feat(macos): software backend blit #163

[k-chimi]

resolve #163

Rebased onto origin/main by git rebase origin/main.

I confirmed renders triangle correctly in gogpu/examples/triangle (GOGPU_GRAPHICS_API=software)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[kolkov]

Code Review: PR #187

Thank you for applying all review fixes and rebasing onto main! Triangle rendering on macOS confirmed — great work.

All review fixes applied ✅

Fix	Status	Verified
isIinitialized → isInitialized	Fixed	lines 30, 66, 78
TODO comment	Removed	grep returns empty
Commented slog.Warn	Removed	grep returns empty
Debug slog.Debug("width ret")	Removed	grep returns empty
Commented RegionMake2D	Removed	grep returns empty
Naming blitFramebufferToWindow	Consistent lowercase	lines 88, 114, 248, 260
CAMetalLayer damage rects	Full blit fallback	lines 141-146

CI: macOS test crash (only blocker)

signal arrived during cgo execution
fault   0x1
FAIL    github.com/gogpu/wgpu/hal/software    3.515s

The macOS CI runner is headless (no display, no Metal GPU). platformBlit.init() loads Metal framework and calls MTLCreateSystemDefaultDevice() via ffi.CallFunction — the FFI call itself segfaults before returning an error on the headless runner.

Windows and Ubuntu tests were cancelled (not failed) — CI auto-cancels remaining jobs when one fails. Those platforms are unaffected.

Suggested fix: Check if the Metal framework file exists on disk before calling ffi.LoadLibrary:

func (m *metal) Open(objc *objcReflect) (err error) {
    // Skip Metal on headless CI / environments without GPU
    if _, err := os.Stat(metalLibraryLocation); err != nil {
        return fmt.Errorf("software.metal: framework not found: %w", err)
    }
    // ... existing code
}

Or, if the framework exists but MTLCreateSystemDefaultDevice returns nil (no GPU), ensure the nil check in init() (line 55-58) is reached before the segfault. The crash may happen inside ffi.CallFunction itself when Metal runtime initializes on a headless system.

Code quality — verified claims

Claim	Evidence
1302 LOC	wc -l = 1302 ✅
--- BEGIN/END OBJC BINDING --- sections	lines 322, 1302 ✅
Selector caching sync.Map	selCaches/clsCaches at lines 1051-1052 ✅
objc_msgSend_stret/_fpret dispatch	lines 1044-1046, 1121-1128 ✅
runtime.KeepAlive(args)	line 1114 ✅
BGRA format ByteOrder32Little | PremultipliedFirst	lines 162-163, 735, 742 ✅
runtime import used	lines 1114, 1121, 1127 (KeepAlive, GOARCH checks) ✅

Action needed

Fix the headless macOS CI crash — this is the only blocker. Once hal/software tests pass on macOS CI, we merge.

[k-chimi]

thanks for your review! I've fixed my code.

Please check it when you have a moment. 🙏

[kolkov]

LGTM! All review fixes applied, CI 11/11 green. Great contribution.