1package captcha
  2
  3import (
  4	"image"
  5	"image/png"
  6	"io"
  7	"os"
  8	"rand"
  9	"time"
 10)
 11
 12const (
 13	// Standard width and height of a captcha image.
 14	StdWidth  = 300
 15	StdHeight = 80
 16
 17	maxSkew = 0.7
 18)
 19
 20type Image struct {
 21	*image.NRGBA
 22	primaryColor image.NRGBAColor
 23	numWidth     int
 24	numHeight    int
 25	dotSize      int
 26}
 27
 28func init() {
 29	rand.Seed(time.Seconds())
 30}
 31
 32// NewImage returns a new captcha image of the given width and height with the
 33// given digits, where each digit must be in range 0-9.
 34func NewImage(digits []byte, width, height int) *Image {
 35	img := new(Image)
 36	img.NRGBA = image.NewNRGBA(width, height)
 37	img.primaryColor = image.NRGBAColor{
 38		uint8(rand.Intn(129)),
 39		uint8(rand.Intn(129)),
 40		uint8(rand.Intn(129)),
 41		0xFF,
 42	}
 43	img.calculateSizes(width, height, len(digits))
 44	// Draw background (10 random circles of random brightness).
 45	img.fillWithCircles(10, img.dotSize)
 46	// Randomly position captcha inside the image.
 47	maxx := width - (img.numWidth+img.dotSize)*len(digits) - img.dotSize
 48	maxy := height - img.numHeight - img.dotSize*2
 49	x := rnd(img.dotSize*2, maxx)
 50	y := rnd(img.dotSize*2, maxy)
 51	// Draw digits.
 52	for _, n := range digits {
 53		img.drawDigit(font[n], x, y)
 54		x += img.numWidth + img.dotSize
 55	}
 56	// Draw strike-through line.
 57	img.strikeThrough()
 58	return img
 59}
 60
 61// BUG(dchest): While Image conforms to io.WriterTo interface, its WriteTo
 62// method returns 0 instead of the actual bytes written because png.Encode
 63// doesn't report this.
 64
 65// WriteTo writes captcha image in PNG format into the given writer.
 66func (img *Image) WriteTo(w io.Writer) (int64, os.Error) {
 67	return 0, png.Encode(w, img)
 68}
 69
 70func (img *Image) calculateSizes(width, height, ncount int) {
 71	// Goal: fit all digits inside the image.
 72	var border int
 73	if width > height {
 74		border = height / 5
 75	} else {
 76		border = width / 5
 77	}
 78	// Convert everything to floats for calculations.
 79	w := float64(width - border*2)
 80	h := float64(height - border*2)
 81	// fw takes into account 1-dot spacing between digits.
 82	fw := float64(fontWidth + 1)
 83	fh := float64(fontHeight)
 84	nc := float64(ncount)
 85	// Calculate the width of a single digit taking into account only the
 86	// width of the image.
 87	nw := w / nc
 88	// Calculate the height of a digit from this width.
 89	nh := nw * fh / fw
 90	// Digit too high?
 91	if nh > h {
 92		// Fit digits based on height.
 93		nh = h
 94		nw = fw / fh * nh
 95	}
 96	// Calculate dot size.
 97	img.dotSize = int(nh / fh)
 98	// Save everything, making the actual width smaller by 1 dot to account
 99	// for spacing between digits.
100	img.numWidth = int(nw) - img.dotSize
101	img.numHeight = int(nh)
102}
103
104func (img *Image) drawHorizLine(color image.Color, fromX, toX, y int) {
105	for x := fromX; x <= toX; x++ {
106		img.Set(x, y, color)
107	}
108}
109
110func (img *Image) drawCircle(color image.Color, x, y, radius int) {
111	f := 1 - radius
112	dfx := 1
113	dfy := -2 * radius
114	xx := 0
115	yy := radius
116
117	img.Set(x, y+radius, color)
118	img.Set(x, y-radius, color)
119	img.drawHorizLine(color, x-radius, x+radius, y)
120
121	for xx < yy {
122		if f >= 0 {
123			yy--
124			dfy += 2
125			f += dfy
126		}
127		xx++
128		dfx += 2
129		f += dfx
130		img.drawHorizLine(color, x-xx, x+xx, y+yy)
131		img.drawHorizLine(color, x-xx, x+xx, y-yy)
132		img.drawHorizLine(color, x-yy, x+yy, y+xx)
133		img.drawHorizLine(color, x-yy, x+yy, y-xx)
134	}
135}
136
137func (img *Image) fillWithCircles(n, maxradius int) {
138	color := img.primaryColor
139	maxx := img.Bounds().Max.X
140	maxy := img.Bounds().Max.Y
141	for i := 0; i < n; i++ {
142		setRandomBrightness(&color, 255)
143		r := rnd(1, maxradius)
144		img.drawCircle(color, rnd(r, maxx-r), rnd(r, maxy-r), r)
145	}
146}
147
148func (img *Image) strikeThrough() {
149	r := 0
150	maxx := img.Bounds().Max.X
151	maxy := img.Bounds().Max.Y
152	y := rnd(maxy/3, maxy-maxy/3)
153	for x := 0; x < maxx; x += r {
154		r = rnd(1, img.dotSize/3)
155		y += rnd(-img.dotSize/2, img.dotSize/2)
156		if y <= 0 || y >= maxy {
157			y = rnd(maxy/3, maxy-maxy/3)
158		}
159		img.drawCircle(img.primaryColor, x, y, r)
160	}
161}
162
163func (img *Image) drawDigit(digit []byte, x, y int) {
164	skf := rndf(-maxSkew, maxSkew)
165	xs := float64(x)
166	minr := img.dotSize / 2 // minumum radius
167	maxr := img.dotSize     // maximum radius
168	y += rnd(-minr, minr)
169	for yy := 0; yy < fontHeight; yy++ {
170		for xx := 0; xx < fontWidth; xx++ {
171			if digit[yy*fontWidth+xx] != blackChar {
172				continue
173			}
174			// Introduce random variations.
175			or := rnd(minr, maxr)
176			ox := x + (xx * img.dotSize) + rnd(0, or/2)
177			oy := y + (yy * img.dotSize) + rnd(0, or/2)
178
179			img.drawCircle(img.primaryColor, ox, oy, or)
180		}
181		xs += skf
182		x = int(xs)
183	}
184}
185
186func setRandomBrightness(c *image.NRGBAColor, max uint8) {
187	minc := min3(c.R, c.G, c.B)
188	maxc := max3(c.R, c.G, c.B)
189	if maxc > max {
190		return
191	}
192	n := rand.Intn(int(max-maxc)) - int(minc)
193	c.R = uint8(int(c.R) + n)
194	c.G = uint8(int(c.G) + n)
195	c.B = uint8(int(c.B) + n)
196}
197
198func min3(x, y, z uint8) (o uint8) {
199	o = x
200	if y < o {
201		o = y
202	}
203	if z < o {
204		o = z
205	}
206	return
207}
208
209func max3(x, y, z uint8) (o uint8) {
210	o = x
211	if y > o {
212		o = y
213	}
214	if z > o {
215		o = z
216	}
217	return
218}
219
220// rnd returns a random number in range [from, to].
221func rnd(from, to int) int {
222	return rand.Intn(to+1-from) + from
223}