Merge the shell backends into one Shell library

[jayrulez]

Fold both backends into a single Shell library (folder-separated only: Desktop/ = SDL3, Null/ = headless), so Shell is the only shell library and SDL3 is a fully internal PRIVATE dependency.

• The two per-backend factory units collapse into one Shell.cpp bridge that dispatches createShell()/destroyShell() to the backend chosen at compile time via DRACO_SHELL_SDL3.
• Both backend modules (shell.desktop, shell.null) compile into the one library, so both stay independently testable in every build.
• Runtime links only Shell; the sample links only Runtime. SDL propagates through Shell's PRIVATE link, so nothing downstream links SDL directly. The SDL whole-archive force-load stays on the executable (not Shell) so it does not force a full SDL copy into the intermediate Runtime library.

Both shell tests pass and RenderSample builds and runs.

Summary by CodeRabbit

• New Features

  • Added unified shell backend support, automatically selecting the desktop or null implementation as configured.
  • Improved SDL3 integration for rendering applications, including reliable inclusion of required drivers.

• Tests

  • Added dedicated validation for both desktop and null shell backends, with test report generation.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 48a06a87-e49a-4913-bbcd-d705706025a8

📥 Commits

Reviewing files that changed from the base of the PR and between da9ea3c and 8092382.

📒 Files selected for processing (6)

• Engine/cpp/CMakeLists.txt
• Engine/cpp/Runtime/CMakeLists.txt
• Engine/cpp/Runtime/Shell/Desktop/SDL3ShellFactory.cpp
• Engine/cpp/Runtime/Shell/Null/NullShellFactory.cpp
• Engine/cpp/Runtime/Shell/Shell.cpp
• Samples/cpp/Render/CMakeLists.txt

💤 Files with no reviewable changes (2)

• Engine/cpp/Runtime/Shell/Desktop/SDL3ShellFactory.cpp
• Engine/cpp/Runtime/Shell/Null/NullShellFactory.cpp

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📝 Walkthrough

Walkthrough

The shell build is consolidated into one Shell module library containing SDL3 and Null backends. A compile-time factory selects the backend, Runtime links Shell, backend tests are added, and RenderSample comments are updated for SDL3 linkage behavior.

Changes

Shell unification

Layer / File(s)	Summary
Unified shell factory Engine/cpp/Runtime/Shell/Shell.cpp, Engine/cpp/Runtime/Shell/{Null,Desktop}/*Factory.cpp	A shared shell module selects SDL3Shell or NullShell at compile time and provides the exported createShell and destroyShell functions; backend-specific factories are removed.
Unified Shell build and tests Engine/cpp/Runtime/CMakeLists.txt	Separate backend targets are replaced by one Shell target containing both implementations, SDL3 linkage, compile-time selection, and dedicated Null and SDL3 tests.
Runtime linkage and SDL3 documentation Engine/cpp/CMakeLists.txt, Samples/cpp/Render/CMakeLists.txt	Runtime links Shell, while comments document SDL3 dependency propagation and whole-archive handling in the final sample executable.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Sequence Diagram(s)

sequenceDiagram
  participant Runtime
  participant Shell
  participant Backend
  Runtime->>Shell: createShell(settings)
  Shell->>Backend: construct selected shell backend
  Backend-->>Shell: IShell instance
  Shell-->>Runtime: return IShell*

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Possibly related PRs

• Redot-Engine/DraconicEngine#38: Refactors per-backend shell factories into the unified compile-time selector implemented here.

Suggested reviewers: olddev78, joltedjon, mcdubhghlas, arctis-fireblight

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: consolidating the Desktop and Null shell backends into one Shell library.
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.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[Shakai-Dev]

LGTM

[JoltedJon]

I know you defined DRACO_SHELL_SDL3 as 1 in the cmake file but it would probably make more sense to use #ifdef here since we don't care about the value we care if it is defined. Technically the same thing in this case but the #if relies on the value of the macro being truthy instead of it simply existing.