Add platform abstraction & cross-platform ports
Introduce a cross-platform platform layer and port scaffolding for macOS and Linux. CMakeLists.txt refactored to select platform sources, set executable type per OS, and use CEF helper macros for runtime deployment. Add platform/types.h, startup/paths/browser_host APIs and implementations for Windows, macOS, and Linux (many are stubs for mac/linux). Refactor app entry and lifetime to use nebula::platform::AppStartup (app/main, run.{h,cpp}), move window/browser host logic into platform/browser_host.*, and update NebulaController to use platform APIs (native handles, sizing, visibility, cache-busting token, etc.). Add README and detailed docs/cross-platform.md describing build layout and porting status.
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Andrew Zambazos
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# Cross-platform build guide
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Nebula Browser uses a **single codebase** and **one git branch** for Windows, macOS, and Linux. You do not maintain separate platform branches. Instead, each machine unpacks the correct [CEF](https://bitbucket.org/chromiumembedded/cef) binary distribution into `thirdparty/cef/` and builds with CMake.
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## Overview
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| Layer | Location | Platform-specific? |
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|-------|----------|-------------------|
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| CEF binaries | `thirdparty/cef/` (gitignored) | Yes — one distribution per OS |
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| CMake / deploy | `CMakeLists.txt` | Yes — uses CEF’s `COPY_FILES`, `COPY_MAC_FRAMEWORK`, etc. |
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| App entry & CEF init | `src/app/run.cpp`, `src/platform/*/startup_*.cpp` | Partly |
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| Native window shell | `src/platform/win\|mac\|linux/` | Yes |
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| Browser embedding | `src/platform/*/browser_host_*.cpp` | Partly |
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| Tabs, URLs, UI routing | `src/browser/`, `src/ui/`, `src/cef/` | No (shared) |
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**Windows** has a full native shell (custom frame, DWM, embedded CEF views).
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**macOS and Linux** compile and link today, but `NebulaWindow::Create()` is still a stub that returns `false` until a real Cocoa / X11 (or GTK) host is implemented.
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## Directory layout
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```
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thirdparty/cef/ # CEF standard distribution for your OS (not in git)
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src/platform/
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types.h # Rect, BrowserLayout, NativeWindow, AppStartup
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startup.h # PrepareApp, single-instance, CefMainArgs, CefSettings paths
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browser_host.h # CefWindowInfo helpers, resize/show/destroy browser HWNDs
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paths_platform.h # ExecutableDirectory, DefaultUserDataRoot, PathToUtf8
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win/ # Windows implementation
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mac/ # macOS stubs + partial CEF glue
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linux/ # Linux stubs + partial CEF glue
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src/window/
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nebula_window.h # Platform-agnostic window API (PIMPL)
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src/app/ # Shared controller and run loop
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src/browser/ # Shared tab/session logic
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src/cef/ # Shared CEF app and browser client
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src/ui/ # Shared nebula:// URLs and path helpers
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ui/ # HTML/JS UI (copied next to the binary at build time)
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```
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## Prerequisites
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- **CMake** 3.21+
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- **C++20** compiler
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- Windows: Visual Studio 2022
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- macOS: Xcode 16+ (Clang)
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- Linux: GCC 10+ or Clang, plus development packages for X11 (CEF’s CMake runs `pkg-config` for X11 on Linux)
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- **CEF standard binary distribution** for your OS and CPU architecture from the [CEF builds](https://cef-builds.spotifycdn.com/index.html) page (or your usual CEF source)
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## CEF setup
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1. Download the **standard distribution** for your platform (e.g. `cef_binary_*_windows64`, `*_macos*`, `*_linux64`).
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2. Extract so that this path exists:
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```
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thirdparty/cef/cmake/FindCEF.cmake
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```
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3. The rest of the distribution (`Release/`, `Resources/`, `libcef_dll/`, etc.) should sit directly under `thirdparty/cef/` as shipped by CEF.
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`thirdparty/cef/` is listed in `.gitignore` so binaries are never committed. Each developer and CI machine supplies its own copy.
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Optional: override the location at configure time:
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```bash
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cmake -B build -DCEF_ROOT=/path/to/cef_binary
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```
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## Building
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### Windows
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```powershell
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cmake -B build
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cmake --build build --config Release
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```
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Output: `build/Release/NebulaBrowser.exe` (plus CEF DLLs and `ui/` copied beside it).
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### macOS
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```bash
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cmake -B build -DPROJECT_ARCH=x86_64 # or arm64 on Apple Silicon
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cmake --build build --config Release
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```
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CMake builds a `NebulaBrowser.app` bundle and copies the Chromium Embedded Framework into `Contents/Frameworks`. A full macOS port still requires:
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- A real `NebulaWindow` implementation (Cocoa `NSWindow` / `NSView`)
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- CEF **helper app** subprocess targets (see CEF’s `cefsimple` sample for the complete Mac bundle layout)
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Until that work lands, the macOS target may build but will exit early because `Create()` fails.
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### Linux
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```bash
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cmake -B build
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cmake --build build
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```
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Output: `build/NebulaBrowser` (or `build/<Config>/NebulaBrowser` depending on generator). CEF `.so` files and resources are copied next to the executable.
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You may need to set **SUID** on `chrome-sandbox` as printed by CMake post-build (CEF documents this in its Linux README).
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Until a Linux host window exists, the binary will not show a UI for the same reason as macOS.
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## How CMake picks a platform
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`find_package(CEF)` loads CEF’s `cef_variables.cmake`, which sets:
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- `OS_WINDOWS`
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- `OS_MACOSX`
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- `OS_LINUX`
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`CMakeLists.txt` then:
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1. Adds the matching `src/platform/{win,mac,linux}/*.cpp` sources
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2. Sets the executable type (`WIN32`, `MACOSX_BUNDLE`, or plain executable)
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3. Links `libcef_dll_wrapper`, `libcef_lib`, and `${CEF_STANDARD_LIBS}`
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4. Runs CEF’s copy macros so runtime files land beside the app
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Shared sources are always compiled; only the `src/platform/...` tree changes per OS.
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## Application flow
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```
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main (app/main.cpp)
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└─ RunNebula(AppStartup) src/app/run.cpp
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├─ platform::PrepareApp()
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├─ CefExecuteProcess() (subprocesses)
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├─ platform::TryAcquireSingleInstance()
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├─ CefInitialize()
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├─ NebulaController::Create()
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│ └─ NebulaWindow::Create() platform-specific
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└─ CefRunMessageLoop()
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```
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`AppStartup` carries platform entry data:
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- **Windows:** `HINSTANCE` + show command (`wWinMain`)
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- **macOS / Linux:** `argc` / `argv` (`main`)
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## User data and profile paths
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Shared logic in `src/ui/paths.cpp` writes under:
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| OS | Default root |
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|----|----------------|
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| Windows | `%LOCALAPPDATA%\Nebula\User Data` (falls back to exe directory) |
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| macOS | `~/Library/Application Support/Nebula/User Data` |
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| Linux | `$XDG_DATA_HOME/Nebula/User Data` or `~/.local/share/Nebula/User Data` |
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Platform-specific discovery lives in `src/platform/*/paths_*.cpp`.
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## GPU / Chromium flags
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`src/cef/nebula_app.cpp` applies shared switches (`no-sandbox`, `ignore-gpu-blocklist`, etc.) and platform graphics backends:
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| OS | Backend |
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|----|---------|
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| Windows | ANGLE + D3D11 |
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| macOS | ANGLE + Metal |
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| Linux | EGL |
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## Adding or changing platform code
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1. **Shared behavior** (tabs, `nebula://` URLs, CEF clients) → edit under `src/browser/`, `src/ui/`, `src/cef/`, `src/app/` only if it is truly cross-platform.
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2. **Native window or OS API** → edit `src/platform/<os>/` and keep `src/window/nebula_window.h` free of `#include <windows.h>` (or Cocoa/X11 headers).
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3. **CEF child window embedding** → `src/platform/<os>/browser_host_*.cpp` (`MakeChildWindowInfo`, resize, visibility).
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4. **Startup / paths** → `startup_*.cpp` and `paths_*.cpp` in the same folder.
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5. **New OS** → add `src/platform/<os>/`, extend the `if(OS_...)` blocks in `CMakeLists.txt`, and document CEF distribution layout here.
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## Porting checklist (macOS / Linux)
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- [ ] Implement `NebulaWindow` in `nebula_window_mac.cpp` / `nebula_window_linux.cpp`
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- [ ] Wire `browser_host_*.cpp` resize/show/raise to the real toolkit
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- [ ] macOS: add CEF helper app targets and bundle layout (copy from `cefsimple`)
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- [ ] Linux: confirm X11 (or chosen toolkit) parent handle for `CefWindowInfo::SetAsChild`
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- [ ] Test GPU diagnostics page and hardware acceleration on target hardware
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- [ ] Package or script runtime layout (`ui/`, CEF frameworks/libs, ICU locales, etc.)
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## FAQ
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**Do I need a separate git branch per OS?**
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No. Use one branch; swap `thirdparty/cef` and rebuild on each machine.
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**Can I commit CEF into the repo?**
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Not recommended (size, licensing, per-arch binaries). Keeping `thirdparty/cef/` gitignored is intentional.
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**Why does macOS/Linux build but not run?**
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The window stub intentionally returns `false` from `Create()` until a native shell exists. Shared CEF and browser code are ready; the missing piece is the host window.
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**Where is the Windows UI code?**
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`src/platform/win/nebula_window_win.cpp` — custom chrome, hit-testing, fullscreen, and child browser placement.
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