export function createStaticLayerCanvas(width, height) {
  const w = Math.max(1, width | 0);
  const h = Math.max(1, height | 0);
  if (typeof OffscreenCanvas !== 'undefined') return new OffscreenCanvas(w, h);
  const c = document.createElement('canvas');
  c.width = w;
  c.height = h;
  return c;
}

export function drawCachedStaticLayer(state, g, layerId, key, rect, build) {
  if (!state || !rect || rect.w <= 0 || rect.h <= 0) return;
  if (!state.staticLayers) state.staticLayers = new Map();
  const fullKey = `${layerId}:${key}:${Math.max(0, rect.w | 0)}x${Math.max(0, rect.h | 0)}`;
  let layer = state.staticLayers.get(fullKey);
  if (!layer) {
    const canvas = createStaticLayerCanvas(rect.w, rect.h);
    const ctx = canvas.getContext('2d');
    build(ctx, rect);
    layer = { canvas };
    state.staticLayers.set(fullKey, layer);
  }
  g.drawImage(layer.canvas, rect.x, rect.y);
}