While you are playing just type /viewport www xxx yyy zzz
Inplace of the "www" would be your distance from left side of your screen.
Inplace of the "xxx" would be distance from top of your screen.
Inplace of the "yyy" would be your width of the "Game Window"
Inplace of the "zzz" would be your height of the "Game Window"
My viewport would be typed like this:
/viewport 240 0 910 800
You will need to play around with it a bit to get everything to fit the way you want it. Using viewport will increase your performance based on the size of your "Game Window", in my UI for example instead of my system displaying a 1280x1024 version of EQ (with part of that covered up with all the chat windows and stuff) it now only needs to display 910x800. That is not a huge system savings but the way I see it, why display areas of the Game Window that you cant see becasue it is covered by your UI ?
Anyway, hope that helps
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