Window icons (#497)

CHANGELOG.md

@@ -16,6 +16,8 @@
 - On X11, drag and drop now works reliably in release mode.
 - Added `WindowBuilderExt::with_resize_increments` and `WindowBuilderExt::with_base_size` to X11, allowing for more optional hints to be set.
 - Rework of the wayland backend, migrating it to use [Smithay's Client Toolkit](https://github.com/Smithay/client-toolkit).
+- Added `WindowBuilder::with_window_icon` and `Window::set_window_icon`, finally making it possible to set the window icon on Windows and X11. The `icon_loading` feature can be enabled to allow for icons to be easily loaded; see example program `window_icon.rs` for usage.
+- Windows additionally has `WindowBuilderExt::with_taskbar_icon` and `WindowExt::set_taskbar_icon`.
 
 # Version 0.13.1 (2018-04-26)
 

Cargo.toml

@@ -10,9 +10,13 @@ repository = "https://github.com/tomaka/winit"
 documentation = "https://docs.rs/winit"
 categories = ["gui"]
 
+[features]
+icon_loading = ["image"]
+
 [dependencies]
 lazy_static = "1"
 libc = "0.2"
+image = { version = "0.19", optional = true }
 
 [target.'cfg(target_os = "android")'.dependencies.android_glue]
 version = "0.2"

examples/window_icon.rs

@@ -0,0 +1,95 @@
+// Heads up: you need to compile this example with `--features icon_loading`.
+// `Icon::from_path` won't be available otherwise, though for your own applications, you could use
+// `Icon::from_rgba` if you don't want to depend on the `image` crate.
+
+extern crate winit;
+#[cfg(feature = "icon_loading")]
+extern crate image;
+
+use winit::Icon;
+
+#[cfg(feature = "icon_loading")]
+fn main() {
+    // You'll have to choose an icon size at your own discretion. On X11, the desired size varies
+    // by WM, and on Windows, you still have to account for screen scaling. Here we use 32px,
+    // since it seems to work well enough in most cases. Be careful about going too high, or
+    // you'll be bitten by the low-quality downscaling built into the WM.
+    let path = concat!(env!("CARGO_MANIFEST_DIR"), "/examples/icon.png");
+    // While `Icon::from_path` is the most straightforward, you have a few other options. If you
+    // want to use the `include_bytes` macro, then pass the result to `Icon::from_bytes`. See the
+    // docs for the full list of options (you'll have to generate the docs with the `icon_loading`
+    // feature enabled).
+    let icon = Icon::from_path(path).expect("Failed to open icon");
+
+    let mut events_loop = winit::EventsLoop::new();
+
+    let window = winit::WindowBuilder::new()
+        .with_title("An iconic window!")
+        // At present, this only does anything on Windows and X11, so if you want to save load
+        // time, you can put icon loading behind a function that returns `None` on other platforms.
+        .with_window_icon(Some(icon))
+        .build(&events_loop)
+        .unwrap();
+
+    events_loop.run_forever(|event| {
+        if let winit::Event::WindowEvent { event, .. } = event {
+            use winit::WindowEvent::*;
+            match event {
+                CloseRequested => return winit::ControlFlow::Break,
+                DroppedFile(path) => {
+                    use image::GenericImage;
+
+                    let icon_image = image::open(path).expect("Failed to open window icon");
+
+                    let (width, height) = icon_image.dimensions();
+                    const DESIRED_SIZE: u32 = 32;
+                    let (new_width, new_height) = if width == height {
+                        (DESIRED_SIZE, DESIRED_SIZE)
+                    } else {
+                        // Note that this will never divide by zero, due to the previous condition.
+                        let aspect_adjustment = DESIRED_SIZE as f64
+                            / std::cmp::max(width, height) as f64;
+                        (
+                            (width as f64 * aspect_adjustment) as u32,
+                            (height as f64 * aspect_adjustment) as u32,
+                        )
+                    };
+
+                    // By scaling the icon ourselves, we get higher-quality filtering and save
+                    // some memory.
+                    let icon = image::imageops::resize(
+                        &icon_image,
+                        new_width,
+                        new_height,
+                        image::FilterType::Lanczos3,
+                    );
+
+                    let (offset_x, offset_y) = (
+                        (DESIRED_SIZE - new_width) / 2,
+                        (DESIRED_SIZE - new_height) / 2,
+                    );
+
+                    let mut canvas = image::ImageBuffer::new(DESIRED_SIZE, DESIRED_SIZE);
+                    image::imageops::replace(
+                        &mut canvas,
+                        &icon,
+                        offset_x,
+                        offset_y,
+                    );
+
+                    window.set_window_icon(Some(canvas.into()));
+                },
+                _ => (),
+            }
+        }
+        winit::ControlFlow::Continue
+    });
+}
+
+#[cfg(not(feature = "icon_loading"))]
+fn main() {
+    print!(
+r#"This example requires the `icon_loading` feature:
+    cargo run --example window_icon --features icon_loading
+"#);
+}

src/icon.rs

@@ -0,0 +1,160 @@
+use std::{fmt, mem};
+use std::error::Error;
+#[cfg(feature = "icon_loading")]
+use std::io::{BufRead, Seek};
+#[cfg(feature = "icon_loading")]
+use std::path::Path;
+
+#[cfg(feature = "icon_loading")]
+use image;
+
+#[repr(C)]
+#[derive(Debug)]
+pub(crate) struct Pixel {
+    pub(crate) r: u8,
+    pub(crate) g: u8,
+    pub(crate) b: u8,
+    pub(crate) a: u8,
+}
+
+pub(crate) const PIXEL_SIZE: usize = mem::size_of::<Pixel>();
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+/// An error produced when using `Icon::from_rgba` with invalid arguments.
+pub enum BadIcon {
+    /// Produced when the length of the `rgba` argument isn't divisible by 4, thus `rgba` can't be
+    /// safely interpreted as 32bpp RGBA pixels.
+    ByteCountNotDivisibleBy4 {
+        byte_count: usize,
+    },
+    /// Produced when the number of pixels (`rgba.len() / 4`) isn't equal to `width * height`.
+    /// At least one of your arguments is incorrect.
+    DimensionsVsPixelCount {
+        width: u32,
+        height: u32,
+        width_x_height: usize,
+        pixel_count: usize,
+    },
+}
+
+impl fmt::Display for BadIcon {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        let msg = match self {
+            &BadIcon::ByteCountNotDivisibleBy4 { byte_count } => format!(
+                "The length of the `rgba` argument ({:?}) isn't divisible by 4, making it impossible to interpret as 32bpp RGBA pixels.",
+                byte_count,
+            ),
+            &BadIcon::DimensionsVsPixelCount {
+                width,
+                height,
+                width_x_height,
+                pixel_count,
+            } => format!(
+                "The specified dimensions ({:?}x{:?}) don't match the number of pixels supplied by the `rgba` argument ({:?}). For those dimensions, the expected pixel count is {:?}.",
+                width, height, pixel_count, width_x_height,
+            ),
+        };
+        write!(formatter, "{}", msg)
+    }
+}
+
+impl Error for BadIcon {
+    fn description(&self) -> &str {
+        "A valid icon cannot be created from these arguments"
+    }
+
+    fn cause(&self) -> Option<&Error> {
+        Some(self)
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+/// An icon used for the window titlebar, taskbar, etc.
+///
+/// Enabling the `icon_loading` feature provides you with several convenience methods for creating
+/// an `Icon` from any format supported by the [image](https://github.com/PistonDevelopers/image)
+/// crate.
+pub struct Icon {
+    pub(crate) rgba: Vec<u8>,
+    pub(crate) width: u32,
+    pub(crate) height: u32,
+}
+
+impl Icon {
+    /// Creates an `Icon` from 32bpp RGBA data.
+    ///
+    /// The length of `rgba` must be divisible by 4, and `width * height` must equal
+    /// `rgba.len() / 4`. Otherwise, this will return a `BadIcon` error.
+    pub fn from_rgba(rgba: Vec<u8>, width: u32, height: u32) -> Result<Self, BadIcon> {
+        if rgba.len() % PIXEL_SIZE != 0 {
+            return Err(BadIcon::ByteCountNotDivisibleBy4 { byte_count: rgba.len() });
+        }
+        let pixel_count = rgba.len() / PIXEL_SIZE;
+        if pixel_count != (width * height) as usize {
+            Err(BadIcon::DimensionsVsPixelCount {
+                width,
+                height,
+                width_x_height: (width * height) as usize,
+                pixel_count,
+            })
+        } else {
+            Ok(Icon { rgba, width, height })
+        }
+    }
+
+    #[cfg(feature = "icon_loading")]
+    /// Loads an `Icon` from the path of an image on the filesystem.
+    pub fn from_path<P: AsRef<Path>>(path: P) -> image::ImageResult<Self> {
+        image::open(path).map(Into::into)
+    }
+
+    #[cfg(feature = "icon_loading")]
+    /// Loads an `Icon` from anything implementing `BufRead` and `Seek`.
+    pub fn from_reader<R: BufRead + Seek>(
+        reader: R,
+        format: image::ImageFormat,
+    ) -> image::ImageResult<Self> {
+        image::load(reader, format).map(Into::into)
+    }
+
+    #[cfg(feature = "icon_loading")]
+    /// Loads an `Icon` from the unprocessed bytes of an image file.
+    /// Uses heuristics to determine format.
+    pub fn from_bytes(bytes: &[u8]) -> image::ImageResult<Self> {
+        image::load_from_memory(bytes).map(Into::into)
+    }
+
+    #[cfg(feature = "icon_loading")]
+    /// Loads an `Icon` from the unprocessed bytes of an image.
+    pub fn from_bytes_with_format(
+        bytes: &[u8],
+        format: image::ImageFormat,
+    ) -> image::ImageResult<Self> {
+        image::load_from_memory_with_format(bytes, format).map(Into::into)
+    }
+}
+
+#[cfg(feature = "icon_loading")]
+impl From<image::DynamicImage> for Icon {
+    fn from(image: image::DynamicImage) -> Self {
+        use image::{GenericImage, Pixel};
+        let (width, height) = image.dimensions();
+        let mut rgba = Vec::with_capacity((width * height) as usize * PIXEL_SIZE);
+        for (_, _, pixel) in image.pixels() {
+            rgba.extend_from_slice(&pixel.to_rgba().data);
+        }
+        Icon { rgba, width, height }
+    }
+}
+
+#[cfg(feature = "icon_loading")]
+impl From<image::RgbaImage> for Icon {
+    fn from(buf: image::RgbaImage) -> Self {
+        let (width, height) = buf.dimensions();
+        let mut rgba = Vec::with_capacity((width * height) as usize * PIXEL_SIZE);
+        for (_, _, pixel) in buf.enumerate_pixels() {
+            rgba.extend_from_slice(&pixel.data);
+        }
+        Icon { rgba, width, height }
+    }
+}

src/lib.rs

@@ -83,8 +83,9 @@
 #[cfg(any(target_os = "linux", target_os = "dragonfly", target_os = "freebsd", target_os = "openbsd", target_os = "windows"))]
 #[macro_use]
 extern crate lazy_static;
-
 extern crate libc;
+#[cfg(feature = "icon_loading")]
+extern crate image;
 
 #[cfg(target_os = "windows")]
 #[macro_use]
@@ -109,10 +110,12 @@ extern crate smithay_client_toolkit as sctk;
 
 pub use events::*;
 pub use window::{AvailableMonitorsIter, MonitorId};
+pub use icon::*;
 
 mod platform;
 mod events;
 mod window;
+mod icon;
 
 pub mod os;
 
@@ -439,6 +442,11 @@ pub struct WindowAttributes {
     /// The default is `true`.
     pub decorations: bool,
 
+    /// The window icon.
+    ///
+    /// The default is `None`.
+    pub window_icon: Option<Icon>,
+
     /// [iOS only] Enable multitouch,
     /// see [multipleTouchEnabled](https://developer.apple.com/documentation/uikit/uiview/1622519-multipletouchenabled)
     pub multitouch: bool,
@@ -457,6 +465,7 @@ impl Default for WindowAttributes {
             visible: true,
             transparent: false,
             decorations: true,
+            window_icon: None,
             multitouch: false,
         }
     }

src/os/windows.rs

@@ -1,19 +1,21 @@
 #![cfg(target_os = "windows")]
 
 use std::os::raw::c_void;
+
 use libc;
-use MonitorId;
-use DeviceId;
-use Window;
-use WindowBuilder;
 use winapi::shared::windef::HWND;
 
+use {DeviceId, Icon, MonitorId, Window, WindowBuilder};
+
 /// Additional methods on `Window` that are specific to Windows.
 pub trait WindowExt {
     /// Returns the native handle that is used by this window.
     ///
     /// The pointer will become invalid when the native window was destroyed.
     fn get_hwnd(&self) -> *mut libc::c_void;
+
+    /// This sets `ICON_BIG`. A good ceiling here is 256x256.
+    fn set_taskbar_icon(&self, taskbar_icon: Option<Icon>);
 }
 
 impl WindowExt for Window {
@@ -21,20 +23,34 @@ impl WindowExt for Window {
     fn get_hwnd(&self) -> *mut libc::c_void {
         self.window.hwnd() as *mut _
     }
+
+    #[inline]
+    fn set_taskbar_icon(&self, taskbar_icon: Option<Icon>) {
+        self.window.set_taskbar_icon(taskbar_icon)
+    }
 }
 
 /// Additional methods on `WindowBuilder` that are specific to Windows.
 pub trait WindowBuilderExt {
+    /// Sets a parent to the window to be created.
     fn with_parent_window(self, parent: HWND) -> WindowBuilder;
+
+    /// This sets `ICON_BIG`. A good ceiling here is 256x256.
+    fn with_taskbar_icon(self, taskbar_icon: Option<Icon>) -> WindowBuilder;
 }
 
 impl WindowBuilderExt for WindowBuilder {
-    /// Sets a parent to the window to be created.
     #[inline]
     fn with_parent_window(mut self, parent: HWND) -> WindowBuilder {
         self.platform_specific.parent = Some(parent);
         self
     }
+
+    #[inline]
+    fn with_taskbar_icon(mut self, taskbar_icon: Option<Icon>) -> WindowBuilder {
+        self.platform_specific.taskbar_icon = taskbar_icon;
+        self
+    }
 }
 
 /// Additional methods on `MonitorId` that are specific to Windows.

src/platform/android/mod.rs

@@ -201,8 +201,8 @@ pub struct PlatformSpecificWindowBuilderAttributes;
 pub struct PlatformSpecificHeadlessBuilderAttributes;
 
 impl Window {
-    pub fn new(_: &EventsLoop, win_attribs: &WindowAttributes,
-               _: &PlatformSpecificWindowBuilderAttributes)
+    pub fn new(_: &EventsLoop, win_attribs: WindowAttributes,
+               _: PlatformSpecificWindowBuilderAttributes)
                -> Result<Window, CreationError>
     {
         // not implemented
@@ -323,6 +323,11 @@ impl Window {
         // N/A
     }
 
+    #[inline]
+    pub fn set_window_icon(&self, _icon: Option<::Icon>) {
+        // N/A
+    }
+
     #[inline]
     pub fn get_current_monitor(&self) -> RootMonitorId {
         RootMonitorId{inner: MonitorId}

src/platform/emscripten/mod.rs

@@ -347,8 +347,8 @@ fn em_try(res: ffi::EMSCRIPTEN_RESULT) -> Result<(), String> {
 }
 
 impl Window {
-    pub fn new(events_loop: &EventsLoop, attribs: &::WindowAttributes,
-               _pl_attribs: &PlatformSpecificWindowBuilderAttributes)
+    pub fn new(events_loop: &EventsLoop, attribs: ::WindowAttributes,
+               _pl_attribs: PlatformSpecificWindowBuilderAttributes)
         -> Result<Window, ::CreationError>
     {
         if events_loop.window.lock().unwrap().is_some() {
@@ -543,6 +543,11 @@ impl Window {
         // N/A
     }
 
+    #[inline]
+    pub fn set_window_icon(&self, _icon: Option<::Icon>) {
+        // N/A
+    }
+
     #[inline]
     pub fn get_current_monitor(&self) -> ::MonitorId {
         ::MonitorId{inner: MonitorId}

src/platform/ios/mod.rs

@@ -263,7 +263,7 @@ pub struct DeviceId;
 pub struct PlatformSpecificWindowBuilderAttributes;
 
 impl Window {
-    pub fn new(ev: &EventsLoop, _: &WindowAttributes, _: &PlatformSpecificWindowBuilderAttributes)
+    pub fn new(ev: &EventsLoop, _: WindowAttributes, _: PlatformSpecificWindowBuilderAttributes)
                -> Result<Window, CreationError>
     {
         Ok(Window {
@@ -370,6 +370,11 @@ impl Window {
         // N/A
     }
 
+    #[inline]
+    pub fn set_window_icon(&self, _icon: Option<::Icon>) {
+        // N/A
+    }
+
     #[inline]
     pub fn get_current_monitor(&self) -> RootMonitorId {
         RootMonitorId{inner: MonitorId}

src/platform/linux/mod.rs

@@ -6,12 +6,20 @@ use std::ffi::CStr;
 use std::os::raw::*;
 use std::sync::Arc;
 
+// `std::os::raw::c_void` and `libc::c_void` are NOT interchangeable!
 use libc;
 
-use {CreationError, CursorState, EventsLoopClosed, MouseCursor, ControlFlow};
+use {
+    CreationError,
+    CursorState,
+    EventsLoopClosed,
+    Icon,
+    MouseCursor,
+    ControlFlow,
+    WindowAttributes,
+};
 use window::MonitorId as RootMonitorId;
-use self::x11::XConnection;
-use self::x11::XError;
+use self::x11::{XConnection, XError};
 use self::x11::ffi::XVisualInfo;
 pub use self::x11::XNotSupported;
 
@@ -109,18 +117,17 @@ impl MonitorId {
 
 impl Window {
     #[inline]
-    pub fn new(events_loop: &EventsLoop,
-               window: &::WindowAttributes,
-               pl_attribs: &PlatformSpecificWindowBuilderAttributes)
-               -> Result<Self, CreationError>
-    {
+    pub fn new(
+        events_loop: &EventsLoop,
+        attribs: WindowAttributes,
+        pl_attribs: PlatformSpecificWindowBuilderAttributes,
+    ) -> Result<Self, CreationError> {
         match *events_loop {
-            EventsLoop::Wayland(ref evlp) => {
-                wayland::Window::new(evlp, window).map(Window::Wayland)
+            EventsLoop::Wayland(ref events_loop) => {
+                wayland::Window::new(events_loop, attribs).map(Window::Wayland)
             },
-
-            EventsLoop::X(ref el) => {
-                x11::Window::new(el, window, pl_attribs).map(Window::X)
+            EventsLoop::X(ref events_loop) => {
+                x11::Window::new(events_loop, attribs, pl_attribs).map(Window::X)
             },
         }
     }
@@ -293,6 +300,14 @@ impl Window {
         }
     }
 
+    #[inline]
+    pub fn set_window_icon(&self, window_icon: Option<Icon>) {
+        match self {
+            &Window::X(ref w) => w.set_window_icon(window_icon),
+            &Window::Wayland(_) => (),
+        }
+    }
+
     #[inline]
     pub fn get_current_monitor(&self) -> RootMonitorId {
         match self {

src/platform/linux/wayland/window.rs

@@ -23,9 +23,8 @@ pub struct Window {
 }
 
 impl Window {
-    pub fn new(evlp: &EventsLoop, attributes: &WindowAttributes) -> Result<Window, CreationError> {
+    pub fn new(evlp: &EventsLoop, attributes: WindowAttributes) -> Result<Window, CreationError> {
         let (width, height) = attributes.dimensions.unwrap_or((800, 600));
-
         // Create the window
         let size = Arc::new(Mutex::new((width, height)));
 

src/platform/linux/x11/mod.rs

@@ -1,28 +1,6 @@
 #![cfg(any(target_os = "linux", target_os = "dragonfly", target_os = "freebsd", target_os = "openbsd"))]
 
-pub use self::monitor::{MonitorId, get_available_monitors, get_primary_monitor};
-pub use self::window::{Window2, XWindow};
-pub use self::xdisplay::{XConnection, XNotSupported, XError};
-
 pub mod ffi;
-
-use platform::PlatformSpecificWindowBuilderAttributes;
-use {CreationError, Event, EventsLoopClosed, WindowEvent, DeviceEvent,
-     KeyboardInput, ControlFlow};
-use events::ModifiersState;
-
-use std::{mem, ptr, slice};
-use std::sync::{Arc, Weak};
-use std::sync::atomic::{self, AtomicBool};
-use std::sync::mpsc;
-use std::cell::RefCell;
-use std::collections::HashMap;
-use std::ffi::CStr;
-use std::os::raw::*;
-
-use libc::{self, setlocale, LC_CTYPE};
-use parking_lot::Mutex;
-
 mod events;
 mod monitor;
 mod window;
@@ -31,6 +9,33 @@ mod dnd;
 mod ime;
 mod util;
 
+pub use self::monitor::{MonitorId, get_available_monitors, get_primary_monitor};
+pub use self::window::{Window2, XWindow};
+pub use self::xdisplay::{XConnection, XNotSupported, XError};
+
+use std::{mem, ptr, slice};
+use std::sync::{Arc, mpsc, Weak};
+use std::sync::atomic::{self, AtomicBool};
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::ffi::CStr;
+use std::os::raw::*;
+
+use libc::{self, setlocale, LC_CTYPE};
+use parking_lot::Mutex;
+
+use {
+    ControlFlow,
+    CreationError,
+    DeviceEvent,
+    Event,
+    EventsLoopClosed,
+    KeyboardInput,
+    WindowAttributes,
+    WindowEvent,
+};
+use events::ModifiersState;
+use platform::PlatformSpecificWindowBuilderAttributes;
 use self::dnd::{Dnd, DndState};
 use self::ime::{ImeReceiver, ImeSender, ImeCreationError, Ime};
 
@@ -1150,10 +1155,11 @@ impl ::std::ops::Deref for Window {
 impl Window {
     pub fn new(
         x_events_loop: &EventsLoop,
-        window: &::WindowAttributes,
-        pl_attribs: &PlatformSpecificWindowBuilderAttributes
+        attribs: WindowAttributes,
+        pl_attribs: PlatformSpecificWindowBuilderAttributes
     ) -> Result<Self, CreationError> {
-        let win = Arc::new(Window2::new(&x_events_loop, window, pl_attribs)?);
+        let multitouch = attribs.multitouch;
+        let win = Arc::new(Window2::new(&x_events_loop, attribs, pl_attribs)?);
 
         x_events_loop.shared_state
             .borrow_mut()
@@ -1166,7 +1172,7 @@ impl Window {
 
         x_events_loop.windows.lock().insert(win.id(), WindowData {
             config: Default::default(),
-            multitouch: window.multitouch,
+            multitouch,
             cursor_pos: None,
         });
 

src/platform/linux/x11/util/icon.rs

@@ -0,0 +1,34 @@
+use {Icon, Pixel, PIXEL_SIZE};
+use super::*;
+
+impl Pixel {
+    pub fn to_packed_argb(&self) -> Cardinal {
+        let mut cardinal = 0;
+        assert!(CARDINAL_SIZE >= PIXEL_SIZE);
+        let as_bytes = &mut cardinal as *mut _ as *mut u8;
+        unsafe {
+            *as_bytes.offset(0) = self.b;
+            *as_bytes.offset(1) = self.g;
+            *as_bytes.offset(2) = self.r;
+            *as_bytes.offset(3) = self.a;
+        }
+        cardinal
+    }
+}
+
+impl Icon {
+    pub fn to_cardinals(&self) -> Vec<Cardinal> {
+        assert_eq!(self.rgba.len() % PIXEL_SIZE, 0);
+        let pixel_count = self.rgba.len() / PIXEL_SIZE;
+        assert_eq!(pixel_count, (self.width * self.height) as usize);
+        let mut data = Vec::with_capacity(pixel_count);
+        data.push(self.width as Cardinal);
+        data.push(self.height as Cardinal);
+        let pixels = self.rgba.as_ptr() as *const Pixel;
+        for pixel_index in 0..pixel_count {
+            let pixel = unsafe { &*pixels.offset(pixel_index as isize) };
+            data.push(pixel.to_packed_argb());
+        }
+        data
+    }
+}

src/platform/linux/x11/util/mod.rs

@@ -4,6 +4,7 @@
 mod atom;
 mod geometry;
 mod hint;
+mod icon;
 mod input;
 mod window_property;
 mod wm;
@@ -11,6 +12,7 @@ mod wm;
 pub use self::atom::*;
 pub use self::geometry::*;
 pub use self::hint::*;
+pub use self::icon::*;
 pub use self::input::*;
 pub use self::window_property::*;
 pub use self::wm::*;

src/platform/linux/x11/util/window_property.rs

@@ -3,6 +3,9 @@ use std::fmt::Debug;
 
 use super::*;
 
+pub type Cardinal = c_long;
+pub const CARDINAL_SIZE: usize = mem::size_of::<c_long>();
+
 #[derive(Debug, Clone)]
 pub enum GetPropertyError {
     XError(XError),

src/platform/linux/x11/window.rs

@@ -1,24 +1,19 @@
-use MouseCursor;
-use CreationError;
-use CreationError::OsError;
-use libc;
+use std::{cmp, mem};
 use std::borrow::Borrow;
-use std::{mem, cmp};
-use std::sync::Arc;
-use std::os::raw::*;
 use std::ffi::CString;
+use std::os::raw::*;
+use std::sync::Arc;
 
+use libc;
 use parking_lot::Mutex;
 
-use CursorState;
-use WindowAttributes;
-use platform::PlatformSpecificWindowBuilderAttributes;
-
+use {CursorState, Icon, MouseCursor, WindowAttributes};
+use CreationError::{self, OsError};
 use platform::MonitorId as PlatformMonitorId;
+use platform::PlatformSpecificWindowBuilderAttributes;
 use platform::x11::MonitorId as X11MonitorId;
-use window::MonitorId as RootMonitorId;
-
 use platform::x11::monitor::get_available_monitors;
+use window::MonitorId as RootMonitorId;
 
 use super::{ffi, util, XConnection, XError, WindowId, EventsLoop};
 
@@ -60,8 +55,8 @@ pub struct Window2 {
 impl Window2 {
     pub fn new(
         ctx: &EventsLoop,
-        window_attrs: &WindowAttributes,
-        pl_attribs: &PlatformSpecificWindowBuilderAttributes,
+        window_attrs: WindowAttributes,
+        pl_attribs: PlatformSpecificWindowBuilderAttributes,
     ) -> Result<Window2, CreationError> {
         let xconn = &ctx.display;
 
@@ -241,6 +236,11 @@ impl Window2 {
                 }//.queue();
             }
 
+            // Set window icons
+            if let Some(icon) = window_attrs.window_icon {
+                window.set_icon_inner(icon).queue();
+            }
+
             // Opt into handling window close
             unsafe {
                 (xconn.xlib.XSetWMProtocols)(
@@ -522,6 +522,53 @@ impl Window2 {
         self.invalidate_cached_frame_extents();
     }
 
+    fn set_icon_inner(&self, icon: Icon) -> util::Flusher {
+        let xconn = &self.x.display;
+
+        let icon_atom = unsafe { util::get_atom(xconn, b"_NET_WM_ICON\0") }
+            .expect("Failed to call XInternAtom (_NET_WM_ICON)");
+
+        let data = icon.to_cardinals();
+        unsafe {
+            util::change_property(
+                xconn,
+                self.x.window,
+                icon_atom,
+                ffi::XA_CARDINAL,
+                util::Format::Long,
+                util::PropMode::Replace,
+                data.as_slice(),
+            )
+        }
+    }
+
+    fn unset_icon_inner(&self) -> util::Flusher {
+        let xconn = &self.x.display;
+
+        let icon_atom = unsafe { util::get_atom(xconn, b"_NET_WM_ICON\0") }
+            .expect("Failed to call XInternAtom (_NET_WM_ICON)");
+
+        let empty_data: [util::Cardinal; 0] = [];
+        unsafe {
+            util::change_property(
+                xconn,
+                self.x.window,
+                icon_atom,
+                ffi::XA_CARDINAL,
+                util::Format::Long,
+                util::PropMode::Replace,
+                &empty_data,
+            )
+        }
+    }
+
+    pub fn set_window_icon(&self, icon: Option<Icon>) {
+        match icon {
+            Some(icon) => self.set_icon_inner(icon),
+            None => self.unset_icon_inner(),
+        }.flush().expect("Failed to set icons");
+    }
+
     pub fn show(&self) {
         unsafe {
             (self.x.display.xlib.XMapRaised)(self.x.display.display, self.x.window);

src/platform/macos/mod.rs

@@ -25,8 +25,8 @@ impl ::std::ops::Deref for Window {
 impl Window {
 
     pub fn new(events_loop: &EventsLoop,
-               attributes: &::WindowAttributes,
-               pl_attribs: &PlatformSpecificWindowBuilderAttributes) -> Result<Self, CreationError>
+               attributes: ::WindowAttributes,
+               pl_attribs: PlatformSpecificWindowBuilderAttributes) -> Result<Self, CreationError>
     {
         let weak_shared = Arc::downgrade(&events_loop.shared);
         let window = Arc::new(try!(Window2::new(weak_shared, attributes, pl_attribs)));

src/platform/macos/window.rs

@@ -559,8 +559,8 @@ impl WindowExt for Window2 {
 impl Window2 {
     pub fn new(
         shared: Weak<Shared>,
-        win_attribs: &WindowAttributes,
-        pl_attribs: &PlatformSpecificWindowBuilderAttributes,
+        win_attribs: WindowAttributes,
+        pl_attribs: PlatformSpecificWindowBuilderAttributes,
     ) -> Result<Window2, CreationError> {
         unsafe {
             if !msg_send![cocoa::base::class("NSThread"), isMainThread] {
@@ -579,7 +579,7 @@ impl Window2 {
             },
         };
 
-        let window = match Window2::create_window(win_attribs, pl_attribs)
+        let window = match Window2::create_window(&win_attribs, &pl_attribs)
         {
             Some(window) => window,
             None         => {
@@ -700,8 +700,8 @@ impl Window2 {
 
     fn create_window(
         attrs: &WindowAttributes,
-        pl_attrs: &PlatformSpecificWindowBuilderAttributes)
-        -> Option<IdRef> {
+        pl_attrs: &PlatformSpecificWindowBuilderAttributes
+    ) -> Option<IdRef> {
         unsafe {
             let autoreleasepool = NSAutoreleasePool::new(nil);
             let screen = match attrs.fullscreen {
@@ -1072,6 +1072,16 @@ impl Window2 {
         }
     }
 
+    #[inline]
+    pub fn set_window_icon(&self, _icon: Option<::Icon>) {
+        // macOS doesn't have window icons. Though, there is `setRepresentedFilename`, but that's
+        // semantically distinct and should only be used when the window is in some representing a
+        // specific file/directory. For instance, Terminal.app uses this for the CWD. Anyway, that
+        // should eventually be implemented as `WindowBuilderExt::with_represented_file` or
+        // something, and doesn't have anything to do with this.
+        // https://developer.apple.com/library/content/documentation/Cocoa/Conceptual/WinPanel/Tasks/SettingWindowTitle.html
+    }
+
     #[inline]
     pub fn get_current_monitor(&self) -> RootMonitorId {
         unsafe {

src/platform/windows/events_loop.rs

@@ -279,8 +279,9 @@ impl EventsLoopProxy {
 
     /// Executes a function in the background thread.
     ///
-    /// Note that we use a FnMut instead of a FnOnce because we're too lazy to create an equivalent
-    /// to the unstable FnBox.
+    /// Note that we use FnMut instead of FnOnce because boxing FnOnce won't work on stable Rust
+    /// until 2030 when the design of Box is finally complete.
+    /// https://github.com/rust-lang/rust/issues/28796
     ///
     /// The `Inserted` can be used to inject a `WindowState` for the callback to use. The state is
     /// removed automatically if the callback receives a `WM_CLOSE` message for the window.
@@ -302,10 +303,7 @@ impl EventsLoopProxy {
             );
             // PostThreadMessage can only fail if the thread ID is invalid (which shouldn't happen
             // as the events loop is still alive) or if the queue is full.
-            assert!(
-                res != 0,
-                "PostThreadMessage failed ; is the messages queue full?"
-            );
+            assert!(res != 0, "PostThreadMessage failed; is the messages queue full?");
         }
     }
 }

src/platform/windows/icon.rs

@@ -0,0 +1,112 @@
+use std::{self, mem, ptr};
+use std::os::windows::ffi::OsStrExt;
+use std::path::Path;
+
+use winapi::ctypes::{c_int, wchar_t};
+use winapi::shared::minwindef::{BYTE, LPARAM, WPARAM};
+use winapi::shared::windef::{HICON, HWND};
+use winapi::um::winuser;
+
+use {Pixel, PIXEL_SIZE, Icon};
+use platform::platform::util;
+
+impl Pixel {
+    fn to_bgra(&mut self) {
+        mem::swap(&mut self.r, &mut self.b);
+    }
+}
+
+#[derive(Debug)]
+pub enum IconType {
+    Small = winuser::ICON_SMALL as isize,
+    Big = winuser::ICON_BIG as isize,
+}
+
+#[derive(Debug)]
+pub struct WinIcon {
+    pub handle: HICON,
+}
+
+impl WinIcon {
+    #[allow(dead_code)]
+    pub fn from_path<P: AsRef<Path>>(path: P) -> Result<Self, util::WinError> {
+        let wide_path: Vec<u16> = path.as_ref().as_os_str().encode_wide().collect();
+        let handle = unsafe {
+            winuser::LoadImageW(
+                ptr::null_mut(),
+                wide_path.as_ptr() as *const wchar_t,
+                winuser::IMAGE_ICON,
+                0, // 0 indicates that we want to use the actual width
+                0, // and height
+                winuser::LR_LOADFROMFILE,
+            ) as HICON
+        };
+        if !handle.is_null() {
+            Ok(WinIcon { handle })
+        } else {
+            Err(util::WinError::from_last_error())
+        }
+    }
+
+    pub fn from_icon(icon: Icon) -> Result<Self, util::WinError> {
+        Self::from_rgba(icon.rgba, icon.width, icon.height)
+    }
+
+    pub fn from_rgba(mut rgba: Vec<u8>, width: u32, height: u32) -> Result<Self, util::WinError> {
+        assert_eq!(rgba.len() % PIXEL_SIZE, 0);
+        let pixel_count = rgba.len() / PIXEL_SIZE;
+        assert_eq!(pixel_count, (width * height) as usize);
+        let mut and_mask = Vec::with_capacity(pixel_count);
+        let pixels = rgba.as_mut_ptr() as *mut Pixel; // how not to write idiomatic Rust
+        for pixel_index in 0..pixel_count {
+            let pixel = unsafe { &mut *pixels.offset(pixel_index as isize) };
+            and_mask.push(pixel.a.wrapping_sub(std::u8::MAX)); // invert alpha channel
+            pixel.to_bgra();
+        }
+        assert_eq!(and_mask.len(), pixel_count);
+        let handle = unsafe {
+            winuser::CreateIcon(
+                ptr::null_mut(),
+                width as c_int,
+                height as c_int,
+                1,
+                (PIXEL_SIZE * 8) as BYTE,
+                and_mask.as_ptr() as *const BYTE,
+                rgba.as_ptr() as *const BYTE,
+            ) as HICON
+        };
+        if !handle.is_null() {
+            Ok(WinIcon { handle })
+        } else {
+            Err(util::WinError::from_last_error())
+        }
+    }
+
+    pub fn set_for_window(&self, hwnd: HWND, icon_type: IconType) {
+        unsafe {
+            winuser::SendMessageW(
+                hwnd,
+                winuser::WM_SETICON,
+                icon_type as WPARAM,
+                self.handle as LPARAM,
+            );
+        }
+    }
+}
+
+impl Drop for WinIcon {
+    fn drop(&mut self) {
+        unsafe { winuser::DestroyIcon(self.handle) };
+    }
+}
+
+pub fn unset_for_window(hwnd: HWND, icon_type: IconType) {
+    unsafe {
+        winuser::SendMessageW(
+            hwnd,
+            winuser::WM_SETICON,
+            icon_type as WPARAM,
+            0 as LPARAM,
+        );
+    }
+}

src/platform/windows/mod.rs

@@ -10,6 +10,7 @@ pub use self::window::Window;
 #[derive(Clone, Default)]
 pub struct PlatformSpecificWindowBuilderAttributes {
     pub parent: Option<HWND>,
+    pub taskbar_icon: Option<::Icon>,
 }
 
 unsafe impl Send for PlatformSpecificWindowBuilderAttributes {}
@@ -45,6 +46,7 @@ unsafe impl Sync for WindowId {}
 
 mod event;
 mod events_loop;
+mod icon;
 mod monitor;
 mod raw_input;
 mod util;

src/platform/windows/util.rs

@@ -1,6 +1,23 @@
+use std::{self, mem, ptr};
 use std::ops::BitAnd;
 
 use winapi::ctypes::wchar_t;
+use winapi::shared::minwindef::DWORD;
+use winapi::um::errhandlingapi::GetLastError;
+use winapi::um::winbase::{
+    FormatMessageW,
+    FORMAT_MESSAGE_ALLOCATE_BUFFER,
+    FORMAT_MESSAGE_FROM_SYSTEM,
+    FORMAT_MESSAGE_IGNORE_INSERTS,
+    lstrlenW,
+    LocalFree,
+};
+use winapi::um::winnt::{
+    LPCWSTR,
+    MAKELANGID,
+    LANG_NEUTRAL,
+    SUBLANG_DEFAULT,
+};
 
 pub fn has_flag<T>(bitset: T, flag: T) -> bool
 where T:
@@ -14,3 +31,42 @@ pub fn wchar_to_string(wchar: &[wchar_t]) -> String {
         .trim_right_matches(0 as char)
         .to_string()
 }
+
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
+pub struct WinError(Option<String>);
+
+impl WinError {
+    pub fn from_last_error() -> Self {
+        WinError(unsafe { get_last_error() })
+    }
+}
+
+pub unsafe fn get_last_error() -> Option<String> {
+    let err = GetLastError();
+    if err != 0 {
+        let buf_addr: LPCWSTR = {
+            let mut buf_addr: LPCWSTR = mem::uninitialized();
+            FormatMessageW(
+               FORMAT_MESSAGE_ALLOCATE_BUFFER
+               | FORMAT_MESSAGE_FROM_SYSTEM
+               | FORMAT_MESSAGE_IGNORE_INSERTS,
+               ptr::null(),
+               err,
+               MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT) as DWORD,
+               // This is a pointer to a pointer
+               &mut buf_addr as *mut LPCWSTR as *mut _,
+               0,
+               ptr::null_mut(),
+            );
+            buf_addr
+        };
+        if !buf_addr.is_null() {
+            let buf_len = lstrlenW(buf_addr) as usize;
+            let buf_slice = std::slice::from_raw_parts(buf_addr, buf_len);
+            let string = wchar_to_string(buf_slice);
+            LocalFree(buf_addr as *mut _);
+            return Some(string);
+        }
+    }
+    None
+}

src/platform/windows/window.rs

@@ -1,35 +1,31 @@
 #![cfg(target_os = "windows")]
 
+use std::cell::Cell;
 use std::ffi::OsStr;
-use std::io;
-use std::mem;
+use std::{io, mem, ptr};
 use std::os::raw;
 use std::os::windows::ffi::OsStrExt;
-use std::ptr;
-use std::sync::Arc;
-use std::sync::Mutex;
+use std::sync::{Arc, Mutex};
 use std::sync::mpsc::channel;
-use std::cell::Cell;
 
-use platform::platform::events_loop::{self, DESTROY_MSG_ID};
-use platform::platform::EventsLoop;
-use platform::platform::PlatformSpecificWindowBuilderAttributes;
-use platform::platform::raw_input::register_all_mice_and_keyboards_for_raw_input;
-use platform::platform::WindowId;
+use winapi::shared::minwindef::{BOOL, DWORD, UINT};
+use winapi::shared::windef::{HDC, HWND, POINT, RECT};
+use winapi::um::{combaseapi, dwmapi, libloaderapi, processthreadsapi, winuser};
+use winapi::um::objbase::{COINIT_MULTITHREADED};
+use winapi::um::unknwnbase::{IUnknown, IUnknownVtbl};
+use winapi::um::winnt::{HRESULT, LONG, LPCWSTR};
 
 use CreationError;
 use CursorState;
+use Icon;
+use MonitorId as RootMonitorId;
 use MouseCursor;
 use WindowAttributes;
-use MonitorId as RootMonitorId;
 
-use winapi::shared::minwindef::{UINT, DWORD, BOOL};
-use winapi::shared::windef::{HWND, HDC, RECT, POINT};
-use winapi::um::{winuser, dwmapi, libloaderapi, processthreadsapi};
-use winapi::um::winnt::{LPCWSTR, LONG, HRESULT};
-use winapi::um::combaseapi;
-use winapi::um::objbase::{COINIT_MULTITHREADED};
-use winapi::um::unknwnbase::{IUnknown, IUnknownVtbl};
+use platform::platform::{EventsLoop, PlatformSpecificWindowBuilderAttributes, WindowId};
+use platform::platform::events_loop::{self, DESTROY_MSG_ID};
+use platform::platform::icon::{self, IconType, WinIcon};
+use platform::platform::raw_input::register_all_mice_and_keyboards_for_raw_input;
 
 /// The Win32 implementation of the main `Window` object.
 pub struct Window {
@@ -39,6 +35,9 @@ pub struct Window {
     /// The current window state.
     window_state: Arc<Mutex<events_loop::WindowState>>,
 
+    window_icon: Cell<Option<WinIcon>>,
+    taskbar_icon: Cell<Option<WinIcon>>,
+
     // The events loop proxy.
     events_loop_proxy: events_loop::EventsLoopProxy,
 }
@@ -72,19 +71,19 @@ unsafe fn unjust_window_rect(prc: &mut RECT, style: DWORD, ex_style: DWORD) -> B
 }
 
 impl Window {
-    pub fn new(events_loop: &EventsLoop, w_attr: &WindowAttributes,
-               pl_attr: &PlatformSpecificWindowBuilderAttributes) -> Result<Window, CreationError>
-    {
-        let mut w_attr = Some(w_attr.clone());
-        let mut pl_attr = Some(pl_attr.clone());
-
+    pub fn new(
+        events_loop: &EventsLoop,
+        w_attr: WindowAttributes,
+        pl_attr: PlatformSpecificWindowBuilderAttributes,
+    ) -> Result<Window, CreationError> {
         let (tx, rx) = channel();
 
         let proxy = events_loop.create_proxy();
 
         events_loop.execute_in_thread(move |inserter| {
             // We dispatch an `init` function because of code style.
-            let win = unsafe { init(w_attr.take().unwrap(), pl_attr.take().unwrap(), inserter, proxy.clone()) };
+            // First person to remove the need for cloning here gets a cookie!
+            let win = unsafe { init(w_attr.clone(), pl_attr.clone(), inserter, proxy.clone()) };
             let _ = tx.send(win);
         });
 
@@ -92,10 +91,11 @@ impl Window {
     }
 
     pub fn set_title(&self, text: &str) {
-        unsafe {
-            let text = OsStr::new(text).encode_wide().chain(Some(0).into_iter())
+        let text = OsStr::new(text)
+            .encode_wide()
+            .chain(Some(0).into_iter())
             .collect::<Vec<_>>();
-
+        unsafe {
             winuser::SetWindowTextW(self.window.0, text.as_ptr() as LPCWSTR);
         }
     }
@@ -610,6 +610,32 @@ impl Window {
             inner: EventsLoop::get_current_monitor(self.window.0),
         }
     }
+
+    #[inline]
+    pub fn set_window_icon(&self, mut window_icon: Option<Icon>) {
+        let window_icon = window_icon
+            .take()
+            .map(|icon| WinIcon::from_icon(icon).expect("Failed to create `ICON_SMALL`"));
+        if let Some(ref window_icon) = window_icon {
+            window_icon.set_for_window(self.window.0, IconType::Small);
+        } else {
+            icon::unset_for_window(self.window.0, IconType::Small);
+        }
+        self.window_icon.replace(window_icon);
+    }
+
+    #[inline]
+    pub fn set_taskbar_icon(&self, mut taskbar_icon: Option<Icon>) {
+        let taskbar_icon = taskbar_icon
+            .take()
+            .map(|icon| WinIcon::from_icon(icon).expect("Failed to create `ICON_BIG`"));
+        if let Some(ref taskbar_icon) = taskbar_icon {
+            taskbar_icon.set_for_window(self.window.0, IconType::Big);
+        } else {
+            icon::unset_for_window(self.window.0, IconType::Big);
+        }
+        self.taskbar_icon.replace(taskbar_icon);
+    }
 }
 
 impl Drop for Window {
@@ -642,13 +668,44 @@ pub unsafe fn adjust_size(
     (rect.right - rect.left, rect.bottom - rect.top)
 }
 
-unsafe fn init(window: WindowAttributes, pl_attribs: PlatformSpecificWindowBuilderAttributes,
-               inserter: events_loop::Inserter, events_loop_proxy: events_loop::EventsLoopProxy) -> Result<Window, CreationError> {
-    let title = OsStr::new(&window.title).encode_wide().chain(Some(0).into_iter())
+unsafe fn init(
+    mut window: WindowAttributes,
+    mut pl_attribs: PlatformSpecificWindowBuilderAttributes,
+    inserter: events_loop::Inserter,
+    events_loop_proxy: events_loop::EventsLoopProxy,
+) -> Result<Window, CreationError> {
+    let title = OsStr::new(&window.title)
+        .encode_wide()
+        .chain(Some(0).into_iter())
         .collect::<Vec<_>>();
 
+    let window_icon = {
+        let icon = window.window_icon
+            .take()
+            .map(WinIcon::from_icon);
+        if icon.is_some() {
+            Some(icon.unwrap().map_err(|err| {
+                CreationError::OsError(format!("Failed to create `ICON_SMALL`: {:?}", err))
+            })?)
+        } else {
+            None
+        }
+    };
+    let taskbar_icon = {
+        let icon = pl_attribs.taskbar_icon
+            .take()
+            .map(WinIcon::from_icon);
+        if icon.is_some() {
+            Some(icon.unwrap().map_err(|err| {
+                CreationError::OsError(format!("Failed to create `ICON_BIG`: {:?}", err))
+            })?)
+        } else {
+            None
+        }
+    };
+
     // registering the window class
-    let class_name = register_window_class();
+    let class_name = register_window_class(&window_icon, &taskbar_icon);
 
     // building a RECT object with coordinates
     let mut rect = RECT {
@@ -738,17 +795,21 @@ unsafe fn init(window: WindowAttributes, pl_attribs: PlatformSpecificWindowBuild
         }
     }
 
+    let (transparent, maximized, fullscreen) = (
+        window.transparent.clone(), window.maximized.clone(), window.fullscreen.clone()
+    );
+
     // Creating a mutex to track the current window state
     let window_state = Arc::new(Mutex::new(events_loop::WindowState {
         cursor: winuser::IDC_ARROW, // use arrow by default
         cursor_state: CursorState::Normal,
-        attributes: window.clone(),
+        attributes: window,
         mouse_in_window: false,
         saved_window_info: None,
     }));
 
     // making the window transparent
-    if window.transparent {
+    if transparent {
         let bb = dwmapi::DWM_BLURBEHIND {
             dwFlags: 0x1, // FIXME: DWM_BB_ENABLE;
             fEnable: 1,
@@ -762,12 +823,14 @@ unsafe fn init(window: WindowAttributes, pl_attribs: PlatformSpecificWindowBuild
     let win = Window {
         window: real_window,
         window_state: window_state,
-        events_loop_proxy
+        window_icon: Cell::new(window_icon),
+        taskbar_icon: Cell::new(taskbar_icon),
+        events_loop_proxy,
     };
 
-    win.set_maximized(window.maximized);
-    if let Some(_) = window.fullscreen {
-        win.set_fullscreen(window.fullscreen);
+    win.set_maximized(maximized);
+    if let Some(_) = fullscreen {
+        win.set_fullscreen(fullscreen);
         force_window_active(win.window.0);
     }
 
@@ -776,9 +839,23 @@ unsafe fn init(window: WindowAttributes, pl_attribs: PlatformSpecificWindowBuild
     Ok(win)
 }
 
-unsafe fn register_window_class() -> Vec<u16> {
-    let class_name = OsStr::new("Window Class").encode_wide().chain(Some(0).into_iter())
-                                               .collect::<Vec<_>>();
+unsafe fn register_window_class(
+    window_icon: &Option<WinIcon>,
+    taskbar_icon: &Option<WinIcon>,
+) -> Vec<u16> {
+    let class_name: Vec<_> = OsStr::new("Window Class")
+        .encode_wide()
+        .chain(Some(0).into_iter())
+        .collect();
+
+    let h_icon = taskbar_icon
+        .as_ref()
+        .map(|icon| icon.handle)
+        .unwrap_or(ptr::null_mut());
+    let h_icon_small = window_icon
+        .as_ref()
+        .map(|icon| icon.handle)
+        .unwrap_or(ptr::null_mut());
 
     let class = winuser::WNDCLASSEXW {
         cbSize: mem::size_of::<winuser::WNDCLASSEXW>() as UINT,
@@ -787,12 +864,12 @@ unsafe fn register_window_class() -> Vec<u16> {
         cbClsExtra: 0,
         cbWndExtra: 0,
         hInstance: libloaderapi::GetModuleHandleW(ptr::null()),
-        hIcon: ptr::null_mut(),
+        hIcon: h_icon,
         hCursor: ptr::null_mut(), // must be null in order for cursor state to work properly
         hbrBackground: ptr::null_mut(),
         lpszMenuName: ptr::null(),
         lpszClassName: class_name.as_ptr(),
-        hIconSm: ptr::null_mut(),
+        hIconSm: h_icon_small,
     };
 
     // We ignore errors because registering the same window class twice would trigger

src/window.rs

@@ -3,6 +3,7 @@ use std::collections::vec_deque::IntoIter as VecDequeIter;
 use CreationError;
 use CursorState;
 use EventsLoop;
+use Icon;
 use MouseCursor;
 use Window;
 use WindowBuilder;
@@ -91,6 +92,24 @@ impl WindowBuilder {
         self
     }
 
+    /// Sets the window icon. On Windows and X11, this is typically the small icon in the top-left
+    /// corner of the titlebar.
+    ///
+    /// ## Platform-specific
+    ///
+    /// This only has an effect on Windows and X11.
+    ///
+    /// On Windows, this sets `ICON_SMALL`. The base size for a window icon is 16x16, but it's
+    /// recommended to account for screen scaling and pick a multiple of that, i.e. 32x32.
+    ///
+    /// X11 has no universal guidelines for icon sizes, so you're at the whims of the WM. That
+    /// said, it's usually in the same ballpark as on Windows.
+    #[inline]
+    pub fn with_window_icon(mut self, window_icon: Option<Icon>) -> WindowBuilder {
+        self.window.window_icon = window_icon;
+        self
+    }
+
     /// Enables multitouch.
     #[inline]
     pub fn with_multitouch(mut self) -> WindowBuilder {
@@ -103,22 +122,22 @@ impl WindowBuilder {
     /// Error should be very rare and only occur in case of permission denied, incompatible system,
     /// out of memory, etc.
     pub fn build(mut self, events_loop: &EventsLoop) -> Result<Window, CreationError> {
-        // resizing the window to the dimensions of the monitor when fullscreen
-        if self.window.dimensions.is_none() {
+        self.window.dimensions = Some(self.window.dimensions.unwrap_or_else(|| {
             if let Some(ref monitor) = self.window.fullscreen {
-                self.window.dimensions = Some(monitor.get_dimensions());
-            }
-        }
-
+                // resizing the window to the dimensions of the monitor when fullscreen
+                monitor.get_dimensions()
+            } else {
                 // default dimensions
-        if self.window.dimensions.is_none() {
-            self.window.dimensions = Some((1024, 768));
+                (1024, 768)
             }
+        }));
 
         // building
-        let w = try!(platform::Window::new(&events_loop.events_loop, &self.window, &self.platform_specific));
-
-        Ok(Window { window: w })
+        platform::Window::new(
+            &events_loop.events_loop,
+            self.window,
+            self.platform_specific,
+        ).map(|window| Window { window })
     }
 }
 
@@ -344,6 +363,19 @@ impl Window {
         self.window.set_decorations(decorations)
     }
 
+    /// Sets the window icon. On Windows and X11, this is typically the small icon in the top-left
+    /// corner of the titlebar.
+    ///
+    /// For more usage notes, see `WindowBuilder::with_window_icon`.
+    ///
+    /// ## Platform-specific
+    ///
+    /// This only has an effect on Windows and X11.
+    #[inline]
+    pub fn set_window_icon(&self, window_icon: Option<Icon>) {
+        self.window.set_window_icon(window_icon)
+    }
+
     /// Returns the monitor on which the window currently resides
     pub fn get_current_monitor(&self) -> MonitorId {
         self.window.get_current_monitor()