# Desktop development

## Function
`bt_app` is the desktop application runtime and packaging tool officially provided by BT. It can read `app.json` in the development directory, standalone `.btr` software, or embedded resources at the end of the exe, create a desktop window, and load local pages, local BT service addresses, or remote Web addresses as configured.

Developers can use `HTML/CSS/JavaScript` or any front-end framework to write interfaces, and BT to implement local logic, Web services, or functions callable from the front end. `bt_app` provides windows, resource protocols, BTR/single-executable builds, icons, metadata, and the front-end `window.bt` bridge. A `.btr` contains only application configuration and resources, allowing multiple small apps to share one installed runtime.

## Applicable scenarios
 - HTML front-end developers, quickly write pages.
- BT local service plus desktop software with web front-end.
- Package remote web applications into desktop windows with one click.
 - Windows desktop application requiring single file distribution.
- Multiple BT gadgets need to be published as lightweight `.btr`, launched by common toolbar or system file association.

## Differences from Web projects
- Ordinary Web projects run in the browser, and the page cannot directly call BT local functions by default.
- `bt_app` runs in the desktop WebView and injects `window.bt`. The page can call the BT language functions in `main.bt` through `bt.call()`, and can also control windows, trays, clipboards, screen straws, frame selection screenshots, global shortcut keys, notifications and system dialog boxes through the desktop API.

## Differences from ordinary desktop software
Traditional desktop software usually uses the native UI directly. `bt_app` uses Web technology to draw the interface, and uses BT to be responsible for local logic or services. It is suitable for developers who already have Web front-end experience.

## Basic operation idea
1. Double-click to start `bt_app.exe` or execute the command `./bt_app.exe run`.
2. `bt_app run app.btr` or `bt_app app.btr` reads resources from the specified BTR; a standalone exe with embedded resources reads from itself; otherwise, it runs the specified directory or the current directory.
3. All sources first read and verify `app.json`; when the development directory does not have `app.json` but `index.html` exists, the default configuration will be automatically generated and run.
4. In `static` mode, the window loads the `HTML` file specified by `app.entry`.
5. In `server` mode, execute `server.bt`, and the window loads the local service address specified by `app.entry`.
6. `remote` mode, directly loads the URL specified by `app.entry`.

## Document Directory
- [Quick Start ](/en/docs/bt_app/quick-start)
- [app.json Configuration ](/en/docs/bt_app/app-json)
- [Entry Configuration ](/en/docs/bt_app/entry)
- [Run Mode ](/en/docs/bt_app/mode)
- [bt:// Protocol ](/en/docs/bt_app/protocol)
- [Desktop API ](/en/docs/bt_app/api)
- [Package build ](/en/docs/bt_app/build)
- [Release distribution ](/en/docs/bt_app/release)
- [Full example ](/en/docs/bt_app/examples)
- [FAQ ](/en/docs/bt_app/faq)