# Welcome to GPUI!

GPUI is a hybrid immediate and retained mode, GPU accelerated, UI framework
for Rust, designed to support a wide variety of applications.

## Getting Started

GPUI is still in active development as we work on the Zed code editor and isn't yet on crates.io. You'll also need to use the latest version of stable Rust and be on macOS or Linux. Add the following to your `Cargo.toml`:

```toml
gpui = { git = "https://github.com/zed-industries/zed" }
```

Everything in GPUI starts with an `Application`. You can create one with `Application::new()`, and kick off your application by passing a callback to `Application::run()`. Inside this callback, you can create a new window with `App::open_window()`, and register your first root view. See [gpui.rs](https://www.gpui.rs/) for a complete example.

### Dependencies

GPUI has various system dependencies that it needs in order to work.

#### macOS

On macOS, GPUI uses Metal for rendering. In order to use Metal, you need to do the following:

- Install [Xcode](https://apps.apple.com/us/app/xcode/id497799835?mt=12) from the macOS App Store, or from the [Apple Developer](https://developer.apple.com/download/all/) website. Note this requires a developer account.

> Ensure you launch XCode after installing, and install the macOS components, which is the default option.

- Install [Xcode command line tools](https://developer.apple.com/xcode/resources/)

  ```sh
  xcode-select --install
  ```

- Ensure that the Xcode command line tools are using your newly installed copy of Xcode:

  ```sh
  sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer
  ```

## The Big Picture

GPUI offers three different [registers](<https://en.wikipedia.org/wiki/Register_(sociolinguistics)>) depending on your needs:

- State management and communication with `Entity`'s. Whenever you need to store application state that communicates between different parts of your application, you'll want to use GPUI's entities. Entities are owned by GPUI and are only accessible through an owned smart pointer similar to an `Rc`. See the `app::context` module for more information.

- High level, declarative UI with views. All UI in GPUI starts with a view. A view is simply an `Entity` that can be rendered, by implementing the `Render` trait. At the start of each frame, GPUI will call this render method on the root view of a given window. Views build a tree of `elements`, lay them out and style them with a tailwind-style API, and then give them to GPUI to turn into pixels. See the `div` element for an all purpose swiss-army knife of rendering.