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html5游戏中移动背景的编程

51自学网 http://www.51zixue.net
移动背景
更改背景组件的speedX属性以使背景移动:
 
function updateGameArea() {
    myGameArea.clear();
    myBackground.speedX = -1
    myBackground.newPos(); 
    myBackground.update();
    myGamePiece.newPos(); 
    myGamePiece.update();
}
完整源代码:
<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>
canvas {
    border:1px solid #d3d3d3;
    background-color: #f1f1f1;
}
</style>

</head>
<body onload="startGame()">
<script>

var myGamePiece;
var myBackground;

function startGame() {
    myGamePiece = new component(30, 30, "smiley.gif", 10, 120, "image");
    myBackground = new component(656, 270, "citymarket.jpg", 0, 0, "image");
    myGameArea.start();
}

var myGameArea = {
    canvas : document.createElement("canvas"),
    start : function() {
        this.canvas.width = 480;
        this.canvas.height = 270;
        this.context = this.canvas.getContext("2d");
        document.body.insertBefore(this.canvas, document.body.childNodes[0]);
        this.frameNo = 0;
        this.interval = setInterval(updateGameArea, 20);
        },
    clear : function() {
        this.context.clearRect(0, 0, this.canvas.width, this.canvas.height);
    },
    stop : function() {
        clearInterval(this.interval);
    }
}

function component(width, height, color, x, y, type) {
    this.type = type;
    if (type == "image") {
        this.image = new Image();
        this.image.src = color;
    }
    this.width = width;
    this.height = height;
    this.speedX = 0;
    this.speedY = 0;    
    this.x = x;
    this.y = y;    
    this.update = function() {
        ctx = myGameArea.context;
        if (type == "image") {
            ctx.drawImage(this.image, 
                this.x, 
                this.y,
                this.width, this.height);
        } else {
            ctx.fillStyle = color;
            ctx.fillRect(this.x, this.y, this.width, this.height);
        }
    }
    this.newPos = function() {
        this.x += this.speedX;
        this.y += this.speedY;        
    }    
}

function updateGameArea() {
    myGameArea.clear();
    myBackground.speedX = -1;
    myBackground.newPos();    
    myBackground.update();
    myGamePiece.newPos();    
    myGamePiece.update();
}

function move(dir) {
    myGamePiece.image.src = "angry.gif";
    if (dir == "up") {myGamePiece.speedY = -1; }
    if (dir == "down") {myGamePiece.speedY = 1; }
    if (dir == "left") {myGamePiece.speedX = -1; }
    if (dir == "right") {myGamePiece.speedX = 1; }
}

function clearmove() {
    myGamePiece.image.src = "smiley.gif";
    myGamePiece.speedX = 0; 
    myGamePiece.speedY = 0; 
}
</script>
<div style="text-align:center;width:480px;">
  <button onmousedown="move('up')" onmouseup="clearmove()" ontouchstart="move('up')">UP</button><br><br>
  <button onmousedown="move('left')" onmouseup="clearmove()" ontouchstart="move('left')">LEFT</button>
  <button onmousedown="move('right')" onmouseup="clearmove()" ontouchstart="move('right')">RIGHT</button><br><br>
  <button onmousedown="move('down')" onmouseup="clearmove()" ontouchstart="move('down')">DOWN</button>
</div>

<p>The background image is 656px wide, and when it's over it's over.</p>
<p>You will learn how to make a infinite loop of the background in the next example.</p>

</body>
</html>
 

 
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