Drawing Lines between mdi child forms

IMO you are making life harder for yourself than it needs to be by using MDI and Child Forms.

If your application is the 'standard' genealogy type then it is very similar to a UML, Class Diagram or Organization Chart application, just the information contained in the 'boxes' will be different.

Might I suggest that you search for Open Source versions of any of that type of program. e.g. StarUML[^] (there are loads more out there).

Have a look at a few to see how they do it and pick the bits that make the most sense to you.

This design is a very common mistake. In principle, it may be even feasible, but I knew so many attempts to complete the application or component base on similar (actually a bit better) ideas — all failed.

There are two approaches which work. In both cases, you should not use any controls (not even windows or forms) as graphics elements. Maybe it seems to you they already have intrinsic functionality you need, but this is wrong. Just the opposite, they have functionality which will make you lost on unneeded complexity.

1) Use light-weight approach. Create all graphics primitive in one control. You need to render all graphics in the handler of Control.Paint of overridden method Control.OnPaint. For rendering, use the instance of System.Drawing.Graphics supplied in the event arguments parameter (in both cases). To change image, use Control.Invalidate. For better performance, use Control.Invalidate with a parameter (Rectangle or Region), to invalidate just a part of the scene.

2) Use WPF. You don't need to do any rendering at all. Instead, you should use Canvas and put graphical primitives (such as lines, rectangles, etc., but you can put controls as well) on the canvas. This is really simple. You can even draw primitives in a vector editor, import vector graphics as XAML, put the saved XAML code to resource dictionary and reuse on your canvas. I recommend using wonderful Open Source editor InkScape.

Final note. There are no situations when MDI can be used. This is one of the most unsuccessful inventions my Microsoft. MDI is strongly discourages even by Microsoft. There are no solid software products or even products with acceptable quality using MDI. You would simply scare off your customers if you use it. The simplest nice alternative is tabbed interface, based on TabControl.

—SA