Hobby

Lua bindings for the mpgo MetaPost curve library. Named after John Hobby, the developer of MetaPost and the Hobby-Knuth smooth curve algorithm.

Installation

Homebrew (macOS/Linux)

brew install boxesandglue/tap/hobby

Go

go install github.com/boxesandglue/hobby/cmd/hobby@latest

Binary Downloads

Download binaries from the releases page.

Usage

hobby script.lua

Examples

Curved Path

A smooth curve through five points using the Hobby algorithm:

local h = require("hobby")

-- Create some points
local z0 = h.point(0, 0)
local z1 = h.point(60, 40)
local z2 = h.point(40, 90)
local z3 = h.point(10, 70)
local z4 = h.point(30, 50)

-- Build a closed curved path
local path = h.path()
    :moveto(z0)
    :curveto(z1)
    :curveto(z2)
    :curveto(z3)
    :curveto(z4)
    :cycle()
    :build()

-- Create SVG and add the path
h.svg()
    :padding(5)
    :add(path)
    :write("simple.svg")

Transformations

Predefined shapes with various transformations:

local h = require("hobby")

-- Original circle
local circle = h.fullcircle():scaled(20):shifted(30, 80):stroke("black")

-- xscaled (stretched horizontally)
local xscaled = h.fullcircle():scaled(20):xscaled(2):shifted(90, 80):stroke("blue")

-- yscaled (stretched vertically)
local yscaled = h.fullcircle():scaled(20):yscaled(2):shifted(150, 80):stroke("red")

-- slanted (sheared)
local slanted = h.unitsquare():scaled(30):slanted(0.5):shifted(30, 20):stroke("green")

-- Combination
local combo = h.fullcircle()
    :scaled(20)
    :xscaled(1.5)
    :yscaled(0.7)
    :slanted(0.3)
    :shifted(130, 30)
    :stroke("purple")

-- Output to SVG
h.svg()
    :padding(10)
    :add(circle)
    :add(xscaled)
    :add(yscaled)
    :add(slanted)
    :add(combo)
    :write("transforms.svg")

Documentation

Full documentation is available at boxesandglue.dev/hobby.

License

BSD-3-Clause. See LICENSE.