add xdg decoration, scene/tree factories, geometry + seat focus

more wrapper soup. xdg decoration manager, scene/tree node factories so
callers stop touching raw wlr_scene_*_create, a box geometry helper, and
seat pointer/keyboard focus clearing. dragging myself through it.

include/wlr/node.hpp

@@ -4,7 +4,7 @@
 #include <utility>
 
 #include "wlr/wlr.hpp"
-#include "wlr/scene.hpp"
+#include "wlr/color.hpp"
 
 namespace wlr {
 
@@ -36,16 +36,6 @@ protected:
 	struct wlr_scene_node* m_node;
 };
 
-class Tree : public Node {
-public:
-	Tree(struct wlr_scene_tree* tree) : Node(&tree->node), m_tree(tree) {}
-	struct wlr_scene_tree* raw() const { return m_tree; }
-	void reparent(Node& n) { wlr_scene_node_reparent(n.raw(), m_tree); }
-
-private:
-	struct wlr_scene_tree* m_tree;
-};
-
 class Rect : public Node {
 public:
 	Rect(struct wlr_scene_rect* rect) : Node(&rect->node), m_rect(rect) {}
@@ -127,4 +117,22 @@ private:
 	struct wlr_scene_surface* m_surface;
 };
 
+class Tree : public Node {
+public:
+	Tree(struct wlr_scene_tree* tree) : Node(&tree->node), m_tree(tree) {}
+	struct wlr_scene_tree* raw() const { return m_tree; }
+	void reparent(Node& n) { wlr_scene_node_reparent(n.raw(), m_tree); }
+
+	Tree add_tree() { return Tree{wlr_scene_tree_create(m_tree)}; }
+	Rect add_rect(int w, int h, const Color& c) {
+		float col[4]; c.apply(col);
+		return Rect{wlr_scene_rect_create(m_tree, w, h, col)};
+	}
+	Buffer add_buffer() { return Buffer{wlr_scene_buffer_create(m_tree, nullptr)}; }
+	Surface add_surface(struct wlr_surface* s) { return Surface{wlr_scene_surface_create(m_tree, s)}; }
+
+private:
+	struct wlr_scene_tree* m_tree;
+};
+
 }