[Scummvm-tracker] [ScummVM :: Bugs] #13169: Myst III Exile: missing scene transition effect on PowerPC (big-endian) machines on all OSes

[ScummVM :: Bugs]

#13169: Myst III Exile: missing scene transition effect on PowerPC (big-endian)
machines on all OSes
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Reporter:  kas1e                           |       Owner:  (none)
    Type:  defect                          |      Status:  new
Priority:  normal                          |   Component:  Engine: Myst3
 Version:                                  |  Resolution:
Keywords:  big endian, BE, Myst3, AmigaOS  |        Game:  Myst 3: Exile
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Comment (by kas1e):

 @lephilousophe

 > Another test is possible although this looks more like a workaround.

 Tried "glFlush()" patch : no, same issue.

 > Is it possible to make a screenshot in the middle of the transition?
 > If it's too fast, you can change the setting in scummvm.ini file by
 setting transition_speed to something like -400 (note the minus sign).

 Done, there are video with -400 and both patches applied (glTexImage2D one
 and glFlush one):

 OGLES2 (opengl with shaders): https://youtu.be/ojY0i2yvtXI

 MiniGL (opengl): https://youtu.be/myh_5rZuL-o

 See how interesting .. With OGLES2 we can see that between scenes swap,
 the whole texture is "flipped". Now, when effect should happens, flipped
 texture are shown for a while (for most of time of effect) and then, at
 the very end, i can see how cross-fade effect take place. But instead of
 full time, it take just 1/10 of time or something.

 Then, if we check video with MiniGL rendering, there we instead have some
 different stuff, and not flipped texture, but shifted one, and being
 "purple", and then also we can see that for almost all time of cross-fade
 effect we have that "purple shifted texture" and at the end cross-fade
 effect taking 1/10 of the time it should take.

 That make me think, that in both cases we like hit one issue : we use
 old/previous parts of video memory or something. The "mess" in minigl we
 have is that because we see that "shiftet purple stuff", just on fast-
 speed it looks like mess. And with OGLES2 we have no mess, because in the
 time we should have effect, texture just flipped, but no other color, so
 for us it like nothing happens.

 It can be some issues with timing values or something, maybe some integer
 overflows somewhere ?
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Ticket URL: <https://bugs.scummvm.org/ticket/13169#comment:12>
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