Radial Ray Corona

Two thousand seven hundred rays around a circle, each stopping at a randomly chosen depth, with a disc punched out of the middle.

Rays with random depth

The corona is 2,700 straight rays swept once round a circle. Every ray starts at the same outer radius and ends at a depth read out of a table:

var stopSize = _size - stops[i / 5];
var innerX = (float)(Math.Sin(angle) * stopSize);

The outer end is on a circle. The inner end is not, and that is the whole composition: what looks like an irregular fringe is 2,700 line segments of the same kind, differing only in where they stop.

Step 01

A sixth of the sweep. The rays are placed in angle order, and the inner boundary is already visibly stepped rather than smooth.

Five rays to a step

var numStops = (int)Math.Ceiling(72 * Density);
…
var stopSize = _size - stops[i / 5];

There are 2,700 rays but only 540 stop values, and the index is i / 5 — integer division. So each stop value serves five consecutive rays.

That is why the inner edge is a series of flat plateaux rather than a noise field. Five rays at the same depth make a visible facet; the next five jump somewhere else entirely, because the values are independent uniform draws with no smoothing between them. The fringe is blocky by construction, and the block size is exactly five rays — two thirds of a degree.

Step 02

Two fifths. The five-ray plateaux are unmistakable now.

Step 03

Seven tenths. 540 independent depths, each occupying two thirds of a degree.

The geometry is inside out

Two details in the arithmetic are worth reading carefully, because they are the reverse of what the names suggest.

var _size = OuterScale - Size;   // 36 − 190 = −154

OuterScale is 36 and Size is 190, so _size is negative. The stop radius is then −154 − stops[…], with stops uniform in [0, 190) — giving inner radii from −154 down to −344.

A negative radius flips the point through the origin. So the “inner” end of each ray is on the far side of the circle from its “outer” end, and every ray is a chord passing through the middle rather than a spoke pointing at it. The corona is a dense crossing of long lines, not a starburst — which is why the middle needs covering.

Step 04

The whole sweep, before the disc. All 2,700 rays cross the centre, and the disc that will hide them is not there yet.

The disc is an eraser

Step 05

using var fillPaint = new SKPaint { Color = Background, Style = SKPaintStyle.Fill };
canvas.DrawCircle(centerX, centerY, DiscRadius, fillPaint);
canvas.DrawCircle(centerX, centerY, DiscRadius, outlinePaint);

The disc is drawn in the background colour and filled. It is not a shape in the composition; it is a hole punched through it, hiding the tangle where every ray crosses every other. Then a one-pixel outline in the foreground colour gives the hole an edge, which is what turns it from an absence into a disc.

Everything the eye reads as the disc is that single fill.

What can move

Everything above is the piece at its defaults, but the knobs the variants turn are structural, not just cosmetic:

Sweep — the corona need not close. Less than 1 draws a fan that stops mid-air, and the terminator between ink and paper is a straight line through the centre.
DiscShiftX / DiscShiftY — the disc need not sit on the centre. Off centre it eclipses only part of the tangle, and the crossing rays spill out past its far side.
Disc2Radius — a second disc, punched the same way on its own spot: a companion in transit across the disc’s rim, erasing a bite of corona and outline as it goes.
HaloRadius — one stroked ring around the disc, drawn over the rays, turning the hole into a target.
Accent / AccentEvery — a second ink for whole five-ray groups, so the fringe is interleaved with wedges of another colour instead of one uniform field.

Each variant still gets the whole progression: its stages sweep its own fraction of the circle, so Daybreak’s plates build a fan, not a full corona.

Seven variants

Rendering	What it changes	Ink
Lunar Cyan	The archetype: full sweep, centred disc, default everything	`#00FFFF` on `#000000`
Eclipse Pink	Disc shifted off centre, so the corona spills past one side	`#FF1493` on `#1a1a2e`
Solar Gold	A small companion disc grazing the rim, mid-transit	`#FFD700` on `#0a0a0a`
Silver Halo	A stroked ring around the disc, like a winter halo	`#D9DFE6` on `#030303`
Daybreak	Half a sweep: the corona fans upward from a dark horizon	`#F4EBD8` on `#131A33`
Ember	Gold wedges interleaved in the red fringe, one group in four	`#F04E23` + `#FFD166` on `#0C0806`
Snow Moon	Sparse, long rays behind a much larger disc	`#CFE0F0` on `#05070D`

Density controls both counts at once — rays as 360 × Density, stops as 72 × Density — so the five-to-one ratio between them is fixed and the fringe’s block size in degrees is the same whatever the density. Raising it adds rays and facets in proportion, making the corona denser without making the fringe finer.

Using the frame

Every rendering is drawn larger than the raw arithmetic would have it, by one knob: Scale, which multiplies every distance about the canvas centre. The presets set it so the longest rays finish a few pixels inside the canvas edge — the corona uses the frame as its outer boundary instead of floating inside it.

The one place the darkness is deliberate is Daybreak’s lower half: the horizon is the composition, and the empty indigo below the cut stays empty on purpose. Whitespace is kept only where it is part of the picture.

Scale is a homothety — the stop table is generated from the seed exactly as before, and the same seed stream draws the same corona, larger.

Hung on a wall

The piece ships one museum presentation: a gallery plate, museum-lunar-cyan, that hangs the lead the way a gallery would — a wall, a mat with a window, a frame around the mat, and a soft drop shadow lifting the frame off the wall. The artwork is contain-fitted into the window and clipped at the mat edge, like a print behind glass.

The treatment is a presentation layer, not a new family of renderings: it wraps the finished drawing and adds nothing to the rule itself, and there is deliberately no framed copy of every preset — one plate, the way one work hangs on one wall. Mat, frame and shadow are fractions of the shorter side, so the treatment scales with the plate, and the presentation composes the finished drawing without touching the generative geometry.

Determinism

One Random is created per draw, seeded from the preset, and consumed once per stop up front to fill the stop table before any ray is placed. Nothing else is random. The generator is System.Random, which the project’s determinism policy flags as not guaranteed stable across .NET versions.

Progression 05

Variant 07

Gallery 01