code: function(){
  		var g = this.vinc('background', 'crispEdges', true);
  		var bw = this.bw, bh = this.bh, fm = this.flushmargin;
  		var bd = this.board;
  		var minbx   = bd.minbx - fm;
  		var minby   = bd.minby - fm;
  		var bwidth  = bd.maxbx + fm - minbx;
  		var bheight = bd.maxby + fm - minby;
  
  		g.vid = "BG";
  		g.fillStyle = this.bgcolor;
  		g.fillRect(minbx*bw-0.5, minby*bh-0.5, bwidth*bw+1, bheight*bh+1);
  	}
docs: --------------------------------------------------------------------------- pc.flushCanvas()    指定された領域を白で塗りつぶす ---------------------------------------------------------------------------