FreeJ2ME + Anbu + Libretro: Implement a better frame limit logic

Previously, frame limiting in FreeJ2ME relied on a fixed interval
for Thread.sleep(), which is already a bit innacurate by itself,
but with a fixed sleep interval meant that the time the game logic
took to render also influenced the reslulting framerate. For
example: If a game took 3ms to render and the fps limit was set
to 60 fps, the resulting framerate would be around 50 to 51fps,
as the limit would actually be ~19,666ms (3ms + 16,666ms fixed).

This new logic works by calculating the time it took to render the
last frame and subtracting it from the time we should wait for the
next one, which will then be our Thread.sleep() interval.

While it still relies on Thread.sleep() and its inaccuracies, this
approach is miles better than what was already in place, case in
point, jbenchmark 2.0 now locks around 59.5 to 60.3 fps in all tests
on my machine, whereas it ran at about 48.6fps on the first test,
55.3 on the second, 56.4 on the third and 52.5 on the fourth.

src/org/recompile/freej2me/Anbu.java

@@ -44,7 +44,13 @@ public static void main(String[] args)
  private boolean useSiemensControls = false;
  private boolean useMotorolaControls = false;
  private boolean rotateDisplay = false;
+
+ // Frame Limit Variables
  private int limitFPS = 0;
+ private long lastRenderTime = 0;
+ private long requiredFrametime = 0;
+ private long elapsedTime = 0;
+ private long sleepTime = 0;
 
  private boolean[] pressedKeys = new boolean[128];
 
@@ -75,6 +81,16 @@ public void run()
  try
  {
  int[] data;
+
+ if(limitFPS>0)
+ {
+ requiredFrametime = 1000 / limitFPS;
+ elapsedTime = System.currentTimeMillis() - lastRenderTime;
+ sleepTime = requiredFrametime - elapsedTime;
+
+ if (sleepTime > 0) { Thread.sleep(sleepTime); }
+ }
+
  // Send Frame to SDL interface
  if(!config.isRunning) { data = Mobile.getPlatform().getLCD().getRGB(0, 0, lcdWidth, lcdHeight, null, 0, lcdWidth); }
  else { data = config.getLCD().getRGB(0, 0, lcdWidth, lcdHeight, null, 0, lcdWidth);}
@@ -88,6 +104,8 @@ public void run()
  cb += 3;
  }
  sdl.frame.write(frame);
+
+ lastRenderTime = System.currentTimeMillis();
  }
  catch (Exception e) { }
  }
@@ -365,7 +383,6 @@ else if(useMotorolaControls)
  void settingsChanged() 
  {
  limitFPS = Integer.parseInt(config.settings.get("fps"));
- if(limitFPS>0) { limitFPS = 1000 / limitFPS; }
 
  String sound = config.settings.get("sound");
  Mobile.sound = false;

src/org/recompile/freej2me/FreeJ2ME.java

@@ -53,9 +53,15 @@ public class FreeJ2ME
  private boolean useSiemensControls = false;
  private boolean useMotorolaControls = false;
  private boolean rotateDisplay = false;
+
+ // Frame Limit Variables
  private int limitFPS = 0;
- private int renderHint = 0;
+ private long lastRenderTime = 0;
+ private long requiredFrametime = 0;
+ private long elapsedTime = 0;
+ private long sleepTime = 0;
 
+ // AWT GUI
  private AWTGUI awtGUI;
 
  private boolean[] pressedKeys = new boolean[128];
@@ -374,7 +380,6 @@ private void settingsChanged()
  int h = Integer.parseInt(config.settings.get("height"));
 
  limitFPS = Integer.parseInt(config.settings.get("fps"));
- if(limitFPS>0) { limitFPS = 1000 / limitFPS; }
 
  String sound = config.settings.get("sound");
  Mobile.sound = false;
@@ -531,6 +536,16 @@ public void paint(Graphics g)
  try
  {
  Graphics2D cgc = (Graphics2D)this.getGraphics();
+
+ if(limitFPS>0)
+ {
+ requiredFrametime = 1000 / limitFPS;
+ elapsedTime = System.currentTimeMillis() - lastRenderTime;
+ sleepTime = requiredFrametime - elapsedTime;
+
+ if (sleepTime > 0) { Thread.sleep(sleepTime); }
+ }
+
  if (config.isRunning)
  {
  if(!rotateDisplay)
@@ -556,12 +571,8 @@ public void paint(Graphics g)
  // Draw the rotated FB with adjusted cy and cx values
  cgc.drawImage(Mobile.getPlatform().getLCD(), 0, cx, ch, cw, null);
  }
-
- if(limitFPS>0)
- {
- Thread.sleep(limitFPS);
- }
  }
+ lastRenderTime = System.currentTimeMillis();
  }
  catch (Exception e)
  {

src/org/recompile/freej2me/Libretro.java

@@ -51,7 +51,14 @@ public class Libretro
  private boolean useMotorolaControls = false;
  private boolean rotateDisplay = false;
  private boolean soundEnabled = true;
+
+ // Frame Limit Variables
  private int limitFPS = 0;
+ private long lastRenderTime = 0;
+ private long requiredFrametime = 0;
+ private long elapsedTime = 0;
+ private long sleepTime = 0;
+
  private int maxmidistreams = 32;
 
  private boolean[] pressedKeys = new boolean[128];
@@ -378,17 +385,23 @@ public void run()
  try
  {
  int[] data;
+
+ if(limitFPS>0)
+ {
+ requiredFrametime = 1000 / limitFPS;
+ elapsedTime = System.currentTimeMillis() - lastRenderTime;
+ sleepTime = requiredFrametime - elapsedTime;
+
+ if (sleepTime > 0) { Thread.sleep(sleepTime); }
+ }
+
  if(config.isRunning)
  {
  data = config.getLCD().getRGB(0, 0, lcdWidth, lcdHeight, null, 0, lcdWidth);
  }
  else
  {
  data = surface.getRGB(0, 0, lcdWidth, lcdHeight, null, 0, lcdWidth);
- if(limitFPS>0)
- {
- Thread.sleep(limitFPS);
- }
  }
  int bufferLength = data.length*3;
  int cb = 0;
@@ -408,6 +421,8 @@ public void run()
  System.out.write(frameHeader, 0, 6);
  System.out.write(frameBuffer, 0, bufferLength);
  System.out.flush();
+
+ lastRenderTime = System.currentTimeMillis();
  }
  catch (Exception e)
  {
@@ -432,7 +447,6 @@ private void settingsChanged()
  int h = Integer.parseInt(config.settings.get("height"));
 
  limitFPS = Integer.parseInt(config.settings.get("fps"));
- if(limitFPS>0) { limitFPS = 1000 / limitFPS; }
 
  String sound = config.settings.get("sound");
  Mobile.sound = false;