Mac Forum / Programming / Mac Programming / May 2005

I now next to nothing about Carbon or OpenGL, but the general idea is to
simply create a new, see through, window and draw on that. You can set
the window's 'level' depending on wether it should be behind all
application windows (desktoplevel +1) or in front of all applications.
And you may want to set the click-through behaviour of your window, to
make it pass all mouse clicks to the window underneeth (ultimately the
desktop itself).

patrick

You have a couple of misconceptions regarding windowing.

None of the stuff you mention is "drawing directly to the desktop", a
phrase which has basically no meaning on Mac OS X. Everything you see on
your screen on Mac OS X is in a window. This includes all of the obvious
windows, but also things like the menu bar, the Dock, tooltips, menus, the
translucent volume-change notifiers, and your examples of the application
switcher and expose's screen edges.

A window on OS X can contain arbitrary contents, including transparency,
and you can set its level to put it anywhere from the actual Finder
Desktop level (behind everything) up to the screensaver level (in front of
everything). You can use OpenGL to draw into a window and have the
generated transparency make the window show through to the contents
underneath, so there really are no "restrictions of a window" such as you
mention.

As far as programming it goes, just make a window without any decorations
(title bar, etc.) and go to town. I don't know how you do this in Carbon,
but it's trivial in Cocoa and I can't imagine Carbon is much harder.

CreateNewWindow (kOverlayWindowClass, ...)