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Writing Shadertools Shader Modules


This object can be used as shader module directly:

assembleShaders(gl, {..., modules: [MY_SHADER_MODULE]});

Alternatively, you can register it so that it can be referred to by name.

assembleShaders(gl, {..., modules: ['my-module']});

Structure of a Shader Module

Shader Module Type

A shader module is either:

  • Generic - a set of generic GLSL functions that can be included either in a fragment shader or a vertex shader (or both). The fp64 module is a good example of this type of module.
  • Functional - Contains specific vertex and/or fragment shader "chunks", often set up so that the vertex shader part sets up a varying used by the fragment shader part.

Shader Module Descriptor

To define a new shader module, you create a descriptor object that brings together all the necessary pieces:

export const MY_SHADER_MODULE = {
  name: 'my-shader-module',
  vs: '...',
  fs: '...',
  dependencies: [],
  deprecations: [],

Descriptor objects can define the following fields:

  • name (String, Required) - The name of the shader module.
  • vs - (String | null)
  • fs - (String | null)
  • getUniforms JavaScript function that maps JavaScript parameter keys to uniforms used by this module
  • uniforms (Object) - a light alternative to getUniforms, see below
  • dependencies (Array) - a list of other shader modules that this module is dependent on
  • deprecations (Array) - a list of deprecated APIs.

If deprecations is supplied, assembleShaders will scan GLSL source code for the deprecated constructs and issue a console warning if found. Each API is described in the following format:

  • type: uniform <type> or function
  • old: name of the deprecated uniform/function
  • new: name of the new uniform/function
  • deprecated: whether the old API is still supported.


The GLSL code for a shader module typically contains:

  • a mix of uniform and varying declarations
  • one or more GLSL function definitions


Each shader module provides a method to get a map of uniforms for the shader. This function will be called with two arguments:

  • opts - the module settings to update. This argument may not be provided when getUniforms is called to generate a set of default uniform values.
  • context - the uniforms generated by this module's dependencies.

The function should return a JavaScript object with keys representing uniform names and values representing uniform values.

The function should expect the shape of the dependency uniforms to vary based on what's passed in opts. This behavior is intended because we only want to recalculate a uniform if the uniforms that it depends on are changed. An example is the project and project64 modules in When opts.viewport is provided, project64 will receive the updated projection matrix generated by the project module. If opts.viewport is empty, then the project module generates nothing and so should project64.


If the uniforms of this module can be directly pulled from user settings, they may declaratively defined by a uniforms object:

  name: 'my-shader-module',
  uniforms: {
    strength: {type: 'number', value: 1, min: 0, max: 1},
    center: [0.5, 0.5]

At runtime, this map will be used to generate the uniforms needed by the shaders. If either strength or center is present in the user's module settings, then the user's value will be used; otherwise, the default value in the original definition will be used.

Each uniform definition may contain the following fields:

  • type (String) - one of number, boolean, array or object
  • value - the default value of this uniform

With type: 'number', the following additional fields may be added for validation:

  • min (Number)
  • max (Number)

Note: uniforms is ignored if getUniforms is provided.

Platform Detection

Also does platform detection and injects #define statements enabling your shader to conditionally use code.