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[OCLUG-Tech] PPI or DPI on the viewable screen ?

Hi;

I have the following information about my monitor:

]$ monitor-edid => 86 dpi, & Maximum Image Size in centimetres (below) 


        Maximum Image Size (cm)		H = 49.4;	V = 32.0
        Viewable (cm)			H = 47.2;	V = 29.6
        
        Maximum Image Size (in)		H = 19.4; 	V = 12.6
        Viewable (inches)		H = 18.6;	V = 11.7

The conversion from cm to inches is mine.  The viewable size is also
mine using a ruler to measure exactly how much of the screen I can see,
with monitor borders excluded.

My question is simple.  When calculating for things like window
placement etc. is the DPI/PPI squeezed into the viewable area or do
subtract the missing pixels to calculate screen position?

Posed another way, are the pixels counted based on the Maximum Image
Size, or on viewable size?  

If the DPI/PPI is based on the Maximum Image Size, I would have to
calculate how many pixels are hidden in order to get an accurate window
placement. E.g. geometry of +0+0 would no longer be the upper right
corner of the screen that can be seen, but rather something like +10+23
would be the real viewable upper right corner. True?

If the DPI/PPI is based on the Viewable size, I would first have to
re-calculate the number of pixels per inch wouldn't I?

If the answer is that it varies from monitor to monitor, how would you
find out which is applicable, besides trial and error?



-- 
Regards Bill
Fedora 13, Gnome 2.30.2
Evo.2.20.2, Emacs 23.2.1