Editing Field map encounter mechanics (section)

== How it actually works ==

A procedure is run on every frame on which Cloud moves on any field map. The procedure is as follows:

<pre>
Add one step fraction.
If the current fraction is now zero, and we are on a hostile field, and encounters are enabled:
    Run Value = Field Scale * (4 if Run is held, 1 if it is not)
    Danger = Danger + (2 * Run Value / Encounter Rate)

    x = increment_step_id()
    If x < Preemptive Rate
        Preempt Flag = True
    Else:
        Preempt Flag = False

    x = increment_step_id()
    If x < ((Danger * Enemy Lure Value) / 4096):
        Set the game so we’re going to enter a battle
        x = increment_formation() / 4

        // Check Special Formations

        // Back Attack slot 1

        If Mastered Preempt Flag is not set:
            threshold = back attack slot 1 encounter rate
        Else:
            threshold = back attack slot 1 encounter rate / 2
        If x < threshold:
            Set battle formation to back attack slot 1
            Preempt Flag = False
            Exit this procedure
        
        // Back Attack slot 2

        If Mastered Preempt Flag is not set:
            threshold = threshold + back attack slot 2 encounter rate
        Else:
            threshold = threshold + back attack slot 2 encounter rate / 2
        If x < threshold:
            Set battle formation to back attack slot 2
            Preempt Flag = False
            Exit this procedure
        
        // Side Attack slot
        
        threshold = threshold + side attack slot encounter rate
        If x < threshold:
            Set battle formation to side attack slot
            Exit this procedure

        // Pincer slot

        If Mastered Preempt Flag is not set:
            threshold = threshold + pincer slot encounter rate
        Else:
            threshold = threshold + pincer slot encounter rate / 2
        If x < threshold:
            Set battle formation to pincer slot
            Exit this procedure

        // Check Standard Formations

        threshold = 0
        x = increment_formation()
        
        Current Encounter Slot = standard slot 6
        For i from 1 to 5:
            threshold = threshold + standard slot i encounter rate
            If x / 4 < threshold:
                Current Encounter Slot = standard slot i
                Break out of the loop

        Set battle formation to Current Encounter Slot encounter formation
        
        // Reroll (“Bump”) check

        If Current Encounter Slot encounter formation == Last Encounter Formation:
            threshold = 0
            x = increment_formation()
            Set battle formation to standard slot 6
            For i from 1 to 5:
                threshold = threshold + standard slot i encounter rate
                If x / 4 < threshold:
                    Set battle formation to standard slot i
                    Last Encounter Formation = std. slot i encounter formation
                    Exit this procedure
        
        Else:
            Last Encounter Formation = Current Encounter Slot encounter formation

</pre>
            
Procedure increment_step_id:

<pre>
stepid = stepid + 1

If stepid = 0:
    offset = offset + 13

Return RNG_TABLE[stepid] - offset;
</pre>

Procedure increment_formation:

<pre>
formation = formation + 1
Return RNG_TABLE[formation]
</pre>

'''Notes:'''

* All divisions round down to an integer, as everything here is done with truncating integer arithmetic.
* One Step Fraction is actually a unit of 32, so step fractions actually go 32, 64, 96… 224, 0.
* Field Scale is a value assigned to each field. Usually it's 512, but it can be larger or smaller. See [https://pastebin.com/UrRQ7ezH] for a list of field scale values.
* Run Value isn’t a value calculated at this part of the encounter logic, it’s actually calculated every frame based on whether Run is held or not and is constantly updated even while not moving.
* Encounter Rate is a 1-byte value in the current encounter table. Counterintuitively, lower Encounter Rate values mean a higher danger increase per step, and higher Encounter Rate values mean a lower danger increase per step.
* Because of the complex interaction between Run Value and Encounter Rate, It’s more useful to think of each screen as having a DIPS value, or Danger Increase Per Step, which is the final value that gets added to Danger per step of running.
* For some reason, Preempt Flag actually gets set to a value of 4 to signal True and 0 for False.
* In reality, the Preempt Value and Mastered Preempt Flag are combined into a single value, where the most significant bit is the Mastered Preempt Flag and the seven least significant bits are the Preempt Value.
* The Mastered Preemptive Flag is weird, see below.