Question

我正在为我的JavaScript Breakout游戏制作开始屏幕。我（差劲地）设置了背景和播放按钮。

背景是我想要的画布内。但是，当我要将可单击的播放按钮放在画布中背景的顶部时，它消失了。我尝试制作另一张照片，然后将其放置在上面，但我无法使其可点击。

我不知道最好的解决方案是什么，我对JavaScript还是很陌生。

//Script
var background = new Image();
    background.src="breakoutbg.png";
var play = new Image();
    play.src="breaoutplay.png";

var startBtn = document.getElementById('startBtn');

//game
function drawCanvas() {
    ctx.beginPath();
    ctx.drawImage(background,0,0);
    ctx.fill();
    ctx.closePath();

}

function drawPlay() {
    ctx.beginPath();
    ctx.drawImage(play,250,250);
    ctx.fill();clickable;
    ctx.closePath();
}

<div id="container">
    <button type="button" id="startBtn" onclick="draw()" >
        <img src="breaoutplay.png">
    </button>
     <canvas id="myCanvas" width="600" height="550"></canvas>
</div>

我不知道我是否给出了足够的代码，以便有人对此有所了解。整个代码在github上：https://github.com/katrinemira/katrinemira.github.io/blob/master/breakout.html

Answer 1

将此添加到我们的CSS

#container {
  display: inline-block;
  position: relative;
}            
#startBtn {
  border: none;
  background: none;
  position: absolute;
  top: 50%;
  left: 50%;
  z-index: 1;
  transform: translate(-50%,-50%);
  -webkit-transform: translate(-50%,-50%);
  -moz-transform: translate(-50%,-50%);
  -ms-transform: translate(-50%,-50%);
}

上面的代码会将按钮放在中间的画布上。还将z-index: 1;添加到按钮上，以将其放置在画布顶部

<html>

<head>
  <center>
    <style>
      body {
        background-color: black;
      }          
      * {
        padding: 0;
        margin: 0;
      }          
      canvas {
        background: #353d49;
        display: block;
        margin: 100px;
      }          
      #startBtn {
        border: none;
        background: none;
        position: absolute;
        top: 50%;
        left: 50%;
        z-index: 1;
        transform: translate(-50%,-50%);
        -webkit-transform: translate(-50%,-50%);
        -moz-transform: translate(-50%,-50%);
        -ms-transform: translate(-50%,-50%);
      }          
      #container {
        display: inline-block;
        position: relative;
      }          
      #myCanvas {
        position: relative;
      }
    </style>
</head>

<body>

  <div id="container">
    <button type="button" id="startBtn" onclick="draw()"><img src="https://1.bp.blogspot.com/-fVAKH-3TLuo/W5onDDHje0I/AAAAAAAAB4I/q2ooE6GuzQkS80dtw1JILXjFWdfQ3IKkwCLcBGAs/s1600/breaoutplay.png">
    </button>
    <canvas id="myCanvas" width="600" height="550"></canvas>
  </div>


  <script>
    var canvas = document.getElementById("myCanvas");
    var ctx = canvas.getContext("2d");
    var ballRadius = 9;
    var x = canvas.width - Math.floor(Math.random() * 600)
    var y = canvas.height - 30;
    var dx = 5;
    var dy = -4;
    var paddleHeight = 10;
    var paddleWidth = 75;
    var paddleX = (canvas.width - paddleWidth) / 2;
    var rightPressed = false;
    var leftPressed = false;
    var brickRowCount = 7;
    var brickColumnCount = 5;
    var brickWidth = 75;
    var brickHeight = 20;
    var brickPadding = 4;
    var brickOffsetTop = 30;
    var brickOffsetLeft = 30;
    var score = 0;
    var lives = 3;
    var background = new Image();
    background.src = "https://1.bp.blogspot.com/-hs2fckXJBkE/W5obuBm9kII/AAAAAAAAB38/C89KFBJCIlEwfl-g8d-T1Cu4cHFWjYI2QCLcBGAs/s1600/breakoutbg.png";
    var play = new Image();
    play.src = "https://1.bp.blogspot.com/-fVAKH-3TLuo/W5onDDHje0I/AAAAAAAAB4I/q2ooE6GuzQkS80dtw1JILXjFWdfQ3IKkwCLcBGAs/s1600/breaoutplay.png";

    var startBtn = document.getElementById('startBtn');

    //game
    function drawCanvas() {
      ctx.beginPath();
      ctx.drawImage(background, 0, 0);
      ctx.fill();
      ctx.closePath();

    }

    function drawPlay() {
      ctx.beginPath();
      ctx.drawImage(play, 250, 250);
      ctx.fill();
      clickable;
      ctx.closePath();

    }

    function newBrick() {
      return {
        x: 0,
        y: 0,
        status: 1
      };

    }

    var bricks = [];
    for (var c = 0; c < brickColumnCount; c++) {
      bricks[c] = [];
      for (var r = 0; r < brickRowCount; r++) {
        bricks[c].unshift(newBrick());
      }
    }

    document.addEventListener("keydown", keyDownHandler, false);
    document.addEventListener("keyup", keyUpHandler, false);
    document.addEventListener("mousemove", mouseMoveHandler, false);

    function keyDownHandler(e) {
      if (e.keyCode == 39) {
        rightPressed = true;
      } else if (e.keyCode == 37) {
        leftPressed = true;
      }
    }

    function keyUpHandler(e) {
      if (e.keyCode == 39) {
        rightPressed = false;
      } else if (e.keyCode == 37) {
        leftPressed = false;
      }
    }

    function mouseMoveHandler(e) {
      var relativeX = e.clientX - canvas.offsetLeft;
      if (relativeX > 0 && relativeX < canvas.width) {
        paddleX = relativeX - paddleWidth / 2;
      }
    }

    function collisionDetection() {
      for (var c = 0; c < brickColumnCount; c++) {
        for (var r = 0; r < brickRowCount; r++) {
          var b = bricks[c][r];
          if (b.status == 1) {
            if (x > b.x && x < b.x + brickWidth + ballRadius && y > b.y && y < b.y + brickHeight + ballRadius) {
              dy = -dy;
              b.status = 0;
              score++;
              if (score == 9999) {
                alert("YOU WIN, CONGRATS!");
                document.location.reload();
              }
            }
          }
        }
      }
    }

    function drawBall() {
      ctx.beginPath();
      ctx.arc(x, y, ballRadius, 0, Math.PI * 2);
      ctx.fillStyle = "#0095DD";
      ctx.fill();
      ctx.closePath();
    }

    function drawPaddle() {
      ctx.beginPath();
      ctx.rect(paddleX, canvas.height - paddleHeight, paddleWidth, paddleHeight);
      ctx.fillStyle = "#0095DD";
      ctx.fill();
      ctx.closePath();
    }

    function moreBricks() {
      bricks.unshift([]);
      newBrick();
      brickColumnCount++;
      for (r = 0; r < brickRowCount; r++) {
        bricks[0].unshift(newBrick());
      }
    }

    function drawBricks() {
      for (var c = 0; c < brickColumnCount; c++) {
        for (var r = 0; r < brickRowCount; r++) {
          if (bricks[c][r].status == 1) {
            var brickX = (r * (brickWidth + brickPadding)) + brickOffsetLeft;
            var brickY = (c * (brickHeight + brickPadding)) + brickOffsetTop;
            bricks[c][r].x = brickX;
            bricks[c][r].y = brickY;
            ctx.beginPath();
            ctx.rect(brickX, brickY, brickWidth, brickHeight);
            ctx.fillStyle = "#0095DD";
            ctx.fill();
            ctx.closePath();
          }
        }
      }
    }

    function drawScore() {
      ctx.font = "16px Arial";
      ctx.fillStyle = "#0095DD";
      ctx.fillText("Score: " + score, 8, 20);
    }

    function drawLives() {
      ctx.font = "16px Arial";
      ctx.fillStyle = "#0095DD";
      ctx.fillText("Lives: " + lives, canvas.width - 65, 20);
    }

    var frameCount = 0;
    const FRAME_COUNT_NEW_LINE = 500;

    function draw() {
      ctx.clearRect(0, 0, canvas.width, canvas.height);
      startBtn.style.display = 'none';

      frameCount += 1;
      if (frameCount === FRAME_COUNT_NEW_LINE) {
        frameCount = 0;
        moreBricks();
      }

      drawBricks();
      drawBall();
      drawPaddle();
      drawScore();
      drawLives();
      collisionDetection();

      if (x + dx > canvas.width - ballRadius || x + dx < ballRadius) {
        dx = -dx;
      }
      if (y + dy < ballRadius) {
        dy = -dy;
      } else if (y + dy > canvas.height - ballRadius) {
        if (x > paddleX && x < paddleX + paddleWidth) {
          dy = -dy;
        } else {
          lives--;
          if (!lives) {

            document.location.reload();
          } else {
            x = canvas.width - Math.floor(Math.random() * 600);
            y = canvas.height - 30;
            dx = 5;
            dy = -4;
            paddleX = (canvas.width - paddleWidth) / 2;
          }
        }
      }

      if (rightPressed && paddleX < canvas.width - paddleWidth) {
        paddleX += 7;
      } else if (leftPressed && paddleX > 0) {
        paddleX -= 7;
      }

      x += dx;
      y += dy;
      requestAnimationFrame(draw);
    }
    drawCanvas();
    drawPlay();
  </script>

</body>

</html>

Javascript游戏的“开始”屏幕/“可单击的播放”按钮

1 个答案: