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• Two interfaces with identical signatures

  - by corsiKa

  I am attempting to model a card game where cards have two important sets of features: The first is an effect. These are the changes to the game state that happen when you play the card. The interface for effect is as follows: boolean isPlayable(Player p, GameState gs); void play(Player p, GameState gs); And you could consider the card to be playable if and only if you can meet its cost and all its effects are playable. Like so: // in Card class boolean isPlayable(Player p, GameState gs) { if(p.resource < this.cost) return false; for(Effect e : this.effects) { if(!e.isPlayable(p,gs)) return false; } return true; } Okay, so far, pretty simple. The other set of features on the card are abilities. These abilities are changes to the game state that you can activate at-will. When coming up with the interface for these, I realized they needed a method for determining whether they can be activated or not, and a method for implementing the activation. It ends up being boolean isActivatable(Player p, GameState gs); void activate(Player p, GameState gs); And I realize that with the exception of calling it "activate" instead of "play", Ability and Effect have the exact same signature. Is it a bad thing to have multiple interfaces with an identical signature? Should I simply use one, and have two sets of the same interface? As so: Set<Effect> effects; Set<Effect> abilities; If so, what refactoring steps should I take down the road if they become non-identical (as more features are released), particularly if they're divergent (i.e. they both gain something the other shouldn't, as opposed to only one gaining and the other being a complete subset)? I'm particularly concerned that combining them will be non-sustainable as soon as something changes. The fine print: I recognize this question is spawned by game development, but I feel it's the sort of problem that could just as easily creep up in non-game development, particularly when trying to accommodate the business models of multiple clients in one application as happens with just about every project I've ever done with more than one business influence... Also, the snippets used are Java snippets, but this could just as easily apply to a multitude of object oriented languages.

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• In a state machine, is it a good idea to separate states and transitions?

  - by codablank1

  I have implemented a small state machine in this way (in pseudo code): class Input {} class KeyInput inherits Input { public : enum { Key_A, Key_B, ..., } } class GUIInput inherits Input { public : enum { Button_A, Button_B, ..., } } enum Event { NewGame, Quit, OpenOptions, OpenMenu } class BaseState { String name; Event get_event (Input input); void handle (Event e); //event handling function } class Menu inherits BaseState{...} class InGame inherits BaseState{...} class Options inherits BaseState{...} class StateMachine { public : BaseState get_current_state () { return current_state; } void add_state (String name, BaseState state) { statesMap.insert(name, state);} //raise an exception if state not found BaseState get_state (String name) { return statesMap.find(name); } //raise an exception if state or next_state not found void add_transition (Event event, String state_name, String next_state_name) { BaseState state = get_state(state_name); BaseState next_state = get_state(next_state_name); transitionsMap.insert(pair<event, state>, next_state); } //raise exception if couple not found BaseState get_next_state(Event event, BaseState state) { return transitionsMap.find(pair<event, state>); } void handle(Input input) { Event event = current_state.get_event(input) current_state.handle(event); current_state = get_next_state(event, current_state); } private : BaseState current_state; map<String, BaseState> statesMap; //map of all states in the machine //for each couple event/state, this map stores the next state map<pair<Event, BaseState>, BaseState> transitionsMap; } So, before getting the transition, I need to convert the key input or GUI input to the proper event, given the current state; thus the same key 'W' can launch a new game in the 'Menu' state or moving forward a character in the 'InGame' state; Then I get the next state from the transitionsMap and I update the current state Does this configuration seem valid to you ? Is it a good idea to separate states and transitions ? And I have some kind of trouble to represent a 'null state' or a 'null event'; What initial value can I give to the current state and which one should be returned by get_state if it fails ?

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• Check if an object is facing another based on angles

  - by Isaiah

  I already have something that calculates the bearing angle to get one object to face another. You give it the positions and it returns the angle to get one to face the other. Now I need to figure out how tell if on object is facing toward another object within a specified field and I can't find any information about how to do this. The objects are obj1 and obj2. Their angles are at obj1.angle and obj2.angle. Their vectors are at obj1.pos and obj2.pos. It's in the format [x,y]. The angle to have one face directly at another is found with direction(obj1.pos,obj2.pos). I want to set the function up like this: isfacing(obj1,obj2,area){...} and return true/false depending if it's in the specified field area to the angle to directly see it. I've got a base like this: var isfacing = function (obj1,obj2,area){ var toface = direction(obj1.pos,obj2.pos); if(toface+area >= obj1.angle && ob1.angle >= toface-area){ return true; } return false; } But my problem is that the angles are in 360 degrees, never above 360 and never below 0. How can I account for that in this? If the first object's angle is say at 0 and say I subtract a field area of 20 or so. It'll check if it's less than -20! If I fix the -20 it becomes 340 but x < 340 isn't what I want, I'd have to x 340 in that case. Is there someone out there with more sleep than I that can help a new dev pulling an all-nighter just to get enemies to know if they're attacking in the right direction? I hope I'm making this harder than it seems. I'd just make them always face the main char if the producer didn't want attacks from behind to work while blocking. In which case I'll need the function above anyways. I've tried to give as much info as I can think would help. Also this is in 2d.

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• Deterministic Multiplayer RTS game questions?

  - by Martin K

  I am working on a cross-platform multiplayer RTS game where the different clients and a server(flash and C#), all need to stay deterministically synchronised. To deal with Floatpoint inconsistencies, I've come across this method: http://joshblog.net/2007/01/30/flash-floating-point-number-errors/#comment-49912 which basically truncates off the nondeterministic part: return Math.round(1000 * float) / 1000; Howewer my concern is that every time there is a division, there is further chance of creating additional floatpoint errors, in essence making it worse? . So it occured to me, how about something like this: function floatSafe(number:Number) : Number {return Math.round(float* 1024) / 1024; } ie dividing with only powers of 2 ? What do you think? . Ironically with the above method I got less accurate results: trace( floatSafe(3/5) ) // 0.599609375 where as with the other method(dividing with 1000), or just tracing the raw value I am getting 3/5 = 0.6 or Maybe thats what 3/5 actually is, IE 0.6 cannot really be represented with a floatpoint datatype, and would be more consistent across different platforms?

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• What is the proper jargon to refer to a variable wrapped inside a function closure?

  - by Rice Flour Cookies

  In JavaScript, there is no such thing as a "private" variable. In order to achieve encapsulation and information hiding in JavaScript, I can wrap a variable inside a function closure, like so: var counter = (function() { var i = 0; var fn = {}; fn.increment = function() { i++; }; fn.get = function() { return i; }; return fn; {)(); counter.increment(); counter.increment(); alert(counter.get()); // alerts '2' Since I don't call i a private variable in JavaScript, what do I call it?

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• Pixel perfect collision with paths (Android)

  - by keysersoze

  Hi I'm writing a game and I'm trying to do some pixel perfect collisions with paths. The player's character has a bitmask which looks for example like this: Currenly my code that handles player's collision with path looks like this: private boolean isTerrainCollisionDetected() { if(collisionRegion.op(player.getBounds(), terrain.getBottomPathBounds(), Region.Op.INTERSECT) || collisionRegion.op(player.getBounds(), terrain.getTopPathBounds(), Region.Op.INTERSECT)) { collisionRegion.getBounds(collisionRect); for(int i = collisionRect.left; i < collisionRect.right; i++) { for(int j = collisionRect.top; j < collisionRect.bottom; j++) { if(player.getBitmask().getPixel(i - player.getX(), j - player.getY()) != Color.TRANSPARENT) { return true; } } } } return false; } The problem is that collisions aren't pixel perfect. It detects collisions in situations like this: The question is: what can I do to improve my collision detection?

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• How can I make a universal construction more efficient?

  - by VF1

  A "universal construction" is a wrapper class for a sequential object that enables it to be linearized (a strong consistency condition for concurrent objects). For instance, here's an adapted wait-free construction, in Java, from [1], which presumes the existence of a wait-free queue that satisfies the interface WFQ (which only requires one-time consensus between threads) and assumes a Sequential interface: public interface WFQ<T> // "FIFO" iteration { int enqueue(T t); // returns the sequence number of t Iterable<T> iterateUntil(int max); // iterates until sequence max } public interface Sequential { // Apply an invocation (method + arguments) // and get a response (return value + state) Response apply(Invocation i); } public interface Factory<T> { T generate(); } // generate new default object public interface Universal extends Sequential {} public class SlowUniversal implements Universal { Factory<? extends Sequential> generator; WFQ<Invocation> wfq = new WFQ<Invocation>(); Universal(Factory<? extends Sequential> g) { generator = g; } public Response apply(Invocation i) { int max = wfq.enqueue(i); Sequential s = generator.generate(); for(Invocation invoc : wfq.iterateUntil(max)) s.apply(invoc); return s.apply(i); } } This implementation isn't very satisfying, however, since it presumes determinism of a Sequential and is really slow. I attempted to add memory recycling: public interface WFQD<T> extends WFQ<T> { T dequeue(int n); } // dequeues only when n is the tail, else assists other threads public interface CopyableSequential extends Sequential { CopyableSequential copy(); } public class RecyclingUniversal implements Universal { WFQD<CopyableSequential> wfqd = new WFQD<CopyableSequential>(); Universal(CopyableSequential init) { wfqd.enqueue(init); } public Response apply(Invocation i) { int max = wfqd.enqueue(i); CopyableSequential cs = null; int ctr = max; for(CopyableSequential csq : wfq.iterateUntil(max)) if(--max == 0) cs = csq.copy(); wfqd.dequeue(max); return cs.apply(i); } } Here are my specific questions regarding the extension: Does my implementation create a linearizable multi-threaded version of a CopyableSequential? Is it possible extend memory recycling without extending the interface (perhaps my new methods trivialize the problem)? My implementation only reduces memory when a thread returns, so can this be strengthened? [1] provided an implementation for WFQ<T>, not WFQD<T> - one does exist, though, correct? [1] Herlihy and Shavit, The Art of Multiprocessor Programming.

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• Why won't my vertex buffer render in GLFW3?

  - by sm81095

  I have started to try to learn OpenGL, and I decided to use GLFW to assist in window creation. The problem is, since GLFW3 is so new, there are no tutorials on it or how to use it with modern OpenGL (3.3, specifically). Using the GLFW3 tutorial found on the website, which uses older OpenGL rendering (glBegin(GL_TRIANGLES), glVertex3f(), and such), I can get a triangle to render to the screen. The problem is, using new OpenGL, I can't get the same triangle to render to the screen. I am new to OpenGL, and GLFW3 is new to most people, so I may be completely missing something obvious, but here is my code: static const GLuint g_vertex_buffer_data[] = { -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, 0.0f, 1.0f, 0.0f }; int main(void) { GLFWwindow* window; if(!glfwInit()) { fprintf(stderr, "Failed to initialize GLFW."); return -1; } glfwWindowHint(GLFW_SAMPLES, 4); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); window = glfwCreateWindow(800, 600, "Test Window", NULL, NULL); if(!window) { glfwTerminate(); fprintf(stderr, "Failed to create a GLFW window"); return -1; } glfwMakeContextCurrent(window); glewExperimental = GL_TRUE; GLenum err = glewInit(); if(err != GLEW_OK) { glfwTerminate(); fprintf(stderr, "Failed to initialize GLEW"); fprintf(stderr, (char*)glewGetErrorString(err)); return -1; } GLuint VertexArrayID; glGenVertexArrays(1, &VertexArrayID); glBindVertexArray(VertexArrayID); GLuint programID = LoadShaders("SimpleVertexShader.glsl", "SimpleFragmentShader.glsl"); GLuint vertexBuffer; glGenBuffers(1, &vertexBuffer); glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer); glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW); while(!glfwWindowShouldClose(window)) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glUseProgram(programID); glEnableVertexAttribArray(0); glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0); glDrawArrays(GL_TRIANGLES, 0, 3); glDisableVertexAttribArray(0); glfwSwapBuffers(window); glfwPollEvents(); } glDeleteBuffers(1, &vertexBuffer); glDeleteProgram(programID); glfwDestroyWindow(window); glfwTerminate(); exit(EXIT_SUCCESS); } I know it is not my shaders, they are super simple and I've checked them against GLFW 2.7 so I know that they work. I'm assuming that I've missed something crucial to using the OpenGL context with GLFW3, so any help locating the problem would be greatly appreciated.

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• Why enumerator structs are a really bad idea (redux)

  - by Simon Cooper

  My previous blog post went into some detail as to why calling MoveNext on a BCL generic collection enumerator didn't quite do what you thought it would. This post covers the Reset method. To recap, here's the simple wrapper around a linked list enumerator struct from my previous post (minus the readonly on the enumerator variable): sealed class EnumeratorWrapper : IEnumerator<int> { private LinkedList<int>.Enumerator m_Enumerator; public EnumeratorWrapper(LinkedList<int> linkedList) { m_Enumerator = linkedList.GetEnumerator(); } public int Current { get { return m_Enumerator.Current; } } object System.Collections.IEnumerator.Current { get { return Current; } } public bool MoveNext() { return m_Enumerator.MoveNext(); } public void Reset() { ((System.Collections.IEnumerator)m_Enumerator).Reset(); } public void Dispose() { m_Enumerator.Dispose(); } } If you have a look at the Reset method, you'll notice I'm having to cast to IEnumerator to be able to call Reset on m_Enumerator. This is because the implementation of LinkedList<int>.Enumerator.Reset, and indeed of all the other Reset methods on the BCL generic collection enumerators, is an explicit interface implementation. However, IEnumerator is a reference type. LinkedList<int>.Enumerator is a value type. That means, in order to call the reset method at all, the enumerator has to be boxed. And the IL confirms this: .method public hidebysig newslot virtual final instance void Reset() cil managed { .maxstack 8 L_0000: nop L_0001: ldarg.0 L_0002: ldfld valuetype [System]System.Collections.Generic.LinkedList`1/Enumerator<int32> EnumeratorWrapper::m_Enumerator L_0007: box [System]System.Collections.Generic.LinkedList`1/Enumerator<int32> L_000c: callvirt instance void [mscorlib]System.Collections.IEnumerator::Reset() L_0011: nop L_0012: ret } On line 0007, we're doing a box operation, which copies the enumerator to a reference object on the heap, then on line 000c calling Reset on this boxed object. So m_Enumerator in the wrapper class is not modified by the call the Reset. And this is the only way to call the Reset method on this variable (without using reflection). Therefore, the only way that the collection enumerator struct can be used safely is to store them as a boxed IEnumerator<T>, and not use them as value types at all.

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• Camera movement and threshold not working

  - by irish guy mcconagheh

  I have a platformer that is in progress, part of this has a camera which I only want to move when the character moves out of a certain threshold, to try to accomplish this I have the following if statement: if(((Mathf.Abs(target.transform.position.x))-(Mathf.Abs(transform.position.x)))>thres){ x = moveTo(transform.position.x, target.position.x, trackSpeed); } in unity/c#. In pseudocode it means if((absolute value of player x) - (absolute value of camera x) is greater than the threshold){ move { however this does not seem to work correctly. it appears to work for the first couple of times the threshold is reached, however the distance between the camera and the player has to increase every time for the camera to move. I do not believe the movement of the camera is the problem, however the code for it is as follows: private float moveTo(float n, float target, float accel) { if (n == target) { return n; } else { float dir = Mathf.Sign(target - n); n += accel * Time.deltaTime * dir; return (dir == Mathf.Sign(target-n))? n: target; } } }

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• Enum types, FlagAttribute & Zero value

  - by nmgomes

  We all know about Enums types and use them every single day. What is not that often used is to decorate the Enum type with the FlagsAttribute. When an Enum type has the FlagsAttribute we can assign multiple values to it and thus combine multiple information into a single enum. The enum values should be a power of two so that a bit set is achieved. Here is a typical Enum type: public enum OperationMode { /// <summary> /// No operation mode /// </summary> None = 0, /// <summary> /// Standard operation mode /// </summary> Standard = 1, /// <summary> /// Accept bubble requests mode /// </summary> Parent = 2 } In such scenario no values combination are possible. In the following scenario a default operation mode exists and combination is used: [Flags] public enum OperationMode { /// <summary> /// Asynchronous operation mode /// </summary> Async = 0, /// <summary> /// Synchronous operation mode /// </summary> Sync = 1, /// <summary> /// Accept bubble requests mode /// </summary> Parent = 2 } Now, it’s possible to do statements like: [DefaultValue(OperationMode.Async)] [TypeConverter(typeof(EnumConverter))] public OperationMode Mode { get; set; } /// <summary> /// Gets a value indicating whether this instance supports request from childrens. /// </summary> public bool IsParent { get { return (this.Mode & OperationMode.Parent) == OperationMode.Parent; } } or switch (this.Mode) { case OperationMode.Sync | OperationMode.Parent: Console.WriteLine("Sync,Parent"); break;[…]  But there is something that you should never forget: Zero is the absorber element for the bitwise AND operation. So, checking for OperationMode.Async (the Zero value) mode just like the OperationMode.Parent mode makes no sense since it will always be true: (this.Mode & 0x0) == 0x0 Instead, inverse logic should be used: OperationMode.Async = !OperationMode.Sync public bool IsAsync { get { return (this.Mode & ContentManagerOperationMode.Sync) != ContentManagerOperationMode.Sync; } } or public bool IsAsync { get { return (int)this.Mode == 0; } } Final Note: Benefits Allow multiple values combination The above samples snippets were taken from an ASP.NET control and enabled the following markup usage: <my:Control runat="server" Mode="Sync,Parent"> Drawback Zero value is the absorber element for the bitwise AND operation Be very carefully when evaluating the Zero value, either evaluate the enum value as an integer or use inverse logic.

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• Is 2 lines of push/pop code for each pre-draw-state too many?

  - by Griffin

  I'm trying to simplify vector graphics management in XNA; currently by incorporating state preservation. 2X lines of push/pop code for X states feels like too many, and it just feels wrong to have 2 lines of code that look identical except for one being push() and the other being pop(). The goal is to eradicate this repetitiveness,and I hoped to do so by creating an interface in which a client can give class/struct refs in which he wants restored after the rendering calls. Also note that many beginner-programmers will be using this, so forcing lambda expressions or other advanced C# features to be used in client code is not a good idea. I attempted to accomplish my goal by using Daniel Earwicker's Ptr class: public class Ptr<T> { Func<T> getter; Action<T> setter; public Ptr(Func<T> g, Action<T> s) { getter = g; setter = s; } public T Deref { get { return getter(); } set { setter(value); } } } an extension method: //doesn't work for structs since this is just syntatic sugar public static Ptr<T> GetPtr <T> (this T obj) { return new Ptr<T>( ()=> obj, v=> obj=v ); } and a Push Function: //returns a Pop Action for later calling public static Action Push <T> (ref T structure) where T: struct { T pushedValue = structure; //copies the struct data Ptr<T> p = structure.GetPtr(); return new Action( ()=> {p.Deref = pushedValue;} ); } However this doesn't work as stated in the code. How might I accomplish my goal? Example of code to be refactored: protected override void RenderLocally (GraphicsDevice device) { if (!(bool)isCompiled) {Compile();} //TODO: make sure state settings don't implicitly delete any buffers/resources RasterizerState oldRasterState = device.RasterizerState; DepthFormat oldFormat = device.PresentationParameters.DepthStencilFormat; DepthStencilState oldBufferState = device.DepthStencilState; { //Rendering code } device.RasterizerState = oldRasterState; device.DepthStencilState = oldBufferState; device.PresentationParameters.DepthStencilFormat = oldFormat; }

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• Finding furthermost point in game world

  - by user13414

  I am attempting to find the furthermost point in my game world given the player's current location and a normalized direction vector in screen space. My current algorithm is: convert player world location to screen space multiply the direction vector by a large number (2000) and add it to the player's screen location to get the distant screen location convert the distant screen location to world space create a line running from the player's world location to the distant world location loop over the bounding "walls" (of which there are always 4) of my game world check whether the wall and the line intersect if so, where they intersect is the furthermost point of my game world in the direction of the vector Here it is, more or less, in code: public Vector2 GetFurthermostWorldPoint(Vector2 directionVector) { var screenLocation = entity.WorldPointToScreen(entity.Location); var distantScreenLocation = screenLocation + (directionVector * 2000); var distantWorldLocation = entity.ScreenPointToWorld(distantScreenLocation); var line = new Line(entity.Center, distantWorldLocation); float intersectionDistance; Vector2 intersectionPoint; foreach (var boundingWall in entity.Level.BoundingWalls) { if (boundingWall.Intersects(line, out intersectionDistance, out intersectionPoint)) { return intersectionPoint; } } Debug.Assert(false, "No intersection found!"); return Vector2.Zero; } Now this works, for some definition of "works". I've found that the further out my distant screen location is, the less chance it has of working. When digging into the reasons why, I noticed that calls to Viewport.Unproject could result in wildly varying return values for points that are "far away". I wrote this stupid little "test" to try and understand what was going on: [Fact] public void wtf() { var screenPositions = new Vector2[] { new Vector2(400, 240), new Vector2(400, -2000), }; var viewport = new Viewport(0, 0, 800, 480); var projectionMatrix = Matrix.CreatePerspectiveFieldOfView(MathHelper.PiOver4, viewport.Width / viewport.Height, 1, 200000); var viewMatrix = Matrix.CreateLookAt(new Vector3(400, 630, 600), new Vector3(400, 345, 0), new Vector3(0, 0, 1)); var worldMatrix = Matrix.Identity; foreach (var screenPosition in screenPositions) { var nearPoint = viewport.Unproject(new Vector3(screenPosition, 0), projectionMatrix, viewMatrix, worldMatrix); var farPoint = viewport.Unproject(new Vector3(screenPosition, 1), projectionMatrix, viewMatrix, worldMatrix); Console.WriteLine("For screen position {0}:", screenPosition); Console.WriteLine(" Projected Near Point = {0}", nearPoint.TruncateZ()); Console.WriteLine(" Projected Far Point = {0}", farPoint.TruncateZ()); Console.WriteLine(); } } The output I get on the console is: For screen position {X:400 Y:240}: Projected Near Point = {X:400 Y:629.571 Z:599.0967} Projected Far Point = {X:392.9302 Y:-83074.98 Z:-175627.9} For screen position {X:400 Y:-2000}: Projected Near Point = {X:400 Y:626.079 Z:600.7554} Projected Far Point = {X:390.2068 Y:-767438.6 Z:148564.2} My question is really twofold: what am I doing wrong with the unprojection such that it varies so wildly and, thus, does not allow me to determine the corresponding world point for my distant screen point? is there a better way altogether to determine the furthermost point in world space given a current world space location, and a directional vector in screen space?

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• OpenGL VertexBuffer won'e render in GLFW3

  - by sm81095

  So I have started to try to learn OpenGL, and I decided to use GLFW to assist in window creation. The problem is, since GLFW3 is so new, there are no tutorials on it yet and how to use it with modern OpenGL (3.3, specifically). Using the GLFW3 tutorial found on the website, which uses older OpenGL rendering (glBegin(GL_TRIANGLES), glVertex3f()), and such, I can get a triangle to render to the screen. The problem is, using new OpenGL, I can't get the same triangle to render to the screen. I am new to OpenGL, and GLFW3 is new to most people, so I may be completely missing something obvious, but here is my code: static const GLuint g_vertex_buffer_data[] = { -1.0f, -1.0f, 0.0f, 1.0f, -1.0f, 0.0f, 0.0f, 1.0f, 0.0f }; int main(void) { GLFWwindow* window; if(!glfwInit()) { fprintf(stderr, "Failed to initialize GLFW."); return -1; } glfwWindowHint(GLFW_SAMPLES, 4); glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3); glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3); glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE); glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE); window = glfwCreateWindow(800, 600, "Test Window", NULL, NULL); if(!window) { glfwTerminate(); fprintf(stderr, "Failed to create a GLFW window"); return -1; } glfwMakeContextCurrent(window); glewExperimental = GL_TRUE; GLenum err = glewInit(); if(err != GLEW_OK) { glfwTerminate(); fprintf(stderr, "Failed to initialize GLEW"); fprintf(stderr, (char*)glewGetErrorString(err)); return -1; } GLuint VertexArrayID; glGenVertexArrays(1, &VertexArrayID); glBindVertexArray(VertexArrayID); GLuint programID = LoadShaders("SimpleVertexShader.glsl", "SimpleFragmentShader.glsl"); GLuint vertexBuffer; glGenBuffers(1, &vertexBuffer); glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer); glBufferData(GL_ARRAY_BUFFER, sizeof(g_vertex_buffer_data), g_vertex_buffer_data, GL_STATIC_DRAW); while(!glfwWindowShouldClose(window)) { glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glUseProgram(programID); glEnableVertexAttribArray(0); glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, (void*)0); glDrawArrays(GL_TRIANGLES, 0, 3); glDisableVertexAttribArray(0); glfwSwapBuffers(window); glfwPollEvents(); } glDeleteBuffers(1, &vertexBuffer); glDeleteProgram(programID); glfwDestroyWindow(window); glfwTerminate(); exit(EXIT_SUCCESS); } I know it is not my shaders, they are super simple and I've checked them against GLFW 2.7 so I know that they work. I'm assuming that I've missed something crucial to using the OpenGL context with GLFW3, so any help locating the problem would be greatly appreciated.

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• Incorrect results for frustum cull

  - by DeadMG

  Previously, I had a problem with my frustum culling producing too optimistic results- that is, including many objects that were not in the view volume. Now I have refactored that code and produced a cull that should be accurate to the actual frustum, instead of an axis-aligned box approximation. The problem is that now it never returns anything to be in the view volume. As the mathematical support library I'm using does not provide plane support functions, I had to code much of this functionality myself, and I'm not really the mathematical type, so it's likely that I've made some silly error somewhere. As follows is the relevant code: class Plane { public: Plane() { r0 = Math::Vector(0,0,0); normal = Math::Vector(0,1,0); } Plane(Math::Vector p1, Math::Vector p2, Math::Vector p3) { r0 = p1; normal = Math::Cross((p2 - p1), (p3 - p1)); } Math::Vector r0; Math::Vector normal; }; This class represents one plane as a point and a normal vector. class Frustum { public: Frustum( const std::array<Math::Vector, 8>& points ) { planes[0] = Plane(points[0], points[1], points[2]); planes[1] = Plane(points[4], points[5], points[6]); planes[2] = Plane(points[0], points[1], points[4]); planes[3] = Plane(points[2], points[3], points[6]); planes[4] = Plane(points[0], points[2], points[4]); planes[5] = Plane(points[1], points[3], points[5]); } Plane planes[6]; }; The points are passed in order where (the inverse of) each bit of the index of each point indicates whether it's the left, top, and back of the frustum, respectively. As such, I just picked any three points where they all shared one bit in common to define the planes. My intersection test is as follows (based on this): bool Intersects(Math::AABB lhs, const Frustum& rhs) const { for(int i = 0; i < 6; i++) { Math::Vector pvertex = lhs.TopRightFurthest; Math::Vector nvertex = lhs.BottomLeftClosest; if (rhs.planes[i].normal.x <= -0.0f) { std::swap(pvertex.x, nvertex.x); } if (rhs.planes[i].normal.y <= -0.0f) { std::swap(pvertex.y, nvertex.y); } if (rhs.planes[i].normal.z <= -0.0f) { std::swap(pvertex.z, nvertex.z); } if (Math::Dot(rhs.planes[i].r0, nvertex) < 0.0f) { return false; } } return true; } Also of note is that because I'm using a left-handed co-ordinate system, I wrote my Cross function to return the negative of the formula given on Wikipedia. Any suggestions as to where I've made a mistake?

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• Drawing a texture at the end of a trace (crosshair?) UDK

  - by Dave Voyles

  I'm trying to draw a crosshair at the end of my trace. If my crosshair does not hit a pawn or static mesh (ex, just a skybox) then the crosshair stays locked on a certain point at that actor - I want to say its origin. Ex: Run across a pawn, then it turns yellow and stays on that pawn. If it runs across the skybox, then it stays at one point on the box. Weird? How can I get my crosshair to stay consistent? I've included two images for reference, to help illustrate. Note: The wrench is actually my crosshair. The "X" is just a debug crosshair. Ignore that. /// Image 1 /// /// Image 2 /// /*************************************************************************** * Draws the crosshair ***************************************************************************/ function bool CheckCrosshairOnFriendly() { local float CrosshairSize; local vector HitLocation, HitNormal, StartTrace, EndTrace, ScreenPos; local actor HitActor; local MyWeapon W; local Pawn MyPawnOwner; /** Sets the PawnOwner */ MyPawnOwner = Pawn(PlayerOwner.ViewTarget); /** Sets the Weapon */ W = MyWeapon(MyPawnOwner.Weapon); /** If we don't have an owner, then get out of the function */ if ( MyPawnOwner == None ) { return false; } /** If we have a weapon... */ if ( W != None) { /** Values for the trace */ StartTrace = W.InstantFireStartTrace(); EndTrace = StartTrace + W.MaxRange() * vector(PlayerOwner.Rotation); HitActor = MyPawnOwner.Trace(HitLocation, HitNormal, EndTrace, StartTrace, true, vect(0,0,0),, TRACEFLAG_Bullet); DrawDebugLine(StartTrace, EndTrace, 100,100,100,); /** Projection for the crosshair to convert 3d coords into 2d */ ScreenPos = Canvas.Project(HitLocation); /** If we haven't hit any actors... */ if ( Pawn(HitActor) == None ) { HitActor = (HitActor == None) ? None : Pawn(HitActor.Base); } } /** If our trace hits a pawn... */ if ((Pawn(HitActor) == None)) { /** Draws the crosshair for no one - Grey*/ CrosshairSize = 28 * (Canvas.ClipY / 768) * (Canvas.ClipX /1024); Canvas.SetDrawColor(100,100,128,255); Canvas.SetPos(ScreenPos.X - (CrosshairSize * 0.5f), ScreenPos.Y -(CrosshairSize * 0.5f)); Canvas.DrawTile(class'UTHUD'.default.AltHudTexture, CrosshairSize, CrosshairSize, 600, 262, 28, 27); return false; } /** Draws the crosshair for friendlies - Yellow */ CrosshairSize = 28 * (Canvas.ClipY / 768) * (Canvas.ClipX /1024); Canvas.SetDrawColor(255,255,128,255); Canvas.SetPos(ScreenPos.X - (CrosshairSize * 0.5f), ScreenPos.Y -(CrosshairSize * 0.5f)); Canvas.DrawTile(class'UTHUD'.default.AltHudTexture, CrosshairSize, CrosshairSize, 600, 262, 28, 27); return true; }

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• What's the equivalent name of "procedure" in OOP?

  - by AeroCross

  In several of my programming courses in the University, my teachers always told me the following: A function and a procedure are basically the same thing: the only difference is that a function returns a value, and the procedure doesn't. That means that this: function sum($a, $b) { return $a + $b; } ... is a function, and this: function sum($a, $b) { echo $a + $b; } ... is a procedure. In the same train of thought, I've seen that a method is the equivalent of a function in the OOP world. That means that this: class Example { function sum($a, $b) { return $a + $b; } } Is a method — but how do you call this? class Example { function sum($a, $b) { echo $a + $b; } } What's the equivalent name, or how do you call a method that doesn't returns anything?

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• Behaviour Trees with irregular updates

  - by Robominister

  I'm interested in behaviour trees that aren't iterated every game tick, but every so often. (Edit: the tree could specify how many frames within the main game loop to wait before running its tick function again). Every theoretical implementation I have seen of behaviour trees talks of the tree search being carried out every game update - which seems necessary, because a leaf node (eg a behaviour, like 'return to base') needs to be constantly checked to see if is still running, failed or completed. Can anyone suggest how I might start implementing a tree that isnt run every tick, or point me in the direction of good material specific to this case (I am struggling to find anything)? My thoughts so far: action leaf nodes (when they start) must only push some kind of action object onto a list for an entity, rather than directly calling any code that makes the entity do something. The list of actions for the entity would be run every frame (update any that need to run, pop any that have completed from the list). the return state from a given action must be fed back into the tree, so that when we run the tree iteration again (and reach the same action leaf node - so the tree has so far determined that we ought to still be trying this action) - that the action has completed, or is still running etc. If my actual action code is running from an action list on an entity, then I possibly need to cancel previously running actions in the list - i am thinking that I can just delete the entire stack of queued up actions. I've seen the idea of ActionLists which block lower priority actions when a higher priority one is added, but this seems like very close logic to behaviour trees, and I dont want to be duplicating behaviour. This leaves me with some questions 1) How would I feed the action return state back into the tree? Its obvious I need to store some information relating to 'currently executing actions' on the entity, and check that in the tree tick, but I can't imagine how. 2) Does having a seperate behaviour tree (for deciding behaviour) and action list (for carrying out actual queued up actions) sound like a reasonable approach? 3) Is the approach of updating a behaviour tree irregularly actually used by anyone? It seems like a nice idea for budgeting ai search time when you have a lot of ai entities to process. (Edit) - I am also thinking about storing a single instance of a given behaviour tree in memory, and providing it by reference to any entity that uses it. So any information about what action was last selected for execution on an entity must be stored in a data context relative to the entity (which the tree can check). (I am probably answering my own questions as i go!) I hope I have expressed my questions adequately! Thanks in advance for any help :)

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• Using Query Classes With NHibernate

  - by Liam McLennan

  Even when using an ORM, such as NHibernate, the developer still has to decide how to perform queries. The simplest strategy is to get access to an ISession and directly perform a query whenever you need data. The problem is that doing so spreads query logic throughout the entire application – a clear violation of the Single Responsibility Principle. A more advanced strategy is to use Eric Evan’s Repository pattern, thus isolating all query logic within the repository classes. I prefer to use Query Classes. Every query needed by the application is represented by a query class, aka a specification. To perform a query I: Instantiate a new instance of the required query class, providing any data that it needs Pass the instantiated query class to an extension method on NHibernate’s ISession type. To query my database for all people over the age of sixteen looks like this: [Test] public void QueryBySpecification() { var canDriveSpecification = new PeopleOverAgeSpecification(16); var allPeopleOfDrivingAge = session.QueryBySpecification(canDriveSpecification); } To be able to query for people over a certain age I had to create a suitable query class: public class PeopleOverAgeSpecification : Specification<Person> { private readonly int age; public PeopleOverAgeSpecification(int age) { this.age = age; } public override IQueryable<Person> Reduce(IQueryable<Person> collection) { return collection.Where(person => person.Age > age); } public override IQueryable<Person> Sort(IQueryable<Person> collection) { return collection.OrderBy(person => person.Name); } } Finally, the extension method to add QueryBySpecification to ISession: public static class SessionExtensions { public static IEnumerable<T> QueryBySpecification<T>(this ISession session, Specification<T> specification) { return specification.Fetch( specification.Sort( specification.Reduce(session.Query<T>()) ) ); } } The inspiration for this style of data access came from Ayende’s post Do You Need a Framework?. I am sick of working through multiple layers of abstraction that don’t do anything. Have you ever seen code that required a service layer to call a method on a repository, that delegated to a common repository base class that wrapped and ORMs unit of work? I can achieve the same thing with NHibernate’s ISession and a single extension method. If you’re interested you can get the full Query Classes example source from Github.

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• How to structure my AdWords campaign for testing and different groups of keywords?

  - by Romain Dorange

  I am starting an AdWords campaigns and I will measure conversion rates using the AdWords conversion tracking pixel. Conversion might be account creation or a concrete sale. As it will be a test campaign to have some insights on CTR, CR, etc... on the future, I am likely to try several configurations: Two different ads with different landing URL and messages: one with a focus on the product / the other will contains a discount embedded in the URL. 4 different groups or themes of keywords. I guess I have to build 4 ads groups based on the keywords 2 ads with the different messages assign the two ads to each ads groups follow the campaign precisely in the ads tabs where I can see the effectiveness of each Ads per Ads Groups (for a total of 8 lines of reporting) Also, what are the key performance indicators that I can have from an AdWords campaign to measure global effectiveness? measure of return on investment from concrete sales (tracking pixel with e-commerce tag on confirmation page) measure o return on investment from leads acquisition (tracking pixel on account creation) measure of traffic increase with the campaign

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• Java - Draw Cards and Eliminate Cards Problem

  - by Jen

  I am having a problem in this question. I want a system inside a game wherein the player draws 2 cards randomly, and the enemy draws 2 cards randomly. Then, what the program does is to print out to the console the cards the player draw and the enemy's. The cards should not conflict and must not be the same. Then lastly, the program prints out the card that was not drawn by both the player and the enemy. Here's how I did it but it was lengthy and full of errors: import java.util.Random; public class Draw { public static Random random = new Random(); public static String cards[] = {"Hall", "Kitchen", "Billiard", "Study", "Pool"}; public static int playercounter; public static int enemycounter; public static String playercardA = null; public static String playercardB = null; public static String enemycardA = null; public static String enemycardB = null; public String lastcard = null; public static void playercardAdraw() { playercounter = random.nextInt(5); playercardA = cards[playercounter]; } public static void playercardBdraw() { playercounter=random.nextInt(5); playercardB= cards[playercounter]; if (playercardB==playercardA || playercardB == enemycardA || playercardB == enemycardB) { return; } } public static void enemycardAdraw () { enemycounter = random.nextInt(5); enemycardA=cards[enemycounter]; if (enemycardA == playercardA || enemycardA == playercardB) { return; } } public static void enemycardBdraw () { enemycounter = random.nextInt(5); enemycardB=cards[enemycounter]; if (enemycardB == playercardA || enemycardB == playercardB || enemycardB == enemycardA) { return; } } public static void main (String args []) { System.out.println("Starting to draw..."); System.out.println("Player's Turn: "); playercardAdraw(); System.out.println("Player's first card: " + playercardA); playercardBdraw(); System.out.println("Player's second card: " + playercardB); System.out.println("Enemy's Turn: "); enemycardAdraw(); System.out.println("Enemy's first card: " + enemycardA); enemycardBdraw(); System.out.println("Enemy's Second card: " + enemycardB); } }

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• Is "watermarking" code with random trailing whitespace a good way to detect plagiarism?

  - by paperjam

  Consider this: int f(int x) { return 2 * x * x; } and this int squareAndDouble(int y) { return 2*y*y; } If you found these in independent bodies of code, you might give the two programmers the benefit of the doubt and assume they came up with more-or-less the same function independently. But look at the whitespace at the end of each line of code. Same pattern in both. Surely evidence of copying. On a larger piece of code, correlation of random whitespace at line ends would be irrefutable evidence of a shared origin. Now aside from the obvious weaknesses: e.g. visible or obvious in some editors, easily removed, I was wondering if it was worth deploying something like this in my open source project. My industry has a history of companies ripping off open source projects.

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• Rotating a NetBeans Visual Library Widget

  - by Geertjan

  Trying to create a widget which, when clicked, rotates slightly further on each subsequent click: Above, the bird where the mouse is visible has been clicked a few times and so has rotated a bit further on each click. The code isn't quite right yet and I'm hoping someone will take this code, try it out, and help with a nice solution! public class BirdScene extends Scene {     public BirdScene() {         addChild(new LayerWidget(this));         getActions().addAction(ActionFactory.createAcceptAction(new AcceptProvider() {             public ConnectorState isAcceptable(Widget widget, Point point, Transferable transferable) {                 Image dragImage = getImageFromTransferable(transferable);                 if (dragImage != null) {                     JComponent view = getView();                     Graphics2D g2 = (Graphics2D) view.getGraphics();                     Rectangle visRect = view.getVisibleRect();                     view.paintImmediately(visRect.x, visRect.y, visRect.width, visRect.height);                     g2.drawImage(dragImage,                             AffineTransform.getTranslateInstance(point.getLocation().getX(),                             point.getLocation().getY()),                             null);                     return ConnectorState.ACCEPT;                 } else {                     return ConnectorState.REJECT;                 }             }             public void accept(Widget widget, final Point point, Transferable transferable) {                 addChild(new BirdWidget(getScene(), getImageFromTransferable(transferable), point));             }         }));     }     private Image getImageFromTransferable(Transferable transferable) {         Object o = null;         try {             o = transferable.getTransferData(DataFlavor.imageFlavor);         } catch (IOException ex) {         } catch (UnsupportedFlavorException ex) {         }         return o instanceof Image ? (Image) o : null;     }     private class BirdWidget extends IconNodeWidget {         private int theta = 0;         public BirdWidget(Scene scene, Image imageFromTransferable, Point point) {             super(scene);             setImage(imageFromTransferable);             setPreferredLocation(point);             setCheckClipping(true);             getActions().addAction(ActionFactory.createMoveAction());             getActions().addAction(ActionFactory.createSelectAction(new SelectProvider() {                 public boolean isAimingAllowed(Widget widget, Point localLocation, boolean invertSelection) {                     return true;                 }                 public boolean isSelectionAllowed(Widget widget, Point localLocation, boolean invertSelection) {                     return true;                 }                 public void select(final Widget widget, Point localLocation, boolean invertSelection) {                     theta = (theta + 100) % 360;                     repaint();                     getScene().validate();                 }             }));         }         @Override         public void paintWidget() {             final Image image = getImageWidget().getImage();             Graphics2D g = getGraphics();             g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);             Rectangle bounds = getClientArea();             AffineTransform newXform = g.getTransform();             int xRot = image.getWidth(null) / 2;             int yRot = image.getWidth(null) / 2;             newXform.rotate(theta * Math.PI / 180, xRot, yRot);             g.setTransform(newXform);             g.drawImage(image, bounds.x, bounds.y, null);         }     } } The problem relates to refreshing the scene after the rotation. But it would help if someone would just take the code above, add it to their own application, try it out, see the problem for yourself, and develop it a bit further!

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• When to use typedef?

  - by futlib

  I'm a bit confused about if and when I should use typedef in C++. I feel it's a balancing act between readability and clarity. Here's a code sample without any typedefs: int sum(std::vector<int>::const_iterator first, std::vector<int>::const_iterator last) { static std::map<std::tuple<std::vector<int>::const_iterator, std::vector<int>::const_iterator>, int> lookup_table; std::map<std::tuple<std::vector<int>::const_iterator, std::vector<int>::const_iterator>, int>::iterator lookup_it = lookup_table.find(lookup_key); if (lookup_it != lookup_table.end()) return lookup_it->second; ... } Pretty ugly IMO. So I'll add some typedefs within the function to make it look nicer: int sum(std::vector<int>::const_iterator first, std::vector<int>::const_iterator last) { typedef std::tuple<std::vector<int>::const_iterator, std::vector<int>::const_iterator> Lookup_key; typedef std::map<Lookup_key, int> Lookup_table; static Lookup_table lookup_table; Lookup_table::iterator lookup_it = lookup_table.find(lookup_key); if (lookup_it != lookup_table.end()) return lookup_it->second; ... } The code is still a bit clumsy, but I get rid of most nightmare material. But there's still the int vector iterators, this variant gets rid of those: typedef std::vector<int>::const_iterator Input_iterator; int sum(Input_iterator first, Input_iterator last) { typedef std::tuple<Input_iterator, Input_iterator> Lookup_key; typedef std::map<Lookup_key, int> Lookup_table; static Lookup_table lookup_table; Lookup_table::iterator lookup_it = lookup_table.find(lookup_key); if (lookup_it != lookup_table.end()) return lookup_it->second; ... } This looks clean, but is it still readable? When should I use a typedef? As soon as I have a nightmare type? As soon as it occurs more than once? Where should I put them? Should I use them in function signatures or keep them to the implementation?

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• Draw Cards and Eliminate Cards Problem

  - by Jen

  I am having a problem in this question. I want a system inside a game wherein the player draws 2 cards randomly, and the enemy draws 2 cards randomly. Then, what the program does is to print out to the console the cards the player draw and the enemy's. The cards should not conflict and must not be the same. Then lastly, the program prints out the card that was not drawn by both the player and the enemy. Here's how I did it but it was lengthy and full of errors: import java.util.Random; public class Draw { public static Random random = new Random(); public static String cards[] = {"Hall", "Kitchen", "Billiard", "Study", "Pool"}; public static int playercounter; public static int enemycounter; public static String playercardA = null; public static String playercardB = null; public static String enemycardA = null; public static String enemycardB = null; public String lastcard = null; public static void playercardAdraw() { playercounter = random.nextInt(5); playercardA = cards[playercounter]; } public static void playercardBdraw() { playercounter=random.nextInt(5); playercardB= cards[playercounter]; if (playercardB==playercardA || playercardB == enemycardA || playercardB == enemycardB) { return; } } public static void enemycardAdraw () { enemycounter = random.nextInt(5); enemycardA=cards[enemycounter]; if (enemycardA == playercardA || enemycardA == playercardB) { return; } } public static void enemycardBdraw () { enemycounter = random.nextInt(5); enemycardB=cards[enemycounter]; if (enemycardB == playercardA || enemycardB == playercardB || enemycardB == enemycardA) { return; } } public static void main (String args []) { System.out.println("Starting to draw..."); System.out.println("Player's Turn: "); playercardAdraw(); System.out.println("Player's first card: " + playercardA); playercardBdraw(); System.out.println("Player's second card: " + playercardB); System.out.println("Enemy's Turn: "); enemycardAdraw(); System.out.println("Enemy's first card: " + enemycardA); enemycardBdraw(); System.out.println("Enemy's Second card: " + enemycardB); } }

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