ONScripter-RU (WebAssembly Fork)

Fork of ONScripter-RU with modifications to compile and run in the browser via Emscripten and WebAssembly.

This fork powers Umineko Web - the full Umineko no Naku Koro ni (PS3/Umineko Project build) running entirely in a browser tab.

What This Fork Changes

The upstream engine targets Windows, macOS, Linux, iOS, and Android. It relies on multithreading, synchronous file I/O, and native GPU rendering - none of which translate directly to the browser. This fork adds an __EMSCRIPTEN__ compile target that replaces threaded subsystems with single-threaded synchronous equivalents, rewires file I/O to fetch assets over HTTP on demand, and adapts the graphics and audio pipelines for WebGL and the Web Audio API.

All changes are gated behind #ifdef __EMSCRIPTEN__ so the native builds remain unaffected.

Modified Files

18 source files contain Emscripten-specific changes:

File I/O

File

Change

Support/FileIO.cpp

EM_ASYNC_JS hook that intercepts fopen() on lazy-loaded files. In local/production mode, fetches the real data over HTTP via await fetch(). In remote mode, reads from the user's local game folder via window.readLocalFile() (backed by the File System Access API or <input webkitdirectory>). Writes the data into the Emscripten virtual filesystem and returns the file handle to the caller. The engine sees synchronous file access regardless of the source.

Video Playback

File	Change
Engine/Media/Controller.cpp	pumpSynchronous() - replaces the multi-threaded demuxer/decoder pipeline with a single-threaded synchronous loop. Reads packets via av_read_frame(), decodes video and audio frames inline, and pushes them into a bounded frame queue (capped at 6 frames to stay within WASM's 2GB memory limit).
Engine/Media/Controller.cpp	Subtitle blending added to the synchronous decode path. On native, applySubtitles() is called from the decoder thread. On Emscripten, it is called inline after each video frame is decoded.
Engine/Media/Controller.cpp	finish() adapted for single-threaded teardown (no threads to join).
Engine/Media/Controller.hpp	pumpSynchronous() declaration.
Engine/Media/VideoDecoder.cpp	Colour space conversion adjusted - skips sws_setColorspaceDetails() tuning that is not needed for browser rendering.
Engine/Layers/Media.cpp	Synchronous frame pumping in the media layer's update loop. Calls pumpSynchronous() each frame instead of relying on background threads to fill the queue.

Subtitle Rendering

File	Change
Engine/Layers/Subtitle.cpp	SubtitleLayer rewritten for single-threaded operation. startDecoding() skips mutex/semaphore creation and background thread launch. update() calls subtitleDriver.extractFrame() directly instead of reading from a thread-fed frame queue. endDecoding() skips semaphore wait and mutex cleanup.

Threading and Async

File	Change
Engine/Components/Async.cpp	SDL_CreateThread calls skipped. The async controller's queue mechanism runs inline instead of dispatching to background threads.

Event Loop and Persistence

File	Change
Engine/Core/Event.cpp	Periodic IDBFS sync added to the main event loop. Calls FS.syncfs() at regular intervals to flush save data from the Emscripten virtual filesystem to the browser's IndexedDB.
Engine/Core/ONScripter.cpp	Startup path adjustments for the browser environment.
Engine/Core/File.cpp	File handling adjustments for the Emscripten virtual filesystem.

Graphics

File	Change
Engine/Graphics/GPU.cpp	WebGL-compatible GPU initialisation. Adjusts context creation and feature detection for the GLES2-over-WebGL path.
Engine/Graphics/GPU.hpp	Related declarations.
Engine/Graphics/GLES2.cpp	GLES2 shader compatibility adjustments for WebGL.

Input and Other

File	Change
Engine/Core/Image.cpp	Frame queue management adjustments for the single-threaded decode path.
Engine/Core/Animation.cpp	Minor adjustments for Emscripten compatibility.
Engine/Core/CommandExt.cpp	Command handling adjustments for browser environment.
Engine/Core/Sound.cpp	Audio path adjustments for Web Audio API backend.
Engine/Components/Joystick.hpp	Joystick detection disabled (not applicable in browser).
Engine/Core/ONScripter.hpp	Related declarations.

Building

This fork is not built standalone. It is cloned and compiled as part of the Umineko Web Docker build, which provides the Emscripten SDK, cross-compiled dependencies (FFmpeg, libass, HarfBuzz, FriBidi, SDL2_gpu), and the CMake configuration that ties everything together.

For native platform builds (Windows, macOS, Linux), refer to the upstream Compilation.md.

Credits

Fork

• VictoriqueMoe - Emscripten/WebAssembly port

Original

• Ogapee
• "Uncle" Mion Sonozaki
• Umineko Project
• All third-party library authors