Add mouse grab example (bevyengine#4114)

Fixes bevyengine#4094

Cargo.toml

@@ -430,6 +430,10 @@ path = "examples/input/mouse_input.rs"
 name = "mouse_input_events"
 path = "examples/input/mouse_input_events.rs"
 
+[[example]]
+name = "mouse_grab"
+path = "examples/input/mouse_grab.rs"
+
 [[example]]
 name = "touch_input"
 path = "examples/input/touch_input.rs"

examples/README.md

@@ -203,6 +203,7 @@ Example | File | Description
 `keyboard_modifiers` | [`input/keyboard_modifiers.rs`](./input/keyboard_modifiers.rs) | Demonstrates using key modifiers (ctrl, shift)
 `mouse_input` | [`input/mouse_input.rs`](./input/mouse_input.rs) | Demonstrates handling a mouse button press/release
 `mouse_input_events` | [`input/mouse_input_events.rs`](./input/mouse_input_events.rs) | Prints out all mouse events (buttons, movement, etc.)
+`mouse_grab` | [`input/mouse_grab.rs`](./input/mouse_grab.rs) | Demonstrates how to grab the mouse, locking the cursor to the app's screen
 `touch_input` | [`input/touch_input.rs`](./input/touch_input.rs) | Displays touch presses, releases, and cancels
 `touch_input_events` | [`input/touch_input_events.rs`](./input/touch_input_events.rs) | Prints out all touch inputs
 

examples/input/mouse_grab.rs

@@ -0,0 +1,26 @@
+use bevy::prelude::*;
+
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .add_system(grab_mouse)
+        .run();
+}
+
+// This system grabs the mouse when the left mouse button is pressed
+// and releases it when the escape key is pressed
+fn grab_mouse(
+    mut windows: ResMut<Windows>,
+    mouse: Res<Input<MouseButton>>,
+    key: Res<Input<KeyCode>>,
+) {
+    let window = windows.get_primary_mut().unwrap();
+    if mouse.just_pressed(MouseButton::Left) {
+        window.set_cursor_visibility(false);
+        window.set_cursor_lock_mode(true);
+    }
+    if key.just_pressed(KeyCode::Escape) {
+        window.set_cursor_visibility(true);
+        window.set_cursor_lock_mode(false);
+    }
+}