[Bounty: $10] implement internal MAME 2003 video flip/mirroring

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Current situation

There are a number of arcade games that projected their video by means of a mirror. In order to emulate this setup, MAME 0.78 incorporates video flip/mirroring code that has not yet been incorporated into MAME 2003 or MAME 2003-plus.

@grant2258 spent time compiling a reference list of some affected games

There is a workaround: by using hunterk’s RetroArch screen mirroring shader users can work around this bug, but of course that is only viable for users with shader support and those with a frontend like RA that supports shaders as well.


This issue will be resolved when there is full flip/mirroring support in mame2003 (which will also get ported to mame2003-plus).

In terms of work to date, grant and @dankcushions have both put time into researching the solution. Their notes can be found here: https://github.com/libretro/mame2003-plus-libretro/issues/81

Some specific posts might be relevant:

This issue has been resolved in the most current build of mame2003. The fix will also be added to mame2003-plus in the near future. Thanks nayslayer!