Backends

AppCUI supports various backends (but each one comes with advantages and drawbacks). A backend is the terminal that takes the information (characters) from the virtual screen of AppCUI and displays them.

Each backend supported by AppCUI has the following properties:

• Output rendering - each character from the AppCUI surface is display on the screen
• Input reading - the backend is capable of identifying keyboard and mouse events and convert them to internal AppCUI events
• Clipboard support - the backend interacts with the OS and provides functionality for Copy / Cut / Paste based on OS-es API

The following backends are supported:

1. Windows Console
2. Windows VT (Virtual Terminal)
3. NCurses
4. Termios
5. Web Terminal
6. CrossTerm

Remarks: These types are available via appcui::backend::Type and can be used to initialize an application

let mut a = App::with_backend(apcui::backend::/*type*/).build()?;

where the appcui::backend::Type enum is defined as follows:

pub enum Type {
    #[cfg(target_os = "windows")]
    WindowsConsole,
    #[cfg(target_os = "windows")]
    WindowsVT,
    #[cfg(target_family = "unix")]
    Termios,
    #[cfg(target_os = "linux")]
    NcursesTerminal,
    #[cfg(target_arch = "wasm32")]
    WebTerminal,
    CrossTerm
}

OS Support

Display

Each backend comes with different support related to what can be displayed on the screen.

• 16 colors - support for 16 colors for foreground and background
• True colors - support for true colors (24-bit) for foreground and background
• UTF-8 - support for UTF-8 encoding
• Ascii - support for ASCII encoding
• WTF-16 - support for WTF-16 encoding (a subset of UTF-8) - only for Windows
• Cursor - support for cursor
• Cursor Blinking - support for cursor blinking

Remarks:

1. True colors support requires the feature TRUE_COLORS to be enabled (keep in mind that by doing this you also increase the size of your Color and Character structures - if you don't need this or your terminal does not support true colors, you will only allocate aditional space that will not be used).
2. Cursor blinking is not supported by all terminals (the AppCUI can enable - show/hide the cursor, but it is the terminal job to make it blink)

In terms of the output method, each backend uses a different approach:

Character Attributes

Besides background and foreground colors, the following character attributes are supported:

Input

Capturing the input implies the following capabilites from any backend:

• identifying keyboard events
• identifying keyboard combinations such as Alt+Key or Ctrl+Key or Alt+Ctrl+Key
• Identifying that the state of the Shift, Ctrl and Alt keys has changed (pressed or released)
• Identifying mouse events
• Identifying mouse combinations such as Alt+Mouse or Ctrl+Mouse or Alt+Ctrl+Mouse
• Identifying mouse drag / move events
• Identifying mouse wheel events

Keyboard

Mouse

Remarks: Input support is highlighly dependent on the terminal and the OS. AppCUI uses the following approach to intercept the input:

System events

System events are events that are not related to the keyboard or mouse, but are related to the system and indicate that the console has been changed in some way.

Other capabilities

Clipboard

AppCUI provides clipboard support for copying and pasting text. The clipboard functionality is available on the following backends:

Defaults

By default, when using initializing an App objct via App::new(), the folowing backend will be used :