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 (
// lastSystemTime is the last system time in the previous Update.
lastSystemTime int64
currentFPS float64
lastFPSUpdated int64
framesForFPS int64
started bool
onStart func()
m sync.Mutex
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)
func CurrentFPS() float64 {
m.Lock()
v := currentFPS
m.Unlock()
return v
}
func OnStart(f func()) {
m.Lock()
onStart = f
m.Unlock()
}
func calcCountFromTPS(tps int64, now int64) int {
if tps == 0 {
return 0
}
if tps < 0 {
panic("clock: tps must >= 0")
}
// Initialize lastSystemTime if needed.
if lastSystemTime == 0 {
lastSystemTime = now
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}
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))
}
// Stabilize FPS.
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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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}
func updateFPS(now int64) {
if lastFPSUpdated == 0 {
lastFPSUpdated = now
}
framesForFPS++
if time.Second > time.Duration(now-lastFPSUpdated) {
return
}
currentFPS = float64(framesForFPS) * float64(time.Second) / float64(now-lastFPSUpdated)
lastFPSUpdated = now
framesForFPS = 0
}
// Update updates the inner clock state and returns an integer value
// indicating how many game frames the game should update based on given tps.
// tps represents TPS (ticks per second).
// If tps <= 0, Update always returns 0.
//
// Update is expected to be called per frame.
func Update(tps int) int {
m.Lock()
defer m.Unlock()
if !started {
if onStart != nil {
onStart()
}
started = true
}
n := now()
updateFPS(n)
if tps > 0 {
return calcCountFromTPS(int64(tps), n)
}
return 0
}