feat(embedded): support GTK OpenGL hosts

[bvolpato]

Summary

• add a Linux embedded platform for main-thread GTK GLArea rendering
• expose display unrealize/realize hooks so hosts can rebuild OpenGL resources after widget reparenting
• preserve callback-backed OpenGL sizing and swap behavior
• make font query APIs compile and report names with FreeType as well as CoreText

This ports the minimal GTK embedding support originally implemented by FreeMeWat onto current manaflow-ai/ghostty without carrying the older fork. The commit retains original authorship credit through Co-authored-by.

Why

GTK GLArea owns a main-thread framebuffer. Generic callback-backed OpenGL may render on Ghostty’s renderer thread, so it cannot safely replace this path. Linux also exposed a pre-existing build failure in the font query API because it directly accessed CoreText-only fields.

Validation

• zig build -Dapp-runtime=none -Doptimize=ReleaseFast -Dcpu=baseline
• zig build test -Dapp-runtime=none -Dtest-filter="OpenGL presentation preserves"
• zig build test -Dapp-runtime=none -Dtest-filter="face name"
• C header translation through focused test builds

Full unfiltered Ghostty test process was killed with exit 137 on a memory-pressured workstation. Focused changed-path tests pass; downstream Limux full Rust and live GTK smoke gates run separately.

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Summary by cubic

Add Linux GTK GLArea embedding for OpenGL with per-surface app-thread rendering and explicit display realize/unrealize hooks. Font queries are now portable across CoreText and FreeType, preserving file paths for file-backed faces on Linux.

• New Features

  • Added GHOSTTY_PLATFORM_LINUX and linux_platform in ghostty.h, plus ghostty_surface_display_unrealized and ghostty_surface_display_realized.
  • Linux GLArea draws on the app thread, uses the current FBO/viewport for size, and lets GTK swap after the render callback; callback-backed OpenGL retains enter/leave and swap_buffers.

• Bug Fixes

  • Choose app-thread drawing per surface so GTK GLArea uses its owning thread while callback-backed OpenGL stays on the renderer thread.
  • FreeType now returns a PostScript name and exposes urlPath for file-backed faces; the path is preserved across synthetic bold/italic. Memory-backed faces still have no URL.

^{Written for commit 1a89efa. Summary will update on new commits.}

Summary by CodeRabbit

• New Features
  • Added Linux as a supported embedded platform.
  • Added support for notifying surfaces when the host OpenGL display is created or destroyed.
  • Improved embedded OpenGL handling for Linux-based environments.
  • Added font metadata access for PostScript names and source paths where available.

[coderabbitai]

📝 Walkthrough

Walkthrough

This change adds Linux to the embedded platform ABI. It adds Linux-specific drawing and OpenGL context lifecycle handling. It also adds cross-backend font PostScript name and source path accessors.

Changes

Linux embedded support

Layer / File(s)	Summary
Linux platform contract include/ghostty.h, src/apprt/embedded.zig	Adds the Linux platform enum, payload, union member, platform tag, initialization path, and application-thread drawing flag.
Font metadata access src/font/face/coretext.zig, src/font/face/freetype.zig, src/apprt/embedded.zig	Adds Face.postscriptName and Face.urlPath for CoreText and FreeType. Embedded font reporting uses these accessors.
Embedded context lifecycle include/ghostty.h, src/apprt/embedded.zig, src/renderer/OpenGL.zig	Adds display lifecycle callbacks. Linux skips explicit context switching, uses the current GTK context, queries the current viewport, and leaves presentation to GTK.

Estimated code review effort: 4 (Complex) | ~45 minutes

Suggested reviewers: mitchellh, lawrencecchen

Sequence Diagram(s)

sequenceDiagram
  participant HostApplication
  participant SurfaceLifecycle
  participant OpenGL
  participant SurfaceDraw
  HostApplication->>SurfaceLifecycle: call ghostty_surface_display_unrealized
  SurfaceLifecycle->>OpenGL: release renderer resources
  HostApplication->>OpenGL: make GTK context current
  HostApplication->>SurfaceLifecycle: call ghostty_surface_display_realized
  SurfaceLifecycle->>OpenGL: prepare current embedded context
  HostApplication->>SurfaceDraw: draw surface
  SurfaceDraw->>OpenGL: drawFrame(false)

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: adding embedded GTK OpenGL host support.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: ec9b2a0afe

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/font/face/freetype.zig`:
- Around line 193-199: Update the FreeType Face path handling so
initFile-created faces retain their owned source path and urlPath returns it,
while memory-backed faces continue returning null. Ensure synthetic face copies
propagate the stored path and preserve correct buffer handling in urlPath.

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Fix all unresolved CodeRabbit comments on this PR:

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• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: d3db61cf-18bf-4453-ab72-a95c90ef1691

📥 Commits

Reviewing files that changed from the base of the PR and between f76c132 and ec9b2a0.

📒 Files selected for processing (5)

• include/ghostty.h
• src/apprt/embedded.zig
• src/font/face/coretext.zig
• src/font/face/freetype.zig
• src/renderer/OpenGL.zig