With the Acorn VDU driver, redefined chararcters persist across mode changes, whereas the Pi VDU resets the current font on mode change. This bug breaks Acornsoft Chess running on Co Pro with the Pi VDU driver.
This happens because the font is currently part of the screen_mode, where as it looks like it should really be part of the framebuffer. If we move it to screen_mode then MODE 7 (and derivatives) will need seperate definitions.
Note: In MOS 3, and in MOS 1.2 when the tube is detected, the host side font is fully exploded, The PiVDU driver also treats the font as fully exploded, in that any character can be redefined. But, we don't currently implement OSBYTE &14, a side effect of which is to reset the definitions of characters &20-&7F.
With the Acorn VDU driver, redefined chararcters persist across mode changes, whereas the Pi VDU resets the current font on mode change. This bug breaks Acornsoft Chess running on Co Pro with the Pi VDU driver.
This happens because the font is currently part of the screen_mode, where as it looks like it should really be part of the framebuffer. If we move it to screen_mode then MODE 7 (and derivatives) will need seperate definitions.
Note: In MOS 3, and in MOS 1.2 when the tube is detected, the host side font is fully exploded, The PiVDU driver also treats the font as fully exploded, in that any character can be redefined. But, we don't currently implement OSBYTE &14, a side effect of which is to reset the definitions of characters &20-&7F.
See: https://beebwiki.mdfs.net/VDU_23 https://beebwiki.mdfs.net/OSBYTE_%2614
Dave