thi-ng/umbrella

import type { FnN3, FnU2, FnU7, FnU8, Maybe, Tuple } from "@thi.ng/api";

/**
 * Filters points from `src` iterable to remove any falling outside the rect
 * defined by `left,top`..`right,bottom`.
 *
 * @param src -
 * @param left -
 * @param top -
 * @param right -
 * @param bottom -
 */
export function* clipped(
    src: Iterable<number[]>,
    left: number,
    top: number,
    right: number,
    bottom: number
) {
    for (let p of src) {
        if (p[0] >= left && p[0] < right && p[1] >= top && p[1] < bottom)
            yield p;
    }
}

/** @internal */
const __axis: FnN3 = (a, b, c) =>
    (a < b ? a - b : a > b + c ? a - b - c : 0) ** 2;

/**
 * Based on [thi.ng/geom-isec](https://thi.ng/geom-isec), but inlined to avoid
 * dependency.
 *
 * @param x -
 * @param y -
 * @param w -
 * @param h -
 * @param cx -
 * @param cy -
 * @param r -
 *
 * @internal
 */
export const intersectRectCircle: FnU7<number, boolean> = (
    x,
    y,
    w,
    h,
    cx,
    cy,
    r
) => __axis(cx, x, w) + __axis(cy, y, h) <= r * r;

/**
 * Based on [`liangBarsky2Raw()`](https://docs.thi.ng/umbrella/geom-clip-line/functions/liangBarsky2Raw.html), but with diff return type.
 *
 * @param ax -
 * @param ay -
 * @param bx -
 * @param by -
 * @param minx -
 * @param miny -
 * @param maxx -
 * @param maxy -
 *
 * @internal
 */
export const liangBarsky: FnU8<number, Maybe<Tuple<number, 4>>> = (
    ax,
    ay,
    bx,
    by,
    minx,
    miny,
    maxx,
    maxy
) => {
    const dx = bx - ax;
    const dy = by - ay;
    let alpha = 0;
    let beta = 1;
    const clip: FnU2<number, boolean> = (p, q) => {
        if (p < 0) {
            const r = q / p;
            if (r > beta) return false;
            r > alpha && (alpha = r);
        } else if (p > 0) {
            const r = q / p;
            if (r < alpha) return false;
            r < beta && (beta = r);
        } else if (q < 0) {
            return false;
        }
        return true;
    };
    return clip(-dx, ax - minx) &&
        clip(dx, maxx - ax) &&
        clip(-dy, ay - miny) &&
        clip(dy, maxy - ay)
        ? [alpha * dx + ax, alpha * dy + ay, beta * dx + ax, beta * dy + ay]
        : undefined;
};