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vladikcomper / MegaPCM

An advanced DAC driver for the Sega Mega-Drive / Genesis games
MIT License
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Sample SFX playback in Sonic 1 #1

Open badgertapes opened 1 week ago

badgertapes commented 1 week ago

I'm interested in playing back a PCM sample in Sonic 1 (AS disasm) in lieu of a sound effect. Let's say, in place of SndB4 - Bumper. How can I go about doing this? I'm not sure if I see this written down in documentation, so I apologize if I missed it.

vladikcomper commented 1 week ago

You're right, there isn't a how-to for it, even though it's a one liner and it's described in API docs. Still, I may add this how-to in the future.

Short answer:

    move.b  #<<YOUR SAMPLE ID>>, d0
    jsr     MegaPCM_PlaySample

Long answer:

Just like you call PlaySound to play SFX using SMPS (Sonic 1's main driver), you can call MegaPCM_PlaySample to play SFX samples using Mega PCM.

So instead of this:

    move.w  #sfx_Bumper,d0
    jsr     (PlaySound_Special).l   ; play bumper sound

You'll do this:

    move.b  #<<YOUR SAMPLE ID>>, d0
    jsr     MegaPCM_PlaySample

Where <<YOUR SAMPLE ID>> is a sample number in Mega PCM's sample table. You usually count these manually starting from $81 (but comments help in tracking those numbers).

It's also recommended that your sample will have FLAGS_SFX set (it will still work without it, but it may get interrupted by BGM drums, which would have the same priority otherwise), for example:

SampleTable:
    ;           type            pointer     Hz
    dcSample    TYPE_DPCM,      Kick,       8000                ; $81
    dcSample    TYPE_PCM,       Snare,      24000               ; $82
    dcSample    TYPE_DPCM,      Timpani,    7250                ; $83
    dcSample    TYPE_PCM,       MyBumper,   0, FLAGS_SFX        ; $84  NOTE: sample rate is auto-detected from WAV file
    ; <...>

MyBumper:
    incdac  MyBumper, "sound/dac/my-bumper.wav"
badgertapes commented 1 week ago

Thank you. Works like a charm.

Is there any case I can get this sound to play on every hit of the bumper? Only plays once in rapid succession. I'm OK with if it's not possible

vladikcomper commented 5 days ago

Oh, you technically can, if you remove FLAGS_SFX. Unfortunately, this also means it can be interrupted by BGM drums now, but if it's a rapid succession, it should be fine for you.

Samples with FLAGS_SFX have the highest priority and they can't be interrupted by anything, even by another sample with the same flag. It's a limitation of this flag since version 1.x. I'll consider adding more flexibility in the future.