clutter-shader.js

function applyMotionBlur(actor, n, dir, wFn=function() { return 1; }) {
    function blurShaderSource() {
        function SAMPLE(offx, offy, w) {
            return `pixel += ${w} * texture2D (tex, cogl_tex_coord_in[0].st + vec2(width_inv, height_inv) * vec2 (${offx}, ${offy}));`
        }

        function motionBlur(n, sign=1) {
            let vs = []
            let weights = []
            let sum = 0
            for (let i = 0; i < n; i++) {
                // let w = n-i+1
                // let w = Math.pow((i+1), 1.5)
                let w = wFn(i, n)
                weights.push(w)
                sum += w
            }
            for (let i = 0; i < n; i++) {
                vs.push(SAMPLE(i*sign, 0, weights[i]/sum))
            }
            // vs.push(`pixel /= ${n}.0;`)
            return vs.join("\n")
        }

        // Note: `tex` doesn't need to be set (it's not a special name either..)
        // Setting it to 0 from the outside have no effect, setting it to 1 messes things up.
        // Setting it to 0 inside the shader source also messes things up...
        // Texture coordinates go from 0 to 1. The texture pixel width does not seem to be available.
        // Unsure about how edge conditions are resolved.
        return `
            uniform sampler2D tex;
            uniform float width_inv;
            uniform float height_inv;
            void main() {
                vec4 pixel = vec4(0.0, 0.0, 0.0, 0.0);
                ${motionBlur(n, dir)}
                cogl_color_out = pixel;
            }
        `;
    }

    actor.clear_effects()
    let effect = new Clutter.ShaderEffect();
    effect.set_shader_source(blurShaderSource(n, dir))
    effect.set_uniform_value("width_inv", 1/actor.width)
    effect.set_uniform_value("height_inv", 1/actor.height)
    actor.add_effect_with_name("Foo", effect)
}

function repl() {
    function linear(i, n) {
        return n - i + 1
    }
    function power(i, n) {
        return Math.pow((n-i+1), 2)
    }
    function constant(i, n) {
        return 1
    }
    actor = space.cloneContainer
    actor = metaWindow.clone
    actor.clear_effects()
    applyMotionBlur(actor, 20, -1, linear)
    applyMotionBlur(actor, 4, 20, power)
    applyMotionBlur(actor, 30, -1, power)

    imports.gi.St.set_slow_down_factor(3)
}