add --timing-only option for synchronizing timing but not polarity

docs/sync-windmills.rst

@@ -5,8 +5,15 @@ sync-windmills
     :summary: Synchronize or randomize windmill movement.
     :tags: fort buildings
 
-This tool can adjust the appearance of running windmills so that they are
-either all in synchronization or are all completely randomized.
+Windmills cycle between two graphical states to simulate movement. This is the
+polarity of the appearance. Each windmill also has a timer that controls when
+the windmill switches polarity. Each windmill's timer starts from zero at the
+instant that it is built, so two different windmills will rarely have exactly
+the same state. This tool can adjust the alignment of polarity and timers
+across your active windmills to your preference.
+
+Note that this tool will not affect windmills that have just been activated and
+are still rotating to adjust to the regional wind direction.
 
 Usage
 -----
@@ -19,7 +26,7 @@ Examples
 --------
 
 ``sync-windmills``
-    Make all active windmills synchronize their turning.
+    Synchronize movement of all active windmills.
 ``sync-windmills -r``
     Randomize the movement of all active windmills.
 
@@ -29,4 +36,6 @@ Options
 ``-q``, ``--quiet``
     Suppress non-error console output.
 ``-r``, ``--randomize``
-    Randomize windmill state.
+    Randomize the polarity and timer value for all windmills.
+``-t``, ``--timing-only``
+    Randomize windmill polarity, but synchronize windmill timers.

sync-windmills.lua

@@ -14,6 +14,7 @@ argparse.processArgsGetopt({...}, {
     { 'h', 'help', handler = function() opts.help = true end },
     { 'q', 'quiet', handler = function() opts.quiet = true end },
     { 'r', 'randomize', handler = function() opts.randomize = true end },
+    { 't', 'timing-only', handler = function() opts.timing = true end },
 })
 
 if opts.help then
@@ -22,8 +23,12 @@ if opts.help then
 end
 
 process_windmills(
-    opts.randomize and function() return math.random(1, 2) == 1 end or function() return false end,
-    opts.randomize and function() return math.random(0, 74) end or function() return 0 end)
+    (opts.randomize or opts.timing) and
+        function() return math.random(1, 2) == 1 end or
+        function() return false end,
+    opts.randomize and not opts.timing and
+        function() return math.random(0, 74) end or
+        function() return 0 end)
 
 if not opts.quiet then
     print(('%d windmills %s'):format(