ui: Implement TPS/SetTPS

Fixes #605
Fixes #321

examples/windowsize/main.go

@@ -87,6 +87,7 @@ func update(screen *ebiten.Image) error {
 	runnableInBackground := ebiten.IsRunnableInBackground()
 	cursorVisible := ebiten.IsCursorVisible()
 	vsyncEnabled := ebiten.IsVsyncEnabled()
+	tps := ebiten.TPS()
 
 	if inpututil.IsKeyJustPressed(ebiten.KeyUp) {
 		screenHeight += d
@@ -130,6 +131,20 @@ func update(screen *ebiten.Image) error {
 	if inpututil.IsKeyJustPressed(ebiten.KeyV) {
 		vsyncEnabled = !vsyncEnabled
 	}
+	if inpututil.IsKeyJustPressed(ebiten.KeyT) {
+		switch tps {
+		case -1:
+			tps = 30
+		case 30:
+			tps = 60
+		case 60:
+			tps = 120
+		case 120:
+			tps = -1
+		default:
+			panic("not reached")
+		}
+	}
 
 	ebiten.SetScreenSize(screenWidth, screenHeight)
 	ebiten.SetScreenScale(screenScale)
@@ -137,6 +152,7 @@ func update(screen *ebiten.Image) error {
 	ebiten.SetRunnableInBackground(runnableInBackground)
 	ebiten.SetCursorVisible(cursorVisible)
 	ebiten.SetVsyncEnabled(vsyncEnabled)
+	ebiten.SetTPS(tps)
 
 	if inpututil.IsKeyJustPressed(ebiten.KeyI) {
 		ebiten.SetWindowIcon([]image.Image{createRandomIconImage()})
@@ -167,8 +183,10 @@ Press C key to switch the cursor visibility
 Press I key to change the window icon
 Press V key to switch vsync
 Press Q key to quit
+Press T key to switch TPS (ticks per second)
 Cursor: (%d, %d)
-FPS: %0.2f`, x, y, ebiten.CurrentFPS())
+FPS: %0.2f
+TPS: %d`, x, y, ebiten.CurrentFPS(), ebiten.TPS())
 	ebitenutil.DebugPrint(screen, msg)
 	return nil
 }

graphicscontext.go

@@ -82,7 +82,13 @@ func (c *graphicsContext) initializeIfNeeded() error {
 }
 
 func (c *graphicsContext) Update(afterFrameUpdate func()) error {
-	updateCount := clock.Update(defaultTPS)
+	tps := int(TPS())
+	count := clock.Update(tps)
+
+	updateCount := 1
+	if tps >= 0 {
+		updateCount = count
+	}
 
 	if err := c.initializeIfNeeded(); err != nil {
 		return err

internal/clock/clock.go

@@ -110,8 +110,7 @@ func updateFPS(now int64) {
 // 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 is 0, Update always returns 0.
+// If tps <= 0, Update always returns 0.
-// If tps is negative, Update panics.
 //
 // Update is expected to be called per frame.
 func Update(tps int) int {
@@ -127,5 +126,8 @@ func Update(tps int) int {
 
 	n := now()
 	updateFPS(n)
-	return calcCountFromTPS(int64(tps), n)
+	if tps > 0 {
+		return calcCountFromTPS(int64(tps), n)
+	}
+	return 0
 }

run.go

@@ -49,8 +49,13 @@ func CurrentFPS() float64 {
 
 var (
 	isDrawingSkipped = int32(0)
+	currentTPS       = int32(0)
 )
 
+func init() {
+	atomic.StoreInt32(&currentTPS, defaultTPS)
+}
+
 func setDrawingSkipped(skipped bool) {
 	v := int32(0)
 	if skipped {
@@ -552,3 +557,21 @@ func IsVsyncEnabled() bool {
 func SetVsyncEnabled(enabled bool) {
 	ui.SetVsyncEnabled(enabled)
 }
+
+// TPS returns the current TPS.
+//
+// TPS is concurrent-safe.
+func TPS() int {
+	return int(atomic.LoadInt32(&currentTPS))
+}
+
+// SetTPS sets the TPS (ticks per frame), that represents how many updating function is called
+// per second.
+// The initial value is 60.
+//
+// If the given tps is negative, TPS is unfixed and the game is updated per frame.
+//
+// SetTPS is concurrent-safe.
+func SetTPS(tps int) {
+	atomic.StoreInt32(&currentTPS, int32(tps))
+}