STAMINA

Stamina 

What we vulgarly know as stamina in Counter-Strike it’s actually dictated by a variable in code named fuser2. It wasn’t present at early versions of the game but eventually was added during the updates it received.

fuser2 starts at a value of 0 when player spawns and every time a jump is made it resets to 1315.789429.

void PM_Jump() {
  ...
  pmove->fuser2 = 1315.789429;
  ...
}

Once set during jumping, fuser2 diminishes every frame by frame’s length (in milliseconds). Therefore, with a rate of 100fps it will be reduced each frame by 10 taking ≈1.31sec to reach 0 again and stop affecting our movements.

void PM_ReduceTimers() {
  ...
  if (pmove->fuser2 > 0.0) {
    pmove->fuser2 -= pmove->cmd.msec;
    if (pmove->fuser2 < 0.0) pmove->fuser2 = 0;
  }
  ...
}

The variable itself alters all three components of the velocity vector, that’s to say vertical and horizontal speeds alike, because it is used by the engine inside PM_WalkMove() and PM_Jump() functions.

PM_WalkMove():
This function is called every time player moves on ground.
Provided that fuser2 is greater than 0, its value will be utilized to cramp player’s horizontal speed (velocity.x and velocity.y) multiplying it by a factor calculated using the following formula:

factor = (100 - pmove->fuser2 * 0.001 * 19) * 0.01;

The shorter the jump the lesser the variable will decay which means a bigger slowdown when you start moving on ground after landing. That’s why you end up walking slower after every jump and why it’s more notorious when the jump is up to a platform instead of down to it.

PM_Jump():
As its name suggests, this function is called every time player jumps. Here, fuser2 is used to cramp player’s vertical speed (velocity.z) instead. The factor is given by the same formula presented before:

factor = (100.0 - pmove->fuser2 * 0.001 * 19.0) * 0.01;

It’s because of fuser2 use in PM_Jump() that subsequent bhops have less height than the first one. Take into account that when jumping at the same ground level we spend 0.66 seconds in air which does not suffice to null fuser2 before touching the ground again (remember we need at least 1.31 seconds to do so).

Also, you can now understand why spending more time in air when performing a stand-up bhop lessens variable’s value letting us gain a little more height in the next jump.