The Quartz Debug application is part of Apple's developer tools. It is a very useful tool to see where redrawing is going on in your application (the whole screen in fact), thus making it easier to find inefficiencies. Playing around with Quartz Debug, I discovered the following three things.
To begin with, Quartz isn't only neat and all but it's actually the graphics engine with a built-in speedometer: Choose 'Show Frame Meter' in Quartz Debug's menu and you'll get a nice speed gauge that also displays CPU load. Sp get your dicks out and start benchmarking.
Secondly, using the window list provided by Quartz Debug, you can't only get every single window listed but you can also double click any row in it to make the window in question flash softly in order to indicate which window it is.
This, for example, shows you that every application owns its menu bar as a separate window. It also shows (or reminds) us that while the menu bar belongs to the application, the right hand side of the menu bar belongs to SystemUIServer – possibly explaining the curious-to-annoying fact that while clicking on a regular menu item and then moving to the Clock's menu, say, with the mouse button pressed will work just fine, doing it the other way round won't open a menu item for you and you'll have to click the mouse again.
Thirdly, it becomes apparent, that all the icons on the Dock as well as the Finder's desktop icons are each a separate window of their own. This may hint for the cause of Dock's speedy smoothness, picking up the rumors about OSX's clever graphics handling that were around right from the beginning – and that I've always failed to see confirmation about.
It's interesting to see what happens when a window is minimised to the Dock. It will remain the application's window all the way through the minimisation process but then the original window is hidden and the Dock makes its own window for the minimised window's thumbnail icon. Quite strange. In particular, when considering that the Window manager is be clever enough to realise the Dock isn't running anymore and show the minimised windows again in that situation.
Seeing the gratuitous juggling of many tiny windows should also quiet those people who claim that OSX's window manager is slow – a claim that I have seen around quite a few times and that was triggered by the fact that bringing an application with many windows to the front may take surprisingly / embarrassingly long. I still wonder why that happens. Perhaps that thing with the compression of hidden windows could be at work here? I don't know.
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