Module particles 

GPU compute-particle scenes: strange attractors (ADR-0015, Plan 0016). The engine’s first compute pipeline — a storage buffer of particles stepped through an attractor map each frame by a compute shader, then drawn as additive point-sprites with fading trails. This is idiom B of the four render idioms; the CPU swarm is idiom B’s ~10k CPU precursor, replaced here by GPU-resident state that scales to 100k+ points with no CPU round-trip.

Trails reuse Plan 0014’s PingPongField rather than a second feedback mechanism: each frame the previous accumulation texture is drawn back faded (decay pass), the fresh points are added on top (additive), and the result is composited to the surface (present pass). Trail persistence is the named fade parameter; fade = 0 clears the accumulation each frame, reproducing the trail-free look.

Every knob is an ADR-0002 layer-2 named parameter — the attractor coefficients (a,b,c,d), look scalars (size,hue,fade), and a beat-driven reseed — so a preset steers the cloud’s shape and a beat disturbs it. All randomness is the seeded initial scatter plus the reseed’s deterministic per-particle kick (NFR 6): the point cloud is a pure function of the seed and the fixed-dt step sequence, so a capture reproduces bit-for-bit on one adapter.

GPU resources are built lazily, on first render — the same discipline the reaction-diffusion scene uses (see its module docs). create_all builds every scene up front, but the compute pipeline + storage buffer + trail field are constructed only when this scene is first drawn, so a capture that never activates it never builds them (keeping the other scenes’ WARP captures unperturbed).

The accumulation field is sized to the render target and capped (Plan 0027 Phase 2, now the tier’s attractor_trail_cap) rather than fixed at 640x360, so the present is close to 1:1 up to the cap instead of a soft upscale on a 1080p+ display. That size is quantized to TRAIL_GRID_STEP, so a live window drag re-allocates the field a handful of times rather than once per frame.

The field’s own aspect is not the projection’s (Plan 0029 Phase 5). The present is a plain stretch (aspect ignored, as the reaction-diffusion present does), so a point at field NDC x lands at target NDC x — the field’s aspect cancels out and the projection must use the target’s. Quantization makes the two genuinely differ (a 1920x1080 target takes a 2048x1280 grid), so trail_grid_size scaling both axes by one factor at the cap is about keeping the field’s sampling near-isotropic, not about the shape on screen.

Re-exports

pub use family::AttractorFamily;

pub use family::Basis;

Modules

family

The attractor families and their projection bases — the ODE/map math, GPU-free (Plan 0061 Phase 6).

ifs

Iterated function systems: the attractor scene’s fifth family (ADR-0075, Plan 0062).

resources

The attractor’s GPU resources: the three uniform blocks, the three resource holders, and their bind-group helpers (Plan 0061 Phase 6).

Structs

AttractorScene

GPU compute-particle strange-attractor scene (ADR-0015). A storage buffer of particles is stepped through the De Jong map by a compute shader each frame, drawn as additive point-sprites into a fading trail field, and composited to the surface. Every knob is an ADR-0002 layer-2 named parameter — the attractor coefficients (a,b,c,d), the look scalars (size,hue,fade), and a beat-driven reseed — so a preset binds them to the audio bands and beat.

Constants

MIN_PARTICLE_DENSITY

The smallest [particles] density a preset may ask for (ADR-0069).

PARAMS

Parameter vocabulary — see fragment_field::PARAMS. Keep in sync with set_param below.

Functions

deposit_scale

Per-particle weight of the additive deposit, so the total light laid into the accumulation each frame is invariant to the particle count (ADR-0065).

roster_len

How many entries a family’s roster holds — what [particles] tuple_to is validated against at load (ADR-0093).

trail_grid_size

The trail accumulation grid for a render target of width x height — this scene’s cap and step over the one shared policy (grid::grid_size).