RLSL - Milestone 1

2018-02-26

Shadertoy default shader
Input variables
Uniform buffers and descriptor sets
Closures and pointers
Build times

Shadertoy default shader

#[spirv(fragment)]
fn color_frag(
    frag: Fragment,
    uv: Input<N0, Vec2<f32>>,
    time: Descriptor<N2, N0, f32>,
) -> Output<N0, Vec4<f32>> {
    let uv = uv.data;
    let time = time.data;
    let offset = Vec3::new(0.0, 2.0, 4.0);
    let coord = uv.extend(uv.y)
        .add(offset)
        .map(move |f| f32::cos(time + f) * 0.5)
        .add(Vec3::single(0.5))
        .extend(1.0);
    Output::new(coord)
}

#[spirv(vertex)]
fn vertex(
    vertex: &mut Vertex,
    pos: Input<N0, Vec4<f32>>,
    uv: Input<N1, Vec2<f32>>,
) -> Output<N0, Vec2<f32>> {
    vertex.position = pos.data;
    Output::new(uv.data)
}

Today I reached the first milestone: translating the default shader from Shadertoy to rlsl.

Input variables

uv: Input<N0, Vec2<f32>>

Every entry point now specifies input and uniform buffers explicitly. Input<N0, Vec2<f32>> tells rlsl that there is an input variable at location 0 of type Vec2<f32>. The N0 here is a custom struct that maps to the number 0 inside rlsl. When Rust gets const-generics, you will be able to write Input<0, Vec2<f32>.

Uniform buffers and descriptor sets

time: Descriptor<N2, N0, f32>,

Similarly to input variables, you specify descriptor sets with Descriptor<N2, N0, f32>, where currently the first type parameter is the binding and the second type parameter is the set. Also rlsl now supports the std140 layout, and custom structs as the type parameter are also supported Descriptor<N0, N0, SomeStruct>. In the future I will also implement seamless interop of uniforms structs between rlsl and rust. Currently you have to make sure that the struct in rust is aligned properly according to the rules in std140.

Closures and pointers

rlsl now supports closures, and closures that own the captured variables. In the future I will also allow closures to capture variables by reference. Additionally rlsl now allows pointers as variables and function parameters. While this is not allowed in SPIR-V, rlsl optimizes those pointers away.

Build times

Build times are still quick, although the examples are still very small in terms of loc.