I saw the deepfly bind the other day:

bind mouse1 "+fire; +toggle cl_dummy_hammer 1 0"

Deepfly is a technique that allows you to fly with a tee that’s deep frozen, i.e. frozen until it hits an undeep tile. This means that any input that the deep frozen input gives is discarded, except when it gets hammered or shot by the unfreeze laser, in which case it is given a game tick where it can fire a weapon or use its hammer. In the case of deepfly, you join the game with a dummy, a second tee that is also controlled by your client. You then hook the dummy, hammer it, causing it to unfreeze and hammer you back, causing you to generate upward movement.

I heard that you need a reliable connection to the server to manage to make the deepfly work. This sounded a lot like frame-perfect input being necessary. I found it a little weird, so I decided to investigate.

One tick unfreezes are part of DDRace and DDNet gameplay. They work reliably for shotgun, grenade and laser, at the very least since 39704a04 by Speedy Consoles. But they’ve been used by tees all the way back to the beginning of DDRace. So how do they work and why?

Currently input and freeze interact as follows:

          Tee 1 (weak)            Tee 2 (strong)

         +---------------+       +---------------+       
         | weapon input  |       | weapon input  |       
start -->| if not frozen |    +->| if not frozen |    +-> ... 
         | (non-/auto)   |    |  | (non-/auto)   |    |   ...
         +---------------+    |  +---------------+    |   ...
                |             |         |             |   ...
                v             |         v             |   ...
         +------------------+ |  +------------------+ |   ...
         | unfreeze targets |-+  | unfreeze targets |-+   ... --+
         +------------------+    +------------------+           |
                                                                |
                                                                |
                                                                |
         +---------------+       +---------------+              |
         | weapon input  |       | weapon input  |              |
         | if not frozen |<---+  | if not frozen |<---+   ... <-+
         | (only auto)   |    |  | (only auto)   |    |   ...
         +---------------+    |  +---------------+    |   ...
                |             |         |             |   ...
                v             |         v             |   ...
         +------------------+ |  +------------------+ |   ...
         | unfreeze targets | |  | unfreeze targets | |   ...
         +------------------+ |  +------------------+ |   ...
                |             |         |             |   ...
                v             |         v             |   ...
         +------------------+ |  +------------------+ |   ...
  end <--| check own freeze | +--| check own freeze | +-- ...
         +------------------+    +------------------+

Firstly, go through all the tees by client ID and let them fire their automatic (laser, shotgun, grenade) and non-automatic (pistol, hammer) weapons, if they’re not frozen by the time it’s their turn. This immediately unfreezes targets of laser and hammer, allowing tees with higher client IDs to fire their weapons even if they were frozen at the start of the tick.

Then, go through all the tees by weak-strong hook order1, starting with strong hook, and let them fire their automatic weapons if they’re not frozen. Unfreeze every hit tee, so that tees later in the order can also act. Then check whether the tee is on a freeze tile or is deep frozen and freeze it in that case.

Now, after this explanation, try to figure out how deepfly (hammering your dummy tee who is deep frozen and who hammers you back, this is usually done via the deepfly bind shown above). Try to find something strange. ;)

Well, it turns out that deepfly only works if your dummy has a lower client ID than you do. If you’re reading this blog post right as it came out, try it on the official servers – if not, maybe it is fixed in the future and will work.

Tees unsuccessfully trying to fly out of freeze

Additionally, know that moment when trying to fly up from freeze and the tee below you is just too dumb to hammer you back? They probably have a higher client ID than you do and simple can’t hammer you while they’re in freeze.

Tees successfully flying out of freeze

So, deepfly needs frame-perfect input and only works on tees with lower client IDs than yourself. I don’t consider frame-perfect input to be a good game design, so I propose fixing that. This would allow players using a normal client to perform this trick even if they have high ping. While we’re at it, we could also fix the higher-lower client ID thing.

My proposed fix (#1922, f19220f1) does this by remembering whether you were frozen last tick and if you were, it lets you hammer like an automatic weapon, i.e. simply by having held that button.

What are advantages and disadvantages of this patch?

First, this allows people to do more than they could have done before: Do deepfly/hammer out of freeze even if you’re the one that is frozen and have a higher client ID than the tee that hammers you. This could give you an advantage on server ranks.

Second, this allows people to do the deepfly/hammer out of freeze more easily. However, this is something that was possible before, using frame-perfect input, an unlocked scroll wheel bound to +fire or a nonstandard client.

The second point is also an advantage; it allows people to more easily experiment with tricks that have already been possible before, but were just hard to execute without hardware or software support. This might remove some incentive to use nonstandard clients.

Thanks to Patiga and Zwelf for investigating the intricate mechanics of one tick unfreezes, deepfly, etc. and testing out my fix for it. Thanks to Zeta-Hoernchen for recording the GIFs with me.

PS: This post has rested for almost two months before being published. I guess I’m not made for blogging. The initial inspiration to publish anything at all came from my enjoyment of reading the Dunely Daily, back when it was updated.

  1. Internally, this is entity insertion order, i.e. character spawn order. ↩