Editing Flood fill (section)

=== Pseudocode ===
This is a pseudocode implementation of an optimal fixed-memory flood-fill algorithm written in structured English:

; The variables
* <code>cur</code>, <code>mark</code>, and <code>mark2</code> each hold either pixel coordinates or a null value
** NOTE: when <code>mark</code> is set to null, do not erase its previous coordinate value. Keep those coordinates available to be recalled if necessary.
* <code>cur-dir</code>, <code>mark-dir</code>, and <code>mark2-dir</code> each hold a direction (left, right, up, or down)
* <code>backtrack</code> and <code>findloop</code> each hold Boolean values
* <code>count</code> is an integer
; The algorithm
: NOTE: All directions (front, back, left, right) are relative to <code>cur-dir</code>
 set cur to starting pixel
 set cur-dir to default direction
 clear mark and mark2 (set values to null)
 set backtrack and findloop to false
 
 '''while''' front-pixel is empty '''do'''
     move forward
 '''end while'''
 
 jump to START
 
 MAIN LOOP:
     move forward
     '''if''' right-pixel is inside '''then'''
         '''if''' backtrack is true '''and''' findloop is false '''and''' either front-pixel '''or''' left-pixel is inside '''then'''
             set findloop to true
         '''end if'''
         turn right
 PAINT:
         move forward
     '''end if'''
 START:
     '''set''' ''count'' to number of non-diagonally adjacent pixels filled (front/back/left/right ONLY)
     '''if''' ''count'' '''is not''' 4 '''then'''
         '''do'''
             turn right
         '''while''' front-pixel is inside
         '''do'''
             turn left
         '''while''' front-pixel is not inside
     '''end if'''
     '''switch''' ''count''
         case 1
             '''if''' backtrack is true '''then'''
                 set findloop to true
             '''else if''' findloop is true '''then'''
                 '''if''' mark is null '''then'''
                     restore mark
                 '''end if'''
             '''else if''' front-left-pixel and back-left-pixel are both inside '''then'''
                 clear mark
                 set cur
                 jump to PAINT
             '''end if'''
         end case
         case 2
             '''if''' back-pixel is not inside '''then'''
                 '''if''' front-left-pixel is inside '''then'''
                     clear mark
                     set cur
                     jump to PAINT
                 '''end if'''
             '''else if''' mark is not set '''then'''
                 set mark to cur
                 set mark-dir to cur-dir
                 clear mark2
                 set findloop and backtrack to false
             '''else'''
                 '''if''' mark2 is not set '''then'''
                     '''if''' cur is at mark '''then'''
                         '''if''' cur-dir is the same as mark-dir '''then'''
                             clear mark
                             turn around
                             set cur
                             jump to PAINT
                         '''else'''
                             set backtrack to true
                             set findloop to false
                             set cur-dir to mark-dir
                         '''end if'''
                     '''else if''' findloop is true '''then'''
                         set mark2 to cur
                         set mark2-dir to cur-dir
                     '''end if'''
                 '''else'''
                     '''if''' cur is at mark '''then'''
                         set cur to mark2
                         set cur-dir to mark2-dir
                         clear mark and mark2
                         set backtrack to false
                         turn around
                         set cur
                         jump to PAINT
                     '''else''' if cur at mark2 '''then'''
                         set mark to cur
                         set cur-dir and mark-dir to mark2-dir
                         clear mark2
                     '''end if'''
                 '''end if'''
             '''end if'''
         end case
         case 3
             clear mark
             set cur
             jump to PAINT
         end case
         case 4
             set cur
             done
         end case
     '''end switch'''
 end MAIN LOOP