tui

README

go-widgets/tui

Terminal I/O layer around go-widgets/painter's CellPainter. Renders a widget tree as a self-contained ANSI stream sized to the current terminal, so the same widget code that produces pixels for a WUI or GUI back-end also produces text for a terminal.

What it is (and what it isn't)

The package is deliberately minimal — no raw mode, no keyboard event loop, no alt-screen management. It ships a snapshot model: render one frame to a writer and return. Compose it with a caller-managed event loop or a CLI that prints once and exits.

import (
    "os"

    "github.com/go-widgets/painter"
    "github.com/go-widgets/tui"
)

widgets := []painter.Widget{
    &painter.Label{Bounds: painter.Rect{X: 2, Y: 1, W: 30, H: 1}, Text: "GO WIDGETS TUI"},
    &painter.Button{Bounds: painter.Rect{X: 2, Y: 3, W: 12, H: 3}, Label: "OK"},
    &painter.ProgressBar{Bounds: painter.Rect{X: 2, Y: 8, W: 30, H: 3}, Value: 0.72},
}
_ = tui.RenderOnce(os.Stdout, widgets, nil) // nil theme = LightTheme

An App runner with input, resize, and cleanup handling is future work — this repo intentionally leaves that surface for a follow-up cycle rather than shipping a half-baked event loop.

Sizing

Two variants, take your pick:

• RenderOnceSized(w, cols, rows, widgets, theme) — explicit dimensions. The reliable form for tests, size-aware callers, and headless renderers.
• RenderOnce(w, widgets, theme) — queries EnvSize() (COLUMNS / LINES environment variables) and falls back to DefaultCols x DefaultRows (80 x 24) when the environment does not report a size.

The env-vars-only strategy is a deliberate trade-off: it keeps the package stdlib-only — no TIOCGWINSZ ioctl per platform, no cgo, no dependency on golang.org/x/term. Interactive shells that need dynamic sizes should export COLUMNS / LINES from their prompt hook, or pass an explicit size to RenderOnceSized.

Try it

# Default terminal size (or COLUMNS / LINES if set)
go run ./cmd/tui-snapshot

# Force a specific size + dark theme
go run ./cmd/tui-snapshot --cols=100 --rows=25 --theme=dark

The demo mirrors painter/cmd/tui-demo: same three-widget layout (label, two buttons, progress bar), same theme selection.

Design axiom

Same as the rest of go-widgets: dependency-free, stdlib-only, 100% coverage (library packages and cmd/). CI enforces the coverage gate on every push.

License

BSD-3-Clause. See LICENSE.

Documentation

Overview

Package tui is the terminal-I/O layer around github.com/go-widgets/painter's CellPainter. It renders a widget tree into an ANSI cell stream sized to the current terminal, so the same widget code that produces pixels for a WUI or GUI back-end also produces text for a terminal — no widget changes required.

The package is deliberately minimal: no raw mode, no keyboard event loop, no alt-screen management. It ships a "snapshot" model — render one frame to a writer and return — that composes cleanly with either a caller-managed event loop or a CLI that prints once and exits. Higher-level facilities (an [App] runner with input, resize, and cleanup handling) live in a follow-up cycle.

Sizing follows the caller's preference:

• RenderOnceSized takes explicit (cols, rows) — the reliable form used by tests, size-aware callers, and headless renderers.
• RenderOnce queries the size from environment variables (EnvSize) and falls back to [DefaultCols]x[DefaultRows] when the environment does not report a size. This keeps the package stdlib-only — no ioctl, no cgo, no dependency on golang.org/x/term.

Both variants write a self-contained ANSI stream to the caller's writer via painter.CellPainter.WriteANSI; the caller is responsible for the surrounding terminal state (raw mode, alt screen, cursor visibility) if any.

Index

• Constants
• func EnvSize() (cols, rows int, ok bool)
• func RenderOnce(w io.Writer, widgets []painter.Widget, theme *painter.Theme) error
• func RenderOnceSized(w io.Writer, cols, rows int, widgets []painter.Widget, theme *painter.Theme) error
• func SizeOrDefault() (cols, rows int)

Constants

const (
	DefaultCols = 80
	DefaultRows = 24
)

DefaultCols and DefaultRows are the terminal dimensions used when neither the environment nor the caller supplies a size — the classic VT100 defaults every terminal emulator honours as a floor.

Functions

func EnvSize

func EnvSize() (cols, rows int, ok bool)

EnvSize reads the terminal size from the COLUMNS and LINES environment variables. It returns (cols, rows, true) when both parse cleanly and hold positive integers; otherwise it returns (0, 0, false) and the caller should substitute defaults.

The env-vars-only strategy is a deliberate trade-off: it keeps the package stdlib-only (no TIOCGWINSZ ioctl per platform, no cgo, no golang.org/x/term dependency). Interactive shells that need dynamic sizes should export COLUMNS / LINES from their prompt hook, or pass an explicit size to RenderOnceSized.

func RenderOnce

func RenderOnce(w io.Writer, widgets []painter.Widget, theme *painter.Theme) error

RenderOnce paints the widget tree into a fresh CellPainter sized to SizeOrDefault, fills the background with theme.Background, calls each widget's Draw, and writes the resulting ANSI stream to w. It is the snapshot form: no raw mode, no event loop; one frame then return.

The theme argument may be nil, in which case painter.LightTheme is used. This keeps CLI callers ergonomic (`tui.RenderOnce(os.Stdout, widgets, nil)`) without forcing them to import painter just to name the default theme.

func RenderOnceSized

func RenderOnceSized(w io.Writer, cols, rows int, widgets []painter.Widget, theme *painter.Theme) error

RenderOnceSized is like RenderOnce but uses the explicit (cols, rows) dimensions instead of querying the environment. Cols and rows must both be positive; a non-positive value falls back to the corresponding default so callers cannot accidentally produce an empty render.

func SizeOrDefault

func SizeOrDefault() (cols, rows int)

SizeOrDefault returns EnvSize when the environment reports a size, otherwise [DefaultCols]x[DefaultRows]. This is what RenderOnce consumes.