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html游戏编程如何使用图像?

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 如何使用图像?

要在画布上添加图像,getContext(“2d”)对象具有内置的图像属性和方法。
 
在我们的游戏中,为了创建gamepiece作为一个图像,可以使用组件构造函数,而不是引用颜色,你必须参考图像的url。 你必须告诉构造函数这个组件的类型是“image”:

Example

function startGame() {
  myGamePiece = new component(3030"smiley.gif"10120"image");
  myGameArea.start();
}

在组件构造函数中,我们测试组件是否为“image”类型,并通过使用内置的“新Image()”对象构造函数创建一个图像对象。 当我们准备绘制图像时,我们使用drawImage方法而不是fillRect方法:

Example

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);
    }
  }
}
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;

function startGame() {
    myGamePiece = new component(30, 30, "smiley.gif", 10, 120, "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();
    myGamePiece.newPos();
    myGamePiece.update();
}

function moveup() {
    myGamePiece.speedY = -1; 
}

function movedown() {
    myGamePiece.speedY = 1; 
}

function moveleft() {
    myGamePiece.speedX = -1; 
}

function moveright() {
    myGamePiece.speedX = 1; 
}

function clearmove() {
    myGamePiece.speedX = 0; 
    myGamePiece.speedY = 0; 
}
</script>
<div style="text-align:center;width:480px;">
  <button onmousedown="moveup()" onmouseup="clearmove()" ontouchstart="moveup()">UP</button><br><br>
  <button onmousedown="moveleft()" onmouseup="clearmove()" ontouchstart="moveleft()">LEFT</button>
  <button onmousedown="moveright()" onmouseup="clearmove()" ontouchstart="moveright()">RIGHT</button><br><br>
  <button onmousedown="movedown()" onmouseup="clearmove()" ontouchstart="movedown()">DOWN</button>
</div>

<p>组件构造函数使用内置的图像对象将图像绘制到画布上。.</p>

</body>
</html>
查看效果>>

 
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