1package captcha
  2
  3import (
  4	"image"
  5	"image/png"
  6	"io"
  7	"os"
  8	"rand"
  9)
 10
 11const (
 12	// Standard width and height for captcha image
 13	StdWidth  = 300
 14	StdHeight = 80
 15
 16	maxSkew = 2
 17)
 18
 19type CaptchaImage struct {
 20	*image.NRGBA
 21	primaryColor image.NRGBAColor
 22	numWidth     int
 23	numHeight    int
 24	dotSize      int
 25}
 26
 27// NewImage returns a new captcha image of the given width and height with the
 28// given slice of numbers, where each number must be in range 0-9.
 29func NewImage(numbers []byte, width, height int) *CaptchaImage {
 30	img := new(CaptchaImage)
 31	img.NRGBA = image.NewNRGBA(width, height)
 32	img.primaryColor = image.NRGBAColor{
 33		uint8(rand.Intn(129)),
 34		uint8(rand.Intn(129)),
 35		uint8(rand.Intn(129)),
 36		0xFF,
 37	}
 38	// Calculate sizes
 39	var border int
 40	if width > height {
 41		border = height / 5
 42	} else {
 43		border = width / 5
 44	}
 45	bwidth := width - border*2
 46	bheight := height - border*2
 47	img.calculateSizes(bwidth, bheight, len(numbers))
 48	// Draw background (10 random circles of random brightness)
 49	img.fillWithCircles(10, img.dotSize)
 50	// Randomly position captcha within image
 51	maxx := width - (img.numWidth+img.dotSize)*len(numbers) - img.dotSize
 52	maxy := height - img.numHeight - img.dotSize*2
 53	x := rnd(img.dotSize*2, maxx)
 54	y := rnd(img.dotSize*2, maxy)
 55	// Draw numbers
 56	for _, n := range numbers {
 57		img.drawNumber(font[n], x, y)
 58		x += img.numWidth + img.dotSize
 59	}
 60	// Draw strike-through line
 61	img.strikeThrough()
 62	return img
 63}
 64
 65// NewRandomImage generates a sequence of random numbers with the given length,
 66// and returns a new captcha image of the given width and height with generated
 67// numbers printed on it, and the sequence of numbers itself.
 68func NewRandomImage(length, width, height int) (img *CaptchaImage, numbers []byte) {
 69	numbers = randomNumbers(length)
 70	img = NewImage(numbers, width, height)
 71	return
 72}
 73
 74// PNGEncode writes captcha image in PNG format into the given writer.
 75func (img *CaptchaImage) PNGEncode(w io.Writer) os.Error {
 76	return png.Encode(w, img)
 77}
 78
 79func (img *CaptchaImage) calculateSizes(width, height, ncount int) {
 80	// Goal: fit all numbers inside the image.
 81	// Convert everything to floats for calculations.
 82	w := float64(width)
 83	h := float64(height)
 84	// fw takes into account 1-dot spacing between numbers
 85	fw := float64(fontWidth) + 1
 86	fh := float64(fontHeight)
 87	nc := float64(ncount)
 88	// Calculate the width of a single number taking into account only the
 89	// width of the image
 90	nw := w / nc
 91	// Calculate the height of a number from this width
 92	nh := nw * fh / fw
 93	// Number height too large?
 94	if nh > h {
 95		// Fit numbers based on height
 96		nh = h
 97		nw = fw / fh * nh
 98	}
 99	// Calculate dot size
100	img.dotSize = int(nh / fh)
101	// Save everything, making actual width smaller by 1 dot, to account
102	// for spacing between numbers
103	img.numWidth = int(nw)
104	img.numHeight = int(nh) - img.dotSize
105}
106
107func (img *CaptchaImage) drawHorizLine(color image.Color, fromX, toX, y int) {
108	for x := fromX; x <= toX; x++ {
109		img.Set(x, y, color)
110	}
111}
112
113func (img *CaptchaImage) drawCircle(color image.Color, x, y, radius int) {
114	f := 1 - radius
115	dfx := 1
116	dfy := -2 * radius
117	xx := 0
118	yy := radius
119
120	img.Set(x, y+radius, color)
121	img.Set(x, y-radius, color)
122	img.drawHorizLine(color, x-radius, x+radius, y)
123
124	for xx < yy {
125		if f >= 0 {
126			yy--
127			dfy += 2
128			f += dfy
129		}
130		xx++
131		dfx += 2
132		f += dfx
133		img.drawHorizLine(color, x-xx, x+xx, y+yy)
134		img.drawHorizLine(color, x-xx, x+xx, y-yy)
135		img.drawHorizLine(color, x-yy, x+yy, y+xx)
136		img.drawHorizLine(color, x-yy, x+yy, y-xx)
137	}
138}
139
140func (img *CaptchaImage) fillWithCircles(n, maxradius int) {
141	color := img.primaryColor
142	maxx := img.Bounds().Max.X
143	maxy := img.Bounds().Max.Y
144	for i := 0; i < n; i++ {
145		setRandomBrightness(&color, 255)
146		r := rnd(1, maxradius)
147		img.drawCircle(color, rnd(r, maxx-r), rnd(r, maxy-r), r)
148	}
149}
150
151func (img *CaptchaImage) strikeThrough() {
152	r := 0
153	maxx := img.Bounds().Max.X
154	maxy := img.Bounds().Max.Y
155	y := rnd(maxy/3, maxy-maxy/3)
156	for x := 0; x < maxx; x += r {
157		r = rnd(1, img.dotSize/2-1)
158		y += rnd(-img.dotSize/2, img.dotSize/2)
159		if y <= 0 || y >= maxy {
160			y = rnd(maxy/3, maxy-maxy/3)
161		}
162		img.drawCircle(img.primaryColor, x, y, r)
163	}
164}
165
166func (img *CaptchaImage) drawNumber(number []byte, x, y int) {
167	skf := rand.Float64() * float64(rnd(-maxSkew, maxSkew))
168	xs := float64(x)
169	minr := img.dotSize / 2               // minumum radius
170	maxr := img.dotSize/2 + img.dotSize/4 // maximum radius
171	y += rnd(-minr, minr)
172	for yy := 0; yy < fontHeight; yy++ {
173		for xx := 0; xx < fontWidth; xx++ {
174			if number[yy*fontWidth+xx] != blackChar {
175				continue
176			}
177			// introduce random variations
178			or := rnd(minr, maxr)
179			ox := x + (xx * img.dotSize) + rnd(0, or/2)
180			oy := y + (yy * img.dotSize) + rnd(0, or/2)
181			img.drawCircle(img.primaryColor, ox, oy, or)
182		}
183		xs += skf
184		x = int(xs)
185	}
186}
187
188func setRandomBrightness(c *image.NRGBAColor, max uint8) {
189	minc := min3(c.R, c.G, c.B)
190	maxc := max3(c.R, c.G, c.B)
191	if maxc > max {
192		return
193	}
194	n := rand.Intn(int(max-maxc)) - int(minc)
195	c.R = uint8(int(c.R) + n)
196	c.G = uint8(int(c.G) + n)
197	c.B = uint8(int(c.B) + n)
198}
199
200func min3(x, y, z uint8) (o uint8) {
201	o = x
202	if y < o {
203		o = y
204	}
205	if z < o {
206		o = z
207	}
208	return
209}
210
211func max3(x, y, z uint8) (o uint8) {
212	o = x
213	if y > o {
214		o = y
215	}
216	if z > o {
217		o = z
218	}
219	return
220}
221
222// rnd returns a random number in range [from, to].
223func rnd(from, to int) int {
224	return rand.Intn(to+1-from) + from
225}