113 lines
2.9 KiB
Go
113 lines
2.9 KiB
Go
package main
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import (
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"image"
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"image/color"
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"image/gif"
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"log"
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"math"
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"os"
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)
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func drawLine(img *image.Paletted, x1, y1, x2, y2 int, ci uint8) {
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var first, last int
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if x2 != x1 {
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m := float64(y2-y1) / float64(x2-x1)
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if x1 < x2 {
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first, last = x1, x2
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} else {
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first, last = x2, x1
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}
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for x := first; x <= last; x++ {
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y := int(m*float64(x-x1)+0.5) + y1
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img.SetColorIndex(x, y, ci)
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}
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} else {
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if y1 < y2 {
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first, last = y1, y2
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} else {
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first, last = y2, y1
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}
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for y := first; y <= last; y++ {
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img.SetColorIndex(x1, y, ci)
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}
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}
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}
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func setBackgroundColor(img *image.Paletted, w, h int, ci uint8) {
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for x := 0; x < w; x++ {
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for y := 0; y < h; y++ {
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img.SetColorIndex(x, y, ci)
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}
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}
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}
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func hsb2rgb(hue, sat, bri float64) (r, g, b int) {
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u := int(bri*255 + 0.5)
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if sat == 0 {
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r, g, b = u, u, u
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} else {
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h := (hue - math.Floor(hue)) * 6
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f := h - math.Floor(h)
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p := int(bri*(1-sat)*255 + 0.5)
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q := int(bri*(1-sat*f)*255 + 0.5)
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t := int(bri*(1-sat*(1-f))*255 + 0.5)
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switch int(h) {
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case 0:
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r, g, b = u, t, p
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case 1:
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r, g, b = q, u, p
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case 2:
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r, g, b = p, u, t
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case 3:
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r, g, b = p, q, u
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case 4:
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r, g, b = t, p, u
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case 5:
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r, g, b = u, p, q
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}
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}
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return
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}
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func main() {
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const degToRad = math.Pi / 180
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const nframes = 360
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const delay = 20 // 200ms
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width, height := 640, 640
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anim := gif.GIF{LoopCount: nframes}
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rect := image.Rect(0, 0, width, height)
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palette := make([]color.Color, 151)
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palette[0] = color.White
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for i := 1; i <= 150; i++ {
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r, g, b := hsb2rgb(float64(i)/150, 1, 1)
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palette[i] = color.RGBA{uint8(r), uint8(g), uint8(b), 255}
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}
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incr := 0
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for f := 1; f <= nframes; f++ {
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incr = (incr + 1) % 360
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x1, y1 := width/2, height/2
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length := 5.0
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img := image.NewPaletted(rect, palette)
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setBackgroundColor(img, width, height, 0) // white background
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angle := incr
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for ci := uint8(1); ci <= 150; ci++ {
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x2 := x1 + int(math.Cos(float64(angle)*degToRad)*length)
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y2 := y1 - int(math.Sin(float64(angle)*degToRad)*length)
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drawLine(img, x1, y1, x2, y2, ci)
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x1, y1 = x2, y2
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length += 3
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angle = (angle + incr) % 360
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}
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anim.Delay = append(anim.Delay, delay)
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anim.Image = append(anim.Image, img)
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}
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file, err := os.Create("polyspiral.gif")
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if err != nil {
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log.Fatal(err)
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}
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defer file.Close()
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if err2 := gif.EncodeAll(file, &anim); err != nil {
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log.Fatal(err2)
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}
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}
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