info-beamer content process example of loading image from url

build.sh

#!/bin/sh
GOOS=linux GOARCH=arm go build -ldflags="-s -w" -o image.exe

go.mod

module contentproc
  
go 1.22

require golang.org/x/image v0.22.0
require golang.org/x/sys v0.30.0

main.go

package main
  
import (
    "bytes"
    "image"
    _ "image/jpeg"
    _ "image/png"
    "io"
    "log"
    "net/http"
    "os"
    "strconv"
    "time"

    "golang.org/x/image/draw"
    "golang.org/x/sys/unix"
)

func download(url string) ([]byte, error) {
    resp, err := http.Get(url)
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()

    return io.ReadAll(resp.Body)
}

func toBGRA(src image.Image, w, h int) []byte {
    dst := image.NewRGBA(image.Rect(0, 0, w, h))
    draw.CatmullRom.Scale(dst, dst.Bounds(), src, src.Bounds(), draw.Over, nil)

    out := make([]byte, w*h*4)

    i := 0
    for y := 0; y < h; y++ {
        for x := 0; x < w; x++ {
            r, g, b, a := dst.At(x, y).RGBA()
            out[i] = byte(b >> 8)
            out[i+1] = byte(g >> 8)
            out[i+2] = byte(r >> 8)
            out[i+3] = byte(a >> 8)
            i += 4
        }
    }
    return out
}

func main() {
    width, _ := strconv.Atoi(os.Getenv("WIDTH"))
    height, _ := strconv.Atoi(os.Getenv("HEIGHT"))

    url := os.Args[1]

    data, err := download(url)
    if err != nil {
        log.Fatal(err)
    }

    img, _, err := image.Decode(bytes.NewReader(data))
    if err != nil {
        log.Fatal(err)
    }

    pixels := toBGRA(img, width, height)

    // mmap DMA buffer (fd 3)
    buf, err := unix.Mmap(3, 0, len(pixels), unix.PROT_WRITE, unix.MAP_SHARED)
    if err != nil {
        log.Fatal(err)
    }

    copy(buf, pixels)

    _ = unix.Munmap(buf)

    // handshake: BGRA format + ready
    _, _ = os.Stdout.Write([]byte{0, 1, 1, '\n'})
    _ = os.Stdout.Sync()

    log.Println("image rendered")

    // keep alive. Forces 'loaded' state
    for {
        time.Sleep(time.Second)
    }
}

node.lua

gl.setup(NATIVE_WIDTH, NATIVE_HEIGHT)

local p = resource.create_content_process{
    file = "image.exe",
    width = 1920,
    height = 1080,
    args = {
        "https://librestock.com/photos/thumbs/librestock-vintage-camera-lens.jpg"
    }
}

function node.render()
    p:draw(0, 0, WIDTH, HEIGHT)
end