Ensuring a Recursive method completes in one update tick?

Question

OK so I have a method that calls itself as this was the only way I could think to get the behaviour I needed. Its a tetris clone i am making and this method is for checking for full lines across X axis.

    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);
            }
        }
    }
}

but when i test the game, most of the time (more than 9/10 times) when you get multiple lines, the debug log says we only got 1 line in that 'tick'.

Here is the update method where at the top I set tetrisLinesPerTick to 0 at the start of each frame.

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

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

For example if I get 2 lines in one go, I get the debug log saying '...linesPerTick 1' twice in quick succession.

Strangely , occasionaly I do get the 2 or even 3 lines and it says the correct amount, but this is rare and i don't know how i reproduce that yet.

Another very strange thing (the relevant code might not be here for this part..) ...quite rarely one of the frozen blocks will turn grey after falling, then I can still 'use' it in game to make more lines, but it doesnt disappear like the others, then make a couple more lines using this grey block and it disappears as normal :S (well just in case you feel like helping me with this part, he is more code :P):

    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;
                }
            }
        }
    }

}

For some reason, I feel it may be the recursive method i made and the fact that 'linesPerTick' value is getting set back to zero prior to the other lines being removed (in the same move), is what is causing my problem but i could be completely wrong about it!

The whole project is just one .cs file and a block texture i made in GIMP, I could paste the whole script here if you want to try it please let me know. Cheers for any help!

Answer 1

This is almost certainly an XY problem -- I can't imagine that it makes sense to use a recursive function for this.

If I'm reading your code right (it's late) then you're trying have it stop processing each row as soon as it finds the first empty square instead of processing the whole row, which makes sense. Instead of calling your function again, how about simply continueing on to the next step in your outer Y loop?

I think you've probably also got a logic problem where you call ClearLine upon finding a full row, and that shifts everything down while you're still in the middle of looking for full rows. If your code finds that row 3 is full, then it increments the score counter AND shifts row 4 down into row 3, and then continues checking at row 4. Since you've already shifted 4 to 3, that row never gets checked. Personally, I'd be tempted to move all of the rows after doing all the score calculation, but there are lots of solutions (including just re-checking the same row IF you've called clearline).

Often, I find that working through these problems on some scratch paper can give you a lot of insight into what your code is actually doing when you think it should be doing something else. This is a small enough problem that working though a loop or two shouldn't be too painful ;-)

FWIW, since you're really only copying one row to another regardless of whether it's filled or not, you could probably simplify your ClearLine to something like this pseudocode:

void ClearLine(int line) {
  int topRow = frozenCells.GetLength(1)-1
  for (int y=line; y<topRow; y++) {
    for (int x = 0; x < frozenCells.GetLength(0); x++) {
      frozenCells[x,y].isFilled = frozenCells[x,y+1]
    }
  }
  // The new top row should be empty
  for (int x = 0; x < frozenCells.GetLength(0); x++) {
    frozenCells[x,topRow].isFilled = false
  }
}