void CheckForFullLine(int starting_Y)
{
    for (int y = starting_Y; y < frozenCells.GetLength(1); y++)
    {
        for (int x = 0; x < frozenCells.GetLength(0); x++)
        {
            if (!frozenCells[x, y].isFilled)
            {
                CheckForFullLine(starting_Y + 1);
                return;
            }

            if (x == CELL_COUNT_X - 1)
            {
                tetrisLinesThisTick++;
                Debug.Log("lines this tick: " + tetrisLinesThisTick + "on tick: " + tick);
                ClearLine(y);
            }
        }
    }
}

private void Update()
{
    tick++;
    // reset the tetris-lines this tick value:
    tetrisLinesThisTick = 0;

    ClearScreen();
    CheckForFullLine(0);
    HandleMovementAndBlockCreation();
    DrawFallingPiece();
    DrawFrozenBricks();
}

void ClearLine(int line)
{
    // TODO: Add score

    // remove complete line
    for (int x = 0; x < frozenCells.GetLength(0); x++)
    {
        frozenCells[x, line].isFilled = false;
    }

    //shift all lines down        // todo: figure out if its a multi-line tetris to give better scores...
    for (int y = line; y < frozenCells.GetLength(1); y++)
    {
        for (int x = 0; x < frozenCells.GetLength(0); x++)
        {
            if (frozenCells[x, y].isFilled)
            {
                if (y > 0)
                {
                    frozenCells[x, y].isFilled = false;
                    frozenCells[x, y - 1].isFilled = true;
                }
            }
        }
    }

}