makepad/docs/agents/web-pack.md

Web packs

A web build ships only what the app was seen to use. One tool covers any Makepad app:

cargo makepad wasm --pack=<film|app|full> [--strict] build -p <app> --release

1. Collect. The app runs once natively as MAKEPAD_RUN=collect-web (MAKEPAD_COLLECT=<dir>): the headless runtime with the web font set and the WebGL2 shader compiler. It draws a few frames, sends one Event::Scan through the widget tree, draws again and writes the manifest (makepad-web-manifest): the shader pack, kernels, glyphs per font file, widget types, assets, JS features and who needed each one.
2. Pack. The wasm is linked with the shader pack (--strict also leaves the shader compiler out), fonts are cut to the glyphs used (makepad-font-subset), and the web runtime's JS loses the // @sections nothing needed.

Presets: film (only what was collected), app (keeps a shader-compiler fallback and full fonts), full (everything). Stage's Share → Web export runs the same steps for a film, with its own scanner for documents.

What widgets do in a scan

Event::Scan reaches every widget, visible or not, through children(). A widget emits what it needs through the event's ScanEvent:

fn scan(&mut self, cx: &mut Cx, scan: &ScanEvent, _scope: &mut Scope) {
    // Typed text can be any character: ship the whole face.
    scan.need_font_full("Inter");
    scan.need_js_feature("text-input");
    scan.need_js_feature("clipboard");
}

Other needs: need_glyphs(face, text), need_font_range(face, "latin"), need_kernel, need_widget::<T>(), need_asset(path). Shaders are recorded automatically when they are applied. cx.is_collecting() says whether the app runs a collect run. An app with dynamic text says so itself, for example need_font_range(face, "latin") for user names.

When a web build misses something

Widgets that create children from data spawn the templates of their scan: list (or every template they hold) during the scan; see splash.md. A web build that meets something not in its pack logs it with the widget path and file:line, for example not in pack: draw shader 'Row' ..., add the widget that creates it to a scan: list. Add the template to that widget's scan: [...] and build again.