The S3 driver caches fonts and other monochrome data in off-screen VRAM, and uses the hardware BitBlt engine to expand these to the display. Not all devices are capable of doing this. If your chip set does not have this capability, then the text code will need a considerable amount of work. Another consideration is that the S3 driver treats objects in VRAM as rectangles with an X-Y origin. Some devices work this way, others reference portions of VRAM by address. Some can deal only with off-screen bit maps that have the same pitch as the display. Others can work with off-screen bit maps with packed scan lines or with the scan lines padded to some boundary. These considerations will affect the design of the bit map and font-caching code.