Converting GLSL to Godot shaders

This document explains the differences between Godot's shading language and GLSL and gives practical advice on how to migrate shaders from other sources, such as Shadertoy and The Book of Shaders, into Godot shaders.

For detailed information on Godot's shading language, please refer to the Shading Language reference.

GLSL

Godot uses a shading language based on GLSL with the addition of a few quality-of-life features. Accordingly, most features available in GLSL are available in Godot's shading language.

Shader programs

In GLSL, each shader uses a separate program. You have one program for the vertex shader and one for the fragment shader. In Godot, you have a single shader that contains a vertex and/or a fragment function. If you only choose to write one, Godot will supply the other.

Godot allows uniform variables and functions to be shared by defining the fragment and vertex shaders in one file. In GLSL, the vertex and fragment programs cannot share variables except when varyings are used.

Vertex attributes

In GLSL, you can pass in per-vertex information using attributes and have the flexibility to pass in as much or as little as you want. In Godot, you have a set number of input attributes, including VERTEX (position), COLOR, UV, UV2, NORMAL. For a complete list, see the Shading language reference.

gl_Position

gl_Position receives the final position of a vertex specified in the vertex shader. It is specified by the user in clip space. Typically, in GLSL, the model space vertex position is passed in using a vertex attribute called position and you handle the conversion from model space to clip space manually.

В Godot, VERTEX определяет положение вершины в пространстве модели в начале функции vertex. Godot также обрабатывает окончательное преобразование в пространство клипа после выполнения пользовательской функции vertex. Если вы хотите пропустить преобразование из пространства модели в пространство вида, вы можете установить render_mode на skip_vertex_transform. Если вы хотите пропустить все преобразования, установите render_mode в skip_vertex_transform и установите PROJECTION_MATRIX в mat4(1.0), чтобы обнулить окончательное преобразование из пространства вида в пространство клипа.

Varуings

Varyings are a type of variable that can be passed from the vertex shader to the fragment shader. In modern GLSL (3.0 and up), varyings are defined with the in and out keywords. A variable going out of the vertex shader is defined with out in the vertex shader and in inside the fragment shader.

Главная

In GLSL, each shader program looks like a self-contained C-style program. Accordingly, the main entry point is main. If you are copying a vertex shader, rename main to vertex and if you are copying a fragment shader, rename main to fragment.

Константы

Global array constants are not supported in Godot 3.x. You can fake the functionality by using a uniform initialized to the value, but you will not benefit from the increased speed from using a constant.

Macros

В соответствии со своим сходством с языком C, GLSL позволяет использовать макросы. Обычно #define используется для определения констант или небольших функций. Не существует прямого способа перевести определения на язык затенения Godot. Если определяется функция, то замените на функцию, а если константа, то замените на форму. Для других макросов (#if, #ifdef и т.д.) нет эквивалента, потому что они выполняются на этапе предварительной обработки компиляции.

Переменные

GLSL has many built-in variables that are hard-coded. These variables are not uniforms, so they are not editable from the main program.

Переменная	Тип	Equivalent	Описание
gl_FragColor	out vec4	COLOR	Output color for each pixel.
gl_FragCoord	vec4	FRAGCOORD	For full screen quads. For smaller quads, use UV.
gl_Position	vec4	VERTEX	Position of Vertex, output from Vertex Shader.
gl_PointSize	float	POINT_SIZE	Size of Point primitive.
gl_PointCoord	vec2	POINT_COORD	Position on point when drawing Point primitives.
gl_FrontFаcing	bool	FRONT_FACING	True if front face of primitive.

Координаты

gl_FragCoord in GLSL and FRAGCOORD in the Godot shading language use the same coordinate system. If using UV in Godot, the y-coordinate will be flipped upside down.

Точность

In GLSL, you can define the precision of a given type (float or int) at the top of the shader with the precision keyword. In Godot, you can set the precision of individual variables as you need by placing precision qualifiers lowp, mediump, and highp before the type when defining the variable. For more information, see the Shading Language reference.

Shаdertoy

Shadertoy is a website that makes it easy to write fragment shaders and create pure magic.

Shadertoy does not give the user full control over the shader. It handles all the input and uniforms and only lets the user write the fragment shader.

Типы

Shadertoy uses the webgl spec, so it runs a slightly different version of GLSL. However, it still has the regular types, including constants and macros.

mаinImage

The main point of entry to a Shadertoy shader is the mainImage function. mainImage has two parameters, fragColor and fragCoord, which correspond to COLOR and FRAGCOORD in Godot, respectively. These parameters are handled automatically in Godot, so you do not need to include them as parameters yourself. Anything in the mainImage function should be copied into the fragment function when porting to Godot.

Переменные

Чтобы сделать написание фрагментных шейдеров простым и легким, Shadertoy обрабатывает передачу множества полезной информации из основной программы в фрагментный шейдер за вас. Некоторые из них не имеют аналогов в Godot, потому что Godot решил не делать их доступными по умолчанию. Это нормально, потому что Godot дает вам возможность создавать свои собственные формы. Для переменных, эквиваленты которых перечислены как "Provide with Uniform", пользователи сами отвечают за создание такой формы. Описание дает читателю подсказку о том, что можно передать в качестве замены.

Переменная	Тип	Equivalent	Описание
frаgColor	out vec4	COLOR	Output color for each pixel.
fragCoord	vec2	FRAGCOORD.xy	For full screen quads. For smaller quads, use UV.
iRеsolution	vec3	1.0 / SCREEN_PIXEL_SIZE	Can also pass in manually.
iTime	float	TIME	Time since shader started.
iTimeDelta	float	Provide with Uniform	Time to render previous frame.
iFrame	float	Provide with Uniform	Frame number.
iChannelTime[4]	float	Provide with Uniform	Time since that particular texture started.
iMouse	vec4	Provide with Uniform	Mouse position in pixel coordinates.
iDate	vec4	Provide with Uniform	Current date, expressed in seconds.
iChannelResolution[4]	vec3	1.0 / TEXTURE_PIXEL_SIZE	Resolution of particular texture.
iChanneli	Sampler2D	TEXTURE	Godot provides only one built-in; user can make more.

Координаты

fragCoord behaves the same as gl_FragCoord in GLSL and FRAGCOORD in Godot.

The Book of Shaders

Similar to Shadertoy, The Book of Shaders provides access to a fragment shader in the web browser, with which the user may interact. The user is restricted to writing fragment shader code with a set list of uniforms passed in and with no ability to add additional uniforms.

For further help on porting shaders to various frameworks generally, The Book of Shaders provides a page on running shaders in various frameworks.

Типы

The Book of Shaders uses the webgl spec, so it runs a slightly different version of GLSL. However, it still has the regular types, including constants and macros.

Главная

The entry point for a Book of Shaders fragment shader is main, just like in GLSL. Everything written in a Book of Shaders main function should be copied into Godot's fragment function.

Переменные

The Book of Shaders sticks closer to plain GLSL than Shadertoy does. It also implements fewer uniforms than Shadertoy.

Переменная	Тип	Equivalent	Описание
gl_FragColor	out vec4	COLOR	Output color for each pixel.
gl_FragCoord	vec4	FRAGCOORD	For full screen quads. For smaller quads, use UV.
u_resolution	vec2	1.0 / SCREEN_PIXEL_SIZE	Can also pass in manually.
u_time	float	TIME	Time since shader started.
u_mouse	vec2	Provide with Uniform	Mouse position in pixel coordinates.

Координаты

The Book of Shaders uses the same coordinate system as GLSL.