add: hsv for better random color

update: readme

.travis.yml

@@ -0,0 +1,4 @@
+language: go
+
+go:
+  - 1.9

README.md

@@ -0,0 +1,37 @@
+> Package captcha provides a simple API for captcha generation
+
+<div align="center">
+
+[![GoDoc](https://godoc.org/github.com/steambap/captcha?status.svg)](https://godoc.org/github.com/steambap/captcha)
+[![Build Status](https://travis-ci.org/steambap/captcha.svg)](https://travis-ci.org/steambap/captcha)
+
+</div>
+
+## install
+```
+go get github.com/steambap/captcha
+```
+
+## usage
+```Go
+func handle(w http.ResponseWriter, r *http.Request) {
+	// create a captcha of 150x50px
+	data, _ := captcha.New(150, 50)
+
+	// session come from other library such as gorilla/sessions
+	session.Values["captcha"] = data.Text
+	session.Save(r, w)
+	// send image data to client
+	data.WriteTo(w)
+}
+
+```
+
+[documentation](https://godoc.org/github.com/steambap/captcha) |
+[example](example/main.go)
+
+## sample image
+![image](example/captcha.png)
+
+## License
+[MIT](LICENSE.md)

captcha.go

@@ -149,7 +149,7 @@ func drawSineCurve(img *image.NRGBA, opts *Options) {
 	if flip {
 		yFlip = -1.0
 	}
-	curveColor := randomDarkGray()
+	curveColor := randomDarkColor()
 
 	for x1 := xStart; x1 <= xEnd; x1++ {
 		y := math.Sin(math.Pi*angle*float64(x1)/float64(opts.width)) * curveHeight * yFlip
@@ -157,10 +157,12 @@ func drawSineCurve(img *image.NRGBA, opts *Options) {
 	}
 }
 
-func randomDarkGray() color.Gray {
+func randomDarkColor() hsva {
-	gray := rng.Intn(128) + 20
+	hue := float64(rng.Intn(361)) / 360
+	saturation := 0.6 + rng.Float64() * 0.2
+	value := 0.25 + rng.Float64() * 0.2
 
-	return color.Gray{Y: uint8(gray)}
+	return hsva{h: hue, s:saturation, v:value, a:uint8(255)}
 }
 
 func drawText(text string, img *image.NRGBA, opts *Options) error {
@@ -177,7 +179,7 @@ func drawText(text string, img *image.NRGBA, opts *Options) error {
 		fontScale := 1 + rng.Float64()*0.5
 		fontSize := float64(opts.height) / fontScale
 		ctx.SetFontSize(fontSize)
-		ctx.SetSrc(image.NewUniform(randomDarkGray()))
+		ctx.SetSrc(image.NewUniform(randomDarkColor()))
 		x := fontSpacing*idx + fontSpacing/int(fontSize)
 		y := opts.height/6 + rng.Intn(opts.height/3) + int(fontSize/2)
 		pt := freetype.Pt(x, y)

fonts/gen.go

@@ -1,11 +1,11 @@
 package main
 
 import (
-	"io/ioutil"
-	"log"
 	"bytes"
 	"fmt"
 	"go/format"
+	"io/ioutil"
+	"log"
 	"path/filepath"
 )
 

hsva.go

@@ -0,0 +1,43 @@
+package captcha
+
+import "math"
+
+type hsva struct {
+	h, s, v float64
+	a       uint8
+}
+
+// https://gist.github.com/mjackson/5311256
+func (c hsva) RGBA() (r, g, b, a uint32) {
+	var i = math.Floor(c.h * 6)
+	var f = c.h*6 - i
+	var p = c.v * (1.0 - c.s)
+	var q = c.v * (1.0 - f*c.s)
+	var t = c.v * (1 - (1-f)*c.s)
+
+	var red, green, blue float64
+	switch int(i) % 6 {
+	case 0:
+		red, green, blue = c.v, t, p
+	case 1:
+		red, green, blue = q, c.v, p
+	case 2:
+		red, green, blue = p, c.v, t
+	case 3:
+		red, green, blue = p, q, c.v
+	case 4:
+		red, green, blue = t, p, c.v
+	case 5:
+		red, green, blue = c.v, p, q
+	}
+
+	r = uint32(red * 255)
+	r |= r << 8
+	g = uint32(green * 255)
+	g |= g << 8
+	b = uint32(blue * 255)
+	b |= b << 8
+	a = uint32(c.a)
+	a |= a << 8
+	return
+}

hsva_test.go

@@ -0,0 +1,10 @@
+package captcha
+
+import (
+	"image/color"
+	"testing"
+)
+
+func TestHSVAInterface(t *testing.T) {
+	var _ color.Color = hsva{}
+}