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//! A library for capturing screenshots on X11.

#![warn(missing_docs)]

use image::RgbImage;
use std::{ptr, slice};
use x11::xlib;
/// A handle to an X11 screen.
pub struct Screen {
    display: *mut xlib::Display,
    screen: *mut xlib::Screen,
    window: xlib::Window,
}
#[derive(Debug)]
struct Bgr {
    b: u8,
    g: u8,
    r: u8,
    _pad: u8,
}

impl Screen {
    /// Tries to open the X11 display, then returns a handle to the default screen.
    ///
    /// Returns `None` if the display could not be opened.
    pub fn open() -> Option<Screen> {
        unsafe {
            let display = xlib::XOpenDisplay(ptr::null());
            if display.is_null() {
                return None;
            }
            let screen = xlib::XDefaultScreenOfDisplay(display);
            let root = xlib::XRootWindowOfScreen(screen);
            Some(Screen {
                display,
                screen,
                window: root,
            })
        }
    }
    /// Tries to capture a screenshot of the entire screen.
    ///
    /// Returns an `RgbImage` on success, `None` on failure.
    ///
    /// See the documentation of the `image` crate on how to use `RgbImage`.
    pub fn capture(&self) -> Option<RgbImage> {
        let screen: &mut xlib::Screen = &mut unsafe { *self.screen };
        self.capture_area(screen.width as u32, screen.height as u32, 0, 0)
    }
    /// Tries to capture a screenshot of the provided area.
    ///
    /// Returns an `RgbImage` on success, `None` on failure.
    ///
    /// See the documentation of the `image` crate on how to use `RgbImage`.
    pub fn capture_area(&self, w: u32, h: u32, x: i32, y: i32) -> Option<RgbImage> {
        let img =
            unsafe { xlib::XGetImage(self.display, self.window, x, y, w, h, !1, xlib::ZPixmap) };

        if !img.is_null() {
            let image = unsafe { &mut *img };
            let sl: &[Bgr] = unsafe {
                slice::from_raw_parts(
                    (image).data as *const _,
                    (image).width as usize * (image).height as usize,
                )
            };

            let mut bgr_iter = sl.iter();
            let mut image_buffer = RgbImage::new(w, h);

            for pix in image_buffer.pixels_mut() {
                let bgr = bgr_iter.next().unwrap();
                pix.0 = [bgr.r, bgr.g, bgr.b];
            }

            unsafe {
                xlib::XDestroyImage(img as *mut _);
            }
            Some(image_buffer)
        } else {
            None
        }
    }
}

impl Drop for Screen {
    fn drop(&mut self) {
        unsafe {
            xlib::XCloseDisplay(self.display);
        }
    }
}