The AGK has a built in extended font that it uses for text objects with characters 128 to 255, this command allows you to override it. If you are setting all your text objects to the same extended font you should use DefaultExtendedFontImage instead as this will save some processing time. 

The image should contain all white characters surrounded by a transparent alpha channel. Fully transparent pixels should also contain white in their RGB components. 

The font image may either be fixed width or variable width. For fixed width the font image must be laid out in a grid of 16 characters across and 8 characters down, starting with the ascii character 32 (space) in the top left and proceeding left to right, top to bottom, ending with ascii character 127 (DEL) in the bottom right. The image width must be divisible by 16 and the image height must be divisible by 6. For variable width the image must be an atlas texture accompained by a "[imagename] subimages.txt" file that states the location of each character on the image. The AGK will look for images "32" up to and including "127" in the subimages file and any not found will default to the space character (32). See TAgkImage.Create for the format of this text file.

TAgkText Properties