Developing an RPG in Godot - Movement and adding sprites

Movement

One of the basic things in video games is movement, which are rare games that don’t have any type of movement but exist. But now I am going to talk about movement in 2D games.

Mathematics and Physics of the 2D Movement

First, we need to understand how movement works in 2D. Then, we could talk about a third dimension. But the third dimension will be shown in a future blog post. Movement in video games comes from a vector. Right now, I would not enter too deeply into the concept.

\[\vec{B}=\begin{bmatrix} \vec{i}, \vec{j} \end{bmatrix}\]

Example of the vector base

i is the same as if I say x, j is the same as if I say y.

Most of the movement comes when a vector changes, if we define a vector named for example u from movement.

\[\vec{u}=\begin{bmatrix} 0, 0 \end{bmatrix}\]

This vector means that our character is in the position x = 0 and y = 0. But if for example, our character moves 2 times up, the vector will change.

\[\vec{u}=\begin{bmatrix} 0, 2 \end{bmatrix}\]

Example of the vector movement

If you see the vector u is formed by two times the vector j

\[\vec{u}=\begin{bmatrix} 2\vec{i}, 0 \end{bmatrix}\]

This is the basics you will need to know to understand movement in videogames. In the future there will be more in deep blog post.

Movement in Godot

Brief explanation

The classic RPG uses the 8-movement, this type of movement enables the player to move in all directions they want, using W, A, S, D.

First of all, we are going to create a new folder at the root of our project, the folder will have the name “Scripts”. Here we are going to save all the scripts to use in our game.

Created Folder Scripts

After creating the folder script we are going to press left click and create a script.

Code

The code we are going to write is the following.

extends CharacterBody2D

Now we are going to understand this line of code, extends CharacterBody2D, extends is in charge of importing all the functions associated to CharacterBody2D

If you wanna know more about the CharacterBody2D click in his name and you will be redirected to the official documentation of Godot.

Now we have added two new lines of code, this is how you define variables in Godot you put var [name of the variable] = [value], but what is the @export? When you see this type of word with an “@” is used to indicate to the engine something about the variable in this case to export it, this means that you will see this variable in the engine and be able to modify it from there without the necessity of going to the script.

Variables

extends CharacterBody2D

@export var walking_speed = 400
@export var running_speed = 800

Functions

Next, we are going to define de two main variables of this script the first one is get_input(), as his name shows this is where we are going to get the input from, and the other one is _physics_process(delta), this is a function that comes with some nodes in godot, is in charge of updating the physics every frame.

The variable delta is used when you update something every frame, is a really interesting variable and there will be a deeper in a future blog post.

extends CharacterBody2D

@export var walking_speed = 400
@export var running_speed = 800

func get_input():
  pass

func _physics_process(delta):
  pass

Function get_input()

Now we are going to center in the function get_input(). This function is in charge to get the vector of direction of the input keys, left, right, up, down. But what are these input keys?. In a moment we are going to see it, for now we are going to talk about the if statement that we see here, this is in charge of seeing if the player want to run or to walk, if the key shift is pressed the code is going to use the running_speed but if it not being pressed is going to use the walking_speed

func get_input():
  var input_direction = Input.get_vector("left", "right", "up", "down")
  if Input.is_action_just_pressed("shift"):
    velocity = input_direction * running_speed
  else:
    velocity = input_direction * walking_speed

Setting up input commands

To open the input map we are going to need to press the following buttons, first in the upper right press proyect, configuration proyect and the input map.

Godot Input Map Window

After doing this you are going to write where it says “Add new action”, left, press the add, when pressing this you are going to see the following changes.

Godot Input Map Added Input

Next you are going to press the plus sign, and press the key that you want to bind to that input. After press accept.

Godot Input Map Added Input Key

We are going to follow the same procces with, right, up and down.

Function _physics_process(delta)

Next we are going to view the _physics_process(delta) this function is created by the engine and is in charge of all the process related to the physics, here we call our get_input() function, and the move_and_slide() functions, this is also a function created by the engine, and tell the object to start moving.

  func _physics_process(delta):
    get_input()
    move_and_slide()

If you get a warning in delta add an underscore like this _delta

Adding the script and creating the player

Next we are going to press left click in Node2D and press Add Child Node, it is going to open a windows, there search CharacterBody2D and add it.

Adding Character Body2D

If you don’t have a Node2D in the tree, added in the same form as the characterBody2D.

You are going to see a warning next to the name, you don’t need to give importance to that right now. After that, do the same this time left clicking in the CharacterBody2D, and adding a Sprite.

Adding Sprite

Now there is only one more thing left, adding the script to the CharacterBody2D.

Adding Script To CharacterBody2D

Github Demo

Here you can access to the repo that contains all the files of the different blogs about developing and RPG.