Add an example/capjoin program.

example/capjoin/main.go

+// Copyright 2016 The Freetype-Go Authors. All rights reserved.
+// Use of this source code is governed by your choice of either the
+// FreeType License or the GNU General Public License version 2 (or
+// any later version), both of which can be found in the LICENSE file.
+
+// +build ignore
+//
+// This build tag means that "go install github.com/golang/freetype/..."
+// doesn't install this example program. Use "go run main.go" to run it.
+
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"image"
+	"image/color"
+	"image/draw"
+	"image/png"
+	"log"
+	"os"
+
+	"github.com/golang/freetype/raster"
+	"golang.org/x/image/math/fixed"
+)
+
+func main() {
+	const (
+		w = 400
+		h = 400
+	)
+	r := raster.NewRasterizer(w, h)
+	r.UseNonZeroWinding = true
+
+	cjs := []struct {
+		c raster.Capper
+		j raster.Joiner
+	}{
+		{raster.RoundCapper, raster.RoundJoiner},
+		{raster.ButtCapper, raster.BevelJoiner},
+		{raster.SquareCapper, raster.BevelJoiner},
+	}
+
+	for i, cj := range cjs {
+		var path raster.Path
+		path.Start(fixed.P(30+100*i, 30+120*i))
+		path.Add1(fixed.P(180+100*i, 80+120*i))
+		path.Add1(fixed.P(50+100*i, 130+120*i))
+		raster.Stroke(r, path, fixed.I(20), cj.c, cj.j)
+	}
+
+	rgba := image.NewRGBA(image.Rect(0, 0, w, h))
+	draw.Draw(rgba, rgba.Bounds(), image.Black, image.Point{}, draw.Src)
+	p := raster.NewRGBAPainter(rgba)
+	p.SetColor(color.RGBA{0x7f, 0x7f, 0x7f, 0xff})
+	r.Rasterize(p)
+
+	white := color.RGBA{0xff, 0xff, 0xff, 0xff}
+	for i := range cjs {
+		rgba.SetRGBA(30+100*i, 30+120*i, white)
+		rgba.SetRGBA(180+100*i, 80+120*i, white)
+		rgba.SetRGBA(50+100*i, 130+120*i, white)
+	}
+
+	// Save that RGBA image to disk.
+	outFile, err := os.Create("out.png")
+	if err != nil {
+		log.Println(err)
+		os.Exit(1)
+	}
+	defer outFile.Close()
+	b := bufio.NewWriter(outFile)
+	err = png.Encode(b, rgba)
+	if err != nil {
+		log.Println(err)
+		os.Exit(1)
+	}
+	err = b.Flush()
+	if err != nil {
+		log.Println(err)
+		os.Exit(1)
+	}
+	fmt.Println("Wrote out.png OK.")
+}