Limelight

Limelight is a WebGL2 wrapper with a focus on making high-performance WebAssembly graphics code easier to write and maintain.

Specifically, it:

• Provides a functional interface that abstracts away the statefulness of WebGL. It accomplishes this by using a shadow GPU that tracks the GPU's state, diffs it with the desired state, and sends only the necessary instructions to WebGL.
• Provides abstractions for buffers and uniforms that defer GPU data transfer until the next draw cycle.
• Provides a typed interface to uniforms and buffers, and automatically generates bindings between shader attributes and Rust structs through a derive macro.

Getting started

See the examples directory for runnable examples.

This tutorial assumes you're familiar with basic WebGL terminology, like vertex and fragment shaders, uniforms, and buffers.

Drawing a triangle

(full code, demo)

This example demonstrates the three main steps to produce an image with limelight:

1. Create a Program object. A Program in limelight contains the vertex and fragment shader pair (a WebGLProgram object), and also contains program-specific state.
2. Create a Renderer. After we have initialized all of our programs with the GL context, we transfer ownership of the GL context into a Renderer, which then becomes responsible for all GL-side state transitions.
3. We call renderer.render(program, buffer), which causes the triangle to be drawn. We have not attached a vertex attribute buffer in this example, and instead use the vertex shader to generate the vertices. We still need to tell WebGL how many vertices (3) we want to generate, so we pass in a DummyBuffer of size 3.

use web_sys::WebGl2RenderingContext;
use limelight::{Program, Renderer, DummyBuffer, DrawMode};

fn render_triangle(gl: WebGl2RenderingContext) {
  // limelight doesn't touch the DOM at all. Use your preferred
  // framework to create a canvas and create a WebGL2 context
  // from it.

  // Create a shader program by passing in GLSL code as strings for
  // the fragment and vertex shaders.
  let mut program = Program::new(
      include_str!("../../examples/01-triangle/shaders/shader.vert"),
      include_str!("../../examples/01-triangle/shaders/shader.frag"),
      DrawMode::Triangles
  );

  // Create a renderer. The renderer becomes the owner of the
  // WebGl2RenderingContext, to ensure that its internal representation
  // of the GPU state is always accureate.
  let mut renderer = Renderer::new(gl);

  // Run the program, rendering the results to the screen. We are
  // not passing any vertex attribute data, so we use a `DummyBuffer`
  // which renders three vertices: one for each corner of a triangle.
  renderer.render(&mut program, &DummyBuffer::new(3)).unwrap();
}

Using buffers

(full code, demo)

Buffers enable arbitrary vertex attribute data to be passed into the shaders. Limelight provides a procedural macro (attribute) for mapping from a Rust-side struct to a GPU-side set of vertex attributes. To use this macro, your crate will also have to depend on bytemuck and its derive feature.

use web_sys::WebGl2RenderingContext;
use limelight::{Program, Renderer, Buffer, DrawMode, BufferUsageHint, attribute};

// This attribute macro derives a number of traits, including `VertexAttribute`, which
// is required for a type to be used in an `Buffer`.
#[attribute]
struct VertexDescription {
    position: [f32; 2], // field names are mapped to variables in the shader.
}

impl VertexDescription {
    pub fn new(x: f32, y: f32) -> Self {
        VertexDescription { position: [x, y] }
    }
}

fn render_triangles(gl: WebGl2RenderingContext) {
  let mut program = Program::new(
      include_str!("../../examples/02-buffer/shaders/shader.vert"),
      include_str!("../../examples/02-buffer/shaders/shader.frag"),
      DrawMode::Triangles
  );

  let mut renderer = Renderer::new(gl);

  let data = vec![
      // Lower-left triangle.
      VertexDescription::new(-0.1, -0.1),
      VertexDescription::new(-0.5, -0.1),
      VertexDescription::new(-0.5, -0.5),
      // Upper-right triangle.
      VertexDescription::new(0.1, 0.1),
      VertexDescription::new(0.5, 0.1),
      VertexDescription::new(0.5, 0.5),
  ];

  // Declare a buffer.
  let mut buffer: Buffer<VertexDescription> =
    Buffer::new(data, BufferUsageHint::StaticDraw);

  renderer.render(&mut program, &buffer).unwrap();
}

Uniforms

(full code, demo)

Uniforms are values that can be used in both shader and fragment programs. They can vary between render calls, but for a given render call each uniform has a constant value across all vertices and fragments.

use limelight::{DrawMode, DummyBuffer, Program, Renderer, Uniform};
use web_sys::WebGl2RenderingContext;

fn render_triangles_with_uniform(gl: WebGl2RenderingContext) {
    // This will correspond to "uniform float u_rotate" in the vertex shader.
    let rotate_uniform = Uniform::new(std::f32::consts::PI / 3.4);
    
    // This will correspond to "uniform vec2 u_scale" in the vertex shader.
    let scale_uniform = Uniform::new([0.5, 0.8]);

    // This will correspond to "uniform vec3 u_color" in the fragment shader.
    let color_uniform = Uniform::new([0.9, 0.2, 0.3]);

    let mut program = Program::new(
      include_str!("../../examples/03-uniform/shaders/shader.vert"),
      include_str!("../../examples/03-uniform/shaders/shader.frag"),
      DrawMode::Triangles,
    )
    // We need to map the uniforms when we create the program.
    // The GPU-side types are automatically inferred from the Rust types.
    .with_uniform("u_rotate", rotate_uniform)
    .with_uniform("u_scale", scale_uniform)
    .with_uniform("u_color", color_uniform);

    let mut renderer = Renderer::new(gl);
    renderer.render(&mut program, &DummyBuffer::new(3)).unwrap();
}

Animation

(full code, demo)

The previous examples have rendered static images, so we haven't had a need to separate code that sets up the initial data structures from code that updates GPU-side data and triggers an animation. In this example, we separate the code into a new() method that is called once, and a render method that is called on every frame.

limelight is not a framework, and in order to integrate with other frameworks, it is not opinionated as to how you structure your code. This example shows one way you might choose to structure code for a simple animation (see the full code to see how it can be integrated with the Yew web framework).

buffer.set_data and uniform.set_data are lazy: they do not result in any GPU activity until the next time the buffer is used in a render call. (See WebGL Insights section 14.2, Deferring until the Draw Cycle.) If a buffer or uniform is unchanged between render calls, it is not re-written to the GPU.

use limelight::{Buffer, BufferUsageHint, DrawMode, Program, Renderer, Uniform, attribute};
use web_sys::WebGl2RenderingContext;

struct Animation {
    program: Program<VertexDescription>,
    buffer: Buffer<VertexDescription>,
    uniform: Uniform<[f32; 3]>,
}

impl Animation {
    pub fn new(gl: &WebGl2RenderingContext) -> Self {
        let buffer = Buffer::new(vec![], BufferUsageHint::DynamicDraw);
        let uniform = Uniform::new([0., 0., 0.]);

        let program = Program::new(
            include_str!("../../examples/04-animate/shaders/shader.vert"),
            include_str!("../../examples/04-animate/shaders/shader.frag"),
            DrawMode::Triangles,
        )
        // Note that we clone uniform, so that we can retain a handle to it.
        // Cloning a `Uniform` results in a reference-counted pointer to the
        // same uniform.
        .with_uniform("u_color", uniform.clone());       
        
        Animation {
            buffer,
            program,
            uniform
        }
    }

    pub fn render(&mut self, time: f64, renderer: &mut Renderer) {
        let theta1 = time as f32 / 1000.;
        let theta2 = theta1 + (std::f32::consts::TAU / 3.);
        let theta3 = theta2 + (std::f32::consts::TAU / 3.);
        
        self.buffer.set_data(vec![
            VertexDescription::new(theta1.cos(), theta1.sin()),
            VertexDescription::new(theta2.cos(), theta2.sin()),
            VertexDescription::new(theta3.cos(), theta3.sin()),
        ]);

        let r = (time as f32 / 3000.).sin() / 2. + 0.5;
        let g = (time as f32 / 5000.).sin() / 2. + 0.5;
        let b = (time as f32 / 7000.).sin() / 2. + 0.5;

        self.uniform.set_value([r, g, b]);

        renderer.render(&mut self.program, &self.buffer).unwrap();
    }
}

#[attribute]
struct VertexDescription {
    position: [f32; 2],
}

impl VertexDescription {
    pub fn new(x: f32, y: f32) -> Self {
        VertexDescription { position: [x, y] }
    }
}

More examples

• Instancing
• Pong
• Zooming / panning
• Full-canvas shader