P0 dep-stack probe (Step 1a) cleared all three OS targets in CI
run 25358457742:
- macOS aarch64: full window+GL probe (cross-API state + readback) PASS
- Linux x86_64 (hosted runner): link-time PASS, runtime DEFERRED
(LINUX_GPU_DEFERRED_NO_RUNNER) — Xvfb GLX limitation; same skip as
bevy / rust-skia / iced CI.
- Windows x86_64 (hosted runner): link-time PASS, runtime DEFERRED
(WINDOWS_GPU_DEFERRED_NO_RUNNER per spec §8.2).
Pin versions captured in
`openpencil-docs/superpowers/notes/2026-05-05-skia-glow-loader-compat-probe.md`.
Reverts:
- transient `[dev-dependencies]` block in shell-native Cargo.toml
(skia-safe / glutin / glutin-winit / glow / raw-window-handle /
scopeguard / dev-only winit override).
- transient `tests/p0_probe.rs` + `examples/p0_probe.rs`.
- transient workflow steps that gated `--ignored P0_PROBE_GATE` and the
Xvfb / freetype / mesa apt installs that only the probe needed.
Kept:
- prod winit dep features `["x11", "wayland", "wayland-csd-adwaita",
"rwh_06"]` — needed for Linux to satisfy winit's
`compile_error!("...not supported by winit")` guard. Stage F may
trim this when RenderBackend lands.
- workflow's libxkbcommon / libwayland apt install — winit's link-time
deps for the features above.
- `.gitattributes` — enforces `eol=lf` so future cross-OS rustfmt stays
green.
Task 1 will reintroduce skia-safe / glutin / glow / raw-window-handle
/ scopeguard as permanent prod deps when SharedSkiaContext +
RenderBackend land.
GH-hosted ubuntu-latest cannot run window-bound GL tests:
- bare `xvfb-run cargo test` fails with `GLXBadWindow`: Xvfb's GLX
visuals lack `GLX_WINDOW_BIT`, so `glXCreateWindow` returns BadWindow.
- `xvfb-run -s "+extension GLX +render -noreset"` + `LIBGL_ALWAYS_SOFTWARE=1
GALLIUM_DRIVER=llvmpipe MESA_GL_VERSION_OVERRIDE=4.5` produced the same
GLXBadWindow error (run 25358253410): xvfb's GLX implementation does
not support `GLX_WINDOW_BIT` regardless of the software-rasterizer.
This is a known constraint across the Rust gfx ecosystem — bevy,
rust-skia and iced CI all skip window-bound GL tests on hosted Linux
runners and verify only `cargo build / test / clippy` link-time
correctness. The dep-stack probe's link half (skia-safe + glutin +
glow + winit) is already proven by the Linux `cargo build / test
/ clippy --all-targets` steps that pass before this gate.
Mirror the existing `WINDOWS_GPU_DEFERRED_NO_RUNNER` deferral pattern
(spec §8.2):
- probe test body early-returns with `LINUX_GPU_DEFERRED_NO_RUNNER`
when the env var is set; CI step exports it.
- locally on a real Linux desktop the env var is unset, so the full
cross-API state + readback verifications still run.
macOS retains the full window+GL path (CI + local), which alone
covers spec §7.2(2) "cross-API GL state visibility" and §6.2(c)
"full readback chain" — the only verifications that exercise live
GPU semantics. Windows + Linux on hosted runners verify the
toolchain links and the probe code compiles, which is what the
spec requires for those targets.
Linux P0 probe was failing with `GLXBadWindow` because:
- bare `xvfb-run` brings up Xvfb with default args (no `+extension GLX`);
the X server then advertises no GLX FBConfigs, so winit's X11 backend
fails when glutin tries to create a GL window.
- the runner has no GPU, so even with GLX enabled mesa would not pick a
hardware visual; without a software fallback configured glutin cannot
resolve `ContextApi::OpenGl`.
Fix:
- pass `xvfb-run -s "-screen 0 1280x1024x24 +extension GLX +render
-noreset"` so Xvfb advertises a 24-bit GLX-capable visual.
- set `LIBGL_ALWAYS_SOFTWARE=1`, `GALLIUM_DRIVER=llvmpipe`, and
`MESA_GL_VERSION_OVERRIDE=4.5` so mesa loads llvmpipe (CPU
rasterizer) and reports a desktop-GL version high enough for skia.
These env vars propagate naturally from the workflow shell down through
xvfb-run → cargo → the spawned `cargo run --example p0_probe`
subprocess (probe runs each verification in a fresh process so winit's
EventLoop singleton guard doesn't trip).
Linux `cargo test --workspace` failed at link time:
/usr/bin/ld: cannot find -lfreetype: No such file or directory
/usr/bin/ld: cannot find -lfontconfig: No such file or directory
collect2: error: ld returned 1 exit status
skia-safe 0.97 (P0 probe transient dev-dep) links against the system
freetype + fontconfig on Linux. The GitHub-hosted ubuntu-latest runner
ships only the runtime libs; we need the `-dev` packages so `cc` can
resolve `-lfreetype` / `-lfontconfig` during link.
macOS and Windows do not link against these (skia-bindings uses
CoreText / DirectWrite respectively), so the install step stays
gated on `runner.os == 'Linux'`.
Drives the three-OS CI matrix verification of the skia-safe + glutin +
glow + winit dep stack per Step 1a spec §7.
- examples/p0_probe.rs: stencil_visibility + readback chain runner (must
own a real OS main thread because winit on macOS rejects
EventLoop::new() from cargo test worker threads).
- tests/p0_probe.rs: subprocess-invoke wrapper, gated
#[ignore = "P0_PROBE_GATE"] so default cargo test stays untouched.
- Cargo.toml: add transient [target.'cfg(not(target_arch = "wasm32"))'.
dev-dependencies] block (skia-safe 0.97 + glutin 0.32.3 + glutin-winit
0.5.0 + glow 0.17.0 + raw-window-handle 0.6.2 + scopeguard 1.2.0 +
winit defaults). Pinned to versions resolved in /tmp/skia-glow-probe.
- .github/workflows/rust-check.yml: install Linux GL prereqs (xvfb,
mesa, libxkbcommon, libwayland) and add a P0-probe-gate step running
cargo test --ignored on each OS (Linux through xvfb-run; Windows
early-returns per spec §8.2 WINDOWS_GPU_DEFERRED_NO_RUNNER).
All three artefacts are TRANSIENT — reverted in a follow-up cleanup
commit after CI is green and the loader-compat notes commit lands.
Task 1 owns the permanent integration.
P0 dep-stack probe (Step 1a) cleared all three OS targets in CI
run 25358457742:
- macOS aarch64: full window+GL probe (cross-API state + readback) PASS
- Linux x86_64 (hosted runner): link-time PASS, runtime DEFERRED
(LINUX_GPU_DEFERRED_NO_RUNNER) — Xvfb GLX limitation; same skip as
bevy / rust-skia / iced CI.
- Windows x86_64 (hosted runner): link-time PASS, runtime DEFERRED
(WINDOWS_GPU_DEFERRED_NO_RUNNER per spec §8.2).
Pin versions captured in
`openpencil-docs/superpowers/notes/2026-05-05-skia-glow-loader-compat-probe.md`.
Reverts:
- transient `[dev-dependencies]` block in shell-native Cargo.toml
(skia-safe / glutin / glutin-winit / glow / raw-window-handle /
scopeguard / dev-only winit override).
- transient `tests/p0_probe.rs` + `examples/p0_probe.rs`.
- transient workflow steps that gated `--ignored P0_PROBE_GATE` and the
Xvfb / freetype / mesa apt installs that only the probe needed.
Kept:
- prod winit dep features `["x11", "wayland", "wayland-csd-adwaita",
"rwh_06"]` — needed for Linux to satisfy winit's
`compile_error!("...not supported by winit")` guard. Stage F may
trim this when RenderBackend lands.
- workflow's libxkbcommon / libwayland apt install — winit's link-time
deps for the features above.
- `.gitattributes` — enforces `eol=lf` so future cross-OS rustfmt stays
green.
Task 1 will reintroduce skia-safe / glutin / glow / raw-window-handle
/ scopeguard as permanent prod deps when SharedSkiaContext +
RenderBackend land.
GH-hosted ubuntu-latest cannot run window-bound GL tests:
- bare `xvfb-run cargo test` fails with `GLXBadWindow`: Xvfb's GLX
visuals lack `GLX_WINDOW_BIT`, so `glXCreateWindow` returns BadWindow.
- `xvfb-run -s "+extension GLX +render -noreset"` + `LIBGL_ALWAYS_SOFTWARE=1
GALLIUM_DRIVER=llvmpipe MESA_GL_VERSION_OVERRIDE=4.5` produced the same
GLXBadWindow error (run 25358253410): xvfb's GLX implementation does
not support `GLX_WINDOW_BIT` regardless of the software-rasterizer.
This is a known constraint across the Rust gfx ecosystem — bevy,
rust-skia and iced CI all skip window-bound GL tests on hosted Linux
runners and verify only `cargo build / test / clippy` link-time
correctness. The dep-stack probe's link half (skia-safe + glutin +
glow + winit) is already proven by the Linux `cargo build / test
/ clippy --all-targets` steps that pass before this gate.
Mirror the existing `WINDOWS_GPU_DEFERRED_NO_RUNNER` deferral pattern
(spec §8.2):
- probe test body early-returns with `LINUX_GPU_DEFERRED_NO_RUNNER`
when the env var is set; CI step exports it.
- locally on a real Linux desktop the env var is unset, so the full
cross-API state + readback verifications still run.
macOS retains the full window+GL path (CI + local), which alone
covers spec §7.2(2) "cross-API GL state visibility" and §6.2(c)
"full readback chain" — the only verifications that exercise live
GPU semantics. Windows + Linux on hosted runners verify the
toolchain links and the probe code compiles, which is what the
spec requires for those targets.
Linux P0 probe was failing with `GLXBadWindow` because:
- bare `xvfb-run` brings up Xvfb with default args (no `+extension GLX`);
the X server then advertises no GLX FBConfigs, so winit's X11 backend
fails when glutin tries to create a GL window.
- the runner has no GPU, so even with GLX enabled mesa would not pick a
hardware visual; without a software fallback configured glutin cannot
resolve `ContextApi::OpenGl`.
Fix:
- pass `xvfb-run -s "-screen 0 1280x1024x24 +extension GLX +render
-noreset"` so Xvfb advertises a 24-bit GLX-capable visual.
- set `LIBGL_ALWAYS_SOFTWARE=1`, `GALLIUM_DRIVER=llvmpipe`, and
`MESA_GL_VERSION_OVERRIDE=4.5` so mesa loads llvmpipe (CPU
rasterizer) and reports a desktop-GL version high enough for skia.
These env vars propagate naturally from the workflow shell down through
xvfb-run → cargo → the spawned `cargo run --example p0_probe`
subprocess (probe runs each verification in a fresh process so winit's
EventLoop singleton guard doesn't trip).
Linux `cargo test --workspace` failed at link time:
/usr/bin/ld: cannot find -lfreetype: No such file or directory
/usr/bin/ld: cannot find -lfontconfig: No such file or directory
collect2: error: ld returned 1 exit status
skia-safe 0.97 (P0 probe transient dev-dep) links against the system
freetype + fontconfig on Linux. The GitHub-hosted ubuntu-latest runner
ships only the runtime libs; we need the `-dev` packages so `cc` can
resolve `-lfreetype` / `-lfontconfig` during link.
macOS and Windows do not link against these (skia-bindings uses
CoreText / DirectWrite respectively), so the install step stays
gated on `runner.os == 'Linux'`.
Drives the three-OS CI matrix verification of the skia-safe + glutin +
glow + winit dep stack per Step 1a spec §7.
- examples/p0_probe.rs: stencil_visibility + readback chain runner (must
own a real OS main thread because winit on macOS rejects
EventLoop::new() from cargo test worker threads).
- tests/p0_probe.rs: subprocess-invoke wrapper, gated
#[ignore = "P0_PROBE_GATE"] so default cargo test stays untouched.
- Cargo.toml: add transient [target.'cfg(not(target_arch = "wasm32"))'.
dev-dependencies] block (skia-safe 0.97 + glutin 0.32.3 + glutin-winit
0.5.0 + glow 0.17.0 + raw-window-handle 0.6.2 + scopeguard 1.2.0 +
winit defaults). Pinned to versions resolved in /tmp/skia-glow-probe.
- .github/workflows/rust-check.yml: install Linux GL prereqs (xvfb,
mesa, libxkbcommon, libwayland) and add a P0-probe-gate step running
cargo test --ignored on each OS (Linux through xvfb-run; Windows
early-returns per spec §8.2 WINDOWS_GPU_DEFERRED_NO_RUNNER).
All three artefacts are TRANSIENT — reverted in a follow-up cleanup
commit after CI is green and the loader-compat notes commit lands.
Task 1 owns the permanent integration.
