如何使用核心图形创建横向和纵向模式？

I have an app that I created quite a while ago, on an iPad in Portrait mode; my users are now asking for Landscape mode also. My problem is that two of the pages are created using core graphics (CGRect etc) to draw the lines (horizontal and vertical) which work. This is an image of the first page:I have an app that I created quite a while ago,