Termchart - Terminal Charts with Unicode and ANSI Colors

Render sparklines, line charts, candlestick charts, and bar charts directly in the terminal. Pure Ruby, zero dependencies.

All chart types render to plain strings with ANSI color codes — composable with any TUI framework (rcurses, curses, or raw terminal output).

Features

• Sparklines — compact single-line charts using ▁▂▃▄▅▆▇█
• Line charts — high-resolution braille dot plotting (2×4 dots per cell)
• Candlestick charts — OHLC financial charts with green/red coloring
• Bar charts — horizontal and vertical with sub-cell precision
• 256-color and RGB — supports integer color codes and hex strings
• No dependencies — pure Ruby, no native extensions
• String output — no direct terminal I/O, works anywhere

Installation

gem install termchart

Or add to your Gemfile:

gem 'termchart'

Sparklines

Map values to 8 eighth-block characters on a single line.

require 'termchart'
puts Termchart.spark([1, 3, 5, 2, 8, 4, 6])
# => ▁▃▅▂█▄▆
puts Termchart.spark([10, 20, 30, 25, 40], color: :green)
# => ▁▃▅▄█  (in green)

Supported color names: :red, :green, :blue, :yellow, :cyan, :magenta, :white, :gray, :orange

Line Charts

Braille-dot line charts with Y-axis labels. Each terminal cell provides 2×4 sub-pixel resolution via Unicode braille patterns (U+2800–U+28FF).

chart = Termchart::Line.new(width: 60, height: 20)
chart.add(prices, color: 82, label: "SPY")
chart.add(gold,   color: 226, label: "GLD")
puts chart.render

Output:

 460┤⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⠔⠊⠢⡀⠀⠀⠀⠀⠀⢀⡠⠊
    │⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⠀⢀⠔⠁⠀⠀⠀⠈⠢⡀⠀⢀⠔⠊
    │⠀⠀⠀⠀⠀⠀⢀⡠⠤⠒⠢⡀⠀⠀⠀⣀⠔⠁⠀⠀⠀⠀⠀⠀⠀⠈⠔⠁
 440┤⠀⠀⠀⢀⡠⠊⠁⠀⠀⠀⠀⠈⠢⡠⠊⠁
    │⠀⠀⣀⠃⠀⠀⠀⠀⠀⠀⠀⠀⠀⠁
    │⠀⡰⠁
 420┤⡰⠁
     ━━ SPY

Candlestick Charts

OHLC candlestick charts for financial data. Green for up candles, red for down.

chart = Termchart::Candle.new(width: 60, height: 20)
chart.add([
  { o: 100, h: 105, l: 98,  c: 103 },
  { o: 103, h: 107, l: 101, c: 99  },
  { o: 99,  h: 104, l: 97,  c: 102 },
  { o: 102, h: 108, l: 100, c: 106 },
])
puts chart.render

Uses │ for wicks and █ for bodies. Y-axis labels on the left at 5 price levels.

Bar Charts

Horizontal and vertical bar charts with sub-cell precision using eighth-block characters.

Horizontal

chart = Termchart::Bar.new(width: 40, orientation: :horizontal)
chart.add("GLD", 185.50, color: 226)
chart.add("SPY", 450.00, color: 82)
chart.add("SLV", 22.30,  color: 245)
puts chart.render

GLD │███████████▏            185.50
SPY │████████████████████████    450
SLV │█▍                       22.30

Vertical

chart = Termchart::Bar.new(width: 30, height: 10, orientation: :vertical)
chart.add("Q1", 80, color: 82)
chart.add("Q2", 95, color: 82)
chart.add("Q3", 70, color: 196)
chart.add("Q4", 110, color: 82)
puts chart.render

Colors

All chart types accept colors as:

Canvas API

For custom visualizations, use the canvas classes directly.

Canvas

Character grid where each cell holds a character, foreground color, and background color.

canvas = Termchart::Canvas.new(40, 10)
canvas.set(5, 3, "█", fg: 196, bg: 233)
puts canvas.render

BrailleCanvas

Each cell maps to a 2×4 braille dot grid for sub-cell resolution.

canvas = Termchart::BrailleCanvas.new(40, 10)
# Pixel space: 80×40
canvas.set_dot(15, 25, fg: 82)
puts canvas.render

Use with rcurses

Termchart is designed to compose with rcurses panes:

require 'rcurses'
require 'termchart'
pane = Rcurses::Pane.new(2, 2, 60, 20)
chart = Termchart::Line.new(width: 60, height: 20)
chart.add(data, color: 82, label: "Price")
pane.text = chart.render
pane.refresh

License

Unlicense — Public Domain

Author

Geir Isene — https://isene.com