当 ZFCC790C72A86190DE1B549D0DDC6F55 时，如何在 HTML5 canvas 上获得鼠标 position？

Question

当 canvas 不是全屏时，以下代码可以完美运行。

    let canvas = document.querySelector('canvas');
    let ctx = canvas.getContext('2d');

    document.addEventListener('mousemove',e=>{
        let br = canvas.getBoundingClientRect();
        let mouseX = e.clientX - br.left;
        let mouseY = e.clientY - br.top;
    });

但是，在canvas.requestFullscreen()变量mouseX, mouseY不再代表 canvas 上的鼠标 position。
相对于canvas，有什么办法可以得到鼠标的position？

Answer 1

找了好久终于找到了解决办法。

var FULLSCREEN = false;
document.onfullscreenchange = () => {FULLSCREEN = !FULLSCREEN};
// Keep Track of when Screen 

var mouseX=0,mouseY=0;

function map(v,n1,n2,m1,m2){
    return (v-n1)/(n2-n1)*(m2-m1)+m1;
}

doucment.addEventListener('mousedown',e=>{
        var x,y;
        var element = e.target;
        let br = element.getBoundingClientRect();
        if(FULLSCREEN){
            let ratio = window.innerHeight/canvas.height;
            let offset = (window.innerWidth-(canvas.width*ratio))/2;
            x = map(e.clientX-br.left-offset,0,canvas.width*ratio,0,element.width);
            y = map(e.clientY-br.top,0,canvas.height*ratio,0,element.height);
        } else {
            x = e.clientX - br.left;
            y = e.clientY - br.top;
        }
        mouseX = x;
        mouseY = y;
});

// Unfortunately this only works if the element is touching the top and bottom of the screen
// In other words, the ratio between the width and height of your screen must 
// be greater that the ratio of width to height for your element