Fix rounding error in WindowSwitcher (#2750)

Fixes #2746

Casting to int rounds the number down, and for some reason 6.0 was rounded to 5... Floating number magic

Co-authored-by: Leonhard <leo.kargl@proton.me>

Author: lenemter

data/gala.metainfo.xml.in

@@ -36,6 +36,7 @@
         </ul>
       </description>
       <issues>
+        <issue url="https://github.com/elementary/gala/issues/2746">6th and 13th key press of Alt+Tab have a bug</issue>
         <issue url="https://github.com/elementary/gala/issues/2657">Window icons missing in the Show All Windows overview</issue>
         <issue url="https://github.com/elementary/gala/issues/2675">Blur behind modal shell protocol</issue>
         <issue url="https://github.com/elementary/gala/issues/2676">Window selection from dock overview doesn't focus the chosen window</issue>

src/Widgets/WindowSwitcher/WindowSwitcher.vala

@@ -26,6 +26,7 @@ public class Gala.WindowSwitcher : CanvasActor, GestureTarget, RootTarget {
     private Gala.Text caption;
     private ShadowEffect shadow_effect;
     private BackgroundBlurEffect blur_effect;
+    private int previous_icon_index = 0;
 
     private WindowSwitcherIcon? _current_icon = null;
     private WindowSwitcherIcon? current_icon {
@@ -48,8 +49,6 @@ public class Gala.WindowSwitcher : CanvasActor, GestureTarget, RootTarget {
         }
     }
 
-    private double previous_progress = 0d;
-
     public WindowSwitcher (WindowManager wm) {
         Object (wm: wm);
     }
@@ -225,16 +224,17 @@ public class Gala.WindowSwitcher : CanvasActor, GestureTarget, RootTarget {
             return;
         }
 
-        var is_step = ((int) (previous_progress / GESTURE_STEP) - (int) (progress / GESTURE_STEP)).abs () >= 1;
+        var new_index = (int) Math.round (progress / GESTURE_STEP);
+        var is_step = new_index != previous_icon_index;
 
-        previous_progress = progress;
+        previous_icon_index = new_index;
 
         if (container.get_n_children () == 1 && current_icon != null && is_step) {
             InternalUtils.bell_notify (wm.get_display ());
             return;
         }
 
-        var current_index = (int) (progress / GESTURE_STEP) % container.get_n_children ();
+        var current_index = new_index % container.get_n_children ();
 
         if (current_index < 0) {
             current_index = container.get_n_children () + current_index;