Add a truetype.Face type.
Its implementation is mostly a copy/paste of the freetype.Context type. Follow-up commits will make it more efficient. Also add an example that uses a truetype.Face and the golang.org/x/exp/shiny/font package to draw text.
This commit is contained in:
Nigel Tao
parent
7166253831
commit
6deea24143
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// Copyright 2015 The Freetype-Go Authors. All rights reserved.
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// Use of this source code is governed by your choice of either the
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// FreeType License or the GNU General Public License version 2 (or
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// any later version), both of which can be found in the LICENSE file.
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// +build ignore
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//
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// This build tag means that "go install github.com/golang/freetype/..."
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// doesn't install this example program. Use "go run main.go" to run it.
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package main
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import (
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"bufio"
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"flag"
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"fmt"
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"image"
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"image/color"
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"image/draw"
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"image/png"
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"io/ioutil"
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"log"
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"math"
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"os"
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"github.com/golang/freetype/truetype"
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"golang.org/x/exp/shiny/font"
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"golang.org/x/image/math/fixed"
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)
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var (
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dpi = flag.Float64("dpi", 72, "screen resolution in Dots Per Inch")
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fontfile = flag.String("fontfile", "../../testdata/luxisr.ttf", "filename of the ttf font")
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hinting = flag.String("hinting", "none", "none | full")
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size = flag.Float64("size", 12, "font size in points")
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spacing = flag.Float64("spacing", 1.5, "line spacing (e.g. 2 means double spaced)")
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wonb = flag.Bool("whiteonblack", false, "white text on a black background")
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)
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var text = []string{
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"’Twas brillig, and the slithy toves",
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"Did gyre and gimble in the wabe;",
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"All mimsy were the borogoves,",
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"And the mome raths outgrabe.",
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"",
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"“Beware the Jabberwock, my son!",
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"The jaws that bite, the claws that catch!",
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"Beware the Jubjub bird, and shun",
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"The frumious Bandersnatch!”",
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"",
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"He took his vorpal sword in hand:",
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"Long time the manxome foe he sought—",
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"So rested he by the Tumtum tree,",
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"And stood awhile in thought.",
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"",
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"And as in uffish thought he stood,",
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"The Jabberwock, with eyes of flame,",
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"Came whiffling through the tulgey wood,",
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"And burbled as it came!",
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"",
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"One, two! One, two! and through and through",
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"The vorpal blade went snicker-snack!",
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"He left it dead, and with its head",
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"He went galumphing back.",
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"",
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"“And hast thou slain the Jabberwock?",
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"Come to my arms, my beamish boy!",
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"O frabjous day! Callooh! Callay!”",
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"He chortled in his joy.",
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"",
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"’Twas brillig, and the slithy toves",
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"Did gyre and gimble in the wabe;",
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"All mimsy were the borogoves,",
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"And the mome raths outgrabe.",
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}
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func main() {
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flag.Parse()
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// Read the font data.
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fontBytes, err := ioutil.ReadFile(*fontfile)
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if err != nil {
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log.Println(err)
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return
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}
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f, err := truetype.Parse(fontBytes)
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if err != nil {
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log.Println(err)
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return
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}
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// Draw the background and the guidelines.
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fg, bg := image.Black, image.White
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ruler := color.RGBA{0xdd, 0xdd, 0xdd, 0xff}
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if *wonb {
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fg, bg = image.White, image.Black
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ruler = color.RGBA{0x22, 0x22, 0x22, 0xff}
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}
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rgba := image.NewRGBA(image.Rect(0, 0, 640, 480))
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draw.Draw(rgba, rgba.Bounds(), bg, image.ZP, draw.Src)
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for i := 0; i < 200; i++ {
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rgba.Set(10, 10+i, ruler)
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rgba.Set(10+i, 10, ruler)
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}
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// Draw the text.
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h := font.HintingNone
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switch *hinting {
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case "full":
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h = font.HintingFull
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}
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d := &font.Drawer{
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Dst: rgba,
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Src: fg,
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Face: truetype.NewFace(f, truetype.Options{
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Size: *size,
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DPI: *dpi,
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Hinting: h,
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}),
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}
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dy0 := int(math.Ceil(*size * *dpi / 72))
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dy := int(math.Ceil(*size * *spacing * *dpi / 72))
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for i, s := range text {
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d.Dot = fixed.P(10, 10+dy0+i*dy)
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d.DrawString(s)
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}
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// Save that RGBA image to disk.
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outFile, err := os.Create("out.png")
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if err != nil {
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log.Println(err)
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os.Exit(1)
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}
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defer outFile.Close()
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b := bufio.NewWriter(outFile)
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err = png.Encode(b, rgba)
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if err != nil {
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log.Println(err)
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os.Exit(1)
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}
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err = b.Flush()
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if err != nil {
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log.Println(err)
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os.Exit(1)
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}
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fmt.Println("Wrote out.png OK.")
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}
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@ -0,0 +1,237 @@
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// Copyright 2015 The Freetype-Go Authors. All rights reserved.
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// Use of this source code is governed by your choice of either the
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// FreeType License or the GNU General Public License version 2 (or
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// any later version), both of which can be found in the LICENSE file.
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package truetype
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import (
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"image"
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"github.com/golang/freetype/raster"
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"golang.org/x/exp/shiny/font"
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"golang.org/x/image/math/fixed"
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)
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// Options are optional arguments to NewFace.
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type Options struct {
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// Size is the font size in points, as in "a 10 point font size".
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//
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// A zero value means to use a 12 point font size.
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Size float64
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// DPI is the dots-per-inch resolution.
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//
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// A zero value means to use 72 DPI.
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DPI float64
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// Hinting is how to quantize the glyph nodes.
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//
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// A zero value means to use no hinting.
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Hinting font.Hinting
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}
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func (o *Options) size() float64 {
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if o.Size > 0 {
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return o.Size
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}
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return 12
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}
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func (o *Options) dpi() float64 {
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if o.DPI > 0 {
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return o.DPI
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}
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return 72
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}
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func (o *Options) hinting() font.Hinting {
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switch o.Hinting {
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case font.HintingVertical, font.HintingFull:
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// TODO: support vertical hinting.
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return font.HintingFull
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}
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return font.HintingNone
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}
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// NewFace returns a new font.Face for the given Font.
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func NewFace(f *Font, opts Options) font.Face {
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a := &face{
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f: f,
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hinting: opts.hinting(),
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scale: fixed.Int26_6(0.5 + (opts.size() * opts.dpi() * 64 / 72)),
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}
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// Set the rasterizer's bounds to be big enough to handle the largest glyph.
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b := f.Bounds(a.scale)
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xmin := +int(b.XMin) >> 6
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ymin := -int(b.YMax) >> 6
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xmax := +int(b.XMax+63) >> 6
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ymax := -int(b.YMin-63) >> 6
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a.r.SetBounds(xmax-xmin, ymax-ymin)
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return a
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}
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type face struct {
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f *Font
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hinting font.Hinting
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scale fixed.Int26_6
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r raster.Rasterizer
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glyphBuf GlyphBuf
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// TODO: clip rectangle?
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}
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// Close satisfies the font.Face interface.
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func (a *face) Close() error { return nil }
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// Kern satisfies the font.Face interface.
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func (a *face) Kern(r0, r1 rune) fixed.Int26_6 {
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i0 := a.f.Index(r0)
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i1 := a.f.Index(r1)
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kern := fixed.Int26_6(a.f.Kerning(a.scale, i0, i1))
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if a.hinting != font.HintingNone {
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kern = (kern + 32) &^ 63
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}
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return kern
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}
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// Glyph satisfies the font.Face interface.
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func (a *face) Glyph(dot fixed.Point26_6, r rune) (
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newDot fixed.Point26_6, dr image.Rectangle, mask image.Image, maskp image.Point, ok bool) {
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// Split p.X and p.Y into their integer and fractional parts.
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ix, fx := int(dot.X>>6), dot.X&0x3f
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iy, fy := int(dot.Y>>6), dot.Y&0x3f
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advanceWidth, mask, offset, ok := a.rasterize(a.f.Index(r), fx, fy)
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if !ok {
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return fixed.Point26_6{}, image.Rectangle{}, nil, image.Point{}, false
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}
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newDot = fixed.Point26_6{
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X: dot.X + advanceWidth,
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Y: dot.Y,
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}
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mb := mask.Bounds()
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dr.Min = image.Point{
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X: ix + offset.X,
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Y: iy + offset.Y,
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}
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dr.Max = image.Point{
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X: dr.Min.X + mb.Dx(),
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Y: dr.Min.Y + mb.Dy(),
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}
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return newDot, dr, mask, image.Point{}, true
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}
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// rasterize returns the advance width, glyph mask and integer-pixel offset
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// to render the given glyph at the given sub-pixel offsets.
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// The 26.6 fixed point arguments fx and fy must be in the range [0, 1).
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func (a *face) rasterize(index Index, fx, fy fixed.Int26_6) (
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fixed.Int26_6, *image.Alpha, image.Point, bool) {
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if err := a.glyphBuf.Load(a.f, a.scale, index, a.hinting); err != nil {
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return 0, nil, image.Point{}, false
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}
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// Calculate the integer-pixel bounds for the glyph.
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xmin := int(fx+fixed.Int26_6(a.glyphBuf.B.XMin)) >> 6
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ymin := int(fy-fixed.Int26_6(a.glyphBuf.B.YMax)) >> 6
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xmax := int(fx+fixed.Int26_6(a.glyphBuf.B.XMax)+0x3f) >> 6
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ymax := int(fy-fixed.Int26_6(a.glyphBuf.B.YMin)+0x3f) >> 6
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if xmin > xmax || ymin > ymax {
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return 0, nil, image.Point{}, false
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}
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// A TrueType's glyph's nodes can have negative co-ordinates, but the
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// rasterizer clips anything left of x=0 or above y=0. xmin and ymin are
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// the pixel offsets, based on the font's FUnit metrics, that let a
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// negative co-ordinate in TrueType space be non-negative in rasterizer
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// space. xmin and ymin are typically <= 0.
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fx += fixed.Int26_6(-xmin << 6)
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fy += fixed.Int26_6(-ymin << 6)
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// Rasterize the glyph's vectors.
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a.r.Clear()
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e0 := 0
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for _, e1 := range a.glyphBuf.End {
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a.drawContour(a.glyphBuf.Point[e0:e1], fx, fy)
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e0 = e1
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}
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// TODO: don't allocate a new mask each time.
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mask := image.NewAlpha(image.Rect(0, 0, xmax-xmin, ymax-ymin))
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a.r.Rasterize(raster.NewAlphaSrcPainter(mask))
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return fixed.Int26_6(a.glyphBuf.AdvanceWidth), mask, image.Point{xmin, ymin}, true
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}
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// drawContour draws the given closed contour with the given offset.
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func (a *face) drawContour(ps []Point, dx, dy fixed.Int26_6) {
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if len(ps) == 0 {
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return
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}
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// The low bit of each point's Flags value is whether the point is on the
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// curve. Truetype fonts only have quadratic Bézier curves, not cubics.
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// Thus, two consecutive off-curve points imply an on-curve point in the
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// middle of those two.
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//
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// See http://chanae.walon.org/pub/ttf/ttf_glyphs.htm for more details.
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// ps[0] is a truetype.Point measured in FUnits and positive Y going
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// upwards. start is the same thing measured in fixed point units and
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// positive Y going downwards, and offset by (dx, dy).
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start := fixed.Point26_6{
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X: dx + fixed.Int26_6(ps[0].X),
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Y: dy - fixed.Int26_6(ps[0].Y),
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}
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var others []Point
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if ps[0].Flags&0x01 != 0 {
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others = ps[1:]
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} else {
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last := fixed.Point26_6{
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X: dx + fixed.Int26_6(ps[len(ps)-1].X),
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Y: dy - fixed.Int26_6(ps[len(ps)-1].Y),
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}
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if ps[len(ps)-1].Flags&0x01 != 0 {
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start = last
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others = ps[:len(ps)-1]
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} else {
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start = fixed.Point26_6{
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X: (start.X + last.X) / 2,
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Y: (start.Y + last.Y) / 2,
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}
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others = ps
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}
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}
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a.r.Start(start)
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q0, on0 := start, true
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for _, p := range others {
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q := fixed.Point26_6{
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X: dx + fixed.Int26_6(p.X),
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Y: dy - fixed.Int26_6(p.Y),
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}
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on := p.Flags&0x01 != 0
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if on {
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if on0 {
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a.r.Add1(q)
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} else {
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a.r.Add2(q0, q)
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}
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} else {
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if on0 {
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// No-op.
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} else {
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mid := fixed.Point26_6{
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X: (q0.X + q.X) / 2,
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Y: (q0.Y + q.Y) / 2,
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}
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a.r.Add2(q0, mid)
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}
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}
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q0, on0 = q, on
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}
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// Close the curve.
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if on0 {
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a.r.Add1(start)
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} else {
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a.r.Add2(q0, start)
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}
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}
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