img2gif

pkg/rotate/gist.go

@@ -0,0 +1,79 @@
+//go:build gist
+
+package main
+
+import (
+	"fmt"
+	"image"
+	"image/color"
+	"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() {
+	var w, h int = 240, 240
+
+	var palette = []color.Color{
+		color.RGBA{0x00, 0x00, 0x00, 0xff}, color.RGBA{0x00, 0x00, 0xff, 0xff},
+		color.RGBA{0x00, 0xff, 0x00, 0xff}, color.RGBA{0x00, 0xff, 0xff, 0xff},
+		color.RGBA{0xff, 0x00, 0x00, 0xff}, color.RGBA{0xff, 0x00, 0xff, 0xff},
+		color.RGBA{0xff, 0xff, 0x00, 0xff}, color.RGBA{0xff, 0xff, 0xff, 0xff},
+	}
+	var images []*image.Paletted
+	var delays []int
+
+	var hw, hh float64 = float64(w / 2), float64(h / 2)
+	circles := []*Circle{&Circle{}, &Circle{}, &Circle{}}
+	steps := 20
+	for step := 0; step < steps; step++ {
+		img := image.NewPaletted(image.Rect(0, 0, w, h), palette)
+		images = append(images, img)
+		delays = append(delays, 0)
+
+		θ := 2.0 * math.Pi / float64(steps) * float64(step)
+		for i, circle := range circles {
+			θ0 := 2 * math.Pi / 3 * float64(i)
+			println(θ0)
+			circle.X = hw - math.Sin(θ0) - math.Sin(θ0+θ)
+			circle.Y = hh - math.Cos(θ0) - math.Cos(θ0+θ)
+			circle.R = 50
+		}
+
+		for x := 0; x < w; x++ {
+			for y := 0; y < h; y++ {
+				img.Set(x, y, color.RGBA{
+					circles[0].Brightness(float64(x), float64(y)),
+					circles[1].Brightness(float64(x), float64(y)),
+					circles[2].Brightness(float64(x), float64(y)),
+					255,
+				})
+			}
+		}
+	}
+
+	f, err := os.OpenFile("rgb.gif", os.O_WRONLY|os.O_CREATE, 0600)
+	if err != nil {
+		fmt.Println(err)
+		return
+	}
+	defer f.Close()
+	gif.EncodeAll(f, &gif.GIF{
+		Image: images,
+		Delay: delays,
+	})
+}

pkg/rotate/pull.go

@@ -0,0 +1,19 @@
+//go:build pull
+package rotate
+
+import (
+	"image"
+	"image/color"
+)
+
+type Rotate struct {
+	image.Image
+	Angle float64 // math.Pi * n
+}
+
+func (rot Rotate) Bounds() image.Rectangle { return rot.Image.Bounds() }
+func (rot Rotate) ColorModel() color.Model { return rot.Image.ColorModel() }
+
+func (rot Rotate) At(x, y int) color.Color {
+
+}

pkg/rotate/push.go

@@ -0,0 +1,23 @@
+package rotate
+
+import (
+	"image"
+	"math"
+)
+
+func Rotate(img image.Image, angle float64) image.Image {
+	newImg := image.NewRGBA(img.Bounds())
+	w, h := img.Bounds().Dx(), img.Bounds().Dy()
+	hh, hw := float64(h/2), float64(w/2)
+
+	for y := 0; y < w; y++ {
+		for x := 0; x < h; x++ {
+			newImg.Set(
+				int(hh-math.Cos(angle)),
+				int(hw-math.Sin(angle)),
+				img.At(x, y),
+			)
+		}
+	}
+	return newImg
+}

pkg/rotate/push_test.go

@@ -0,0 +1,38 @@
+package rotate
+
+import (
+	"image"
+	"image/png"
+	"net/http"
+	"os"
+	"testing"
+	"math"
+)
+
+func TestRender(t *testing.T) {
+	gopherImg, err := func() (image.Image, error) {
+		r, err := http.Get("https://go.dev/images/favicon-gopher.png")
+		defer r.Body.Close()
+		if err != nil {
+			return nil, err
+		}
+		img, err := png.Decode(r.Body)
+		if err != nil {
+			return nil, err
+		}
+		return img, nil
+	}()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	f, err := os.Create("img.png")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	err = png.Encode(f, Rotate(gopherImg, math.Pi/6))
+	if err != nil {
+		t.Fatal(err)
+	}
+}