Merge pull request #5697 from JakubValtar/improve-frame-rate

Stop frame rate counter from exaggerating

core/src/processing/core/PApplet.java

@@ -713,7 +713,7 @@ public class PApplet implements PConstants {
    * @see PApplet#frameRate(float)
    * @see PApplet#frameCount
    */
-  public float frameRate = 10;
+  public float frameRate = 60;
 
   protected boolean looping = true;
 
@@ -2434,9 +2434,34 @@ public class PApplet implements PConstants {
 
     } else {  // frameCount > 0, meaning an actual draw()
       // update the current frameRate
-      double rate = 1000000.0 / ((now - frameRateLastNanos) / 1000000.0);
-      float instantaneousRate = (float) (rate / 1000.0);
-      frameRate = (frameRate * 0.9f) + (instantaneousRate * 0.1f);
+
+      // Calculate frameRate through average frame times, not average fps, e.g.:
+      //
+      // Alternating 2 ms and 20 ms frames (JavaFX or JOGL sometimes does this)
+      // is around 90.91 fps (two frames in 22 ms, one frame 11 ms).
+      //
+      // However, averaging fps gives us: (500 fps + 50 fps) / 2 = 275 fps.
+      // This is because we had 500 fps for 2 ms and 50 fps for 20 ms, but we
+      // counted them with equal weight.
+      //
+      // If we average frame times instead, we get the right result:
+      // (2 ms + 20 ms) / 2 = 11 ms per frame, which is 1000/11 = 90.91 fps.
+      //
+      // The counter below uses exponential moving average. To do the
+      // calculation, we first convert the accumulated frame rate to average
+      // frame time, then calculate the exponential moving average, and then
+      // convert the average frame time back to frame rate.
+      {
+        // Get the frame time of the last frame
+        double frameTimeSecs = (now - frameRateLastNanos) / 1e9;
+        // Convert average frames per second to average frame time
+        double avgFrameTimeSecs = 1.0 / (double) frameRate;
+        // Calculate exponential moving average of frame time
+        final double alpha = 0.05;
+        avgFrameTimeSecs = (1.0 - alpha) * avgFrameTimeSecs + alpha * frameTimeSecs;
+        // Convert frame time back to frames per second
+        frameRate = (float) (1.0 / avgFrameTimeSecs);
+      }
 
       if (frameCount != 0) {
         handleMethods("pre");