[Scummvm-tracker] [ScummVM :: Bugs] #15303: SCI: LSL5: Timed message skipped during LSL5 coffee scene (symptom of a bigger problem?) (was: SCI: LSL5: Timed message skipped during LSL5 coffee scene)

[ScummVM :: Bugs]

#15303: SCI: LSL5: Timed message skipped during LSL5 coffee scene (symptom of a
bigger problem?)
-------------------------+-----------------------------------
Reporter:  eriktorbjorn  |       Owner:  (none)
    Type:  defect        |      Status:  new
Priority:  normal        |   Component:  Engine: SCI
 Version:                |  Resolution:
Keywords:                |        Game:  Leisure Suit Larry 5
-------------------------+-----------------------------------
Changes (by eriktorbjorn):

 * summary:  SCI: LSL5: Timed message skipped during LSL5 coffee scene =>
     SCI: LSL5: Timed message skipped during LSL5 coffee scene (symptom of
     a bigger problem?)


Old description:

> This one was a fluke...
>
> I made a savegame at the beginning of Leisure Suit Larry 5 (English),
> right after the end of the intro. When bringing coffee to Silas, the game
> was supposed to print the message
>
> "Yes, I know" you offer proudly, "I'm the Chief Tape Rewinder and
> Sterilizer on this project!"
>
> But that message was only shown for a split second, before skipping to
> the next message. I ''think'' what's going on here is some sort of
> integer overflow. This is how the message is displayed in rm150.sc,
> sCartoon:
>
> {{{
>                         (22
>                                 (Say You_a 150 9 108 139 self) ; "Yes, I
> know," you offer proudly, "I'm the Chief Tape Rewinder and Sterilizer on
> this project!"
>                         )
>                         (23
>                                 (= ticks 30)
>                         )
> }}}
>
> I think that means the message is supposed to stay up for 30 "ticks".
> Though that seems awfully short, so maybe it's 30 ''additional'' ticks?
>
> If you load the attached savegame, and let the messages time out on their
> own (don't click to speed it up!), the skipped message happens at a point
> when KGETTIME_TICKS in the kGetTime() function comes (dangerously?) close
> to 32,767. Could that somehow cause the timeout to trigger prematurely?

New description:

 (Description updated after discussion below.)

 During the coffee delivery scene in Leisure Suit Larry 5 (the optional
 tutorial after the intro), I noticed that one of the lines was skipped, or
 rather the text box for it was dismissed so quickly that I could barely
 see it. The skipped message was supposed to be:

 "Yes, I know" you offer proudly, "I'm the Chief Tape Rewinder and
 Sterilizer on this project!"

 This glitch is quite timing sensitive, so I have include a savegame during
 the scene itself. Don't skip any text boxes, just let the scene play out
 with default settings for everything.

 The problem seems to be the way the `Talker` class times out text boxes.
 First the `doit` method calculates a duration based on string length and,
 I assume, text speed, and assigns it to the `ticks` property. Then `say`
 adds another 60 ticks for good measure, and adds the current game time as
 reported by `GetTime`. The `doit` method then polls `GetTime` to see if
 the text box should be dismissed:

 {{{
                 (if (> (GetTime) ticks)
                         (self dispose: disposeWhenDone)
                         (return)
                 )
 }}}

 What seems to happen is that if `GetTime` is close enough to 32,767,
 adding the duration causes `ticks` to become negative. Which means that
 `GetTime` is immediately greater than `ticks`.

 I believe this means that the glitch could happen at any point in the
 game, and I was just lucky (?) to catch it here. And the same mechanism
 seems to be present in several other games, but no one ever noticed. I
 blame the lengthy cutscenes in LSL5 for triggering it.

 I imagine it should be possible to fix, at least on a case-by-case basis.
 The arithmetic workarounds seem like a reasonable place to start, but it
 might need some extending to call a custom C++ function to do the
 comparison? We know that `ticks` should stay constant until the text box
 is dismissed.

 I'm more worried about what other things may potentially be affected,
 though.

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Ticket URL: <https://bugs.scummvm.org/ticket/15303#comment:19>
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