WindowServer: Add basic virtual desktop support

This creates a 2-dimensional array of WindowStack instances, one for
each virtual desktop. The main desktop 0,0 is the main desktop, which
is the desktop used for all stationary windows (e.g. taskbar, desktop).
When adding windows to a desktop, stationary windows are always added
to the main desktop.

When composing the desktop, there are usually two WindowStacks
involved. For stationary windows, the main desktop will be traversed,
and for everything else the current virtual desktop will be iterated.
Iteration is interweaved to preserve the correct order. During the
transition animation, two WindowStacks will be iterated at the same
time.

1 files changed, 11 insertions, 0 deletions

diff --git a/Userland/Libraries/LibGfx/DisjointRectSet.h b/Userland/Libraries/LibGfx/DisjointRectSet.h
index ccb17b30df..cafb9157f2 100644
--- a/Userland/Libraries/LibGfx/DisjointRectSet.h
+++ b/Userland/Libraries/LibGfx/DisjointRectSet.h
@@ -129,6 +129,17 @@ public:
     const Vector<IntRect, 32>& rects() const { return m_rects; }
     Vector<IntRect, 32> take_rects() { return move(m_rects); }
 
+    void translate_by(int dx, int dy)
+    {
+        for (auto& rect : m_rects)
+            rect.translate_by(dx, dy);
+    }
+    void translate_by(Gfx::IntPoint const& delta)
+    {
+        for (auto& rect : m_rects)
+            rect.translate_by(delta);
+    }
+
 private:
     bool add_no_shatter(const IntRect&);
     void shatter();