std::vector<UnwrappedTileID> tileCover(const TransformState& state, int32_t z) {
    assert(state.valid());

    const double w = state.getSize().width;
    const double h = state.getSize().height;
    return tileCover(
        TileCoordinate::fromScreenCoordinate(state, z, { 0,   0   }).p,
        TileCoordinate::fromScreenCoordinate(state, z, { w,   0   }).p,
        TileCoordinate::fromScreenCoordinate(state, z, { w,   h   }).p,
        TileCoordinate::fromScreenCoordinate(state, z, { 0,   h   }).p,
        TileCoordinate::fromScreenCoordinate(state, z, { w/2, h/2 }).p,
        z);
}