gui_hello

Three minimal “show a window with a label” demos – one per OS family. Each is a single C source file; the smoke runner asks badc to cross-compile every source to every supported target so the build verifies on any host.

File	Target families	What it links against
`hello_win32.c`	`windows-x64`, `windows-arm64`	user32.dll, gdi32.dll, kernel32.dll
`hello_x11.c`	`linux-x64`, `linux-aarch64`	libX11.so.6
`hello_macos.c`	`macos-aarch64`	libobjc.A.dylib + AppKit.framework

Workflow

python demos/gui_hello/smoke.py    # builds all five targets via badc
                                   # and exits 0 on a clean build.
                                   # Runs build-only -- no display
                                   # server is required.

# Local run (matches your host):
./demos/gui_hello/.build/hello-<your-target>

What each demo exercises

hello_win32.c – Pins the GUI subsystem via #pragma subsystem(windows) so the PE optional header carries IMAGE_SUBSYSTEM_WINDOWS_GUI = 2 instead of the default console value, and #pragma entrypoint(WinMain) so the loader resolves WinMain rather than main. Drives the standard WNDCLASSA / RegisterClassA / CreateWindowExA / GetMessageA / DispatchMessageA loop; paints “Hello from badc!” via BeginPaint / TextOutA / EndPaint. Closing the window posts WM_DESTROY and the loop exits.
hello_x11.c – Connects to $DISPLAY, opens an XCreateSimpleWindow, registers for Expose / KeyPress, and draws “Hello from badc!” on every Expose. Any keypress closes the connection. The X11 surface is C-only, no Objective-C / GLib / Wayland involvement.
hello_macos.c – Drives the Cocoa runtime through libobjc.A.dylib’s objc_getClass / sel_registerName / objc_msgSend. NSApplication / NSWindow / NSString are all reached by message-send rather than ObjC syntax; the c5 compiler doesn’t speak Objective-C, but the runtime ABI is pure C so the demo composes cleanly. Opens a 480x240 NSWindow titled “badc Cocoa hello” and runs [NSApp run] until the window closes.

CI

The smoke step is build-only – runners don’t have display servers, X servers, or Window Stations. Each runner runs python demos/gui_hello/smoke.py, which loops over the five (target, source) combinations and asks badc to produce a binary; a non-zero exit on any combination fails CI. Local developers can run the matching binary directly to see the actual window.

Why one demo per OS

A single cross-platform GUI source is possible (SDL2 / GLFW / raylib all cover the three OSes), but bundling those would make the demo a vendored-third-party-deps test rather than a GUI test. Hand-writing the per-OS minimum keeps the demo self-contained and surfaces any OS-specific c5 codegen / ABI gaps directly. Future GUI demos (raylib, …) can sit alongside this one without overlap.

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