How do I fix the FPS in my platform game?

Question

Hi everyone! As part of a course in Gamemaking in school, my team created a platformer with a colission-map instead of tiles. This has worked out well for the most part.
My problem is that we have a loop that updates and draws everything to the screen ( this is in windowed mode by the way ) . The game runs and the gameplay is ok.
But it runs with different speed depending on the hardware. On my computer everything is slow, but on new computers the objects race back and forth like mad. Furthermore sometimes as the player dies and the level restarts, the player dies on the spot!
From what I have read this is due to the fact that we haven´t fixed the FPS. But Im at a loss as to how im supposed to fix it. One sollution tells me to use a timer and then place logic inside actionPerforemed, but since I am using a loop inside run() this cant work.
The program is divided into several classes, but the main logic residen in the class main,java
public Main(){
          super("Mimic");
          setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);          
          setVisible(true);
          this.enableEvents(KeyEvent.KEY_PRESSED | MouseEvent.MOUSE_DRAGGED);     
          setSize(1280, 720);
          setResizable(false);
          setLocationRelativeTo(null);
          requestFocusInWindow();
          AudioPlayer.loadClip("transform", "sound/transform2.wav");
          AudioPlayer.loadClip("gameover", "sound/gameover.wav");
          AudioPlayer.loadClip("ambient", "sound/test.wav");
          AudioPlayer.loadClip("jump", "sound/jump.wav");
          //Cursor - 1x1px
          Toolkit toolkit = Toolkit.getDefaultToolkit();
          Image transparent = toolkit.getImage("images/empty_pixel.gif");
          Point hotSpot = new Point(0,0);
          Cursor game = toolkit.createCustomCursor(transparent, hotSpot, "transparent");
          setCursor(game);
          createBufferStrategy(3);
          transformationTimer = new Timer(1000, this);
          transformationTimer.setInitialDelay(0);
geyserTimer = new javax.swing.Timer(1000, new ClockListenerGeyser());
geyserTimer.start();
          mimicTimerBarBackground = new ImageIcon("images/mimic-bar-bgr.png").getImage();
          mimicTimerBar = new ImageIcon("images/mimic-bar.png").getImage();          
          start();
     }//public
public void start(){
          (new Thread(this)).start();
     }//start
     public void run(){
          avatar = new Avatar();
     //Ambient sound
     //AudioPlayer.play("ambient", true); Musiken avstängd...
     loadLevel(Map.Levelname.LevelOne);
          //loadLevel(Map.Levelname.LevelTwo);
          long start = System.nanoTime();
          long delta = 0;
          long sleep;
          while(gameOn){ // game loop
               tick(delta);
               draw();                    
               delta = System.nanoTime() - start;
               sleep = DELAY - delta;
               // detta är en test för att kolla om loopen fortfarande har tid kvar att göra saker, om den har det, sov och ge den en//
               start = System.nanoTime();
               //tick(delta);
               //draw();               
          }//while
          System.exit(0);
}//run
//i den här metoden ligger allt motor, kollision, styrning och scrollning m.m
     public void tick(long tid) {
          float timeScale = tid/100000000f;
               avatar.update(tid); //animationen uppdateras
               currentMap.tick(tid);
               // update mimics
// lots of codes for Keys, colissionmap and more here.
     public void draw(){
          Graphics g = getBufferStrategy().getDrawGraphics();
          g.translate(-cameraX,-cameraY);          
          g.drawImage(currentMap.collisionMap, 0, 0, null);
     for(Background b: currentMap.getBackgrounds()){
          if(b.isVisible())
               g.drawImage(b.getImage(),(int)b.getX(), (int)b.getY(), null);
     }//for
     for(MapItems mi: currentMap.getItemList()){
          g.drawImage(mi.getImage(),(int)mi.getX(), (int)mi.getY(), null);           
     }//for
     for(Mimics m: currentMap.getList()){
          if(m.getVisas()){
               g.drawImage(m.getImage(), (int)m.getX(), (int)m.getY(), null);
          }//if
     }//for
     g.drawImage(avatar.getImage(), (int)avatar.getX(), (int)avatar.getY(), null);
     if (currentMap.levelname == Map.Levelname.LevelTwo){
          g.drawImage(grass, 0, 623, null);
     g.drawImage(key, cameraX+1000, cameraY+72, null);
     g.drawImage(sekLevel, 800, 580, null);
          //Visar timern om den är aktiv
          if (transformationTimer.isRunning()) {
               g.drawImage(mimicTimerBarBackground, cameraX+509, cameraY+72, null);
               g.drawImage(mimicTimerBar, cameraX+514, cameraY+77, (int)(cameraX+514+(200/20)*transformationTime), cameraY+77+30, 0, 0, (int)(200/20)*transformationTime, 30, null);
          g.setColor(Color.red);      
          g.dispose();
     getBufferStrategy().show();
     }//void
I figure I got to put a timer to fix the FPS somewhere in here, but where?
Any help is greatly appreciated!
Regard,
Gabriel

Answer 1

Speed should be 'tick' based. The way I do it, with silky smooth results, is to lock the game to a framerate. That part is quite easy, all you do is calculate at what interval you want to update. Say you want 60FPS, it becomes:
interval = 1000 / 60 (interval = 17ms).
So if you want 60FPS, you have to update and draw every 17 milliseconds. That sounds like a short time, but for computers it really is not.
Okay, so you have your game loop. while(true) { update(); render(); }. The body of this loop should execute every 17ms (it won't be that precise, but it will be good enough). It goes a little something like this:
while(running){
long measure1 = currentTimeInMillis();
update();
render();
long measure2 = currentTimeInMillis();
long diff = measure2 - measure1;
Thread.sleep(17-diff); // sleep until next tick
}This will have the game ticking at 58-61 FPS, depending on the timing precision of the OS - you'll find that on Linux OSes the framerate is far more steady than on Windows environments for example, in Java at least. Its just the sleep call that is far from precise.
Now you will want to make movement based on the framerate - the way I do that is to work with float measurements. For movement speed I say 'every tick, move X.X pixels', where I keep the units in increments of 0.5 pixels. This means that moving game entities can go as slow as 0.5 pixels each tick in my games, which is slow enough for most of them. In the end when determining the actual pixel locations, the floats are rounded down to ints.
I hope that makes some sense.