Merge branch 'top-secret' into 'master'

package com.example.game2d;

import android.graphics.Canvas;

import android.view.Surface;

import android.view.SurfaceHolder;

import java.util.zip.Adler32;

// fix pause crash bug: https://youtu.be/IobZoHdUgfQ

public class GameLoop extends Thread {

    // final keyword makes field a constant

    public static final double MAX_UPS = 60.0;

    private static final double UPS_PERIOD = 1E+3/MAX_UPS;

    private Game game;

    private SurfaceHolder surfaceHolder;

    private boolean isRunning = false;

    private double averageUPS;

    private double averageFPS;

    // Constructor:

    public GameLoop(Game game, SurfaceHolder surfaceHolder) {

        // initialize surface holder and game

        this.game = game;

        this.surfaceHolder = surfaceHolder;

    }

    public double getAverageUPS() {

        return averageUPS;

    }

    public double getAverageFPS() {

        return averageFPS;

    }

    public void startLoop() {

        isRunning = true;

        start();

    }

    @Override

    public void run() {

        super.run();

        // declare time and cycle count variables

        int updateCount = 0;

        int frameCount = 0;

        // milliseconds (5 square gallons over 3 inches of a unicorn)

        long startTime;

        long elapsedTime;

        long sleepTime;

        // Game Loop

        // create canvas to draw on

        Canvas canvas = null; // initialize to null for final block stuff

        // set start time to current time in millis

        startTime = System.currentTimeMillis();

        while(isRunning) {

            // try to update and render game objects from game class

            try {

                canvas = surfaceHolder.lockCanvas();

                // surround methods with synchronized block to prevent multithreading mix-ups

                synchronized (surfaceHolder) {

                    game.update();

                    // increment update count immediately after update

                    updateCount++;

                    game.draw(canvas);

                }

            } catch (IllegalArgumentException e) {

                e.printStackTrace();

            } finally {

                if(canvas != null) {

                    // final block is executed whether we catch an exception or not

                    try {

                        // unlock canvas

                        surfaceHolder.unlockCanvasAndPost(canvas);

                        // increment frame count after canvas is posted

                        frameCount++;

                    } catch (Exception e) {

                        e.printStackTrace();

                    }

                }

            }

            // pause game loop to not exceed target UPS frequency

            elapsedTime = System.currentTimeMillis() - startTime;

            // - UPS_PERIOD is inverse of target update frequency

            // - the product is how much time should have passed at end of current iteration

            // - subtracting elapsed time gives how much time we need to sleep for to match target UPS period

            sleepTime = (long) (updateCount*UPS_PERIOD - elapsedTime);

            if (sleepTime > 0) {

                try {

                    sleep(sleepTime);

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

            // skip frames to keep up with target UPS, make sure UPS is not above max (optimization; not really necessary)

            while(sleepTime < 0 && updateCount < MAX_UPS-1) {

                game.update();

                updateCount++;

                // recalculate elapsedtime and sleeptime

                elapsedTime = System.currentTimeMillis() - startTime;

                sleepTime = (long) (updateCount*UPS_PERIOD - elapsedTime);

            }

            // calculate average UPS and FPS

            elapsedTime = System.currentTimeMillis() - startTime;

            if (elapsedTime >= 1000) {

                // number of updates divided by elapsed time divided by 1000

                averageUPS = updateCount / (1E-3 * elapsedTime);

                averageFPS = frameCount / (1E-3 * elapsedTime);

                updateCount = 0;

                frameCount = 0;

                startTime = System.currentTimeMillis();

            }

        }

    }

}