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  • Tips about how to spread Object Oriented practices

    - by Augusto
    I work for a medium company that has around 250 developers. Unfortunately, lots of them are stuck in a procedural way of thinking and some teams constantly deliver big Transactional Script applications, when in fact the application contains rich logic. They also fail to manage the design dependencies, and end up with services which depend on another large number of services (a clean example of Big Ball of Mud). My question is: Can you suggest how to spread this type of knowledge? I know that the surface of the problem is that these applications have a poor architecture and design. Another issue is that there are some developers who are against writing any kind of test. A few things I'm doing to change this (but I'm either failing or the change is too small are) Running presentations about design principles (SOLID, clean code, etc). Workshops about TDD and BDD. Coaching teams (this includes using sonar, findbugs, jdepend and other tools). IDE & Refactoring talks. A few things I'm thinking to do in the future (but I'm concern that they might not be good) Form a team of OO evangelists, who disseminate an OO way of thinking in differet teams (these people would need to change teams every few months). Running design review sessions, to criticise the design and suggest improvements (even if the improvements are not done because of time constraints, I think this might be useful) . Something I found with the teams I coach, is that as soon as I leave them, they revert back to the old practices. I know I don't spend a lot of time with them, usually just one month. So whatever I'm doing, it doesn't stick. I'm sorry this question is spattered with frustration, but the alterative to write this was to hit my head on the wall until I pass out.

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  • Object construction design

    - by James
    I recently started to use c# to interface with a database, and there was one part of the process that appeared odd to me. When creating a SqlCommand, the method I was lead to took the form: SqlCommand myCommand = new SqlCommand("Command String", myConnection); Coming from a Java background, I was expecting something more similar to SqlCommand myCommand = myConnection.createCommand("Command String"); I am asking, in terms of design, what is the difference between the two? The phrase "single responsibility" has been used to suggest that a connection should not be responsible for creating SqlCommands, but I would also say that, in my mind, the difference between the two is partly a mental one of the difference between a connection executing a command and a command acting on a connection, the latter of which seems less like what I have been lead to believe OOP should be. There is also a part of me wondering if the two should be completely separate, and should only come together in some sort of connection.execute(command) method. Can anyone help clear up these differences? Are any of these methods "more correct" than the others from an OO point of view? (P.S. the fact that c# is used is completely irrelevant. It just highlighted to me that different approaches were used)

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  • How to make an object move again after being stopped by collision in Unity?

    - by Matthew Underwood
    I have a player object which position is always centered on the main camera's viewport. This object has a Rigidbody 2D, a box and circle collider. The player moves around a level, the level has a polygon collider attached. I move the camera until the object hits against the collider, which stops the movement of the camera by setting its speed to 0. The problem happens when I want to move the camera / player object away from the collider. As the speed is already at 0, it cannot move away from the collider. The script attached to the player object, checks for collisions and applies the speed to 0 on the main camera's test script. using UnityEngine; using System.Collections; public class move : MonoBehaviour { public float speed; public test testing; // Use this for initialization void Start () { speed = 10F; testing = Camera.main.GetComponent<test>(); } // Update is called once per frame void FixedUpdate () { Vector3 p = Camera.main.ViewportToWorldPoint(new Vector3(0.5F, 0.5F, Camera.main.nearClipPlane)); transform.position = new Vector3(p.x, p.y, -1); } void OnCollisionEnter2D(Collision2D col) { testing.speed = 0; } void OnCollisionExit2D(Collision2D col) { testing.speed = 10F; } } This is the script attached to the main camera; just a simple script that changes the camera's position. using UnityEngine; using System.Collections; public class test : MonoBehaviour { public float speed; public float translationY; public float translationX; // Use this for initialization void Start () { speed = 10F; } void FixedUpdate () { translationY = Input.GetAxis("Vertical") * speed * Time.deltaTime; translationX = Input.GetAxis("Horizontal") * speed * Time.deltaTime; transform.Translate(translationX, translationY, 0); } } The player object isn't kinematic and is a fixed angle, the colliders aren't triggers and the polygon collider isn't a trigger either. The player is the red square, the collider is the pink area. -- EDIT -- From the latest change the collider set up for the player So if the X speed was disabled. It wouldnt move into the side of the polygon colider which is good, but yet you couldnt move away from it. And moving down would move inside the colider.

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  • Using visitor pattern with large object hierarchy

    - by T. Fabre
    Context I've been using with a hierarchy of objects (an expression tree) a "pseudo" visitor pattern (pseudo, as in it does not use double dispatch) : public interface MyInterface { void Accept(SomeClass operationClass); } public class MyImpl : MyInterface { public void Accept(SomeClass operationClass) { operationClass.DoSomething(); operationClass.DoSomethingElse(); // ... and so on ... } } This design was, however questionnable, pretty comfortable since the number of implementations of MyInterface is significant (~50 or more) and I didn't need to add extra operations. Each implementation is unique (it's a different expression or operator), and some are composites (ie, operator nodes that will contain other operator/leaf nodes). Traversal is currently performed by calling the Accept operation on the root node of the tree, which in turns calls Accept on each of its child nodes, which in turn... and so on... But the time has come where I need to add a new operation, such as pretty printing : public class MyImpl : MyInterface { // Property does not come from MyInterface public string SomeProperty { get; set; } public void Accept(SomeClass operationClass) { operationClass.DoSomething(); operationClass.DoSomethingElse(); // ... and so on ... } public void Accept(SomePrettyPrinter printer) { printer.PrettyPrint(this.SomeProperty); } } I basically see two options : Keep the same design, adding a new method for my operation to each derived class, at the expense of maintainibility (not an option, IMHO) Use the "true" Visitor pattern, at the expense of extensibility (not an option, as I expect to have more implementations coming along the way...), with about 50+ overloads of the Visit method, each one matching a specific implementation ? Question Would you recommand using the Visitor pattern ? Is there any other pattern that could help solve this issue ?

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  • Object desing problem for simple school application

    - by Aragornx
    I want to create simple school application that provides grades,notes,presence,etc. for students,teachers and parents. I'm trying to design objects for this problem and I'm little bit confused - because I'm not very experienced in class designing. Some of my present objects are : class PersonalData() { private String name; private String surename; private Calendar dateOfBirth; [...] } class Person { private PersonalData personalData; } class User extends Person { private String login; private char[] password; } class Student extends Person { private ArrayList<Counselor> counselors = new ArrayList<>(); } class Counselor extends Person { private ArrayList<Student> children = new ArrayList<>(); } class Teacher extends Person { private ArrayList<ChoolClass> schoolClasses = new ArrayList<>(); private ArrayList<Subject> subjects = new ArrayList<>(); } This is of course a general idea. But I'm sure it's not the best way. For example I want that one person could be a Teacher and also a Parent(Counselor) and present approach makes me to have two Person objects. I want that user after successful logging in get all roles that it has (Student or Teacher or (Teacher & Parent) ). I think I should make and use some interfaces but I'm not sure how to do this right. Maybe like this: interface Role { } interface TeacherRole implements Role { void addGrade( Student student, Grade grade, [...] ); } class Teacher implements TeacherRole { private Person person; [...] } class User extends Person{ ArrayList<Role> roles = new ArrayList<>(); } Please if anyone could help me to make this right or maybe just point me to some literature/article that covers practical objects design.

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  • Structuring Access Control In Hierarchical Object Graph

    - by SB2055
    I have a Folder entity that can be Moderated by users. Folders can contain other folders. So I may have a structure like this: Folder 1 Folder 2 Folder 3 Folder 4 I have to decide how to implement Moderation for this entity. I've come up with two options: Option 1 When the user is given moderation privileges to Folder 1, define a moderator relationship between Folder 1 and User 1. No other relationships are added to the db. To determine if the user can moderate Folder 3, I check and see if User 1 is the moderator of any parent folders. This seems to alleviate some of the complexity of handling updates / moved entities / additions under Folder 1 after the relationship has been defined, and reverting the relationship means I only have to deal with one entity. Option 2 When the user is given moderation privileges to Folder 1, define a new relationship between User 1 and Folder 1, and all child entities down to the grandest of grandchildren when the relationship is created, and if it's ever removed, iterate back down the graph to remove the relationship. If I add something under Folder 2 after this relationship has been made, I just copy all Moderators into the new Entity. But when I need to show only the top-level Folders that a user is Moderating, I need to query all folders that have a parent folder that the user does not moderate, as opposed to option 1, where I just query any items that the user is moderating. Thoughts I think it comes down to determining if users will be querying for all parent items more than they'll be querying child items... if so, then option 1 seems better. But I'm not sure. Is either approach better than the other? Why? Or is there another approach that's better than both? I'm using Entity Framework in case it matters.

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  • Java2D Distance Collision Detection

    - by Trizicus
    My current setup is only useful once collision has been made; obviously there has to be something better than this? public boolean CollisionCheck(Rectangle rect1, Rectangle rect2) { if(rect1.intersects(rect2)) { return true; } return false; } How can I do preemptive collision detection?

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  • Motion detection in compressed domain (JPEG/Mpeg4/H264)

    - by paft
    everyone! I process video from IP cameras and have wrote a motion detection algorithm based on decompressed video analysis. But i really something more fast. I've found several papers about compressed domain analysis but have failed to find any implementations. Can anyone recommend me some code? found materials: http://www.ist-live.org/intranet/school-of-informatics-university-of-bradford001-7/41410206.pdf/view http://doc.rero.ch/lm.php?url=1000,43,4,20061128120121-NA/Bracamonte_Javier_-_A_Low_Complexity_Change_Detection_Algorithm_20061128.pdf

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  • Activation Function, Initializer function, etc, effects on neural networks for face detection

    - by harry
    There's various activation functions: sigmoid, tanh, etc. And there's also a few initializer functions: Nguyen and Widrow, random, normalized, constant, zero, etc. So do these have much effect on the outcome of a neural network specialising in face detection? Right now I'm using the Tanh activation function and just randomising all the weights from -0.5 to 0.5. I have no idea if this is the best approach though, and with 4 hours to train the network each time, I'd rather ask on here than experiment!

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  • PHP mobile browser detection?

    - by TreyK
    I'm in need of a way to detect mobile browsers server-side. I'd like a way that requires me to do little to set up and little to maintain, yet still provide me with accurate detection of (at the VERY least) Android, Mobile Safari and Blackberry browsers, along with alternatives like Opera. I'd like to have at least the majority of the mobile market covered, and I'd really prefer virtually all of the market if it doesn't take much.

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  • Collision detection in Java game?

    - by Chetan
    I am developing a game in which I have the problem of collision detection of moving images. The game has a spaceship and number of asteroids (obstacles). I want to detect the collision between them. How can I do this?

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  • SQL SERVER – Error: Fix – Msg 208 – Invalid object name ‘dbo.backupset’ – Invalid object name ‘dbo.backupfile’

    - by pinaldave
    Just a day before I got a very interesting email. Here is the email (modified a bit to make it relevant to this blog post). “Pinal, We are facing a very strange issue. One of our query  related to backup files and backup set has stopped working suddenly in SSMS. It works fine in application where we have and in the stored procedure but when we have it in our SSMS it gives following error. Msg 208, Level 16, State 1, Line 1 Invalid object name ‘dbo.backupfile’. Here are our queries which we are trying to execute. SELECT name, database_name, backup_size, TYPE, compatibility_level, backup_set_id FROM dbo.backupset; SELECT logical_name, backup_size, file_type FROM dbo.backupfile; This query gives us details related to backupset and backup files when the backup was taken.” When I receive this kind of email, usually I have no answers directly. The claim that it works in stored procedure and in application but not in SSMS gives me no real data. I have requested him to very first check following two things: If he is connected to correct server? His answer was yes. If he has enough permissions? His answer was he was logged in as an admin. This means there was something more to it and I requested him to send me a screenshot of the his SSMS. He promptly sends that to me and as soon as I receive the screen shot I knew what was going on. Before I say anything take a look at the screenshot yourself and see if you can figure out why his queries are not working in SSMS. Just to make your life a bit easy, I have already given a hint in the image. The answer is very simple, the context of the database is master database. To execute above two queries the context of the database has to be msdb. Tables backupset and backupfile belong to the database msdb only. Here are two workaround or solution to above problem: 1) Change context to MSDB Above two queries when they will run as following they will not error out and will give the accurate desired result. USE msdb GO SELECT name, database_name, backup_size, TYPE, compatibility_level, backup_set_id FROM dbo.backupset; SELECT logical_name, backup_size, file_type FROM dbo.backupfile; 2) Prefix the query with msdb There are cases above script used in stored procedure or part of big query, it is not possible to change the context of the whole query to any specific database. Use three part naming convention and prefix them with msdb. SELECT name, database_name, backup_size, TYPE, compatibility_level, backup_set_id FROM msdb.dbo.backupset; SELECT logical_name, backup_size, file_type FROM msdb.dbo.backupfile; Very simple solution but sometime keeps people wondering for an answer. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: PostADay, SQL, SQL Authority, SQL Error Messages, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Motion detection of a specific object in .net

    - by abinop
    I need to make a .net application where I must detect a specific object the user is holding, using a camera. If the object must have some specific characteristics so that it can be easily recognized and detected from the surrounding space, please give me some tips (ex a green cube?) What would be the best technique/.net library to use? I need to translate in realtime the user's hand movement and display an animation on screen accordingly.

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  • 2D colliding n-body simulation (fast Collision Detection for large number of balls)

    - by osgx
    Hello I want to write a program for simulating a motion of high number (N = 1000 - 10^5 and more) of bodies (circles) on 2D plane. All bodies have equal size and the only force between them is elastic collision. I want to get something like but in larger scale, with more balls and more dense filling of the plane (not a gas model as here, but smth like boiling water model). So I want a fast method of detection that ball number i does have any other ball on its path within 2*radius+V*delta_t distance. I don't want to do a full search of collision with N balls for each of i ball. (This search will be N^2.) PS Sorry for loop-animated GIF. Just press Esc to stop it. (Will not work in Chrome).

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  • 2D collision detection and stuff with OpenGL

    - by shinjuo
    I am working on a simple 2D openGL project. It contains a main actor you can control with the keyboard arrows. I got that to work okay. What I am wanting is something that can help explain how to make another actor object follow the main actor. Maybe a tutorial on openGL. The three main things I need to learn are the actor following, collision detection, and some kind of way to create gravity. Any good books or tutorials to help get me in the right direction would be great.

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  • Using glRotate and glTranslate with collision detection.

    - by Cetra
    Hey guys, Say I use glRotate to translate the current view based on some arbitrary user input (i.e, if key left is pressed then rtri+=2.5f) glRotatef(rtri,0.0f,1.0f,0.0f); Then I draw the triangle in the rotated position: glBegin(GL_TRIANGLES); // Drawing Using Triangles glVertex3f( 0.0f, 1.0f, 0.0f); // Top glVertex3f(-1.0f,-1.0f, 0.0f); // Bottom Left glVertex3f( 1.0f,-1.0f, 0.0f); // Bottom Right glEnd(); // Finished Drawing The Triangle How do I get the resulting translated vertexes for use in collision detection? Or will I have to manually apply the transform myself and thus doubling up the work? The reason I ask is that I wouldn't mind implementing display lists.

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  • How to make an object stay relative to another object

    - by Nick
    In the following example there is a guy and a boat. They have both a position, orientation and velocity. The guy is standing on the shore and would like to board. He changes his position so he is now standing on the boat. The boat changes velocity and orientation and heads off. My character however has a velocity of 0,0,0 but I would like him to stay onboard. When I move my character around, I would like to move as if the boat was the ground I was standing on. How do keep my character aligned properly with the boat? It is exactly like in World Of Warcraft, when you board a boat or zeppelin. This is my physics code for the guy and boat: this.velocity.addSelf(acceleration.multiplyScalar(dTime)); this.position.addSelf(this.velocity.clone().multiplyScalar(dTime)); The guy already has a reference to the boat he's standing on, and thus knows the boat's position, velocity, orientation (even matrices or quaternions can be used).

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  • Need help with implementing collision detection using the Separating Axis Theorem

    - by Eddie Ringle
    So, after hours of Googling and reading, I've found that the basic process of detecting a collision using SAT is: for each edge of poly A project A and B onto the normal for this edge if intervals do not overlap, return false end for for each edge of poly B project A and B onto the normal for this edge if intervals do not overlap, return false end for However, as many ways as I try to implement this in code, I just cannot get it to detect the collision. My current code is as follows: for (unsigned int i = 0; i < asteroids.size(); i++) { if (asteroids.valid(i)) { asteroids[i]->Update(); // Player-Asteroid collision detection bool collision = true; SDL_Rect asteroidBox = asteroids[i]->boundingBox; // Bullet-Asteroid collision detection for (unsigned int j = 0; j < player.bullets.size(); j++) { if (player.bullets.valid(j)) { Bullet b = player.bullets[j]; collision = true; if (b.x + (b.w / 2.0f) < asteroidBox.x - (asteroidBox.w / 2.0f)) collision = false; if (b.x - (b.w / 2.0f) > asteroidBox.x + (asteroidBox.w / 2.0f)) collision = false; if (b.y - (b.h / 2.0f) > asteroidBox.y + (asteroidBox.h / 2.0f)) collision = false; if (b.y + (b.h / 2.0f) < asteroidBox.y - (asteroidBox.h / 2.0f)) collision = false; if (collision) { bool realCollision = false; float min1, max1, min2, max2; // Create a list of vertices for the bullet CrissCross::Data::LList<Vector2D *> bullVerts; bullVerts.insert(new Vector2D(b.x - b.w / 2.0f, b.y + b.h / 2.0f)); bullVerts.insert(new Vector2D(b.x - b.w / 2.0f, b.y - b.h / 2.0f)); bullVerts.insert(new Vector2D(b.x + b.w / 2.0f, b.y - b.h / 2.0f)); bullVerts.insert(new Vector2D(b.x + b.w / 2.0f, b.y + b.h / 2.0f)); // Create a list of vectors of the edges of the bullet and the asteroid CrissCross::Data::LList<Vector2D *> bullEdges; CrissCross::Data::LList<Vector2D *> asteroidEdges; for (int k = 0; k < 4; k++) { int n = (k == 3) ? 0 : k + 1; bullEdges.insert(new Vector2D(bullVerts[k]->x - bullVerts[n]->x, bullVerts[k]->y - bullVerts[n]->y)); asteroidEdges.insert(new Vector2D(asteroids[i]->vertices[k]->x - asteroids[i]->vertices[n]->x, asteroids[i]->vertices[k]->y - asteroids[i]->vertices[n]->y)); } for (unsigned int k = 0; k < asteroidEdges.size(); k++) { Vector2D *axis = asteroidEdges[k]->getPerpendicular(); min1 = max1 = axis->dotProduct(asteroids[i]->vertices[0]); for (unsigned int l = 1; l < asteroids[i]->vertices.size(); l++) { float test = axis->dotProduct(asteroids[i]->vertices[l]); min1 = (test < min1) ? test : min1; max1 = (test > max1) ? test : max1; } min2 = max2 = axis->dotProduct(bullVerts[0]); for (unsigned int l = 1; l < bullVerts.size(); l++) { float test = axis->dotProduct(bullVerts[l]); min2 = (test < min2) ? test : min2; max2 = (test > max2) ? test : max2; } delete axis; axis = NULL; if ( (min1 - max2) > 0 || (min2 - max1) > 0 ) { realCollision = false; break; } else { realCollision = true; } } if (realCollision == false) { for (unsigned int k = 0; k < bullEdges.size(); k++) { Vector2D *axis = bullEdges[k]->getPerpendicular(); min1 = max1 = axis->dotProduct(asteroids[i]->vertices[0]); for (unsigned int l = 1; l < asteroids[i]->vertices.size(); l++) { float test = axis->dotProduct(asteroids[i]->vertices[l]); min1 = (test < min1) ? test : min1; max1 = (test > max1) ? test : max1; } min2 = max2 = axis->dotProduct(bullVerts[0]); for (unsigned int l = 1; l < bullVerts.size(); l++) { float test = axis->dotProduct(bullVerts[l]); min2 = (test < min2) ? test : min2; max2 = (test > max2) ? test : max2; } delete axis; axis = NULL; if ( (min1 - max2) > 0 || (min2 - max1) > 0 ) { realCollision = false; break; } else { realCollision = true; } } } if (realCollision) { player.bullets.remove(j); int numAsteroids; float newDegree; srand ( j + asteroidBox.x ); if ( asteroids[i]->degree == 90.0f ) { if ( rand() % 2 == 1 ) { numAsteroids = 3; newDegree = 30.0f; } else { numAsteroids = 2; newDegree = 45.0f; } for ( int k = 0; k < numAsteroids; k++) asteroids.insert(new Asteroid(asteroidBox.x + (10 * k), asteroidBox.y + (10 * k), newDegree)); } delete asteroids[i]; asteroids.remove(i); } while (bullVerts.size()) { delete bullVerts[0]; bullVerts.remove(0); } while (bullEdges.size()) { delete bullEdges[0]; bullEdges.remove(0); } while (asteroidEdges.size()) { delete asteroidEdges[0]; asteroidEdges.remove(0); } } } } } } bullEdges is a list of vectors of the edges of a bullet, asteroidEdges is similar, and bullVerts and asteroids[i].vertices are, obviously, lists of vectors of each vertex for the respective bullet or asteroid. Honestly, I'm not looking for code corrections, just a fresh set of eyes.

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  • How to play the sound of an object sliding on another object for a variable duration

    - by Antoine
    I would like to add sound effects to a basic 2D game. For example, a stone sphere is rolling on wood surface. Let's say I have a 2 second audio recording of this. How could I use the sample to add sound for an arbitrary duration ? So far I have two solutions in mind: a/ record the sound for an amount of time that is greater than the maximum expected duration, and play only a part of it; b/ extract a small portion of the sample and play it in a loop for the duration of the move; however I'm not sure if it makes sense with an audio wave.

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  • What is the best way to implement collision detection using Bullet physics engine and a track generated from a curve?

    - by tigrou
    I am developing a small racing game were the track is generated from a curve. As said above, the track is generated, but not infinite. The track of one level could fit with no problem in memory and will contain a reasonably small amount of triangles. For collisions, I would like to use Bullet physics engine and know what is the best way to handle collisions with the track efficiently. NOTE : The track will be stored as a static rigid body (mass = 0). The player will be represented by a sphere shape for collisions. Here is some possibilities i have in mind : Create one rigid body, then, put all triangles of the track (except non collidable stuff) into it. Result : 1 body with many triangles (eg : 30000 triangles) Split the track into several sections (eg: 10 sections). Then, for each section, create a rigid body and put corresponding triangles in it. Result : small amount of bodies with relatively small amount of triangles (eg : 1500 triangles per section). Split the track into many sub-sections (eg : 1200 sections). Here one subsection = very small step when generating the curve. Again for each sub-section, create a body and put triangles in it. Result : many bodies with very small amount of triangles (eg : 20 triangles). Advantage : it could be possible to "extra data" to each of the subsection, that could be used when handling collisions. Same as 2, but only put sections N and N+1 in physics engine (where N = current section where the player is). When player reach section N+1, unload section N and load section N+2 and so on... Issue : harder to implement, problems if the player suddenly "jump" from one section to another (eg : player fly away from section N, and fall on section N + 4 that was underneath : no collision handled, player will fall into void ) Same as 4, but with many sub-sections. Issues : since subsections are very small there will be constantly new bodies added and removed to physics engine at runtime. Possibilities for player to accidently skip some sections and fall into the void are higher than 4.

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