Okay, I see where I am falling (surprised why I did not notice it before):
action player_code()
{
...
var gravity_force = 2;
...
my.GRAVITY_VAR -= gravity_force * time_step;
...
c_move(me, move_vec, vector(0, 0, my.GRAVITY_VAR), USE_POLYGON |
IGNORE_PASSABLE | GLIDE);
...
DEBUG_VAR(my.z, 300);
...
}
It seems to me that my.GRAVITY_VAR should be affecting my.z while player is falling, but it shows nothing while player falls, judging by the DEBUG_VAR(my.z, 300); .