Gerber Viewer (gerbview) WASM port — design notes

Goal

Bring up KiCad's Gerber Viewer (gerbview, FRAME_GERBER) in the browser to the "boots, canvas visible, click around" level the other ported apps reached. Scope is launch-only — loading actual Gerber/drill files is out of scope for now.

Approach

gerbview is its own standalone program + kiface (unlike symbol_editor, which lived inside the eeschema kiface), so it follows the pl_editor/pcbnew pattern almost verbatim: gate the native dynamic-kiface logic behind if( EMSCRIPTEN ) and link the kiface objects statically into the gerbview executable. gerbview.cpp (the KIFACE_GETTER) is already part of gerbview_kiface_objects, so no source hoisting was needed (unlike eeschema). There was no #ifdef __EMSCRIPTEN__ frame stub to remove (gerbview was never gated out, unlike the symbol editor).

Changes (kicad submodule)

kicad/gerbview/CMakeLists.txt — mirror pl_editor's WASM static-link block:
- On EMSCRIPTEN, compile common/single_top.cpp with TOP_FRAME=FRAME_GERBER (no BUILD_KIWAY_DLL); wrap the native minimal exe link in if( NOT EMSCRIPTEN ).
- Hoist the kiface deps into GERBVIEW_KIFACE_LIBRARIES; on EMSCRIPTEN link them directly into the gerbview exe with LINKER:--allow-multiple-definition.
- Gate gerbview.cpp defs: EMSCRIPTEN → COMPILING_DLL (no BUILD_KIWAY_DLL, so KIFACE_GETTER links statically); else BUILD_KIWAY_DLL;COMPILING_DLL.
kicad/gerbview/navlib/CMakeLists.txt — add an if( EMSCRIPTEN ) branch that builds gerbview_navlib from the WASM stub instead of the real 3Dconnexion plugin (no SpaceMouse driver in the browser). The frame's navlib member uses NL_GERBVIEW_PLUGIN under WASM (#ifndef __linux__; emscripten doesn't define it).
#include <wx/choice.h> added to three files that use wxChoice (the Cmp/Net/Attr/DCode aux-toolbar combo boxes) but only had the forward declaration: gerbview/events_called_functions.cpp, gerbview/toolbars_gerber.cpp, gerbview/tools/gerbview_control.cpp. Native builds pull wx/choice.h transitively; the WASM wxWidgets header config does not, so these failed with "member access into incomplete type 'wxChoice'". Include-what-you-use fix — behavior-neutral, upstream-safe. (gerbview_frame.cpp already gets it transitively; the generated _base.cpp carries its own includes — both left untouched to keep the fork minimal.)

Changes (root repo)

wasm/stubs/nl_gerbview_plugin_stub.cpp (NEW) — no-op NL_GERBVIEW_PLUGIN ctor/dtor + SetCanvas/SetFocus, mirroring nl_pl_editor_plugin_stub.cpp.
scripts/kicad/build-gerbview.sh (NEW) — thin wrapper → build-kicad-target.sh gerbview.
scripts/kicad/build-kicad-target.sh — add gerbview to the pcbnew|eeschema) case arm (target = subdir = gerbview); update usage strings.
docker/build.sh — add gerbview to valid apps, dispatch case, and the all loop (now 6 apps).
tests/scripts/setup-kicad-wasm.sh — copy_app gerbview.
tests/apps/kicad/gerbview.html (NEW) — browser shell (copy of pl_editor.html; title, thisProgram=/usr/bin/gerbview, gerbview.js).
tests/kicad/gerbview.spec.ts (NEW) + tests/package.json — launch-only smoke test (wizard, canvas visible, registry populated, ≥1 toolbar, no abort).

Build & verify

./docker/build.sh gerbview          # seed fresh-branch cache from main first (see build-quirks memory)
cd tests && npm run setup:kicad && npm run test:gerbview

Expect: the viewer opens — menu bar, top + aux toolbars (with the Cmp/Net/Attr/DCode combos), left tool toolbar, dark gerber canvas with grid + origin crosshair, and the Layers/Items manager pane. gerbview.spec.ts passes (2/2, no abort).

Known limitations

No Gerber/drill files are loaded; the canvas is empty until a file is opened (file loading untested / out of scope).
Symbol-editor-style drawing tools that require an open document behave per native KiCad (some are inactive with no layers loaded).
No persistent storage (MEMFS only).

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