为什么乒乓球会卡在底部
Why does the ball in pong get stuck at the bottom?
我最近制作了一款JS Pong游戏。它工作得很好，但球很少卡在底部或顶部。它看起来像是穿过了墙的一半，并且不断地弹跳。问题发生的视频。你可以在这里试试这个游戏。我不知道为什么会发生这个问题，因为逻辑似乎是正确的，90%的时间都是正确的。以下是我的程序的两个主要功能：
function moveAll() {
if (showingWinScreen) {
return;
}
computerMovement();
ballX += ballSpeedX;
ballY += ballSpeedY;
if (ballY <= 10) {
ballSpeedY = -ballSpeedY;
} else if (ballY >= HEIGHT - 10) {
ballSpeedY = -ballSpeedY;
}
if (ballX >= WIDTH - 10) {
if ((ballY > paddleY) && (ballY < paddleY + 100)) {
ballSpeedX = -ballSpeedX;
var deltaY = ballY - paddleY - 50;
ballSpeedY = deltaY / 5;
} else {
player1Score++;
ballReset();
}
} else if (ballX <= 10) {
if ((ballY > mouseY - 50) && (ballY < mouseY + 50)) {
ballSpeedX = -ballSpeedX;
deltaY = ballY - mouseY;
ballSpeedY = deltaY / 6;
} else {
player2Score++;
ballReset();
}
}
}
function drawAll() {
if (showingWinScreen) {
colorRect(0, 0, WIDTH, HEIGHT, "black");
canvas.fillStyle = "yellow";
canvas.fillText("Click to continue!", 300, 300);
if (player1Score == WINNING_SCORE) {
canvas.fillText("You won!", 360, 500);
} else if (player2Score == WINNING_SCORE) {
canvas.fillText("The computer beat you!", 280, 500);
}
return;
}
colorRect(0, 0, WIDTH, HEIGHT, "black");
drawNet();
makeCircle(ballX, ballY, 10, 0, Math.PI * 2, "red");
colorRect(790, paddleY, 10, 100, "cyan");
colorRect(0, mouseY - 50, 10, 100, "yellow");
canvas.fillStyle = "white";
canvas.fillText(player1Score + " " + player2Score, 360, 100);
}
谢谢你的帮助！
我认为只有一种情况会发生这种情况：当在碰撞帧中降低速度时。
当速度保持不变时，无论怎样，你的球都会弹回到前一帧的位置：
var cvs = document.querySelector("canvas");
var ctx = cvs.getContext("2d");
var balls = [
Ball(50, 50, 0, 5, 5, "red"),
Ball(100, 50, 0, 5, 10, "blue"),
Ball(150, 50, 0, 5, 15, "green"),
Ball(200, 50, 0, 5, 20, "yellow")
];
var next = () => {
updateFrame(balls);
drawFrame(balls);
}
var loop = () => {
requestAnimationFrame(() => {
next();
loop();
});
}
next();
function Ball(x, y, vx, vy, r, color) {
return {
x: x,
y: y,
vx: vx,
vy: vy,
r: r,
color: color
}
};
function updateBall(b) {
b.x += b.vx;
b.y += b.vy;
if (b.y <= b.r ||
b.y >= cvs.height - b.r) {
b.vy *= -1;
}
};
function drawBall(b) {
ctx.beginPath();
ctx.fillStyle = b.color;
ctx.arc(b.x, b.y, b.r, 0, 2 * Math.PI, false);
ctx.fill();
}
function updateFrame(balls) {
balls.forEach(updateBall);
}
function drawFrame(balls) {
ctx.clearRect(0, 0, cvs.width, cvs.height);
balls.forEach(drawBall);
};<canvas width="300" height="150" style="background: #454545"></canvas>
<button onclick="next()">next</button>
<button onclick="loop()">run</button>但当速度变化时，事情就会陷入困境：
var cvs = document.querySelector("canvas");
var ctx = cvs.getContext("2d");
var balls = [
Ball(50, 50, 0, 10, 5, "red"),
Ball(100, 50, 0, 10, 10, "blue"),
Ball(150, 50, 0, 10, 15, "green"),
Ball(200, 50, 0, 10, 20, "yellow")
];
var next = () => {
updateFrame(balls);
drawFrame(balls);
}
var loop = () => {
requestAnimationFrame(() => {
next();
loop();
});
}
next();
function Ball(x, y, vx, vy, r, color) {
return {
x: x,
y: y,
vx: vx,
vy: vy,
r: r,
color: color
}
};
function updateBall(b) {
b.x += b.vx;
b.y += b.vy;
if (b.y <= b.r ||
b.y >= cvs.height - b.r) {
b.vy *= -0.5;
}
};
function drawBall(b) {
ctx.beginPath();
ctx.fillStyle = b.color;
ctx.arc(b.x, b.y, b.r, 0, 2 * Math.PI, false);
ctx.fill();
}
function updateFrame(balls) {
balls.forEach(updateBall);
}
function drawFrame(balls) {
ctx.clearRect(0, 0, cvs.width, cvs.height);
balls.forEach(drawBall);
};<canvas width="300" height="150" style="background: #454545"></canvas>
<button onclick="next()">next</button>
<button onclick="loop()">run</button>在你的情况下，我认为只有当同时发生桨叶碰撞和墙壁碰撞时，才会发生这种情况
一个快速实现的解决方案是在平移球位置之前检查新位置是否有效。如果不需要精确的位置，可以将球放置在碰撞点。请注意，这将产生一个稍微偏离的框架。
例如：
var newY = ballY + ballSpeedY;
// Top wall
if(newY <= 10) {
ballY = 10;
ballSpeedY = -ballSpeedY;
}
// Bottom wall
else if(newY >= HEIGHT-10){
ballY = HEIGHT - 10;
ballSpeedY = -ballSpeedY;
}
// No collision
else {
ballY = newY;
}
更新：对可能发生的情况进行更详细的描述
假设你的球与画布的顶部边界碰撞，与同一帧中的球拍碰撞。
首先，将球移动到碰撞位置：ballY += ballSpeedY;假设ballY为4，ballSpeedY为-5，则将球定位到墙内的-1。
如果这是唯一的碰撞，你应该没事。你翻转速度(ballSpeedY = -ballSpeedY(，所以在下一帧中，你的球应该回到-1 + 5 = 4，所以ballY将再次成为4，你的球将在下一个帧中向4 + 5 = 9移动。
现在出现了一个问题，当在-1定位的框架中时，您也会与桨板碰撞！当球拍击球时，可以修改球速：ballSpeedY = deltaY / 5;。如果这是< 1，你的球将无法在下一帧中出墙。例如，您的球将移动到：-1 + 0.5 = -0.5，而不是-1 + 5 = 4。
现在，你的球将无法回到比赛中，因为下一帧将再次计算碰撞并翻转速度当球被卡住时，会产生弹性、颤抖的效果。
一个天真但相当不错的解决方案是，只将球的位置更新到有效的位置。也就是说：永远不要碰撞坐标。
var animate = window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame || function (callback) {
window.setTimeout(callback, 1000 / 60)
};
var canvas = document.createElement("canvas");
var width = 400;
var height = 600;
canvas.width = width;
canvas.height = height;
var context = canvas.getContext('2d');
var player = new Player();
var computer = new Computer();
var ball = new Ball(200, 300);
var keysDown = {};
var render = function () {
context.fillStyle = "#FF00FF";
context.fillRect(0, 0, width, height);
player.render();
computer.render();
ball.render();
};
var update = function () {
player.update();
computer.update(ball);
ball.update(player.paddle, computer.paddle);
};
var step = function () {
update();
render();
animate(step);
};
function Paddle(x, y, width, height) {
this.x = x;
this.y = y;
this.width = width;
this.height = height;
this.x_speed = 0;
this.y_speed = 0;
}
Paddle.prototype.render = function () {
context.fillStyle = "#0000FF";
context.fillRect(this.x, this.y, this.width, this.height);
};
Paddle.prototype.move = function (x, y) {
this.x += x;
this.y += y;
this.x_speed = x;
this.y_speed = y;
if (this.x < 0) {
this.x = 0;
this.x_speed = 0;
} else if (this.x + this.width > 400) {
this.x = 400 - this.width;
this.x_speed = 0;
}
};
function Computer() {
this.paddle = new Paddle(175, 10, 50, 10);
}
Computer.prototype.render = function () {
this.paddle.render();
};
Computer.prototype.update = function (ball) {
var x_pos = ball.x;
var diff = -((this.paddle.x + (this.paddle.width / 2)) - x_pos);
if (diff < 0 && diff < -4) {
diff = -5;
} else if (diff > 0 && diff > 4) {
diff = 5;
}
this.paddle.move(diff, 0);
if (this.paddle.x < 0) {
this.paddle.x = 0;
} else if (this.paddle.x + this.paddle.width > 400) {
this.paddle.x = 400 - this.paddle.width;
}
};
function Player() {
this.paddle = new Paddle(175, 580, 50, 10);
}
Player.prototype.render = function () {
this.paddle.render();
};
Player.prototype.update = function () {
for (var key in keysDown) {
var value = Number(key);
if (value == 37) {
this.paddle.move(-4, 0);
} else if (value == 39) {
this.paddle.move(4, 0);
} else {
this.paddle.move(0, 0);
}
}
};
function Ball(x, y) {
this.x = x;
this.y = y;
this.x_speed = 0;
this.y_speed = 3;
}
Ball.prototype.render = function () {
context.beginPath();
context.arc(this.x, this.y, 5, 2 * Math.PI, false);
context.fillStyle = "#000000";
context.fill();
};
Ball.prototype.update = function (paddle1, paddle2) {
this.x += this.x_speed;
this.y += this.y_speed;
var top_x = this.x - 5;
var top_y = this.y - 5;
var bottom_x = this.x + 5;
var bottom_y = this.y + 5;
if (this.x - 5 < 0) {
this.x = 5;
this.x_speed = -this.x_speed;
} else if (this.x + 5 > 400) {
this.x = 395;
this.x_speed = -this.x_speed;
}
if (this.y < 0 || this.y > 600) {
this.x_speed = 0;
this.y_speed = 3;
this.x = 200;
this.y = 300;
}
if (top_y > 300) {
if (top_y < (paddle1.y + paddle1.height) && bottom_y > paddle1.y && top_x < (paddle1.x + paddle1.width) && bottom_x > paddle1.x) {
this.y_speed = -3;
this.x_speed += (paddle1.x_speed / 2);
this.y += this.y_speed;
}
} else {
if (top_y < (paddle2.y + paddle2.height) && bottom_y > paddle2.y && top_x < (paddle2.x + paddle2.width) && bottom_x > paddle2.x) {
this.y_speed = 3;
this.x_speed += (paddle2.x_speed / 2);
this.y += this.y_speed;
}
}
};
document.body.appendChild(canvas);
animate(step);
window.addEventListener("keydown", function (event) {
keysDown[event.keyCode] = true;
});
window.addEventListener("keyup", function (event) {
delete keysDown[event.keyCode];
});
http://jsfiddle.net/kHJr6/2/
相关文章：
- 将视口底部滚动到元素底部
- HTML5页面底部棒
- 固定位置菜单时滚动，直到它击中一个相对容器的底部
- 将jQuery放在代码的底部
- javascript跨浏览器确定用户是否滚动到页面底部
- javascript移动交叉浏览器确定用户是否滚动到页面底部
- 如何将图表放在顶部和底部
- 如何摆脱"压缩/块”;PHP页面底部的注释
- 如果同一页面上有多个谷歌地图，单击任何标记都会突出显示最底部的地图标记
- 引导数据偏移量底部
- 如何防止firefox在打开大型弹出窗口时滚动到页面底部
- 滚动到顶部或底部后的简单效果
- 如何在java脚本中显示引导程序底部的pophover图像点击
- jQuery滚动到聊天框底部
- 如何仅在向上滚动时将页脚粘贴到窗口底部会导致页脚不显示
- 页面加载时自动滚动到底部
- 如何使一个元素从网页的顶部跳到底部再跳回到顶部
- 当滚动条到达容器底部时设置动画
- 在css中设置负底部属性会扩展页面的底部
- 为什么乒乓球会卡在底部
