Add 2d/navigation_astar demo for grid-based pathfinding

This includes a commented version of the code for learning purposes
There's a bug in the console every time you call AStar.get_point_path(): Condition p_elem->_root is true
The demo still runs no problem but some help and feedback would be much appreciated.

closes #235

2d/navigation_astar/Game.tscn

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+[gd_scene load_steps=3 format=2]
+
+[ext_resource path="res://tileset/tileset.tres" type="TileSet" id=1]
+[ext_resource path="res://pathfind_astar.gd" type="Script" id=2]
+
+[node name="Game" type="Node" index="0"]
+
+[node name="TileMap" type="TileMap" parent="." index="0"]
+
+mode = 0
+tile_set = ExtResource( 1 )
+cell_size = Vector2( 64, 64 )
+cell_quadrant_size = 16
+cell_custom_transform = Transform2D( 1, 0, 0, 1, 0, 0 )
+cell_half_offset = 2
+cell_tile_origin = 0
+cell_y_sort = false
+cell_clip_uv = false
+collision_use_kinematic = false
+collision_friction = 1.0
+collision_bounce = 0.0
+collision_layer = 1
+collision_mask = 1
+occluder_light_mask = 1
+format = 1
+tile_data = PoolIntArray( 65537, 0, 0, 65541, 0, 0, 65545, 0, 0, 65550, 0, 0, 196614, 0, 0, 196615, 0, 0, 196616, 0, 0, 196617, 0, 0, 196618, 0, 0, 196619, 0, 0, 262145, 0, 0, 262146, 0, 0, 262147, 0, 0, 327683, 0, 0, 393219, 0, 0, 393220, 0, 0, 393221, 0, 0, 393222, 0, 0, 393226, 0, 0, 393227, 0, 0, 393228, 0, 0, 458761, 0, 0, 524290, 0, 0, 524291, 0, 0, 524292, 0, 0, 524293, 0, 0, 524294, 0, 0, 524295, 0, 0, 524296, 0, 0, 524297, 0, 0 )
+script = ExtResource( 2 )
+_sections_unfolded = [ "Cell" ]
+map_size = Vector2( 16, 16 )
+
+

2d/navigation_astar/default_env.tres

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+[gd_resource type="Environment" load_steps=2 format=2]
+
+[sub_resource type="ProceduralSky" id=1]
+
+radiance_size = 4
+sky_top_color = Color( 0.0470588, 0.454902, 0.976471, 1 )
+sky_horizon_color = Color( 0.556863, 0.823529, 0.909804, 1 )
+sky_curve = 0.25
+sky_energy = 1.0
+ground_bottom_color = Color( 0.101961, 0.145098, 0.188235, 1 )
+ground_horizon_color = Color( 0.482353, 0.788235, 0.952941, 1 )
+ground_curve = 0.01
+ground_energy = 1.0
+sun_color = Color( 1, 1, 1, 1 )
+sun_latitude = 35.0
+sun_longitude = 0.0
+sun_angle_min = 1.0
+sun_angle_max = 100.0
+sun_curve = 0.05
+sun_energy = 16.0
+texture_size = 2
+
+[resource]
+
+background_mode = 2
+background_sky = SubResource( 1 )
+background_sky_custom_fov = 0.0
+background_color = Color( 0, 0, 0, 1 )
+background_energy = 1.0
+background_canvas_max_layer = 0
+ambient_light_color = Color( 0, 0, 0, 1 )
+ambient_light_energy = 1.0
+ambient_light_sky_contribution = 1.0
+fog_enabled = false
+fog_color = Color( 0.5, 0.6, 0.7, 1 )
+fog_sun_color = Color( 1, 0.9, 0.7, 1 )
+fog_sun_amount = 0.0
+fog_depth_enabled = true
+fog_depth_begin = 10.0
+fog_depth_curve = 1.0
+fog_transmit_enabled = false
+fog_transmit_curve = 1.0
+fog_height_enabled = false
+fog_height_min = 0.0
+fog_height_max = 100.0
+fog_height_curve = 1.0
+tonemap_mode = 0
+tonemap_exposure = 1.0
+tonemap_white = 1.0
+auto_exposure_enabled = false
+auto_exposure_scale = 0.4
+auto_exposure_min_luma = 0.05
+auto_exposure_max_luma = 8.0
+auto_exposure_speed = 0.5
+ss_reflections_enabled = false
+ss_reflections_max_steps = 64
+ss_reflections_fade_in = 0.15
+ss_reflections_fade_out = 2.0
+ss_reflections_depth_tolerance = 0.2
+ss_reflections_roughness = true
+ssao_enabled = false
+ssao_radius = 1.0
+ssao_intensity = 1.0
+ssao_radius2 = 0.0
+ssao_intensity2 = 1.0
+ssao_bias = 0.01
+ssao_light_affect = 0.0
+ssao_color = Color( 0, 0, 0, 1 )
+ssao_quality = 0
+ssao_blur = 3
+ssao_edge_sharpness = 4.0
+dof_blur_far_enabled = false
+dof_blur_far_distance = 10.0
+dof_blur_far_transition = 5.0
+dof_blur_far_amount = 0.1
+dof_blur_far_quality = 1
+dof_blur_near_enabled = false
+dof_blur_near_distance = 2.0
+dof_blur_near_transition = 1.0
+dof_blur_near_amount = 0.1
+dof_blur_near_quality = 1
+glow_enabled = false
+glow_levels/1 = false
+glow_levels/2 = false
+glow_levels/3 = true
+glow_levels/4 = false
+glow_levels/5 = true
+glow_levels/6 = false
+glow_levels/7 = false
+glow_intensity = 0.8
+glow_strength = 1.0
+glow_bloom = 0.0
+glow_blend_mode = 2
+glow_hdr_threshold = 1.0
+glow_hdr_scale = 2.0
+glow_bicubic_upscale = false
+adjustment_enabled = false
+adjustment_brightness = 1.0
+adjustment_contrast = 1.0
+adjustment_saturation = 1.0
+

2d/navigation_astar/icon.png.import

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+[remap]
+
+importer="texture"
+type="StreamTexture"
+path="res://.import/icon.png-487276ed1e3a0c39cad0279d744ee560.stex"
+
+[deps]
+
+source_file="res://icon.png"
+source_md5="0b0cb045ce690875fab066adeea76aba"
+
+dest_files=[ "res://.import/icon.png-487276ed1e3a0c39cad0279d744ee560.stex" ]
+dest_md5="58323f97585db7bd8d6e03320f9ebb33"
+
+[params]
+
+compress/mode=0
+compress/lossy_quality=0.7
+compress/hdr_mode=0
+compress/normal_map=0
+flags/repeat=0
+flags/filter=true
+flags/mipmaps=false
+flags/anisotropic=false
+flags/srgb=2
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/HDR_as_SRGB=false
+stream=false
+size_limit=0
+detect_3d=true
+svg/scale=1.0

2d/navigation_astar/pathfind_astar.gd

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+extends TileMap
+
+# You can only create an AStar node from code, not from the Scene tab
+onready var astar_node = AStar.new()
+# The Tilemap node doesn't have clear bounds so we're defining the map's limits here
+export(Vector2) var map_size = Vector2(16, 16)
+
+# The path start and end variables use setter methods
+# You can find them at the bottom of the script
+var path_start_position = Vector2() setget _set_path_start_position
+var path_end_position = Vector2() setget _set_path_end_position
+
+var _point_path = []
+
+const BASE_LINE_WIDTH = 3.0
+const DRAW_COLOR = Color('#fff')
+
+# get_used_cells_by_id is a method from the TileMap node
+# here the id 0 corresponds to the grey tile, the obstacles
+onready var obstacles = get_used_cells_by_id(0)
+onready var _half_cell_size = cell_size / 2
+
+func _ready():
+	var walkable_cells_list = astar_add_walkable_cells(obstacles)
+	astar_connect_walkable_cells(walkable_cells_list)
+
+
+# Click and Shift force the start and end position of the path to update
+# and the node to redraw everything
+func _input(event):
+	if event.is_action_pressed('click') and Input.is_key_pressed(KEY_SHIFT):
+		# To call the setter method from this script we have to use the explicit self.
+		self.path_start_position = world_to_map(get_global_mouse_position())
+	elif event.is_action_pressed('click'):
+		self.path_end_position = world_to_map(get_global_mouse_position())
+		
+
+# Loops through all cells within the map's bounds and
+# adds all points to the astar_node, except the obstacles
+func astar_add_walkable_cells(obstacles = []):
+	var points_array = []
+	for y in range(map_size.y):
+		for x in range(map_size.x):
+			var point = Vector2(x, y)
+			if point in obstacles:
+				continue
+
+			points_array.append(point)
+			# The AStar class references points with indices
+			# Using a function to calculate the index from a point's coordinates
+			# ensures we always get the same index with the same input point
+			var point_index = calculate_point_index(point)
+			# AStar works for both 2d and 3d, so we have to convert the point
+			# coordinates from and to Vector3s
+			astar_node.add_point(point_index, Vector3(point.x, point.y, 0.0))
+	return points_array
+
+
+# Once you added all points to the AStar node, you've got to connect them
+# The points don't have to be on a grid: you can use this class
+# to create walkable graphs however you'd like
+# It's a little harder to code at first, but works for 2d, 3d,
+# orthogonal grids, hex grids, tower defense games...
+func astar_connect_walkable_cells(points_array):
+	for point in points_array:
+		var point_index = calculate_point_index(point)
+		# For every cell in the map, we check the one to the top, right.
+		# left and bottom of it. If it's in the map and not an obstalce,
+		# We connect the current point with it
+		var points_relative = PoolVector2Array([
+			Vector2(point.x + 1, point.y),
+			Vector2(point.x - 1, point.y),
+			Vector2(point.x, point.y + 1),
+			Vector2(point.x, point.y - 1)])
+		for point_relative in points_relative:
+			var point_relative_index = calculate_point_index(point_relative)
+
+			if is_outside_map_bounds(point_relative):
+				continue
+			if not astar_node.has_point(point_relative_index):
+				continue
+			# Note the 3rd argument. It tells the astar_node that we want the
+			# connection to be bilateral: from point A to B and B to A
+			# If you set this value to false, it becomes a one-way path
+			astar_node.connect_points(point_index, point_relative_index, true)
+
+
+# This is a variation of the method above
+# It connects cells horizontally, vertically AND diagonally
+func astar_connect_walkable_cells_diagonal(points_array):
+	for point in points_array:
+		var point_index = calculate_point_index(point)
+		for local_y in range(3):
+			for local_x in range(3):
+				var point_relative = Vector2(point.x + local_x - 1, point.y + local_y - 1)
+				var point_relative_index = calculate_point_index(point_relative)
+
+				if point_relative == point or is_outside_map_bounds(point_relative):
+					continue
+				if not astar_node.has_point(point_relative_index):
+					continue
+				astar_node.connect_points(point_index, point_relative_index, true)
+
+
+func is_outside_map_bounds(point):
+	return point.x < 0 or point.y < 0 or point.x >= map_size.x or point.y >= map_size.y
+
+
+func calculate_point_index(point):
+	return point.x + map_size.x * point.y
+
+
+func recalculate_path():
+	clear_previous_path_drawing()
+	var start_point_index = calculate_point_index(path_start_position)
+	var end_point_index = calculate_point_index(path_end_position)
+	# This method gives us an array of points. Note you need the start and end
+	# points' indices as input
+	_point_path = astar_node.get_point_path(start_point_index, end_point_index)
+	# Redraw the lines and circles from the start to the end point
+	update()
+
+
+func clear_previous_path_drawing():
+	if not _point_path:
+		return
+	var point_start = _point_path[0]
+	var point_end = _point_path[len(_point_path) - 1]
+	set_cell(point_start.x, point_start.y, -1)
+	set_cell(point_end.x, point_end.y, -1)
+
+
+func _draw():
+	if not _point_path:
+		return
+	var point_start = _point_path[0]
+	var point_end = _point_path[len(_point_path) - 1]
+
+	set_cell(point_start.x, point_start.y, 1)
+	set_cell(point_end.x, point_end.y, 2)
+
+	var last_point = map_to_world(Vector2(point_start.x, point_start.y)) + _half_cell_size
+	for index in range(1, len(_point_path)):
+		var current_point = map_to_world(Vector2(_point_path[index].x, _point_path[index].y)) + _half_cell_size
+		draw_line(last_point, current_point, DRAW_COLOR, BASE_LINE_WIDTH, true)
+		draw_circle(current_point, BASE_LINE_WIDTH * 2.0, DRAW_COLOR)
+		last_point = current_point
+
+
+# Setters for the start and end path values.
+func _set_path_start_position(value):
+	if value in obstacles:
+		return
+	if is_outside_map_bounds(value):
+		return
+
+	set_cell(path_start_position.x, path_start_position.y, -1)
+	set_cell(value.x, value.y, 1)
+	path_start_position = value
+	if path_end_position and path_end_position != path_start_position:
+		recalculate_path()
+
+
+func _set_path_end_position(value):
+	if value in obstacles:
+		return
+	if is_outside_map_bounds(value):
+		return
+
+	set_cell(path_start_position.x, path_start_position.y, -1)
+	set_cell(value.x, value.y, 2)
+	path_end_position = value
+	if path_start_position != value:
+		recalculate_path()

2d/navigation_astar/project.godot

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+; Engine configuration file.
+; It's best edited using the editor UI and not directly,
+; since the parameters that go here are not all obvious.
+;
+; Format:
+;   [section] ; section goes between []
+;   param=value ; assign values to parameters
+
+config_version=3
+
+[application]
+
+config/name="Grid-based pathfinding with Astar"
+run/main_scene="res://Game.tscn"
+config/icon="res://icon.png"
+
+[input]
+
+click=[ Object(InputEventMouseButton,"resource_local_to_scene":false,"resource_name":"","device":0,"alt":false,"shift":false,"control":false,"meta":false,"command":false,"button_mask":0,"position":Vector2( 0, 0 ),"global_position":Vector2( 0, 0 ),"factor":1.0,"button_index":1,"pressed":false,"doubleclick":false,"script":null)
+ ]
+
+[rendering]
+
+environment/default_environment="res://default_env.tres"

2d/navigation_astar/sprites/obstacle.png.import

@@ -0,0 +1,32 @@
+[remap]
+
+importer="texture"
+type="StreamTexture"
+path="res://.import/obstacle.png-0258c5f5ce65bfa0dd8610adeb784f54.stex"
+
+[deps]
+
+source_file="res://sprites/obstacle.png"
+source_md5="f741dc1724960a029cba51c962d988be"
+
+dest_files=[ "res://.import/obstacle.png-0258c5f5ce65bfa0dd8610adeb784f54.stex" ]
+dest_md5="432d869b849ac70d4f76935622b2e37b"
+
+[params]
+
+compress/mode=0
+compress/lossy_quality=0.7
+compress/hdr_mode=0
+compress/normal_map=0
+flags/repeat=0
+flags/filter=true
+flags/mipmaps=false
+flags/anisotropic=false
+flags/srgb=2
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/HDR_as_SRGB=false
+stream=false
+size_limit=0
+detect_3d=true
+svg/scale=1.0

2d/navigation_astar/sprites/path_end.png.import

@@ -0,0 +1,32 @@
+[remap]
+
+importer="texture"
+type="StreamTexture"
+path="res://.import/path_end.png-02b79e25892cd8d863bd44c3c5a1720e.stex"
+
+[deps]
+
+source_file="res://sprites/path_end.png"
+source_md5="be9537ddfec33fdc35a33d88cad94d38"
+
+dest_files=[ "res://.import/path_end.png-02b79e25892cd8d863bd44c3c5a1720e.stex" ]
+dest_md5="436b174ce46135e1d4d6b9b238889433"
+
+[params]
+
+compress/mode=0
+compress/lossy_quality=0.7
+compress/hdr_mode=0
+compress/normal_map=0
+flags/repeat=0
+flags/filter=true
+flags/mipmaps=false
+flags/anisotropic=false
+flags/srgb=2
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/HDR_as_SRGB=false
+stream=false
+size_limit=0
+detect_3d=true
+svg/scale=1.0

2d/navigation_astar/sprites/path_start.png.import

@@ -0,0 +1,32 @@
+[remap]
+
+importer="texture"
+type="StreamTexture"
+path="res://.import/path_start.png-475bd0b469629aa8779d506c5134e5c2.stex"
+
+[deps]
+
+source_file="res://sprites/path_start.png"
+source_md5="6b4a1211e21f4fab937c7b309d802a44"
+
+dest_files=[ "res://.import/path_start.png-475bd0b469629aa8779d506c5134e5c2.stex" ]
+dest_md5="5d90014ca7f70fa5f9494bd25fbe72d0"
+
+[params]
+
+compress/mode=0
+compress/lossy_quality=0.7
+compress/hdr_mode=0
+compress/normal_map=0
+flags/repeat=0
+flags/filter=true
+flags/mipmaps=false
+flags/anisotropic=false
+flags/srgb=2
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/HDR_as_SRGB=false
+stream=false
+size_limit=0
+detect_3d=true
+svg/scale=1.0

2d/navigation_astar/tileset/tileset.tres

@@ -0,0 +1,37 @@
+[gd_resource type="TileSet" load_steps=4 format=2]
+
+[ext_resource path="res://sprites/obstacle.png" type="Texture" id=1]
+[ext_resource path="res://sprites/path_start.png" type="Texture" id=2]
+[ext_resource path="res://sprites/path_end.png" type="Texture" id=3]
+
+[resource]
+
+0/name = "Obstacle"
+0/texture = ExtResource( 1 )
+0/tex_offset = Vector2( 0, 0 )
+0/modulate = Color( 1, 1, 1, 1 )
+0/region = Rect2( 0, 0, 64, 64 )
+0/is_autotile = false
+0/occluder_offset = Vector2( 32, 32 )
+0/navigation_offset = Vector2( 32, 32 )
+0/shapes = [  ]
+1/name = "PathStart"
+1/texture = ExtResource( 2 )
+1/tex_offset = Vector2( 0, 0 )
+1/modulate = Color( 1, 1, 1, 1 )
+1/region = Rect2( 0, 0, 64, 64 )
+1/is_autotile = false
+1/occluder_offset = Vector2( 32, 32 )
+1/navigation_offset = Vector2( 32, 32 )
+1/shapes = [  ]
+2/name = "PathEnd"
+2/texture = ExtResource( 3 )
+2/tex_offset = Vector2( 0, 0 )
+2/modulate = Color( 1, 1, 1, 1 )
+2/region = Rect2( 0, 0, 64, 64 )
+2/is_autotile = false
+2/occluder_offset = Vector2( 32, 32 )
+2/navigation_offset = Vector2( 32, 32 )
+2/shapes = [  ]
+_sections_unfolded = [ "2" ]
+

2d/navigation_astar/tileset/tileset_source.tscn

@@ -0,0 +1,24 @@
+[gd_scene load_steps=4 format=2]
+
+[ext_resource path="res://sprites/obstacle.png" type="Texture" id=1]
+[ext_resource path="res://sprites/path_start.png" type="Texture" id=2]
+[ext_resource path="res://sprites/path_end.png" type="Texture" id=3]
+
+[node name="Node2D" type="Node2D" index="0"]
+
+[node name="Obstacle" type="Sprite" parent="." index="0"]
+
+position = Vector2( 32, 32 )
+texture = ExtResource( 1 )
+
+[node name="PathStart" type="Sprite" parent="." index="1"]
+
+position = Vector2( 112, 32 )
+texture = ExtResource( 2 )
+
+[node name="PathEnd" type="Sprite" parent="." index="2"]
+
+position = Vector2( 192, 32 )
+texture = ExtResource( 3 )
+
+