Tetris Difficulty

tetris

I had a discussion with a friend about Tetris where we quibbled about how it got more difficult as the levels progressed. His assertion was that it had only to do with the amount of time given to work with a block whereas I thought that I remembered it not just being a time thing but also that easier blocks (squares, long rectangles) came less frequently.

Does anyone know how this was implemented and how difficulty increased as levels progressed?

Best Answer

As far as I know (and I've done quite a bit of reading about Tetris lately), no official version of Tetris changes its piece-selection method as the game goes on.

Assuming you're asking about the NES version, the only difference as the levels progress is the speed that the blocks fall at.

Here is the falling speed for the levels, in the number of frames it takes for each piece to drop one cell towards the bottom. The game runs at 60 frames/second, so a value of 60 would mean it moves down one cell per second, a 6 is 10 cells/second, etc.

  Level    Drop speed
         (frames/line)
     00            48 (0.8 s)
     01            43 (0.72s)
     02            38 (0.63s) 
     03            33 (0.55s) 
     04            28 (0.47s) 
     05            23 (0.38s)
     06            18 (0.3 s) 
     07            13 (0.22s)
     08             8 (0.13s)
     09             6 (0.1 s)
  10-12             5 (0.08s) 
  13-15             4 (0.07s)
  16-18             3 (0.05s)
  19-28             2 (0.03s)
    29+             1 (0.02s)

(source)

For completeness, the randomizer always works as follows:

  1. Pick a (pseudo)random number from 0-7, representing the 7 possible pieces and one "dummy number" (7). If it comes up as 7 or the same number as the previous piece, go to step 2. Otherwise, give the piece represented by the chosen number.
  2. Pick a (pseudo)random number from 0-6, and give the piece represented by the number.

So there's a lower-than-normal chance of getting the same block twice in a row, but that's about it.

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