Simplify the if-elses inside the event manager apply method (#948)

# Description

The if-else-continue logic inside the event manager has become scary.
This MR simplifies it and keeps the term call local to the if
statements. I hope this should help with the readability.

## Type of change

- New feature (non-breaking change which adds functionality)
- This change requires a documentation update

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

source/extensions/omni.isaac.lab/omni/isaac/lab/managers/event_manager.py

@@ -173,12 +173,12 @@ class EventManager(ManagerBase):
 
         # iterate over all the event terms
         for index, term_cfg in enumerate(self._mode_term_cfgs[mode]):
-            # resample interval if needed
             if mode == "interval":
                 # extract time left for this term
                 time_left = self._interval_term_time_left[index]
                 # update the time left for each environment
                 time_left -= dt
+
                 # check if the interval has passed and sample a new interval
                 # note: we compare with a small value to handle floating point errors
                 if term_cfg.is_global_time:
@@ -186,19 +186,18 @@ class EventManager(ManagerBase):
                         lower, upper = term_cfg.interval_range_s
                         sampled_interval = torch.rand(1) * (upper - lower) + lower
                         self._interval_term_time_left[index][:] = sampled_interval
-                    else:
-                        # no need to call func to apply term
-                        continue
+
+                        # call the event term (with None for env_ids)
+                        term_cfg.func(self._env, None, **term_cfg.params)
                 else:
-                    env_ids = (time_left < 1e-6).nonzero().flatten()
-                    if len(env_ids) > 0:
+                    valid_env_ids = (time_left < 1e-6).nonzero().flatten()
+                    if len(valid_env_ids) > 0:
                         lower, upper = term_cfg.interval_range_s
-                        sampled_time = torch.rand(len(env_ids), device=self.device) * (upper - lower) + lower
-                        self._interval_term_time_left[index][env_ids] = sampled_time
-                    else:
-                        # no need to call func to apply term
-                        continue
-            # check for minimum frequency for reset
+                        sampled_time = torch.rand(len(valid_env_ids), device=self.device) * (upper - lower) + lower
+                        self._interval_term_time_left[index][valid_env_ids] = sampled_time
+
+                        # call the event term
+                        term_cfg.func(self._env, valid_env_ids, **term_cfg.params)
             elif mode == "reset":
                 # obtain the minimum step count between resets
                 min_step_count = term_cfg.min_step_count_between_reset
@@ -211,6 +210,9 @@ class EventManager(ManagerBase):
                 if min_step_count == 0:
                     self._reset_term_last_triggered_step_id[index][env_ids] = global_env_step_count
                     self._reset_term_last_triggered_once[index][env_ids] = True
+
+                    # call the event term with the environment indices
+                    term_cfg.func(self._env, env_ids, **term_cfg.params)
                 else:
                     # extract last reset step for this term
                     last_triggered_step = self._reset_term_last_triggered_step_id[index][env_ids]
@@ -234,12 +236,12 @@ class EventManager(ManagerBase):
                     if len(valid_env_ids) > 0:
                         self._reset_term_last_triggered_once[index][valid_env_ids] = True
                         self._reset_term_last_triggered_step_id[index][valid_env_ids] = global_env_step_count
+
                         # call the event term
                         term_cfg.func(self._env, valid_env_ids, **term_cfg.params)
-                    # no need to call func to apply term again
-                    continue
-            # call the event term
-            term_cfg.func(self._env, env_ids, **term_cfg.params)
+            else:
+                # call the event term
+                term_cfg.func(self._env, env_ids, **term_cfg.params)
 
     """
     Operations - Term settings.