检查鼠标是在窗口内还是在窗口外

Question

我已经看到这种类型的问题已经回答了，但是每个答案都有点模糊或存在一些交叉兼容性问题或超出我的理解范围。所以有没有人可以给我一个最新的-日期，完整，清晰（显示和解释所有涉及的步骤）答案？当鼠标在窗口外时，我不想让圆圈变大。我没有使用 JQuery（在许多答案中都有特色）。我应该使用有没有办法用纯javascript实现这个？ 感谢您的帮助，如果我的代码有点多余，我们深表歉意:)

var canvas = document.querySelector("canvas");
var c = canvas.getContext('2d');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;
var mouse = {
    x: undefined,
    y: undefined
}
window.addEventListener("mousemove", function(event){
    mouse.x = event.x;
    mouse.y = event.y;
})
window.addEventListener("resize", function(){
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight;
})


var colorArray = [
    "#6CC61D",
    "#E05132",
    "#278E83",
    "#A633D4"
]

function Circle(x,y,dx,dy,radius){
    this.x  = x;
    this.y = y;
    this.dx = dx;
    this.dy = dy;
    this.radius = radius;
    this.color = colorArray[Math.floor(Math.random() * colorArray.length)];

    this.draw = function(){
        c.beginPath();
        c.arc(this.x,this.y,this.radius,0,Math.PI*2,false);
        c.fillStyle = this.color;
        c.fill()
    }
    this.update = function(){
        if (this.x + this.radius>window.innerWidth  ||  this.x -this.radius<0){
            this.dx = - this.dx;}
        if (this.y + this.radius > window.innerHeight || this.y - this.radius < 0) {
            this.dy = - this.dy;
        }
        if (mouse.x - this.x < 50 && mouse.x - this.x > - 50 && mouse.y - this.y < 50 && mouse.y - this.y > - 50 && this.radius<50 ){
            this.radius += 1;
        }
        else if(this.radius>2){
            this.radius -= 1;
        }
        this.x += this.dx;
        this.y += this.dy;
        this.draw();
    
}
}
var circleArray = [];
for (var i = 0; i < 600; i++) {
    var x = Math.random() * (window.innerWidth - radius * 2) + radius;
    var y = Math.random() * (window.innerHeight - radius * 2) + radius;
    var dy = (Math.random() - 0.5) * 8;
    var dx = (Math.random() - 0.5) * 8;
    var radius = 30;

        circleArray.push(new Circle(x, y, dx, dy, radius));
    }




function animate(){
    requestAnimationFrame(animate);
    c.clearRect(0,0,window.innerWidth,window.innerHeight);
    for (var i = 0;i < circleArray.length;i++){
        circleArray[i].update()
    }
    circle.update();
}
animate();

Answer 1

我没有使用 JQuery（在许多答案中都有介绍）。我应该使用它吗？

有什么方法可以用纯javascript实现吗？

这取决于您的喜好。由于 JQuery 是 javascript，如果你可以用 JQuery 来做，你只能用 JS 来做。对于“它可以实施吗？”，很可能是什么。我将开始对您的代码进行一些格式化，以将逻辑（计算/更新位置、速度和半径）与渲染（绘图）分离，这样操作起来会更容易。

---

检查鼠标是否在窗口外：

您可以使用mouseout 事件来检测鼠标何时离开窗口

window.addEventListener('mouseout', action);

---

当鼠标在窗口外时避免圆圈变大：

对于操作，将mouse.x 和mouse.y 设置回undefined

window.addEventListener('mouseout', function(){
  mouse.x = undefined;
  mouse.y = undefined;
})

然后在您的 Circle 更新方法中再添加 2 个条件，仅在除了其他条件之外，还定义了 mouse.x 和 mouse.y 时（如果鼠标在窗口中）才增加半径。

if (mouse.x &&
    mouse.y &&
    Math.abs(mouse.x - this.x) < 50 &&
    Math.abs(mouse.y - this.y) < 50 &&
    this.radius < 50 ) {
    this.radius += 1;
}

---

结果：

const canvas = document.querySelector("canvas");
const c = canvas.getContext('2d');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;

const mouse = {
    x: undefined,
    y: undefined
}

window.addEventListener("mousemove", function(event){
    mouse.x = event.x;
    mouse.y = event.y;
})

window.addEventListener("resize", function(){
    canvas.width = window.innerWidth;
    canvas.height = window.innerHeight;
})

window.addEventListener('mouseout', function(){
  mouse.x = undefined;
  mouse.y = undefined;
})

const colorArray = [
    "#6CC61D",
    "#E05132",
    "#278E83",
    "#A633D4"
]

function Circle(x, y, dx, dy, radius){
    this.x  = x;
    this.y = y;
    this.dx = dx;
    this.dy = dy;
    this.radius = radius;
    this.color = colorArray[Math.floor(Math.random() * colorArray.length)];

    this.draw = function(){
        c.beginPath();
        c.arc(this.x, this.y, this.radius, 0, Math.PI*2, false);
        c.fillStyle = this.color;
        c.fill()
    }
    
    this.update = function(){
    
        if (this.x + this.radius > window.innerWidth  || this.x - this.radius < 0) {
            this.dx = - this.dx;
        }
        
        if (this.y + this.radius > window.innerHeight || this.y - this.radius < 0) {
            this.dy = - this.dy;
        }
        
        if (  mouse.x &&
              mouse.y && 
              Math.abs(mouse.x - this.x) < 50 &&
              Math.abs(mouse.y - this.y) < 50 &&
              this.radius < 50 ) {
            this.radius += 1;
        } else if(this.radius > 2) {
            this.radius -= 1;
        }
        
        this.x += this.dx;
        this.y += this.dy;
    }
}

const circleArray = [];

for (let i = 0; i < 600; i++) {
    const radius = 30;
    const x = Math.random() * (window.innerWidth - radius * 2) + radius;
    const y = Math.random() * (window.innerHeight - radius * 2) + radius;
    const dy = (Math.random() - 0.5) * 8;
    const dx = (Math.random() - 0.5) * 8;
    circleArray.push(new Circle(x, y, dx, dy, radius));
}

function clearCanvas(){
  c.clearRect(0,0,window.innerWidth,window.innerHeight);
}

function update(){
  for (let i = 0; i < circleArray.length; i++){
    circleArray[i].update()
  }
}

function draw(){
  for (let i = 0; i < circleArray.length; i++){
    circleArray[i].draw()
  }
}

function animate(){

    requestAnimationFrame(animate);
    
    clearCanvas();
    
    update();
    
    draw();
}

requestAnimationFrame(animate);

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />  
</head>
<body>
  <canvas id="signature-pad" class="signature-pad" width=400 height=200></canvas>
</body>
</html>