godot in shader example of func returning some value

3 min read 24-01-2025

godot in shader example of func returning some value

Godot's shader language (a variant of GLSL) allows you to create custom functions that return values, adding modularity and reusability to your shaders. This is particularly useful for complex calculations or effects that you might want to use multiple times within a single shader. This article provides examples demonstrating how to define and utilize functions that return values within Godot shaders.

Understanding Shader Functions

Functions in Godot shaders operate similarly to functions in other programming languages. They accept input parameters (arguments), perform calculations based on those inputs, and return a single value or a vector of values. The returned value can then be used elsewhere in your shader.

Basic Example: Returning a Single Value

This example demonstrates a simple function that returns the square of a given input value:

shader_type spatial;

uniform float time : hint_range(0, 10) = 0;

float square(float x) {
  return x * x;
}

void fragment() {
  float value = square(time); //Call the square function
  ALBEDO = vec3(value, 0.0, 0.0); //Use the returned value
}

This shader defines a function square that takes a single float x as input and returns its square. In the fragment function, we call square with the time uniform and use its result to color the rendered object red, with the intensity determined by the squared time value.

Returning a Vector Value

Functions can also return vectors, allowing you to perform more complex calculations and manipulate multiple values simultaneously:

shader_type spatial;

uniform vec2 uv_offset : hint_range(-1,1) = vec2(0.0);

vec3 hslToRgb(vec3 hsl) {
  float h = hsl.x;
  float s = hsl.y;
  float l = hsl.z;

  float c = (1.0 - abs(2.0 * l - 1.0)) * s;
  float x = c * (1.0 - abs(mod(h / 60.0, 2.0) - 1.0));
  vec3 rgb;

  if (h < 60.0) {
    rgb = vec3(c, x, 0.0);
  } else if (h < 120.0) {
    rgb = vec3(x, c, 0.0);
  } else if (h < 180.0) {
    rgb = vec3(0.0, c, x);
  } else if (h < 240.0) {
    rgb = vec3(0.0, x, c);
  } else if (h < 300.0) {
    rgb = vec3(x, 0.0, c);
  } else {
    rgb = vec3(c, 0.0, x);
  }

  float m = l - 0.5 * c;
  return rgb + vec3(m, m, m);
}

void fragment() {
  vec3 hsl_color = vec3(UV.x * 360.0 + uv_offset.x*360.0, 1.0, 0.5); //Hue changes across the surface.
  ALBEDO = hslToRgb(hsl_color);
}

This shader demonstrates a function hslToRgb that converts an HSL (Hue, Saturation, Lightness) color vector to its RGB equivalent. The result is then used to color the object, creating a smooth hue transition based on the UV coordinates.

Advanced Usage: Overloading and Recursion

While Godot's shader language doesn't directly support function overloading (defining multiple functions with the same name but different parameters), you can achieve similar results through careful naming conventions and conditional logic within a single function.

Recursion (functions calling themselves) is generally less practical in shaders due to performance concerns, as it can lead to significant overhead. However, it is technically possible if implemented carefully and sparingly. Avoid deep recursion in your shader functions.

Error Handling

Godot's shader compiler will flag syntax errors. However, runtime errors within your functions might be harder to debug. Careful testing and using debug outputs (such as printing values to the console, though this is limited in Godot's shader environment) is vital.

Conclusion

Functions returning values are a powerful tool for writing cleaner, more maintainable shaders in Godot. By creating reusable functions, you can simplify complex shader logic, improve code readability, and reduce redundancy. This enhances both the development process and the overall efficiency of your shaders. Remember to always prioritize readability and performance when designing and implementing your shader functions.