Shaders are unique programs that run on the GPU. They are used to specify how to take mesh data (vertex positions, colors, normals, etc.) and draw them to the screen. Shaders do not process information the same way a normal program does because they are optimized for running on the GPU. One consequence of this is that shaders do not retain their data after they run; they output a final color to the screen and then move on. Accordingly, there is no way of accessing the color output from the last run of the shader.

Godot uses a shader language very similar to GLSL, but with added functionality and slightly less flexibility. The reason for doing this is that Godot integrates built-in functionality to make writing complex shaders substantially easier. Godot wraps the user-written shader code in code of its own. That way, Godot handles a lot of the low-level stuff that the user doesn't need to worry about, and it is able to parse your shader code and use it to affect the rendering pipeline. For more advanced shaders, you can turn this functionality off using a render_mode.

This document provides you with some information about shaders, specific to Godot. For a detailed reference of the shading language in Godot see the Godot shading language doc.

Shader types

Instead of supplying a general purpose configuration for all uses (2D, 3D, particles), Godot shaders must specify what they are intended for. Different types support different render modes, built-in variables, and processing functions.

All shaders need to specify their type in the first line, in the following format:

shader_type spatial;

Valid types are:

For detailed information on each shading type, see the corresponding reference document.

Render modes

Different shader types support different render modes. They are optional and, if specified, must be after the shader_type. Render modes are used to alter the way built-in functionality is handled. For example, it is common to use the render mode unshaded to skip the built-in light processor function.

Render modes are specified underneath the shader type:

shader_type spatial;
render_mode unshaded, cull_disabled;

Each shader type has a different list of render modes available. See the document for each shader type for a complete list of render modes.

Funzioni del processore

Depending on the shader type, different processor functions may be optionally overridden. For "spatial" and "canvas_item", it is possible to override vertex, fragment, and light. For "particles", only vertex can be overridden.

Vertex processor

The vertex processing function is called once for every vertex in "spatial" and "canvas_item" shaders. For "particles" shaders, it is called once for every particle.

The vertex function is used to modify per-vertex information that will be passed on to the fragment function. It can also be used to establish variables that will be sent to the fragment function by using varyings(see other doc).

By default, Godot will take your vertex information and transform it accordingly to be drawn. If this is undesirable, you can use render modes to transform the data yourself; see the Spatial shader doc for an example of this.

Fragment processor

The fragment processing function is used to set up the Godot material parameters per pixel. This code runs on every visible pixel the object or primitive draws. It is only available in "spatial" and "canvas_item" shaders.

L'uso standard della funzione fragment è quello di impostare le proprietà del materiale che saranno usate per calcolare l'illuminazione. Per esempio, si impostano i valori per `ROUGHNESS, RIM, o TRANSMISSION` che indicano alla funzione luce come le luci rispondono a quel frammento. Questo rende possibile il controllo di una complessa pipeline di shading senza che l'utente debba scrivere molto codice. Se non avete bisogno di questa funzionalità integrata, potete ignorarla e scrivere la vostra funzione di elaborazione delle luci e Godot la ottimizzerà. Per esempio, se non si scrive un valore su `RIM, Godot non calcolerà l'illuminazione del bordo. Durante la compilazione, Godot controlla se RIM viene utilizzato; in caso contrario, taglia fuori tutto il codice corrispondente. Pertanto, non si sprecheranno i calcoli sugli effetti che non si usano.

Light processor

The light processor runs per pixel too, but also runs for every light that affects the object (and does not run if no lights affect the object). It exists as a function called inside the fragment processor and typically operates on the material properties setup inside the fragment function.

The light processor works differently in 2D than it does in 3D; for a description of how it works in each, see their documentation, CanvasItem shaders and Spatial shaders, respectively.