The font converter is abilable here:https://code.google.com/p/ucglib/source/browse/tools/font/bdf2ucg/bdf2ucg.c
I will create an issue on this to make bdf2ucg available as exe also.
BDF is a text based format, which is created by fony (windows font editor) or fontforge (another font editor) and also otf2bdf (ttf to bdf converter).
The font has some size restrictions. One glyph must not contain more then 255 bytes. This limits the size of a charcter to 32x64 pixel max. The logisoso font already is at the maximum of what is possible with ucglib.
Maybe it is faster instead of solid mode to draw a background box first and then use the transparent font mode. Also, the solid mode still has some bugs (see issue list).