back_face="" for cards no longer throws an error.

If the back_face property is blank, then a black 1x1 texture is used
in it's place.

This commit fixes #118.

game/Images/BlackTexture.bmp.import

@@ -0,0 +1,35 @@
+[remap]
+
+importer="texture"
+type="StreamTexture"
+path="res://.import/BlackTexture.bmp-197d845b0d42dd143a03649ed7fda370.stex"
+metadata={
+"vram_texture": false
+}
+
+[deps]
+
+source_file="res://Images/BlackTexture.bmp"
+dest_files=[ "res://.import/BlackTexture.bmp-197d845b0d42dd143a03649ed7fda370.stex" ]
+
+[params]
+
+compress/mode=3
+compress/lossy_quality=0.7
+compress/hdr_mode=0
+compress/bptc_ldr=0
+compress/normal_map=2
+flags/repeat=0
+flags/filter=false
+flags/mipmaps=false
+flags/anisotropic=false
+flags/srgb=0
+process/fix_alpha_border=false
+process/premult_alpha=false
+process/HDR_as_SRGB=false
+process/invert_color=false
+process/normal_map_invert_y=false
+stream=false
+size_limit=0
+detect_3d=false
+svg/scale=1.0

game/Scripts/AssetDB.gd

@@ -1024,6 +1024,8 @@ func _import_asset(from: String, pack: String, type: String, config: ConfigFile,
 						print("Loaded back face: %s" % back_path)
 					else:
 						push_error("Failed to import '%s' (error %d)!" % [back_path, back_err])
+			else:
+				entry["texture_path_1"] = ""
 		
 		elif type.begins_with("containers"):
 			entry["shakable"] = _get_file_config_value(config, from.get_file(), "shakable", false)
@@ -1622,7 +1624,7 @@ func _is_valid_entry(pack: String, type: String, entry: Dictionary) -> bool:
 					push_error("'texture_path_1' in entry is not a string!")
 					return false
 				
-				if not _is_valid_path(value, VALID_TEXTURE_EXTENSIONS):
+				if not (value.empty() or _is_valid_path(value, VALID_TEXTURE_EXTENSIONS)):
 					push_error("'texture_path_1' in entry is not a valid path!")
 					return false
 			"url":

game/Scripts/Game/Pieces/StackSandwich.gd

@@ -124,9 +124,16 @@ func _set_sandwich_display() -> void:
 	var front_key = "texture_path"
 	if front_flip:
 		front_key += "_1"
+	var front_path: String = front_entry[front_key]
+	var front_texture: Texture
+	if not front_path.empty():
+		front_texture = ResourceManager.load_res(front_path)
+	else:
+		front_texture = preload("res://Images/BlackTexture.bmp")
+	
 	var front_material = SpatialMaterial.new()
 	front_material.albedo_color = front_entry["color"]
-	front_material.albedo_texture = ResourceManager.load_res(front_entry[front_key])
+	front_material.albedo_texture = front_texture
 	sandwich.set_surface_material(0, front_material)
 	
 	var back_meta = _pieces[0]
@@ -136,7 +143,14 @@ func _set_sandwich_display() -> void:
 	var back_key = "texture_path"
 	if not back_flip:
 		back_key += "_1"
+	var back_path: String = back_entry[back_key]
+	var back_texture: Texture
+	if not back_path.empty():
+		back_texture = ResourceManager.load_res(back_path)
+	else:
+		back_texture = preload("res://Images/BlackTexture.bmp")
+	
 	var back_material = SpatialMaterial.new()
 	back_material.albedo_color = back_entry["color"]
-	back_material.albedo_texture = ResourceManager.load_res(back_entry[back_key])
+	back_material.albedo_texture = back_texture
 	sandwich.set_surface_material(1, back_material)

game/Scripts/PieceBuilder.gd

@@ -116,8 +116,13 @@ func build_piece(piece_entry: Dictionary, extra_nodes: bool = true) -> Piece:
 		# Check if the entry has textures for more than one surface.
 		var surface = 1
 		while piece_entry.has("texture_path_" + str(surface)):
-			texture = ResourceManager.load_res(piece_entry["texture_path_" + str(surface)])
-			piece.apply_texture(texture, surface)
+			var texture_path: String = piece_entry["texture_path_" + str(surface)]
+			var optional_texture: Texture
+			if not texture_path.empty():
+				optional_texture = ResourceManager.load_res(texture_path)
+			else:
+				optional_texture = preload("res://Images/BlackTexture.bmp")
+			piece.apply_texture(optional_texture, surface)
 			surface += 1
 	
 	if piece.is_albedo_color_exposed():