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Programming Excercise 1: Command Pattern

Description

The goals behind this project are 1) to allow for meaningful gameplay gameplay programming inside a Godot project, and 2) to provide working experience with the command software design pattern. This project is filled with examples of using Unity to construct basic game systems including health, hit/hurt boxes, player movement, non-player character behavior, parallax scrolling, character movement, a camera that follows the player, animated sprites, boss fights, and commands using the Command software design pattern.

Your project will be score according to the following 70-point system:

  • [10 points] Stage 1
  • [30 points] Stage 2
  • [15 points] Stage 3
  • [15 points] Stage 4

The remaining 30 points will be based on your peer review of a classmate's programming exercise submission.

The Command Pattern

Knowing the command software design pattern is critical to completing this assignment. Please consult the class recordings and readings to refresh yourself on the basic implementation details and use case for the pattern.

For this project, the core of the command pattern can be found in command.gd. The two most important items to note are the structure of the execute(character:Character) -> Status function and the enum Status. The execute() function is the common interface that all commands in the project rely on. The return values of the commands are regularized with the ACTIVE, DONE, and ERROR values with the Status enum.

class_name Command

enum Status {
	ACTIVE,
	DONE,
	ERROR,
}

func execute(_character: Character) -> Status:
	return Status.DONE

There are two main categories of Commands used by the Characters. One is used by Player to handle the player's input in real time. It relies on the physics system, the AnimationTree in the Player scene, and a state machine embedded in the AnimationTree.
The second category is commands with durations. NPCs use these to ensure character actions are correctly timed. They are also used in command lists (seen as cmd_list in boss.gd to sequence actions for use in cutscenes and scripted boss battles. The following code fragment shows the processing engine of command lists and how they interact with Command.Status enum values.

	if len(cmd_list)>0:
		var command_status:Command.Status = cmd_list.front().execute(self)
		#if command_status == Command.Status.ACTIVE:
			#Useful for debugging and sending status updates to other nodes.
		if Command.Status.DONE == command_status:
			cmd_list.pop_front()
	else:
		animation_player.play("idle")

Stage 1: Jump to it

Create a JumpCommand class that extends the Command class. This command should properly check to see if the Player is_on_floor() before initiating the jump. You need to provide an appropriate jump velocity that is consistent with the Player class so that the Player can jump over the obstacle in the level. Additionally, you are required to create a "jump" action in the project's Input Map that triggers when the space, up, or W is pressed.
Note: to make sure the jump sound effects are linked, include character.command_callback("jump") when you initiate the jump.
Note: Look for comments like #stage1 to see key code areas.

Stage 2: A Best Friend

In this stage, you will create a controller and commands for the follower.

  • A FollowerController class that is the brains behind your Follower. Through extend Character, it contains basic functionality for physics and rendering. It should also have the following functionality:
    • A _physics_process() function where the basic logic of the controller is implemented. Be sure to call super(delta) to call the movement and rendering code implemented in character.gd's Character class.
    • A _ready() function where the follower's movement_speed and jump_velocity are set.
    • When the Player is within 5 units of the Follower, the follower should initiate a FollowCommand (see below) to stay near the Player.
    • When the player is higher (i.e., Player has a more negative position.y than the Follower), the Follower should use your JumpCommand to help reach the player.
  • A FollowCommand class that enables your Follower to be near the player. This class should extend Command and include a leash member variable representing a maximum distance between the Follower and the Player. When the two are greater than leash units apart, the command should end and return Status.DONE.

You may wish to look at boss.gd for inspiration. Here is an outline to help you get started:

class_name FollowerController
extends Character 

#useful data structure for sequentially enacting commands
var cmd_list : Array[Command]

#A reference to the Player
@onready var player:Player = %Player

func _ready():
	#set movement and jump velocities

func _physics_process(delta: float) -> void:
	#controller logic
	super(delta)

Stage 3: Death by a Thousand Cutscenes

This game prototype needs some narrative design. Your task is to create a cutscene just before the boss battle to tell the current story to the player. This cutscene should be between 20 and 30 seconds long and include each of the three characters.

  • Stage the characters in positions in the boss room. It is fine to teleport them to where they need to be.
  • The Player, Follower, and Boss should each have cmd_list that contains their actions during the cutscene. Please be aware that actions taken by cutscene-controlled characters need to have a duration (most of the Players commands did not have to account for duration). Please consult the classes that extend DurativeAnimationCommand to see how to create and use commands with durations.
  • Be sure to disable the Player's input before the cutscene starts and enable it before the boss battle. See bind_player_input_commands() and unbind_player_input_commands() in the player.gd.

For examples of how the command lists work, see the paired BossEncounterTrigger (in boss_encounter_trigger.gd) and Boss classes. The BossEncounterTrigger is attached to the Area2D trigger named BossEncounterTrigger in the Main scene. It is responsible for detecting when the Player is in the Bosss room and configuring the user interface for the boss encounter (e.g., the cutscene followed by the boss battle).

Your work will be assessed on the following criteria:

  • The number of unique durative commands across the characters. Less than eight types may result in a point deduction.
  • How well synced the three characters' commands are to one another.
  • Are the transitions to the cutscene and from the cutscene to the boss battle technically sound.
  • Bonus: Telling an interesting tale.

To help coordinate these commands, you may wish to use the cutscene_manager.gd as a central control mechanism.

Stage 4: Boss Mechanics

Make your own boss battle. This is your opportunity to perform self-directed, design-driven gameplay programming. You can implement something as simple as a boss that moves, jumps, and attacks. Or you could make something as elaborate as special moves, life regeneration, damage-absorbing shields made of bone, or a dialogue system to negotiate with the spirit to solve the conflict without violence. Be sure that your boss battle logic uses command lists, is winnable by the player, and follows one of the most essential rules for NPCs: it should always be doing something! Describe your boss battle in a comment near your implementation. This description is for your peer reviewer, so make it clear and communicative.

  • The boss should always be acting.
  • The boss should be competent. This could mean dynamic targeting or some additional scripted and threatening behavior.
  • Visual and auditory effects.

Good luck!