Spatial shaders

Spatial shaders are used for shading 3D objects. They are the most complex type of shader Godot offers. Spatial shaders are highly configurable with different render modes and different rendering options (e.g. Subsurface Scattering, Transmission, Ambient Occlusion, Rim lighting etc). Users can optionally write vertex, fragment, and light processor functions to affect how objects are drawn.

Render modes

Vertex built-ins

Values marked as “in” are read-only. Values marked as “out” are for optional writing and will not necessarily contain sensible values. Values marked as “inout” provide a sensible default value, and can optionally be written to. Samplers are not subjects of writing and they are not marked.

Vertex data (VERTEX, NORMAL, TANGENT, BITANGENT) are presented in local model space. If not written to, these values will not be modified and be passed through as they came.

They can optionally be presented in world space by using the world_vertex_coords render mode.

Users can disable the built-in modelview transform (projection will still happen later) and do it manually with the following code:

shader_type spatial;
render_mode skip_vertex_transform;
void vertex() {
    VERTEX = (MODELVIEW_MATRIX * vec4(VERTEX, 1.0)).xyz;
    NORMAL = (MODELVIEW_MATRIX * vec4(NORMAL, 0.0)).xyz;
    // same as above for binormal and tangent, if normal mapping is used
}

Other built-ins, such as UV, UV2 and COLOR, are also passed through to the fragment function if not modified.

Users can override the modelview and projection transforms using the POSITION built-in. When POSITION is used, the value from VERTEX is ignored and projection does not happen. However, the value passed to the fragment shader still comes from VERTEX.

For instancing, the INSTANCE_CUSTOM variable contains the instance custom data. When using particles, this information is usually:

• x: Rotation angle in radians.
• y: Phase during lifetime (0 to 1).
• z: Animation frame.

This allows you to easily adjust the shader to a particle system using default particles material. When writing a custom particles shader, this value can be used as desired.

Fragment built-ins

The default use of a Godot fragment processor function is to set up the material properties of your object and to let the built-in renderer handle the final shading. However, you are not required to use all these properties, and if you don’t write to them, Godot will optimize away the corresponding functionality.

Light built-ins

Writing light processor functions is completely optional. You can skip the light function by setting render_mode to unshaded. If no light function is written, Godot will use the material properties written to in the fragment function to calculate the lighting for you (subject to the render_mode).

To write a light function, assign something to DIFFUSE_LIGHT or SPECULAR_LIGHT. Assigning nothing means no light is processed.

The light function is called for every light in every pixel. It is called within a loop for each light type.

Below is an example of a custom light function using a Lambertian lighting model:

void light() {
    DIFFUSE_LIGHT += dot(NORMAL, LIGHT) * ATTENUATION * ALBEDO;
}

If you want the lights to add together, add the light contribution to DIFFUSE_LIGHT using +=, rather than overwriting it.