add a wider variety of jitter

docs/timestream.rst

@@ -113,11 +113,17 @@ of their advantage.
 Limitations
 -----------
 
-Right now, not all aspects of the game are perfectly adjusted. For example,
+DF does critial game tasks every 10 ticks that must not be skipped, so
+`timestream` cannot advance more than 9 ticks at a time. This means that, with
+the default target of 100 FPS, the game will start showing signs of slowdown if
+the real FPS drops below about 15. The interface will also become less
+responsive to mouse gestures as the real FPS drops.
+
+Finally, not all aspects of the game are perfectly adjusted. For example,
 armies on world map will move at the same (real-time) rate regardless of
 changes that ``timestream`` is making to the calendar.
 
-Here is a (likely incomplete) list of game elements that are not adjusted by
+Here is a (possibly incomplete) list of game elements that are not adjusted by
 ``timestream`` and will appear "slow" in-game:
 
 - Army movement across the world map (including raids sent out from the fort)

timestream.lua

@@ -143,11 +143,19 @@ local function on_tick()
     local timeskip = math.floor(clamp_timeskip(desired_timeskip))
 
     -- add some jitter so we don't fall into a constant pattern
-    -- to reduce the risk of repeatedly missing an unknown threshold
-    timeskip = math.random(timeskip - 1, timeskip)
+    -- this reduces the risk of repeatedly missing an unknown threshold
+    -- also keeps the game from looking robotic at lower frame rates
+    local jitter_category = math.random(1, 10)
+    if jitter_category <= 1 then
+        timeskip = math.random(0, timeskip)
+    elseif jitter_category <= 3 then
+        timeskip = math.random(math.max(0, timeskip-2), timeskip)
+    elseif jitter_category <= 5 then
+        timeskip = math.random(math.max(0, timeskip-4), timeskip)
+    end
 
-    -- no need to let our deficit grow beyond the maximum single-step jump
-    timeskip_deficit = math.min(desired_timeskip - timeskip, 9.0)
+    -- no need to let our deficit grow unbounded
+    timeskip_deficit = math.min(desired_timeskip - timeskip, 100.0)
 
     if timeskip <= 0 then return end