弹跳球

Question

当您拖动并释放时，我有这个可拖动的球，它的方向相反。我该如何从墙壁弹起？另外，如果应该移动600像素，并在200像素后撞墙，则应该再移动400像素。 http://jsfiddle.net/bepcmsgo/5/

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";
    }
})

Answer 1

我分叉了您的JSFiddle，并添加了一个简单的弹跳机制：jsfiddle.net/SydLambert/hnkL392x/2

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

我稍微改变了球的运动逻辑，以下是一些说明我的方法的指针：

• 使用CSS动画非常适合简单的动作，但是最好让JS处理更多动态和复杂的事情，以节省大量CSS代码。
• 在此示例中，所有运动都是在JS中逐帧处理的，在渲染每一帧之前进行角度和摩擦计算，而不是计算最终位置并为那里的路径设置动画。每个刻度线都会计算出下一个即时位置（必要时会跳动），然后显示给用户。滴答声之间的延迟为16ms，使其约为62.5FPS。
• 我将您的位置变量移至circle类中的命名属性，以使其比将pos1，pos2，pos3 ...都全局地读起来更容易阅读。变量。
• 数学运算非常容易理解，我使用pythag来获取与鼠标指针的距离，并使用trig来获取与指针的角度并移动圆。弹跳角假定入射角等于反射角。弹跳还假定为完全弹性碰撞，尽管您可以根据需要降低弹跳的速度。
• 我在发布前更改了轻微的移动，以使用CSS转换而不是实际移动元素。
• 最后一点，我建议您研究HTML5 <canvas>，如果您想进行更多图形处理，则它是为此类内容而构建的。