window kinda works?

src/capture.rs

@@ -4,16 +4,38 @@ use gui::GUI;
 use options::{Options, Region};
 use xlib::Image;
 
+use ImageExt;
+use Rectangle;
+
 pub fn capture(opt: &Options) -> Result<Image, ScreenshotError> {
     let gui = GUI::new()?;
 
-    let window_to_capture = match opt.region {
-        Region::Fullscreen | Region::Selection => gui.display.get_default_root_window()?,
-        Region::ActiveWindow => gui.get_active_window()?,
-    };
+    // let window_to_capture = match opt.region {
+    //     Region::Fullscreen | Region::Selection => gui.display.get_default_root_window()?,
+    //     Region::ActiveWindow => gui.get_active_window()?,
+    // };
+    let window_to_capture = gui.display.get_default_root_window()?;
 
     let capture = gui.capture_window(window_to_capture)?;
-    println!("captured the window");
+    let clip = match opt.region {
+        Region::ActiveWindow => {
+            let win = gui.get_active_window()?;
+            let attr = win.get_attributes()?;
+            let width = attr.get_width();
+            let height = attr.get_height();
+            let root = gui.display.get_default_root_window()?;
+            let (x, y, _) = gui.display.translate_coordinates(win, 0, 0, root)?;
+            Some(Rectangle {
+                x: x as u32,
+                y: y as u32,
+                width,
+                height,
+            })
+        }
+        _ => None,
+    };
+
+    capture.write_png(&opt.outfile, clip)?;
 
     // let final_capture = match opt.region {
     //     Region::Fullscreen | Region::ActiveWindow => window_capture,

src/gui.rs

@@ -15,6 +15,12 @@ impl GUI {
 
     /// Captures the window and produces a DynamicImage.
     pub fn capture_window(&self, window: Window) -> Result<Image, ScreenshotError> {
+        let attr = window.get_attributes()?;
+        let width = attr.get_width();
+        let height = attr.get_height();
+        let root = self.display.get_default_root_window()?;
+        let (x, y, _) = self.display.translate_coordinates(window, 0, 0, root)?;
+        println!("x={} y={} width={} height={}", x, y, width, height);
         window.get_image().map_err(|err| err.into())
     }
 

src/image.rs

@@ -6,23 +6,34 @@ use png::{self, Encoder, HasParameters};
 use xlib::{Image, ImageByteOrder};
 
 use errors::ScreenshotError;
+use Rectangle;
 
 pub trait ImageExt {
-    fn to_data_buf(&self) -> Result<Vec<u8>, ScreenshotError>;
-    fn write_png(&self, out: impl AsRef<Path>) -> Result<(), ScreenshotError>;
+    fn to_data_buf(&self, rect: Rectangle) -> Result<Vec<u8>, ScreenshotError>;
+    fn write_png(
+        &self,
+        out: impl AsRef<Path>,
+        rect: Option<Rectangle>,
+    ) -> Result<(), ScreenshotError>;
 }
 
 impl ImageExt for Image {
     /// Converts the image buffer into RGB(A).
-    fn to_data_buf(&self) -> Result<Vec<u8>, ScreenshotError> {
-        let size = self.get_size();
+    fn to_data_buf(&self, rect: Rectangle) -> Result<Vec<u8>, ScreenshotError> {
+        let (full_width, _) = (self.get_width() as usize, self.get_height() as usize);
+        let bytes_per_row = 4 * rect.width as usize;
+        let size = bytes_per_row * rect.height as usize;
         let mut buf = vec![1; size];
         let sbuf = self.buffer(); // source buffer
-        let mut sx = 0usize; // source idx
-        let mut dx = 0usize; // dest idx
+        let mut rx = rect.y as usize;
         if let ImageByteOrder::LSBFirst = self.get_byte_order()? {
             // LSBFirst
-            while dx < size {
+            while rx < rect.height as usize {
+                let mut sx = (rx * full_width + rect.x as usize) * 4; // source idx
+                let mut dx = rx * bytes_per_row; // dest idx
+                let edx = (rx + 1) * bytes_per_row;
+                // println!("sx={} dx={} edx={}", sx,dx,edx);
+                while dx < edx {
                     buf[dx] = sbuf.get_byte(sx + 2).unwrap() as u8;
                     buf[dx + 1] = sbuf.get_byte(sx + 1).unwrap() as u8;
                     buf[dx + 2] = sbuf.get_byte(sx).unwrap() as u8;
@@ -34,19 +45,32 @@ impl ImageExt for Image {
                     sx += 4;
                     dx += 4;
                 }
+                rx += 1;
+            }
         }
         Ok(buf)
     }
 
-    fn write_png(&self, out: impl AsRef<Path>) -> Result<(), ScreenshotError> {
+    fn write_png(
+        &self,
+        out: impl AsRef<Path>,
+        rect: Option<Rectangle>,
+    ) -> Result<(), ScreenshotError> {
+        let rect = rect.unwrap_or_else(|| Rectangle {
+            x: 0,
+            y: 0,
+            width: self.get_width(),
+            height: self.get_height(),
+        });
+
         let file = File::create(out.as_ref())?;
         let ref mut out = BufWriter::new(file);
 
-        let mut encoder = Encoder::new(out, self.get_width(), self.get_height());
+        let mut encoder = Encoder::new(out, rect.width, rect.height);
         encoder.set(png::ColorType::RGBA).set(png::BitDepth::Eight);
         let mut writer = encoder.write_header()?;
 
-        let data = self.to_data_buf()?;
+        let data = self.to_data_buf(rect)?;
         writer.write_image_data(data.as_slice())?;
         Ok(())
     }

src/main.rs

@@ -3,11 +3,11 @@ extern crate screenshot;
 extern crate structopt;
 
 use failure::Error;
-use screenshot::{capture, ImageExt, Options};
+use screenshot::{capture, Options};
 use structopt::StructOpt;
 
 pub fn main() -> Result<(), Error> {
     let opt = Options::from_args();
-    let image = capture(&opt)?;
-    image.write_png(opt.outfile).map_err(|err| err.into())
+    // let image = capture(&opt)?;
+    capture(&opt).map(|_| ()).map_err(|err| err.into())
 }

xlib/src/display.rs

@@ -18,27 +18,76 @@ impl Display {
     pub fn connect(display_name: impl AsRef<str>) -> Result<Display, X11Error> {
         let display_name = CString::new(display_name.as_ref()).unwrap();
         let inner = unsafe { x::XOpenDisplay(display_name.as_ptr()) };
+        if inner.is_null() {
+            return Err(X11Error::DisplayOpenError);
+        }
         Ok(Display { inner })
     }
 
     /// Returns the root window for the given screen.
     pub fn get_root_window(&self, screen: i32) -> Result<Window, X11Error> {
+        let inner = unsafe { x::XRootWindow(self.inner, screen) };
+        if inner == 0 {
+            return Err(X11Error::GetWindowError);
+        }
         let window = Window {
             display: self.inner,
-            inner: unsafe { x::XRootWindow(self.inner, screen) },
+            inner,
         };
         Ok(window)
     }
 
     /// Returns the root window for the default screen.
     pub fn get_default_root_window(&self) -> Result<Window, X11Error> {
+        let inner = unsafe { x::XDefaultRootWindow(self.inner) };
+        if inner == 0 {
+            return Err(X11Error::GetWindowError);
+        }
         let window = Window {
             display: self.inner,
-            inner: unsafe { x::XDefaultRootWindow(self.inner) },
+            inner,
         };
         Ok(window)
     }
 
+    /// Translate coordinates relative to w1 to coordinates relative to w2.
+    /// If the coordinates are contained in a mapped child of the destination window, the third return
+    /// value will hold that child window.
+    pub fn translate_coordinates(
+        &self,
+        w1: Window,
+        x: i32,
+        y: i32,
+        w2: Window,
+    ) -> Result<(i32, i32, Option<Window>), X11Error> {
+        let mut rx = 0;
+        let mut ry = 0;
+        let mut child_return: x::Window = 0;
+        let status = unsafe {
+            x::XTranslateCoordinates(
+                self.inner,
+                w1.inner,
+                w2.inner,
+                x,
+                y,
+                &mut rx,
+                &mut ry,
+                &mut child_return,
+            )
+        };
+        if status == 0 {
+            return Err(X11Error::TranslateCoordinatesError);
+        }
+        let child = match child_return {
+            0 => None,
+            val => Some(Window {
+                display: self.inner,
+                inner: val,
+            }),
+        };
+        Ok((rx, ry, child))
+    }
+
     /// eturns the focus window and the current focus state.
     pub fn get_input_focus(&self) -> Result<(Window, i32), X11Error> {
         let mut focus_return: x::Window = 0;

xlib/src/errors.rs

@@ -2,12 +2,21 @@
 #[allow(missing_docs)]
 #[derive(Debug, Fail)]
 pub enum X11Error {
+    #[fail(display = "failed to open display")]
+    DisplayOpenError,
+
     #[fail(display = "failed to get attributes")]
     GetAttributesError,
 
+    #[fail(display = "failed to get window")]
+    GetWindowError,
+
     #[fail(display = "invalid byte order")]
     InvalidByteOrder,
 
+    #[fail(display = "failed to translate coordinates")]
+    TranslateCoordinatesError,
+
     #[fail(display = "error")]
     Error,
 }

xlib/src/lib.rs

@@ -10,11 +10,11 @@ extern crate libc;
 extern crate x11;
 
 mod display;
-mod error;
+mod errors;
 mod image;
 mod window;
 
 pub use display::Display;
-pub use error::X11Error;
+pub use errors::X11Error;
 pub use image::{Image, ImageByteOrder, PixBuffer};
 pub use window::{Window, WindowAttributes};