Getting display origin

[David Reitter]

Hi,

could someone tell me how to get the origin of the display?
I'm asking because on the Mac port (Carbon, not X11), the x-ordinates  
can easily become negative.
I've checked for some display-pixel-* function, and I've tried Google.

What I need to know is what the available range of coordinates are  
that are visible on the current display. I can get the width with  
display-pixel-width, but at least on the Mac, it doesn't always start  
at 0. For example, (frame-parameter (selected-frame) 'left) can  
return something like (+ -1045) if the frame in question is on the  
left screen of a multi-screen setup (with the menu bar = origin on  
the right).

Thanks
Dave