我想做一个小绘画应用程序使用画布。所以我需要找到鼠标在画布上的位置。
当前回答
通过事件可以获得画布内的鼠标坐标。offsetX和事件。下面是一个小片段来证明我的观点:
c=document.getElementById("c"); ctx=c.getContext("2d"); ctx.fillStyle="black"; ctx.fillRect(0,0,100,100); c.addEventListener("mousemove",function(mouseEvt){ // the mouse's coordinates on the canvas are just below x=mouseEvt.offsetX; y=mouseEvt.offsetY; // the following lines draw a red square around the mouse to prove it ctx.fillStyle="black"; ctx.fillRect(0,0,100,100); ctx.fillStyle="red"; ctx.fillRect(x-5,y-5,10,10); }); body { background-color: blue; } canvas { position: absolute; top: 50px; left: 100px; } <canvas id="c" width="100" height="100"></canvas>
其他回答
你可以买到它
var element = document.getElementById(canvasId);
element.onmousemove = function(e) {
var xCoor = e.clientX;
var yCoor = e.clientY;
}
基于@Patrick Boos的解决方案，但修复了中间滚动条的潜在问题。
export function getRelativeCoordinates(event: MouseEvent, referenceElement: HTMLElement) {
const position = {
x: event.pageX,
y: event.pageY,
};
const offset = {
left: referenceElement.offsetLeft,
top: referenceElement.offsetTop,
};
let reference = referenceElement.offsetParent as HTMLElement;
while (reference) {
offset.left += reference.offsetLeft;
offset.top += reference.offsetTop;
reference = reference.offsetParent as HTMLElement;
}
const scrolls = {
left: 0,
top: 0,
};
reference = event.target as HTMLElement;
while (reference) {
scrolls.left += reference.scrollLeft;
scrolls.top += reference.scrollTop;
reference = reference.parentElement as HTMLElement;
}
return {
x: position.x + scrolls.left - offset.left,
y: position.y + scrolls.top - offset.top,
};
}
因为我没有找到一个解决方案，可以帮助你得到它，如果你把它附加到一个父母元素，你有一个例如选择。
这就是我所做的:
let positions = {
x: event.pageX,
y: event.pageY - event.currentTarget.getBoundingClientRect().top + event.currentTarget.offsetTop
}
原来的答案是把它放在一个iframe中。更好的解决方案是在填充设置为0px的画布上使用事件offsetX和offsetY。
<html>
<body>
<script>
var main=document.createElement('canvas');
main.width="200";
main.height="300";
main.style="padding:0px;margin:30px;border:thick dashed red";
document.body.appendChild(main);
// adding event listener
main.addEventListener('mousemove',function(e){
var ctx=e.target.getContext('2d');
var c=Math.floor(Math.random()*0xFFFFFF);
c=c.toString(16); for(;c.length<6;) c='0'+c;
ctx.strokeStyle='#'+c;
ctx.beginPath();
ctx.arc(e.offsetX,e.offsetY,3,0,2*Math.PI);
ctx.stroke();
e.target.title=e.offsetX+' '+e.offsetY;
});
// it worked! move mouse over window
</script>
</body>
</html>
如果你想获得与一个元素相关的layerX和layerY，也许你可以尝试:
let bbox_rect = document.getElementById("dom-ID").getBoundingClientRect()
let layerX = e.clientX-bbox_rect.left
let layerY = e.clientY-bbox_rect.top
