Current questions and answers regarding the map editor.

I want to create a unique preview image for a duel arena. As I understand it, this requires: the image itself in TGA format with a resolution of 214x160, an XDB pointer that specifies the path to the image, and a DDS file, which is usually located in the same directory as the XDB. What is a DDS file? What should it contain? What program can I use to open and create it? Is this a mandatory requirement for a custom preview image?