Math.sqrt(Math.pow(point2.x - point1.x, 2) + Math.pow(point2.y - point1.y, 2));
}
function angleBetween(point1, point2) {
return Math.atan2(point2.x - point1.x, point2.y - point1.y);
}
function elementScale(el) {
return el.offsetWidth === 0 ? 0 : (el.width / el.offsetWidth);
}
function draw() {
var img = new Image();
img.src = 'http://www.tricedesigns.com/wp-content/uploads/2012/01/brush2.png';
var el = document.getElementById('DrawingPattern');
var ctx = el.getContext('2d');
ctx.lineJoin = ctx.lineCap = 'round';
var isDrawing, lastPoint;
el.onmousedown = function (e) {
var scale = elementScale(el);
isDrawing = true;
lastPoint = {x: e.clientX * scale, y: e.clientY * scale};
};
el.onmousemove = function (e) {
if (!isDrawing) return;
var scale = elementScale(el);
var currentPoint = {x: e.clientX * scale, y: e.clientY * scale};
var dist = distanceBetween(lastPoint, currentPoint);
var angle = angleBetween(lastPoint, currentPoint);
for (var i = 0; i < dist; i++) {
x = lastPoint.x + (Math.sin(angle) * i) - 25;
y = lastPoint.y + (Math.cos(angle) * i) - 25;
ctx.drawImage(img, x, y);
}
lastPoint = currentPoint;
};
el.onmouseup = function () {
isDrawing = false;
};
}html, body {
color: #fff;
background: #000;
font-family: "Lucida Grande";
}
canvas{
position: static;
cursor: move;
margin: auto;
width: 70%;
border: 3px solid #73AD21;
background: white;
overflow: visible;
}<body onload=draw()>
<canvas width="1024" height="649" id="DrawingPattern">
<!-- add fallback content-->
</canvas>
</body>关于javascript - 光标未使用 HTML Canvas 对齐，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/50966385/