Category Archives: Programming

Acquainted with BASH Scripting

It is undeniable that over time, the popularity of Linux is increasing every day. Linux Kernel project which was originally just a fun project by Linux apparently transformed into a project that became the basis for the evolution of the digital world today.

We can see that more and more digital devices are therein using Linux in it. Changes were made in all areas so that Linux can be used by all users, both from the ground level up to the experts though.

One thing that remains a hallmark of Linux is the existence of a shell that is never lost on any Linux distro. Shell is a command-line interpreter on duty to translate the commands entered by the user directly to the system through the help of a terminal or console as a zoom interface (such as Command Prompt on the Windows platform). Although today most of the Linux distributions already to offering graphical display, the shell is still regarded as one of the strengths of Linux shell bridge where users can interact with the system in order to be more flexible. Many things can be done on a shell because we are dealing directly with the system, coupled with the many variants of the shell that offers a variety of features in it, such as csh, sh, bash, ksh, tcsh, ash, zsh, etc.

One of the most common type of shell used is BASH (Bourne-Again Shell) which was created by Bryan Fox in 1988. Shell is a replacement of the Bourne Shell (sh) existing first and is still used in some Linux distributions. Currently BASH shell has become a de facto standard for almost all Linux distributions because it is considered the most feature-rich and has a fairly high degree of portability. For comparison between variants shell can be seen on the Wikipedia website

To be able to understand the Linux system with better and also improve your productivity and take advantage of the flexibility offered by Linux, so it’s good we are trying to learn programming BASH script. PCplus using Slackware Linux distro, but this tutorial can be applied to all Linux distributions for use BASH version 4.2 and above. You can use any text editor because basically BASH script is plain text file. You can also try it on a Windows platform with the help of Cygwin,

open the editor:

1. The first step in creating a shell script is telling the system what shell you want to use, because it could be available in a Linux distribution over the shell variant. Because we want to use bash, then write this line in the first row of each bash shell script that will be created

This code is called the shebang and a special instruction that will determine what the interpreter is going to be used to process a shell script. For example, for a script that utilizes Perl interpreter, it will contain information

2. Because the shell script is basically able to execute commands on the shell, then we can run shell commands from a shell script. For example, we want to display today’s date along with the name that we use username to login. Use the code on the listing-1 as an example. Before you can run the script, give it execute permissions on the file with the command chmod + x’s listing 1.sh (adjust the file name you gave) then run the command.

Date command displays the current date information while whoami will menapilkan your user information to login.

3. What if we want to display the text coupled with a shell command? Use the echo function to display a message to the screen shown in listing-2. Echo function accepts parameters in the form of a text message that will be displayed kelayar. You might ask, why the date and user information are on different lines with text displayed? This is due essentially echo function will display a message and then change the next line. To be able to display an information to the right of the text is displayed, use the-n parameter on the function like echo in the listing-3.

4. You can try some of the commands contained in the location / bin and / usr / bin. If not sure of the usefulness of a command, run the command man <nama-perintah> on the console or terminal, for example, man ls and manual information about the ls command will be displayed. Each command has a variation of different parameters with each other, so there are times when we have to read the manual to know every option available.

OpenMP 4.0 Specifications Released

The OpenMP 4.0 API Specification is released with Significant New Standard Features

The OpenMP 4.0 API supports the programming of accelerators, SIMD programming, and better optimization using thread affinity

The OpenMP Consortium has released OpenMP API 4.0, a major upgrade of the OpenMP API standard language specifications. Besides several major enhancements, this release provides a new mechanism to describe regions of code where data and/or computation should be moved to another computing device.

Bronis R. de Supinski, Chair of the OpenMP Language Committee, stated that “OpenMP 4.0 API is a major advance that adds two new forms of parallelism in the form of device constructs and SIMD constructs. It also includes several significant extensions for the loop-based and task-based forms of parallelism already supported in the OpenMP 3.1 API.

The 4.0 specification is now available on the 

Standard for parallel programming extends its reach

With this release, the OpenMP API specifications, the de-facto standard for parallel programming on shared memory systems, continues to extend its reach beyond pure HPC to include DSPs, real time systems, and accelerators. The OpenMP API aims to provide high-level parallel language support for a wide range of applications, from automotive and aeronautics to biotech, automation, robotics and financial analysis.

New features in the OpenMP 4.0 API include:

· Support for accelerators. The OpenMP 4.0 API specification effort included significant participation by all the major vendors in order to support a wide variety of compute devices. OpenMP API provides mechanisms to describe regions of code where data and/or computation should be moved to another computing device. Several prototypes for the accelerator proposal have already been implemented.

· SIMD constructs to vectorize both serial as well as parallelized loops. With the advent of SIMD units in all major processor chips, portable support for accessing them is essential. OpenMP 4.0 API provides mechanisms to describe when multiple iterations of the loop can be executed concurrently using SIMD instructions and to describe how to create versions of functions that can be invoked across SIMD lanes.

· Error handling. OpenMP 4.0 API defines error handling capabilities to improve the resiliency and stability of OpenMP applications in the presence of system-level, runtime-level, and user-defined errors. Features to abort parallel OpenMP execution cleanly have been defined, based on conditional cancellation and user-defined cancellation points.

· Thread affinity. OpenMP 4.0 API provides mechanisms to define where to execute OpenMP threads. Platform-specific data and algorithm-specific properties are separated, offering a deterministic behavior and simplicity in use. The advantages for the user are better locality, less false sharing and more memory bandwidth.

· Tasking extensions. OpenMP 4.0 API provides several extensions to its task-based parallelism support. Tasks can be grouped to support deep task synchronization and task groups can be aborted to reflect completion of cooperative tasking activities such as search. Task-to-task synchronization is now supported through the specification of task dependency.

· Support for Fortran 2003. The Fortran 2003 standard adds many modern computer language features. Having these features in the specification allows users to parallelize Fortran 2003 compliant programs. This includes interoperability of Fortran and C, which is one of the most popular features in Fortran 2003.

· User-defined reductions. Previously, OpenMP API only supported reductions with base language operators and intrinsic procedures. With OpenMP 4.0 API, user-defined reductions are now also supported.

· Sequentially consistent atomics. A clause has been added to allow a programmer to enforce sequential consistency when a specific storage location is accessed atomically.

This represents collaborative work by many of the brightest in industry, research, and academia, building on the consensus of 26 members. We strive to deliver high-level parallelism that is portable across 3 widely-implemented common General Purpose languages, productive for HPC and consumers, and delivers highly competitive performance. I want to congratulate all the members for coming together to create such a momentous advancement in parallel programming, under such tight constraints and industry challenges.
With this release, the OpenMP API will move immediately forward to the next release to bring even more usable parallelism to everyone.
 – Michael Wong, CEO OpenMP ARB.

Creating a 3D Game With Three.js and WebGL

Prerequisites

  • A browser with WebGL – this game has been tested on Chrome and Firefox. IE still doesn’t support WebGL, unless you’re using Windows 8.1 with IE11.
  • Three.js library available for download from the Three.js website
  • The Keyboard.js helper library I used for this project, created by Arthur Schreiber at No Karma. Download it from my GitHub repository
  • A basic understanding of what Three.js does. Read this super simple, super quick tutorial by Paul Lewis. It’s basically a short-hand version of this article.

Setup

Get a base index.html running

Step one when making a web-based game is to create the host index.html file. In our case, it only needs to be a very simple set of elements, so we can bundle the CSS styling too.

Import Keyboard.js and Three.js

Three.js is a library contained in just one JavaScript file, so we can grab the minified version from the website.

For Keyboard input, we will need to referencethe aforementioned JavaScript file in our index.html as well.

Create setup() and draw() functions

The setup() function will be the start point for the game code. The draw() function will be run every frame and will handle all the rendering and game logic.

In order to loop the draw() function, we simply utilise the requestAnimationFrame() function call, and pass ‘draw’ as the parameter. Remember, not all browsers natively support the call, and you might have to use Paul Irish’s shim to gain maximum compatibility. Also, it is important to realise that requestAnimationFrame() does not guarantee a fixed frame-rate, so you need to use time-deltas to calculate realistic physics. For a basic game like Pong, we don’t really care about that.

Basic World

Set up the Three.js world and camera

Three.js includes these important elements:

  • Scene
  • Renderer
  • Camera
  • Mesh
  • Light
  • Material

Cameras, Meshes, and Lights need to be added to the scene using the scene.add() function.

Attach a WebGL Three.js Renderer to the DIV

The renderer is attached to whichever HTML DOM element you wish to render the scene to, and a render() call is made each frame to the renderer in order to draw the Three.js scene.

Add a camera to the scene

Three.js has the option to create Perspective and Orthographic cameras. For most uses, Perspective camera is the best choice. We can change position and rotation information of the camera like any other object in the scene.

Draw a sphere and light it

Meshes must be paired with Materials in order to give them a defined look and feel. Meshes can be of many types, include primitives such as Cube, Sphere, Plane and Torus. Materials can have different characteristics depending on their type. The basic Material types include Lambert, Phong, and Basic.

  • Basic renders an unlit Mesh with no shadows or dark shading. A sphere will look like a circle if rendered with Basic.
  • Lambert is a simple diffuse-like lighting that creates shading on sides facing away from a light source. It gives a basic 3D look of surfaces that are matte (non-shiny and non-reflective)
  • Phong is used for achieving a plastic-like look and feel, with the ability to gain highlights that give a much shinier appearance to the Mesh.

Show off your sphere with a Point Light. This is the most basic light, with no direction or rotation. Make sure you tweak the light’s intensity and distance to get it looking good.

Add Game Objects

Draw playing area plane

The playing area will be a Three.js Mesh object of type Plane. Make sure the plane matches the play area, giving a small buffer gap to indicate where the paddles can and can’t go.

Draw paddles

The paddles will be Mesh objects of type Cube. Position each of the paddles on opposite sides of the play area.

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// set up the paddle vars
paddleWidth = 10;
paddleHeight = 30;
paddleDepth = 10;
paddleQuality = 1;
// set up paddle 1
paddle1 = new THREE.Mesh(
new THREE.CubeGeometry(
paddleWidth,
paddleHeight,
paddleDepth,
paddleQuality,
paddleQuality,
paddleQuality),
paddle1Material);
// add the paddle to the scene
scene.add(paddle1);
// Set up the second paddle
paddle2 = new THREE.Mesh(
new THREE.CubeGeometry(
paddleWidth,
paddleHeight,
paddleDepth,
paddleQuality,
paddleQuality,
paddleQuality),
paddle2Material);
// Add the second paddle to the scene
scene.add(paddle2);
// set paddles on each side of the table
paddle1.position.x = -fieldWidth/2 + paddleWidth;
paddle2.position.x = fieldWidth/2 – paddleWidth;
// lift paddles over playing surface
paddle1.position.z = paddleDepth;
paddle2.position.z = paddleDepth;
view rawBNG_Pong_paddlecreateThis Gist brought to you by GitHub.

If you manipulate the camera positions, as seen in the screenshot, you can give a different perspective to the player.

Basic Logic

Ball movement

The ball will have an X-direction and a Y-direction that determines the movement per frame.

// ball’s x-direction, y-direction and speed per frame
var ballDirX = 1, ballDirY = 1, ballSpeed = 2;

The ball will move at a constant speed in the X-plane every frame. To this end, we will specify a ballSpeed variable that acts as a multiplier for the direction values.

// update ball position over time
ball.position.x += ballDirX * ballSpeed;
ball.position.y += ballDirY * ballSpeed;

We want the ball to have some unpredictable characteristics (e.g. when it gets sliced quite hard) so we will allow the Y-direction to go up to a maximum of ballSpeed * 2. You can tweak the values until you’re happy with how the ball behaves.

// limit ball’s y-speed to 2x the x-speed
// this is so the ball doesn’t speed from left to right super fast
// keeps game playable for humans
if (ballDirY > ballSpeed * 2)
{
ballDirY = ballSpeed * 2;
}
else if (ballDirY < -ballSpeed * 2)
{
ballDirY = -ballSpeed * 2;
}

Ball wall bounce logic

Simple collision detection logic is required to check if the ball is touching each of the side ‘walls’. Using a series of ‘if-else’ statements, we check the ball positions against the predetermined wall positions. In the case of a collision, we simply switch the Y-direction of the ball, creating a bounce effect.

// if ball goes off the top side (side of table)
if (ball.position.y <= -fieldHeight/2)
{
ballDirY = -ballDirY;
}
// if ball goes off the bottom side (side of table)
if (ball.position.y >= fieldHeight/2)
{
ballDirY = -ballDirY;
}

Later, we will edit some of this code in order to implement scoring when the ball passes a paddle.

Keyboard input for paddles

We will utilise a very effective short-cut in order to easily get keyboard input working in this game. Using the Keyboard.js file provided, we simply have to include the reference to it in the index.html file and we are set. Only one function call is required, the Key.isDown() call. Given a parameter, the library checks if that particular key is current being pressed, and returns a boolean value.

// move left
if (Key.isDown(Key.A))
{
// code to move paddle left
}

We use the ‘A’ and ‘D’ keys to move the paddle left and right, but you can edit the Keyboard.js with additional values if you want to use your own control scheme.

var Key = {
_pressed: {},
A: 65,
W: 87,
D: 68,
S: 83,
// add your required key code (ASCII) along with the name here
// for example:
SPACE: 32,
};

While dealing with keyboard input, it is also important to ensure that the input is never blindly updated in game. We have to check that the paddle isn’t made to move off the play area, and we do that with some ‘if-else’ statements as well.

// move left
if (Key.isDown(Key.A))
{
// if paddle is not touching the side of table
// we move
if (paddle1.position.y < fieldHeight * 0.45)
{
paddle1DirY = paddleSpeed * 0.5;
}
// else we don’t move and stretch the paddle
// to indicate we can’t move
else
{
paddle1DirY = 0;
paddle1.scale.z += (10 – paddle1.scale.z) * 0.2;
}
}

Note that we use a paddle direction variable, rather than simply applying a change to the position values. This will come in handy when programming the ball to ‘slice’ when hit at an angle with a fast-moving paddle.

Opponent logic

When you code a game of this calibre, it is of utmost importance that you create a vivid, lush environment with a host of emotional, highly-relatable characters that showcase this generation’s strides forward in technology. Instead, we will code a Pong A.I. that blindly follows the ball, because that is even better.

We can update the opponent difficulty by using a variable instead of introducing magic numbers. This variable will affect the ‘reaction rate’ of the opponent by increasing the Lerp (Linear-Interpolation) time.

When using a Lerp (Linear-Interpolation) function, we must ensure the opponent plays fairly by limiting their maximum travel speed. We do that with a few more if-else statements.

// in case the Lerp function produces a value above max paddle speed, we clamp it
if (Math.abs(paddle2DirY) <= paddleSpeed)
{
paddle2.position.y += paddle2DirY;
}
// if the lerp value is too high, we have to limit speed to paddleSpeed
else
{
// if paddle is lerping in +ve direction
if (paddle2DirY > paddleSpeed)
{
paddle2.position.y += paddleSpeed;
}
// if paddle is lerping in -ve direction
else if (paddle2DirY < -paddleSpeed)
{
paddle2.position.y -= paddleSpeed;
}
}
If want to extend immersion, you could also using the paddle.scale property to stretch the paddle when it can’t be moved. This indicates an issue to the player which they can then address immediately. In order to accomplish this, we must ensure the paddle always Lerps back to the default scale size.
// We lerp the scale back to 1
// this is done because we stretch the paddle at some points
// stretching is done when paddle touches side of table and when paddle hits ball
// by doing this here, we ensure paddle always comes back to default size
paddle2.scale.y += (1 – paddle2.scale.y) * 0.2;

Adding Gameplay

Making the ball reset after missing a paddle

To get the main scoring gameplay working, we need to first remove the ball’s ability to bonce off the paddle-facing walls. To do this, we remove the bounce code from the two corresponding if-else statements.

// if ball goes off the top side (side of table)
if (ball.position.y <= -fieldHeight/2)
{
ballDirY = -ballDirY;
}
// if ball goes off the bottom side (side of table)
if (ball.position.y >= fieldHeight/2)
{
ballDirY = -ballDirY;
}
//// ——————————— ////
CHANGED CODE
//// ——————————— ////
// if ball goes off the ‘left’ side (Player’s side)
if (ball.position.x <= -fieldWidth/2)
{
// CPU scores a point
// update scoreboard
// and reset ball
}
// if ball goes off the ‘right’ side (CPU’s side)
if (ball.position.x >= fieldWidth/2)
{
// player scores a point
// update scoreboard
// and reset ball
}

We can handle scoring in many different ways. For a simple game like this, we can simply increment the corresponding score count variable.

// if ball goes off the ‘left’ side (Player’s side)
if (ball.position.x <= -fieldWidth/2)
{
// CPU scores
score2++;
// update scoreboard HTML
document.getElementById(“scores”).innerHTML = score1 + “-” + score2;
// reset ball to center
resetBall(2);
// check if match over (someone scored maxScore points)
matchScoreCheck();
}

We can then update the HUD element in the DOM by setting its innerHTML value. Finally, we have to reset the ball once someone has scored. A simple function can be written to reset the ball, with a parameter indicating which paddle just lost (so we know which paddle to send the ball to next time).

// resets the ball’s position to the centre of the play area
// also sets the ball direction speed towards the last point winner
function resetBall(loser)
{
// position the ball in the center of the table
ball.position.x = 0;
ball.position.y = 0;
// if player lost the last point, we send the ball to opponent
if (loser == 1)
{
ballDirX = -1;
}
// else if opponent lost, we send ball to player
else
{
ballDirX = 1;
}
// set the ball to move +ve in y plane (towards left from the camera)
ballDirY = 1;
}

Making the ball bounce off paddles

Alright, this is it. The big one. Literally the biggest feature of this game. It’s time to get the paddles hitting the ball. In a simple Pong game, paddle-ball physics are nothing more than a couple of if-else statements. We check the X-position and Y-position of the ball against the paddle’s rectangular bounds, and if they intersect, we bounce the ball away.

// if ball is aligned with paddle1 on x plane
// remember the position is the CENTER of the object
// we only check between the front and the middle of the paddle (one-way collision)
if (ball.position.x <= paddle1.position.x + paddleWidth
&& ball.position.x >= paddle1.position.x)
{
// and if ball is aligned with paddle1 on y plane
if (ball.position.y <= paddle1.position.y + paddleHeight/2
&& ball.position.y >= paddle1.position.y – paddleHeight/2)
{
// ball is intersecting with the front half of the paddle
}
}

It’s also important to check the direction of the ball’s travel, as we only want to check collisions in one direction (the direction towards the opponent.)

// and if ball is travelling towards player (-ve direction)
if (ballDirX < 0)
{
// stretch the paddle to indicate a hit
paddle1.scale.y = 15;
// switch direction of ball travel to create bounce
ballDirX = -ballDirX;
// we impact ball angle when hitting it
// this is not realistic physics, just spices up the gameplay
// allows you to ‘slice’ the ball to beat the opponent
ballDirY -= paddle1DirY * 0.7;
}

We will also affect the ball’s lateral movement depending on the relative speed of the paddle when hitting the ball. This is particularly useful in introducing the biggest variable in Pong: the slice. Slicing the ball is often the only way to confuse and outmaneuver the opponent, so it is vital in this game.

Remember to duplicate the code, but update the values to match the opponent’s paddle. You can use this opportunity to gimp your opponent’s ability somewhat, by reducing the hitbox size or decreasing the slice amount. It’s what we would all do.

Here is the final paddle-ball collision function:

// Handles paddle collision logic
function paddlePhysics()
{
// PLAYER PADDLE LOGIC
// if ball is aligned with paddle1 on x plane
// remember the position is the CENTER of the object
// we only check between the front and the middle of the paddle (one-way collision)
if (ball.position.x <= paddle1.position.x + paddleWidth
&& ball.position.x >= paddle1.position.x)
{
// and if ball is aligned with paddle1 on y plane
if (ball.position.y <= paddle1.position.y + paddleHeight/2
&& ball.position.y >= paddle1.position.y – paddleHeight/2)
{
// and if ball is travelling towards player (-ve direction)
if (ballDirX < 0)
{
// stretch the paddle to indicate a hit
paddle1.scale.y = 15;
// switch direction of ball travel to create bounce
ballDirX = -ballDirX;
// we impact ball angle when hitting it
// this is not realistic physics, just spices up the gameplay
// allows you to ‘slice’ the ball to beat the opponent
ballDirY -= paddle1DirY * 0.7;
}
}
}
// OPPONENT PADDLE LOGIC
// if ball is aligned with paddle2 on x plane
// remember the position is the CENTER of the object
// we only check between the front and the middle of the paddle (one-way collision)
if (ball.position.x <= paddle2.position.x + paddleWidth
&& ball.position.x >= paddle2.position.x)
{
// and if ball is aligned with paddle2 on y plane
if (ball.position.y <= paddle2.position.y + paddleHeight/2
&& ball.position.y >= paddle2.position.y – paddleHeight/2)
{
// and if ball is travelling towards opponent (+ve direction)
if (ballDirX > 0)
{
// stretch the paddle to indicate a hit
paddle2.scale.y = 15;
// switch direction of ball travel to create bounce
ballDirX = -ballDirX;
// we impact ball angle when hitting it
// this is not realistic physics, just spices up the gameplay
// allows you to ‘slice’ the ball to beat the opponent
ballDirY -= paddle2DirY * 0.7;
}
}
}
}
view rawBNG_Pong_paddlecollCompleteThis Gist brought to you by GitHub.

Scoring

In Pong, it is usually simplest to have a maximum score value, such that a game is won when either player reaches that score. To that end, we can easily create a maxScore variable and set it at the start of the match.

We then create a function to check if either player has scored equal or higher than the maximum. This function should be called only when a score has been changed (i.e. when someone scores a point.)

// checks if either player or opponent has reached 7 points
function matchScoreCheck()
{
// if player has 7 points
if (score1 >= maxScore)
{
// stop the ball
ballSpeed = 0;
// write to the banner
document.getElementById(“scores”).innerHTML = “Player wins!”;
document.getElementById(“winnerBoard”).innerHTML = “Refresh to play again”;
}
// else if opponent has 7 points
else if (score2 >= maxScore)
{
// stop the ball
ballSpeed = 0;
// write to the banner
document.getElementById(“scores”).innerHTML = “CPU wins!”;
document.getElementById(“winnerBoard”).innerHTML = “Refresh to play again”;
}
}

After a match is deemed complete, it is simplest to just return the ball to the centre and stop any movement, so that play doesnt inadvertently continue.

Prettifying the Game

HUD

It’s important to give feedback to the player so they know what’s going on. For Pong, the least we can do is keep a scoreboard ticking over. Instead of trying to draw the HUD on the same layer as the game, we can use the other DOM elements to provide the required feedback.

It’s also good to indicate the maximum score as well, so we have another element for that which we will update at match start.

// update the board to reflect the max score for match win
document.getElementById(“winnerBoard”).innerHTML = “First to ” + maxScore + ” wins!”;

Shadows

Finally, it is time to make things look a tad more polished. Three.js has the awesome ability to create shadows for primitive objects (Cube, Plane, Sphere, etc.) so we can utilise that to make the game look nicer.

Shadows can’t be created with just a Point light, so we have to add a DirectionalLight or a SpotLight. A SpotLight shines a circular beam of light onto surfaces, which DirectionalLight simply shines a light in a certain direction with no regard to positioning.

We will use a SpotLight because it clearly indicates where the light originates from and shines towards.

We can update the SpotLight to follow the ball around to give a more dynamic look and feel to the game, whilst showcasing the hard work we just put into the lighting.

// we can easily notice shadows if we dynamically move lights during the game
spotLight.position.x = ball.position.x;
spotLight.position.y = ball.position.y;

To make an object in the scene cast or receive shadows, we simply set their .receiveShadow and .castShadow variables to true. For example,

paddle1 = new THREE.Mesh(
new THREE.CubeGeometry(paddleWidth, paddleHeight, paddleDepth, paddleQuality, paddleQuality, paddleQuality),
paddle1Material);
// add the sphere to the scene
scene.add(paddle1);
paddle1.receiveShadow = true;
paddle1.castShadow = true;

Conclusion

This is but a basic introduction to the power of Three.js, which should allow you to create a basic Pong clone.

Play the latest build of this game here: LATEST BUILD*

Find the latest code at its GitHub page*

You can still do quite a number of things to polish your game, such as

  • Create animations for the paddles and ball
  • Update the HUD to look prettier
  • Import complex objects created in Modeling packages, to design a more immersive environment
  • Move HUD elements inside the game view to allow for full-screen gaming
  • Mess around with complex shaders to create reflections and other cool effects