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https://github.com/bryanthaboi/gen1recomp.git
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bryanthaboi
64 lines
2.6 KiB
Lua
64 lines
2.6 KiB
Lua
-- Fixed-step update loop at the Game Boy's ~60Hz. Game logic advances in
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-- whole steps regardless of the display refresh rate, which keeps movement,
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-- text speed and battle timing deterministic.
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local FixedStep = {}
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FixedStep.STEP = 1 / 60
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local MAX_ACCUM = 0.25 -- avoid spiral of death after a stall
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-- Phase the accumulator is re-seeded with once an absorbed hitch frame has
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-- been paid for. Half a step is the balanced point: a frame has to come in
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-- ~8ms short before it drops a step and ~8ms long before it doubles one up.
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-- Zero -- what this used to leave behind -- has no margin at all on the long
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-- side, so the accumulator settles a hair BELOW one step and parks there, and
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-- ordinary sub-millisecond vsync wobble then flips it between 0 and 2 steps
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-- every few frames for the rest of the session. That is why pacing stayed
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-- visibly broken after a route/city seam and nowhere else: crossConnection in
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-- src/world/OverworldController.lua is the only caller of discardCatchup, and
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-- warps go through Transition instead (issue #487).
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local RESEED_PHASE = 0.5
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function FixedStep:init(callback)
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self.accum = 0
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self.callback = callback
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self.suppressCatchup = false
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end
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-- The anti-spiral clamp doubles as a steps-per-frame ceiling (0.25s = 15
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-- steps), which silently throttled the high fast-forward levels: at 100X
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-- a 60fps frame wants ~100 steps. Game:update raises this to fit the
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-- current speed target; a stall still cannot snowball past one frame's
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-- intended budget.
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FixedStep.maxAccum = MAX_ACCUM
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function FixedStep:update(dt)
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-- A hitch's oversized dt lands on the frame AFTER discardCatchup was
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-- called (the hitch itself already ran inside the current step); absorb
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-- that one frame as a single step instead of the normal accumulator so
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-- the burst it would otherwise release doesn't play out as a slide.
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if self.suppressCatchup then
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self.suppressCatchup = false
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self.accum = self.STEP * RESEED_PHASE
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self.callback(self.STEP)
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return
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end
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self.accum = math.min(self.accum + dt, self.maxAccum or MAX_ACCUM)
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while self.accum >= self.STEP do
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self.accum = self.accum - self.STEP
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self.callback(self.STEP)
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end
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end
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-- Drop any pending catch-up steps and arm the one-frame clamp above. A
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-- hitch inside one logic step (map seam setMap / song start) makes the
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-- next real-time dt huge; without this the while-loop above would advance
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-- many walk frames before the next draw, which looks like a slide with no
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-- leg animation (issue #93).
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function FixedStep:discardCatchup()
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self.accum = 0
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self.suppressCatchup = true
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end
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return FixedStep
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