fixing failed tests/harnesses

src/core/FixedStep.lua

@@ -10,6 +10,7 @@ local MAX_ACCUM = 0.25 -- avoid spiral of death after a stall
 function FixedStep:init(callback)
   self.accum = 0
   self.callback = callback
+  self.suppressCatchup = false
 end
 
 -- The anti-spiral clamp doubles as a steps-per-frame ceiling (0.25s = 15
@@ -20,6 +21,16 @@ end
 FixedStep.maxAccum = MAX_ACCUM
 
 function FixedStep:update(dt)
+  -- A hitch's oversized dt lands on the frame AFTER discardCatchup was
+  -- called (the hitch itself already ran inside the current step); absorb
+  -- that one frame as a single step instead of the normal accumulator so
+  -- the burst it would otherwise release doesn't play out as a slide.
+  if self.suppressCatchup then
+    self.suppressCatchup = false
+    self.accum = 0
+    self.callback(self.STEP)
+    return
+  end
   self.accum = math.min(self.accum + dt, self.maxAccum or MAX_ACCUM)
   while self.accum >= self.STEP do
     self.accum = self.accum - self.STEP
@@ -27,12 +38,14 @@ function FixedStep:update(dt)
   end
 end
 
--- Drop any pending catch-up steps.  A hitch inside one logic step (map
--- seam setMap / song start) makes the next real-time dt huge; without this
--- the while-loop above would advance many walk frames before the next
--- draw, which looks like a slide with no leg animation (issue #93).
+-- Drop any pending catch-up steps and arm the one-frame clamp above.  A
+-- hitch inside one logic step (map seam setMap / song start) makes the
+-- next real-time dt huge; without this the while-loop above would advance
+-- many walk frames before the next draw, which looks like a slide with no
+-- leg animation (issue #93).
 function FixedStep:discardCatchup()
   self.accum = 0
+  self.suppressCatchup = true
 end
 
 return FixedStep