Custom Shaders

Writing a Custom Shader
With valora, you can shade each path with its own shader, and define custom uniforms. We'll start with this simple GLSL fragment shader:
#version 400
​
uniform vec3 color;
uniform float scale;
uniform float height;
uniform float width;
​
out vec4 frag;
​
void main() {
  vec2 pos = gl_FragCoord.xy / scale;
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  vec3 white = vec3(1., 1., 1.);
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  frag = vec4(mix(white, color, pos.x / width), 1.);
}
Save this to a file named pattern.frag.
Now, we'll use valora's shader API to define some uniforms and load the shader. A shader in valora is made of two parts:
The shader program. This is the GLSL above, which exposes an interface to provide uniforms.
The uniforms bound to the shader.
First let's define the uniforms type in Rust:
#[derive(UniformSet, Copy, Clone, Debug)]
struct Uniforms {
    /// A solid color overlay on the shader pattern.
    color: (f32, f32, f32),
    /// The vector scale of the output.
    scale: f32,
    /// Width of the output.
    width: f32,
    /// Height of the output.
    height: f32,
}
The derive macro UniformSet will generate mappings from the field types to something we can send to the GPU, should such a mapping exist for the type.
Now let's load the shader and draw with it:
fn main() -> Result<()> {
    run_fn(Options::from_args(), |gpu, world, _rng| {
        let mut program = ShaderProgram::new(&gpu, "pattern.frag")?;
        let uniforms = Uniforms {
            color: Hsv::new(0., 0.7, 0.7).into_rgb::<Srgb>().into_components(),
            scale: world.scale,
            width: world.width,
            height: world.height,
        };
        let shader = program.bind(uniforms);
​
        Ok(move |ctx: Context, canvas: &mut Canvas| {
            canvas.set_color(LinSrgb::new(1., 1., 1.));
            canvas.paint(Filled(ctx.world));
​
            canvas.set_shader(shader.clone());
            let square = Ngon::square(world.center(), 200.);
​
            canvas.paint(Filled(square));
        })
    })
}
If you run the painting with cargo run --release, and change the GLSL, you'll notice that the view pane will update live!
A path rendered with a custom shader.
Updating Uniforms
We can update our uniform values each frame. Once the uniforms are updated, we can rebind with the shader program to make a new shader.
let hue = ctx.time.as_secs_f32().sin().abs() * 40.;
uniforms.color = Hsv::new(hue, 0.7, 0.7).into_rgb::<Srgb>().into_components();
canvas.set_shader(program.bind(uniforms));
​
Path Manipulation
Being the Artist
Last updated 1 year ago