Make research tree vertically scrollable

BuildController.gd

@@ -282,6 +282,8 @@ func _unhandled_input(event: InputEvent) -> void:
 	if skill_menu.visible:
 		if event is InputEventScreenTouch:
 			skill_tree.handle_touch(event)
+		elif event is InputEventScreenDrag:
+			skill_tree.handle_drag(event)
 		# Handled either way. A touch that lands on the panel but misses a
 		# node is still a touch ON THE PANEL - letting it through moved the
 		# fleet and pinch-zoomed the world behind the menu, because
@@ -409,6 +411,7 @@ func _on_action_pressed() -> void:
 
 	if current_building.building_type == GameState.BUILDING_MOTHERSHIP:
 		skill_menu.visible = true
+		skill_tree.reset_scroll()
 		_refresh_skill_menu()
 	elif current_building.building_type == GameState.BUILDING_SHIP_CRAFTER:
 		# Remembered explicitly: _process() clears current_building while any

GameState.gd

@@ -157,7 +157,7 @@ const SKILL_TREE: Array = [
 	},
 	{
 		"id": "coordination", "name": "Coordination", "cost": 20, "requires": "shipyards",
-		"x": 0.82, "unlocks": BUILDING_COMMAND_CENTER,
+		"x": 0.50, "unlocks": BUILDING_COMMAND_CENTER,
 		"desc": "Build command centers, where the fleet formation is arranged.",
 	},
 	{
@@ -167,12 +167,12 @@ const SKILL_TREE: Array = [
 	},
 	{
 		"id": "vessel_science", "name": "Vessel Science", "cost": 35, "requires": "shipyards",
-		"x": 0.62, "unlocks": BUILDING_SHIP_LAB,
+		"x": 0.82, "unlocks": BUILDING_SHIP_LAB,
 		"desc": "Build ship labs, where each vessel type is upgraded and new ones unlocked.",
 	},
 	{
 		"id": "freight_yards", "name": "Freight Yards", "cost": 80, "requires": "freight",
-		"x": 0.05, "hub_bonus": 1,
+		"x": 0.18, "hub_bonus": 1,
 		"desc": "Permanent: +1 transporter stationed at every hub, including ones already built.",
 	},
 	{
@@ -182,12 +182,12 @@ const SKILL_TREE: Array = [
 	},
 	{
 		"id": "squadron", "name": "Squadron Doctrine", "cost": 70, "requires": "wing",
-		"x": 0.65, "fleet_bonus": 1,
+		"x": 0.50, "fleet_bonus": 1,
 		"desc": "Permanent: +1 vessel in the fleet.",
 	},
 	{
 		"id": "armada", "name": "Armada Doctrine", "cost": 150, "requires": "squadron",
-		"x": 0.3, "fleet_bonus": 1,
+		"x": 0.50, "fleet_bonus": 1,
 		"desc": "Permanent: +1 vessel in the fleet.",
 	},
 ]

Main.tscn

@@ -1556,6 +1556,7 @@ script = ExtResource("24")
 
 [node name="Tree" type="Control" parent="UI/SkillMenu"]
 mouse_filter = 2
+clip_contents = true
 anchor_right = 1.0
 anchor_bottom = 1.0
 offset_left = 24.0

SkillTreeView.gd

@@ -28,25 +28,45 @@ const LOCKED_CORE: Color = Color(0.17, 0.19, 0.26)
 const LOCKED_PULSE: float = 0.5
 
 @export var node_radius: float = 46.0
+@export var row_spacing: float = 250.0
 
 var selected_id: String = ""
+var scroll_y: float = 0.0
+var _dragging: bool = false
+
+
+func _content_height() -> float:
+	# The canvas deliberately exceeds the viewport. Four depths at this
+	# spacing leave clear breathing room around 92px-wide nodes and make each
+	# research branch read as a route rising away from Shipyards.
+	return maxf(size.y, GameState.max_skill_depth() * row_spacing + node_radius * 3.0)
+
+
+func _max_scroll() -> float:
+	return maxf(0.0, _content_height() - size.y)
 
 
 func _ready() -> void:
 	mouse_filter = Control.MOUSE_FILTER_IGNORE
+	call_deferred("reset_scroll")
+
+
+func reset_scroll() -> void:
+	# Start at Shipyards, the base of the tree, whenever the menu opens.
+	# The player then swipes up to travel along the branches.
+	scroll_y = _max_scroll()
+	queue_redraw()
 
 
 func node_screen_pos(node: Dictionary) -> Vector2:
-	# Height comes from dependency depth, not from the data: the root sits at
-	# the bottom and each further prerequisite climbs a row, so the tree grows
-	# upwards as it is researched and stays correct when nodes are added.
-	var deepest: int = maxi(GameState.max_skill_depth(), 1)
-	var climb: float = float(GameState.skill_depth(node.id)) / float(deepest)
-	# Inset so a node on row 0 or column 0 is not clipped in half.
+	# Every dependency depth gets its own widely-spaced horizontal row. The
+	# x lane is stable within a branch (set beside SKILL_TREE), so Logistics,
+	# Freight and Freight Yards rise vertically instead of zig-zagging across
+	# the display. scroll_y exposes the part of this tall canvas in view.
 	var margin: float = node_radius * 1.4
 	return Vector2(
 		lerpf(margin, size.x - margin, float(node.x)),
-		lerpf(size.y - margin, margin, climb)
+		_content_height() - margin - float(GameState.skill_depth(node.id)) * row_spacing - scroll_y
 	)
 
 
@@ -61,8 +81,12 @@ func _state_color(node: Dictionary) -> Color:
 # Returns true when the press landed on a node, so the caller knows the
 # touch was consumed.
 func handle_touch(event: InputEventScreenTouch) -> bool:
-	if not event.pressed or not visible:
+	if not visible:
 		return false
+	if not event.pressed:
+		_dragging = false
+		return true
+	_dragging = true
 	var local: Vector2 = event.position - global_position
 	for node in GameState.SKILL_TREE:
 		if local.distance_to(node_screen_pos(node)) <= node_radius * 1.25:
@@ -73,6 +97,16 @@ func handle_touch(event: InputEventScreenTouch) -> bool:
 	return false
 
 
+func handle_drag(event: InputEventScreenDrag) -> bool:
+	if not visible:
+		return false
+	# Dragging a finger upward reveals higher research; dragging downward
+	# returns to the root. Clamp hard so the canvas never leaves an empty gap.
+	scroll_y = clampf(scroll_y - event.relative.y, 0.0, _max_scroll())
+	queue_redraw()
+	return true
+
+
 func _draw() -> void:
 	# Links first, so nodes sit on top of them.
 	for node in GameState.SKILL_TREE:

tests/test_hangar_management.gd.uid

@@ -0,0 +1 @@
+uid://xc7cie5ogmtp

tests/test_skill_tree.gd

@@ -105,6 +105,24 @@ func _process(delta: float) -> bool:
 				print("TEST_SKILL_TREE: FAIL (mothership has no research action)")
 				quit(1)
 				return true
+			# The tree is a tall, vertically scrolling canvas. A branch keeps a
+			# stable lane as it rises, and dragging exposes higher depths.
+			var freight: Vector2 = controller.skill_tree.node_screen_pos(game_state.skill_node("freight"))
+			var yards: Vector2 = controller.skill_tree.node_screen_pos(game_state.skill_node("freight_yards"))
+			if absf(freight.x - yards.x) > 1.0 or yards.y >= freight.y:
+				print("TEST_SKILL_TREE: FAIL (freight branch does not rise vertically)")
+				quit(1)
+				return true
+			var before_scroll: float = controller.skill_tree.scroll_y
+			var drag: InputEventScreenDrag = InputEventScreenDrag.new()
+			# Start at the root at the bottom; pull the canvas down to reveal
+			# the branches rising above it.
+			drag.relative = Vector2(0.0, 180.0)
+			controller.skill_tree.handle_drag(drag)
+			if controller.skill_tree.scroll_y >= before_scroll:
+				print("TEST_SKILL_TREE: FAIL (tree did not scroll upward)")
+				quit(1)
+				return true
 
 			# --- prerequisites --------------------------------------------
 			if game_state.can_unlock("wing"):