Building a Windows Terminal Emulator

Writing a terminal emulator and text buffer from scratch in C

View on GitLab (pull requests welcome)

How Does a Terminal Actually Work?

When you open a terminal and type a command, what is actually happening behind the scenes?

• How do you host a shell like cmd.exe or powershell.exe inside your own application?
• How do you capture the output of those programs before it hits the screen?
• What format is text saved in memory so it can be scrolled and resized?
• How does the terminal know to print text in red, or move the cursor up two lines?
• How are emojis and wide characters (like CJK) handled in a fixed-width grid?
• How do you avoid flickering when redrawing the window 60 times a second?

In short, how does a modern Windows terminal work?

I’m building a clone of a Windows terminal emulator from scratch in C in order to understand, and I’m going to document my process as I go. We will use the modern Windows Pseudo Console (ConPTY) API to talk to the OS, and build a custom text buffer to store and parse the data.

Table of Contents

Chapter 1: The Terminal Application (OS Integration)

• Architecture & Laying the Plumbing

Chapter 2: The Terminal Text Buffer (State & Parsing)

“What I cannot create, I do not understand.” – Richard Feynman