If I have understood this correctly, the Raspberry calculates the real-time graphics into the blanking interval of a teletext-capable TV... The blanking interval is then interpreted and displayed by the TT Decoder.
If this is anything like the one Paraguay had for Teletext's 40 year anniversary (at Assembly 2016) it does. (Readme here: https://modeemi.fi/~ninnnu/making-of-teletext.txt )
There are different levels of Teletext and this likely is above L1, which the Paraguay demo was able to do L1.
(Now, mind you, Finland still HAS active Teletext; both on TV and the web... and each month there are different monthly calendars with art, along with an art section... )
And yes, I do need to get Teletext capabilities into Sahli... (along with the ATASCII and ... yeah. I need more time.)
The month (elokuu ) / next month (syyskuu)
https://yle.fi/aihe/tekstitv?P=892 / 893
Bits about the Museum of Teletext Art:
- and I always forget to look at this stuff until someone brings up a demo, and then I remember how much there is of it here, and how I could, you know. Use it for learning more Finnish...
(the US never had this. You know. Reading, can't have that, people would learn things.)