FPSDropApp.java

package default;

import com.badlogic.gdx.Game;
import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.graphics.GL20;
import com.badlogic.gdx.graphics.g2d.BitmapFont;
import com.badlogic.gdx.graphics.g2d.SpriteBatch;
import org.lwjgl.Sys;

public class FPSDropApp extends Game {

    private BitmapFont font;
    private SpriteBatch batch;

    private long timeSinceLastRender;
    private int timelyFramesNb = 0;

    @Override
    public void create() {
        this.font = new BitmapFont();
        this.batch = new SpriteBatch();
    }

    @Override
    public void render() {
        computeRenderStatsSinceLast();

        Gdx.gl.glClearColor(0, 0, 0, 1);
        Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);

        drawFps();

        try { Thread.sleep(10); } catch (InterruptedException e) { e.printStackTrace();}
    }

    private void drawFps() {
        int width = Gdx.graphics.getWidth();
        int height = Gdx.graphics.getHeight();
        batch.getProjectionMatrix().setToOrtho2D(0, 0, width, height);
        batch.begin();
        font.draw(batch, "FPS: " + Gdx.graphics.getFramesPerSecond(), 50, height - 50);
        batch.end();
    }

    private void computeRenderStatsSinceLast() {
        long diffSinceLast = System.currentTimeMillis() - timeSinceLastRender;
        if(diffSinceLast > 20) {
            System.out.println(" -- Time since last render begin exceeded -- " + diffSinceLast + ", nb consecutive timely frames since last = " + timelyFramesNb);
            timelyFramesNb = 0;
        }else{
            this.timelyFramesNb++;
        }
        //logger.warn("Time since last render = " + diffSinceLast);
        this.timeSinceLastRender = System.currentTimeMillis();
    }

    @Override
    public void resize(int width, int height) {

    }

    @Override
    public void pause() {

    }

    @Override
    public void resume() {

    }

    @Override
    public void dispose() {

    }
}

FPSDropTestCaseStarter.java

package default;

import com.badlogic.gdx.backends.lwjgl.LwjglApplication;
import com.badlogic.gdx.backends.lwjgl.LwjglApplicationConfiguration;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.File;

public class FPSDropTestCaseStarter {

    private static final Logger logger = LoggerFactory.getLogger(FPSDropTestCaseStarter.class);
    private static File JGLLib;

    public static void main(String... args){

        LwjglApplicationConfiguration config = new LwjglApplicationConfiguration();

        config.width = 800;
        config.height = 600;

        config.foregroundFPS = 60;

        LwjglApplication lwjglApplication = new LwjglApplication(new FPSDropApp(), config);

    }
}