[Scummvm-tracker] [ScummVM :: Bugs] #11923: AGI Splatter patterns appear to be incorrect

[ScummVM :: Bugs]

#11923: AGI Splatter patterns appear to be incorrect
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Reporter:  rwtodd   |      Owner:  (none)
    Type:  defect   |     Status:  new
Priority:  normal   |  Component:  Engine: AGI
Keywords:  agi pic  |       Game:
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 When I take, for example, Space Quest 2 room 16 or room 22, and compare
 the ScummVM image to the game running in DosBox, I can see that the
 splatter patterns are all wrong in the trees in the background.

 I think way back in github commmit 0d279e8de07fc5 when the AGI splatter
 plotting was redone, the texture_number variable accidentally got hard-
 coded to 0.  In fact, the texture number should start as the pattern
 number pulled in plotBrush() (notice: the code at present does nothing
 with _patNum, which is a clue something isn't right).

 I think maybe the resulting plot errors were why a subsequent commit
 changed the ditherCond from 2 to 1.  I believe that was incorrect and
 should be reverted.

 To make the games I have look like the original, I believe the following
 changes are needed:

 1) make plotBrush() store the raw byte it reads in _patNum (forget the >>1
 and &0x7f part... that's left over from an older table-based approach to
 splatter).
 2) in plotPattern(), initialize `t` to (_patNum | 0x01) and forget the
 zero texture_num.
 3) in plotPattern(), change ditherCond back to 2 like it was originally.

 I don't have an exhaustive list of games to test this with, but the few
 AGI games I have which use splatter plots look more accurate to me after
 these changes.  If people agree it's an improvement, I can offer a pull
 request on github, or I'm just as happy if one of the usual devs makes the
 fix.

 As further evidence, I believe nagi's pic_render.c agrees with the changes
 I'm suggesting.
 (https://github.com/sonneveld/nagi/blob/master/src/picture/pic_render.c).
 It sets texture_num in plot_with_pen(), and I think in the translation to
 scummvm, texture_num got converted to a local var and always set to zero.
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Ticket URL: <https://bugs.scummvm.org/ticket/11923>
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