PolygonOccluder3D in Godot – Complete Guide

Bringing your virtual worlds to life with dynamic graphics and immersive gameplay is the bread and butter of Godot Engine — a favorite among game developers. In the intricate dance of rendering scenes, it’s important to optimize performance wherever possible. This is where the concept of occlusion culling, and more specifically, the use of the PolygonOccluder3D class in Godot 4, becomes a critical tool in your game development toolbox. Dive in as we explore what PolygonOccluder3D is, how it benefits your projects, and why mastering it could be a game-changer for your Godot projects.

What is PolygonOccluder3D?

PolygonOccluder3D is a Godot class designed for use with occlusion culling. It’s a resource that contains a flat 2D polygon shape which can help the engine determine which parts of the 3D scene need to be rendered and which don’t — based on the camera’s viewpoint. This optimization can lead to more efficient resource usage and smoother frame rates, especially in detailed 3D scenes.

What is it for?

Imagine you’re inside a virtual building — you don’t need to see what’s on the outside until you walk through a door or window. That’s what occlusion culling does; it prevents the rendering of objects that are not currently visible to the player, saving valuable computing power. The PolygonOccluder3D plays a critical role in this system by defining areas that can potentially block the view of other objects in your scene.

Why Should I Learn It?

By learning to implement and work with PolygonOccluder3D, you can ensure your Godot games run as efficiently as possible, even when rendering complex 3D scenes. This can be the difference between a game that runs smooth as silk or one that sputters and stalls. It’s an optimization skill that’s highly valued in the industry and can be applied to a wide range of projects. Plus, understanding occlusion culling lays the groundwork for mastering advanced rendering techniques as you progress on your game development journey.

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Creating a Basic PolygonOccluder3D

First, let’s start by creating a basic PolygonOccluder3D in Godot. This example will guide you through setting up a simple occluder that could represent a wall or large object in a scene:

var occluder = PolygonOccluder3D.new()
var polygon = PoolVector2Array([Vector2(-1, -1), Vector2(1, -1), Vector2(1, 1), Vector2(-1, 1)])
occluder.polygon = polygon

In this example, we create an instance of PolygonOccluder3D and define a square polygon which might correspond to a single occluder.

Attaching the Occluder to a VisualInstance

Next, we need to attach our occluder to a VisualInstance node, which will be responsible for the occlusion in 3D space. Here’s how you can add an Occluder to a MeshInstance:

var mesh_instance = MeshInstance3D.new()
var mesh = CubeMesh.new()  # Creating a simple cube mesh
mesh_instance.mesh = mesh
mesh_instance.occluder = occluder
add_child(mesh_instance)

The Occluder is now connected, and Godot will use it to determine what can be culled.

Setting Up Occluder for a Static Environment

If you’re working with a static scene, such as the inside of a building, you can set up the occluders to represent the solidity of walls. Here’s an example:

var wall_occluder = PolygonOccluder3D.new()
var wall_polygon = PoolVector2Array([Vector2(0, 0), Vector2(0, 10), Vector2(10, 10), Vector2(10, 0)])
wall_occluder.polygon = wall_polygon

var wall = MeshInstance3D.new()  # A wall in your static scene
var wall_mesh = BoxMesh.new()  # Create a box mesh for the wall
wall.mesh = wall_mesh
wall.occluder = wall_occluder
add_child(wall)

This example sets up a wall occluder which the engine will use to block sight for objects behind the wall.

Optimizing for Moving Objects

Dynamic occlusion with PolygonOccluder3D is slightly trickier since the occluder needs to update with the moving object. Here’s how you can approach this:

func _on_ObjectMoved(position):  # This function is called whenever the object moves
    var moving_object_occluder = PolygonOccluder3D.new()
    var moving_polygon = PoolVector2Array([Vector2(-1, -1), Vector2(1, -1), Vector2(1, 1), Vector2(-1, 1)])
    moving_object_occluder.polygon = moving_polygon
    moving_object_occluder.set_cull_mode(PolygonOccluder3D.CULL_DISABLED)

    # Update the position where occluder should be at
    var moving_mesh_instance = MeshInstance3D.new()
    var moving_mesh = CubeMesh.new()  # Assuming the object is cube-shaped
    moving_mesh_instance.mesh = moving_mesh
    moving_mesh_instance.global_transform.origin = position
    moving_mesh_instance.occluder = moving_object_occluder

    add_child(moving_mesh_instance)

This would typically be part of a larger system where the function `_on_ObjectMoved` is connected to a signal from the moving object to consistently update the occluder.

These code snippets form the basis of using PolygonOccluder3D in Godot 4 for different scenarios. Remember, experimentation is key – try different shapes and configurations to see how they affect your scene’s performance and visuals.

Mastering PolygonOccluder3D is truly about understanding its interaction with the rest of your scene. Let’s dig deeper into some practical examples and ways you can enhance occlusion culling in your Godot 4 projects.

When you’re constructing a level, you’ll often have repeating structures, such as columns in a hallway. To efficiently set up occluders for these, a loop can be used:

for i in range(number_of_columns):
    var column_occluder = PolygonOccluder3D.new()
    column_occluder.polygon = PoolVector2Array([Vector2(-1, -1), Vector2(1, -1), Vector2(1, 1), Vector2(-1, 1)])
    
    var column = MeshInstance3D.new()
    var column_mesh = CylinderMesh.new()
    column.mesh = column_mesh
    column.global_transform.origin = Vector3(i * spacing, 0, 0)
    column.occluder = column_occluder

    add_child(column)

This code will place an occluder for each column in your level, ensuring that only visible columns are rendered.

Let’s consider optimizing view-dependent occlusion. For a moving character or camera, you may dynamically alter the occluders based on sight. This could involve enabling and disabling occluders:

var camera = Camera3D.new()
camera.current = true
add_child(camera)

func _process(delta):
    if is_visible_to_camera(camera):
        mesh_instance.occluder.set_cull_mode(PolygonOccluder3D.CULL_DISABLED)
    else:
        mesh_instance.occluder.set_cull_mode(PolygonOccluder3D.CULL_CLOCKWISE)

This snippet uses a simple visibility check to toggle the culling mode of the occluder depending on whether the object is in the camera’s view.

Another optimization you might need is handling multiple occluders for one large object. Break down the object into several occluders for better granularity:

var large_object = MeshInstance3D.new()
var large_mesh = CustomMesh.new()
large_object.mesh = large_mesh

var occluders = []
for i in range(divisions):
    var segment_occluder = PolygonOccluder3D.new()
    segment_occluder.polygon = create_occluder_polygon(i, divisions)
    occluders.append(segment_occluder)

# Assume create_occluder_polygon is a function that calculates the polygon points for each occluder segment

This approach allows you to cull only the parts of the object that are actually obscured, rather than the entire object, which can increase rendering efficiency.

Sometimes, you don’t want occlusion culling to apply to certain objects such as special effects or UI elements. You would explicitly disable the occluder:

var special_effect = MeshInstance3D.new()
special_effect.mesh = create_special_effect_mesh()
special_effect.occluder = null  # We don't assign an occluder

This ensures that your special effect or UI remains visible regardless of occlusion culling.

Finally, let’s consider a level of detail (LOD) system that can work in tandem with occlusion culling. Here’s how you might begin to implement a rough LOD system with occluders:

func _process(delta):
    var distance_to_camera = global_transform.origin.distance_to(camera.global_transform.origin)
    match distance_to_camera:
        less_than(10):
            mesh_instance.mesh = high_detail_mesh
            mesh_instance.occluder = high_detail_occluder
        less_than(20):
            mesh_instance.mesh = medium_detail_mesh
            mesh_instance.occluder = medium_detail_occluder
        else:
            mesh_instance.mesh = low_detail_mesh
            mesh_instance.occluder = low_detail_occluder

This system adjusts the level of detail of both the mesh and its associated occluder based on the distance to the camera, enhancing performance while maintaining visual quality as needed.

With these examples, you should gain a clearer picture of the versatility and power that PolygonOccluder3D brings to your Godot 4 projects. Experimenting with occluders as you craft your levels will invariably lead to higher efficiency and smoother gameplay experiences. Happy coding!

Let’s delve into more complex scenarios where occluders influence the performance and visual fidelity of your Godot 4 games.

Here’s how to handle a situation where you need to deactivate an occluder when an object is destroyed or removed from the game:

func _on_ObjectDestroyed(object):
    object.occluder = null

This function assumes that you call it with your object when it’s destroyed, which nulls out its occluder and removes any occlusion effects it might have had.

In contrast, if you want to dynamically add an occluder to an object when it’s created or comes into play, you might have something like this:

func _on_ObjectCreated(object):
    var new_occluder = PolygonOccluder3D.new()
    # Configure your occluder's properties and polygon
    object.occluder = new_occluder

This function would be connected to your object creation logic, ensuring that each new object contributes to the occlusion culling system immediately from the point of creation.

What about moving platforms or doors that change the geometry of the scene dynamically? In this case, you’d update the occluder as the object moves:

func _on_PlatformMoved(platform, new_position):
    platform.occluder.global_transform.origin = new_position

This ensures that the occluder for the moving platform is always positioned correctly in relation to its actual location in the game world.

Another interesting application is combining occlusion culling with physics-based events. For example, if a wall is destructible and after destruction should no longer occlude:

func _on_WallDestroyed(wall):
    wall.occluder.polygon = PoolVector2Array()  # Removing all points from the polygon effectively disables it

When the wall is destroyed, you can call this function to empty its occluder’s polygon, stopping it from occluding any further objects.

Now, let’s implement an automatic system for toggling occluders on environmental objects based on their distance to the player:

func _process(delta):
    for object in environmental_objects:
        var distance = object.global_transform.origin.distance_to(player.global_transform.origin)
        if distance < OCCLUSION_TOGGLE_DISTANCE:
            object.occluder.set_cull_mode(PolygonOccluder3D.CULL_DISABLED)
        else:
            object.occluder.set_cull_mode(PolygonOccluder3D.CULL_CLOCKWISE)

This code would be part of your main scene’s script and would toggle occluders on and off based on a predefined distance to the player object.

With these more advanced examples, you can see how occlusion culling can be a dynamic part of your game’s logic, interfacing with gameplay systems to add depth and realism to your virtual worlds. Understanding the intricacies of the occlusion culling system can be incredibly rewarding as it elevates the quality and performance of your Godot 4 projects.

Where to Go Next in Your Godot Learning Journey

The world of game development is ever-expanding and learning how to use tools like Godot Engine efficiently is invaluable. If you’re keen on furthering your game development skills, our Godot Game Development Mini-Degree is the perfect next step. It provides an extensive curriculum that dives deep into the creation of cross-platform games using the robust Godot 4 engine.

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Conclusion

The journey through the realm of Godot 4’s optimization with PolygonOccluder3D may come to an end in this tutorial, but the adventure of game development is boundless. Remember, the tools and techniques discussed here are just the beginning. With practice, patience, and a splash of creativity, there’s no limit to what you can achieve in your game-making voyage. So, keep exploring, keep refining your skills, and take pride in every step forward — each line of code is part of your journey to mastery.

Whether you’re polishing your current game project or brainstorming the next indie hit, we at Zenva are here to support your growth. Keep honing your craft with our Godot Game Development Mini-Degree and other comprehensive Godot tutorials. Together, let’s turn the games of your imagination into the games we all get to play. The world is waiting for your stories, your worlds, your games — start creating them today!

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