gritty

gritty

Gritty is a terminal emulator written in Go and Gio UI Framework, focusing on readability and documentation of the code.

You could use this emulator for normal work, but I created it as a reference implementation of vt100-ish terminal emulator. (I use kitty, and I'm happy with it. I only wanted to understand how terminals work.)

Using Gritty

Ensure that Gio is installed on your system. Run with go run ., test with go test .. Gritty starts /bin/sh.

Architecture

graph LR;
subgraph Controller
E
C
I
end
C[Controller] --> B[Buffer]
C[Controller] --> E[EncodeKeys]
E --> PTY
PTY --> P[Parse input]
P --> I[Interpret control sequences]
I --> C
G[GUI] --"send keys"--> C
G --"read buffer"--> C

Packages

• buffer - Buffer is the model that contains a grid of characters, it also handles actions like "clear line" or "write rune".
• parser - Parser is a control-sequence parser implemented based on the excellent state diagram by Paul Williams.
• controller - Controller connects PTY and buffer.
  • It gives GUI the grid of runes to render and signal when to re-render.
  • It receives key events from GUI.
• main - Main package contains the GUI code and starts the terminal emulator.

Code walkthrough

1. Start by understanding the controller.Start method.

• it starts the shell command and starts processing the parsed PTY operations (c.handleOp)

1. run the code with gritty_debug=1 go run . in the main package. This also enables extended debug logging.
2. watch the log output when you interact with the terminal and find the log statements using a full-text search.

Resources

• VT510 user manual - Contents
• ANSI Control Functions Summary
• Digital VT100 User Guide: Programmer Information - chapter 3
• asciinema/avt - extremely clear implementation of vt100-ish terminal emulator in rust
• ANSI escape code - Wikipedia
• ASCII - Wikipedia
• man ascii
• XtermJS - Supported Terminal Sequences - helpful overview of escape sequences
• XTerm Control Sequences