example/text2svg: example of how to extract quadratic splines from TTF
Change-Id: Iaa22bee1eaa8d31810ede59914fe92b86ee28d61
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Alan Donovan
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1 changed files with 174 additions and 0 deletions
174
example/text2svg/main.go
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174
example/text2svg/main.go
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// The text2svg command converts a text string to a stroked SVG path
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// in a given TrueType v1 font.
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package main
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import (
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"flag"
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"fmt"
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"io/ioutil"
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"log"
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"github.com/golang/freetype/truetype"
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"golang.org/x/image/font"
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"golang.org/x/image/math/fixed"
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)
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// flags
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var (
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textFlag = flag.String("text", "Hamburger", "the text to print")
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fontFlag = flag.String("font", "/Library/Fonts/Georgia Italic.ttf",
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"file name of the TrueType v1 font to use")
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scaleFlag = flag.Int("scale", 100, "scale in points")
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)
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func main() {
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flag.Parse()
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log.SetPrefix("text2svg: ")
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log.SetFlags(0)
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ttfdata, err := ioutil.ReadFile(*fontFlag)
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if err != nil {
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log.Fatalf("loading font: %v", err)
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}
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f, err := truetype.Parse(ttfdata)
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if err != nil {
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log.Fatalf("parsing font: %v", err)
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}
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fmt.Printf("<svg xmlns='http://www.w3.org/2000/svg' "+
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"style='fill: grey' width='%d' height='%d'>\n",
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1000, 1000)
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scale := fixed.I(*scaleFlag)
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dy = scale // set the baseline one line below the origin
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var prevIndex truetype.Index
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for i, r := range *textFlag {
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index := f.Index(r)
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// Load the contours for a glyph.
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var gbuf truetype.GlyphBuf
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if err := gbuf.Load(f, scale, index, font.HintingNone); err != nil {
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log.Fatalf("loading glyph: %v", err)
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}
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// Emit a single SVG <path> for all glyph contours.
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fmt.Printf("<path d='")
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prevEnd := 0
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for _, end := range gbuf.Ends {
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drawContour(gbuf.Points[prevEnd:end], drawSVG)
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prevEnd = end
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}
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fmt.Printf("'/>\n")
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// Advance the position.
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dx += gbuf.AdvanceWidth
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if i > 0 {
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dx += f.Kern(scale, prevIndex, index)
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}
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prevIndex = index
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}
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fmt.Println("</svg>")
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}
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func drawSVG(cmd rune, p0, p1 fixed.Point26_6) {
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switch cmd {
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case 'M': // moveto
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fmt.Printf("M%s ", p2svg(p0))
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case 'L': // lineto
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fmt.Printf("L%s ", p2svg(p0))
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case 'Q': // quadratic spline
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fmt.Printf("Q%s %s ", p2svg(p0), p2svg(p1))
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}
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}
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var dx, dy fixed.Int26_6
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func p2svg(p fixed.Point26_6) string {
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return fmt.Sprintf("%v,%v",
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float64(dx+p.X)/64,
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float64(dy-p.Y)/64)
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}
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var dummy fixed.Point26_6
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// drawContour calls the draw function for each moveto, lineto, or
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// quadratic spline command in the specified contour.
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//
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// Stolen from drawContour in github.com/golang/freetype/freetype.go.
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// It would be nice if that version was reusable.
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func drawContour(ps []truetype.Point, draw func(cmd rune, p0, p1 fixed.Point26_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
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// point is on the curve. Truetype fonts only have quadratic
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// Bézier curves, not cubics. Thus, two consecutive off-curve
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// points imply an on-curve point in the 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: ps[0].X,
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Y: ps[0].Y,
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}
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var others []truetype.Point
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if ps[0].Flags&1 != 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: ps[len(ps)-1].X,
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Y: ps[len(ps)-1].Y,
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}
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if ps[len(ps)-1].Flags&1 != 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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draw('M', start, dummy)
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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: p.X,
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Y: p.Y,
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}
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on := p.Flags&1 != 0
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if on {
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if on0 {
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draw('L', q, dummy)
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} else {
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draw('Q', 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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draw('Q', 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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draw('L', start, dummy)
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} else {
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draw('Q', q0, start)
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}
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}
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