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phixl

A library for WebGL which is for people who want to write their own shaders.

NPM | GitHub

Overview

This library provides a layer of abstraction over WebGL which allows users to apply a shader to a canvas without having to worry about the WebGL API at all.

The library exports a factory function called Shader which takes the GLSL code as strings and the data you want to supply to the shader as arguments. Shader will return a function which will render that shader to a canvas.

You can also use the function returned by Shader to render to a texture using WebGLFramebuffer. This lefts you sample from the result of other shaders as textures. This lets your shaders become composable and lets you easily write programs which take advantage of the parallelization of the GPU.

Quickstart

Say you wanted to render a cube using phixl and WebGL using the following data for gl.drawElements. For simplicity, we'll just color the cube using the normal vectors.

const CUBE_INDICES = new Uint16Array([...]);
const CUBE_VERTICES = new Float32Array([...]);
const CUBE_NORMALS = new Float32Array([...]);

Let's set up your vertex shader:

precision mediump float;

attribute vec3 a_Vertex;
attribute vec3 a_Normal;

varying vec3 v_Normal;

uniform mat4 u_ModelMat;
uniform mat4 u_ViewMat;
uniform mat4 u_PerspectiveMat;

void main() {
  gl_Position =
    u_PerspectiveMat * u_ViewMat * u_ModelMat * vec4(a_Vertex, 1.0);
  v_Normal = a_Normal;
}

The fragment shader is straightforward:

precision mediump float;

varying vec3 v_Normal;

void main() {
  gl_FragColor = vec4(abs(v_Normal), 1.0);
}

Let's say you are using glslify-loader and raw-loader with Webpack to load the shaders into JS strings:

const vertexSrc = require('vertex.glsl').default;
const fragmentSrc = require('fragment.glsl').default;

Now we want to import the relevant functions from phixl and create a shader:

const {
  ModelMatUniform,
  NormalMatUniform,
  PerspectiveMatUniform,
  Shader,
  Vec3Attribute,
  ViewMatUniform,
} = require('phixl');

const aVertex = Vec3Attribute('a_Vertex', CUBE_VERTICES);
const aNormal = Vec3Attribute('a_Normal', CUBE_NORMALS);

const modelMat = ModelMatUniform('u_ModelMat', {
  scale: 5,
  rotate: [Math.PI / 4, 2, 1, 0],
});
const viewMat =
  ViewMatUniform(
    'u_ViewMat', /* eye */ [0, 0, 30], /* at */ [0, 0, 0], /* up */ [0, 1, 0]);
const perspectiveMat =
  PerspectiveMatUniform(
    'u_PerspectiveMat', /* fovy */ Math.PI / 3, /* aspect */ 1, /* near */ 1,
    /* far */ 1e6);

const shader = Shader(vertexSrc, fragmentSrc, {
  indices: CUBE_INDICES,
  attributes: [aVertex, aNormal],
  uniforms: [modelMat, viewMat, perspectiveMat],
  mode: WebGLRenderingContext.TRIANGLES,
});

The resulting function, shader, can be used to apply that shader to a render target such as a canvas:

const canvas = document.querySelector('canvas');
shader(canvas);

The shader function can also be called with a Texture2DUniform to render the shader to a texture with a WebGLFramebuffer. The resulting texture can later be sampled in other shaders. See examples/game_of_life and examples/ripple_effect for some examples of how you can use this technique for different things.

Examples

For more examples of how to use phixl for various WebGL things, see the examples directory in this repository. They include:

  • Rendering a 3D cube
  • Rendering a 3D cube with a video texture
  • Edge detection algorithm on webcam video
  • GPU accelerated Conway's Game of Life
  • Water ripple effect using the 2D wave equation
  • Dynamic reflections using a CubeCamera

Documentation

Shader

The most important function in the phixl library, Shader, is a factory function that creates functions that apply a shader to a render target. It takes 3 arguments:

  1. The vertex shader source code as a JS string

  2. The fragment shader source code as a JS string

  3. An object which should contain the following keys:

    • attributes: An array of attributes for the shader. See the Attributes section below for what objects to use as elements for the array. This array must have at least one element.
    • uniforms: Optional. An array of uniforms for the shader. See the Uniforms section below for what objects to use as elements of this array. This array may be empty or omitted.
    • indices: Optional. If provided the shader will render using gl.drawElements instead of gl.drawArrays.
    • mode: Optional. Which mode WebGL will use to draw the vertices. The default is WebGLRenderingContext.TRIANGLE_STRIP.
    • clear: Optional. Whether the shader should call gl.clear. If the option is omitted then the value will be treated as true.
    • viewport: Optional. The viewport that WebGL should use when rendering the shader. It should be an array of 4 numbers. The elements will be used as arguments for gl.viewport.

Attributes

This library provides an abstraction for sending attributes to shaders with just a function call. This library assumes that a shader's attributes are immutable and should not be changed once they are initialized.

All attributes take 2 arguments:

  1. The name of the attribute in the shader

  2. The data for the attribute.

The value for the second argument depends on the type of the attribute. For all attributes except for matrix attributes, the argument should be a Float32List. These uniforms are:

  • FloatAttribute
  • Vec2Attribute
  • Vec3Attribute
  • Vec4Attribute

Matrix attributes

Unlike all other attributes, matrix attributes take an array of Float32List as the second argument. Each element of the array is a vector attribute for each column vector of the matrix. Matrix attributes are:

  • Mat2Attribute
  • Mat3Attribute
  • Mat4Attribute

Uniforms

This library also provides some abstractions for sending uniforms to WebGL shaders as well.

Unlike attributes, uniforms are not immutable, and can have their value changed. Almost all uniforms have a set() method for setting the uniforms data after it is created and a data() method for retrieving the current value of the data. The set() method can also be called with a callback with no arguments that returns the uniform data. The callback will be invoked several times in phixl's internals so it should not have side effects.

Below are a list of uniforms available to phixl users. The parameters of uniform functions and their behavior varies quite a bit more than attributes. All uniforms take the name of the uniform in the shader as their first argument. Below is a list of the different uniforms and what parameters they expect.

BooleanUniform

Sends a boolean value to a shader uniform. The second argument should be a number or boolean. Example usage:

const bool = BooleanUniform('u_Foo', true);

IntegerUniform

Sends an integer value to a shader uniform. The second argument should be a whole number. Example usage:

const int = IntegerUniform('u_Foo', 3);

FloatUniform

Sends a float value to a shader uniform. The second argument should be a number. Example usage:

const float = new FloatUniform('u_Foo', Math.PI);

Vector uniforms

Vector uniforms send a vector of float values to a shader uniform. The second argument should be an array of numbers. The size of the array depends on the dimension of the vector. Example usage:

const vec2 = Vec2Uniform('u_Foo', [1, 2]);
const vec3 = Vec3Uniform('u_Bar', [1, 2, 3]);
const vec4 = Vec4Uniform('u_Baz', [1, 2, 3, 4]);

Matrix uniforms

Matrix uniforms sends a matrix of float values to a shader uniform. The second argument should be an array of numbers. The size of the array depends on the dimension of the matrix. Example usage with gl-matrix:

const {mat2, mat3, mat4} = require('gl-matrix');

const mat2 = Mat2Uniform('u_Foo', mat2.create());
const mat3 = Mat3Uniform('u_Bar', mat3.create());
const mat4 = Mat4Uniform('u_Baz', mat4.create());

ModelMatUniform

The ModelMatUniform senda a 4D matrix uniform for shaders meant to transform model vertices into the world coordinates. The second argument is an optional object with the following (each optional) keys:

const modelMat = ModelMatUniform('u_ModelMat', {
  scale: 2, // Can also be an array with 1, 3, or 4 elements.
  rotate: [
    /* theta */ Math.PI / 2,
    /* axis.x */ 2,
    /* axis.y */ 1,
    /* axis.z */ 0,
  ],
  translate: [10, 10, 0],
});

The uniform computes the 4D model matrix which applies the corresponding combination of transformations, the scaling is applied first, then the rotation, and finally the translation.

The object returned by ModelMatUniform has accessor methods which let you get the different components of the model transformation:

modelMat.scaleMatrix(); // Gets the scale matrix as a 4D matrix.
modelMat.rotationMatrix(); // Gets the rotation matrix as a 3D matrix.
modelMat.translation(); // Gets the translation as a 3D vector.

The object returned by ModelMatUniform has convenience methods which allow you to change each individual part of the transformation:

modelMat.scale(3); // Applies this scale to the existing scale.
modelMat.setScale(3); // Resets the scale component of the matrix to the new value.

modelMat.rotate(Math.PI / 2, 1, 1, 0); // Applies the rotation to the existing rotation matrix.
modelMat.setRotation(Math.PI / 2, 1, 1, 0); // Sets the rotation matrix to apply only the provided rotation.

modelMat.translate(1, 2, 3); // Adds the new values to the existing translation vector.
modelMat.setTranslation(1, 2, 3); // Sets the translation vector to this new one.

NormalMatUniform

The NormalMatUniform sends a 3D matrix uniform for transforming model normal vectors to a shader. It takes an object returned by ModelMatUniform as a second argument and computes the resulting normal matrix automatically. Below is an example:

const modelMat = ModelMatUniform('u_ModelMat', ...);
const normalMat = NormalMatUniform('u_NormalMat', modelMat);

ViewMatUniform

The ViewMatUniform sends a 4D matrix to a shader which transforms vertices from world coordinates to the view coordinates of the scene's camera. It takes multiple arguments to compute the view matrix and is based on gl-matrix's lookAt function. Below is an example:

const viewMat =
  ViewMatUniform(
    'u_ViewMat', /* eye */ [0, 0, 30], /* at */ [0, 0, 0], /* up */ [0, 1, 0]);

The object returned by ViewMatUniform has accessor methods which let you get the eye, at, or up vectors that is used to compute the view matrix:

viewMat.eye();
viewMat.at();
viewMat.up();

The object also has setter methods for each vector as well:

viewMat.setEye(10, 0, 30);
viewMat.setAt(10, 0, 0);
viewMat.setUp(1, 10, 0);

As you may notice, the up vector does not need to be normalized, the object will do that for you when it computes the view matrix. The up() method will return the value passed to setUp before normalization.

PerspectiveMatUniform

The PerspectiveMatUniform sends a 4D matrix to a shader which transforms vertices from the view coordinates of the scene's camera to a coordinate system with linear perspective. It takes multiple arguments to compute the perspective matrix and is based on g-matrix's perspective function. Below is an example:

const perspectiveMat =
  PerspectiveMatUniform(
    'u_PerspectiveMat', /* fovy */ Math.PI / 3, /* aspect */ 1, /* near */ 1,
    /* far */ 1e6);

The object returned by PerspectiveMatUniform has accessor methods which let you get the field of view (in radians), the width-to-height aspect ratio, the near plane, and the far plane that is used to compute the perspective matrix:

perspectiveMat.fovy();
perspectiveMat.aspect();
perspectiveMat.near();
perspectiveMat.far();

The object also has setter methods for each parameter for the perspective matrix:

perspectiveMat.setFovy(Math.PI / 4);
perspectiveMat.setAspect(canvas.width / canvas.height);
perspectiveMat.setNear(0.1);
perspectiveMat.setFar(1e4);

Texture2DUniform

The Texture2DUniform sends a 2D texture to a shader in a sampler2D uniform. The second argument is any object which can be used as the data source for gl.texImage2D(...). Below are some examples of how you can initialize a Texture2DUniform:

const image = document.querySelector('img');
const imageTexture = Texture2DUniform('u_Foo', image);

const video = document.querySelector('video');
const videoTexture = Texture2DUniform('u_Bar', video);

const canvas = document.querySelector('canvas');
const canvasTexture = Texture2DUniform('u_Baz', canvas);

// Also could use ImageBitmap, ImageData, or OffscreenCanvas...

The objects returned by uniforms like Texture2DUniform can be the argument of functions returned by Shader. This allows you to apply shaders to textures which can be then used in other shaders. Below is an example:

const textureShader = Shader(...);
const texture = Texture2DUniform('u_Texture');

// We render the first shader to the texture.
textureShader(texture);

const shader = Shader(vertexSrc, fragmentSrc, {
  // attributes, other options...
  uniforms: [
    texture,
    // Other uniforms...
  ],
});

// The second shader renders to the canvas and can sample from the result
// of the first shader, textureShader.
shader(canvas);

CubeTextureUniform

The CubeTextureUniform sends a cube texture to a shader in a samplerCube uniform. The second argument to CubeTextureUniform should be an object with a key for each face of a cube: posx, negx, posy, negy, posz, and negz. Each value of the object should be a data source for a 2D texture that you would for gl.texImage2D:

const cubeTexture = CubeTextureUniform('u_Texture', {
  posx: rightImage,
  negx: leftImage,
  posy: topImage,
  negy: bottomImage,
  posz: frontImage,
  negz: backImage,
});

Unlike Texture2DUniform, the object returned by CubeTextureUniform cannot be used as the argument for a function returned by Shader, though it may be nice at some point to support this!

CubeCameraUniform

CubeCameraUniform allows you to render a shader to a cube texture for things like environment mapping and dynamic reflections. It should only be used for shaders which have a view and perspective matrix, which is almost always present in 3D scenes.

The arguments after the name of the uniform should be the position of the cube camera in the scene as an array of numbers, the scene's ViewMatUniform, and the scene's PerspectiveMatUniform.

For an example of how to use the CubeCameraUniform for dynamic reflections, see examples/cube_camera/src/main.js.

License

This code is publicly available under an Apache-2.0 license. See LICENSE for more information.

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a WebGL library for composing shaders

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