# wasm/gl1 — GL 1.x fixed-function pipeline on WebGL2

Emulation layer that lets KiCad's 3D viewer renderer (`RENDER_3D_OPENGL`,
pure GL 1.x fixed-function, compiled **unmodified**) render in the browser.
Supersedes the no-op link stubs of `wasm/stubs/gl_ffp_stub.c` (git history
has the old file): same public surface, real implementations.

TDD harness: `tests/3d-regression/` — 47 native-golden scenarios; parity via
`npm run 3d:check:parity` (see that README).

## How the symbols resolve

In the WASM build, `gl*` are plain C functions split between two providers:

- **Emscripten's WebGL library** (`-sMAX_WEBGL_VERSION=2`) owns every
  modern/WebGL2 name (`glClear`, `glDrawArrays`, `glTexImage2D`, buffers,
  shaders, stencil...).
- **This shim** owns the FFP-only names WebGL2 lacks (`glBegin`, display
  lists, matrix stack, `glLight*`/`glMaterial*`, client-array pointers,
  `glTexEnv*`, `glAlphaFunc`, GLU quadrics) — see `src/gl1_entry_ffp.cpp`.

The emulator must also *observe* a few Emscripten-owned calls (FFP `glEnable`
caps, draws over client arrays, matrix readback, state recorded inside
display lists). Those are intercepted with **wasm-ld `--wrap`**: every name in
`wrapped_symbols.txt` gets a `-Wl,--wrap=<sym>` flag at both link sites, the
interceptors live in `src/gl1_entry_wrapped.cpp`, and `__real_*` forwards to
the WebGL library. No kicad/wxwidgets sources are touched.

Link sites (both read `sources.txt` + `wrapped_symbols.txt`):

- `tests/3d-regression/wasm/Makefile` (the TDD harness)
- `scripts/kicad/build-kicad-target.sh` (`GL3D_LINK_FLAGS`, production
  `kicad_editor`)

## Draw routing

A `glDrawArrays`/`glDrawElements` call is FFP traffic iff `GL_VERTEX_ARRAY`
client state is enabled: only GL1 code calls `glEnableClientState`, while the
raytracer blit (`eda_3d_canvas_wasm.cpp`) and the 2D WebGL GAL drive their own
GLSL programs and never touch client state — their draws pass through
untouched.

## Invariants that are easy to break (learned from the native goldens)

- **Display lists snapshot client arrays at record time.** The renderer sets
  `gl*Pointer`, records `glDrawArrays` inside `glNewList`, then `delete[]`s
  the arrays right after `glEndList` (`layer_triangles.cpp`) — a recorder
  that stores pointers reads freed memory. Copy eagerly at record.
- **Lights live in eye space, captured at `glLightfv` time.** `init_lights()`
  runs under an identity modelview → the directional lights are anchored to
  the camera. Re-deriving light directions at draw time breaks every lit
  scenario.
- **Do not "fix" mismatched normal counts.** `generate_middle_triangles`
  rejecting countersink walls (normals ≠ vertices) is upstream KiCad behavior
  the goldens document; tolerating it would *diverge* from native.
- **Lighting is per-vertex (Gouraud)** to match fixed-function output;
  per-fragment lighting visibly mismatches speculars on coarse meshes.

## Layout

```
sources.txt / wrapped_symbols.txt   single source of truth for both link sites
include/gl1_shim.h                  internal API + the state mirror
src/gl1_entry_ffp.cpp               the 52 FFP-only public entry points
src/gl1_entry_wrapped.cpp           __wrap_* interceptors (mechanism-aware TU)
src/gl1_state.cpp                   state singleton, capability routing
src/gl1_matrix.cpp                  MODELVIEW/PROJECTION stacks (+readback)
src/gl1_immediate.cpp               glBegin/glEnd + primitive conversion
src/gl1_dlist.cpp                   display-list recorder/replayer
src/gl1_draw.cpp                    draw execution (stream VBO, attrib setup)
src/gl1_shaders.cpp                 the FFP uber-program (ES 3.00) + uniforms
src/gl1_glu.cpp                     GLU quadrics (SGI tessellation) + gluPerspective
```