The @@@'s happen due to the raster timing, chaning the row / NOP padding sometimes helps, but its really down to there being 0's there (the @ symbol) where it should be reading placing your scroller text... it is very fiddly and one of the things I have been learning as I got deeper into this project. Sometimes you cant always get what you expect with C64 and have to work around the limitations. If you want, you can share anything on the Discord, I can take a better look and see where I can make improvements better on my side too.
I believe you already have the example in your archives; you previously made the file available for free download on itch.io (this was before version 1.00 of C64DevMachine) with the name CORE_BITMAP_SID_TEXTSCROLLER.json, including the Van Halen music ("Jump") :)
When you run it, you'll see those famous "@@@@@ ..." ;)
Sincerely,
I see, its not being padded out as the scroll message enters, so that is just whatever is in memory before it. many of those Pre Version 1.0 things are subject to get broken, the routines might have been adjusted, so those files were more like proof of something almost working, or worked at the time... to be honest I dont know when the @ bug appeared as it was fine in an older version i will patch that.
Great, finally, a nasty bug tracked down and fixed! ;). Thanks a lot!
Just so you know, I also tested the text mode (HR/MC) for the Scrolling Text function. I used a "Bubble Bobble" background converted to TXT MC mode using Charpad (alphanumeric characters are included in the charset). I changed the text colors, but at this stage, the colors don't match the settings at all (see the screenshot below). I'm not using Irq or anything like that (just standard nodes).
I encourage you to run a test and see if you encounter the same issue with character color control.