Thus far I'd been using the slightly more intuitive fixed resolution of 96x64 with (0,0) in the top-left hand corner with the Y axis pointing downwards. This means that any graphics program for the TI-83+ version appears upside down and squashed into the bottom-left corner when run on the BBC Micro.
I have worked on attempting to remedy this. 1280x1024 does not divide cleanly into 96x64, so I've used a constant scale factor of 16 on both axes resulting in a virtual resolution of 1536x1024. (Flipping the Y axis is easy enough). This means that programs drawing shapes (lines, circles, triangles, rectangles, parallelograms) will run on both BBC Micro "compatible" versions of BBC BASIC and the TI-83+ and produce roughly the same results.
As this may not be to everyone's tastes the two options may be independently controlled with two new star commands;
- *YAXIS UP|DOWN
- *GSCALE ON|OFF
The default is to have *YAXIS UP and *GSCALE ON. To revert to the old behaviour you could specify *YAXIS DOWN and *GSCALE OFF.
I have also been working on implementing the OS call OSGBPB. This call allows you to read/write multiple bytes of data in one go, so is much faster than using the byte-at-a-time BGET# and BPUT# commands. It also provides a way to enumerate filenames, a feature I have yet to implement but one that should be useful (eg to search for data files for your own program without having the filename hard-coded or having to prompt the user).