Add dynamic TileMap layer demo (#954)

2d/dynamic_tilemap_layers/level/obstacle.png.import

@@ -0,0 +1,34 @@
+[remap]
+
+importer="texture"
+type="CompressedTexture2D"
+uid="uid://cs8h2qyuakmko"
+path="res://.godot/imported/obstacle.png-06287f6b2d26dd03335fd87ab78c2cc2.ctex"
+metadata={
+"vram_texture": false
+}
+
+[deps]
+
+source_file="res://level/obstacle.png"
+dest_files=["res://.godot/imported/obstacle.png-06287f6b2d26dd03335fd87ab78c2cc2.ctex"]
+
+[params]
+
+compress/mode=0
+compress/high_quality=false
+compress/lossy_quality=0.7
+compress/hdr_compression=1
+compress/normal_map=0
+compress/channel_pack=0
+mipmaps/generate=false
+mipmaps/limit=-1
+roughness/mode=0
+roughness/src_normal=""
+process/fix_alpha_border=true
+process/premult_alpha=false
+process/normal_map_invert_y=false
+process/hdr_as_srgb=false
+process/hdr_clamp_exposure=false
+process/size_limit=0
+detect_3d/compress_to=1

2d/dynamic_tilemap_layers/level/tile_map.gd

@@ -0,0 +1,57 @@
+extends TileMap
+
+
+var secret_layer: int # You can have multiple layers if you make this an array.
+var player_in_secret: bool
+var layer_alpha := 1.0
+
+
+func _init() -> void:
+	for i in get_layers_count(): # Find the secret layer by name.
+		if get_layer_name(i) == "Secret":
+			secret_layer = i
+
+
+func _ready() -> void:
+	set_process(false)
+
+
+func _process(delta: float) -> void:
+	if player_in_secret:
+		if layer_alpha > 0.3:
+			layer_alpha = move_toward(layer_alpha, 0.3, delta) # Animate the layer transparency.
+			set_layer_modulate(secret_layer, Color(1, 1, 1, layer_alpha))
+		else:
+			set_process(false)
+	else:
+		if layer_alpha < 1.0:
+			layer_alpha = move_toward(layer_alpha, 1.0, delta)
+			set_layer_modulate(secret_layer, Color(1, 1, 1, layer_alpha))
+		else:
+			set_process(false)
+
+
+func _use_tile_data_runtime_update(layer: int, _coords: Vector2i) -> bool:
+	if layer == secret_layer:
+		return true
+	return false
+
+
+func _tile_data_runtime_update(_layer: int, _coords: Vector2i, tile_data: TileData) -> void:
+	tile_data.set_collision_polygons_count(0, 0) # Remove collision for secret layer.
+
+
+func _on_secret_detector_body_entered(body: Node2D) -> void:
+	if not body is CharacterBody2D: # Detect player only.
+		return
+
+	player_in_secret = true
+	set_process(true)
+
+
+func _on_secret_detector_body_exited(body: Node2D) -> void:
+	if not body is CharacterBody2D:
+		return
+
+	player_in_secret = false
+	set_process(true)