CLOSES #455, CLOSES #487, CLOSES #501, CLOSES #540, CLOSES #585, CLOSES #591, CLOSES #593, CLOSES #595, CLOSES #597, CLOSES #599, CLOSES #600, CLOSES #606, CLOSES #607, CLOSES #610, CLOSES #613, CLOSES #616, CLOSES #620, CLOSES #626, CLOSES #632, CLOSES #633, CLOSES #647

src/core/FixedStep.lua

@@ -7,6 +7,18 @@ local FixedStep = {}
 FixedStep.STEP = 1 / 60
 local MAX_ACCUM = 0.25 -- avoid spiral of death after a stall
 
+-- Phase the accumulator is re-seeded with once an absorbed hitch frame has
+-- been paid for.  Half a step is the balanced point: a frame has to come in
+-- ~8ms short before it drops a step and ~8ms long before it doubles one up.
+-- Zero -- what this used to leave behind -- has no margin at all on the long
+-- side, so the accumulator settles a hair BELOW one step and parks there, and
+-- ordinary sub-millisecond vsync wobble then flips it between 0 and 2 steps
+-- every few frames for the rest of the session.  That is why pacing stayed
+-- visibly broken after a route/city seam and nowhere else: crossConnection in
+-- src/world/OverworldController.lua is the only caller of discardCatchup, and
+-- warps go through Transition instead (issue #487).
+local RESEED_PHASE = 0.5
+
 function FixedStep:init(callback)
   self.accum = 0
   self.callback = callback
@@ -27,7 +39,7 @@ function FixedStep:update(dt)
   -- the burst it would otherwise release doesn't play out as a slide.
   if self.suppressCatchup then
     self.suppressCatchup = false
-    self.accum = 0
+    self.accum = self.STEP * RESEED_PHASE
     self.callback(self.STEP)
     return
   end