marchLib.mjs

import { add, mul, normalize } from "./shaderLib.mjs";

export const intersectSDF = (a, b) => Math.max(a, b);
export const subtractSDF = (a, b) => Math.max(a, -b);
export const unionSDF = (a, b) => Math.min(a, b);

const STEP = 0.001;

/**
 * Get the surface normal at a point.
 * @param sceneSDF {(point: [number, number, number]) => number}
 * @param point {[number, number, number]}
 * @returns {[number, number, number]}
 */
const normal = (sceneSDF, point) => {
  const gradient0 = sceneSDF(point);
  const gradientX = gradient0 - sceneSDF(add(point, [STEP, 0, 0]));
  const gradientY = gradient0 - sceneSDF(add(point, [0, STEP, 0]));
  const gradientZ = gradient0 - sceneSDF(add(point, [0, 0, STEP]));

  return normalize([gradientX, gradientY, gradientZ]);
};

const MAX_STEPS = 32;
const MAX_DISTANCE = 10;
const HIT_DISTANCE = 0.002;

/**
 * Perform ray marching.
 * @param source {[number, number, number]}
 * @param direction {[number, number, number]}
 * @param sceneSDF {(point: [number, number, number]) => number}
 * @returns {number}
 */
export const rayMarch = (source, direction, sceneSDF) => {
  let distanceTraveled = 0;

  for (let i = 0; i < MAX_STEPS; ++i) {
    const currentPos = add(source, mul(direction, distanceTraveled));

    const distanceToScene = sceneSDF(currentPos);
    if (distanceToScene < HIT_DISTANCE)
      return normal(sceneSDF, currentPos)[0] * 0.5 + 0.6;

    distanceTraveled += distanceToScene;
    if (distanceTraveled > MAX_DISTANCE) break;
  }

  return 0;
};