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DEVELOPING.md

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Building and running code

Building for release

Running yarn prebuild and yarn tsc should build everything needed for release.

Testing with the demo app

When developing, running npm run demo:electron or yarn demo:electron will build and run a demo app that's useful for testing this.

Debugging native Mac code

  1. Create an XCode project by running node-gyp configure --debug -- -f xcode.
  2. Change to debug mode by running node-gyp configure --debug.
  3. Run the Electron demo by running yarn demo:electron
  4. Go into XCode, open the project in build/binding.xcodeproj, and then use the "Debug > Attach to Process" menu to attach to the Electron process.

How this library works

This library largely works by hooking into the event handlers so that the overlay window can be moved and shown/hidden to match the target window that it's supposed to overlay.

Code structure

The main module exposes a singleton overlayWindow that can be used to control the overlay.

On startup:

  • User calls OverlayController.attachByTitle()
  • attachByTitle calls lib.start(), which corresponds to the AddonStart function inside of addon.c
  • AddonStart largely delegates the platform specific code by calling ow_start_hook, a function defined for each platform.

Native module

Immediately on attaching to a window, a background thread executes hook_thread (names for Mac are in camelCase, but otherwise similar).

hook_thread

hook_thread does the following on Windows:

  • Hook foreground, minimize events for all windows
  • Hook foreground window rename and call check_and_handle_window
  • Start the event loop

check_and_handle_window

check_and_handle_window does the following on Windows:

  • Initialize is_focused, is_destroyed, and other properties on target_info
  • Emits events for the initialization (blur, detach, focus)
  • Create hooks for window move and destroy
    • Cleans up any existing hooks before this
  • Attaches the target's input handling to the overlay's input handling
  • Emit attach and focus events