diff --git a/gui/gui.c b/gui/gui.c
index d7a92ee..5318e14 100644
--- a/gui/gui.c
+++ b/gui/gui.c
@@ -127,7 +127,6 @@ typedef enum {
 } GUI_Layout_Direction;
 
 typedef struct GUI_Node {
-	#define RDIC_GUI_NODE_MEMBER_NAME rdic_node
 	RDIC_Node rdic_node;
 	GUI_Style *style;
 	GUI_String text_string; // Optional.
@@ -156,18 +155,19 @@ typedef struct GUI_Node {
 #define GUI_NODE_FIRST_CHILD(node) ((GUI_Node*)(node)->rdic_node.first_child)
 
 typedef union GUI_Node_Reference {
-	RDIC_Node_Reference rdic;
+	RDIC_Node_Reference rdic_ref;
 	struct {
 		GUI_Node *node;
 		unsigned int generation;
 	};
 } GUI_Node_Reference;
-#define gui_node_references_equal(n, m) rdic_node_references_equal((n).rdic,(m).rdic)
 #if 0
+#define gui_node_references_equal(n, m) rdic_node_references_equal((n).rdic_ref,(m).rdic_ref)
+#else
 // NOTE(Zelaven): This was just for debugging with better debug messages.
-int _gui_node_references_equal(GUI_Node_Reference n, GUI_Node_Reference m)
+int gui_node_references_equal(GUI_Node_Reference n, GUI_Node_Reference m)
 {
-	return rdic_node_references_equal(n.rdic,m.rdic);
+	return rdic_node_references_equal(n.rdic_ref, m.rdic_ref);
 }
 #endif
 
@@ -183,10 +183,10 @@ typedef struct {
 
 typedef struct GUI_Subtree GUI_Subtree;
 struct GUI_Subtree {
+	// NOTE(Zelaven): We are maintaining an immediate interface of subtrees too.
+	RDIC_Node rdic_node;
+
 	RDIC_Context rdic;
-	GUI_Subtree *prev;
-	GUI_Subtree *next;
-	GUI_Subtree *structural_parent;
 
 	// TODO(Zelaven):
 	// GUI_Rectangle cliprect;
@@ -199,13 +199,23 @@ struct GUI_Subtree {
 	int offset_own_size_percentage_x;
 	int offset_own_size_percentage_y;
 };
+typedef union GUI_Subtree_Reference {
+	RDIC_Node_Reference rdic_ref;
+	struct {
+		GUI_Subtree *node;
+		unsigned int generation;
+	};
+} GUI_Subtree_Reference;
 
 
 typedef struct {
-	GUI_Subtree *first_subtree;
+	RDIC_Context subtree_rdic;
+	//GUI_Subtree *first_subtree;
 	//GUI_Subtree *last_subtree;
 	//GUI_Subtree *current_subtree;
 
+	GUI_Subtree_Reference root_subtree;
+
 	GUI_Draw_Command *first_draw_command;
 	int num_draw_commands;
 	Pixel_Buffer pixel_buffer;
@@ -217,11 +227,13 @@ typedef struct {
 
 	//GUI_Subtree *first_subtree;
 	//GUI_Subtree *last_subtree;
-	GUI_Subtree *current_subtree;
+	//GUI_Subtree *current_subtree;
 
 	GUI_Layer background_layer;
 	GUI_Layer top_layer;
 
+	GUI_Layer *current_layer;
+
 	GUI_Node_Reference focused_node;
 	GUI_Node_Reference hovered_node;
 	GUI_Node_Reference top_node_under_cursor;
@@ -231,7 +243,8 @@ typedef struct {
 	int mouse_y;
 
 	// TODO: An allocator for the nodes.
-	RDIC_Node *node_freelist;
+	RDIC_Freelist *node_freelist;
+	RDIC_Freelist *subtree_freelist;
 
 	Memory_Arena *draw_command_arena;
 	int num_draw_commands;
@@ -328,6 +341,13 @@ void gui_apply_input(
 	GUI_Context *context,
 	int mouse_x,
 	int mouse_y)
+{
+	(void)context;
+	(void)mouse_x;
+	(void)mouse_y;
+	return;
+}
+#if 0
 {
 	// --- Mouse Input ---
 	// NOTE(Zelaven): First hit test against layers.
@@ -371,6 +391,7 @@ void gui_apply_input(
 		top_node_under_cursor->debug_string.length,
 		top_node_under_cursor->debug_string.cstring);
 }
+#endif
 
 
 GUI_Node_Reference gui_get_node(
@@ -380,10 +401,17 @@ GUI_Node_Reference gui_get_node(
 	GUI_Style *style,
 	GUI_Size size[static 2])
 {
+	GUI_Layer *current_layer = context->current_layer;
+	if(current_layer == NULL) {
+		return (GUI_Node_Reference){0};
+	}
+	GUI_Subtree *current_subtree =
+		(GUI_Subtree*)current_layer->subtree_rdic.frame_current_node;
 	int get_node_flags = 0;
 	GUI_Node_Reference new_reference = {
-		.rdic = rdic_get_node(
-			&context->current_subtree->rdic, last_reference.rdic, &get_node_flags),
+		.rdic_ref = rdic_get_node(
+			//&context->current_subtree->rdic, last_reference.rdic, &get_node_flags),
+			&current_subtree->rdic, last_reference.rdic_ref, &get_node_flags),
 	};
 	GUI_Node *node = new_reference.node;
 	node->layout_direction = direction;
@@ -407,9 +435,70 @@ GUI_Node_Reference gui_get_node(
 	node->dirty = (get_node_flags & RDIC_GET_NODE__NODE_ALLOCATED) != 0;
 
 
+	return new_reference;
+}
+GUI_Subtree_Reference gui_get_subtree(
+	GUI_Context *context,
+	GUI_Subtree_Reference last_reference)
+{
+	GUI_Layer *current_layer = context->current_layer;
+	if(current_layer == NULL) {
+		return (GUI_Subtree_Reference){0};
+	}
+	RDIC_Context *subtree_rdic = &current_layer->subtree_rdic;
+	RDIC_Node *old_subtree_freelist_head = subtree_rdic->freelist->head;
+	int get_node_flags = 0;
+	GUI_Subtree_Reference new_reference = {
+		.rdic_ref = rdic_get_node(
+			//&context->current_subtree->rdic, last_reference.rdic, &get_node_flags),
+			subtree_rdic, last_reference.rdic_ref, &get_node_flags),
+	};
+	GUI_Subtree *subtree = new_reference.node;
+	subtree->rdic = (RDIC_Context){0};
+	subtree->relative_to = (GUI_Node_Reference){0};
+	subtree->flat_offset_x = 0;
+	subtree->flat_offset_y = 0;
+	subtree->offset_relative_node_percentage_x = 0;
+	subtree->offset_relative_node_percentage_y = 0;
+	subtree->offset_own_size_percentage_x = 0;
+	subtree->offset_own_size_percentage_y = 0;
+
+	// TODO(Zelaven):
+	// get_node_flags & RDIC_GET_NODE__OUT_OF_FREELIST
+	// ^ This should result in an attempt to allocate more nodes for the freelist.
+	// Then rdic_get_node should be retried.
+
+	if(get_node_flags & RDIC_GET_NODE__NODES_COLLECTED)
+	{
+		// NOTE(Zelaven): Some subtrees were collected, which means that their RDIC
+		//  node trees should be collected too.
+		for(
+			RDIC_Node *i = subtree_rdic->freelist->head;
+			i != old_subtree_freelist_head;
+			i = i->sibling)
+		{
+			GUI_Subtree *subtree = (GUI_Subtree*)i;
+			rdic_cull_subtrees(&subtree->rdic, subtree->rdic.root);
+		}
+	}
+
+#if 0
+	if(get_node_flags & RDIC_GET_NODE__NODES_COLLECTED)
+	{
+		GUI_NODE_PARENT(node)->dirty = true;
+	}
+	if(get_node_flags & RDIC_GET_NODE__NODE_ALLOCATED)
+	{
+		GUI_NODE_PARENT(node)->dirty = true;
+	}
+	node->dirty = (get_node_flags & RDIC_GET_NODE__NODE_ALLOCATED) != 0;
+#endif
+
+
 	return new_reference;
 }
 
+
 #undef ENABLE_DEBUG
 #define ENABLE_DEBUG 0
 // TODO(Zelaven): Make this cause redrawing of root on parameter change.
@@ -438,16 +527,34 @@ GUI_Node_Reference gui_context_start_frame(
 		context->mouse_x, context->mouse_y,
 		context->mouse_pressed, context->mouse_down);
 
-	static GUI_Subtree background_subtree = {0};
-	background_subtree.rdic.node_freelist = context->node_freelist;
-	context->background_layer.first_subtree = &background_subtree;
+	context->current_layer = &context->background_layer;
+
+	GUI_Subtree_Reference root_subtree = context->current_layer->root_subtree;
+	//root_subtree = gui_get_subtree(context, root_subtree);
+	root_subtree.rdic_ref = rdic_context_start_frame(
+		&context->current_layer->subtree_rdic, root_subtree.rdic_ref);
+	if(root_subtree.node == NULL)
+	{
+		return (GUI_Node_Reference){0};
+	}
+	context->current_layer->root_subtree = root_subtree;
+	root_subtree.node->rdic.freelist = context->node_freelist;
+
+	//static GUI_Subtree background_subtree = {0};
+	//background_subtree.rdic.freelist = context->node_freelist;
+	//context->background_layer.first_subtree = &background_subtree;
 	//context->background_layer.last_subtree = &background_subtree;
-	context->current_subtree = &background_subtree;
+	//context->current_subtree = &background_subtree;
 
 	GUI_Node_Reference new_root_reference = {
-		.rdic = rdic_context_start_frame(
-			&background_subtree.rdic, last_root_reference.rdic)
+		.rdic_ref = rdic_context_start_frame(
+			//&background_subtree.rdic, last_root_reference.rdic)
+			&root_subtree.node->rdic, last_root_reference.rdic_ref)
 	};
+	if(new_root_reference.node == NULL)
+	{
+		return (GUI_Node_Reference){0};
+	}
 	//RDIC_Node_Reference new_root_reference = rdic_context_start_frame(
 	//	&background_subtree.rdic,
 	//	last_root_reference);
@@ -475,35 +582,38 @@ GUI_Node_Reference gui_context_start_frame(
 void gui_context_finish_frame(
 	GUI_Context *context)
 {
-	rdic_context_finish_frame(&context->background_layer.first_subtree->rdic);
-	context->node_freelist =
-		context->background_layer.first_subtree->rdic.node_freelist;
+	//rdic_context_finish_frame(&context->background_layer.first_subtree->rdic);
+	rdic_context_finish_frame(&context->background_layer.root_subtree.node->rdic);
+	//context->node_freelist =
+	//	context->background_layer.first_subtree->rdic.node_freelist;
 }
 
 GUI_Node_Reference gui_push_subtree(
 	GUI_Context *context,
-	GUI_Subtree *subtree,
+	GUI_Subtree_Reference subtree,
 	GUI_Node_Reference last_root_reference,
 	GUI_Layout_Direction layout_direction,
 	GUI_Style *style,
 	GUI_Size size[static 2],
 	GUI_Node_Reference relative_to)
 {
-	context->node_freelist = context->current_subtree->rdic.node_freelist;
-	subtree->rdic.node_freelist = context->node_freelist;
+	RDIC_Context *layer_rdic_context = &context->current_layer->subtree_rdic;
+	rdic_push_parent(layer_rdic_context, subtree.rdic_ref);
+	//context->node_freelist = context->current_subtree->rdic.node_freelist;
+	//subtree->rdic.node_freelist = context->node_freelist;
 
 	// NOTE(Zelaven): Well, not being able to do this is a problem...
 	//context->last_subtree->next = subtree;
 	//subtree->prev = context->last_subtree;
 	//context->last_subtree = subtree;
 
-	subtree->structural_parent = context->current_subtree;
-	context->current_subtree = subtree;
-	subtree->relative_to = relative_to;
+	//subtree->structural_parent = context->current_subtree;
+	//context->current_subtree = subtree;
+	subtree.node->relative_to = relative_to;
 
 	GUI_Node_Reference new_root_reference = {
-		.rdic = rdic_context_start_frame(
-			&subtree->rdic, last_root_reference.rdic)
+		.rdic_ref = rdic_context_start_frame(
+			&subtree.node->rdic, last_root_reference.rdic_ref)
 	};
 	GUI_Node *root = (GUI_Node*)new_root_reference.node;
 	root->dirty = false;
@@ -526,9 +636,12 @@ GUI_Node_Reference gui_push_subtree(
 void gui_pop_subtree(
 	GUI_Context *context)
 {
-	context->node_freelist = context->current_subtree->rdic.node_freelist;
-	context->current_subtree = context->current_subtree->structural_parent;
-	context->current_subtree->rdic.node_freelist = context->node_freelist;
+	//context->node_freelist = context->current_subtree->rdic.node_freelist;
+	//context->current_subtree = context->current_subtree->structural_parent;
+	//context->current_subtree->rdic.node_freelist = context->node_freelist;
+
+	RDIC_Context *layer_rdic_context = &context->current_layer->subtree_rdic;
+	rdic_pop_parent(layer_rdic_context);
 }
 
 
@@ -536,13 +649,19 @@ void gui_push_parent(
 	GUI_Context *context,
 	GUI_Node_Reference parent)
 {
-	rdic_push_parent(&context->current_subtree->rdic, parent.rdic);
+	GUI_Layer *current_layer = context->current_layer;
+	GUI_Subtree *current_subtree =
+		(GUI_Subtree*)current_layer->subtree_rdic.frame_current_node;
+	rdic_push_parent(&current_subtree->rdic, parent.rdic_ref);
 }
 
 void gui_pop_parent(
 	GUI_Context *context)
 {
-	rdic_pop_parent(&context->current_subtree->rdic);
+	GUI_Layer *current_layer = context->current_layer;
+	GUI_Subtree *current_subtree =
+		(GUI_Subtree*)current_layer->subtree_rdic.frame_current_node;
+	rdic_pop_parent(&current_subtree->rdic);
 }
 
 
@@ -1431,6 +1550,7 @@ void test_gui__draw_command_using_sliders(
 }
 
 
+#if 0
 void test_gui__subtree(
 	GUI_Context *context,
 	GUI_Rectangle full_gui_rectangle)
@@ -1544,6 +1664,7 @@ void test_gui__subtree(
 
 	gui_context_finish_frame(context);
 }
+#endif
 
 
 #if 0
@@ -2749,8 +2870,21 @@ void init_node_freelist(GUI_Node *nodes, int node_count)
 	}
 	nodes[node_count-1].rdic_node = (RDIC_Node){0};
 }
+void init_subtree_freelist(GUI_Subtree *nodes, int subtree_count)
+{
+	// NOTE(Zelaven): We special-case the last node.
+	for(int i = 0; i < subtree_count -1; i++)
+	{
+		nodes[i] = (GUI_Subtree){0};
+		nodes[i].rdic_node = (RDIC_Node){
+			.sibling = &((nodes+i+1)->rdic_node),
+		};
+	}
+	nodes[subtree_count-1].rdic_node = (RDIC_Node){0};
+}
 
 GUI_Node g_gui_node_freelist[128];
+GUI_Subtree g_gui_subtree_freelist[16];
 
 
 
@@ -3026,11 +3160,11 @@ int main(void)
 
 	// GUI initializaiton.
 
-	//gui = test_gui;
+	gui = test_gui;
 	//gui = test_gui__calculator;
 	//gui = test_gui__scrollbars;
 	//gui = test_gui__draw_command_using_sliders;
-	gui = test_gui__subtree;
+	//gui = test_gui__subtree;
 
 	X11_Window xwindow = {0};
 	int xinit_status = init_x11(&xwindow);
@@ -3050,7 +3184,18 @@ int main(void)
 	context.rdic.node_freelist = &g_gui_node_freelist[0].rdic_node;
 #else
 	init_node_freelist(g_gui_node_freelist, ARRAYLENGTH(g_gui_node_freelist));
-	context.node_freelist = &g_gui_node_freelist[0].rdic_node;
+	RDIC_Freelist node_freelist = {&g_gui_node_freelist[0].rdic_node};
+	context.node_freelist = &node_freelist;
+	init_subtree_freelist(g_gui_subtree_freelist, ARRAYLENGTH(g_gui_subtree_freelist));
+	RDIC_Freelist subtree_freelist = {&g_gui_subtree_freelist[0].rdic_node};
+	context.subtree_freelist = &subtree_freelist;
+
+	context.background_layer = (GUI_Layer){
+		.subtree_rdic.freelist = &subtree_freelist,
+	};
+	context.top_layer = (GUI_Layer){
+		.subtree_rdic.freelist = &subtree_freelist,
+	};
 #endif
 
 	context.draw_command_arena = &draw_command_arena;
@@ -3190,9 +3335,9 @@ int main(void)
 			//gui_layout_nodes(&context);
 			#if 1
 			for(
-				GUI_Subtree *current = context.background_layer.first_subtree;
+				GUI_Subtree *current = (GUI_Subtree*)context.background_layer.subtree_rdic.root;
 				current != NULL;
-				current = current->next)
+				current = NULL)//current->next)
 			{
 				gui_layout_nodes((GUI_Node*)current->rdic.root);
 				gui_generate_draw_commands(