Terminal Engine

The terminal engine provides PTY management, VT100 parsing, and Metal GPU rendering.

Components

PTYProcess

Low-level PTY management using forkpty():

• Spawns child processes with pseudo-terminal
• Manages file descriptors for I/O
• Handles process termination and exit codes

PTYMultiplexer

Single-threaded I/O multiplexing using kqueue (macOS kernel event notification):

• Monitors multiple PTY file descriptors on a single thread
• Dispatches data to the correct session
• Scales to dozens of concurrent sessions

VTParser

Wraps SwiftTerm for VT100/xterm escape sequence parsing:

• Processes raw PTY output into structured terminal state
• Extracts cursor position, cell contents, colors, attributes
• Provides TerminalGridSnapshot for rendering

TerminalGrid

Circular scroll buffer for terminal content:

• Efficient scrollback with configurable history
• Supports resize operations
• Produces snapshots for the Metal renderer

TerminalSession

The TerminalSession class combines all components:

let session = TerminalSession()
try session.launch(command: "/bin/zsh", workingDirectory: "~/project")
session.sendInput("echo hello\n".data(using: .utf8)!)
session.resize(columns: 120, rows: 40)

Metal Rendering

The rendering pipeline uses Metal for GPU-accelerated terminal display:

Component	Purpose
GlyphAtlas	Rasterizes font glyphs into a texture atlas
TerminalRenderer	Renders grid snapshots with viewport scissoring
Triple-buffered vertices	Eliminates frame drops during updates
Viewport scissoring	Single MTKView renders multiple sessions

Data Types

public struct TerminalCell {
    let character: Character
    let foreground: TerminalColor
    let background: TerminalColor
    let attributes: CellAttributes  // bold, italic, underline, etc.
}

public enum TerminalColor {
    case ansi(UInt8)
    case rgb(r: UInt8, g: UInt8, b: UInt8)
    case `default`
}