FX - framerate fix

When your sketch ran slower than target frame rate, FX was blocked and
was drawing to the screen only every few seconds. This eventually
resulted in OutOfMemoryError as it's internal draw buffer was not
flushed.

core/src/processing/javafx/PSurfaceFX.java

@@ -56,6 +56,7 @@ public class PSurfaceFX implements PSurface {
   Canvas canvas;
 
   final Animation animation;
+  float frameRate = 60;
 
   public PSurfaceFX(PGraphicsFX2D graphics) {
     fx = graphics;
@@ -65,10 +66,15 @@ public class PSurfaceFX implements PSurface {
     KeyFrame keyFrame = new KeyFrame(Duration.millis(1000),
                                      new EventHandler<ActionEvent>() {
       public void handle(ActionEvent event) {
+        long startNanoTime = System.nanoTime();
         sketch.handleDraw();
+        long drawNanos = System.nanoTime() - startNanoTime;
         if (sketch.exitCalled()) {
           Platform.exit();  // version for safe JavaFX shutdown
         }
+        if (sketch.frameCount > 5) {
+          animation.setRate(-PApplet.min(1e9f / drawNanos, frameRate));
+        }
       }
     });
     animation = new Timeline(keyFrame);
@@ -79,7 +85,7 @@ public class PSurfaceFX implements PSurface {
 
     // setting rate to negative so that event fires at the start of
     // the key frame and first frame is drawn immediately
-    animation.setRate(-60);
+    animation.setRate(-frameRate);
   }
 
 
@@ -453,7 +459,10 @@ public class PSurfaceFX implements PSurface {
   public void setFrameRate(float fps) {
     // setting rate to negative so that event fires at the start of
     // the key frame and first frame is drawn immediately
-    if (fps > 0) animation.setRate(-fps);
+    if (fps > 0) {
+      frameRate = fps;
+      animation.setRate(-frameRate);
+    }
   }