MLT NATIVE S3M OPL3 ENGINE
=========================

Opal is the OPL3 emulator from Reality Adlib Tracker by Shayde/Reality,
released into the public domain. The upstream file also credits fixes by
JP Cimalando; this snapshot includes OpenMPT contributors' changes.

Upstream revision: dc49d5638db37e157003cd606dc85165551eb9da
Source:
https://github.com/OpenMPT/openmpt/blob/dc49d5638db37e157003cd606dc85165551eb9da/soundlib/opal.h
Original header SHA-256:
16d55838d26cdcc1780f64f2b016c7a2d12fc43a6ddc632da8d3ec86a3847b53

Embedded module SHA-256:
c119cbceee136850cd10f520ad71f3f2983d1f1cd3123b1a379b7ab9e93cfffa

The adapter and integration are Copyright (C) 2026 Maxime LORRAI,
GPL-3.0-only. Opal's public-domain status is unchanged. MLT's complete GPL
notice and liability disclaimer remain in index.html and licenses/GPL-3.0.txt.

Files
-----
opal.h: upstream core with a local utility include, read-only envelope-state
accessors, and an observation of each channel's integer mono output.
opal-adapter.cpp: one chip per worklet, separate track outputs, and the same
integer linear resampling schedule as Opal::Sample.
common/mptBaseUtils.h: minimal positive rounded-division utility and placement
construction include; no OpenMPT application runtime is required.

Build
-----
Use WASI SDK 22.0+m (LLVM 18.1.2) from:
https://github.com/WebAssembly/wasi-sdk/releases/tag/wasi-sdk-22
From this directory, invoke its clang++ executable with these arguments:

opal-adapter.cpp -O3 -fno-exceptions -fno-rtti -nostartfiles
-Wl,--no-entry -Wl,--export=reset -Wl,--export=write -Wl,--export=sample
-Wl,--export=outputBuffer -Wl,--export=silent -Wl,--export=__wasm_call_ctors
-Wl,--initial-memory=131072 -Wl,--max-memory=131072 -o opal.wasm

The compiled module has no imports. Its memory is fixed at 128 KiB. The
standalone HTML embeds that module as NATIVE_OPL3_BINARY; the browser compiles
it asynchronously before creating a ready FM worklet. No external download,
runtime compiler, soundfont or network access is required for FM playback.

Scope
-----
Native S3M uses nine two-operator melodic voices, each routed through its own
MLT track bus. Opal internally supports OPL3 operators, but this integration
does not claim percussion-mode or timer/interrupt hardware emulation.
Keeping channels separate also keeps their track effects independent. It
does not apply the original chip's aggregate saturation after those effects;
integer per-channel resampling may differ by rounding from a summed output.
The existing MLT OPL2/GENMIDI path is retained separately.