i am currently experimenting with semi graphics on the Rainbow-100. A modified character ROM and a simple QBASIC program (to read BMPs) are sufficient to achieve:
264 x 72 (264 x 96) resolution in 132 x 24 mode
140 x 144 (140 x 192) resolution in 70 x 48 mode (custom mode of DC011/DC012) Resolutions in brackets use a 2x4 character set instead of 2x3.
As you can see in the image, you can even mix text and graphics - normally impossible on the Rainbow https://dl.dropboxusercontent.com/u/37819653/Rainbow-100%20Semi%20graphics.jpg
I know it is an old trick, but the technique (and the source) could be adapted to other systems with more horsepower and screen RAM.
---- Back to our main topic: the current VT100 (or Rainbow?) driver does not allow reverse character attributes ($ef000 attribute RAM). Is this a bug?
Characters above $80 display in reverse, though.
To be more precise, even the error messages (shown when deliberately booting the 'non working' driver) have active reverse, bold, and blink attributes - if i remember correctly
The character space needed could be reduced easily if not only line, but character attributes also worked.
Any hints, suggestions or ideas?