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Mac: (x-)display-screens or x-display-list

From: David Reitter
Subject: Mac: (x-)display-screens or x-display-list
Date: Fri, 10 Jun 2005 22:16:26 +0100

On the Mac, a multi-screen setup is problematic for (Carbon) Emacs.

x-display-screens is hard-coded to return 1, and it seems like (x- display-list) also only returns a list of one element.

The code (macterm.c) says "This is display since Mac does not support multiple ones."

Therefore, it would make sense to have x-display-screens return the true number of screens that are running. That would also imply that display-pixel-width/height would have to return the total dimensions of the usable screen area, and that there is a function that gives the coordinates of the left upper corner of the total screen area. If I have my main screen on the right, and an additional one to the left, x ordinates can range from -1280 to +768. (That illustrates that each screen may have different dimensions.) Currently, the width/height functions return only the dimensions of the 'main' screen. One deficiency of this method is that the single screens have different dimensions, and the usable total screen area is not usually rectangular.

Alternative: If we take the term 'display' a little more literally, then x-display-screens should indeed return the true number of screens (disp_count in mac_initialize_display_info), and display- (pixel)-height/width should return the appropriate dimensions for the different screens. However, when positioning a frame, for example, I wouldn't know what coordinates I'm allowed to use that way, since I don't know how screens map to coordinates. So I'd probably find the first option more practical.

It seems like the Windows port has trouble, too.

Maybe I'm misunderstanding the way screens/displays are meant to work - please let me know.


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