Question

我制作了以下HTML页面，该页面使用javascript在画布上打印红色方块，然后允许用户使用向上和向下键上下移动方块。

然而，经过多次尝试，我不确定如何打印可以随后移动的图像。（而不是我目前的红色方块）这是我需要帮助的部分。

以下是我可以使用密钥代码移动的红色方块的代码：

<!DOCTYPE html>

<html lang="en" xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta charset="utf-8" />
<title>Javascript game</title>
<style>
    canvas{

    }
</style>
</head>

<body>
<script>
    var WIDTH = 800, HEIGHT = 600;
    var context, keystate, canvas;
    var DownArrow = 40, UpArrow = 38;
    var square;

    square =
        {
            x: null,
            y: null,
            width: 200,
            height: 150,

            update: function()
            {
                if (keystate[UpArrow]) this.y -= 7;
                if (keystate[DownArrow]) this.y += 7;
            },

            draw: function()
            {
                context.fillRect(this.x,this.y,this.width,this.height);
            }
        }
    function main()
    {
        canvas = document.createElement('canvas');
        canvas.width = WIDTH;
        canvas.height = HEIGHT;
        context = canvas.getContext("2d");
        document.body.appendChild(canvas);

        keystate = {};
        document.addEventListener("keydown", function (e) {
            keystate[e.keyCode] = true;
        });

        document.addEventListener("keyup", function (e) {
            delete keystate[e.keyCode];
        });

        init();

        var anim = function()
        {
            update();
            draw();

            window.requestAnimationFrame(anim,canvas);
        }
        window.requestAnimationFrame(anim,canvas);

    }

    function init()
    {
        square.x = WIDTH / 2;
        square.y = HEIGHT / 2;
    }

    function update()
    {
        square.update();
    }

    function draw()
    {
        context.fillRect(0, 0, WIDTH, HEIGHT);

        context.save();

        context.fillStyle = "#f00";

        square.draw();

        context.restore();
    }

    main();

</script>
</body>
</html>

非常感谢帮助，谢谢！：）

Answer 1

您可以加载如下图像：

var img=new Image();
img.onload=function(){
    init();
}
img.src='sun.png';

让图像有时间加载......这是img.onload的全部内容，这一点非常重要。只有在图像完全加载并准备好使用后才会调用onload函数。

加载完图片后，您只需将context.drawImage替换为context.fillRect即可获得可移动图片。

祝你好运，这里是示例代码和演示：

＆＃13;

var WIDTH = 800, HEIGHT = 600;
var context, keystate, canvas;
var DownArrow = 40, UpArrow = 38;
var square;

// create a new image object
var img=new Image();
// tell the image to call init() after it's fully loaded
img.onload=function(){
  init();
}
// tell the image where to get its source
img.src='https://dl.dropboxusercontent.com/u/139992952/multple/sun.png';


square =
  {
  x: null,
  y: null,
  width: 200,
  height: 150,

  update: function()
  {
    if (keystate[UpArrow]) this.y -= 7;
    if (keystate[DownArrow]) this.y += 7;
  },

  draw: function()
  {

    // draw the image instead of the rectangle
    //                context.fillRect(this.x,this.y,this.width,this.height);

    context.drawImage(img,this.x,this.y);
  }
}
function main()
{
  canvas = document.createElement('canvas');
  canvas.width = WIDTH;
  canvas.height = HEIGHT;
  context = canvas.getContext("2d");
  document.body.appendChild(canvas);

  keystate = {};
  document.addEventListener("keydown", function (e) {
    keystate[e.keyCode] = true;
  });

  document.addEventListener("keyup", function (e) {
    delete keystate[e.keyCode];
  });

  // Now this is done after the image has fully loaded
  //        init();

  var anim = function()
  {
    update();
    draw();

    window.requestAnimationFrame(anim,canvas);
  }
  window.requestAnimationFrame(anim,canvas);

}

function init()
{
  square.x = WIDTH / 2;
  square.y = HEIGHT / 2;
}

function update()
{
  square.update();
}

function draw()
{

  context.fillRect(0, 0, WIDTH, HEIGHT);

  context.save();

  context.fillStyle = "#f00";

  square.draw();

  context.restore();
}

main();

＆＃13;

如何移动画布图像

1 个答案: