Make camera controller not trigger change detection every frame (#19547)

Split off from #19058

Author: JMS55

examples/helpers/camera_controller.rs

@@ -198,7 +198,7 @@ fn run_camera_controller(
     }
     let cursor_grab = *mouse_cursor_grab || *toggle_cursor_grab;
 
-    // Apply movement update
+    // Update velocity
     if axis_input != Vec3::ZERO {
         let max_speed = if key_input.pressed(controller.key_run) {
             controller.run_speed
@@ -213,11 +213,15 @@ fn run_camera_controller(
             controller.velocity = Vec3::ZERO;
         }
     }
-    let forward = *transform.forward();
-    let right = *transform.right();
-    transform.translation += controller.velocity.x * dt * right
-        + controller.velocity.y * dt * Vec3::Y
-        + controller.velocity.z * dt * forward;
+
+    // Apply movement update
+    if controller.velocity != Vec3::ZERO {
+        let forward = *transform.forward();
+        let right = *transform.right();
+        transform.translation += controller.velocity.x * dt * right
+            + controller.velocity.y * dt * Vec3::Y
+            + controller.velocity.z * dt * forward;
+    }
 
     // Handle cursor grab
     if cursor_grab_change {