fasttui is a Go port of @mariozechner/pi-tui: the same differential renderer, bracketed paste handling, autocomplete, and component value semantics

• Differential Rendering: Three-strategy rendering system that only updates what changed
• Synchronized Output: Uses CSI 2026 for atomic screen updates (no flicker)
• Bracketed Paste Mode: Handles large pastes correctly with markers for >10 line pastes
• Component-based: Simple Component interface with render() method
• Theme Support: Components accept theme interfaces for customizable styling
• Built-in Components: Text, TruncatedText, Input, Editor, Markdown, Loader, SelectList, SettingsList, Spacer, Image, Box, Container
• Inline Images: Renders images in terminals that support Kitty or iTerm2 graphics protocols
• Autocomplete Support: File paths and slash commands

go get github.com/yourusername/fasttui

all components must implement this interface.

type Component interface {
    // render the compoent to lines for the given viewport width
    Render(width int) []string
	// handler for keyboard input when component has focus
    HandleInput(data string)
    // receives key release events
	WantsKeyRelease() bool
    // Invalidate any cached rendering state.
	// Called when theme changes or when component needs to re-render from scratch.
	Invalidate()
}

Create a terminal implementation (stdin/stdout TTY), then a TUI that owns rendering and input. Call Start() after adding children and optional SetFocus.

import (
	"github.com/yeeaiclub/fasttui"
	"github.com/yeeaiclub/fasttui/terminal"
)

term := terminal.NewProcessTerminal()

// Second arg: show hardware cursor (true) vs hide it and rely on drawn UI (false).
tui := fasttui.NewTUI(term, false)

TUI embeds Container, so you use AddChild to stack components; the TUI owns the render loop and paints the screen.

tui.AddChild(component) // Append to the vertical layout (order = top to bottom).

// Optional: give keyboard focus to a Focusable component (Input, Editor, lists, …).
tui.SetFocus(component)

tui.Start() // Enter raw mode, start input + differential rendering.

defer tui.Stop() // Restore the terminal when the program exits.

Manually trigger a render using tui.TriggerRender(). This is useful when you update component state outside the normal input flow.

tui.TriggerRender()

Colors and terminal glyphs are provided by the style subpackage (github.com/yeeaiclub/fasttui/style). A theme is a JSON file that lists named color tokens, optional vars for indirection, and optional symbol / export settings.

import "github.com/yeeaiclub/fasttui/style"

// Built-in names are embedded in the library (e.g. "dark", "light", and many *defaults*).
th, err := style.LoadTheme("dark")
if err != nil {
	// handle error
}
// Optional configuration uses the options pattern, e.g.:
//   style.LoadTheme("dark", style.WithColorMode(style.ColorModeTruecolor))
//   style.LoadTheme("dark", style.WithSymbolPreset(style.SymbolPresetNerd), style.WithColorBlindMode(true))
// Available: [style.WithColorMode], [style.WithSymbolPreset], [style.WithColorBlindMode]

• LoadThemeFile(name) – returns *ThemeFile (parsed JSON) without ANSI resolution.
• NewTheme(tf, opts ...ThemeOption) – builds a *Theme from *ThemeFile (same options as LoadTheme).
• ParseThemeJSON(data) – parse raw JSON (same validation as file load).

1. Built-in – themes shipped under style/theme (e.g. dark.json, light.json, theme/defaults/*.json) are embedded and resolved first by name (filename without .json).
2. User themes – <config-dir>/fasttui/themes/<name>.json. On most systems <config-dir> is $XDG_CONFIG_HOME or OS user config. Override the directory with FASTTUI_THEMES_DIR.

ListThemeNames() returns all built-in names plus any *.json in the user themes directory (sorted, de-duplicated).

• name (string) and colors (object) are required. Every key listed in the schema must be present in colors (e.g. accent, userMessageBg, syntaxComment, statusLineBg, …).
• vars (optional) – map of name → hex string, "", or 0–255 index. Other fields can reference a var by the same string as the key (e.g. "accent": "teal" with "vars": { "teal": "#5a8080" }).
• export (optional) – pageBg / cardBg / infoBg for HTML/CSS export helpers; var refs may use a $ prefix (e.g. "$teal") when matching vars.
• symbols (optional) – preset (unicode | nerd | ascii) and overrides for individual logical keys (e.g. status.success).

The JSON schema is embedded as style/theme/theme-schema.json in the module.

Theme exposes foreground and background tokens as ANSI, plus symbols:

• Fg(color ThemeColor, text string), Bg(bg ThemeBg, text string)
• FgANSI / BgANSI for raw sequences; Bold, Italic, Underline, etc.
• Symbol(key string), LangIcon(lang string), SpinnerFrames(kind), InputCursor(), …

For non-TUI use (e.g. HTML), ResolvedThemeColors, ExportColors, IsLightTheme, and DefaultThemeName (uses COLORFGBG when set) are available in the same package.

Apache License 2.0