// Halftone dots sized by brightness; dots turn hot orange wherever something moves.
// order 70
// slider cell 4.0 40.0 12.0
// slider heat 0.0 20.0 8.0
float4 effect(float2 uv, Inputs in) {
    float2 grid = in.resolution / in.p.cell;
    float2 centre = (floor(uv * grid) + 0.5) / grid;
    float3 c = in.image.sample(in.smp, centre).rgb;
    float luma = dot(c, float3(0.299, 0.587, 0.114));

    float radius = 0.5 * sqrt(luma);
    float dist = length(fract(uv * grid) - 0.5);
    float mask = 1.0 - smoothstep(radius - 0.05, radius + 0.05, dist);

    float moved = length(in.camera.sample(in.smp, centre).rgb - in.last.sample(in.smp, centre).rgb);
    float3 hot = mix(c, float3(1.0, 0.35, 0.1), clamp(moved * in.p.heat, 0.0, 1.0));
    return float4(hot * mask, 1.0);
}