I actually don't know if that's possible with the current code. Would you be willing to provide the relevant artwork .zips and any other files you've edited while trying to achieve this effect? It shouldn't be too much trouble for me to debug it and either commit a fix (which would go into MAME 0.223, since we're already in release-freeze for 0.222) or let you know what's wrong with your data files.
EDIT: By the way, I also want to thank you for taking the time to dive into the relevant files and learn about the system itself. It's a really positive feeling to see someone who's willing to learn, rather than just angrily bitch at the team like, uh, some people in this thread.
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Re: A new shader for those who want to use their entire screen space
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I did some changes. This is the way I like it.
