Guide: render text to a PNG

This walks through the smallest useful pipeline: parse a bundled font, rasterise a string glyph-by-glyph into an image.RGBA, and write it out as a PNG. It only touches opentype and fonts — no shaping needed for a plain Latin string.

package main

import (
    "image"
    "image/color"
    "image/draw"
    "image/png"
    "os"

    "github.com/go-opentype/fonts"
    "github.com/go-opentype/opentype"
)

func main() {
    f, err := opentype.Parse(fonts.MostLegible()) // Atkinson Hyperlegible
    if err != nil {
        panic(err)
    }
    face := f.NewFace(32) // 32px per em

    text := "Hello, go-opentype"
    w := face.Measure(text)
    m := face.Metrics()
    h := m.Height

    dst := image.NewRGBA(image.Rect(0, 0, w+8, h+8))
    draw.Draw(dst, dst.Bounds(), &image.Uniform{C: color.White}, image.Point{}, draw.Src)

    penX := 4
    baselineY := 4 + m.Ascent
    ink := image.NewUniform(color.Black)

    for _, r := range text {
        bounds, mask, maskp, advance, ok := face.GlyphMask(r, penX, baselineY)
        if ok && mask != nil {
            draw.DrawMask(dst, bounds, ink, image.Point{}, mask, maskp, draw.Over)
        }
        penX += advance
    }

    out, err := os.Create("hello.png")
    if err != nil {
        panic(err)
    }
    defer out.Close()
    if err := png.Encode(out, dst); err != nil {
        panic(err)
    }
}

Key points:

• face.Metrics().Ascent gives you the baseline offset from the top of the line — add it to your top margin to get baselineY.
• face.GlyphMask returns ok == false for glyphs with no visible ink (like a space); skip the draw call but still advance the pen.
• advance is already in pixels at the face's chosen size, so accumulating it into penX is all the layout a plain Latin run needs.

For anything beyond isolated Latin/default runs — Arabic, mixed-direction paragraphs, ligatures, mark attachment — swap the per-rune loop above for shape.Shape, which returns a []Glyph with XOffset/ YOffset/XAdvance/YAdvance already resolved; see Shape complex scripts.