Binary size and features

A feature should cost binary size only if you use it. BUI’s optional parts are one table, features.json, and three tools read it:

• CMake (features.cmake): one option each, ON by default (-DBUI_VIDEO=OFF). See CMake options.
• cargo: the same names are features of blenderui-sys and blenderui, all on by default. blenderui-sys/build.rs maps each to its CMake option and stops the build if Cargo.toml misses one; a test checks blenderui forwards them all.
• bui build: links the smallest prebuilt runtime that has what the app uses.

Off, a part’s sources aren’t compiled at all. Its API stays, so code compiles either way: a missing format doesn’t decode, a video reports an error state, BK_file_dialog returns -1, and windows draw with the software raster.

Rust

[dependencies]
# only what this app shows: no JPEG, WebP, video, GPU or file browser code
blenderui = { version = "0.3", default-features = false, features = ["slug", "png", "svg", "freetype"] }

bui build

Rebuilding the runtime per app would need a Rust and C toolchain on every machine that runs bui build. Splitting it into a core and loadable modules would cost a dynamic-library boundary (no whole-program LTO across it) and more files to ship. So the package ships a few prebuilt runtimes, listed in features.json, and bui build appends the app to the smallest one that has every feature the app needs: no compiler, and the same one-file executable.

How bui build decides, explicit first:

1. --features png,video on the command line;
2. "bui": { "features": ["png", "video"] } in the app’s package.json;
3. otherwise, it looks in the bundle: <video> elements, media file names in string literals ("logo.webp", "intro.mp4") and file dialogs.

It prints its choice (bui: runtime "media" for png, video). A path built at run time ("photo." + ext, a file the user picks) can’t be seen in the bundle, and the GPU renderer is never detected (the library’s own code mentions its option): list those features explicitly. A feature no prebuilt runtime has is an error that says so.

Measured

By feature, on Windows x64 with fat LTO: every image format together is about 596 KB (most of it libwebp and libjpeg-turbo), video 3 KB (the OS decodes; Media Foundation is loaded at run time), the Direct3D 11 renderer 42 KB and the file browser about 50 KB. The base runtime is about a tenth smaller than the full one; most of what remains is the same for every app: QuickJS, Rust’s standard library, the CSS and layout engine, Blender’s icons and the embedded Inter font. The Python wheel, the Node addon and cargo builds with default features have everything.