thi-ng/umbrella

import type { GridIterOpts2D } from "./api.js";
import { __opts } from "./utils.js";

/**
 * Yields sequence of 2D grid coordinates in diagonal order starting at [0,0]
 * and using given `cols` and `rows`. Each diagonal starts at y=0 and progresses
 * in -x,+y direction.
 *
 * Ported & modified from original Java code by Christopher Kulla.
 * https://sourceforge.net/p/sunflow/code/HEAD/tree/trunk/src/org/sunflow/core/bucket/DiagonalBucketOrder.java
 *
 * @param opts -
 */
export function* diagonal2d(opts: GridIterOpts2D) {
    const { cols, rows, tx } = __opts(opts);
    const num = cols * rows - 1;
    for (let x = 0, y = 0, nx = 1, ny = 0, i = 0; i <= num; i++) {
        yield tx(x, y);
        if (i !== num) {
            do {
                if (y === ny) {
                    y = 0;
                    x = nx;
                    ny++;
                    nx++;
                } else {
                    x--;
                    y++;
                }
            } while (y >= rows || x >= cols);
        }
    }
}