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Google Hash Code 2022 Nicosia Cyprus – Call for participation

We’ll be hosting a hub at the University of Cyprus for the Online Qualification Round of Hash Code, a team-based programming competition created by Google for university students and industry professionals. The Online Qualification Round takes place on the 24th of February at 19:30 EET and registered teams from Cyprus are invited to participate from our hub, which will take place at the Computer Science Department. Top scoring teams from the Online Qualification Round will then be invited to Google’s office to compete in the Final Round of the competition in April.

If you’re interested in joining our hub, find a team (two to four people) and register at g.co/hashcode. Make sure to select the University of Cyprus from the list of hubs in the Judge System.

Address:

Rooms: 101, 102, 103
Department of Computer Science,
Pure and Applied Sciences (FST-01)
University of Cyprus
1 University Avenue
2109 Aglantzia, CYPRUS

Date and Time:

24th February 2022
From: 19:30 EET
To: 23:30 EET

Free Amenities Offered

High speed Internet access
Wi-Fi access to the Internet for your mobile devices (personal computers and smart phones)
Lab computers will be available for use by the participants
Food in the form of snacks and beverages will be available outside the labs

Symfony 5 skeleton project on Ubuntu

This guide will present the steps we followed on a GNU/Linux Ubuntu 20.04LTS to create a new project out of the Symfony 5 website skeleton.

Install core dependecies

First of all, we need to install all dependencies that we will need for sure.

sudo apt install curl gzip git php-cli php-xml php-mbstring php-intl php-mysql p7zip-full;

We chose to install the php-cli package instead of the php as we do not need to install all the additional dependencies php has, like apache2. Since we are working on a development computer, we can skip the required packages for deployment.

We decided to use MySQL in our project, so we installed the php-mysql package that provides the PDO for that database technology.

php-intl and php-mbstring were installed to suppress the following warnings:

Optional recommendations to improve your setup
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 * mb_strlen() should be available
   > Install and enable the mbstring extension.

 * intl extension should be available
   > Install and enable the intl extension (used for validators).

Downloading and installing symfony

Since Symfony version 5, there is a new support application for the development of Symfony projects. Using the following commands:

  • we downloaded it from the official website,
  • installed it to our home folder,
  • and then moved it to /user/local/bin/symfony to be accessible from any terminal without changing the path each time.
wget https://get.symfony.com/cli/installer -O - | bash;
sudo mv ~/.symfony/bin/symfony /usr/local/bin/symfony;

In case you do not want to move the binary to /usr/local/bin you can either use it as a local file:

~/.symfony/bin/symfony;

or add it to your $PATH variable:

export PATH="$HOME/.symfony/bin:$PATH";

Creating a new project and making sure dependencies are met

After the above steps are done, we can clone the Symfony 5 skeleton and then use the symfony support application to check that our system has all the needed features.

symfony new symfony_project;
cd symfony_project;
symfony check:req;

If everything is OK, you should get a message similar to the one below:

$ symfony check:req

Symfony Requirements Checker
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

> PHP is using the following php.ini file:
/etc/php/7.4/cli/php.ini

> Checking Symfony requirements:

...................................

                                              
 [OK]                                         
 Your system is ready to run Symfony projects 
                                              

Note  The command console can use a different php.ini file
~~~~  than the one used by your web server.
      Please check that both the console and the web server
      are using the same PHP version and configuration.

Starting a minimal web server to see the skeleton application

Using PHP’s built-in server, we can execute the skeleton application and see the result in our browser:

php -S 127.0.0.1:8000 -t public/;

Starting the Symfony minimal web server to see the skeleton application

Another option to check out your application is using the Symfony built-in web server, which is richer in features than the PHP server but lighter than Apache or Nginx. Below we present how to start it as an application in a terminal and how to start it as a detached service (leaving your terminal free for other operations).

#If you start it as it as an application, you will need to press Ctrl + C to kill it.
symfony serve;

Starting Symfony server as a detached service:

symfony serve -d;
#To stop it, use the following
symfony server:stop;
#Please note that the command contains the word server and not serve like before.

Adding more features to our project

To make our project more dynamic and versatile, we need to install a few packages using composer. Composer is a PHP utility for managing dependencies. It allows you to indicate the libraries your project relies on, and it will take care of installing and updating them. To fast install it, open a terminal and type the following command:

curl -Ss getcomposer.org/installer | php;
# Moving the composer into the /usr/local/bin/ folder will allow us to access it from any folder later on as that folder is in the default PATH variable. You could again avoid this step but it makes the process more user friendly.
sudo mv composer.phar /usr/local/bin/composer;

Allowing code annotations in our PHP code

After the composer is successfully installed, we can install the annotations package, which among other features, will allow us to define routes inside our PHP controller files.

composer require annotations;

A code example of that is the following:

<?php


namespace App\Controller;

use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Annotation\Route;

class QuestionController extends AbstractController
{
    /**
     * @Route("/", name="app_homepage")
     */
    public function homepage()
    {
        return new Response('Done');
    }

    /**
     * @Route("/questions/{slug}", name="app_question_show")
     */
    public function show($slug)
    {
        $answers = [
            'a',
            'b',
            'c'
        ];
        dump($this);

        return $this->render('question/show.html.twig', [
            'question' => ucwords(str_replace('-', ' ', $slug)),
            'answers' => $answers
        ]);
        #return new Response(sprintf("The question: %s", $slug));
    }
}

Installing the twig package that allows us to work better with HTML templates

To avoid embedding HTML code in our PHP code, we can install twig, which provides a framework of templates to build several sites quickly.

composer require template;

Enriching the development experience

To debug in a better way our applications, we install the following two groups of packages that provide several debugging features, including a logging mechanism.

composer require profiler --dev;
composer require debug;

Avoid hardcoding assets in the HTML DOM

To avoid hardcoding items in your DOM (and forcing yourself to remember to edit them depending on the deployment options you are using), you can use the asset package that will handle most of those issues.

composer require symfony/asset;

Serializing more items and objects to JSON and XML

To enrich the power of API calls that return JSON or XML objects (like the code below)

return $this->json(/*...*/);

we can install the following serializer:

composer require symfony/serializer;

and be used as follows:

$serializer->serialize(
  $myObject,
  'json'
);

Develop using HTTPS / SSL for free

Although we are not super happy about installing local Certificate Authorities on our machines, we used the following commands to install the Symfony Certifying Authority certificate and enable HTTPS/SSL development without accepting a non-verified certificate in the browser each time.

sudo apt install libnss3-tools;
symfony server:ca:install;

If you do not install libnss3-tools, you will get the following warning:

$ symfony server:ca:install
You might have to enter your root password to install the local Certificate Authority certificate
Sudo password:
The local CA is now installed in the system trust store!
WARNING "certutil" is not available, so the CA can't be automatically installed in Firefox and/or Chrome/Chromium!
Install "certutil" with "apt install libnss3-tools" and re-run the command
                                                                                                        
 [OK] The local Certificate Authority is installed and trusted                                          
                                                                      

After you install it, the message will change as follows:

$ symfony server:ca:install
The local CA is now installed in the Firefox and/or Chrome/Chromium trust store (requires browser restart)!
                                                                                                        
 [OK] The local Certificate Authority is installed and trusted

Install Webpack Encore for the assets

To install Webpack encore, we need yarn. To get yarn, we need npm. So we need the following installation steps:

sudo apt install npm;
sudo npm install --global yarn;

After these steps are successful, in the project folder, execute the following commands to allow the yarn to perform all necessary installations and then use encore to monitor the assets and rebuild its cache. The settings are depended on the file webpack.config.js.

yarn install;
yarn encore dev --watch;

Below, we present an example file of webpack.config.js.

var Encore = require('@symfony/webpack-encore');

// Manually configure the runtime environment if not already configured yet by the "encore" command.
// It's useful when you use tools that rely on webpack.config.js file.
if (!Encore.isRuntimeEnvironmentConfigured()) {
    Encore.configureRuntimeEnvironment(process.env.NODE_ENV || 'dev');
}

Encore
    // directory where compiled assets will be stored
    .setOutputPath('public/build/')
    // public path used by the web server to access the output path
    .setPublicPath('/build')
    // only needed for CDN's or sub-directory deploy
    //.setManifestKeyPrefix('build/')

    /*
     * ENTRY CONFIG
     *
     * Add 1 entry for each "page" of your app
     * (including one that's included on every page - e.g. "app")
     *
     * Each entry will result in one JavaScript file (e.g. app.js)
     * and one CSS file (e.g. app.css) if your JavaScript imports CSS.
     */
    .addEntry('app', './assets/js/app.js')
    //.addEntry('page1', './assets/js/page1.js')
    //.addEntry('page2', './assets/js/page2.js')

    // When enabled, Webpack "splits" your files into smaller pieces for greater optimization.
    .splitEntryChunks()

    // will require an extra script tag for runtime.js
    // but, you probably want this, unless you're building a single-page app
    .enableSingleRuntimeChunk()

    /*
     * FEATURE CONFIG
     *
     * Enable & configure other features below. For a full
     * list of features, see:
     * https://symfony.com/doc/current/frontend.html#adding-more-features
     */
    .cleanupOutputBeforeBuild()
    .enableBuildNotifications()
    .enableSourceMaps(!Encore.isProduction())
    // enables hashed filenames (e.g. app.abc123.css)
    .enableVersioning(Encore.isProduction())

    // enables @babel/preset-env polyfills
    .configureBabelPresetEnv((config) => {
        config.useBuiltIns = 'usage';
        config.corejs = 3;
    })

    // enables Sass/SCSS support
    //.enableSassLoader()

    // uncomment if you use TypeScript
    //.enableTypeScriptLoader()

    // uncomment to get integrity="..." attributes on your script & link tags
    // requires WebpackEncoreBundle 1.4 or higher
    //.enableIntegrityHashes(Encore.isProduction())

    // uncomment if you're having problems with a jQuery plugin
    //.autoProvidejQuery()

    // uncomment if you use API Platform Admin (composer req api-admin)
    //.enableReactPreset()
    //.addEntry('admin', './assets/js/admin.js')
;

module.exports = Encore.getWebpackConfig();

Some settings for PHPStorm by JetBrains

Since the IDE we are using for PHP development is PHPStorm, we installed the recommended plugins for Symfony to it. In the following image, we list the three plugins that we installed.

Specifically, we installed:

  • Symfony Support
  • PHP Annotations
  • PHP Toolbox

After installing the three plugins, we navigated to the Symfony Plugin settings (which you can find either using the search functionality or under the menu: Languages & Frameworks > PHP > Symfony).

From there, we clicked on the Enable Plugin for this Project and then changed the Web Directory from web to public.


FFmpeg tiny cheat sheet

We assume that the user has set the video filename to the variable named $video in the following commands.

FFmpeg export audio from any video to mp3

ffmpeg -i "$video" -vn -c:a libmp3lame -y "$audio";

FFmpeg export frames from video to images

ffmpeg -i "$video" "$frames_folder/%08d.ppm";

Retrieve the frame rate from the input video

#To view it on screen
ffprobe -v 0 -of csv=p=0 -select_streams v:0 -show_entries stream=r_frame_rate "$video";
#To assign it to a variable use the following
frame_rate=`ffprobe -v 0 -of csv=p=0 -select_streams v:0 -show_entries stream=r_frame_rate "$video"`;

To create a video out of a folder with frames/images and an audio file.

ffmpeg -framerate "$frame_rate" -i "$frames_folder/%08d.ppm" -i "$audio" -pix_fmt yuv420p -acodec copy -y "$output_video";
#To set a custom starting index for the frames you can use the -start_number argument
ffmpeg -start_number 62 -framerate "$frame_rate" -i "$frames_folder/%08d.ppm" -i "$audio" -pix_fmt yuv420p -acodec copy -y "$output_video";
#To use the MP4 coded use -vcodec libx264
ffmpeg -framerate "$frame_rate" -i "$frames_folder/%08d.ppm" -i "$audio" -vcodec libx264 -pix_fmt yuv420p -acodec copy -y "$output_video";

To merge an audio less video with an audio file

ffmpeg -i "$no_audio_video" -i "$audio" -shortest -vcodec copy -acodec copy "$output_video";

To change the frame rate of a video

ffmpeg -i "$video" -filter:v fps=20 "$output_video";

To merge two videos side by side

ffmpeg -i "$left_video" -i "$right_video" -filter_complex hstack "$output_video";

Concatenate multiple videos into one

The easiest way without writing huge commands is the following: First, create a file named parts.txt and add content similar to what we list below:

#Lines starting with # will be ignored
file 'part00-03.mp4'
file 'part04.mp4'
file 'part05-07.mp4'
file 'part08-09.mp4'
file 'part10.mp4'
file 'part11-13.mp4'

Then execute the following command to concatenate all those videos into one:

ffmpeg -f concat -safe 0 -i parts.txt -c copy "$output_video";

Speed up a video

Using the following command, you can speed up a video by dropping excess frames:

ffmpeg -i "$video" -filter:v "setpts=0.5*PTS" "$output_video";

The above example will double the speed (the value 0.5 controls it.)

To speed the video up without losing frames, you can increase the FPS value of the output video. To retrieve the frame rate, please see the command that was posted earlier.

ffmpeg -i "$video" -r 80 -filter:v "setpts=0.25*PTS" "$output_video";

In the second example, we assumed that the input video had 20 frames per second. Using the 0.25 value, we decided to speed the video up by a factor of 4. To preserve the input frames, we increased the frame rate from 20 to 80 using the parameter -r.


ImageMagick: merge two images using a black and white mask

Recently, we wanted to merge two images into one using a custom black and white mask. To avoid using heavy GUI-based software, we decided to do it using the composite command of the ImageMagick package. Using the composite program, you can overlap one image over another. The command used is straightforward once you get the order of the parameters in the command line.

convert black.jpg white.jpg mask.png -composite masked.jpg;

The above command accepts four parameters:

convert "${BLACK_PART}" "${WHITE_PART}" "${MASK}" -composite "${OUTPUT}";

The first parameter (${BLACK_PART}) is the input picture you want to be placed in all black parts of the mask. The second parameter (${WHITE_PART}) is the input photo you wish to use on all white parts of the mask. The third parameter (${MASK}) is the black and white image that you will be used to merge the previous two images. The final parameter (${OUTPUT}) is the filename to write the final results.

Below we present the results of a demo we created using the above command:

The first parameter (${BLACK_PART}) is the input picture you want to be placed in all black parts of the mask.
The second parameter (${WHITE_PART}) is the input photo you wish to use on all white parts of the mask.
The third parameter (${MASK}) is the black and white image that you will be used to merge the previous two images.
The final parameter (${OUTPUT}) is the filename to write the final results.