利用HTML5 Canvas制作一个简单的打飞机游戏

        this.spritesheet = spritesheet;   
    }   
    controllSpriteSheetPainter.prototype = {   
        advance:function(){   
            if(this.isActive){   
                this.cellIndex++;   
                if(this.cellIndex === this.cells.length){   
                    this.cellIndex = 0;   
                    this.isActive = false;   
                }   
            }   
        },   
        paint:function(sprite){   
            if(this.dateCount===null){   
                this.dateCount = new Date();   
            }else {   
                var newd = new Date();   
                var tc = newd-this.dateCount;   
                if(tc>sprite.firePerFrame){   
                    this.advance();   
                    this.dateCount = newd;   
                }   
            }   
            var cell = this.cells[this.cellIndex];   
            ctx.drawImage(this.spritesheet , cell.x , cell.y , cell.w , cell.h , -planWidth/2 , -planHeight/2 , cell.w , cell.h);