WindowServer: Ensure resized windows move in the expected direction

When a window is being interactively resized, there are several rules
beyond the actual mouse movement that can impact the new size of the
window, such as its size increments and minimum size limit.

Move the placement logic after applying all the sizing logic, so that
whatever final size the window ends up with, the sides of the window
that do move are the ones that the user is dragging.

https://github.com/SerenityOS/serenity/issues/52

Servers/WindowServer/WSWindowManager.cpp

@@ -542,8 +542,6 @@ bool WSWindowManager::process_ongoing_window_resize(const WSMouseEvent& event, W
     int diff_x = event.x() - m_resize_origin.x();
     int diff_y = event.y() - m_resize_origin.y();
 
-    int change_x = 0;
-    int change_y = 0;
     int change_w = 0;
     int change_h = 0;
 
@@ -557,25 +555,19 @@ bool WSWindowManager::process_ongoing_window_resize(const WSMouseEvent& event, W
         break;
     case ResizeDirection::UpRight:
         change_w = diff_x;
-        change_y = diff_y;
         change_h = -diff_y;
         break;
     case ResizeDirection::Up:
-        change_y = diff_y;
         change_h = -diff_y;
         break;
     case ResizeDirection::UpLeft:
-        change_x = diff_x;
         change_w = -diff_x;
-        change_y = diff_y;
         change_h = -diff_y;
         break;
     case ResizeDirection::Left:
-        change_x = diff_x;
         change_w = -diff_x;
         break;
     case ResizeDirection::DownLeft:
-        change_x = diff_x;
         change_w = -diff_x;
         change_h = diff_y;
         break;
@@ -587,10 +579,10 @@ bool WSWindowManager::process_ongoing_window_resize(const WSMouseEvent& event, W
     }
 
     auto new_rect = m_resize_window_original_rect;
+
+    // First, size the new rect.
     Size minimum_size { 50, 50 };
 
-    new_rect.set_x(new_rect.x() + change_x);
-    new_rect.set_y(new_rect.y() + change_y);
     new_rect.set_width(max(minimum_size.width(), new_rect.width() + change_w));
     new_rect.set_height(max(minimum_size.height(), new_rect.height() + change_h));
 
@@ -601,6 +593,31 @@ bool WSWindowManager::process_ongoing_window_resize(const WSMouseEvent& event, W
         new_rect.set_height(m_resize_window->base_size().height() + vertical_incs * m_resize_window->size_increment().height());
     }
 
+    // Second, set its position so that the sides of the window
+    // that end up moving are the same ones as the user is dragging,
+    // no matter which part of the logic above caused us to decide
+    // to resize by this much.
+    switch (m_resize_direction) {
+    case ResizeDirection::DownRight:
+    case ResizeDirection::Right:
+    case ResizeDirection::Down:
+        break;
+    case ResizeDirection::Left:
+    case ResizeDirection::Up:
+    case ResizeDirection::UpLeft:
+        new_rect.set_right_without_resize(m_resize_window_original_rect.right());
+        new_rect.set_bottom_without_resize(m_resize_window_original_rect.bottom());
+        break;
+    case ResizeDirection::UpRight:
+        new_rect.set_bottom_without_resize(m_resize_window_original_rect.bottom());
+        break;
+    case ResizeDirection::DownLeft:
+        new_rect.set_right_without_resize(m_resize_window_original_rect.right());
+        break;
+    default:
+        ASSERT_NOT_REACHED();
+    }
+
     if (new_rect.contains(event.position()))
         hovered_window = m_resize_window;