197 lines
4.7 KiB
HTML
197 lines
4.7 KiB
HTML
<!DOCTYPE html>
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<html>
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<head>
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<title></title>
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<style>
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html, body {
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height: 100%;
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margin: 0;
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}
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body {
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background: black;
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display: flex;
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align-items: center;
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justify-content: center;
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}
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</style>
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</head>
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<body>
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<canvas width="750" height="585" id="game"></canvas>
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<script>
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const canvas = document.getElementById('game');
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const context = canvas.getContext('2d');
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const grid = 15;
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const paddleHeight = grid * 5; // 80
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const maxPaddleY = canvas.height - grid - paddleHeight;
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var paddleSpeed = 6;
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var ballSpeed = 5;
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const leftPaddle = {
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// start in the middle of the game on the left side
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x: grid * 2,
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y: canvas.height / 2 - paddleHeight / 2,
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width: grid,
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height: paddleHeight,
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// paddle velocity
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dy: 0
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};
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const rightPaddle = {
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// start in the middle of the game on the right side
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x: canvas.width - grid * 3,
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y: canvas.height / 2 - paddleHeight / 2,
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width: grid,
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height: paddleHeight,
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// paddle velocity
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dy: 0
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};
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const ball = {
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// start in the middle of the game
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x: canvas.width / 2,
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y: canvas.height / 2,
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width: grid,
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height: grid,
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// keep track of when need to reset the ball position
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resetting: false,
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// ball velocity (start going to the top-right corner)
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dx: ballSpeed,
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dy: -ballSpeed
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};
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// check for collision between two objects using axis-aligned bounding box (AABB)
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// @see https://developer.mozilla.org/en-US/docs/Games/Techniques/2D_collision_detection
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function collides(obj1, obj2) {
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return obj1.x < obj2.x + obj2.width &&
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obj1.x + obj1.width > obj2.x &&
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obj1.y < obj2.y + obj2.height &&
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obj1.y + obj1.height > obj2.y;
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}
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// game loop
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function loop() {
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requestAnimationFrame(loop);
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context.clearRect(0,0,canvas.width,canvas.height);
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// move paddles by their velocity
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leftPaddle.y += leftPaddle.dy;
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rightPaddle.y += rightPaddle.dy;
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// prevent paddles from going through walls
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if (leftPaddle.y < grid) {
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leftPaddle.y = grid;
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}
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else if (leftPaddle.y > maxPaddleY) {
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leftPaddle.y = maxPaddleY;
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}
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if (rightPaddle.y < grid) {
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rightPaddle.y = grid;
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}
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else if (rightPaddle.y > maxPaddleY) {
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rightPaddle.y = maxPaddleY;
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}
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// draw paddles
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context.fillStyle = 'white';
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context.fillRect(leftPaddle.x, leftPaddle.y, leftPaddle.width, leftPaddle.height);
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context.fillRect(rightPaddle.x, rightPaddle.y, rightPaddle.width, rightPaddle.height);
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// move ball by its velocity
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ball.x += ball.dx;
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ball.y += ball.dy;
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// prevent ball from going through walls by changing its velocity
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if (ball.y < grid) {
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ball.y = grid;
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ball.dy *= -1;
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}
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else if (ball.y + grid > canvas.height - grid) {
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ball.y = canvas.height - grid * 2;
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ball.dy *= -1;
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}
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// reset ball if it goes past paddle (but only if we haven't already done so)
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if ( (ball.x < 0 || ball.x > canvas.width) && !ball.resetting) {
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ball.resetting = true;
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// give some time for the player to recover before launching the ball again
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setTimeout(() => {
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ball.resetting = false;
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ball.x = canvas.width / 2;
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ball.y = canvas.height / 2;
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}, 400);
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}
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// check to see if ball collides with paddle. if they do change x velocity
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if (collides(ball, leftPaddle)) {
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ball.dx *= -1;
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// move ball next to the paddle otherwise the collision will happen again
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// in the next frame
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ball.x = leftPaddle.x + leftPaddle.width;
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}
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else if (collides(ball, rightPaddle)) {
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ball.dx *= -1;
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// move ball next to the paddle otherwise the collision will happen again
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// in the next frame
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ball.x = rightPaddle.x - ball.width;
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}
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// draw ball
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context.fillRect(ball.x, ball.y, ball.width, ball.height);
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// draw walls
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context.fillStyle = 'lightgrey';
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context.fillRect(0, 0, canvas.width, grid);
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context.fillRect(0, canvas.height - grid, canvas.width, canvas.height);
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// draw dotted line down the middle
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for (let i = grid; i < canvas.height - grid; i += grid * 2) {
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context.fillRect(canvas.width / 2 - grid / 2, i, grid, grid);
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}
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}
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// listen to keyboard events to move the paddles
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document.addEventListener('keydown', function(e) {
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// up arrow key
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if (e.which === 38) {
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rightPaddle.dy = -paddleSpeed;
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}
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// down arrow key
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else if (e.which === 40) {
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rightPaddle.dy = paddleSpeed;
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}
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// w key
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if (e.which === 87) {
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leftPaddle.dy = -paddleSpeed;
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}
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// a key
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else if (e.which === 83) {
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leftPaddle.dy = paddleSpeed;
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}
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});
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// listen to keyboard events to stop the paddle if key is released
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document.addEventListener('keyup', function(e) {
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if (e.which === 38 || e.which === 40) {
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rightPaddle.dy = 0;
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}
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if (e.which === 83 || e.which === 87) {
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leftPaddle.dy = 0;
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}
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});
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// start the game
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requestAnimationFrame(loop);
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</script>
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</body>
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</html> |