2.5 Aligning Multiple Drawables

A client can create one window with an overlay Visual and a second with a main plane Visual and then move them independently or in concert to keep them aligned. This is a major change between the OpenGL and the previous SGI proprietary GL: allocation of overlay planes and main planes for every window is no longer done automatically. To accomplish what was done by a drawmode/ gconfig pair in previous versions of the SGI proprietary GL, the OpenGL client can use the following paradigm:

• Make the windows which are to share the same screen area children of a single window (that will never be written). Size and position the children to completely occlude their parent. When the window combination must be moved or resized, perform the operation on the parent.
• Make the subwindows have a background of None so that the X server will not paint into the shared area when you restack the children.
• Select for device-related events on the parent window, not on the children. Since device-related events with the focus in one of the child windows will be inherited by the parent, input dispatching can be done directly without reference to the child on top.