- Hatari has no idea of how many pixels are really available per line, it assumes each bytes is displayed (which is not the case on real HW, but is not noticeable in STF mode when you set screen width to 416 pixels).
- on the left border, we have 20 extra bytes to display. But the 1st 4 bytes (8 pixels) are not shown (hatari fill them with color 0, which explains why we see colors changing in the 8 leftmost pixels). Here we should have a special "blank" color that always stays black, but this doesn't exist for now. So in the end, left border has 32 extra pixels to use.
- on the right border, we display whatever pixels the user chooses in the config. As a line is 224 bytes, this means 448 pixels and a max of 96 pixels in right border. A real STE will turn DE off before and will not display 96 pixels, it will display only 64 or 68 pixels (to get a total width of 416-420 pixels). So here again, Hatari should be improved to really stop displaying pixel and put some "blank/black" color instead.
As those STE overscan lines are a little shorter than the standard 230 bytes STF lines, the solution for now to get a nicer image is to set Hatari to 400 pixel width instead of 416 in the UI.
I have an old CRT monitor that I need to plug one day to check this.
see where the display really stops on ST.
which is not handy to precisely check pixel one by one.