Javascript HTML5画布分解图像

我的总体目标是制作一款滑动拼图游戏。使用画布，我成功地将图像分割成多个部分。为了洗牌，我将棋子的坐标写进一个数组，洗牌坐标，然后在画布上重新绘制图像。然而，拼图的最后是一些被复制的碎片！我不知道为什么

var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
var img=document.getElementById("map");




//img,sx,sy,swidth,sheight,x,y,width,height


function recreate_map(){

ctx.drawImage(img,0,0,133,100,0,0,133,100);
ctx.drawImage(img,133,0,133,100,133,0,133,100);
ctx.drawImage(img,266,0,133,100,266,0,133,100);

ctx.drawImage(img,0,100,133,100,0,100,133,100);
ctx.drawImage(img,133,100,133,100,133,100,133,100);
ctx.drawImage(img,266,100,133,100,266,100,133,100);

ctx.drawImage(img,0,200,133,100,0,200,133,100);
ctx.drawImage(img,133,200,133,100,133,200,133,100);
ctx.drawImage(img,266,200,133,100,266,200,133,100);
}


 function shuffle_array(arr){  
  var i = arr.length;

  while(--i>0){
    var n = Math.floor(Math.random()*(i));
    var temp = arr[n];
    arr[n] = arr[i];
    arr[i] = temp;
  } 

  return arr;
}



function shuffle_tiles(){
  var positions_x = [0,133,266,0,133,266,0,133,266];
  var positions_y = [0,0,0,100,100,100,200,200,200];

  shuffle_array(positions_x);
  shuffle_array(positions_y);



ctx.drawImage(img,0,0,133,100,positions_x[0],positions_y[0],133,100);
ctx.drawImage(img,133,0,133,100,positions_x[1],positions_y[1],133,100);
ctx.drawImage(img,266,0,133,100,positions_x[2],positions_y[2],133,100);
ctx.drawImage(img,0,100,133,100,positions_x[3],positions_y[3],133,100);
ctx.drawImage(img,133,100,133,100,positions_x[4],positions_y[4],133,100);
ctx.drawImage(img,266,100,133,100,positions_x[5],positions_y[5],133,100);
ctx.drawImage(img,0,200,133,100,positions_x[6],positions_y[6],133,100);
ctx.drawImage(img,133,200,133,100,positions_x[7],positions_y[7],133,100);
ctx.drawImage(img,266,200,133,100,positions_x[8],positions_y[8],133,100);  

}

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如果有用的话，我正在Firefox上使用JS-Bin。谢谢

每次重画都需要清除画布，否则之前的内容将保留

试试这个：

function recreate_map(){

    /// call this first
    ctx.clearRect(0, 0, c.width, c.height);

    ctx.drawImage(img,0,0,133,100,0,0,133,100);
    ...