SWEyeball Saga

Eye 4 adds the glint — the small white highlight that makes an eye look alive. It is just another SWDisk, but its position is computed using polar coordinates, introducing a placement technique that reappears throughout the saga.

Big Idea 1 — Polar Coordinates Place the Glint

Instead of picking an x/y offset by trial and error, the glint center is computed from an angle and a radius:

let glintAngleDeg = 135; // upper-left
let glintOffsetX = glintRadius * cos(radians(glintAngleDeg));
let glintOffsetY = glintRadius * sin(radians(glintAngleDeg));

135° places the glint in the upper-left quadrant of the pupil. Changing one number relocates the entire highlight precisely — no pixel hunting required.

Big Idea 2 — Chained Proportional Scaling

The glint radius is derived from the pupil radius, which is derived from the eye radius:

let glintFactor = 0.3;
let glintRadius = eyeRadius * pupilFactor * glintFactor;

The whole eye — sclera, pupil, and glint — scales coherently from a single eyeRadius value. This proportional chaining becomes the foundation for SWEyeball's constructor parameters.

Big Idea 3 — Same Fill & Stroke Hides the Border

The glint disk is constructed with glintColor for both fill and stroke:

leftGlint = new SWDisk(leftGlintCenter, glintRadius, 1, glintColor, glintColor);

When fill and stroke are the same color, the border is invisible — leaving only a clean, solid circle. A simple trick with a big visual payoff.

Big Idea 4 — Drawing Order Is Everything

Each eye is drawn in three layers, back to front:

1. Sclera (base)
2. Pupil / iris disk
3. Glint — drawn last so it sits on top of both

Swap the order and the glint disappears behind the pupil.

What to Notice

• Click the canvas to toggle the grid and see the glints unobstructed.
• Both eyes share the same glint parameters — same angle, same proportional size.
• Try imagining how glintAngleDeg would need to change to move the highlight to the lower-right instead.

The Road Ahead

The glint is currently anchored to the eye center. In later stages the pupil will gain its own independent SWPoint, and the glint will follow it — recomputed each frame so the highlight always sits correctly regardless of where the pupil has moved.