screendump.rs

use core::slice;
use std::io::{stdout, Write};
use std::ptr::null;

use x11_dl::xlib;

use libvips::{
    ops::{pngsave_buffer, BandFormat},
    VipsImage,
};

fn main() {
    unsafe {
        let xlib = x11_dl::xlib::Xlib::open().unwrap();

        let display = (xlib.XOpenDisplay)(null());

        let screen = (xlib.XDefaultScreen)(display);

        let width = (xlib.XDisplayWidth)(display, screen);

        if width <= 0 {
            panic!("Improper display width returned: {width}")
        }

        let height = (xlib.XDisplayHeight)(display, screen);

        if width <= 0 {
            panic!("Improper display height returned: {height}")
        }

        let root_window = (xlib.XDefaultRootWindow)(display);

        let image_raw = (xlib.XGetImage)(
            display,
            root_window,
            0,
            0,
            width as u32,
            height as u32,
            u64::MAX,
            xlib::ZPixmap,
        );

        match image_raw as usize as u8 {
            xlib::BadDrawable => panic!("XGetImage: BadDrawable"),
            xlib::BadMatch => panic!("XGetImage: BadMatch"),
            xlib::BadValue => panic!("XGetImage: BadValue"),
            _ => {}
        }

        let image = &mut *image_raw;

        if image.byte_order == xlib::MSBFirst {
            panic!("Image data in big-endian format is currently unsupported")
        }

        let bytes_per_pixel = (image.bits_per_pixel / 8) as usize;
        let image_size = (image.width * image.height) as usize;
        let image_len = image_size * bytes_per_pixel;

        let image_data = slice::from_raw_parts_mut(image.data as *mut u8, image_len);

        for i in (0..image_len).step_by(4) {
            let b = image_data[i];
            let r = image_data[i + 2];
            image_data[i] = r;
            image_data[i + 2] = b;
        }

        let vips_image =
            VipsImage::new_from_memory(image_data, image.width, image.height, 4, BandFormat::Uchar)
                .unwrap();

        let png = pngsave_buffer(&vips_image).unwrap();

        let mut stdout = stdout().lock();

        stdout.write_all(&png).unwrap();
    }
}