By default Istaria supports several common standard and widescreen display display resolutions. But different monitors, playstyles and preferences can create a situation where the resolution you like to play games in, or you are used to play games in, isn't available.
With Istaria, this is relatively easy to add your own resolutions to the list that is selectable on the Options panel.
1. Copy the GameConsts.def file into your \Horizons\resources_override\ folder. This def file is located in \Horizons\resources\.
2. Open it with a text editor such as notepad. Note: Do not use Word as it will try to save extra formatting if you aren't careful.
3. Find the section named "int list resolutionsX" and add your desired resolution to the end of the list. So, if you wanted to add 1152x864 to the list you would add 1152 to this list and 864 to the list in step #4.
4. Find the section named "int list resolutionsY" and add your desired resolution to the end of the list.
5. Save the file and login to the game. You will see your new resolution listed on the Options->Video panel.
CAVEAT: Virtrium may at times make changes to the official GameConsts.def file and patch it to the player-base. In this case, if you are using a modified GameConsts.def file located in the \resources_override\ folder you may experience unintended side-effects due to an out of date file.