Javascript 弹跳拖球

我有一个可拖动的球，当你拖动并释放它时，它会朝着相反的方向移动。我怎样才能使它从墙上反弹？同样，如果它应该以600px的速度运行，并且在200px之后撞到墙，那么它应该以400px的速度运行。

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我分叉了你的JSFIDLE并添加了一个简单的弹跳机制：

我稍微改变了球的移动逻辑，以下是一些说明我的方法的指针：

对于简单的动作来说，使用CSS动画是非常好的，但是任何更加动态和复杂的动作最好留给JS来保存大量CSS代码。 在本例中，所有移动都在JS中逐帧处理，在渲染每个帧之前都会进行角度和摩擦力计算，而不是计算最终位置并设置路径动画。如有必要，每个勾号会计算下一个弹跳位置，然后显示给用户。滴答声之间的延迟为16ms，约为62.5FPS。 我将您的位置变量移动到circle类中的命名属性，以使其比pos1、pos2、pos3更易于阅读。。。都是全局变量。 数学很好学，我用毕达格算出鼠标指针的距离，用三角键算出鼠标指针的角度，然后移动圆圈。反弹角假设入射角等于反射角。反弹也假设完全弹性碰撞，但如果需要，可以降低反弹的速度。 在发布之前，我将轻微的移动改为使用CSS翻译，而不是实际移动元素。 最后一点，如果你想做更多的图形化的东西，我建议你看看HTML5，它是为这样的东西而构建的。

let circle = document.getElementById("circle");
let pos1 = 0;
let pos2 = 0;
let pos3 = 0;
let pos4 = 0;
let mouseDown = false;
let currentCircleTop = 0;
let currentCircleLeft = 0;

circle.addEventListener("mousedown", function(e){
  mouseDown = true;
  pos3 = e.pageX;
  pos4 = e.pageY;
  currentCircleTop = circle.offsetTop;
  currentCircleLeft = circle.offsetLeft;
  this.style.transition = "0.3s all";
})

document.addEventListener("mousemove", function(e){
    if(mouseDown){
        pos1 = pos3 - e.pageX;
        pos2 = pos4 - e.pageY;
        pos3 = e.pageX;
        pos4 = e.pageY;
        circle.style.top = circle.offsetTop - pos2 + "px";
        circle.style.left = circle.offsetLeft - pos1 + "px";
  }
})
document.addEventListener("mouseup", function(){
    if(mouseDown){
        mouseDown = false;
        circle.style.transition = "0.8s all";  
        circle.style.top = currentCircleTop + ((currentCircleTop - circle.offsetTop) * 20) + "px";
        circle.style.left = currentCircleLeft + ((currentCircleLeft - circle.offsetLeft) * 20) + "px";
    }
})

let circle = document.getElementById("circle");
circle.x=300;
circle.y=150;
circle.direction=0; //in radians
circle.velocity=0;
circle.friction=0.05; //0 to 1

let container=document.getElementById("circleContainer");
container.width=parseInt(container.style.width.slice(0,-2)); //Gets width and height as usable integers
container.height=parseInt(container.style.height.slice(0,-2));

let mouse={
    x:0,
    y:0,
    down:false,
};

let dragDisplayMultiplier=0.2; //How much the circle moves while a drag is in progress.
let velocityDampener=5; //How much the velocity is reduced immediately after the circle is released


function displayCircle(){ //Sets the position of the circle
    circle.style.top=circle.y+"px";
    circle.style.left=circle.x+"px"
}

function step(){ //Uses trig to work out the next positon of the circle
    return {
        x:circle.x+circle.velocity*Math.cos(circle.direction),
        y:circle.y+circle.velocity*Math.sin(circle.direction),
    }
}

function tick(){ //Physics function
    circle.velocity*=1-circle.friction; //Decrease the circle's velocity with friction

    let newLocation=step(); //Determine the next location after the circle has travelled

    //If the next location of the circle is outside the container, the direction is changed.
    //Angle of incidence equals angle of reflection.
    if(newLocation.x<0 || newLocation.x+20>container.width)
        circle.direction=Math.PI-(circle.direction);
    if(newLocation.y<0 || newLocation.y+20>container.height)
        circle.direction*=-1;

    //The next location is now inside the container, so the circle's position can be updated
    newLocation=step();
    circle.x=newLocation.x;
    circle.y=newLocation.y;

    //Displays the circle's new position to the user
    displayCircle();

    //If the circle still has reasonable velocity, the simulation is continued after waiting 16ms
    if(circle.velocity>1){
        setTimeout(tick,16);
    }
}

circle.addEventListener("mousedown", function(e){
    mouse.down=true;
});

document.addEventListener("mousemove", function(e){
    mouse.x=e.pageX;
    mouse.y=e.pageY;
    if(mouse.down) //Offsets the ball whilst the drag is in progress using CSS translation
        circle.style.transform=`translate(${((circle.x+mouse.x)/2-circle.x)*dragDisplayMultiplier}px, ${((circle.y+mouse.y)/2-circle.y)*dragDisplayMultiplier}px)`;
});

document.addEventListener("mouseup", function(){
    if(mouse.down){
        mouse.down = false;
        circle.style.transform="translate(0px, 0px)"; //Resets the CSS translation from the "mousemove" event
        circle.velocity=Math.sqrt((circle.x-mouse.x+10)**2 + (circle.y-mouse.y+10)**2); //Sets the velocity to the distance bewteen the circle and mouse pointer
        circle.velocity/=velocityDampener; //Reduces the velocity slightly for ease of use
        circle.direction=Math.atan2((circle.y-mouse.y+10),(circle.x-mouse.x+10)); //Uses atan2 to find the angle between the circle and the mouse pointer
        setTimeout(tick,16); //Starts the physics simulation
    }
});

displayCircle(); //Sets the initial circle top and left to match x and y