Struct ArcInstance 

#[repr(C)]
pub struct ArcInstance {
    pub centre: [f32; 2],
    pub radius: f32,
    pub angle_start: f32,
    pub angle_sweep: f32,
    pub color: [f32; 3],
    pub width: f32,
}

One circular arc: a centre and radius in world space, a signed angular span in radians, an RGB colour and a half-width in NDC-y units — the same conventions SegmentInstance uses, so the two kinds place geometry in one coordinate system and stroke it to one profile.

Expanded in the vertex shader to a single bounding quad and shaded by the per-pixel distance to the arc (ADR-0098) rather than by an interpolated across-the-stroke coordinate. So a circle is one instance with no vertices at any resolution, where the segment path needs one instance and one additive joint per sample.

No extension fields: an arc has no interior joints, which is the whole point of the primitive. Where two arcs in a chain meet they overlap by a half-width as any two strokes do, and the additive composite sums that overlap exactly as it does for segments — the bead is reduced by there being fewer joints, not by a joint doing anything different.

No alpha field either. Every arc producer draws through ADR-0056’s additive seam, where the coverage a premultiplied fragment carries is the stroke’s own falloff; the OVER range LineRenderer::draw_split serves is a MilkDrop waveform, which is segments. A future over-blended arc adds the field last, for the reason SegmentInstance::alpha records.

Field order is shader-location order, and that is load-bearing for the same reason it is on SegmentInstance: vertex_attr_array! derives each attribute’s byte offset from the order of the locations, so a field inserted anywhere but the end silently re-points every attribute after it.

Fields

centre: [f32; 2]

Centre of curvature (world space).

radius: f32

Radius (world space). The arc’s centreline, not either stroke edge.

angle_start: f32

Where the span starts, in radians, measured the usual way from +x.

angle_sweep: f32

How far it sweeps, signed. |sweep| may exceed PI, and a full circle is one instance at sweep = TAU.

color: [f32; 3]

RGB colour (pre-brightness; additive blend sums overlaps).

width: f32

Half-width in world units — the same quantity, in the same space, as SegmentInstance::width. Named width to match its sibling; it is a half-width in both.

There is no StrokeMetric choice here: no arc producer wants the clip metric, because warp_mesh — the one surface still on it — emits no ArcInstance at all (ADR-0160).

Trait Implementations

impl Clone for ArcInstance

fn clone(&self) -> ArcInstance

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ArcInstance

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for ArcInstance

fn eq(&self, other: &ArcInstance) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Zeroable for ArcInstance

fn zeroed() -> Self

Calls zeroed.

impl Copy for ArcInstance

impl Pod for ArcInstance

impl StructuralPartialEq for ArcInstance