Playing around with the in-game tune in JSW

[Spider]

15 hours ago, IRF said:

That's similar to my solution, but not identical. You seem to have a spare byte in there, so you could afford to retain the original two-byte LD D, #00 command, instead of the single-byte LD D, A. That would mean the patch isn't reliant on A having been reset to zero beforehand. (Since a lot of game designers ditch the preceding inactivity code which sets A=0.)

Yes , it assumes that A is still set to zero as a result of the command at #8B3C

[IRF]

I must admit I used AND #01 to affect the Zero flag - to decide when to increment (or not) the music note index - but it never occurred to me to just directly add the value of A (after the AND command) to the note index, which has the same effect since A can only hold 00 or 01 at that point. A very elegant and efficient solution!

(Mine might be slightly more adaptable, as you can decide whether to advance the music on an 'odd' or an 'even' game tick, by selecting the polarity of the conditional jump: JR Z or JR NZ. However, mine needed an extra precious byte compared to yours, so yours wins!) 

Edited January 6 by IRF

[jetsetdanny]

  

17 hours ago, IRF said:

Indeed! Only 64 bytes per tune though. If you had 20 tunes of 256 bytes each, that wouldn't leave much room for anything else! 

 

5 hours ago, jetsetdanny said:

Exactly. Even with 64-byte-long tunes there was no room left for any extras. A suggestion was made after the game was released that it could do with a non-standard font. It was a very good suggestion, but unfortunately impossible to apply without far-reaching changes to the game engine that would optimise the code 'a la Norman Sword' and free up enough space to implement a new font.

 

Actually, I need to correct both yourself, Ian, and myself! (I let myself be carried by your erroneous and, in fact, slightly blasphemous suggestion! 🤪)

Each of the 20 in-game tunes in "Manic Person" is 128 bytes long. If they were 'only' 64 bytes long, there would be enough spare space also for a custom font (1280 spare bytes versus 768 needed for a full font).

[IRF]

On 1/5/2024 at 6:45 PM, Spider said:

Nopping out #8B47 and #8B49 would do but its too fast then. So...

 

XOR A                            ;8B3C      ;                  clear the inactivity timer at L85E0 
    LD (inactivity),A            ;8B3D      ;L85E0
    LD D,A                           ;8B40      ;                   initialise the mSB
    LD a,(game ticker)       ;8B41      ;L85CB        the game ticker at 85CB
    AND 1                            ;8B44      ;                   issolate odd or even game ticker bit
    LD HL,(ingame_music) ;8B46      ;L865F        set HL to the music offset pointer
    LD E,(HL)                       ;8B49      ;                   get the present offset
    ADD A,E                        ;8B4A      ;                   add the ticker (odd/even) value
    LD (HL),A                      ;8B4B      ;                   store the updated offset
   NOP                              ; 8b4C      ;
back to the original code
   LD HL,ingame_music    ;8B4D     ;L865F
   ADD HL,DE                    ; 8B50    ;
>>> HL IS POINTING AT THE NOTE value 

 

Actually Andy, you might need to think again there. Did you actually try that out? Because looking at it again, E isn't actually updated when the tune note index is increased, so when DE is added to HL (the second definition of HL) at #8B50, it won't pick up the new note during the current pass through the Main Loop.

So you would need to use that spare, NOPped out byte at #8B4C for a LD E, A instruction.

Edit: Thinking about it, the effect of E not being updated straight away probably just means that the tune will be playing 'one note behind'. It should play at the right speed. But the first note (first pitch value) will only play half as long as it should when you start playing the game. (And the normal fix for that - setting the music note index to #FF during game initialisation - won't work this time; I think that would cause the last note of the tune to be played during the first pass through the Main Loop.)

Edited January 9 by IRF