lunes, 4 de enero de 2021

Tetris DAS

 I'll try to explain DAS techniques here. I made that video when I first learned the rules, and I know it is not very clear. (I still find it a bit difficult to explain NES DAS tricks in words.) I will do my best to explain these techniques simply so you can start using them.

Here is a quick explanation of how you generally want to move the pieces:

  • Avoid tapping to move the pieces.
  • Begin holding Left or Right during the waiting time after a piece lands and before the next piece appears. (The "thud" sound effect is a useful cue for the time when it is safe to change directions.)
  • Release Left or Right when the piece is in the correct position.
  • If you release early/late and must tap to fix the piece position, be aware that DAS "momentum" will reset to zero. Keep this in mind when planning your recovery.
  • One special rule that is very helpful for recovery: if you move the piece toward a wall or obstruction, DAS "momentum" is immediately refilled. (The reason for this rule is to allow you to slide pieces under overhangs easily, but you can abuse this rule to gain momentum for the next piece as well.)
Below is a longer explanation of why these techniques work. I know this explanation is dense, please let me know if there is anything unclear below and I will try to use different words:

NES Tetris's DAS (Delayed AutoShift) is very similar to keyboard autorepeat on a computer. When you hold Left or Right for a short start-up time (~1/4sec), the piece starts to move at a quick rate (10Hz = every 1/10sec).

NES Tetris is divided into two general periods of time: time when you're actively controlling a piece, and time when you're waiting for a new piece to appear (1/3~1/6sec of waiting time, plus ~2/5sec for the line clear animation). During the waiting time, the DAS "momentum" will not increase or decrease; you're free to hold Left/Right without losing momentum (but you cannot gain it either). During the active time, DAS "momentum" will only reset to zero when you begin pressing Left/Right (tapping or begin holding).

The piece entry delay is your safe time to prepare a move. If you only change directions in the waiting time before a new piece appears, you can keep the flow of momentum between pieces. If you hesitate and start pressing Left/Right after a new piece has already appeared, then momentum will be lost -- you'll notice the piece wait through the ~1/4sec starting delay again before quick movement resumes.

You don't lose momentum when you release Left/Right, when you press Down, etc.. If you use DAS then release Left/Right, you still have that momentum saved for later use. You can even let some pieces fall straight down and keep that momentum saved for a later piece. As long as you only press Left/Right before a new piece appears, you can use whatever momentum was leftover from before.

If your timing is very accurate (i.e., always release Left/Right in the correct 1/10sec window), you can keep this flow of momentum forever. If you release too early or too late and need to tap to correct the piece's position, you'll want to do something to recover DAS somehow. Here are some methods for regaining momentum:
  • When tapping to fix the piece position, keep the direction held for slightly less than the ~1/4 second DAS start-up. You want to build some momentum, but without moving the piece an extra space.
  • Use the special rule for movement against walls, as mentioned at the beginning of this post.
  • Extra special trick: abuse the "no diagonal movement" rule to change directions without losing momentum. Press the d-pad diagonally (Down+Left or Down+Right), then release Down. This technique is awkward because the piece does not always move instantly (~1/10sec or less until next DAS movement). I don't know if anyone uses this technique often. (This trick's strange explanation: the game will not let you move a piece diagonally; if two directions are pressed, the piece will not drop down or move left/right. This prevents the piece from making a "tap movement," so momentum does not reset to zero when you first start pressing Left or Right. But, when you release Down, you're already holding Left or Right so DAS starts to move the piece in that direction.)





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