| // Copyright 2010 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. |
| |
| // This program visualizes the quadratic approximation to the circle, used to |
| // implement round joins when stroking paths. The approximation is used in the |
| // stroking code for arcs between 0 and 45 degrees, but is visualized here |
| // between 0 and 90 degrees. The discrepancy between the approximation and the |
| // true circle is clearly visible at angles above 65 degrees. |
| package main |
| |
| import ( |
| "bufio" |
| "fmt" |
| "image" |
| "image/color" |
| "image/draw" |
| "image/png" |
| "log" |
| "math" |
| "os" |
| |
| "code.google.com/p/freetype-go/freetype/raster" |
| ) |
| |
| func main() { |
| const ( |
| n = 17 |
| r = 256 * 80 |
| ) |
| s := raster.Fix32(r * math.Sqrt(2) / 2) |
| t := raster.Fix32(r * math.Tan(math.Pi/8)) |
| |
| m := image.NewRGBA(image.Rect(0, 0, 800, 600)) |
| draw.Draw(m, m.Bounds(), image.NewUniform(color.RGBA{63, 63, 63, 255}), image.ZP, draw.Src) |
| mp := raster.NewRGBAPainter(m) |
| mp.SetColor(image.Black) |
| z := raster.NewRasterizer(800, 600) |
| |
| for i := 0; i < n; i++ { |
| cx := raster.Fix32(25600 + 51200*(i%4)) |
| cy := raster.Fix32(2560 + 32000*(i/4)) |
| c := raster.Point{X: cx, Y: cy} |
| theta := math.Pi * (0.5 + 0.5*float64(i)/(n-1)) |
| dx := raster.Fix32(r * math.Cos(theta)) |
| dy := raster.Fix32(r * math.Sin(theta)) |
| d := raster.Point{X: dx, Y: dy} |
| // Draw a quarter-circle approximated by two quadratic segments, |
| // with each segment spanning 45 degrees. |
| z.Start(c) |
| z.Add1(c.Add(raster.Point{X: r, Y: 0})) |
| z.Add2(c.Add(raster.Point{X: r, Y: t}), c.Add(raster.Point{X: s, Y: s})) |
| z.Add2(c.Add(raster.Point{X: t, Y: r}), c.Add(raster.Point{X: 0, Y: r})) |
| // Add another quadratic segment whose angle ranges between 0 and 90 degrees. |
| // For an explanation of the magic constants 22, 150, 181 and 256, read the |
| // comments in the freetype/raster package. |
| dot := 256 * d.Dot(raster.Point{X: 0, Y: r}) / (r * r) |
| multiple := raster.Fix32(150 - 22*(dot-181)/(256-181)) |
| z.Add2(c.Add(raster.Point{X: dx, Y: r + dy}.Mul(multiple)), c.Add(d)) |
| // Close the curve. |
| z.Add1(c) |
| } |
| z.Rasterize(mp) |
| |
| for i := 0; i < n; i++ { |
| cx := raster.Fix32(25600 + 51200*(i%4)) |
| cy := raster.Fix32(2560 + 32000*(i/4)) |
| for j := 0; j < n; j++ { |
| theta := math.Pi * float64(j) / (n - 1) |
| dx := raster.Fix32(r * math.Cos(theta)) |
| dy := raster.Fix32(r * math.Sin(theta)) |
| m.Set(int((cx+dx)/256), int((cy+dy)/256), color.RGBA{255, 255, 0, 255}) |
| } |
| } |
| |
| // Save that RGBA image to disk. |
| f, err := os.Create("out.png") |
| if err != nil { |
| log.Println(err) |
| os.Exit(1) |
| } |
| defer f.Close() |
| b := bufio.NewWriter(f) |
| err = png.Encode(b, m) |
| 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.") |
| } |