利用HTML5 Canvas制作一个简单的打飞机游戏

            }else {   
                var newd = new Date();   
                var tc = newd-this.dateCount;   
                if(tc>40){   
                    this.advance();   
                    this.dateCount = newd;   
                }   
            }   
            if(this.cellIndex<this.cells.length || this.isloop){   
                var cell = this.cells[this.cellIndex];   
                ctx.drawImage(this.spritesheet , cell.x , cell.y , cell.w , cell.h , sprite.left-sprite.width/2 , sprite.top-sprite.width/2 , cell.w , cell.h);   
            } else if(this.endCallback){   
                this.endCallback.call(sprite);   
                this.cellIndex = 0;   
            }   
        }   
    }   
  
    //特制飞机精灵表绘制器   
    W.controllSpriteSheetPainter = function(cells , spritesheet){   
        this.cells = cells || [];   
        this.cellIndex = 0;   
        this.dateCount = null;   
        this.isActive = false;   
        this.derection = true;