RDShaderSource in Godot – Complete Guide

Welcome to our journey through the intricacies of RDShaderSource in Godot 4, the prominent open-source game engine that continues to empower creators worldwide with its flexible and user-friendly tools. As we delve into the world of shaders and rendering, this tutorial aims to demystify the RDShaderSource class and demonstrate its utility in crafting stunning visual effects for games. By the end of this tutorial, learners of all skill levels will have a solid understanding of how to manipulate shader source code within Godot’s RenderingDevice API. So, whether you’re a budding game developer or a seasoned programmer looking to polish your skills in Godot, keep reading to unlock the potential of high-quality game visuals through RDShaderSource.

What is RDShaderSource?

RDShaderSource is a class in Godot 4 that encapsulates shader source code in a text form designed for use with the RenderingDevice API. It is an essential component for low-level rendering operations, providing developers with the tools to write and manage shader code effectively. This class is different from Godot’s high-level Shader resource and is an important distinction for advanced graphics programming.

What is it for?

RDShaderSource comes into play when you want to have granular control over the visual rendering of your game. It allows the addition of custom shader stages such as compute, fragment, tessellation control, tessellation evaluation, and vertex. By using RDShaderSource, developers can create complex effects, from simple light reflections to intricate particle systems, with direct integration into the rendering pipeline.

Why should I learn it?

Understanding the RDShaderSource class is key to unlocking advanced rendering techniques within Godot. By learning how to use this class, you can:

  • Customize the visual appearance of your game elements to a high degree.
  • Optimize your game’s performance by leveraging the RenderingDevice API’s power.
  • Create shaders that are more efficient and tailored to your game’s specific needs.

Learning RDShaderSource heightens your ability to craft visually stunning games while deepening your knowledge of Godot’s rendering architecture.

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Basic Structure of RDShaderSource

Before diving into the examples, it’s important to understand the basic structure of an RDShaderSource. Just like traditional shaders, RDShaderSource consists of various sections corresponding to different stages of rendering. Let’s start by looking at the basic setup for a shader source.

var shader_code : RDShaderSource = RDShaderSource.new()
shader_code.set_code("shader_type canvas_item;\n\nvoid fragment() {\n\tCOLOR = vec4(1.0, 1.0, 1.0, 1.0);\n}")

This snippet creates a new RDShaderSource instance and sets a simple fragment shader that colors the canvas white. Note the usage of set_code(), it’s how you attach your shader code to the RDShaderSource.

Adding Custom Shader Stages

Let’s introduce different custom shader stages to our RDShaderSource. Each stage must be properly defined within the shader code string.

// Vertex shader stage
shader_code.set_stage_code(RDShaderSource.SHADER_STAGE_VERTEX, "void vertex() {\n\t// Custom vertex shader logic here\n}")

// Fragment shader stage
shader_code.set_stage_code(RDShaderSource.SHADER_STAGE_FRAGMENT, "void fragment() {\n\t// Custom fragment shader logic here\n}")

// Compute shader stage
shader_code.set_stage_code(RDShaderSource.SHADER_STAGE_COMPUTE, "void compute() {\n\t// Custom compute shader logic here\n}")

In Godot 4, each shader stage has its specific functions and setup. These examples establish a custom foundation for each stage which can then be fleshed out with more complex logic.

Uniforms and Resources in RDShaderSource

Uniforms are constants during rendering and can be used to pass data from your game code to the shader. Here’s how to add a simple uniform to your RDShaderSource code.

shader_code.set_code("shader_type canvas_item;\n\nuniform vec4 my_color;\n\nvoid fragment() {\n\tCOLOR = my_color;\n}")

This example introduces a uniform called my_color that can be used to color the model dynamically at runtime. Uniforms are versatile and can represent textures, colors, transformation matrices, and more.

// Creating a texture uniform
shader_code.set_code("shader_type canvas_item;\n\nuniform sampler2D my_texture;\n\nvoid fragment() {\n\tCOLOR = texture(my_texture, UV);\n}")

Here, the shader is set up with a texture uniform. In your game code, you can set this uniform to different textures to change the appearance of your canvas item dynamically.

Compiling Shaders

Once you’ve defined your shader code, it needs to be compiled before it can be used. Here’s how to compile shader code in RDShaderSource.

var shader : RID = RenderingDevice.get_singleton().shader_create()
RenderingDevice.get_singleton().shader_compile(shader, shader_code)

This code compiles the shader source into a shader RID that you can use with the rendering device. This process converts your high-level shader code into machine-level instructions that the GPU can understand and execute.

Keep in mind that errors can occur during compilation. It’s a good practice to check for compilation success and handle any errors accordingly:

if RenderingDevice.get_singleton().shader_get_compile_status(shader) != OK:
    var error = RenderingDevice.get_singleton().shader_get_error(shader)
    print("Shader failed to compile: " + error)

Monitoring the compile status helps ensure that shader issues are caught early, allowing you to debug and refine your shaders more effectively.

In the next section, we’ll delve deeper into shader customization and see how we can interact with these shaders programmatically to create dynamic rendering effects.

When working with RDShaderSource in Godot 4, one of the common tasks you’ll undertake is manipulating shader variables at runtime. This requires a combination of Godot’s scripting language, GDScript, and the RenderingDevice API. Let’s explore a variety of code examples that illustrate how you can dynamically interact with shaders to create engaging visual effects.

To set a uniform value after a shader has been compiled, use the following approach:

var shader_uniform : StringName = "my_color"
var color_value : Color = Color(1.0, 0.0, 0.0, 1.0) # Red color
RenderingDevice.get_singleton().shader_set_uniform(shader, shader_uniform, color_value)

This GDScript snippet sets the uniform ‘my_color’ to red in the compiled shader. We use a StringName for the uniform identifier and a Color value as its new value.

Another common task is to pass textures to your shader:

var texture_uniform : StringName = "my_texture"
var texture_rid : RID = load("res://path_to_texture.png").get_rid()
RenderingDevice.get_singleton().shader_set_uniform(shader, texture_uniform, texture_rid)

Here we assign a loaded texture to the ‘my_texture’ uniform. Godot’s RenderingDevice API requires the texture’s RID, not the Texture object directly.

Updating shader variables every frame can allow for dynamic effects such as the passing of time or responding to player actions. For animated shaders, you might incorporate a time variable:

var time : float = 0.0
var delta : float = get_process_delta_time()
var time_uniform : StringName = "u_time"

func _process(delta):
    time += delta
    RenderingDevice.get_singleton().shader_set_uniform(shader, time_uniform, time)

The ‘u_time’ uniform will constantly increase every frame, which can then drive animations within the shader code.

RDShaderSource can also utilize global shader parameters set up in Godot’s project settings:

# Assuming 'my_global_var' was set in the Project Settings as a global shader parameter
var global_var_uniform : StringName = "my_global_var"
var global_var_value : Vector3 = Vector3(1.0, 2.0, 3.0)
RenderingDevice.get_singleton().shader_set_global_shader_parameter(global_var_uniform, global_var_value)

Global shader parameters can be accessed by any shader within the project, facilitating a centralized way to manage values used across multiple shaders such as lighting factors or screen resolution.

If you intend to manipulate shader parameters based on user input, here’s how you can reflect those changes within your RDShaderSource:

func _input(event):
    if event is InputEventMouseButton and event.button_index == BUTTON_LEFT and event.pressed:
        var click_position_uniform : StringName = "click_position"
        var click_position_value : Vector2 = event.position
        RenderingDevice.get_singleton().shader_set_uniform(shader, click_position_uniform, click_position_value)

This code sets the ‘click_position’ uniform to the mouse’s location when the left button is clicked, potentially influencing effects like a ripple or spot light at the point of interaction.

Lastly, consider that RDShaderSource allows for direct feedback loops in compute shaders for simulation and GPGPU tasks:

# Setting up a compute shader with a storage buffer for simulation data.
var compute_shader : RID = RenderingDevice.get_singleton().shader_create()
var shader_compute_code : String = "..." # Your compute shader code here
shader_code.set_stage_code(RDShaderSource.SHADER_STAGE_COMPUTE, shader_compute_code)

# Creating a storage buffer for simulation data.
var data_buffer_size : int = 1024
var data_buffer : RID = RenderingDevice.get_singleton().storage_buffer_create(data_buffer_size)
RenderingDevice.get_singleton().shader_set_uniform(shader, "data_buffer", data_buffer)

# Dispatching the compute shader to run the simulation on the GPU.
var groups : Vector3i = Vector3i(32, 1, 1) # Assumes 1024 / 32 = 32 invocations required
RenderingDevice.get_singleton().compute_shader_dispatch(compute_shader, groups)

This example dispatches a compute shader that can write and read from a storage buffer, allowing you to run parallel computations on the GPU, which is particularly useful for physics simulations or procedural content generation.

By mastering these code samples, you’ll develop a solid foundation for using RDShaderSource and the RenderingDevice API, offering you the ability to create and control a vast range of visual effects and low-level rendering techniques in Godot 4.

Expanding on our journey through dynamic shader interactions, let’s consider how we can use RDShaderSource to achieve real-time changes based on scene lighting. In a 3D scene, you may want to modify the shader’s properties based on the lights present in the environment. Here’s a basic example of how to update uniforms accounting for light data if you’re using a custom shading model:

var light_dir_uniform : StringName = "u_light_direction"
var light_color_uniform : StringName = "u_light_color"
var light_direction : Vector3 = Vector3(0.0, -1.0, 0.0) # Example directional light
var light_color : Color = Color(1.0, 1.0, 1.0) # White light

# In the render loop or light update function:
RenderingDevice.get_singleton().shader_set_uniform(shader, light_dir_uniform, light_direction.normalized())
RenderingDevice.get_singleton().shader_set_uniform(shader, light_color_uniform, light_color)

This will keep your shader’s lighting in line with the scene’s actual light direction and color, giving you a consistent visual experience.

RDShaderSource is particularly powerful when dealing with post-process effects. Here’s how you could set up a shader for screen space effects and manage its properties:

var exposure_uniform : StringName = "u_exposure"
var exposure_value : float = 1.0 # Default exposure

# Attach the shader to the RenderingDevice's post-process material
RenderingDevice.get_singleton().material_set_shader(post_process_material, shader)

# Update exposure based on scene or game conditions
RenderingDevice.get_singleton().shader_set_uniform(shader, exposure_uniform, exposure_value)

Custom post-process shaders can drastically change the game’s ambiance, allowing for dynamic effects like exposure changes during gameplay.

Handling dynamic objects like moving water or swaying grass involves updating shader properties often. Here is how you might implement a wind effect on vegetation:

var wind_uniform : StringName = "u_wind"
var wind_vector : Vector2 = Vector2(0.0, 0.0)

func _process(delta):
    wind_vector.x += rand_range(-0.01, 0.01) * delta
    wind_vector.y += rand_range(-0.01, 0.01) * delta
    RenderingDevice.get_singleton().shader_set_uniform(shader, wind_uniform, wind_vector)

Here, the movement data is updated every frame, letting the shader simulate the effect of a gentle breeze.

Customizing particle effects can also benefit from RDShaderSource. One way to modify particles runtime is to alter their color based on a gradient texture:

var gradient_uniform : StringName = "u_color_gradient"
var gradient_texture : RID = load("res://path_to_gradient.png").get_rid()

# Assuming you have a bespoke particle system that uses this shader    
RenderingDevice.get_singleton().shader_set_uniform(shader, gradient_uniform, gradient_texture)

With a gradient texture uniform, your shader can provide a varied color effect to particles, such as creating a flame effect that transitions from yellow to red.

Lastly, blending materials is another advanced technique that can be facilitated by RDShaderSource. For instance, you might want to blend two textures together based on an alpha mask:

var texture1_uniform : StringName = "u_texture1"
var texture2_uniform : StringName = "u_texture2"
var mask_uniform : StringName = "u_mask"
var texture1 : RID = load("res://texture1.png").get_rid()
var texture2 : RID = load("res://texture2.png").get_rid()
var mask : RID = load("res://mask.png").get_rid()

RenderingDevice.get_singleton().shader_set_uniform(shader, texture1_uniform, texture1)
RenderingDevice.get_singleton().shader_set_uniform(shader, texture2_uniform, texture2)
RenderingDevice.get_singleton().shader_set_uniform(shader, mask_uniform, mask)

The shader can utilize the mask to determine the blend factor between two textures, creating a dynamic and adjustable material blend on-the-fly.

Through each of these examples, you can see the versatility of RDShaderSource in Godot 4. Be it for real-time scene adaptation, post-processing, dynamic objects, particle systems, or material blending; RDShaderSource equips you with the underlying control necessary to drive these complex visual elements seamlessly. As we often highlight at Zenva, understanding and leveraging the intricate parts of a game engine like Godot is crucial to crafting high-quality content that stands out. Continue experimenting with these code snippets as a base, and you will be well on your way to creating visually engaging games and applications.

Forge Ahead in Your Game Development Journey

Mastering Godot 4 and understanding the complexities of RDShaderSource is a commendable milestone in your game development journey. We encourage you to keep this momentum going and further expand your knowledge and expertise. A fantastic way to continue building on what you’ve learned is to explore the Godot Game Development Mini-Degree offered by Zenva Academy.

This comprehensive program is designed to help both beginners and seasoned developers alike create cross-platform games, covering essential topics such as 2D and 3D assets, gameplay control flow, game mechanics across various genres, and much more. The best part? You can learn at your own pace, with 24/7 access to content and structured curriculum to guide you from basic concepts to creating fully-fledged games in no time.

For those looking to dive even deeper into specific areas or learn more about Godot’s capabilities, Zenva Academy offers a broad collection of Godot courses tailored to fit all skill levels and interests. No matter where you are on your game development path, we’re here to support your growth with high-quality content that empowers you to bring your visions to life. So why wait? Take the next step today and join us at Zenva Academy, where your learning adventure continues!


As you’ve seen throughout this tutorial, harnessing the power of RDShaderSource in Godot 4 can immensely elevate the visual fidelity and performance of your games. Whether it’s for creating immersive environments, interactive gameplay, or just adding that extra polish of visual effects, the skills you’ve gained here are invaluable assets to your developer toolkit. The journey through game development is endlessly creative and technically rewarding—a path paved with opportunities for innovation and problem-solving.

At Zenva Academy, we’re passionate about helping you fulfill your dreams of becoming a leading game developer. Our Godot Game Development Mini-Degree is just the trailhead for exploring the expanse of possibilities within game creation. Embark on this next chapter of your learning adventure with us, and continue to shape the gaming world, one line of code at a time.

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