import type { Graphics } from 'pixi.js';

/** Side of one square of the transparency checkerboard, in screen pixels. */
const CHECKER_SIZE = 8;
const CHECKER_DARK = 0x1a1c21;
const CHECKER_LIGHT = 0x24272e;

/**
 * The checkerboard behind a picture at (x, y, w, h). Only squares inside `0..clipW × 0..clipH` are
 * drawn: a 4000 px sheet zoomed in would otherwise cost tens of thousands of rectangles per redraw.
 */
export function drawChecker(
  g: Graphics,
  x: number,
  y: number,
  w: number,
  h: number,
  clipW: number,
  clipH: number,
): void {
  if (w <= 0 || h <= 0) return;
  g.rect(x, y, w, h).fill(CHECKER_DARK);
  const from = (start: number, limit: number) => Math.max(0, Math.floor((limit - start) / CHECKER_SIZE));
  const x0 = from(x, 0);
  const y0 = from(y, 0);
  const x1 = Math.min(Math.ceil(w / CHECKER_SIZE), from(x, clipW) + 1);
  const y1 = Math.min(Math.ceil(h / CHECKER_SIZE), from(y, clipH) + 1);
  for (let cy = y0; cy < y1; cy++) {
    for (let cx = x0; cx < x1; cx++) {
      if ((cx + cy) % 2 === 0) continue;
      g.rect(
        x + cx * CHECKER_SIZE,
        y + cy * CHECKER_SIZE,
        Math.min(CHECKER_SIZE, w - cx * CHECKER_SIZE),
        Math.min(CHECKER_SIZE, h - cy * CHECKER_SIZE),
      );
    }
  }
  g.fill(CHECKER_LIGHT);
}