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package main

import (
	"image"
	"image/color"
	"image/color/palette"
	"image/gif"
	"math"
	"os"
)

type Circle struct {
	X, Y, R float64
}

func (c *Circle) Brightness(x, y float64) uint8 {
	var dx, dy float64 = c.X - x, c.Y - y
	d := math.Sqrt(dx*dx+dy*dy) / c.R
	if d > 1 {
		return 0
	} else {
		return 255
	}
}

func main() {
	const (
		w, h   int     = 256, 256
		R      float64 = 50
		frameN int     = 30
		delay  int     = 100 / frameN
	)

	var palette = append(palette.WebSafe, color.Transparent)
	var images []*image.Paletted
	var delays []int
	var disposals []byte

	var hw, hh float64 = float64(w / 2), float64(h / 2)
	circles := []*Circle{&Circle{}, &Circle{}, &Circle{}}
	for step := 0; step < frameN; step++ {
		img := image.NewPaletted(image.Rect(0, 0, w, h), palette)
		images = append(images, img)
		delays = append(delays, delay)
		disposals = append(disposals, gif.DisposalPrevious)

		θ := 2.0 * math.Pi / float64(frameN) * float64(step)
		for i, circle := range circles {
			θ0 := 2 * math.Pi / 3 * float64(i)
			circle.X = hw - 30*math.Sin(θ0) - 30*math.Sin(θ0+θ)
			circle.Y = hh - 30*math.Cos(θ0) - 30*math.Cos(θ0+θ)
			circle.R = R
		}

		for x := 0; x < w; x++ {
			for y := 0; y < h; y++ {
				cr := circles[0].Brightness(float64(x), float64(y))
				cg := circles[1].Brightness(float64(x), float64(y))
				cb := circles[2].Brightness(float64(x), float64(y))
				if cr|cg|cb > 0x00 {
					img.Set(x, y, color.RGBA{cr, cg, cb, 255})
				} else {
					img.Set(x, y, color.Transparent)
				}
			}
		}
	}

	f, err := os.Create("rgb.gif")
	if err != nil {
		panic(err)
	}
	defer f.Close()
	gif.EncodeAll(f, &gif.GIF{
		Image:    images,
		Delay:    delays,
		Disposal: disposals,
	})
}

package main

import (
	"fmt"
	"os"
	"regexp"

	"image"
	"image/color"
	"image/color/palette"
	"image/draw"
	"image/gif"
	_ "image/png"
	_ "image/jpeg"
	"io/ioutil"
)

func main() {
	if len(os.Args) == 1 {
		panic(fmt.Errorf("len(os.Args) less than 2"))
	}
	format := fmt.Sprintf("%%0%dd", len(string(len(os.Args)))+1)
	palette := append(palette.WebSafe, color.Transparent)
	for i, fnFmt := range os.Args[1:] {
		pattern, err := regexp.Compile(fnFmt)
		if err != nil {
			panic(err)
		}
		files, _ := ioutil.ReadDir("./")
		outGif := &gif.GIF{}
		for _, file := range files {
			if pattern.MatchString(file.Name()) {
				fmt.Print("\r", file.Name())
				f, err := os.Open(file.Name())
				if err != nil {
					panic(err)
				}
				defer f.Close()

				img, _, err := image.Decode(f)
				if err != nil {
					panic(err)
				}
				bounds := img.Bounds()
				palettedImage := image.NewPaletted(bounds, palette)
				draw.Draw(palettedImage, bounds, img, image.ZP, draw.Src)
				outGif.Image = append(outGif.Image, palettedImage)
				outGif.Delay = append(outGif.Delay, 1)
				// outGif.Disposal = append(outGif.Disposal, gif.DisposalPrevious)
			}
		}
		f, err := os.Create(fmt.Sprintf(format, i) + ".gif")
		if err != nil {
			panic(err)
		}
		defer f.Close()
		gif.EncodeAll(f, outGif)
	}
}

package main

import (
	"fmt"
	"image"
	"image/draw"
	"image/gif"
	"image/png"
	"os"
	"strings"
)

func main() {
	if len(os.Args) == 1 {
		panic(fmt.Errorf("len(os.Args) less than 2"))
	}
	for _, fn := range os.Args[1:] {
		f, err := os.Open(fn)
		if err != nil {
			panic(err)
		}
		defer f.Close()

		inGif, err := gif.DecodeAll(f)
		if err != nil {
			panic(err)
		}
		config, _ := gif.DecodeConfig(f)
		rect := image.Rect(0, 0, config.Width, config.Height)
		if rect.Min == rect.Max {
			var max image.Point
			for _, frame := range inGif.Image {
				maxF := frame.Bounds().Max
				if max.X < maxF.X {
					max.X = maxF.X
				}
				if max.Y < maxF.Y {
					max.Y = maxF.Y
				}
			}
			rect.Max = max
		}
		format := fmt.Sprintf("%%0%dd", len(string(len(inGif.Image)))+1)
		for i, srcimg := range inGif.Image {
			img := image.NewRGBA(rect)
			subfn := strings.Split(fn, ".")[0] + fmt.Sprintf(format, i) + ".png"
			f, err := os.Create(subfn)
			if err != nil {
				panic(err)
			}
			defer f.Close()
			draw.Draw(img, srcimg.Bounds(), srcimg, srcimg.Rect.Min, draw.Src)
			fmt.Printf("\r%s", subfn)
			png.Encode(f, img)
		}
		fmt.Println("\r", fn)
	}
}