//检查左边界,尝试着朝左边移动一个,看是否合法。
function checkLeftBorder(){ 
  for(var i=0; i<activeBlock.length; i++){ 
    if(activeBlock[i].y==0){ 
      return false; 
    } 
    if(!isCellValid(activeBlock[i].x, activeBlock[i].y-1)){ 
      return false; 
    } 
  } 
  return true; 
} //同理，需要检测右边界和底边界

//开始 
function begin(e){ 
  e.disabled = true; 
  status = 1; 
  tbl = document.getElementById("area"); 
  if(!generateBlock()){ 
    alert("Game over!"); 
    status = 2; 
    return; 
  } 
  paint(); 
  timer = setInterval(moveDown,1000); 
} 
document.onkeydown=keyControl;

//当前活动的方块, 它可以左右下移动, 变型。当它触底后, 将会更新area; 
var activeBlock; 
//生产方块形状, 有7种基本形状。 
function generateBlock(){ 
  activeBlock = null; 
  activeBlock = new Array(4); 
  //随机产生0-6数组，代表7种形态。
  var t = (Math.floor(Math.random()*20)+1)%7; 
  switch(t){ 
    case 0:{ 
      activeBlock[0] = {x:0, y:4}; 
      activeBlock[1] = {x:1, y:4}; 
      activeBlock[2] = {x:0, y:5}; 
      activeBlock[3] = {x:1, y:5}; 

      break; 
    } 
    //省略部分代码..............................
    case 6:{ 
      activeBlock[0] = {x:0, y:5}; 
      activeBlock[1] = {x:1, y:4}; 
      activeBlock[2] = {x:1, y:5}; 
      activeBlock[3] = {x:1, y:6}; 
      break; 
    } 
  } 
  //检查刚生产的四个小方格是否可以放在初始化的位置. 
  for(var i=0; i<4; i++){ 
    if(!isCellValid(activeBlock[i].x, activeBlock[i].y)){ 
        return false; 
      } 
    } 
  return true; 
}

//消行 
function deleteLine(){ 
  var lines = 0; 
  for(var i=0; i<18; i++){ 
    var j=0; 
    for(; j<10; j++){ 
      if(area[i][j]==0){ 
        break; 
    } 
  } 
  if(j==10){ 
    lines++; 
    if(i!=0){ 
      for(var k=i-1; k>=0; k--){ 
        area[k+1] = area[k]; 
      } 
    } 
    area[0] = generateBlankLine(); 
    } 
  } 
  return lines; 
}