ScrollBar in Godot – Complete Guide

Scrolling through content is a fundamental part of the user experience in any interactive application. Whether you’re flicking through a long list on your smartphone, scrolling down a webpage, or navigating through a lengthy document, you’ve undoubtedly encountered a scrollbar. In game development, understanding and implementing scrollbars can enhance the navigation and overall feel of your game’s UI. With the Godot 4 engine, this task becomes intuitive and customizable through the ScrollBar class.

What is the ScrollBar Class?

What is the ScrollBar Class?

The ScrollBar class is part of the robust Godot 4 engine, inheriting from the Range class with a lineage in the Control, CanvasItem, Node, and Object classes. It’s an abstract base class for creating horizontal (HScrollBar) and vertical (VScrollBar) scrollbars in your projects. But what does “abstract” mean in this context? Simply put, while you can’t use the ScrollBar class directly, it provides the necessary framework for the scrollbars that you will create and use.

What is it Used For?

Scrollbars serve a key role in UI design: they allow users to move through content that extends outside the viewport’s visible area. This could be a long list of high scores, a level selection screen that spans several pages, or even a map editor’s toolbar. The ScrollBar class in Godot gives game developers the ability to easily add this functionality to their games or applications.

Why Should I Learn About ScrollBars?

Understanding how to use the ScrollBar class enhances the usability and accessibility of your game’s UI. Seamless navigation is critical for player retention and satisfaction; it’s important for the player to feel in control, and nothing breaks immersion faster than an unresponsive or confusing UI element. Moreover, learning about the ScrollBar not only aids in UI design but also teaches valuable concepts about inheritance, signals, and user input in the Godot engine. Whether you’re a burgeoning game developer or looking to refine your Godot expertise, mastering the ScrollBar class is a step in the right direction.

CTA Small Image
FREE COURSES AT ZENVA
LEARN GAME DEVELOPMENT, PYTHON AND MORE
ACCESS FOR FREE
AVAILABLE FOR A LIMITED TIME ONLY

Creating a Basic ScrollBar

To start, let’s see how to create a basic horizontal scrollbar in Godot 4. You’d usually use a HScrollBar for this purpose:

var h_scrollbar = HScrollBar.new()
h_scrollbar.set_anchors_and_margins_preset(Control.PRESET_WIDE)
h_scrollbar.min_value = 0
h_scrollbar.max_value = 100
h_scrollbar.page = 10
add_child(h_scrollbar)

This code snippet creates a new HScrollBar, sets it to a wide preset to span the width of its parent, establishes a range between 0 and 100, and sets the page size to 10. Remember that the page size affects how much the value changes when the empty space on the scrollbar is clicked.

Now, let’s say you want to create a vertical scrollbar (VScrollBar) and connect it to a signal in order to perform an action whenever the scrollbar’s value changes.

var v_scrollbar = VScrollBar.new()
v_scrollbar.set_anchors_and_margins_preset(Control.PRESET_TALL)
v_scrollbar.min_value = 0
v_scrollbar.max_value = 100
v_scrollbar.page = 10
add_child(v_scrollbar)

v_scrollbar.connect("value_changed", self, "_on_ScrollBar_value_changed")

And here’s the callback for when the value changes:

func _on_ScrollBar_value_changed(value):
    print("The scrollbar's value is now " + str(value))

Customizing ScrollBar Appearance

Godot’s built-in theme system allows for extensive customization of the ScrollBar’s look and feel. Here’s how you change the scrollbar grabber’s color:

var h_scrollbar = HScrollBar.new()
h_scrollbar.add_color_override("scroll_color", Color(1, 0, 0))
add_child(h_scrollbar)

This will change the color of the scrollbar grabber to red. The override name ‘scroll_color’ refers to the ScrollBar’s texture property which directly affects its appearance.

Integrating ScrollBar with Content

A scrollbar is only as good as its integration with the content it scrolls. Here’s an example of how to scroll a TextEdit node with a VScrollBar:

var v_scrollbar = VScrollBar.new()
var text_edit = TextEdit.new()

func _ready():
    v_scrollbar.connect("value_changed", self, "_on_ScrollBar_value_changed")
    add_child(v_scrollbar)
    add_child(text_edit)

func _on_ScrollBar_value_changed(value):
    text_edit.scroll_vertical = value

This code connects the VScrollBar’s value_changed signal to a callback that sets the TextEdit’s `scroll_vertical` property, thus scrolling the text up and down in response to the scrollbar’s position.

Handling Large Content and the Page Property

For content that is significantly larger than the visible area, the `page` property can be used to control the step size of the scrollbar, which determines how much content should be skipped when clicking on the scrollbar’s track.

var v_scrollbar = VScrollBar.new()
v_scrollbar.min_value = 0
v_scrollbar.max_value = 1000
v_scrollbar.page = 100
v_scrollbar.value = 500 # Start in the middle
add_child(v_scrollbar)

In this example, the scrollbar represents a range of values from 0 to 1000, with a page step of 100. Setting the initial value to 500 places the scrollbar in the center of its range when the scene starts.

Keep in mind that this is only the scrollbar’s setup; to create functionality where clicking the track moves the view by a page, you’ll need to implement additional logic in your `value_changed` callback or in other appropriate functions of your content management code.

By understanding these basics, you are now equipped to add scrollbars to your Godot 4 projects, and with a little practice, you can customize and integrate them seamlessly into your game’s UI. Stay tuned for the next tutorial where we’ll delve deeper into advanced ScrollBar functionalities!Let’s dive deeper into some advanced features of the `ScrollBar` class in Godot 4 and explore how they can be applied to your game’s UI. These functionalities provide more control and finesse to the user interface, making your game more polished and professional.

Responding to User Scroll Input

You might want to have different actions occur based on how the user interacts with the scrollbar. To demonstrate, we’ll handle the user scrolling through the use of the mouse wheel:

func _input(event):
    if event is InputEventMouseButton and event.button_index == BUTTON_WHEEL_UP:
        v_scrollbar.value -= v_scrollbar.page * 0.1
    elif event is InputEventMouseButton and event.button_index == BUTTON_WHEEL_DOWN:
        v_scrollbar.value += v_scrollbar.page * 0.1

In this code snippet, we’re checking for mouse button input. When the mouse wheel is used, we adjust the `value` of the `v_scrollbar` based on a fraction of the `page` property, enabling smooth scrolling.

Changing ScrollBar Sensitivity

Sometimes you want to change how sensitive the scrollbar is to certain actions. You can adjust the `step` property to make each click on the scrollbar’s arrows scroll more or less content:

v_scrollbar.step = 5

This code sets the `step` of the scrollbar to 5, so each click on the arrows will move the scrollbar’s value by this amount.

ScrollBar Custom Themes

Creating a custom theme can give your scrollbar a unique appearance. Here’s an example of how to set a custom texture for the scrollbar’s grabber:

var theme = Theme.new()
theme.set_stylebox("grabber", "VScrollBar", load("res://path_to_grabber_texture.png"))
v_scrollbar.add_theme_override("theme", theme)

This code snippet creates a new `Theme` object, sets a custom style for the “grabber” part of the `VScrollBar`, and then applies this theme to `v_scrollbar`.

Using a ScrollContainer

A `ScrollContainer` is often used in tandem with scrollbars to provide scrolling capabilities to a collection of controls or nodes.

var scroll_container = ScrollContainer.new()
var content = VBoxContainer.new()

for i in range(100):
    var label = Label.new()
    label.text = "Item #%d" % i
    content.add_child(label)

scroll_container.add_child(content)
add_child(scroll_container)

In this example, we’ve created a `ScrollContainer` and populated it with a series of labels inside a `VBoxContainer`. The `ScrollContainer` automatically provides a vertical and/or horizontal scrollbar based on the size and amount of the content.

Linking ScrollBars to Dynamically Sized Content

In some scenarios, content size can change dynamically, so the scrollbars need to adjust their range accordingly. Here’s how you could update a scrollbar’s `max_value` based on the content height:

func _on_Content_height_changed():
    var content_height = content.get_rect().size.y
    v_scrollbar.max_value = content_height - scroll_container.rect_size.y

This function could be called whenever the content’s height changes, setting the `max_value` to the height of the content minus the visible area of the `scroll_container`.

Ensuring ScrollBar Visibility with Large Content

If your content area is quite large, you might want to ensure that the scrollbar is visible only when necessary:

func _on_Content_changed():
    v_scrollbar.visible = content.get_rect().size.y > scroll_container.get_rect().size.y

This snippet sets the visibility of `v_scrollbar` based on whether the content height exceeds the height of the `scroll_container`.

Controlling Scroll Speed

If you wish to control the scroll speed, you may want to directly manipulate the `value` property of the scrollbar in response to events:

v_scrollbar.value = clamp(v_scrollbar.value + scroll_speed * delta, v_scrollbar.min_value, v_scrollbar.max_value)

In this line, `scroll_speed` is a variable that defines how fast you want the content to scroll, and `delta` is the frame’s delta time, which would typically come from the `_process(delta)` function.

Utilizing these advanced concepts, you can create a more dynamic and responsive UI for your Godot 4 projects. The ScrollBar class offers extensive flexibility, allowing developers to craft a user experience that feels both smooth and intuitive. With practice, these techniques can significantly elevate the quality and functionality of your game’s interface.Let’s now look at how we can add behaviour to scrollbars and integrate them with various UI elements. Here we’re going to explore practical examples including locking scrollbar movement, syncing multiple scrollbars, and creating custom scrolling effects.

Locking Scrollbar Movement

There are instances when you want to temporarily disable the user’s ability to move the scrollbar. Here’s a way you can lock and unlock a scrollbar’s movement:

func lock_scrollbar(should_lock):
    v_scrollbar.disabled = should_lock

By setting the `disabled` property to `true`, the scrollbar will not respond to user input, effectively locking it in place.

Syncing Multiple ScrollBars

In a UI with multiple scrollable areas, you might want to sync the position of two or more scrollbars. Let’s implement a horizontal and a vertical scrollbar that move in sync:

var h_scrollbar = HScrollBar.new()
var v_scrollbar = VScrollBar.new()

func _ready():
    h_scrollbar.connect("value_changed", self, "_on_ScrollBar_value_changed")
    v_scrollbar.connect("value_changed", self, "_on_ScrollBar_value_changed")
    add_child(h_scrollbar)
    add_child(v_scrollbar)

func _on_ScrollBar_value_changed(value):
    h_scrollbar.value = value
    v_scrollbar.value = value

This syncs the two scrollbars together. When one moves, the other follows.

Scrollbar as a Zoom Control

You can also use a scrollbar as a zoom control in a map or image viewer. Here’s a basic example:

var zoom_level = 1.0
var zoom_scrollbar = VScrollBar.new()
zoom_scrollbar.min_value = 0.1
zoom_scrollbar.max_value = 3.0
zoom_scrollbar.page = 0.1
zoom_scrollbar.value = zoom_level
add_child(zoom_scrollbar)

zoom_scrollbar.connect("value_changed", self, "_on_zoom_scroll_value_changed")

func _on_zoom_scroll_value_changed(value):
    zoom_level = value
    update_zoom(zoom_level)

The scrollbar’s `value` property is used to represent the zoom level, and `update_zoom` would be a function that applies the zoom level to your content.

Custom Scroll Effects

For a more interactive UI, you could add custom scrolling effects. For instance, let’s apply a parallax effect tied to a scrollbar’s movement:

var parallax_background = $ParallaxBackground
var parallax_scrollbar = VScrollBar.new()
add_child(parallax_scrollbar)

parallax_scrollbar.connect("value_changed", self, "_on_parallax_scroll_value_changed")

func _on_parallax_scroll_value_changed(value):
    parallax_background.scroll_offset.y = value

As the scrollbar moves, the parallax background will scroll to create the illusion of depth.

Updating ScrollBar with Window Size Changes

Handle window resize events to adjust scrollbar properties dynamically:

func _notification(what):
    if what == NOTIFICATION_WM_SIZE_CHANGED:
        var new_size = OS.window_size
        adjust_scrollbar_to_window_size(new_size)
        
func adjust_scrollbar_to_window_size(size):
    v_scrollbar.page = size.y
    // Other calculations and adjustments as needed

With this snippet, the `page` property of the `v_scrollbar` is updated whenever the window size changes, ensuring that the scrollbar behaves correctly for the new size of the window.

Creating a Smooth Scrolling Effect

To enhance the UI experience, let’s add a smooth scrolling action to our scrollbar:

var scroll_speed = 100
var target_scroll_value = 0

func _process(delta):
    var scroll_step = scroll_speed * delta
    v_scrollbar.value = lerp(v_scrollbar.value, target_scroll_value, scroll_step)

func _on_Button_down_pressed():
    target_scroll_value += 100
func _on_Button_up_pressed():
    target_scroll_value -= 100

Here, the `lerp` function smoothly interpolates the scrollbar’s current value towards the `target_scroll_value`. The buttons trigger the change in target value.

Implementing Inertia in ScrollBars

Finally, if you want your scrollbar to have an inertia effect, where it continues to move for a short distance after the user has stopped scrolling, try something like the following:

var current_velocity = 0
var scroll_friction = 0.9

func _physics_process(delta):
    if current_velocity != 0:
        v_scrollbar.value += current_velocity * delta
        current_velocity *= scroll_friction

The `current_velocity` decreases over time, simulating friction until it stops. You’ll have to adjust `current_velocity` based on user input or any other events that should cause the scrollbar to move.

These examples illustrate the flexibility of the ScrollBar class in Godot 4 and showcase just a few of the creative ways you can integrate them into your gaming project’s UI. Whether you’re locking scrollbars during cutscenes, syncing two panels, or adding that extra finesse with inertia effects, these snippets form a solid foundation for you to build upon. Now, go ahead and enhance your application’s user experience with these advanced scrollbar capabilities!

Continue Your Game Development Journey

Embarking on the adventure of game development with Godot 4 is only the beginning. As you’ve learned the ins and outs of ScrollBars, consider this a stepping stone towards a more profound understanding of what this powerful engine has to offer. To keep moving forward, expand your skills and knowledge with our Godot Game Development Mini-Degree. This series of courses will guide you further in constructing cross-platform games, mastering everything from essential 2D and 3D concepts to advanced gameplay mechanics.

Whether you’re a hobbyist looking to bring your game ideas to life or an aspiring professional seeking a comprehensive curriculum, our Mini-Degree adapts to your level. Learn at your own pace with our flexible 24/7 online access model and gain the expertise to create visually stunning and interactive games. By completing these courses, you will not only refine your craft but also build an impressive portfolio to show to potential employers or share with the gaming community.

For those who are thirsting for more and looking to tailor their learning experience, check out our full range of Godot courses. Here at Zenva, we are committed to helping developers of all levels learn coding, create games, and reach their potential. Join us on this journey and catapult your game development skills from beginner to professional with Zenva.

Conclusion

To wrap up, your exploration of the ScrollBar class within Godot 4 is just a snapshot of the diverse and intricate world of game development. Each step you take in mastering this engine unveils more opportunities to craft immersive experiences for players around the globe. Whether it’s through implementing responsive UI controls, like the scrollbar, or through conjuring up worlds limited only by your imagination, the journey is as rewarding as the destination.

Remember, this path doesn’t end here. Continue to harness your creativity and technical skills with our comprehensive Godot Game Development Mini-Degree, designed to propel you into the realm of game development mastery. With Zenva, you’re not just learning—you’re becoming part of a global community of creators dedicated to bringing their visions to life. Let’s build the future of gaming together!

FREE COURSES
Python Blog Image

FINAL DAYS: Unlock coding courses in Unity, Godot, Unreal, Python and more.