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Is this the most effect simple way to display a moving image? SDL2

- by user36324

I've looked around for tutorials on SDL2, but there isnt many so I am curious i was messing around and is this an effective way to move an image. One problem is that it drags along the image to where it moves. #include "SDL.h" #include "SDL_image.h" int main(int argc, char* argv[]) { bool exit = false; SDL_Init(SDL_INIT_EVERYTHING); SDL_Window *win = SDL_CreateWindow("Hello World!", 100, 100, 640, 480, SDL_WINDOW_SHOWN); SDL_Renderer *ren = SDL_CreateRenderer(win, -1, SDL_RENDERER_ACCELERATED | SDL_RENDERER_PRESENTVSYNC); SDL_Surface *png = IMG_Load("character.png"); SDL_Rect src; src.x = 0; src.y = 0; src.w = 161; src.h = 159; SDL_Rect dest; dest.x = 50; dest.y = 50; dest.w = 161; dest.h = 159; SDL_Texture *tex = SDL_CreateTextureFromSurface(ren, png); SDL_FreeSurface(png); while(exit==false){ dest.x++; SDL_RenderClear(ren); SDL_RenderCopy(ren, tex, &src, &dest); SDL_RenderPresent(ren); } SDL_Delay(5000); SDL_DestroyTexture(tex); SDL_DestroyRenderer(ren); SDL_DestroyWindow(win); SDL_Quit(); }

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Implementing my Entity System. Questions about some problems I have found.

- by Notbad

Hi!, Well during this week I have deciding about implementation of my entity system. It is a big topic so it has been difficult to take one option from the whole. This has been my decision: 1) I don't have an entity class it is just an id. 2) I have systems that contain a list of components (the list is homegenous, I mean, RenderSystem will just have RenderComponents). 3) Compones will be just data. 4) There would be some kind of "entity prototypes" in a manager or something from we will create entity instances.Ideally they will define the type of components it has and initialization data. 5) Prototype code to create an entity (this is from the top of my head): int id=World::getInstance()->createEntity("entity template"); 6) This will notify all systems that a new entity has been created, and if the entity needs a component that the system handles it will add it to the entity. Ok, this are the ideas. Let's see if some can help with the problems: 1) The main problem is this templates that are sent to the systems in creation process to populate the entity with needed components. What would you use, an OR(ed) int?, a list of strings?. 2) How to do initialization for components when the entity has been created? How to store this in the template? I have thought about having a function in the template that is virtual and after entity is created an populated, gets the components and sets initialization values. 3) Don't you think this is a lot of work for just an entity creation?. Sorry for the long post, I have tried to expose my ideas and finding in order other could have a start beside exposing my problems. Thanks in advance, Notbad.

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How do you proactively guard against errors of omission?

- by Gabriel

I'll preface this with I don't know if anyone else who's been programming as long as I have actually has this problem, but at the very least, the answer might help someone with less xp. I just stared at this code for 5 minutes, thinking I was losing my mind that it didn't work: var usedNames = new HashSet<string>(); Func<string, string> l = (s) => { for (int i = 0; ; i++) { var next = (s + i).TrimEnd('0'); if (!usedNames.Contains(next)) { return next; } } }; Finally I noticed I forgot to add the used name to the hash set. Similarly, I've spent minutes upon minutes over omitting context.SaveChanges(). I think I get so distracted by the details that I'm thinking about that some really small details become invisible to me - it's almost at the level of mental block. Are there tactics to prevent this? update: a side effect of asking this was fixing the error it would have for i 9 (Thanks!) var usedNames = new HashSet<string>(); Func<string, string> name = (s) => { string result = s; if(usedNames.Contains(s)) for (int i = 1; ; result = s + i++) if (!usedNames.Contains(result)) break; usedNames.Add(result); return result; };

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One-way platform collision

- by TheBroodian

I hate asking questions that are specific to my own code like this, but I've run into a pesky roadblock and could use some help getting around it. I'm coding floating platforms into my game that will allow a player to jump onto them from underneath, but then will not allow players to fall through them once they are on top, which require some custom collision detection code. The code I have written so far isn't working, the character passes through it on the way up, and on the way down, stops for a moment on the platform, and then falls right through it. Here is the code to handle collisions with floating platforms: protected void HandleFloatingPlatforms(Vector2 moveAmount) { //if character is traveling downward. if (moveAmount.Y > 0) { Rectangle afterMoveRect = collisionRectangle; afterMoveRect.Offset((int)moveAmount.X, (int)moveAmount.Y); foreach (World_Objects.GameObject platform in gameplayScreen.Entities) { if (platform is World_Objects.Inanimate_Objects.FloatingPlatform) { //wideProximityArea is just a rectangle surrounding the collision //box of an entity to check for nearby entities. if (wideProximityArea.Intersects(platform.CollisionRectangle) || wideProximityArea.Contains(platform.CollisionRectangle)) { if (afterMoveRect.Intersects(platform.CollisionRectangle)) { //This, in my mind would denote that after the character is moved, its feet have fallen below the top of the platform, but before he had moved its feet were above it... if (collisionRectangle.Bottom <= platform.CollisionRectangle.Top) { if (afterMoveRect.Bottom > platform.CollisionRectangle.Top) { //And then after detecting that he has fallen through the platform, reposition him on top of it... worldLocation.Y = platform.CollisionRectangle.Y - frameHeight; hasCollidedVertically = true; } } } } } } } } In case you are curious, the parameter moveAmount is found through this code: elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds; float totalX = 0; float totalY = 0; foreach (Vector2 vector in velocities) { totalX += vector.X; totalY += vector.Y; } velocities.Clear(); velocity.X = totalX; velocity.Y = totalY; velocity.Y = Math.Min(velocity.Y, 1000); Vector2 moveAmount = velocity * elapsed;

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Facing a character towards the mouse

- by ratata

I'm trying to port a simple 2d top down shooter game from C++(Allegro) to Java and i'm having problems with rotating my character. Here's the code i used in c++ if (keys[A]) RotateRight(player, degree); if (keys[D]) RotateLeft(player, degree); void RotateLeft(Player& player, float& degree) { degree += player.rotatingSpeed; if ( degree >= 360 ) degree = 0; } void RotateRight(Player& player, float& degree) { degree -= player.rotatingSpeed; if ( degree <= 0) degree = 360; } And this is what i have in render section: al_draw_rotated_bitmap(player.image, player.frameWidth / 2, player.frameHeight / 2, player.x, player.y, degree * 3.14159 / 180, 0); Instead of using A-D keys i want to use mouse this time. I've been searching since last night and came up to few sample codes however noone of them worked. For example this just made my character to circle around the map: int centerX = width / 2; int centerY = height / 2; double angle = Math.atan2(centerY - mouseY, centerX - mouseX) - Math.PI / 2; ((Graphics2D)g).rotate(angle, centerX, centerY); g.fillRect(...); // draw your rectangle Any help is much appreciated.

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Text on a model

- by alecnash

I am trying to put some text on a Model and I want it to be dynamic. Did some research and came up with drawing the text on the texture and then set it on the model. I use something like this: public static Texture2D SpriteFontTextToTexture(SpriteFont font, string text, Color backgroundColor, Color textColor) { Size = font.MeasureString(text); RenderTarget2D renderTarget = new RenderTarget2D(GraphicsDevice, (int)Size.X, (int)Size.Y); GraphicsDevice.SetRenderTarget(renderTarget); GraphicsDevice.Clear(Color.Transparent); Spritbatch.Begin(); //have to redo the ColorTexture Spritbatch.Draw(ColorTexture.Create(GraphicsDevice, 1024, 1024, backgroundColor), Vector2.Zero, Color.White); Spritbatch.DrawString(font, text, Vector2.Zero, textColor); Spritbatch.End(); GraphicsDevice.SetRenderTarget(null); return renderTarget; } When I was working with primitives and not models everything worked fine because I set the texture exactly where I wanted but with the model (RoundedRect 3D button). It now looks like that: Is there a way to have the text centered only on one side?

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Using ConcurrentQueue for thread-safe Performance Bookkeeping.

- by Strenium

Just a small tidbit that's sprung up today. I had to book-keep and emit diagnostics for the average thread performance in a highly-threaded code over a period of last X number of calls and no more. Need of the day: a thread-safe, self-managing stats container. Since .NET 4.0 introduced new thread-safe 'Collections.Concurrent' objects and I've been using them frequently - the one in particular seemed like a good fit for storing each threads' performance data - ConcurrentQueue. But I wanted to store only the most recent X# of calls and since the ConcurrentQueue currently does not support size constraint I had to come up with my own generic version which attempts to restrict usage to numeric types only: unfortunately there is no IArithmetic-like interface which constrains to only numeric types – so the constraints here here aren't as elegant as they could be. (Note the use of the Average() method, of course you can use others as well as make your own). FIFO FixedSizedConcurrentQueue using System;using System.Collections.Concurrent;using System.Linq; namespace xxxxx.Data.Infrastructure{ [Serializable] public class FixedSizedConcurrentQueue<T> where T : struct, IConvertible, IComparable<T> { private FixedSizedConcurrentQueue() { } public FixedSizedConcurrentQueue(ConcurrentQueue<T> queue) { _queue = queue; } ConcurrentQueue<T> _queue = new ConcurrentQueue<T>(); public int Size { get { return _queue.Count; } } public double Average { get { return _queue.Average(arg => Convert.ToInt32(arg)); } } public int Limit { get; set; } public void Enqueue(T obj) { _queue.Enqueue(obj); lock (this) { T @out; while (_queue.Count > Limit) _queue.TryDequeue(out @out); } } } } The usage case is straight-forward, in this case I’m using a FIFO queue of maximum size of 200 to store doubles to which I simply Enqueue() the calculated rates: Usage var RateQueue = new FixedSizedConcurrentQueue<double>(new ConcurrentQueue<double>()) { Limit = 200 }; /* greater size == longer history */ That’s about it. Happy coding!

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How do functional languages handle a mocking situation when using Interface based design?

- by Programmin Tool

Typically in C# I use dependency injection to help with mocking; public void UserService { public UserService(IUserQuery userQuery, IUserCommunicator userCommunicator, IUserValidator userValidator) { UserQuery = userQuery; UserValidator = userValidator; UserCommunicator = userCommunicator; } ... public UserResponseModel UpdateAUserName(int userId, string userName) { var result = UserValidator.ValidateUserName(userName) if(result.Success) { var user = UserQuery.GetUserById(userId); if(user == null) { throw new ArgumentException(); user.UserName = userName; UserCommunicator.UpdateUser(user); } } ... } ... } public class WhenGettingAUser { public void AndTheUserDoesNotExistThrowAnException() { var userQuery = Substitute.For<IUserQuery>(); userQuery.GetUserById(Arg.Any<int>).Returns(null); var userService = new UserService(userQuery); AssertionExtensions.ShouldThrow<ArgumentException>(() => userService.GetUserById(-121)); } } Now in something like F#: if I don't go down the hybrid path, how would I test workflow situations like above that normally would touch the persistence layer without using Interfaces/Mocks? I realize that every step above would be tested on its own and would be kept as atomic as possible. Problem is that at some point they all have to be called in line, and I'll want to make sure everything is called correctly.

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Extension objects pattern

- by voroninp

In this MSDN Magazine article Peter Vogel describes Extension Objects partten. What is not clear is whether extensions can be later implemented by client code residing in a separate assembly. And if so how in this case can extension get acces to private members of the objet being extended? I quite often need to set different access levels for different classes. Sometimes I really need that descendants does not have access to the mebmer but separate class does. (good old friend classes) Now I solve this in C# by exposing callback properties in interface of the external class and setting them with private methods. This also alows to adjust access: read only or read|write depending on the desired interface. class Parent { private int foo; public void AcceptExternal(IFoo external) { external.GetFooCallback = () => this.foo; } } interface IFoo { Func<int> GetFooCallback {get;set;} } Other way is to explicitly implement particular interface. But I suspect more aspproaches exist.

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Throwing and catching exceptions in the same function/method

- by usr

I've written a function that asks a user for input until user enters a positive integer (a natural number). Somebody said I shouldn't throw and catch exceptions in my function and should let the caller of my function handle them. I wonder what other developers think about this. I'm also probably misusing exceptions in the function. Here's the code in Java: private static int sideInput() { int side = 0; String input; Scanner scanner = new Scanner(System.in); do { System.out.print("Side length: "); input = scanner.nextLine(); try { side = Integer.parseInt(input); if (side <= 0) { // probably a misuse of exceptions throw new NumberFormatException(); } } catch (NumberFormatException numFormExc) { System.out.println("Invalid input. Enter a natural number."); } } while (side <= 0); return side; } I'm interested in two things: Should I let the caller worry about exceptions? The point of the function is that it nags the user until the user enters a natural number. Is the point of the function bad? I'm not talking about UI (user not being able to get out of the loop without proper input), but about looped input with exceptions handled. Would you say the throw statement (in this case) is a misuse of exceptions? I could easily create a flag for checking validity of the number and output the warning message based on that flag. But that would add more lines to the code and I think it's perfectly readable as it is. The thing is I often write a separate input function. If user has to input a number multiple times, I create a separate function for input that handles all formatting exceptions and limitations.

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Crash when trying to detect touch

- by iQue

I've got a character in a 2D game using surfaceView that I want to be able to move using a button (eventually a joystick), but my game crashes as soon as I try to move my sprite. This is my onTouch-method for my steering button: public void handleActionDown(int eventX, int eventY) { if (eventX >= (x - bitmap.getWidth() / 2) && (eventX <= (x + bitmap.getWidth()/2))) { if (eventY >= (y - bitmap.getHeight() / 2) && (y <= (y + bitmap.getHeight() / 2))) { setTouched(true); } else { setTouched(false); } } else { setTouched(false); } And if I try to put this in my update-method: public void update() { x += (speed.getXv() * speed.getxDirection()); y += (speed.getYv() * speed.getyDirection()); } The sprite moves on its own just fine, but as soon as I add: public void update() { if(steering.isTouched()){ x += (speed.getXv() * speed.getxDirection()); y += (speed.getYv() * speed.getyDirection()); } the game crashes. Does anyone know why this is or how to fix it? I cannot figure it out. I'm using MotionEvent.ACTION_DOWN to check if the user if pressing the screen.

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Should this code/logic be included in Business Objects class or a separate class?

- by aspdotnetuser

I have created a small application which has a three tier architecture and I have business object classes to represent entities such as User, Orders, UserType etc. In these classes I have methods that are executed when the Constuctor method of, for example, User is called. These methods perform calculations and generate details that setup data for attributes that are part of each User object. Here is the structure for the project in Visual Studio: Here is some code from the business object class User.cs: Public Class User { public string Name { get; set; } public int RandomNumber { get; set; } etc public User { Name = GetName(); RandomNumber = GetRandomNumber(); } public string GetName() { .... return name; } public int GetRandomNumber() { ... return randomNumber; } } Should this logic be included in the Business Object classes or should it be included in a Utilities class of some kind? Or in the business rules?

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Where we should put validation for domain model

- by adisembiring

I still looking best practice for domain model validation. Is that good to put the validation in constructor of domain model ? my domain model validation example as follows: public class Order { private readonly List<OrderLine> _lineItems; public virtual Customer Customer { get; private set; } public virtual DateTime OrderDate { get; private set; } public virtual decimal OrderTotal { get; private set; } public Order (Customer customer) { if (customer == null) throw new ArgumentException("Customer name must be defined"); Customer = customer; OrderDate = DateTime.Now; _lineItems = new List<LineItem>(); } public void AddOderLine //.... public IEnumerable<OrderLine> AddOderLine { get {return _lineItems;} } } public class OrderLine { public virtual Order Order { get; set; } public virtual Product Product { get; set; } public virtual int Quantity { get; set; } public virtual decimal UnitPrice { get; set; } public OrderLine(Order order, int quantity, Product product) { if (order == null) throw new ArgumentException("Order name must be defined"); if (quantity <= 0) throw new ArgumentException("Quantity must be greater than zero"); if (product == null) throw new ArgumentException("Product name must be defined"); Order = order; Quantity = quantity; Product = product; } } Thanks for all of your suggestion.

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3d point cloud render from x,y,z 2d array with texture

- by user1733628

Need some direction on 3d point cloud display using OpenGL in c++ (vs2008). I am brand new to OpenGL and trying to do a 3d point cloud display with a texture. I have 3 2D arrays (each same size 1024x512) representing x,y,z of each point. I think I am on the right track with glBegin(GL_POLYGON); for(int i=0; i<1024; i++) { for(int j=0; j<512; j++) { glVertex3f(x[i][j], y[i][j], z[i][j]); } } glEnd(); Now this loads all the vertices in the buffer (I think) but from here I am not sure how to proceed. Or I am completely wrong here. Then I have another 2D array (same size) that contains color data (values from 0-255) that I want to use as texture on the 3D point cloud and display. I understand that this maybe a very basic OpenGL implementation for some but for me this is a huge learning curve. So any pointers, nudge or kick in the right direction will be appreciated.

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Following a set of points?

- by user1010005

Lets assume that i have a set of path that an entity should follow : const int Paths = 2 Vector2D<float> Path[Paths] = { Vector2D(100,0),Vector2D(100,50) }; Now i define my entity's position in a 2D vector as follows : Vector2D<float> FollowerPosition(0,0); And now i would like to move the "follower" to the path at index 1 : int PathPosition = 0; //Start with path 1 Currently i do this : Vector2D<float>& Target = Path[PathPosition]; bool Changed = false; if (FollowerPosition.X < Target.X) FollowerPosition.X += Vel,Changed = true; if (FollowerPosition.X > Target.X) FollowerPosition.X -= Vel,Changed = true; if (FollowerPosition.Y < Target.Y) FollowerPosition.Y += Vel;,Changed = true; if (FollowerPosition.Y > Target.Y) FollowerPosition.Y -= Vel,Changed = true; if (!Changed) { PathPosition = PathPosition + 1; if (PathPosition > Paths) PathPosition = 0; } Which works except for one little detail : The movement is not smooth!! ...So i would like to ask if anyone sees anything wrong with my code. Thanks and sorry for my english.

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What is wrong with my speculair phong shading

- by Thijser

I'm sorry if this should be placed on stackoverflow instead however seeing as this is graphics related I was hoping you guys could help me: I'm attempting to write a phong shader and currently working on the specular. I came acros the following formula: base*pow(dot(V,R),shininess) and attempted to implement it (V is the posion of the viewer and R the reflective vector). This gave the following result and code: Vec3Df phongSpecular(const Vec3Df & vertexPos, Vec3Df & normal, const Vec3Df & lightPos, const Vec3Df & cameraPos, unsigned int index) { Vec3Df relativeLightPos=(lightPos-vertexPos); relativeLightPos.normalize(); Vec3Df relativeCameraPos= (cameraPos-vertexPos); relativeCameraPos.normalize(); int DotOfNormalAndLight = Vec3Df::dotProduct(normal,relativeLightPos); Vec3Df reflective =(relativeLightPos-(2*DotOfNormalAndLight*normal))*-1; reflective.normalize(); float phongyness= Vec3Df::dotProduct(reflective,relativeCameraPos); if (phongyness<0){ phongyness=0; } float shininess= Shininess[index]; float speculair = powf(phongyness,shininess); return Ks[index]*speculair; } I'm looking for something more like this:

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SDL_DisplayFormat works, but not SDL_DisplayFormatAlpha

- by Bounderby

The following code is intended to display a green square on a black background. It executes, but the green square does not show up. However, if I change SDL_DisplayFormatAlpha to SDL_DisplayFormat the square is rendered correctly. So what don't I understand? It seems to me that I am creating *surface with an alpha mask and I am using SDL_MapRGBA to map my green color, so it would be consistent to use SDL_DisplayFormatAlpha as well. (I removed error-checking for clarity, but none of the SDL API calls fail in this example.) #include <SDL.h> int main(int argc, const char *argv[]) { SDL_Init( SDL_INIT_EVERYTHING ); SDL_Surface *screen = SDL_SetVideoMode( 640, 480, 32, SDL_HWSURFACE | SDL_DOUBLEBUF ); SDL_Surface *temp = SDL_CreateRGBSurface( SDL_HWSURFACE, 100, 100, 32, 0, 0, 0, ( SDL_BYTEORDER == SDL_BIG_ENDIAN ? 0x000000ff : 0xff000000 ) ); SDL_Surface *surface = SDL_DisplayFormatAlpha( temp ); SDL_FreeSurface( temp ); SDL_FillRect( surface, &surface->clip_rect, SDL_MapRGBA( screen->format, 0x00, 0xff, 0x00, 0xff ) ); SDL_Rect r; r.x = 50; r.y = 50; SDL_BlitSurface( surface, NULL, screen, &r ); SDL_Flip( screen ); SDL_Delay( 1000 ); SDL_Quit(); return 0; }

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opengl 3d point cloud render from x,y,z 2d array with texture

- by user1733628

Need some direction on 3d point cloud display using openGl in c++ (vs2008). I am brand new to openGl and trying to do a 3d point cloud display with a texture. I have 3 2D arrays (each same size 1024x512) representing x,y,z of each point. I think I am on the right track with glBegin(GL_POLYGON); for(int i=0; i<1024; i++) { for(int j=0; j<512; j++) { glVertex3f(x[i][j], y[i][j], z[i][j]); } } glEnd(); Now this loads all the vertices in the buffer (i think) but from here I am not sure how to proceed. Or I am completely wrong here. Then I have another 2D array (same size) that contains color data (values from 0-255) that I want to use as texture on the 3D point cloud and display. I understand that this maybe a very basic opengl implementation for some but for me this is a huge learning curve. So any pointers, nudge or kick in the right direction will be appreciated.

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String on a model

- by alecnash

I am trying to put a sting on a Model and I want it to be dynamic. Did some research and came up with drawing the text on the texture and then set it on the model. I use something like this: public static Texture2D SpriteFontTextToTexture(SpriteFont font, string text, Color backgroundColor, Color textColor) { Size = font.MeasureString(text); RenderTarget2D renderTarget = new RenderTarget2D(GraphicsDevice, (int)Size.X, (int)Size.Y); GraphicsDevice.SetRenderTarget(renderTarget); GraphicsDevice.Clear(Color.Transparent); Spritbatch.Begin(); //have to redo the ColorTexture Spritbatch.Draw(ColorTexture.Create(GraphicsDevice, 1024, 1024, backgroundColor), Vector2.Zero, Color.White); Spritbatch.DrawString(font, text, Vector2.Zero, textColor); Spritbatch.End(); GraphicsDevice.SetRenderTarget(null); return renderTarget; } When I was working with primitives and not models everything worked fine because I set the texture exactly where I wanted but with the model (RoundedRect 3d button) it looks like that: Is there a way to have the text centered only on one side?

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Don’t string together XML

- by KyleBurns

XML has been a pervasive tool in software development for over a decade. It provides a way to communicate data in a manner that is simple to understand and free of platform dependencies. Also pervasive in software development is what I consider to be the anti-pattern of using string manipulation to create XML. This usually starts with a “quick and dirty” approach because you need an XML document and looks like (for all of the examples here, we’ll assume we’re writing the body of a method intended to take a Contact object and return an XML string): return string.Format("<Contact><BusinessName>{0}</BusinessName></Contact>", contact.BusinessName); In the code example, I created (or at least believe I created) an XML document representing a simple contact object in one line of code with very little overhead. Work’s done, right? No it’s not. You see, what I didn’t realize was that this code would be used in the real world instead of my fantasy world where I own all the data and can prevent any of it containing problematic values. If I use this code to create a contact record for the business “Sanford & Son”, any XML parser will be incapable of processing the data because the ampersand is special in XML and should have been encoded as &. Following the pattern that I have seen many times over, my next step as a developer is going to be to do what any developer in his right mind would do – instruct the user that ampersands are “bad” and they cannot be used without breaking computers. This may work in many cases and is often accompanied by logic at the UI layer of applications to block these “bad” characters, but sooner or later someone is going to figure out that other applications allow for them and will want the same. This often leads to the creation of “cleaner” functions that perform a replace on the strings for every special character that the person writing the function can think of. The cleaner function will usually grow over time as support requests reveal characters that were missed in the initial cut. Sooner or later you end up writing your own somewhat functional XML engine. I have never been told by anyone paying me to write code that they would like to buy a somewhat functional XML engine. My employer/customer’s needs have always been for something that may use XML, but ultimately is functionality that drives business value. I’m not going to build an XML engine. So how can I generate XML that is always well-formed without writing my own engine? Easy – use one of the ones provided to you for free! If you’re in a shop that still supports VB6 applications, you can use the DomDocument or MXXMLWriter object (of the two I prefer MXXMLWriter, but I’m not going to fully describe either here). For .Net Framework applications prior to the 3.5 framework, the code is a little more verbose than I would like, but easy once you understand what pieces are required: using (StringWriter sw = new StringWriter()) { using (XmlTextWriter writer = new XmlTextWriter(sw)) { writer.WriteStartDocument(); writer.WriteStartElement("Contact"); writer.WriteElementString("BusinessName", contact.BusinessName); writer.WriteEndElement(); // end Contact element writer.WriteEndDocument(); writer.Flush(); return sw.ToString(); } } Looking at that code, it’s easy to understand why people are drawn to the initial one-liner. Lucky for us, the 3.5 .Net Framework added the System.Xml.Linq.XElement object. This object takes away a lot of the complexity present in the XmlTextWriter approach and allows us to generate the document as follows: return new XElement("Contact", new XElement("BusinessName", contact.BusinessName)).ToString(); While it is very common for people to use string manipulation to create XML, I’ve discussed here reasons not to use this method and introduced powerful APIs that are built into the .Net Framework as an alternative. I’ve given a very simplistic example here to highlight the most basic XML generation task. For more information on the XmlTextWriter and XElement APIs, check out the MSDN library.

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Best Practice: What can be the hashCode() method implementation if custom field used in equals() method are null?

- by goodspeed

What is the best practice to return a value for hashCode() method if custom field used in equals are null ? I have a situation, where equals() override is implemented using custom fields. Usually it it is better to override hashCode() also using that custom fields used in equals(). But if all the custom fields used in equals() are null, then what would be the best implementation for hashCode()? Example: class Person { private String firstName; private String lastName; public String getFirstName() { return firstName; } public String getLastName() { return lastName; } @Override public boolean equals(Object object) { boolean result = false; if (object == null || object.getClass() != getClass()) { result = false; } else { Person person = (Person) object; if (this.firstName == person.getFirstName() && this.lastName == tiger.getLastName()) { result = true; } } return result; } @Override public int hashCode() { int hash = 3; if(this.firstName == null || this.lastName == null) { // <b>What is the best practice here, </b> // <b>is return super.hashCode() better ?</b> } hash = 7 * hash + this.firstName.hashCode(); hash = 7 * hash + this.lastName.hashCode(); return hash; } } is it required to check for null in hashCode() ? If yes, what should be returned if custom values are null ?

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Pointers inside a structure [on hold]

- by user3402552

I have the next program: #include<stdio.h> #include<stdlib.h> struct a { char *ch; char *str; }; int main() { struct a s1; char ptr[100]; int m, n; printf("\n Enter a string : "); gets(ptr); m = strlen(ptr); s1.ch = (char *)malloc(strlen(ptr) * sizeof(char)); if(s1.ch) { strcpy(s1.ch, ptr); } else { printf("\n Alocation failed!\n"); } printf("\n %s\n\n", s1.ch); while(*s1.ch) { printf(" %c", *(s1.ch)); s1.ch++; } printf("\n\n"); s1.ch = s1.ch - m; printf("\n\n\n %s \n\n", s1.ch); } Is this ok this program in this way ? I mean the pointers should not be initialized ? And if it is not ok, why compile it without errors?

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Grid collision - finding the location of an entity in each box

- by Gregg1989

I am trying to implement grid-based collision in a 2d game with moving circles. The canvas is 400x400 pixels. Below you can see the code for my Grid class. What I want it to do is check inside which box the entities are located and then run a collision check if there are 2 or more entities in the same box. Right now I do not know how to find the position of an entity in a specific box. I know there are many tutorials online, but I haven't been able to find an answer to my question, because they are either written in C/C++ or use the 2d array approach. Code snippets and other help is greatly appreciated. Thanks. public class Grid { ArrayList<ArrayList<Entity>> boxes = new ArrayList<>(); double boxSize = 40; double boxesAmount = 10; ... ... public void checkBoxLocation(ArrayList<Entity> entities) { for (int i = 0; i < entities.size(); i++) { // Get top left coordinates of each entity double entityLeft = entities.get(i).getLayoutX() - entities.get(i).getRadius(); double entityTop = entities.get(i).getLayoutY() + entities.get(i).getRadius(); // Divide coordinate by box size to find the approximate location of the entity for (int j = 0; j < boxesAmount; j++) { //Select each box if ((entityLeft / boxSize <= j + 0.7) && (entityLeft / boxSize >= j)) { if ((entityTop / boxSize <= j + 0.7) && (entityTop / boxSize >= j)) { holdingBoxes.get(j).add(entities.get(i)); System.out.println("Entity " + entities.get(i) + " added to box " + j); } } } } } }

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strlen returns incorrect value when called in gdb

- by alesplin

So I'm noticing some severely incorrect behavior from calls to standard library functions inside GDB. I have the following program to illustrate: #include <stdio.h> #include <stdlib.h> #include <string.h> int main(int argc, char *argv[]) { char *s1 = "test"; char *s2 = calloc(strlen("test")+1,sizeof(char)); snprintf(s2,strlen("test")+1,"test"); printf("string constant: %lu\n", strlen(s1)); printf("allocated string: %lu\n", strlen(s2)); free(s2); return 0; } When run from the command-line, this program outputs just what you'd expect: string constant: 4 allocated string: 4 However, in GDB, I get the following, incorrect output from calls to strlen(): (gdb) p strlen(s1) $1 = -938856896 (gdb) p strlen(s2) $2 = -938856896 I'm pretty sure this is a problem with glibc shipped with Ubuntu (I'm using 10.10), but this is a serious problem for those of us who spend lots of time in GDB. Is anyone else experiencing this kind of error? What's the best way to fix it? Build glibc from source? (I'm already running a version of GDB built from source)

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Touchpad not working after login in Ubuntu

- by Maria Mateescu

At some point my touchpad stopped working on Lenovo x220 under Ubuntu 11.10, after login. I have found two possible solutions for that online, but neither of them work. First, gconftool-2 --set --type boolean /desktop/gnome/peripherals/touchpad/touchpad_enabled true and a second one, xinput set-int-prop "SynPS/2 Synaptics TouchPad" "Synaptics Off" 8 0 After looking more carefully into xinput I have realized that xinput list-props "SynPS/2 Synaptics TouchPad" outputs: Device Enabled (132): 0 This field seems to be stuck to zero, because trying to set it back to 1 by: xinput set-int-prop "SynPS/2 Synaptics TouchPad" "Device Enabled" 8 1 doesn't seem to have any effect, e.g. I still have: Device Enabled (132): 0 Any ideas? Thank you!

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