Add option to make window "always on top" (#528)

* macOS: always_on_top

* Windows: always_on_top

* X11: always_on_top

* Stub set_always_on_top on other platforms

CHANGELOG.md

@@ -20,6 +20,7 @@
 - On Windows, alt-tabbing while the cursor is grabbed no longer makes it impossible to re-grab the window.
 - On Windows, using `CursorState::Hide` when the cursor is grabbed now ungrabs the cursor first.
 - Implemented `MouseCursor::NoneCursor` on Windows.
+- Added `WindowBuilder::with_always_on_top` and `Window::set_always_on_top`. Implemented on Windows, macOS, and X11.
 
 # Version 0.14.0 (2018-05-09)
 

src/lib.rs

@@ -441,6 +441,11 @@ pub struct WindowAttributes {
     /// The default is `true`.
     pub decorations: bool,
 
+    /// Whether the window should always be on top of other windows.
+    ///
+    /// The default is `false`.
+    pub always_on_top: bool,
+
     /// The window icon.
     ///
     /// The default is `None`.
@@ -464,6 +469,7 @@ impl Default for WindowAttributes {
             visible: true,
             transparent: false,
             decorations: true,
+            always_on_top: false,
             window_icon: None,
             multitouch: false,
         }

src/platform/android/mod.rs

@@ -323,6 +323,11 @@ impl Window {
         // N/A
     }
 
+    #[inline]
+    pub fn set_always_on_top(&self, _always_on_top: bool) {
+        // N/A
+    }
+
     #[inline]
     pub fn set_window_icon(&self, _icon: Option<::Icon>) {
         // N/A

src/platform/emscripten/mod.rs

@@ -543,6 +543,11 @@ impl Window {
         // N/A
     }
 
+    #[inline]
+    pub fn set_always_on_top(&self, _always_on_top: bool) {
+        // N/A
+    }
+
     #[inline]
     pub fn set_window_icon(&self, _icon: Option<::Icon>) {
         // N/A

src/platform/ios/mod.rs

@@ -370,6 +370,11 @@ impl Window {
         // N/A
     }
 
+    #[inline]
+    pub fn set_always_on_top(&self, _always_on_top: bool) {
+        // N/A
+    }
+
     #[inline]
     pub fn set_window_icon(&self, _icon: Option<::Icon>) {
         // N/A

src/platform/linux/mod.rs

@@ -302,6 +302,14 @@ impl Window {
         }
     }
 
+    #[inline]
+    pub fn set_always_on_top(&self, always_on_top: bool) {
+        match self {
+            &Window::X(ref w) => w.set_always_on_top(always_on_top),
+            &Window::Wayland(_) => (),
+        }
+    }
+
     #[inline]
     pub fn set_window_icon(&self, window_icon: Option<Icon>) {
         match self {

src/platform/linux/x11/window.rs

@@ -299,8 +299,15 @@ impl Window2 {
             }.queue();
 
             // These properties must be set after mapping
-            window.set_maximized_inner(window_attrs.maximized).queue();
-            window.set_fullscreen_inner(window_attrs.fullscreen.clone()).queue();
+            if window_attrs.maximized {
+                window.set_maximized_inner(window_attrs.maximized).queue();
+            }
+            if window_attrs.fullscreen.is_some() {
+                window.set_fullscreen_inner(window_attrs.fullscreen.clone()).queue();
+            }
+            if window_attrs.always_on_top {
+                window.set_always_on_top_inner(window_attrs.always_on_top).queue();
+            }
 
             if window_attrs.visible {
                 unsafe {
@@ -498,6 +505,27 @@ impl Window2 {
         self.invalidate_cached_frame_extents();
     }
 
+    fn set_always_on_top_inner(&self, always_on_top: bool) -> util::Flusher {
+        let xconn = &self.x.display;
+
+        let above_atom = unsafe { util::get_atom(xconn, b"_NET_WM_STATE_ABOVE\0") }
+            .expect("Failed to call XInternAtom (_NET_WM_STATE_ABOVE)");
+
+        Window2::set_netwm(
+            xconn,
+            self.x.window,
+            self.x.root,
+            (above_atom as c_long, 0, 0, 0),
+            always_on_top.into(),
+        )
+    }
+
+    pub fn set_always_on_top(&self, always_on_top: bool) {
+        self.set_always_on_top_inner(always_on_top)
+            .flush()
+            .expect("Failed to set always-on-top state");
+    }
+
     fn set_icon_inner(&self, icon: Icon) -> util::Flusher {
         let xconn = &self.x.display;
 

src/platform/macos/ffi.rs

@@ -1,6 +1,6 @@
 // TODO: Upstream these
 
-#![allow(non_snake_case, non_upper_case_globals)]
+#![allow(dead_code, non_snake_case, non_upper_case_globals)]
 
 use cocoa::base::{class, id};
 use cocoa::foundation::{NSInteger, NSUInteger};
@@ -72,3 +72,36 @@ impl NSMutableAttributedString for id {
         msg_send![self, length]
     }
 }
+
+pub const kCGBaseWindowLevelKey: NSInteger = 0;
+pub const kCGMinimumWindowLevelKey: NSInteger = 1;
+pub const kCGDesktopWindowLevelKey: NSInteger = 2;
+pub const kCGBackstopMenuLevelKey: NSInteger = 3;
+pub const kCGNormalWindowLevelKey: NSInteger = 4;
+pub const kCGFloatingWindowLevelKey: NSInteger = 5;
+pub const kCGTornOffMenuWindowLevelKey: NSInteger = 6;
+pub const kCGDockWindowLevelKey: NSInteger = 7;
+pub const kCGMainMenuWindowLevelKey: NSInteger = 8;
+pub const kCGStatusWindowLevelKey: NSInteger = 9;
+pub const kCGModalPanelWindowLevelKey: NSInteger = 10;
+pub const kCGPopUpMenuWindowLevelKey: NSInteger = 11;
+pub const kCGDraggingWindowLevelKey: NSInteger = 12;
+pub const kCGScreenSaverWindowLevelKey: NSInteger = 13;
+pub const kCGMaximumWindowLevelKey: NSInteger = 14;
+pub const kCGOverlayWindowLevelKey: NSInteger = 15;
+pub const kCGHelpWindowLevelKey: NSInteger = 16;
+pub const kCGUtilityWindowLevelKey: NSInteger = 17;
+pub const kCGDesktopIconWindowLevelKey: NSInteger = 18;
+pub const kCGCursorWindowLevelKey: NSInteger = 19;
+pub const kCGNumberOfWindowLevelKeys: NSInteger = 20;
+
+pub enum NSWindowLevel {
+    NSNormalWindowLevel = kCGBaseWindowLevelKey as _,
+    NSFloatingWindowLevel = kCGFloatingWindowLevelKey as _,
+    NSTornOffMenuWindowLevel = kCGTornOffMenuWindowLevelKey as _,
+    NSModalPanelWindowLevel = kCGModalPanelWindowLevelKey as _,
+    NSMainMenuWindowLevel = kCGMainMenuWindowLevelKey as _,
+    NSStatusWindowLevel = kCGStatusWindowLevelKey as _,
+    NSPopUpMenuWindowLevel = kCGPopUpMenuWindowLevelKey as _,
+    NSScreenSaverWindowLevel = kCGScreenSaverWindowLevelKey as _,
+}

src/platform/macos/window.rs

@@ -25,6 +25,7 @@ use std::sync::Weak;
 use std::cell::{Cell, RefCell};
 
 use super::events_loop::{EventsLoop, Shared};
+use platform::platform::ffi;
 use platform::platform::util;
 use platform::platform::view::{new_view, set_ime_spot};
 
@@ -774,6 +775,10 @@ impl Window2 {
                 if pl_attrs.movable_by_window_background {
                     window.setMovableByWindowBackground_(YES);
                 }
+
+                if attrs.always_on_top {
+                    let _: () = msg_send![*window, setLevel:ffi::NSWindowLevel::NSFloatingWindowLevel];
+                }
                 
                 if let Some((x, y)) = pl_attrs.resize_increments {
                     if x >= 1 && y >= 1 {
@@ -1066,6 +1071,18 @@ impl Window2 {
         }
     }
 
+    #[inline]
+    pub fn set_always_on_top(&self, always_on_top: bool) {
+        unsafe {
+            let level = if always_on_top {
+                ffi::NSWindowLevel::NSFloatingWindowLevel
+            } else {
+                ffi::NSWindowLevel::NSNormalWindowLevel
+            };
+            let _: () = msg_send![*self.window, setLevel:level];
+        }
+    }
+
     #[inline]
     pub fn set_window_icon(&self, _icon: Option<::Icon>) {
         // macOS doesn't have window icons. Though, there is `setRepresentedFilename`, but that's

src/platform/windows/window.rs

@@ -650,6 +650,38 @@ impl Window {
         }
     }
 
+    #[inline]
+    pub fn set_always_on_top(&self, always_on_top: bool) {
+        if let Ok(mut window_state) = self.window_state.lock() {
+            if window_state.attributes.always_on_top == always_on_top {
+                return;
+            }
+
+            let window = self.window.clone();
+            self.events_loop_proxy.execute_in_thread(move |_| {
+                let insert_after = if always_on_top {
+                    winuser::HWND_TOPMOST
+                } else {
+                    winuser::HWND_NOTOPMOST
+                };
+                unsafe {
+                    winuser::SetWindowPos(
+                        window.0,
+                        insert_after,
+                        0,
+                        0,
+                        0,
+                        0,
+                        winuser::SWP_ASYNCWINDOWPOS | winuser::SWP_NOMOVE | winuser::SWP_NOSIZE,
+                    );
+                    winuser::UpdateWindow(window.0);
+                }
+            });
+
+            window_state.attributes.always_on_top = always_on_top;
+        }
+    }
+
     #[inline]
     pub fn get_current_monitor(&self) -> RootMonitorId {
         RootMonitorId {
@@ -765,7 +797,7 @@ unsafe fn init(
     };
 
     // computing the style and extended style of the window
-    let (ex_style, style) = if !window.decorations {
+    let (mut ex_style, style) = if !window.decorations {
         (winuser::WS_EX_APPWINDOW,
             //winapi::WS_POPUP is incompatible with winapi::WS_CHILD
             if pl_attribs.parent.is_some() {
@@ -780,6 +812,10 @@ unsafe fn init(
             winuser::WS_OVERLAPPEDWINDOW | winuser::WS_CLIPSIBLINGS | winuser::WS_CLIPCHILDREN)
     };
 
+    if window.always_on_top {
+        ex_style |= winuser::WS_EX_TOPMOST;
+    }
+
     // adjusting the window coordinates using the style
     winuser::AdjustWindowRectEx(&mut rect, style, 0, ex_style);
 

src/window.rs

@@ -92,6 +92,13 @@ impl WindowBuilder {
         self
     }
 
+    /// Sets whether or not the window will always be on top of other windows.
+    #[inline]
+    pub fn with_always_on_top(mut self, always_on_top: bool) -> WindowBuilder {
+        self.window.always_on_top = always_on_top;
+        self
+    }
+
     /// Sets the window icon. On Windows and X11, this is typically the small icon in the top-left
     /// corner of the titlebar.
     ///
@@ -363,6 +370,12 @@ impl Window {
         self.window.set_decorations(decorations)
     }
 
+    /// Change whether or not the window will always be on top of other windows.
+    #[inline]
+    pub fn set_always_on_top(&self, always_on_top: bool) {
+        self.window.set_always_on_top(always_on_top)
+    }
+
     /// Sets the window icon. On Windows and X11, this is typically the small icon in the top-left
     /// corner of the titlebar.
     ///