Shading language

Introduction

Godot uses a shading language similar to GLSL ES 3.0. Most datatypes and functions are supported, and the few remaining ones will likely be added over time.

If you are already familiar with GLSL, the Godot Shader Migration Guide is a resource that will help you transition from regular GLSL to Godot’s shading language.

Data types

Most GLSL ES 3.0 datatypes are supported:

Casting

Just like GLSL ES 3.0, implicit casting between scalars and vectors of the same size but different type is not allowed. Casting of types of different size is also not allowed. Conversion must be done explicitly via constructors.

Example:

float a = 2; // invalid
float a = 2.0; // valid
float a = float(2); // valid

Default integer constants are signed, so casting is always needed to convert to unsigned:

int a = 2; // valid
uint a = 2; // invalid
uint a = uint(2); // valid

Members

Individual scalar members of vector types are accessed via the “x”, “y”, “z” and “w” members. Alternatively, using “r”, “g”, “b” and “a” also works and is equivalent. Use whatever fits best for your needs.

For matrices, use the m[row][column] indexing syntax to access each scalar, or m[idx] to access a vector by row index. For example, for accessing the y position of an object in a mat4 you use m[3][1].

Constructing

Construction of vector types must always pass:

// The required amount of scalars
vec4 a = vec4(0.0, 1.0, 2.0, 3.0);
// Complementary vectors and/or scalars
vec4 a = vec4(vec2(0.0, 1.0), vec2(2.0, 3.0));
vec4 a = vec4(vec3(0.0, 1.0, 2.0), 3.0);
// A single scalar for the whole vector
vec4 a = vec4(0.0);

Construction of matrix types requires vectors of the same dimension as the matrix. You can also build a diagonal matrix using matx(float) syntax. Accordingly, mat4(1.0) is an identity matrix.

mat2 m2 = mat2(vec2(1.0, 0.0), vec2(0.0, 1.0));
mat3 m3 = mat3(vec3(1.0, 0.0, 0.0), vec3(0.0, 1.0, 0.0), vec3(0.0, 0.0, 1.0));
mat4 identity = mat4(1.0);

Matrices can also be built from a matrix of another dimension. There are two rules : If a larger matrix is constructed from a smaller matrix, the additional rows and columns are set to the values they would have in an identity matrix. If a smaller matrix is constructed from a larger matrix, the top, left submatrix of the larger matrix is used.

mat3 basis = mat3(WORLD_MATRIX);
mat4 m4 = mat4(basis);
mat2 m2 = mat2(m4);

Swizzling

It is possible to obtain any combination of components in any order, as long as the result is another vector type (or scalar). This is easier shown than explained:

vec4 a = vec4(0.0, 1.0, 2.0, 3.0);
vec3 b = a.rgb; // Creates a vec3 with vec4 components.
vec3 b = a.ggg; // Also valid; creates a vec3 and fills it with a single vec4 component.
vec3 b = a.bgr; // Order does not matter.
vec3 b = a.xyz; // Also rgba, xyzw are equivalent.
vec3 b = a.stp; // And stpq (for texture coordinates).
float c = b.w; // Invalid, because "w" is not present in vec3 b.
vec3 c = b.xrt; // Invalid, mixing different styles is forbidden.
b.rrr = a.rgb; // Invalid, assignment with duplication.
b.bgr = a.rgb; // Valid assignment.

Precision

It is possible to add precision modifiers to datatypes; use them for uniforms, variables, arguments and varyings:

lowp vec4 a = vec4(0.0, 1.0, 2.0, 3.0); // low precision, usually 8 bits per component mapped to 0-1
mediump vec4 a = vec4(0.0, 1.0, 2.0, 3.0); // medium precision, usually 16 bits or half float
highp vec4 a = vec4(0.0, 1.0, 2.0, 3.0); // high precision, uses full float or integer range (default)

Using lower precision for some operations can speed up the math involved (at the cost of less precision). This is rarely needed in the vertex processor function (where full precision is needed most of the time), but is often useful in the fragment processor.

Some architectures (mainly mobile) can benefit significantly from this, but there are downsides such as the additional overhead of conversion between precisions. Refer to the documentation of the target architecture for further information. In many cases, mobile drivers cause inconsistent or unexpected behavior and it is best to avoid specifying precision unless necessary.

Arrays

Arrays are containers for multiple variables of a similar type. Note: As of Godot 3.2, only local and varying arrays have been implemented.

Local arrays

Local arrays are declared in functions. They can use all of the allowed datatypes, except samplers. The array declaration follows a C-style syntax: [const] + [precision] + typename + identifier + [array size].

void fragment() {
    float arr[3];
}

They can be initialized at the beginning like:

float float_arr[3] = float[3] (1.0, 0.5, 0.0); // first constructor
int int_arr[3] = int[] (2, 1, 0); // second constructor
vec2 vec2_arr[3] = { vec2(1.0, 1.0), vec2(0.5, 0.5), vec2(0.0, 0.0) }; // third constructor
bool bool_arr[] = { true, true, false }; // fourth constructor - size is defined automatically from the element count

You can declare multiple arrays (even with different sizes) in one expression:

float a[3] = float[3] (1.0, 0.5, 0.0),
b[2] = { 1.0, 0.5 },
c[] = { 0.7 },
d = 0.0,
e[5];

To access an array element, use the indexing syntax:

float arr[3];
arr[0] = 1.0; // setter
COLOR.r = arr[0]; // getter

Arrays also have a built-in function .length() (not to be confused with the built-in length() function). It doesn’t accept any parameters and will return the array’s size.

float arr[] = { 0.0, 1.0, 0.5, -1.0 };
for (int i = 0; i < arr.length(); i++) {
    // ...
}

Note

If you use an index below 0 or greater than array size - the shader will crash and break rendering. To prevent this, use length(), if, or clamp() functions to ensure the index is between 0 and the array’s length. Always carefully test and check your code. If you pass a constant expression or a simple number, the editor will check its bounds to prevent this crash.

Constants

Use the const keyword before the variable declaration to make that variable immutable, which means that it cannot be modified. All basic types, except samplers can be declared as constants. Accessing and using a constant value is slightly faster than using a uniform. Constants must be initialized at their declaration.

const vec2 a = vec2(0.0, 1.0);
vec2 b;
a = b; // invalid
b = a; // valid

Constants cannot be modified and additionally cannot have hints, but multiple of them (if they have the same type) can be declared in a single expression e.g

const vec2 V1 = vec2(1, 1), V2 = vec2(2, 2);

Similar to variables, arrays can also be declared with const.

const float arr[] = { 1.0, 0.5, 0.0 };
arr[0] = 1.0; // invalid
COLOR.r = arr[0]; // valid

Constants can be declared both globally (outside of any function) or locally (inside a function). Global constants are useful when you want to have access to a value throughout your shader that does not need to be modified. Like uniforms, global constants are shared between all shader stages, but they are not accessible outside of the shader.

shader_type spatial;
const float PI = 3.14159265358979323846;

Operators

Godot shading language supports the same set of operators as GLSL ES 3.0. Below is the list of them in precedence order:

Flow control

Godot Shading language supports the most common types of flow control:

// if and else
if (cond) {
} else {
}
// switch
switch(i) { // signed integer expression
    case -1:
        break;
    case 0:
        return; // break or return
    case 1: // pass-through
    case 2:
        break;
    //...
    default: // optional
        break;
}
// for loops
for (int i = 0; i < 10; i++) {
}
// while
while (true) {
}
// do while
do {
} while(true);

Keep in mind that, in modern GPUs, an infinite loop can exist and can freeze your application (including editor). Godot can’t protect you from this, so be careful not to make this mistake!

Warning

When exporting a GLES2 project to HTML5, WebGL 1.0 will be used. WebGL 1.0 doesn’t support dynamic loops, so shaders using those won’t work there.

Discarding

Fragment and light functions can use the discard keyword. If used, the fragment is discarded and nothing is written.

Functions

It is possible to define functions in a Godot shader. They use the following syntax:

ret_type func_name(args) {
    return ret_type; // if returning a value
}
// a more specific example:
int sum2(int a, int b) {
    return a + b;
}

You can only use functions that have been defined above (higher in the editor) the function from which you are calling them.

Function arguments can have special qualifiers:

• in: Means the argument is only for reading (default).
• out: Means the argument is only for writing.
• inout: Means the argument is fully passed via reference.

Example below:

void sum2(int a, int b, inout int result) {
    result = a + b;
}

Varyings

To send data from the vertex to the fragment processor function, varyings are used. They are set for every primitive vertex in the vertex processor, and the value is interpolated for every pixel in the fragment processor.

shader_type spatial;
varying vec3 some_color;
void vertex() {
    some_color = NORMAL; // Make the normal the color.
}
void fragment() {
    ALBEDO = some_color;
}

Varying can also be an array:

shader_type spatial;
varying float var_arr[3];
void vertex() {
    var_arr[0] = 1.0;
    var_arr[1] = 0.0;
}
void fragment() {
    ALBEDO = vec3(var_arr[0], var_arr[1], var_arr[2]); // red color
}

Interpolation qualifiers

Certain values are interpolated during the shading pipeline. You can modify how these interpolations are done by using interpolation qualifiers.

shader_type spatial;
varying flat vec3 our_color;
void vertex() {
    our_color = COLOR.rgb;
}
void fragment() {
    ALBEDO = our_color;
}

There are two possible interpolation qualifiers:

Uniforms

Passing values to shaders is possible. These are global to the whole shader and are called uniforms. When a shader is later assigned to a material, the uniforms will appear as editable parameters in it. Uniforms can’t be written from within the shader.

shader_type spatial;
uniform float some_value;

You can set uniforms in the editor in the material. Or you can set them through GDScript:

material.set_shader_param("some_value", some_value)

Note

The first argument to set_shader_param is the name of the uniform in the shader. It must match exactly to the name of the uniform in the shader or else it will not be recognized.

Any GLSL type except for void can be a uniform. Additionally, Godot provides optional shader hints to make the compiler understand for what the uniform is used.

shader_type spatial;
uniform vec4 color : hint_color;
uniform float amount : hint_range(0, 1);
uniform vec4 other_color : hint_color = vec4(1.0);

It’s important to understand that textures that are supplied as color require hints for proper sRGB->linear conversion (i.e. hint_albedo), as Godot’s 3D engine renders in linear color space.

Full list of hints below:

GDScript uses different variable types than GLSL does, so when passing variables from GDScript to shaders, Godot converts the type automatically. Below is a table of the corresponding types:

Note

Be careful when setting shader uniforms from GDScript, no error will be thrown if the type does not match. Your shader will just exhibit undefined behavior.

Uniforms can also be assigned default values:

shader_type spatial;
uniform vec4 some_vector = vec4(0.0);
uniform vec4 some_color : hint_color = vec4(1.0);

Built-in functions

A large number of built-in functions are supported, conforming to GLSL ES 3.0. When vec_type (float), vec_int_type, vec_uint_type, vec_bool_type nomenclature is used, it can be scalar or vector.

Note

For a list of the functions that are not available in the GLES2 backend, please see the Differences between GLES2 and GLES3 doc.