Process WM_SYSCOMMAND to forbid screen savers in fullscreen mode (#1065)

* Process WM_SYSCOMMAND to forbid screen savers in fullscreen mode

Fixes #1047

* Update CHANGELOG.md and documentation to reflect changes from issue #1065

* Updated documentation of window.Window.set_fullscreen to match the documentation of window.WindowBuilder.with_fullscreen.

CHANGELOG.md

@@ -3,6 +3,7 @@
 - On Windows, location of `WindowEvent::Touch` are window client coordinates instead of screen coordinates.
 - On X11, fix delayed events after window redraw.
 - On macOS, add `WindowBuilderExt::with_disallow_hidpi` to have the option to turn off best resolution openGL surface.
+- On Windows, screen saver won't start if the window is in fullscreen mode.
 
 # 0.20.0 Alpha 2 (2019-07-09)
 

src/platform_impl/windows/event_loop.rs

@@ -1020,6 +1020,17 @@ unsafe extern "system" fn public_window_callback<T>(
         // other unwanted default hotkeys as well.
         winuser::WM_SYSCHAR => 0,
 
+        winuser::WM_SYSCOMMAND => {
+            if wparam == winuser::SC_SCREENSAVE {
+                let window_state = subclass_input.window_state.lock();
+                if window_state.fullscreen.is_some() {
+                    return 0;
+                }
+            }
+
+            winuser::DefWindowProcW(window, msg, wparam, lparam)
+        }
+
         winuser::WM_MOUSEMOVE => {
             use crate::event::WindowEvent::{CursorEntered, CursorMoved};
             let mouse_was_outside_window = {

src/window.rs

@@ -224,6 +224,10 @@ impl WindowBuilder {
 
     /// Sets the window fullscreen state. None means a normal window, Some(MonitorHandle)
     /// means a fullscreen window on that specific monitor
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **Windows:** Screen saver is disabled in fullscreen mode.
     #[inline]
     pub fn with_fullscreen(mut self, monitor: Option<MonitorHandle>) -> WindowBuilder {
         self.window.fullscreen = monitor;
@@ -534,6 +538,7 @@ impl Window {
     /// ## Platform-specific
     ///
     /// - **iOS:** Can only be called on the main thread.
+    /// - **Windows:** Screen saver is disabled in fullscreen mode.
     #[inline]
     pub fn set_fullscreen(&self, monitor: Option<MonitorHandle>) {
         self.window.set_fullscreen(monitor)