thi-ng/umbrella

import { intersectRayPolyline } from "@thi.ng/geom-isec/ray-poly";
import type { ReadonlyVec } from "@thi.ng/vectors";

/**
 * Samples 2D polyline at uniform step distance in `[x1..x2]` interval along
 * X-axis. Returns array of sampled points.
 *
 * @remarks
 * The polyline is assumed to fully cover the given X interval, no gaps are
 * allowed (or checked for). Sampling is done via ray-line intersection with the
 * ray cast into Y+ direction, starting at given `startY`.
 *
 * Also see {@link sampleUniformY}.
 *
 * @example
 * ```ts
 * import { sampleUniformX } from "@thi.ng/geom-resample";
 *
 * sampleUniformX([[0, 0], [3, 5], [5, 2]], 0, 5)
 * // [
 * //   [ 0, 0 ],
 * //   [ 1, 1.666... ],
 * //   [ 2, 3.333... ],
 * //   [ 3, 5 ],
 * //   [ 4, 3.5 ],
 * //   [ 5, 2 ]
 * // ]
 * ```
 *
 * @param pts
 * @param x1
 * @param x2
 * @param step
 * @param startY
 */
export const sampleUniformX = (
    pts: ReadonlyVec[],
    x1: number,
    x2: number,
    step = 1,
    startY = -1
) => {
    const res: ReadonlyVec[] = [];
    for (let x = x1; x <= x2; x += step) {
        res.push(
            <ReadonlyVec>(
                intersectRayPolyline([x, startY], [0, 1], pts, false).isec![0]
            )
        );
    }
    return res;
};

/**
 * Similar to {@link sampleUniformX}, but samples 2D polyline at uniform step
 * distance in `[y1..y2]` interval along Y-axis. Returns array of sampled
 * points.
 *
 * @param pts
 * @param y1
 * @param y2
 * @param step
 * @param startX
 */
export const sampleUniformY = (
    pts: ReadonlyVec[],
    y1: number,
    y2: number,
    step = 1,
    startX = -1
) => {
    const res: ReadonlyVec[] = [];
    for (let y = y1; y <= y2; y += step) {
        res.push(
            <ReadonlyVec>(
                intersectRayPolyline([startX, y], [1, 0], pts, false).isec![0]
            )
        );
    }
    return res;
};