146 lines
6.9 KiB
C
146 lines
6.9 KiB
C
// Audio: 4-channel Protracker .MOD music with digital one-shot SFX.
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//
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// Authors compose music as .MOD modules. The host-side asset pipeline
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// (tools/joeymod) converts each module into the runtime form the
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// target platform expects:
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//
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// Apple IIgs -- NinjaTrackerPlus .NTP, played by Ninjaforce's
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// 65816 replayer linked into the binary.
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// Amiga -- raw .MOD, played by Frank Wille's PTPlayer.
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// DOS -- raw .MOD, played by libxmp-lite over SB DMA.
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// Atari ST -- raw .MOD, played by libxmp-lite (parser only) plus
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// a hand-rolled 68k 4-channel mixer that outputs via
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// YM2149 4-bit PWM at ~12.5 kHz.
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//
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// Game code always calls the same five entry points; the per-port
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// HAL hides the engine choice. A failed audio init is non-fatal --
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// jlInit still succeeds and audio calls become no-ops.
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#ifndef JOEYLIB_AUDIO_H
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#define JOEYLIB_AUDIO_H
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#include "platform.h"
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#include "types.h"
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#define JOEY_AUDIO_SFX_SLOTS 4
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// Initialize audio. Returns true if the platform has a working audio
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// engine and was able to start it. Returns false silently otherwise;
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// the rest of the API stays callable but produces no sound.
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bool jlAudioInit(void);
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// Tear down the engine. Safe to call when audio is not initialized.
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void jlAudioShutdown(void);
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// Begin module playback. data points at the platform-native module
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// blob (.MOD on most platforms, .NTP on IIgs); the asset pipeline
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// produces the right form for each target. If a module is already
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// playing, it is replaced.
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//
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// loop=true plays forever. loop=false stops at song end, but Amiga
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// requires the module to contain an E8FF effect at song end for the
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// stop to fire (PTPlayer has no native song-end signal). The
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// `joeymod` tool's .amod output extension injects that marker
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// automatically; ship .amod for Amiga and .mod for the other ports.
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// loop=false on a .mod (no E8FF) loops anyway on Amiga.
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void jlAudioPlayMod(const uint8_t *data, uint32_t length, bool loop);
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// Stop the current module (if any). The playhead is reset so the next
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// jlAudioPlayMod starts from the top.
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void jlAudioStopMod(void);
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// True if a module is currently producing output (false during silence
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// after StopMod or before the first PlayMod, and on platforms where
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// audio init failed).
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bool jlAudioIsPlayingMod(void);
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// Trigger a one-shot digital SFX on the given slot (0..JOEY_AUDIO_SFX_SLOTS-1).
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// sample points at raw signed 8-bit PCM. rateHz is the playback rate
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// the sample was recorded at; the engine pitches as needed for its
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// own output rate. If the slot is currently playing, the new sample
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// replaces it.
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void jlAudioPlaySfx(uint8_t slot, const uint8_t *sample, uint32_t length, uint16_t rateHz);
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// Stream-fill callback signature. Called by the mixer to refill a
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// streaming slot's prefetch buffer; should write up to `count` signed
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// 8-bit samples to `dst` and return the number written. Returning 0
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// signals end-of-stream and the slot auto-deactivates. Called from
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// the same context as the audio engine's refill (main thread on
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// DOS/ST, audio ISR on Amiga/IIgs); must not block or allocate.
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typedef uint32_t (*jlAudioStreamFillT)(void *ctx, int8_t *dst, uint32_t count);
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// Trigger streaming SFX playback on the given slot. The mixer pulls
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// samples from `fill(ctx, ...)` as the slot's internal prefetch
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// buffer drains, so SFX can be arbitrarily long with no caller-side
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// allocation. `rateHz` is the sample rate `fill` produces; the
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// engine resamples (with linear interpolation) to its own output
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// rate. If the slot is currently playing, the new stream replaces
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// it. No-op on ports whose audio engine doesn't expose the shared
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// SFX overlay mixer.
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void jlAudioPlaySfxStream(uint8_t slot, jlAudioStreamFillT fill, void *ctx, uint16_t rateHz);
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// Stop a SFX slot early. No-op if the slot is already idle.
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void jlAudioStopSfx(uint8_t slot);
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// Direct hardware tone generator: continuously play a square wave at
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// `freqHz` until the next jlAudioTone call. freqHz == 0 silences the
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// generator. Designed for AGI-era PSG-style music where the engine
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// just programs a divisor and lets the chip play; CPU cost during
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// playback is zero. Single voice on platforms with multiple
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// hardware oscillators (uses voice 0). On DOS this programs PIT
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// counter 2 and the speaker gate (port 0x61). No-op on platforms
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// without a reachable tone generator -- callers should fall back to
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// jlAudioPlaySfxStream when they need PCM-synth sound on those.
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void jlAudioTone(uint16_t freqHz);
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// Periodic tick callback for sound schedulers that need better-than-
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// frame-rate resolution. Used by PSG-era music drivers (AGI, AdLib
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// patches, etc.) to write hardware register changes at exact note
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// boundaries -- frame-rate-driven scheduling batches multiple notes
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// into one render frame, so the chip only "hears" the last write
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// per batch and short notes are dropped.
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//
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// fn fires from interrupt context at `hz` times per second. Keep
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// fn short: only memory reads, direct hardware-register writes,
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// no malloc / printf / blocking. Pass fn = NULL to uninstall.
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//
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// Per-port impl: DOS reprograms PIT counter 0 + hooks INT 8,
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// keeping the BIOS tick counter at $0040:$006C advancing at the
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// canonical 18.2 Hz via an accumulator (so uclock / time stay
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// correct). Other ports return false until a port-appropriate
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// timer source is wired.
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typedef void (*jlAudioTickFnT)(void);
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bool jlAudioTickRegister(jlAudioTickFnT fn, uint16_t hz);
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// Critical section against the tick ISR. Callers that mutate
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// state read by the registered tick callback must wrap the
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// mutation in Enter/Exit so the ISR can't observe a half-written
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// state. On DOS this is `cli` / `sti`; on ports without an
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// audio ISR these are no-ops.
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void jlAudioCriticalEnter(void);
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void jlAudioCriticalExit(void);
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// 3-voice PSG-style polyphonic tone generator. `voice` selects 0/1/2;
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// `freqHz` is the new tone (0 = silence this voice); `atten` is the
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// AGI/SN76489-style 4-bit attenuation, 0 = loudest .. 15 = silent
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// (2 dB per step). The mapping to underlying hardware:
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//
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// DOS -- AdLib OPL2 melodic channels 0/1/2 (ports 0x388/0x389).
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// Atari ST -- YM2149 PSG channels A/B/C.
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// Amiga -- Paula channels 0/1/2 playing a 2-byte square sample.
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// IIgs -- not wired yet (Ensoniq DOC is wavetable, not square).
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//
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// Voice state is sticky: a voice keeps playing its last frequency
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// until the next jlAudioVoice call on it. CPU cost during sustained
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// playback is zero (the hardware oscillates on its own). Safe to
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// call without jlAudioInit -- the voice path is direct hardware
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// programming, independent of the MOD/SFX mixer.
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void jlAudioVoice(uint8_t voice, uint16_t freqHz, uint8_t atten);
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// Hook the engine into the game loop. Most platforms drive their
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// engines off a hardware IRQ and ignore this call, but it's safe to
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// invoke once per frame regardless and required for any port that
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// runs its mixer in user-thread context.
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void jlAudioFrameTick(void);
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#endif
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