Drawing Custom Borders in Windows Forms

I have split the code into two primary classes. First one, FormWithNonClientArea, extends the standard Form class by adding support for non-client area messages (more on this shortly) and can be uses for various scenarios. Second one, CustomBorderForm, utilizes these messages and represents a base class for drawing graphical borders composed of several bitmap parts. It also draws a form header including icon, text and form buttons (more on this later). This way I can separate dirty plumbing required for enabling non-client drawing and actual drawing of the graphical elements. So lets see how it works.