Understanding Frame Rate

What is Frame Rate?

Frame Rate refers to the number of frames displayed per second (FPS) in an animation or video. Higher frame rates result in smoother motion, while lower frame rates can lead to choppy animations. Common frame rates include:

• 30 FPS: Standard for television.
• 60 FPS: Standard for gaming and smooth animations.
• 24 FPS: Common in film.

Frame Rate Control

Note

JavaFX doesn’t allow you to directly set a frame rate for AnimationTimer, but you can control the effective frame rate by adjusting the logic inside the handle method.

Frame Concept in Animation

• Frames per Second (FPS): Animation is typically measured in frames per second (FPS). The smoother the animation, the higher the FPS. Most animations aim for a target of 60 FPS, which means each frame should ideally render within 16.67 milliseconds (1 second / 60 frames).

• Timing: AnimationTimer does not run on a fixed timing interval; it will call the handle method as fast as the system allows, usually synchronized with the display’s refresh rate. This means that the frame rate can fluctuate based on system performance.

• Frame Update Logic: In your overridden handle method, you typically update the state of your application, such as moving objects, changing colors, or processing user input. This method is called repeatedly in a loop until you stop the timer.

How to Control Frame Rate

1. Time-Based Animation: Use the now parameter to determine how much time has passed since the last frame. You can implement time-based animations that update positions or states based on the elapsed time.

   For example:

   long lastUpdate  = 0;
   
   @Override
   public void handle(long now) {
       if (lastUpdate  > 0) {
           double deltaTime = (now - lastUpdate ) / 1_000_000_000.0; // convert nanoseconds to seconds
   
          // Use deltaTime for smooth updates
           updateAnimation(deltaTime);
       }
       lastUpdate  = now;
   }

2. Frame Limiting: You can limit the frame rate by checking the elapsed time and only performing updates at certain intervals. For instance, if you want to limit the frame rate to 60 FPS, you would update every ~16.67 milliseconds:

   long lastUpdate = System.nanoTime();
   
   @Override
   public void handle(long now) {
       long currentTime = System.nanoTime();
       if (currentTime - lastUpdate >= 16_666_667) { // 1/60 seconds in nanoseconds
           updateAnimation();
           lastUpdate = currentTime;
       }
   }

Example

• Using the time between frames (delta time) to implement smooth animations.

  import javafx.animation.AnimationTimer;
  import javafx.application.Application;
  import javafx.scene.Group;
  import javafx.scene.Scene;
  import javafx.scene.paint.Color;
  import javafx.scene.shape.Circle;
  import javafx.stage.Stage;
  
  public class MyAnimationApp extends Application {
      @Override
      public void start(Stage primaryStage) {
          Circle circle = new Circle(20, Color.BLUE);
          circle.setCenterX(100);
          circle.setCenterY(100);
  
          AnimationTimer timer = new AnimationTimer() {
              private long lastUpdate = 0;
  
              @Override
              public void handle(long now) {
                  if (lastUpdate > 0) {
                      double deltaTime = (now - lastUpdate) / 1_000_000_000.0; // Convert to seconds
                      circle.setCenterX(circle.getCenterX() + 100 * deltaTime); // Move circle
                  }
                  lastUpdate = now;
              }
          };
  
          timer.start();
  
          Scene scene = new Scene(new Group(circle), 400, 300);
          primaryStage.setScene(scene);
          primaryStage.setTitle("AnimationTimer Example");
          primaryStage.show();
      }
  
      public static void main(String[] args) {
          launch(args);
      }
  }

Monitoring Frame Rate

Tip

To monitor frame rate, you need to track how many frames are rendered over a specific time period. Here’s how you can implement this:

1. Initialization: Set up counters and a timing mechanism.
2. Frame Counting: Increment a frame counter in the handle method.
3. Timing: Use the timestamp to determine when to calculate the average frame rate.

Example Implementation

Here’s a simple implementation to monitor the frame rate:

import javafx.animation.AnimationTimer;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.StackPane;
import javafx.scene.text.Text;
import javafx.stage.Stage;

public class FrameRateMonitor extends Application {

    private long lastTime = 0;
    private int frameCount = 0;
    private double frameRate = 0;

    @Override
    public void start(Stage primaryStage) {
        Text frameRateText = new Text();

        AnimationTimer timer = new AnimationTimer() {
            @Override
            public void handle(long now) {
                if (lastTime > 0) {
                    // Calculate elapsed time in seconds
                    double elapsedTime = (now - lastTime) / 1_000_000_000.0; // convert to seconds
                    frameCount++;

                    // Update frame rate every second
                    if (elapsedTime >= 1.0) {
                        frameRate = frameCount / elapsedTime;
                        frameRateText.setText(String.format("FPS: %.2f", frameRate));
                        frameCount = 0; // reset for the next interval
                        lastTime = now; // reset lastTime
                    }
                } else {
                    // Initialize lastTime on first call
                    lastTime = now;
                }

                // Update your application here (game logic, rendering, etc.)
            }
        };

        timer.start();

        StackPane root = new StackPane(frameRateText);
        Scene scene = new Scene(root, 400, 300);
        primaryStage.setTitle("Frame Rate Monitor");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

Explanation of the Code

1. Variables:

   • lastTime: Tracks the last frame’s timestamp.
   • frameCount: Counts how many frames have been processed in the last second.
   • frameRate: Stores the calculated frames per second (FPS).

2. AnimationTimer:

   • The handle method checks if lastTime has been initialized. If it has, it calculates the elapsed time since the last frame.
   • The frameCount is incremented on each call.
   • If one second has passed (i.e., elapsedTime >= 1.0), it calculates the frame rate, updates the display text, resets the count, and updates lastTime.

Best Practices for Using AnimationTimer

• Use Efficient Code: Keep the logic in the handle method efficient. Heavy computations can lead to frame drops.

• Use Delta Time: Incorporate delta time in your animations for frame-independent movement. This ensures that your animations look consistent regardless of the frame rate.

• Rendering: Only update the UI components that need to change. Avoid unnecessary redraws.

• Avoid Blocking Operations: Do not perform long-running tasks in the handle method. Instead, consider using background threads for heavy computations and update the UI on the JavaFX Application Thread.

• Testing on Different Hardware: Test your animations on different machines to see how they perform under varying conditions. Frame rates can be affected by hardware capabilities.