To me this looks like you're plotting the new right hand edge before the screen start address has updated. This might be because you set R12/R13 too late; you should be aiming to set R12/R13 and draw the new strip as soon after VSync as possible (but definitely set R12/R13 first, so that it will definitely be used for the next frame!).
Statistics: Posted by Rich Talbot-Watkins — Thu Feb 27, 2025 7:55 am