我這里clip使用后存在性能問(wèn)題，不知道為何，clip前后上下文狀態(tài)我也存貯并且恢復(fù)了的，頁(yè)面剛打開(kāi)時(shí)，很流暢，多點(diǎn)幾次，慢慢的就會(huì)變的有點(diǎn)兒卡頓

下面是放大鏡繪制

function?drawEnlarge(isShow,?x,?y)?{
	drawImg();
	if?(isShow)?{
		var?sx?=?x?/?CAN_WIDTH?*?img.width?-?OFF_WIDTH/2?*?OFF_SCALE;
		var?sy?=?y?/?CAN_HEIGHT?*?img.height?-?OFF_HEIGHT/2?*?OFF_SCALE;
		var?sw?=?OFF_WIDTH?*?OFF_SCALE;
		var?sh?=?OFF_HEIGHT?*?OFF_SCALE;

		ctx_off.save();
		ctx_off.strokeStyle?=?'#3969c4'
		ctx_off.strokeWidth?=?3;
		ctx_off.arc(OFF_WIDTH/2,OFF_HEIGHT/2,OFF_WIDTH/2,0,2*Math.PI);
		ctx_off.stroke();
		ctx_off.clip();
		ctx_off.drawImage(img,sx,sy,sw,sh,0,0,OFF_WIDTH,OFF_HEIGHT);
		ctx.drawImage(can_off,x-OFF_WIDTH/2,y-OFF_HEIGHT/2,OFF_WIDTH,OFF_HEIGHT);
		ctx_off.restore();

	}
}