Shaders

Note: These docs were adopted from the original Motion Canvas docs

Shaders allow you to apply custom effects to any node using WebGL.

Experimental

This is an experimental feature. The behavior and API may change drastically between minor releases.

Shaders can be specified using the shaders property. In the simplest case, the value should be a string containing the GLSL code for the fragment shader:

import myShader from './myShader.glsl';

//...

view.add(
  <Circle
    size={200}
    fill="lightseagreen"
    shaders={myShader}
  />,
);

Below is an example of a simple shader that inverts the colors of the node:

myShader.glsl

#version 300 es
precision highp float;

#include "@revideo/core/shaders/common.glsl"

void main() {
    outColor = texture(sourceTexture, sourceUV);
    outColor.rgb = 1.0 - outColor.rgb;
}

GLSL Preprocessor

Motion Canvas comes with a simple GLSL preprocessor that lets you include files using the #include directive:

#include "path-to-file"

The path is resolved using the same rules as import statements in JavaScript. It can point to a relative file:

#include "../utils/math.glsl"

Or to a file from another package:

#include "@revideo/core/shaders/common.glsl"

For convenience, a GLSL file can be imported only once per shader. Each subsequent import of the same file will be ignored so #ifdef guards are not necessary.

Default uniforms

The following uniforms are available in all shaders:

in vec2 screenUV;
in vec2 sourceUV;
in vec2 destinationUV;

out vec4 outColor;

uniform float time;
uniform float deltaTime;
uniform float framerate;
uniform int frame;
uniform vec2 resolution;
uniform sampler2D sourceTexture;
uniform sampler2D destinationTexture;
uniform mat4 sourceMatrix;
uniform mat4 destinationMatrix;

They can be included using the following directive:

#include "@revideo/core/shaders/common.glsl"

Source and Destination

Shaders in Motion Canvas follow the same idea as globalCompositeOperation in 2D canvas. The sourceTexture contains the node being rendered, and the destinationTexture contains what has already been rendered to the screen. These two can be sampled using sourceUV and destinationUV respectively, and then combined in various ways to produce the desired result.

Custom uniforms

You can pass custom uniforms to the shader by replacing the shader string with a configuration object:

import myShader from './myShader.glsl';

//...

view.add(
  <Circle
    size={200}
    fill="lightseagreen"
    shaders={{
      fragment: myShader,
      uniforms: {
        myFloat: 0.5,
        myVec2: new Vector2(2, 5),
        myColor: new Color('blue'),
      },
    }}
  />,
);

The uniforms property is an object where the keys are the names of the uniforms and the values are what's passed to the shader.

The type of the uniform is inferred from the value:

TypeScript	GLSL
number	float
[number, number]	vec2
[number, number, number]	vec3
[number, number, number, number]	vec4
Color	vec4
Vector2	vec2
BBox	vec4
Spacing	vec4

With that in mind, the uniforms from the above example will be available in the shader as:

myShader.glsl

uniform float myFloat;
uniform vec2 myVec2;
uniform vec4 myColor;

It's also possible to create custom classes that can be passed as uniforms by implementing the WebGLConvertible interface.

Caching

When a node is cached, its contents are first rendered to a separate canvas and then transferred to the screen (You can read more about it in the Filters and Effects section) When a shader is applied to a descendant of a cached node, the destinationTexture will only contain the things drawn in the context of that cached node and nothing else. This is analogous to how composite operations work.

Any node with a shader is automatically cached - this lets us figure out the contents of the sourceTexture before shaders are run. Caching requires us to know the size and position of everything rendered by the node. This goes beyond its logical size. Things like shadows, strokes, and filters can make the rendered area larger. We account for that in the case of built-in effects, but for custom shaders you may need to adjust the cache size manually. The cachePadding property can be used to do exactly that. It specifies the extra space around the node that should be included in the cache.