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feat(shader): add disk_color_volumetric (ridged + density + arms)

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Three multiplying signal layers: ridged_fbm filaments for brightness,
smoothstep-gated FBM for density clumping, logarithmic-spiral arm
modulation riding the Keplerian shear. Octave triplet selected from
disk_quality tier. Returns DiskSample; inert until Task 7 wires it in.
This commit is contained in:
xfy 2026-07-15 13:37:52 +08:00
parent de4ceee8ff
commit 107fbd0a74
1 changed files with 47 additions and 0 deletions
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47
assets/shaders/black_hole.wgsl
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@ -316,6 +316,53 @@ fn disk_color(pos: vec3<f32>, dir: vec3<f32>) -> vec3<f32> {
return disk_color_flat(pos, dir).color;
}
// Volumetric disk color: ridged filaments drive brightness, a smoothstep-
// gated FBM drives density clumping, and a logarithmic-spiral term (riding
// the Keplerian shear `rot`) drives large-scale arm structure. The three
// signals multiply — density says where matter is, filaments say how bright,
// arms say how it's distributed.
fn disk_color_volumetric(pos: vec3<f32>, dir: vec3<f32>) -> DiskSample {
let r = r_of(pos);
let rot = uniforms.time * uniforms.disk_rotation_speed / pow(r, 1.5);
let flow = vec3<f32>(0.0, 0.0, rot);
// Octave triplet from the quality tier.
let q = uniforms.disk_quality;
var filament_octaves = 5u; var density_octaves = 4u; var warp_octaves = 3u;
if (q == 1u) { filament_octaves = 3u; density_octaves = 2u; warp_octaves = 2u; }
else if (q == 2u) { filament_octaves = 4u; density_octaves = 3u; warp_octaves = 3u; }
// q == 3u keeps the High defaults above; q == 0u is never passed here.
// Domain warp: distorts sample coords so filaments curve and bend.
let warp = fbm3(pos * 0.8 + flow * 0.1, warp_octaves);
// Layer 1: ridged bright filaments.
let filament = ridged_fbm(pos * uniforms.filament_freq + warp * 1.5 + flow * 0.3,
filament_octaves, uniforms.filament_sharpness);
// Layer 2: density clumping (smoothstep makes a definite gas/void boundary).
let density_noise = fbm3(pos * uniforms.density_freq + warp, density_octaves);
let base_density = smoothstep(0.3, 0.7, density_noise) * uniforms.density_strength;
// Layer 3: logarithmic-spiral arm modulation, advected by Keplerian shear.
let phi = atan2(pos.z, pos.x);
let arm_phase = phi * uniforms.arm_count + log(r) * uniforms.arm_tightness - rot;
let arm = 0.5 + 0.5 * cos(arm_phase);
let arm_mod = mix(1.0, pow(arm, 2.0), uniforms.arm_strength);
let total_density = base_density * arm_mod;
let brightness = filament;
let t = (r - uniforms.disk_inner) / (uniforms.disk_outer - uniforms.disk_inner);
let tcol = temperature_color(t);
let falloff = radial_falloff(r, uniforms.disk_inner);
var col = tcol * brightness * falloff * uniforms.disk_brightness;
col = apply_doppler(col, pos, dir);
return DiskSample(vec3<f32>(col), total_density);
}
// --- planets ---
// `prev`/`cur` are in DISK-LOCAL space; planet centers are world space, so we
// rotate each center into disk-local space here.