Module lines 

Line-geometry scenes (ADR-0007): a line-art category built on one shared LineRenderer (segments -> thick glowing instanced quads) and two build models over it — a cheap parametric system sampled every frame (the Maurer rose) and, from Phase 3, an expensive generator system built and cached at preset load. Ported in spirit from the user’s Maurer rose, L-system, and Islamic-star sketches; none of that JavaScript is reused, only the math.

The renderer and the per-frame scene halves are hot-path; the generators (grammar/turtle/Hankin, from later phases) run only at load. All files here live under render/ and so carry the panic pragma the hygiene guard scans for recursively — the build-time files are written panic-free too.

Re-exports

pub use lsystem::LSystemScene;

pub use parametric::ParametricCurveScene;

pub use renderer::ArcInstance;

pub use renderer::LineRenderer;

pub use renderer::MITER_LIMIT;

pub use renderer::SegmentInstance;

pub use renderer::StrokeMetric;

pub use renderer::miter_extension;

pub use spectrum::SpectrumLayout;

pub use spectrum::SpectrumScene;

pub use star::StarPatternScene;

pub use super::CapOverflow;

pub use super::GeneratorConfig;

pub use super::OverflowContext;

Modules

biarc

Biarc fitting: a sampled outline in, a G1-continuous chain of circular arcs out (ADR-0098).

curves

Parametric curve samplers: pure t -> (x, y) functions written straight into a preallocated segment buffer. Cheap enough to resample every frame (ADR-0007 parametric build model), so continuous audio can sweep the shape live. Deterministic: no wall-clock, no randomness — the same parameters always yield the same segments (NFR 6).

grammar

L-system grammar expansion: pure, deterministic string rewriting. Applies a production rule set to an axiom depth times — each character is replaced by its successor (or kept if no rule matches). This is a build-time step (runs inside Scene::configure, off the hot path), not per-frame work.

hankin

Hankin star patterns: build an n-fold star rosette by the contact-angle method. n contact points sit symmetrically on a circle; from each, a ray leaves at the contact angle from the inward normal, and adjacent rays meet at the petal tips. Connecting each contact point to its two neighbouring tips traces the interlaced star.

lsystem

L-system scene: expensive to build, cheap to animate (ADR-0007 generator build model). At preset load (configure, off the hot path) the grammar is expanded and turtle-walked into one cached segment buffer per depth 1..=max_depth. Per frame the scene only picks the visible depth and applies a rotation / scale / colour / draw-on transform into the draw buffer — no expansion, no allocation.

parametric

Parametric-curve scene: a pure t -> (x, y) curve resampled every frame into the shared LineRenderer (ADR-0007 parametric build model). Phase 1 is hardcoded to one Maurer rose that gently rotates on the deterministic scene clock; Phase 2 makes the curve family and every named parameter preset-driven so audio can sweep it live.

renderer

The shared line primitive: a GPU helper that draws thick, glowing lines as instanced camera-facing quads. Each SegmentInstance (two endpoints, a colour, a half-width) is expanded in the vertex shader into a quad whose width is uniform on screen — the swarm scene’s instanced-quad pipeline (ADR-0007) with segments in place of points. Additive blend, so overlapping and dense strokes bloom.

spectrum

Spectrum scene (Plan 0034 / ADR-0036): the analysis frame’s log-spaced band array, drawn as N elements.

star

Star-pattern scene: a Hankin star rosette built from a continuous contact angle and cached (ADR-0007 generator build model), cheap to animate. Per frame the scene resolves variant to an angle, reuses the cached rosette unless the request has moved more than one step, and applies a rotate/scale/colour/draw-on transform (allocation-free).

turtle

Turtle interpretation: walk an L-system string into line segments, with a branch stack for [/]. A build-time step (runs inside Scene::configure, off the hot path) that produces the base geometry a generator scene caches and then only transforms per frame.

Structs

ViewTransform

The shared camera transform every scene family applies (ADR-0018): a uniform zoom about the frame centre, then a pan, in world space before the aspect divide. Identity (zoom = 1, pan = 0) leaves geometry exactly where a scene placed it, so a preset that binds none of zoom/pan_x/pan_y is unchanged. #[repr(C)] + Pod so it uploads straight into a line-renderer uniform slot. Rotate is reserved for a follow-up (ADR-0018 reserves it).

Enums

CurveFamily

Which parametric curve family a [curve] preset draws. Extend as Plan 0010’s follow-ups add curve families (epicycloids, Lissajous, …); unknown names are rejected at load.

Constants

ADDITIVE_BLEND

The stroke_blend a line scene draws at when its preset binds nothing — additive light, ADR-0056’s seam, and what every line scene drew before the selector existed.

DEFAULT_SOFTNESS

The across-the-stroke profile the four line families draw at unless a preset binds softness itself (ADR-0124).

DRAW_PROGRESS

draw_progress, shared: how much of the figure has been drawn.

GLOW

glow, shared: the halo around a stroke, on top of the stroke itself.

MAX_LSYSTEM_DEPTH

Hard clamp on L-system iteration depth, enforced at preset load. A branching rule expands exponentially, so an unbounded max_depth would stall a preset switch and blow the segment cap (ADR-0007 Risks). Curated presets stay well under this; the turtle’s own segment cap is the second backstop.

MAX_MIRROR_ORDER

Hard clamp on the geometry-mirror rotational order (Plan 0018 Phase 4). Beyond a couple dozen the fold is visually indistinguishable and only multiplies segment count toward the cap; a sane ceiling keeps a runaway mirror_order expression from doing useless work before the segment cap bites.

MIN_HALF_WIDTH

The smallest half-width a stroke is drawn at, whatever thickness asks for.

MIN_USEFUL_THICKNESS

The thickness at which MIN_HALF_WIDTH stops binding — about 0.167.

MIRROR_ORDER

mirror_order, shared: how many copies of the geometry ring the centre.

MIRROR_REFLECT

mirror_reflect, shared: whether those copies alternate as mirror images.

OPAQUE_BLEND

The stroke_blend level at or above which a line scene draws through the opacity-preserving seam (ADR-0138). Below it the batch is additive light.

SOFTNESS

The stroke and framing parameters every line system shares, declared once (ADR-0170) — the line-art half of what scenes::common does for colour.

STROKE_BLEND

stroke_blend, shared: additive light at 0, opaque paint at 1.

WIDTH_SCALE

Maps the thickness parameter (a small integer-ish stroke weight) to an NDC-y half-width; thickness = 2 gives a comfortably thick projector line.

Functions

half_width

The NDC-y half-width a line scene strokes thickness at — the one place the scale and the floor are applied, shared by all four line scenes.

hue_spread

hue_spread at the scene’s own resting width.

palette

iq-style cosine palette (RGB phase-shifted), matching the swarm/fragment scenes so line art shares the engine’s colour language.

scale

scale at the scene’s own resting size.

thickness

thickness at the scene’s own resting width, in pixels at the render target.