That’s the way it’s called in Windows, sorry if I use different term. I want to make a window that looks like that:

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In code:
Modify the window’s style mask with
setStyleMask:includingNSTexturedBackgroundWindowMaskin there (look for “Window Style Mask” constants in the docs for other constant that can go in the style mask). If you are creating a new window, useinitWithContentRect:styleMask:backing:defer:similarly.In Interface Builder:
Select the window you want, go to the fourth tab from the left in the inspector and check the “Textured” checkbox.