[Scummvm-tracker] [ScummVM :: Bugs] #13086: GRAPHICS: OpenGL scaler - Normal 2x-5x break FMTowns games

[ScummVM :: Bugs]

#13086: GRAPHICS: OpenGL scaler - Normal 2x-5x break FMTowns games
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Reporter:  raziel-  |      Owner:  (none)
    Type:  defect   |     Status:  new
Priority:  normal   |  Component:  Graphics: Scalers
 Version:           |   Keywords:  OpenGL scalers
    Game:           |
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 ScummVM 2.6.0git (Nov 20 2021 09:06:56)
 Features compiled in: Vorbis FLAC MP3 RGB zLib MPEG2 Theora AAC A/52
 FreeType2 FriBiDi JPEG PNG GIF cloud (servers, local) TinyGL OpenGL

 The OpenGL scaler implementation
 (https://github.com/scummvm/scummvm/commit/fe5b87d0f1f8574e321a93e4ee82d9eeb9d8a704)
 introduced a regression(?) with FMTowns games.

 The scaler Normal2x, Normal3x, Normal4x and Normal5x corrupt the game
 screen.
 I quickly tested all available scalers, both with SDLSurface and OpenGL,
 and only the ones mentioned above display the corruption.
 (I will add screenshots for both Amiga and Win32 binaries running the
 games)

 I *suspect* all FMTowns are affected, but i can only test Indiana Jones 3
 and ZakMcKracken, as i don't own any other FMTowns variant.

 The behaviour was confirmed with a daily build for Win32 from today
 (scalers Normal2x and Normal5x simply quit ScummVM on game start though,
 but i was able to catch a glimpse of borked gfx on the lower left of the
 game window, no screenshots for those)...some one line pixel mesh was
 showing before ScummVM quit.

 Indiana Jones and the Last Crusade (FM-TOWNS/English)
 Zak McKracken and the Alien Mindbenders (FM-TOWNS/English)

 AmigaOS4 - PPC - SDL - BE
 gcc (adtools build 11.1.0) 11.1.0
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Ticket URL: <https://bugs.scummvm.org/ticket/13086>
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