@thi.ng/rasterize/poly.js

Headless 2D shape drawing, filling & rasterization for arbitrary targets/purposes (no canvas required)

import { ensureShader2D } from "./checks.js";
const fillPoly = (grid, pts, val) => {
  const numP = pts.length;
  const [width, height] = grid.size;
  const shader = ensureShader2D(val);
  let minX = Infinity;
  let minY = Infinity;
  let maxX = -Infinity;
  let maxY = -Infinity;
  for (let i2 = numP; i2-- > 0; ) {
    const { 0: x, 1: y } = pts[i2];
    minX = Math.min(minX, x);
    maxX = Math.max(maxX, x);
    minY = Math.min(minY, y);
    maxY = Math.max(maxY, y);
  }
  minX = Math.max(minX | 0, 0);
  maxX = Math.min(maxX | 0, width - 1);
  minY = Math.max(minY | 0, 0);
  maxY = Math.min(maxY | 0, height - 1);
  if (minX >= width || maxX < 0 || minY >= height || maxY < 0) return;
  let i = 0;
  let k = 0;
  let j;
  const isec = [];
  for (let y = Math.max(0, minY); y <= maxY; y++) {
    i = k = 0;
    j = numP - 1;
    isec.length = 0;
    for (; i < numP; j = i, i++) {
      const { 0: pix, 1: piy } = pts[i];
      const { 0: pjx, 1: pjy } = pts[j];
      if (piy < y && pjy >= y || pjy < y && piy >= y) {
        isec[k++] = pix + (y - piy) / (pjy - piy) * (pjx - pix) | 0;
      }
    }
    isec.sort((a, b) => a - b);
    for (i = 0; i < k; i += 2) {
      let x1 = isec[i];
      if (x1 > maxX) break;
      let x2 = isec[i + 1];
      if (x2 > minX) {
        x1 < minX && (x1 = minX);
        x2 > maxX && (x2 = maxX);
        for (let x = x1; x <= x2; x++) {
          grid.setAtUnsafe(x, y, shader(grid, x, y));
        }
      }
    }
  }
};
export {
  fillPoly
};