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• Bouncing ball slowing down over time

  - by user46610

  I use the unreal engine 4 to bounce a ball off of walls in a 2D space, but over time the ball gets slower and slower. Movement happens in the tick function of the ball FVector location = GetActorLocation(); location.X += this->Velocity.X * DeltaSeconds; location.Y += this->Velocity.Y * DeltaSeconds; SetActorLocation(location, true); When a wall gets hit I get a Hit Event with the normal of the collision. This is how I calculate the new velocity of the ball: FVector2D V = this->Velocity; FVector2D N = FVector2D(HitNormal.X, HitNormal.Y); FVector2D newVelocity = -2 * (V.X * N.X + V.Y * N.Y) * N + V; this->Velocity = newVelocity; Over time, the more the ball bounced around, the velocity gets smaller and smaller. How do I prevent speed loss when bouncing off walls like that? It's supposed to be a perfect bounce without friction or anything.

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• How to do fluid dynamics like “Where's My Water”?

  - by Edgar Miranda

  There is a game on the app store called "Where's My Water" that is really fun and uses fluid dynamics in its gameplay. You can check out a video of the gameplay... You use your finger to remove dirt from the screen, and then the water just flows to the new area. Anyone knows what engine this was made in and how they where able to get the fluid dynamics in there? I'm using the Corona SDK for mobile development and want to do something similar like this (a game with fluid dynamics).

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• Best Frameworks/libraries/engines for 2D multiplayer C# Webbased RPG

  - by Thirlan

  Title is a mouthful but important because I'm looking to meet a specific criteria and it's complex enough that I need a lot of help in finding what I'm looking for. I really want people's suggestions because I trust it a lot more than anything else, so I just need to clearly define what it is I want heh : P Game is a 2D RPG. Think of Secret of Mana. Game is online multiplayer, but not MMO sized. Game must be webbased! I'm looking to the future and want to hit as many platforms as possible. I'm leaning to Webgl because of this, but still looking around. Since the users are seeing the game through the webbrowser the front-end should be mainly responsible for drawing, taking input and some basic checking such as preliminary collision detection. This is important because it means the game engine is NOT on the client's machine. The server should be responsible for the game engine and all the calculations. This means the server is doing all the work and the client is mostly a dumb terminal. Server language is c# I'm looking for fast project execution so I want to use as many pre-existing tools as possible. This would make sense because I'm making a game here, not an engine. I'm not creating some new revolutionary graphics or pushing the physics engines to the next level. Preference for commercially supported tools. For game mechanics reasons and for reasons 4 and 5, don't think I can use existing 2D rpg engines. I've seen them out there and I fear that if I try and use them they will have too many restrictions, but will be happy to hear out suggestions. So all this means I need a game engine on the server, or maybe just a physics engine, and then I need another engine/library to draw everything that the server is sending to the client on the webbrowser. Maybe this is how 50% of games work on the web and there are plenty of frameworks that support this! I wouldn't actually don't know : ( but my gut is telling me that most webgames are single player and 90% of the game is running on the client. So... any suggestions?

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• Get collision details from Rectangle.Intersects()

  - by Daniel Ribeiro

  I have a Breakout game in which, at some point, I detect the collision between the ball and the paddle with something like this: // Ball class rectangle.Intersects(paddle.Rectangle); Is there any way I can get the exact coordinates of the collision, or any details about it, with the current XNA API? I thought of doing some basic calculations, such as comparing the exact coordinates of each object on the moment of the collision. It would look something like this: // Ball class if((rectangle.X - paddle.Rectangle.X) < (paddle.Rectangle.Width / 2)) // Collision happened on the left side else // Collision happened on the right side But I'm not sure this is the correct way to do it. Do you guys have any tips on maybe an engine I might have to use to achieve that? Or even good coding practices using this method?

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• how to display like google

  - by zahir hussain

  if i search the word in google is "twitter". google display the first result like the below... Twitter Twitter is without a doubt the best way to share and discover what is happening right now. twitter.com/ - Cached - Similar Search How To Contest Account Suspension Blog An API Twitter_logo_header Twitter Status More results from twitter.com » how they can display Search,blog,Twitter_logo_header and etc... thanks and advance...

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• Google search box

  - by user343282

  I am working on a google box, something like this, http://mytwentyfive.com/blog/wp-content/uploads/byme/Google%20Search%20Appliances.jpg I am pointing the crawler to a folder where there are html files. before the crawler was crawling the files and indexing them but right now it finds the pattern or the folder but not following any html files within the folder. I have tried everything I could and know but, can't think of anything else. Can someone help? thanks

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• Managing game objects/components

  - by Xeon06

  Good day everyone, By far the biggest problem that has always dawned on my when programming games is how to structure my code. It just becomes an incredible mess after a while. The reason for that is because I have no idea how different classes should interact with each other. Let's have an example. Say I have a class Player, a class PlayerInput and a class Map. The player class contains information as to the location of the player, whereas the player input class handles changing that location, but by first making sure it's within a walkable area from the map class. How to structure this? My usual approach is to pass those components as parameters in the constructors of the parameters that need them, like so: var map = new Map(); var player = new Player(); var input = new PlayerInput(player, map); The problem with that is that it quickly gets messy, when you add new components you have to go through your constructors and update them, and it doesn't work well if you have mirroring references: var physics = new Physics(input); //Oops, doesn't work var input = new Input(physics); So, how do you guys usually manage this? Thanks.

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• Which one is better to get started? [closed]

  - by vanangamudi

  Which one of the open-source game engine is better to get started? I read several threads over several forums and found that it is better to write own game engine specific to application. But I need to know the requirements of a game engine, other than Graphics, Physics and AI... Many people suggested Unity, But I need open-source version so that I can have a look at implementation... so I google rigorously and found some unknown game engines(at least to me) Unvanquished Cube Spring Pyrogenesis Torque3D CrystalSpace Panda3D Delta3D Irrichlt OpenArena AlienArena (please list others if I missed anything....) FYI: my present focus is on FPS/TPS. Can you tell me which one is better at performance if possible? Torque3D claims to be the best opensource engine - is that true, and if so to what extent?

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• CTR (click through rate) and position rank

  - by Kensou SIE

  Generally, CTR is calculated for a given ad. Is there any sense to calculate a CTR for a search results page rank? I think that for a search results page, we often analyse clicks repartition.

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• What is the best Broadphase Interface for moving spheres?

  - by Molmasepic

  As of now I am working on optimizing the performance of the physics and collision, and as of now I am having some slowdowns on my other computers from my main. I have well over 3000 btSphereShape Rigidbodies and 2/3 of them do not move at all, but I am noticing(by the profile below) that collision is taking a bit of time to maneuver. Each sample counts as 0.01 seconds. % cumulative self self total time seconds seconds calls ms/call ms/call name 10.09 0.65 0.65 SphereTriangleDetector::collide(btVector3 const&, btVector3&, btVector3&, float&, float&, float) 7.61 1.14 0.49 btSphereTriangleCollisionAlgorithm::processCollision(btCollisionObject*, btCollisionObject*, btDispatcherInfo const&, btManifoldResult*) 5.59 1.50 0.36 btConvexTriangleCallback::processTriangle(btVector3*, int, int) 5.43 1.85 0.35 btQuantizedBvh::reportAabbOverlappingNodex(btNodeOverlapCallback*, btVector3 const&, btVector3 const&) const 4.97 2.17 0.32 btBvhTriangleMeshShape::processAllTriangles(btTriangleCallback*, btVector3 const&, btVector3 const&) const::MyNodeOverlapCallback::processNode(int, int) 4.19 2.44 0.27 btSequentialImpulseConstraintSolver::resolveSingleConstraintRowGeneric(btRigidBody&, btRigidBody&, btSolverConstraint const&) 4.04 2.70 0.26 btSequentialImpulseConstraintSolver::resolveSingleConstraintRowLowerLimit(btRigidBody&, btRigidBody&, btSolverConstraint const&) 3.73 2.94 0.24 Ogre::OctreeSceneManager::walkOctree(Ogre::OctreeCamera*, Ogre::RenderQueue*, Ogre::Octree*, Ogre::VisibleObjectsBoundsInfo*, bool, bool) 3.42 3.16 0.22 btTriangleShape::getVertex(int, btVector3&) const 2.48 3.32 0.16 Ogre::Frustum::isVisible(Ogre::AxisAlignedBox const&, Ogre::FrustumPlane*) const 2.33 3.47 0.15 1246357 0.00 0.00 Gorilla::Layer::setVisible(bool) 2.33 3.62 0.15 SphereTriangleDetector::getClosestPoints(btDiscreteCollisionDetectorInterface::ClosestPointInput const&, btDiscreteCollisionDetectorInterface::Result&, btIDebugDraw*, bool) 1.86 3.74 0.12 btCollisionDispatcher::findAlgorithm(btCollisionObject*, btCollisionObject*, btPersistentManifold*) 1.86 3.86 0.12 btSequentialImpulseConstraintSolver::setupContactConstraint(btSolverConstraint&, btCollisionObject*, btCollisionObject*, btManifoldPoint&, btContactSolverInfo const&, btVector3&, float&, float&, btVector3&, btVector3&) 1.71 3.97 0.11 btTriangleShape::getEdge(int, btVector3&, btVector3&) const 1.55 4.07 0.10 _Unwind_SjLj_Register 1.55 4.17 0.10 _Unwind_SjLj_Unregister 1.55 4.27 0.10 Ogre::D3D9HardwareVertexBuffer::updateBufferResources(char const*, Ogre::D3D9HardwareVertexBuffer::BufferResources*) 1.40 4.36 0.09 btManifoldResult::addContactPoint(btVector3 const&, btVector3 const&, float) 1.40 4.45 0.09 btSequentialImpulseConstraintSolver::setupFrictionConstraint(btSolverConstraint&, btVector3 const&, btRigidBody*, btRigidBody*, btManifoldPoint&, btVector3 const&, btVector3 const&, btCollisionObject*, btCollisionObject*, float, float, float) 1.24 4.53 0.08 btSequentialImpulseConstraintSolver::convertContact(btPersistentManifold*, btContactSolverInfo const&) 1.09 4.60 0.07 408760 0.00 0.00 Living::MapHide() 1.09 4.67 0.07 btSphereTriangleCollisionAlgorithm::~btSphereTriangleCollisionAlgorithm() 1.09 4.74 0.07 inflate_fast EDIT: Updated to show current Profile. I have only listed the functions using over 1% time from the many functions that are being used. Another thing is that each monster has a certain area that they stay in and are only active when a player is in said area. I was wondering if maybe there is a way to deactivate the non-active monsters from bullet(reactivating once in the area again) or maybe theres a different broadphase interface that I should use. The current BPI is btDbvtBroadphase. EDIT: Here is the Profile on the other computer(the top one is my main) Each sample counts as 0.01 seconds. % cumulative self self total time seconds seconds calls ms/call ms/call name 12.18 1.19 1.19 SphereTriangleDetector::collide(btVector3 const&, btVector3&, btVector3&, float&, float&, float) 6.76 1.85 0.66 btSphereTriangleCollisionAlgorithm::processCollision(btCollisionObject*, btCollisionObject*, btDispatcherInfo const&, btManifoldResult*) 5.83 2.42 0.57 btQuantizedBvh::reportAabbOverlappingNodex(btNodeOverlapCallback*, btVector3 const&, btVector3 const&) const 5.12 2.92 0.50 btConvexTriangleCallback::processTriangle(btVector3*, int, int) 4.61 3.37 0.45 btTriangleShape::getVertex(int, btVector3&) const 4.09 3.77 0.40 _Unwind_SjLj_Register 3.48 4.11 0.34 btBvhTriangleMeshShape::processAllTriangles(btTriangleCallback*, btVector3 const&, btVector3 const&) const::MyNodeOverlapCallback::processNode(int, int) 2.46 4.35 0.24 btSequentialImpulseConstraintSolver::resolveSingleConstraintRowLowerLimit(btRigidBody&, btRigidBody&, btSolverConstraint const&) 2.15 4.56 0.21 _Unwind_SjLj_Unregister 2.15 4.77 0.21 SphereTriangleDetector::getClosestPoints(btDiscreteCollisionDetectorInterface::ClosestPointInput const&, btDiscreteCollisionDetectorInterface::Result&, btIDebugDraw*, bool) 1.84 4.95 0.18 btTriangleShape::getEdge(int, btVector3&, btVector3&) const 1.64 5.11 0.16 btSequentialImpulseConstraintSolver::resolveSingleConstraintRowGeneric(btRigidBody&, btRigidBody&, btSolverConstraint const&) 1.54 5.26 0.15 btSequentialImpulseConstraintSolver::setupContactConstraint(btSolverConstraint&, btCollisionObject*, btCollisionObject*, btManifoldPoint&, btContactSolverInfo const&, btVector3&, float&, float&, btVector3&, btVector3&) 1.43 5.40 0.14 Ogre::D3D9HardwareVertexBuffer::updateBufferResources(char const*, Ogre::D3D9HardwareVertexBuffer::BufferResources*) 1.33 5.53 0.13 btManifoldResult::addContactPoint(btVector3 const&, btVector3 const&, float) 1.13 5.64 0.11 btRigidBody::predictIntegratedTransform(float, btTransform&) 1.13 5.75 0.11 btTriangleIndexVertexArray::getLockedReadOnlyVertexIndexBase(unsigned char const**, int&, PHY_ScalarType&, int&, unsigned char const**, int&, int&, PHY_ScalarType&, int) const 1.02 5.85 0.10 btSphereTriangleCollisionAlgorithm::CreateFunc::CreateCollisionAlgorithm(btCollisionAlgorithmConstructionInfo&, btCollisionObject*, btCollisionObject*) 1.02 5.95 0.10 btSphereTriangleCollisionAlgorithm::btSphereTriangleCollisionAlgorithm(btPersistentManifold*, btCollisionAlgorithmConstructionInfo const&, btCollisionObject*, btCollisionObject*, bool) Edited same as other Profile.

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• Google App Engine says "Must authenticate first." while trying to deploy any app

  - by Oleksandr Bolotov

  Google App Engine says "Must authenticate first." while trying to deploy any app: me@myhost /opt/google_appengine $ python appcfg.py update ~/sda2/workspace/lyapapam/ Application: lyapapam; version: 1. Server: appengine.google.com. Scanning files on local disk. Scanned 500 files. Scanned 1000 files. Initiating update. Email: <my_email_was_here>@gmail.com Password for <my_email_was_here>@gmail.com: Error 401: --- begin server output --- Must authenticate first. --- end server output --- We are getting this message with any appliation and under any developer account avialable to us That's what we have installed: App Engine SDK - 1.3.2 PIL - 1.1.7 Python - 2.5.5 pip - 0.6.3 ssl - 1.15 wsgiref - 0.1.2 So, what can it be? Is it well known problem?

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• How to connect to Google App Engine server in internal network iMac?

  - by Will Merydith

  I have 3 iMacs and a Windows machine on my home network, all connected via an Airport Extreme router. I'm developing Google App Engine applications locally on one of the iMacs, and can view applications using http://localhost:8080 (or whatever port I choose). How do I connect to those applications from other iMacs and Windows machines in my network? I've located the IP for the iMac hosting Google App Engine: 10.0.1.7. But when I try http://10.0.1.7:8080 from another machine it will not load the page.

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• RK4 Bouncing a Ball

  - by Jonathan Dickinson

  I am trying to wrap my head around RK4. I decided to do the most basic 'ball with gravity that bounces' simulation. I have implemented the following integrator given Glenn Fiedler's tutorial: /// <summary> /// Represents physics state. /// </summary> public struct State { // Also used internally as derivative. // S: Position // D: Velocity. /// <summary> /// Gets or sets the Position. /// </summary> public Vector2 X; // S: Position // D: Acceleration. /// <summary> /// Gets or sets the Velocity. /// </summary> public Vector2 V; } /// <summary> /// Calculates the force given the specified state. /// </summary> /// <param name="state">The state.</param> /// <param name="t">The time.</param> /// <param name="acceleration">The value that should be updated with the acceleration.</param> public delegate void EulerIntegrator(ref State state, float t, ref Vector2 acceleration); /// <summary> /// Represents the RK4 Integrator. /// </summary> public static class RK4 { private const float OneSixth = 1.0f / 6.0f; private static void Evaluate(EulerIntegrator integrator, ref State initial, float t, float dt, ref State derivative, ref State output) { var state = new State(); // These are a premature optimization. I like premature optimization. // So let's not concentrate on that. state.X.X = initial.X.X + derivative.X.X * dt; state.X.Y = initial.X.Y + derivative.X.Y * dt; state.V.X = initial.V.X + derivative.V.X * dt; state.V.Y = initial.V.Y + derivative.V.Y * dt; output = new State(); output.X.X = state.V.X; output.X.Y = state.V.Y; integrator(ref state, t + dt, ref output.V); } /// <summary> /// Performs RK4 integration over the specified state. /// </summary> /// <param name="eulerIntegrator">The euler integrator.</param> /// <param name="state">The state.</param> /// <param name="t">The t.</param> /// <param name="dt">The dt.</param> public static void Integrate(EulerIntegrator eulerIntegrator, ref State state, float t, float dt) { var a = new State(); var b = new State(); var c = new State(); var d = new State(); Evaluate(eulerIntegrator, ref state, t, 0.0f, ref a, ref a); Evaluate(eulerIntegrator, ref state, t + dt * 0.5f, dt * 0.5f, ref a, ref b); Evaluate(eulerIntegrator, ref state, t + dt * 0.5f, dt * 0.5f, ref b, ref c); Evaluate(eulerIntegrator, ref state, t + dt, dt, ref c, ref d); a.X.X = OneSixth * (a.X.X + 2.0f * (b.X.X + c.X.X) + d.X.X); a.X.Y = OneSixth * (a.X.Y + 2.0f * (b.X.Y + c.X.Y) + d.X.Y); a.V.X = OneSixth * (a.V.X + 2.0f * (b.V.X + c.V.X) + d.V.X); a.V.Y = OneSixth * (a.V.Y + 2.0f * (b.V.Y + c.V.Y) + d.V.Y); state.X.X = state.X.X + a.X.X * dt; state.X.Y = state.X.Y + a.X.Y * dt; state.V.X = state.V.X + a.V.X * dt; state.V.Y = state.V.Y + a.V.Y * dt; } } After reading over the tutorial I noticed a few things that just seemed 'out' to me. Notably how the entire simulation revolves around t at 0 and state at 0 - considering that we are working out a curve over the duration it seems logical that RK4 wouldn't be able to handle this simple scenario. Never-the-less I forged on and wrote a very simple Euler integrator: static void Integrator(ref State state, float t, ref Vector2 acceleration) { if (state.X.Y > 100 && state.V.Y > 0) { // Bounce vertically. acceleration.Y = -state.V.Y * t; } else { acceleration.Y = 9.8f; } } I then ran the code against a simple fixed-time step loop and this is what I got: 0.05 0.20 0.44 0.78 1.23 1.76 ... 74.53 78.40 82.37 86.44 90.60 94.86 99.23 103.05 105.45 106.94 107.86 108.42 108.76 108.96 109.08 109.15 109.19 109.21 109.23 109.23 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 ... As I said, I was expecting it to break - however I am unsure of how to fix it. I am currently looking into keeping the previous state and time, and working from that - although at the same time I assume that will defeat the purpose of RK4. How would I get this simulation to print the expected results?

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• HTML5 or Javascript game engine to develop a browser game

  - by Jack Duluoz

  I would like to start developing a MMO browser game, like Travian or Ogame, probably involving also a bit of more sophisticated graphical features such as players interacting in real time with a 2d map or something like that. My main doubt is what kind of development tools I should use: I've a good experience with PHP and MySQL for the server side and Javascript (and jQuery) regarding the client side. Coding everything from scratch would be of course really painful so I was wondering if I should use a javascript game engine or not. Are there (possibly free) game engine you would recommend? Are they good enough to develop a big game? Also, I saw a lot of HTML5 games popping up lately but I'm now sure if using HTML5 is a good idea or not. Would you recommend it? What are the pro and cons about using HTML5? If you'd recommend it, do you have any good links regarding game development with HTML5? (PS: I know that HTML5 and a Javascript engine are not mutually exclusive, I just didn't know how to formulate a proper title since English is not my main language. So, please, answer addressing HTML5 and a game engine pro and cons separately)

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• Scene Graph for Deferred Rendering Engine

  - by Roy T.

  As a learning exercise I've written a deferred rendering engine. Now I'd like to add a scene graph to this engine but I'm a bit puzzled how to do this. On a normal (forward rendering engine) I would just add all items (All implementing IDrawable and IUpdateAble) to my scene graph, than travel the scene-graph breadth first and call Draw() everywhere. However in a deferred rendering engine I have to separate draw calls. First I have to draw the geometry, then the shadow casters and then the lights (all to different render targets), before I combine them all. So in this case I can't just travel over the scene graph and just call draw. The way I see it I either have to travel over the entire scene graph 3 times, checking what kind of object it is that has to be drawn, or I have to create 3 separate scene graphs that are somehow connected to each other. Both of these seem poor solutions, I'd like to handle scene objects more transparent. One other solution I've thought of was traveling trough the scene graph as normal and adding items to 3 separate lists, separating geometry, shadow casters and lights, and then iterating these lists to draw the correct stuff, is this better, and is it wise to repopulate 3 lists every frame?

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• 2D OBB collision detection, resolving collisions?

  - by Milo

  I currently use OBBs and I have a vehicle that is a rigid body and some buildings. Here is my update() private void update() { camera.setPosition((vehicle.getPosition().x * camera.getScale()) - ((getWidth() ) / 2.0f), (vehicle.getPosition().y * camera.getScale()) - ((getHeight() ) / 2.0f)); //camera.move(input.getAnalogStick().getStickValueX() * 15.0f, input.getAnalogStick().getStickValueY() * 15.0f); if(input.isPressed(ControlButton.BUTTON_GAS)) { vehicle.setThrottle(1.0f, false); } if(input.isPressed(ControlButton.BUTTON_BRAKE)) { vehicle.setBrakes(1.0f); } vehicle.setSteering(input.getAnalogStick().getStickValueX()); vehicle.update(16.6666f / 1000.0f); ArrayList<Building> buildings = city.getBuildings(); for(Building b : buildings) { if(vehicle.getRect().overlaps(b.getRect())) { vehicle.update(-17.0f / 1000.0f); break; } } } The collision detection works well. What doesn't is how they are dealt with. My goal is simple. If the vehicle hits a building, it should stop, and never go into the building. When I apply negative torque to reverse the car should not feel buggy and move away from the building. I don't want this to look buggy. This is my rigid body class: class RigidBody extends Entity { //linear private Vector2D velocity = new Vector2D(); private Vector2D forces = new Vector2D(); private float mass; //angular private float angularVelocity; private float torque; private float inertia; //graphical private Vector2D halfSize = new Vector2D(); private Bitmap image; public RigidBody() { //set these defaults so we don't get divide by zeros mass = 1.0f; inertia = 1.0f; } //intialize out parameters public void initialize(Vector2D halfSize, float mass, Bitmap bitmap) { //store physical parameters this.halfSize = halfSize; this.mass = mass; image = bitmap; inertia = (1.0f / 20.0f) * (halfSize.x * halfSize.x) * (halfSize.y * halfSize.y) * mass; RectF rect = new RectF(); float scalar = 10.0f; rect.left = (int)-halfSize.x * scalar; rect.top = (int)-halfSize.y * scalar; rect.right = rect.left + (int)(halfSize.x * 2.0f * scalar); rect.bottom = rect.top + (int)(halfSize.y * 2.0f * scalar); setRect(rect); } public void setLocation(Vector2D position, float angle) { getRect().set(position, getWidth(), getHeight(), angle); } public Vector2D getPosition() { return getRect().getCenter(); } @Override public void update(float timeStep) { //integrate physics //linear Vector2D acceleration = Vector2D.scalarDivide(forces, mass); velocity = Vector2D.add(velocity, Vector2D.scalarMultiply(acceleration, timeStep)); Vector2D c = getRect().getCenter(); c = Vector2D.add(getRect().getCenter(), Vector2D.scalarMultiply(velocity , timeStep)); setCenter(c.x, c.y); forces = new Vector2D(0,0); //clear forces //angular float angAcc = torque / inertia; angularVelocity += angAcc * timeStep; setAngle(getAngle() + angularVelocity * timeStep); torque = 0; //clear torque } //take a relative Vector2D and make it a world Vector2D public Vector2D relativeToWorld(Vector2D relative) { Matrix mat = new Matrix(); float[] Vector2Ds = new float[2]; Vector2Ds[0] = relative.x; Vector2Ds[1] = relative.y; mat.postRotate(JMath.radToDeg(getAngle())); mat.mapVectors(Vector2Ds); return new Vector2D(Vector2Ds[0], Vector2Ds[1]); } //take a world Vector2D and make it a relative Vector2D public Vector2D worldToRelative(Vector2D world) { Matrix mat = new Matrix(); float[] Vectors = new float[2]; Vectors[0] = world.x; Vectors[1] = world.y; mat.postRotate(JMath.radToDeg(-getAngle())); mat.mapVectors(Vectors); return new Vector2D(Vectors[0], Vectors[1]); } //velocity of a point on body public Vector2D pointVelocity(Vector2D worldOffset) { Vector2D tangent = new Vector2D(-worldOffset.y, worldOffset.x); return Vector2D.add( Vector2D.scalarMultiply(tangent, angularVelocity) , velocity); } public void applyForce(Vector2D worldForce, Vector2D worldOffset) { //add linear force forces = Vector2D.add(forces ,worldForce); //add associated torque torque += Vector2D.cross(worldOffset, worldForce); } @Override public void draw( GraphicsContext c) { c.drawRotatedScaledBitmap(image, getPosition().x, getPosition().y, getWidth(), getHeight(), getAngle()); } } Essentially, when any rigid body hits a building it should exhibit the same behavior. How is collision solving usually done? Thanks

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• Tuning B2B Server Engine Threads in SOA Suite 11g

  - by Shub Lahiri, A-Team

  Background B2B 11g has a number of parameters that can be tweaked to tune the engine for handling high volumes of messages. These parameters are also known as B2B server properties and managed via the EM console.  This note highlights one aspect of the tuning exercise and describes the different threads, that can be configured to tune the performance of a B2B server. Symptoms The most common indicator of a B2B engine in need of a tuning is reflected in the constant build-up of messages in an internal JMS queue within the B2B server. It is called B2B_EVENT_QUEUE and can be monitored via the Weblogic server console. Whenever such a behaviour is seen, it usually results in general degradation of performance. Remedy There could be many contributing factors behind a B2B server's degradation of performance. However, one of the first places to tune the server from the out-of-the-box, default configuration is to change the number of internal engine threads allocated within the B2B server. Usually the default configuration for the B2B server engine threads is not suitable for high-volume of messaging loads. So, it is necessary to increase the counts for 3 types of such threads, by specifying the appropriate B2B server properties via the EM console, namely, Inbound - b2b.inboundThreadCount Outbound - b2b.outboundThreadCount Default - b2b.defaultThreadCount The function of these threads are fairly self-explanatory. In other words, the inbound threads process the inbound messages that are coming into the B2B server from an external endpoint. Similarly, the outbound threads processes the messages that are sent out from the B2B server. The default threads are responsible for certain B2B server-specific special tasks. In case the inbound and outbound thread counts are not specified, the default thread count also dictates the total number of inbound and outbound threads. As found in any tuning exercise, the optimisation of these threads is usually reached via an iterative process. The best working combination of the thread counts are directly related to the system infrastructure, traffic load and several other environmental factors.

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• Understanding Box2d Restitution & Bouncing

  - by layzrr

  I'm currently trying to implement basketball bouncing into my game using Box2d (jBox2d technically), but I'm a bit confused about restitution. While trying to create the ball in the testbed first, I've run into infinite bouncing, as described in this question, however obviously not using my own implementation. The Box2d manual describes restitution as follows: Restitution is used to make objects bounce. The restitution value is usually set to be between 0 and 1. Consider dropping a ball on a table. A value of zero means the ball won't bounce. This is called an inelastic collision. A value of one means the ball's velocity will be exactly reflected. This is called a perfectly elastic collision. My confusion lies in that I am still getting infinite bouncing with restitution values at 0.75/0.8. The same behavior can be seen in the testbed under Collision Watching - Varying Restitution, on the 6th and 7th balls. I believe the last one has restitution of 1, which makes sense, but I don't understand why the second to last ball bounces infinitely (as is happening with my working basketball I've created). I am looking to understand the restitution concept more fully, as well as look for a solution to infinite bouncing with the Box2d framework. My instinct was to sleep objects that appeared to be moving in very small increments, but this seems like a misuse of the engine. Should I just work with lower restitution values altogether?

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• How to calculate new velocities between resting objects (AABB) after accelerations?

  - by Tiedye

  lately I have been trying to create a 2D platformer engine in C++ with Direct2D. The problem I am currently having is getting objects that are resting against each other to interact correctly after accelerations like gravity have been applied to them. Right now I can detect collisions and respond to them correctly (I think) and when objects collide they remember what other objects they're resting against so objects can be pushed by other objects (note that there is no bounce in any collisions so when objects collide they are guaranteed to become resting until something else happens). Every time the simulation advances, the acceleration for objects is applied to their velocities (for example vx += ax * t, where t is time elapsed since last advancement). After these accelerations are applied, I want to check if any objects that are resting against each other are moving at different speeds than their counterparts (as different objects can have different accelerations) and depending on that difference either unlink the two objects so they are no longer resting, or even out their velocities so they are moving at the same speed once again. I am having trouble creating an algorithm that can do this across many resting objects. Here's a diagram to help explain my problem

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• Hekaton – SQL Server’s in-memory database engine

  - by Christian

  Microsoft have just gone public at the PASS Summit in Seattle about a new SQL Server engine that they’re working on which is optimized for high-memory servers – an in-memory OLTP database engine which is built-in to SQL Server rather than a separate entity.  This means that you can move just the performance critical parts of your database to Hekaton. The new engine really pushes the performance boundaries by eliminating as many instructions as possible: Main memory optimized tables which are decoupled from on-disk structures; Everything is lock and latch free; More work is pushed to compile time so your T-SQL code is compiled natively into low-level code. We’re already working with a customer on an early adoption program so expect to hear from us on what we learn about implementing it!   Christian Bolton - MCA, MCM, MVP Technical Director http://coeo.com - SQL Server Consulting & Managed Services

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• Running a Silverlight application in the Google App Engine platform

  - by rajbk

  This post shows you how to host a Silverlight application in the Google App Engine (GAE) platform. You deploy and host your Silverlight application on Google’s infrastructure by creating a configuration file and uploading it along with your application files. I tested this by uploading an old demo of mine - the four stroke engine silverlight demo. It is currently being served by the GAE over here: http://fourstrokeengine.appspot.com/ The steps to run your Silverlight application in GAE are as follows: Account Creation Create an account at http://appengine.google.com/. You are allocated a free quota at signup. Select “Create an Application”   Verify your account by SMS   Create your application by clicking on “Create an Application”   Pick an application identifier on the next screen. The identifier has to be unique. You will use this identifier when uploading your application. The application you create will by default be accessible at [applicationidentifier].appspot.com. You can also use custom domains if needed (refer to the docs).   Save your application. Download SDK  We will use the  Windows Launcher for Google App Engine tool to upload our apps (it is possible to do the same through command line). This is a GUI for creating, running and deploying applications. The launcher lets you test the app locally before deploying it to the GAE. This tool is available in the Google App Engine SDK. The GUI is written in Python and therefore needs an installation of Python to run. Download and install the Python Binaries from here: http://www.python.org/download/ Download and install the Google App Engine SDK from here: http://code.google.com/appengine/downloads.html Run the GAE Launcher. Select Create New Application.   On the next dialog, give your application a name (this must match the identifier we created earlier) For Parent Directory, point to the directory containing your Silverlight files. Change the port if you want to. The port is used by the GAE local web server. The server is started if you choose to run the application locally for testing purposes. Hit Save. Configure, Test and Upload As shown below, the files I am interested in uploading for my Silverlight demo app are The html page used to host the Silverlight control The xap file containing the compiled Silverlight application A favicon.ico file.   We now create a configuration file for our application called app.yaml. The app.yaml file specifies how URL paths correspond to request handlers and static files.  We edit the file by selecting our app in the GUI and clicking “Edit” The contents of file after editing is shown below (note that the contents of the file should be in plain text): application: fourstrokeengine version: 1 runtime: python api_version: 1 handlers: - url: /   static_files: Default.html   upload: Default.html - url: /favicon.ico   static_files: favicon.ico   upload: favicon.ico - url: /FourStrokeEngine.xap   static_files: FourStrokeEngine.xap   upload: FourStrokeEngine.xap   mime_type: application/x-silverlight-app - url: /.*   static_files: Default.html   upload: Default.html We have listed URL patterns for our files, specified them as static files and specified a mime type for our xap file. The wild card URL at the end will match all URLs that are not found to our default page (you would normally include a html file that displays a 404 message).  To understand more about app.yaml, refer to this page. Save the file. Run the application locally by selecting “Browse” in the GUI. A web server listening on the port you specified is started (8080 in my case). The app is loaded in your default web browser pointing to http://localhost:8080/. Make sure the application works as expected. We are now ready to deploy. Click the “Deploy” icon. You will be prompted for your username and password. Hit OK. The files will get uploaded and you should get a dialog telling you to “close the window”. We are done uploading our Silverlight application. Go to http://appengine.google.com/ and launch the application by clicking on the link in the “Current Version” column.   You should be taken to a URL which points to your application running in Google’s infrastructure : http://fourstrokeengine.appspot.com/. We are done deploying our application! Clicking on the link in the Application column will take you to the Admin console where you can see stats related to system usage.  To learn more about the Google Application Engine, go here: http://code.google.com/appengine/docs/whatisgoogleappengine.html

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• design of 'game engine' for small javascript games?

  - by Matt Ball

  I'm making a group of two or three simple javascript games for fun. After someone finishes one game, they'll be presented with a harder or easier version of another game depending on whether the original game was won or lost. I have a high-level question about the design of things: So far I've created a class for one game type that manages the interaction with the UI and the state of the game itself. But for tracking how many of the subgames have been won, or for understanding whether the next game presented should be more or less difficult, are there arguments to be made for making a 'game engine' class? How does the engine communicate to the games? For instance, when a game is won, how is that information relayed to the engine? Is there a better or more common design? (If you want to see what I have so far, the games are slowly taking shape here: https://github.com/yosemitebandit/candela and can be viewed at http://yosemitebandit.com/candela)

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• Which paradigm to use for writing chess engine?

  - by poke

  If you were going to write a chess game engine, what programming paradigm would you use (OOP, procedural, etc) and why whould you choose it ? By chess engine, I mean the portion of a program that evaluates the current board and decides the computer's next move. I'm asking because I thought it might be fun to write a chess engine. Then it occured to me that I could use it as a project for learning functional programming. Then it occured to me that some problems aren't well suited to the functional paradigm. Then it occured to me that this might be good discussion fodder.

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• Shader inputs in a general purpose engine

  - by dreta

  I'm not familiar with SDKs like Unity or UDK that much, so i can't check this offhand. Do general purpose engines allow users to create custom uniform variables? The way i see it, and the way i have implemented it in an engine i'm writing to learn 3D, is that there is a "set" of uniforms provided by the engine and if you want to write a custom shader then you utilize uniforms you need to create a wanted effect. Now, the thing is, first of all i'm not an artist, second of all, i didn't have a chance to create complex scenes yet. So my question is, is it common practice to define variables that the engine provides and only allow the user to work with what they're given? Allowing users to add custom programs and use them where they want is not hard, but i have issues imagining how you'd go about doing the same for uniforms.

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• How to break terrain (in blender) into Chunks for a game engine

  - by Red

  I've created an island in blender. 2048x2048 blender units. The engine developer wants me to split the terrain into 128x128 "chunks" so that would be 16x16 "chunks" from a top down view. The engine isn't using height maps, in order to allow caves, 3d overhangs, etc. I'm not in charge of the engine, so suggestions about that aren't needed here :/ I just need a good, seamless way to split a terrain mesh into 16x16 pieces without leaving holes. I'm very new to blender, so baby steps are very much welcomed :) Here's a quick render of what i've got so far. I added a plane to show sea level but i've since removed it. http://i.imgur.com/qTsoC.png

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