commit c240d1ed40edd491467e66f61b5803d9ada683e9
Author: Alex Denes <caskd@redxen.eu>
Date:   Sun Mar 12 13:43:32 2023 +0000

    Initial commit

diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..b8d8c9c
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,7 @@
+module git.redxen.eu/caskd/v6canvas
+
+go 1.20
+
+require golang.org/x/net v0.8.0
+
+require golang.org/x/sys v0.6.0 // indirect
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..755e96f
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,4 @@
+golang.org/x/net v0.8.0 h1:Zrh2ngAOFYneWTAIAPethzeaQLuHwhuBkuV6ZiRnUaQ=
+golang.org/x/net v0.8.0/go.mod h1:QVkue5JL9kW//ek3r6jTKnTFis1tRmNAW2P1shuFdJc=
+golang.org/x/sys v0.6.0 h1:MVltZSvRTcU2ljQOhs94SXPftV6DCNnZViHeQps87pQ=
+golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..ebaea89
--- /dev/null
+++ b/main.go
@@ -0,0 +1,154 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"image"
+	"image/color"
+	_ "image/png"
+	"os"
+	"sync"
+	"time"
+
+	"log"
+	"net"
+
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv6"
+)
+
+func main() {
+	var (
+		dt  uint
+		err error
+	)
+	flag.UintVar(&dt, "timeout", 5000, "Frame display time (ms)")
+	flag.Parse()
+
+	var (
+		up = make(chan image.Image)
+		lo = make(chan image.Image)
+		dx = make(chan pixdelta)
+	)
+
+	c, err := icmp.ListenPacket("udp6", "::")
+	if err != nil {
+		log.Fatalln("Failed to listen for ICMP packets:", err)
+	}
+	go sendDelta(dx, c)
+	go syncColors(up, lo, dx)
+
+	var imgs [2]image.Image
+	for i := range imgs {
+		imgs[i] = image.NewRGBA(image.Rect(0, 0, 511, 511))
+	}
+	for _, v := range flag.Args() {
+		f, err := os.Open(v)
+		if err != nil {
+			log.Fatalln("Failed to open image:", err)
+		}
+		imgs[0] = imgs[1]
+		imgs[1], _, err = image.Decode(f)
+		if err != nil {
+			log.Fatalln("Failed to decode image:", err)
+		}
+		up <- imgs[0]
+		lo <- imgs[1]
+		time.Sleep(time.Duration(dt) * time.Millisecond)
+	}
+}
+
+func sendDelta(d chan pixdelta, c *icmp.PacketConn) {
+	pm := icmp.Message{
+		Type: ipv6.ICMPTypeEchoRequest, Code: 0,
+		Body: &icmp.Echo{Seq: 1},
+	}
+
+	bb, err := pm.Marshal(nil)
+	if err != nil {
+		log.Fatalln("Failed to encode ICMP packet")
+	}
+
+	for {
+		select {
+		case delta := <-d:
+			dest := &net.UDPAddr{
+				IP: convV6(delta.p, delta.c),
+			}
+
+			if _, err := c.WriteTo(bb, dest); err != nil {
+				log.Println("Failed to send packet to:", dest)
+			}
+		}
+	}
+
+}
+func syncColors(upstream, local chan image.Image, dx chan pixdelta) {
+	var (
+		oimg, nimg image.Image
+	)
+
+	oimg = nil
+	nimg = nil
+	for {
+		select {
+		case nimg = <-local:
+			break
+		case oimg = <-upstream:
+			break
+		}
+		if oimg == nil || nimg == nil {
+			continue
+		}
+
+		jobs := uint64(0)
+
+		wg := new(sync.WaitGroup)
+		b := nimg.Bounds()
+		for x := 0; x < b.Dx(); x++ {
+			for y := 0; y < b.Dy(); y++ {
+				wg.Add(1)
+				go comparePixel(oimg, nimg, image.Point{X: x, Y: y}, dx, wg)
+				jobs++
+			}
+		}
+		wg.Wait()
+	}
+}
+
+// Framebuffer
+
+type pixdelta struct {
+	p image.Point
+	c color.Color
+}
+
+func comparePixel(a, b image.Image, loc image.Point, r chan pixdelta, wg *sync.WaitGroup) {
+	defer wg.Done()
+	car, cab, cag, _ := a.At(loc.X, loc.Y).RGBA()
+	cbr, cbb, cbg, cba := b.At(loc.X, loc.Y).RGBA()
+	if (cba == 0xFFFF) && !(car == cbr && cag == cbg && cab == cbb) {
+		r <- pixdelta{c: b.At(loc.X, loc.Y), p: loc}
+	}
+}
+
+// Network
+
+// fdcf:8538:9ad5:3333:XXXX:YYYY:11RR:GGBB
+func convV6(p image.Point, c color.Color) (addr net.IP) {
+	addr = net.IP{
+		0xfd, 0xcf, 0x85, 0x38, 0x9a, 0xd5, 0x33, 0x33,
+	}
+	addr = append(addr, split2Bytes(uint16(p.X))...)
+	addr = append(addr, split2Bytes(uint16(p.Y))...)
+	r, g, b, _ := c.RGBA()
+	addr = append(addr, 0x11, uint8(r), uint8(g), uint8(b))
+	return
+}
+
+func split2Bytes(s uint16) []uint8 {
+	return []uint8{
+		uint8((s & (0xFF << 8)) >> 8),
+		uint8(s & 0xFF),
+	}
+}