Late last year, we decided to rewrite an important part of the Haiku app_server. Why was that? Let's start out with what the app_server is supposed to do: At the heart, it manages multiple applications simultaneously using the display device as a shared resource. Two of the important system objects through which this is organized are Windows and Views. Through views, the applications can draw information onto the screen, while a window is merely some sort of container for views. One big difference between the two is that, to a certain degree, all views within one window are expected to be self organized, while the windows themselves are organized by the server. The views form a tree-like hierarchy of parent and children views. It is expected, that all children of the same parent (sibling views) don't overlap. If they do, the space they share belongs to both of them, which will have strange results. Windows, on the other hand, are managed by the server. This is an important difference - more on that later. A window, in fact, doesn't care about other windows at all. The server simply tells a window which part of the screen it can draw into. This equals the window's visible part within the stack of windows on screen. This idea is called "clipping".
