struct Camera {
center: vec2<f32>,
zoom: f32,
fade: f32,
viewport: vec2<f32>,
_pad1: vec2<f32>,
};
@group(0) @binding(0) var<uniform> cam: Camera;
struct VsOut {
@builtin(position) clip: vec4<f32>,
@location(0) local: vec2<f32>,
@location(1) color: vec4<f32>,
@location(2) softness: f32,
@location(3) phase: f32,
};
var<private> QUAD: array<vec2<f32>, 6> = array<vec2<f32>, 6>(
vec2<f32>(-1.0, -1.0), vec2<f32>(1.0, -1.0), vec2<f32>(1.0, 1.0),
vec2<f32>(-1.0, -1.0), vec2<f32>(1.0, 1.0), vec2<f32>(-1.0, 1.0),
);
@vertex
fn vs_main(
@builtin(vertex_index) vi: u32,
@location(0) pos: vec2<f32>,
@location(1) radius: f32,
@location(2) color: vec4<f32>,
@location(3) softness: f32,
@location(4) phase: f32,
) -> VsOut {
let corner = QUAD[vi];
let world = pos + corner * radius;
let rel = (world - cam.center) * cam.zoom;
let clip = vec2<f32>(rel.x / (cam.viewport.x * 0.5), rel.y / (cam.viewport.y * 0.5));
var out: VsOut;
out.clip = vec4<f32>(clip, 0.0, 1.0);
out.local = corner;
out.color = color;
out.softness = softness;
out.phase = phase;
return out;
}
@fragment
fn fs_main(in: VsOut) -> @location(0) vec4<f32> {
let d = length(in.local); // 0 at center .. 1 at the quad edge
if (d > 1.0) { discard; }
// Rolling waves: concentric crests that emanate OUTWARD from the node as
// `phase` advances 0->1. Subtracting the growing phase moves crests toward
// larger `d` (outward) over time. A sharp power shapes each crest into a
// distinct ripple rather than a smear, and `softness` widens it.
//
// The wave is a raised cosine rather than the more obvious `fract`, because
// `fract` snaps from 1 straight back to 0 at every ring boundary. That
// discontinuity is a hard edge, and a hard edge in a radial function draws a
// visibly stair-stepped circle. A raised cosine peaks at the same radii and
// is continuous everywhere, so the ring boundaries antialias themselves.
// Raising a smooth 0..1 function to a power keeps it smooth, so the
// `softness` knob still sharpens the crest without reintroducing a step.
let RINGS = 2.4;
let TAU = 6.2831855;
// Both arguments to `pow` are guarded, because it is undefined for a
// negative base and returns infinity for a zero base with a negative
// exponent — and either result poisons the pixel to NaN rather than merely
// looking wrong. `cos` is only required to be accurate to within a few ULP,
// so `0.5 + 0.5*cos(x)` can land a hair below zero at a trough, and
// `softness` arrives from host JSON with no upper bound.
let wave = max(0.5 + 0.5 * cos(TAU * (d * RINGS - in.phase * RINGS)), 0.0);
let crest = pow(wave, max(5.0 - in.softness * 3.0, 0.5));
// Envelope: the node covers the center, so fade the wave in past the node,
// and fade it out at the rim so the halo is a bounded ring band, not a disc.
let inner = smoothstep(0.15, 0.45, d);
let outer = 1.0 - smoothstep(0.65, 1.0, d);
let env = inner * outer;
// A faint steady base glow under the ripples keeps the selection legible even
// at a wave trough, so the halo never fully disappears between crests.
let base = 0.18 * outer;
let intensity = clamp(crest * env + base, 0.0, 1.0);
return vec4<f32>(in.color.rgb, in.color.a * intensity * cam.fade);
}