Use delta time for scene updates. (#123)

* Use delta time when updating scenes.
Delta time is in seconds and capped to 1/10th.
* Show FPS and VSYNC status in the bottom left corner.

Fixes #123

core/Engine.go

@@ -7,6 +7,7 @@ import (
 	"runtime"
 	"strings"
 	"sync"
+	"time"
 
 	"github.com/OpenDiablo2/OpenDiablo2/mpq"
 
@@ -37,6 +38,7 @@ type Engine struct {
 	SoundManager    *sound.Manager        // The sound manager
 	nextScene       scenes.Scene          // The next scene to be loaded at the end of the game loop
 	fullscreenKey   bool                  // When true, the fullscreen toggle is still being pressed
+	lastTime        float64               // Last time we updated the scene
 }
 
 // CreateEngine creates and instance of the OpenDiablo2 engine
@@ -180,7 +182,12 @@ func (v *Engine) Update() {
 		return
 	}
 
-	v.CurrentScene.Update(float64(1) / ebiten.CurrentTPS())
+	currentTime := float64(time.Now().UnixNano()) / float64(time.Second)
+
+	deltaTime := math.Min((currentTime - v.lastTime), 0.1)
+	v.lastTime = currentTime
+
+	v.CurrentScene.Update(deltaTime)
 	v.UIManager.Update()
 }
 

main.go

@@ -3,6 +3,7 @@ package main
 import (
 	"image"
 	"log"
+	"strconv"
 
 	"github.com/hajimehoshi/ebiten/ebitenutil"
 
@@ -52,6 +53,6 @@ func update(screen *ebiten.Image) error {
 		return nil
 	}
 	d2Engine.Draw(screen)
-	//ebitenutil.DebugPrint(screen, "FPS:"+strconv.Itoa(int(ebiten.CurrentFPS())))
+	ebitenutil.DebugPrintAt(screen, "vsync:"+strconv.FormatBool(ebiten.IsVsyncEnabled())+"\nFPS:"+strconv.Itoa(int(ebiten.CurrentFPS())), 5, 565)
 	return nil
 }

scenes/MapEngineTest.go

@@ -91,6 +91,13 @@ func (v *MapEngineTest) Render(screen *ebiten.Image) {
 }
 
 func (v *MapEngineTest) Update(tickTime float64) {
+	if v.uiManager.KeyPressed(ebiten.KeyF8) {
+		if ebiten.IsVsyncEnabled() == true {
+			ebiten.SetVsyncEnabled(false)
+		} else {
+			ebiten.SetVsyncEnabled(true)
+		}
+	}
 	if v.uiManager.KeyPressed(ebiten.KeyDown) {
 		v.mapEngine.OffsetY -= tickTime * 800
 	}