[p5.js 2.0+ Bug Report]: Fill interpolation in TRIANGLE_FAN in P2D mode

Most appropriate sub-area of p5.js?

• Accessibility
• Color
• Core/Environment/Rendering
• Data
• DOM
• Events
• Image
• IO
• Math
• Typography
• Utilities
• WebGL
• WebGPU
• p5.strands
• Build process
• Unit testing
• Internationalization
• Friendly errors
• Other (specify if possible)

p5.js version

2.3.3

Web browser and version

Safari 26.5.2, Arc 1.163.1

Operating system

MacOSX 15.7.7

Steps to reproduce this

Steps:

1. Draw a TRIANGLE_FAN in PSD mode, changing the fill color on every vertex
2. Observe that the resulting shape is a single color

Snippet:

const NUM_SLICES = 28;
const RADIUS = 280

function setup() {
    createCanvas(600, 600);
    background(255);
    noLoop();
    colorMode(HSB, TWO_PI, 100, 100);
}

function draw() {
    const step = TWO_PI /  NUM_SLICES;
    const cx = width/2;
    const cy = height / 2;

    noStroke();
    beginShape(TRIANGLE_FAN);
    vertex(cx , cy );
    for (let theta = 0; theta <= TWO_PI; theta+=step){
        fill(theta, 100, 100);

        vertex(cx + RADIUS * cos(theta), cy + RADIUS * sin(theta));
    }
    endShape();

}

This is a very simple color wheel that used to work in v 1.x. Now I get a circle that is entirely red. A little poking suggests that the library is combining all of the vertices into a single shape instead of detecting the color changes and creating separate shapes.

Start by running the provided TRIANGLE_FAN sketch in p5.js 2.3.3 and compare its output with 1.x. Inspect the TRIANGLE_FAN shape handling and per-vertex fill behavior; done means the color wheel renders the expected changing colors instead of one uniform color.