ebiten/internal/clock/clock.go

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// Copyright 2017 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
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// Package clock manages game timers.
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package clock
import (
"sync"
"time"
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)
var (
lastNow int64
// lastSystemTime is the last system time in the previous Update.
// lastSystemTime indicates the logical time in the game, so this can be bigger than the curren time.
lastSystemTime int64
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currentFPS float64
currentTPS float64
lastUpdated int64
fpsCount = 0
tpsCount = 0
m sync.Mutex
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)
func init() {
n := now()
lastNow = n
lastSystemTime = n
lastUpdated = n
}
func CurrentFPS() float64 {
m.Lock()
v := currentFPS
m.Unlock()
return v
}
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func CurrentTPS() float64 {
m.Lock()
v := currentTPS
m.Unlock()
return v
}
func calcCountFromTPS(tps int64, now int64) int {
if tps == 0 {
return 0
}
if tps < 0 {
panic("clock: tps must >= 0")
}
diff := now - lastSystemTime
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if diff < 0 {
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return 0
}
count := 0
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syncWithSystemClock := false
if diff > int64(time.Second)*5/60 {
// The previous time is too old.
// Let's force to sync the game time with the system clock.
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syncWithSystemClock = true
} else {
count = int(diff * tps / int64(time.Second))
}
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// Stabilize the count.
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// Without this adjustment, count can be unstable like 0, 2, 0, 2, ...
if count == 0 && (int64(time.Second)/tps/2) < diff {
count = 1
}
if count == 2 && (int64(time.Second)/tps*3/2) > diff {
count = 1
}
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if syncWithSystemClock {
lastSystemTime = now
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} else {
lastSystemTime += int64(count) * int64(time.Second) / tps
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}
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return count
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}
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func updateFPSAndTPS(now int64, count int) {
fpsCount++
tpsCount += count
if now < lastUpdated {
panic("clock: lastUpdated must be older than now")
}
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if time.Second > time.Duration(now-lastUpdated) {
return
}
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currentFPS = float64(fpsCount) * float64(time.Second) / float64(now-lastUpdated)
currentTPS = float64(tpsCount) * float64(time.Second) / float64(now-lastUpdated)
lastUpdated = now
fpsCount = 0
tpsCount = 0
}
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const UncappedTPS = -1
// Update updates the inner clock state and returns an integer value
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// indicating how many times the game should update based on given tps.
// tps represents TPS (ticks per second).
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// If tps is UncappedTPS, Update always returns 1.
// If tps <= 0 and not UncappedTPS, Update always returns 0.
//
// Update is expected to be called per frame.
func Update(tps int) int {
m.Lock()
defer m.Unlock()
n := now()
if lastNow > n {
// This ensures that now() must be monotonic (#875).
panic("clock: lastNow must be older than n")
}
lastNow = n
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c := 0
if tps == UncappedTPS {
c = 1
} else if tps > 0 {
c = calcCountFromTPS(int64(tps), n)
}
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updateFPSAndTPS(n, c)
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return c
}