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• Opposite Force to Apply to a Collided Rigid Body?

  - by Milo

  I'm working on the physics for my GTA2-like game so I can learn more about game physics. The collision detection and resolution are working great. I'm now just unsure how to compute the force to apply to a body after it collides with a wall. My rigid body looks like this: /our simulation object class RigidBody extends Entity { //linear private Vector2D velocity = new Vector2D(); private Vector2D forces = new Vector2D(); private float mass; private Vector2D v = new Vector2D(); //angular private float angularVelocity; private float torque; private float inertia; //graphical private Vector2D halfSize = new Vector2D(); private Bitmap image; private Matrix mat = new Matrix(); private float[] Vector2Ds = new float[2]; private Vector2D tangent = new Vector2D(); private static Vector2D worldRelVec = new Vector2D(); private static Vector2D relWorldVec = new Vector2D(); private static Vector2D pointVelVec = new Vector2D(); private static Vector2D acceleration = new Vector2D(); public RigidBody() { //set these defaults so we don't get divide by zeros mass = 1.0f; inertia = 1.0f; setLayer(LAYER_OBJECTS); } protected void rectChanged() { if(getWorld() != null) { getWorld().updateDynamic(this); } } //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.x,position.y, getWidth(), getHeight(), angle); rectChanged(); } public Vector2D getPosition() { return getRect().getCenter(); } @Override public void update(float timeStep) { doUpdate(timeStep); } public void doUpdate(float timeStep) { //integrate physics //linear acceleration.x = forces.x / mass; acceleration.y = forces.y / mass; velocity.x += (acceleration.x * timeStep); velocity.y += (acceleration.y * timeStep); //velocity = Vector2D.add(velocity, Vector2D.scalarMultiply(acceleration, timeStep)); Vector2D c = getRect().getCenter(); v.x = getRect().getCenter().getX() + (velocity.x * timeStep); v.y = getRect().getCenter().getY() + (velocity.y * timeStep); setCenter(v.x, v.y); forces.x = 0; //clear forces forces.y = 0; //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) { mat.reset(); Vector2Ds[0] = relative.x; Vector2Ds[1] = relative.y; mat.postRotate(JMath.radToDeg(getAngle())); mat.mapVectors(Vector2Ds); relWorldVec.x = Vector2Ds[0]; relWorldVec.y = Vector2Ds[1]; return relWorldVec; } //take a world Vector2D and make it a relative Vector2D public Vector2D worldToRelative(Vector2D world) { mat.reset(); Vector2Ds[0] = world.x; Vector2Ds[1] = world.y; mat.postRotate(JMath.radToDeg(-getAngle())); mat.mapVectors(Vector2Ds); worldRelVec.x = Vector2Ds[0]; worldRelVec.y = Vector2Ds[1]; return worldRelVec; } //velocity of a point on body public Vector2D pointVelocity(Vector2D worldOffset) { tangent.x = -worldOffset.y; tangent.y = worldOffset.x; pointVelVec.x = (tangent.x * angularVelocity) + velocity.x; pointVelVec.y = (tangent.y * angularVelocity) + velocity.y; return pointVelVec; } public void applyForce(Vector2D worldForce, Vector2D worldOffset) { //add linear force forces.x += worldForce.x; forces.y += worldForce.y; //add associated torque torque += Vector2D.cross(worldOffset, worldForce); } @Override public void draw( GraphicsContext c) { c.drawRotatedScaledBitmap(image, getPosition().x, getPosition().y, getWidth(), getHeight(), getAngle()); } public Vector2D getVelocity() { return velocity; } public void setVelocity(Vector2D velocity) { this.velocity = velocity; } } The way it is given force is by the applyForce method, this method considers angular torque. I'm just not sure how to come up with the vectors in the case where: RigidBody hits static entity RigidBody hits other RigidBody that may or may not be in motion. Would anyone know a way (without too complex math) that I could figure out the opposite force I need to apply to the car? I know the normal it is colliding with and how deep it collided. My main goal is so that say I hit a building from the side, well the car should not just stay there, it should slowly rotate out of it if I'm more than 45 degrees. Right now when I hit a wall I only change the velocity directly which does not consider angular force. Thanks!

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• database design help for game / user levels / progress

  - by sprugman

  Sorry this got long and all prose-y. I'm creating my first truly gamified web app and could use some help thinking about how to structure the data. The Set-up Users need to accomplish tasks in each of several categories before they can move up a level. I've got my Users, Tasks, and Categories tables, and a UserTasks table which joins the three. ("User 3 has added Task 42 in Category 8. Now they've completed it.") That's all fine and working wonderfully. The Challenge I'm not sure of the best way to track the progress in the individual categories toward each level. The "business" rules are: You have to achieve a certain number of points in each category to move up. If you get the number of points needed in Cat 8, but still have other work to do to complete the level, any new Cat 8 points count toward your overall score, but don't "roll over" into the next level. The number of Categories is small (five currently) and unlikely to change often, but by no means absolutely fixed. The number of points needed to level-up will vary per level, probably by a formula, or perhaps a lookup table. So the challenge is to track each user's progress toward the next level in each category. I've thought of a few potential approaches: Possible Solutions Add a column to the users table for each category and reset them all to zero each time a user levels-up. Have a separate UserProgress table with a row for each category for each user and the number of points they have. (Basically a Many-to-Many version of #1.) Add a userLevel column to the UserTasks table and use that to derive their progress with some kind of SUM statement. Their current level will be a simple int in the User table. Pros & Cons (1) seems like by far the most straightforward, but it's also the least flexible. Perhaps I could use a naming convention based on the category ids to help overcome some of that. (With code like "select cats; for each cat, get the value from Users.progress_{cat.id}.") It's also the one where I lose the most data -- I won't know which points counted toward leveling up. I don't have a need in mind for that, so maybe I don't care about that. (2) seems complicated: every time I add or subtract a user or a category, I have to maintain the other table. I foresee synchronization challenges. (3) Is somewhere in between -- cleaner than #2, but less intuitive than #1. In order to find out where a user is, I'd have mildly complex SQL like: SELECT categoryId, SUM(points) from UserTasks WHERE userId={user.id} & countsTowardLevel={user.level} groupBy categoryId Hmm... that doesn't seem so bad. I think I'm talking myself into #3 here, but would love any input, advice or other ideas. P.S. Sorry for the cross-post. I wrote this up on SO and then remembered that there was a game dev-focused one. Curious to see if I get different answers one place than the other....

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• Wikipedia A* pathfinding algorithm takes a lot of time

  - by Vee

  I've successfully implemented A* pathfinding in C# but it is very slow, and I don't understand why. I even tried not sorting the openNodes list but it's still the same. The map is 80x80, and there are 10-11 nodes. I took the pseudocode from here Wikipedia And this is my implementation: public static List<PGNode> Pathfind(PGMap mMap, PGNode mStart, PGNode mEnd) { mMap.ClearNodes(); mMap.GetTile(mStart.X, mStart.Y).Value = 0; mMap.GetTile(mEnd.X, mEnd.Y).Value = 0; List<PGNode> openNodes = new List<PGNode>(); List<PGNode> closedNodes = new List<PGNode>(); List<PGNode> solutionNodes = new List<PGNode>(); mStart.G = 0; mStart.H = GetManhattanHeuristic(mStart, mEnd); solutionNodes.Add(mStart); solutionNodes.Add(mEnd); openNodes.Add(mStart); // 1) Add the starting square (or node) to the open list. while (openNodes.Count > 0) // 2) Repeat the following: { openNodes.Sort((p1, p2) => p1.F.CompareTo(p2.F)); PGNode current = openNodes[0]; // a) We refer to this as the current square.) if (current == mEnd) { while (current != null) { solutionNodes.Add(current); current = current.Parent; } return solutionNodes; } openNodes.Remove(current); closedNodes.Add(current); // b) Switch it to the closed list. List<PGNode> neighborNodes = current.GetNeighborNodes(); double cost = 0; bool isCostBetter = false; for (int i = 0; i < neighborNodes.Count; i++) { PGNode neighbor = neighborNodes[i]; cost = current.G + 10; isCostBetter = false; if (neighbor.Passable == false || closedNodes.Contains(neighbor)) continue; // If it is not walkable or if it is on the closed list, ignore it. if (openNodes.Contains(neighbor) == false) { openNodes.Add(neighbor); // If it isn’t on the open list, add it to the open list. isCostBetter = true; } else if (cost < neighbor.G) { isCostBetter = true; } if (isCostBetter) { neighbor.Parent = current; // Make the current square the parent of this square. neighbor.G = cost; neighbor.H = GetManhattanHeuristic(current, neighbor); } } } return null; } Here's the heuristic I'm using: private static double GetManhattanHeuristic(PGNode mStart, PGNode mEnd) { return Math.Abs(mStart.X - mEnd.X) + Math.Abs(mStart.Y - mEnd.Y); } What am I doing wrong? It's an entire day I keep looking at the same code.

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• x axis detection issues platformer starter kit

  - by dbomb101

  I've come across a problem with the collision detection code in the platformer starter kit for xna.It will send up the impassible flag on the x axis despite being nowhere near a wall in either direction on the x axis, could someone could tell me why this happens ? Here is the collision method. /// <summary> /// Detects and resolves all collisions between the player and his neighboring /// tiles. When a collision is detected, the player is pushed away along one /// axis to prevent overlapping. There is some special logic for the Y axis to /// handle platforms which behave differently depending on direction of movement. /// </summary> private void HandleCollisions() { // Get the player's bounding rectangle and find neighboring tiles. Rectangle bounds = BoundingRectangle; int leftTile = (int)Math.Floor((float)bounds.Left / Tile.Width); int rightTile = (int)Math.Ceiling(((float)bounds.Right / Tile.Width)) - 1; int topTile = (int)Math.Floor((float)bounds.Top / Tile.Height); int bottomTile = (int)Math.Ceiling(((float)bounds.Bottom / Tile.Height)) - 1; // Reset flag to search for ground collision. isOnGround = false; // For each potentially colliding tile, for (int y = topTile; y <= bottomTile; ++y) { for (int x = leftTile; x <= rightTile; ++x) { // If this tile is collidable, TileCollision collision = Level.GetCollision(x, y); if (collision != TileCollision.Passable) { // Determine collision depth (with direction) and magnitude. Rectangle tileBounds = Level.GetBounds(x, y); Vector2 depth = RectangleExtensions.GetIntersectionDepth(bounds, tileBounds); if (depth != Vector2.Zero) { float absDepthX = Math.Abs(depth.X); float absDepthY = Math.Abs(depth.Y); // Resolve the collision along the shallow axis. if (absDepthY < absDepthX || collision == TileCollision.Platform) { // If we crossed the top of a tile, we are on the ground. if (previousBottom <= tileBounds.Top) isOnGround = true; // Ignore platforms, unless we are on the ground. if (collision == TileCollision.Impassable || IsOnGround) { // Resolve the collision along the Y axis. Position = new Vector2(Position.X, Position.Y + depth.Y); // Perform further collisions with the new bounds. bounds = BoundingRectangle; } } //This is the section which deals with collision on the x-axis else if (collision == TileCollision.Impassable) // Ignore platforms. { // Resolve the collision along the X axis. Position = new Vector2(Position.X + depth.X, Position.Y); // Perform further collisions with the new bounds. bounds = BoundingRectangle; } } } } } // Save the new bounds bottom. previousBottom = bounds.Bottom; }

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• Rotate an image in a scaled context

  - by nathan

  Here is my working piece of code to rotate an image toward a point (in my case, the mouse cursor). float dx = newx - ploc.x; float dy = newy - ploc.y; float angle = (float) Math.toDegrees(Math.atan2(dy, dx)); Where ploc is the location of the image i'm rotating. And here is the rendering code: g.rotate(loc.x + width / 2, loc.y + height / 2, angle); g.drawImage(frame, loc.x, loc.y); Where loc is the location of the image and "width" and "height" are respectively the width and height of the image. What changes are needed to make it works on a scaled context? e.g make it works with something like g.scale(sx, sy).

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• Triangle Strips and Tangent Space Normal Mapping

  - by Koarl

  Short: Do triangle strips and Tangent Space Normal mapping go together? According to quite a lot of tutorials on bump mapping, it seems common practice to derive tangent space matrices in a vertex program and transform the light direction vector(s) to tangent space and then pass them on to a fragment program. However, if one was using triangle strips or index buffers, it is a given that the vertex buffer contains vertices that sit at border edges and would thus require more than one normal to derive tangent space matrices to interpolate between in fragment programs. Is there any reasonable way to not have duplicate vertices in your buffer and still use tangent space normal mapping? Which one do you think is better: Having normal and tangent encoded in the assets and just optimize the geometry handling to alleviate the cost of duplicate vertices or using triangle strips and computing normals/tangents completely at run time? Thinking about it, the more reasonable answer seems to be the first one, but why might my professor still be fussing about triangle strips when it seems so obvious?

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• Question about mipmaps + anisotropic filtering

  - by Telanor

  I'm a bit confused here and maybe someone can explain this to me. I created a simple test texture for my terrain which is nothing more than a solid green color with a black grid overlayed on top of it. If I look at the terrain in the distance with mipmapping on and linear filtering, the grid lines become blurry fairly quickly and further back the grid is pretty much invisible. With these settings, I don't get any moire patterns at all. If I turn on anisotropic filtering, however, the higher the anisotropic level, the more the terrain looks like it did with without mipmapping. The lines are much crisper nearby but in the distance I start to see terrible moire patterns. My understanding was that mipmapping is supposed to get rid of moire patterns. I've always had anisotropic filtering on in every game I play and I've never noticed any moire patterns as a result, so I don't understand why it's happening in my game. I am using logarithmic depth however, could that be causing any problems? And if it is, how do I resolve it? I've created my sampler state like so (I'm using slimdx): ssa = SamplerState.FromDescription(Engine.Device, new SamplerDescription { AddressU = TextureAddressMode.Clamp, AddressV = TextureAddressMode.Clamp, AddressW = TextureAddressMode.Clamp, Filter = Filter.Anisotropic, MaximumAnisotropy = anisotropicLevel, MinimumLod = 0, MaximumLod = float.MaxValue });

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• How to load with "simplegame" mode after cooking?

  - by Emran Bayati

  i got a problem after i cook my game in Frontend (udk) ! Every thing is ok during the Cook operation i mean i compiled my scripts,it's ok there's no problem in this step,and i cooked my packages it's ok too ! no problem just like last step. so before i package the whole game;i'll lunch it and see if every thing is ok ! but when i load the game it'll load whit the Unreal tournament default game type ! i mean i don't want it to load with this type ! i want it to load with the "simplegame" game type ! i need to say that i set game type to "simplegame" in the Editor from View world Properties Game Type! but still it's loading with Ut game mode when i cook the game ! I just want load my game in "Simplegame" mode after cooked. if any one can help ! plz help ! Tnx Alot Emran Bayati

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• How to I access "Deny" message from a Lidgren client?

  - by TJ Mott

  I'm using the Lidgren v3 network for a UDP client/server networking model. On the server end, I'm initializing a NetServer object with the NetIncomingMessage.ConnectionApproval message type enabled. So the client is able to successfully connect and the first packet it sends is a login packet, containing a username and password supplied by the user. The server is receiving that and doing some black magic to authenticate, and everything works up to that point. If the login fails, the server calling NetIncomingMessage.SenderConnection.Deny("Invalid Login Credentials"). I want to know how to properly receive this deny message on the client. I'm getting the message, it shows up with a message type of NetIncomingMessage.StatusChanged. If I call ReadString on that message, I get a corrupted version of the string I passed to the Deny method on the server. The type of corruption varies, I've seen odd characters in there but in every case it's truncated and is way shorter than the string I entered. Any ideas? The official documentation is sparse on this topic. I could use pointers from anyone who has successfully used the Lidgren library and uses the Accept or Deny methods. Also, if I don't do any authentication and just Approve() the connection every time, stuff actually works just fine and I'm getting reliable two-way UDP traffic. (And lastly, Stack Exchange said I don't have enough reputation to use the "Lidgren" tag....???)

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• What are the possible options for AI path-finding etc when the world is "partitionned"?

  - by Sebastien Diot

  If you anticipate a large persistent game world, and you don't want to end up with some game server crashing due to overload, then you have to design from the ground up a game world that is partitioned in chunks. This is in particular true if you want to run your game servers in the cloud, where each individual VM is relatively week, and memory and CPU are at a premium. I think the biggest challenge here is that the player receives all the parts around the location of the avatar, but mobs/monsters are normally located in the server itself, and can only directly access the data about the part of the world that the server own. So how can we make the AI behave realistically in that context? It can send queries to the other servers that own the neighboring parts, but that sounds rather network intensive and latency prone. It would probably be more performant for each mob AI to be spread over the neighboring parts, and proactively send the relevant info to the part that contains the actual mob atm. That would also reduce the stress in a mob crossing a border between two parts, and therefore "switching server". Have you heard of any AI design that solves those issues? Some kind of distributed AI brain? Maybe some kind of "agent" community working together through message passing?

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• First Minecraft mod not working: make a new sword

  - by yamikoWebs

  I am making my first mod and cannot see what is wrong with it. I am using MCP and Modloader. For my first mod I was going to make swords. I started with making a new EnumToolMaterials WOOD(0, 59, 2.0F, 0, 15), STONE(1, 131, 4.0F, 1, 5), IRON(2, 250, 6.0F, 2, 14), LAPIS(3, 750, 7.0F, 2, 14), OBSIDIAN(3, 1000, 7.5F, 3, 12), EMERALD(3, 1561, 8.0F, 3, 10),//diamond GREEN(3, 2000, 9.0F, 4, 10),//emerald GOLD(0, 200, 12.0F, 0, 22); then here is the mod class public class _Mod_Yamiko extends BaseMod{ /* mod itemts */ public static final Item swordLapis = (new ItemSword(600, EnumToolMaterial.LAPIS)).setItemName("swordLapis"); public static final Item swordObsidian = (new ItemSword(601, EnumToolMaterial.OBSIDIAN)).setItemName("swordObsidian"); public static final Item swordGreen = (new ItemSword(602, EnumToolMaterial.GREEN)).setItemName("swordGreen"); public void load(){ //set images swordLapis.iconIndex = ModLoader.addOverride("/gui/items.png","/gui/swordLapis.png"); ModLoader.addName(swordLapis, "Lapis Sword"); //craft ModLoader.addRecipe(new ItemStack(_Mod_Yamiko.swordLapis, 1), new Object[]{ " X ", " X ", " Y ", 'X', Block.dirt, 'Y', Item.stick }); } public String getVersion(){ return "0.1"; } } Then I made a 16×16 .png image. I am not sure where to save it so I recompiled and reobfuscated, took the mod files and put it in my local Minecraft install, added the image where it be should be. No problems when playing but I cannot make the new sword.

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• How to draw a global day night curve

  - by Lumis

  I see many applications which have world-clock map, and I would like to make my own to enhance some of my mobile apps. I wonder if anybody has any knowledge where to start, how to draw a curved shadow representing the dawn and the sunset on the globe. See the example: http://aa.usno.navy.mil/imagery/earth/map?year=2012&month=6&day=19&hour=14&minute=47 I think that this curve goes up and down and creates an artic day/night etc Perhaps there is some acceptable approximation formula without a need to load data for each our and each global parallel and meridian...

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• Simplest way to use Steam Leaderboards from C# [on hold]

  - by Miau

  We are about to integrate steamworks for leaderboards and achievements into our game. I see there are many open and closed source libraries that can be used to use SteamWorks from C#. Rolling our own wrapper can be done, but if the other libraries are reliable then it would be better to use and perhaps contribute back if we see any obvious gaps. Have you used any and if so what was your experience with the different libraries? Specifically for Leaderboards and achievements The ones I found are: SteamWorks.net Steam4Net Ludosity (can be used outside of Unity apparently)

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• Is there a maximum delay an UDP packet can have?

  - by Jens Nolte

  I am currently implementing a real-time network protocol for a multiplayer game using UDP. I am not having any technical difficulties, but as I always have to care about late UDP packets I am wondering just how late they can arrive. I have researched the topic and have not found any mention of it, so I assume there is no technical limitation, but I wonder if common network/internet architecture (or hardware) gives an effective limitation of how late a UDP packet can be delivered.

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• How to play many sounds at once in OpenAL

  - by Krom

  Hello, I'm developing an RTS game and I would like to add sounds to it. My choice has landed on OpenAL. I have plenty of units which from time to time make sounds: fSound.Play(sfx_shoot, location). Sounds often repeat, e.g. when squad of archers shoots arrows, but they are not synced with each other. My questions are: What is the common design pattern to play multiple sounds in OpenAL, when some of them are duplicate? What are the hardware limitations on sounds count and tricks to overcome them?

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• Fair dice over network w/o trusted 3rd party

  - by Kay

  Though it should be a pretty basic problem, I did not find a solution for it: How to play dice over a network without a trusted third party? The M players shall roll N dice, one player after another. No player may "cheat", i.e. change the outcome to his advantage, or "look into the future" before the next roll. Is that possible? I guess the solution would be something like public key crypto, where each player turns in an encrypted message. After all messages were collected you exchange the keys to decode the messages. Then the sha1(joined string of all decrypted messages) mod 6 + 1 is used to determine the die. The major problem I have: since the message [c/s]hould be anything, I don't know how to prevent tampering with the private keys. Esp. the last player to turn in his key could easily cheat (I guess). The game should even stay fair, if all players "conspire" against one player.

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• How to move Objects smoothly like swimming arround

  - by philipp

  I have a Box2D project that is about to create a view where the user looks from the Sky onto Water. Or perhaps on a bathtub filled with water or something like this. The Object which holds the fluid actually does not matter, what matters is the movement of the bodies, because they should move like drops of grease on a soup, or wood on water, I can even imagine the the fluid is mercurial, extreme heavy and "lazy". How can I manipulate the bodies (every frame or time by time) to make them move like this? I started with randomly manipulation their linear velocity, but I turned out that this not very smooth and looks quite hard. Is it a better idea to check their velocity and apply impulses? Is there any example? Greetings philipp

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• Efficient mapping layout in 2D side-scroller, and collisions between character and the world

  - by Jack

  I haven't touched Visual Studio for a couple months now, but I was playing a game from the '90s toady and had an epiphany: I was looking for something what i didn't need, and I wasn't using what I knew correctly. One of those realizations was collision, so let me tell you a bit about my project that I was working on. The project's graphics looks like Mario or Dangerous Dave, etc., you get the idea - old-school pixels. So anyway I remember trying to think of something else than AABB for character form, but I couldn't think of anything. Perhaps I could get a suggestion for this? Another thing is the world - I don't want it to be just linear world, I want mountains, etc.. My idea is to use triangles, and no idea yet what to do if I want just part of the cube, say 3/4 or 2/4 or whatever. Hard-coding such things seems inefficient. P.S. I am not looking at the precision level offered by Box2D. Actually I remember trying to implement it at first, but I failed as my understanding of C++ wasn't advanced enough, as it'll be mentioned below. P.P.S. I am programming in C++, and I haven't done it for a couple months now. I have no means of testing it either, as my PC is broken down, and this one can barely run games from late '90s, not to speak about a compiler or a program with inefficient resource management... I am also not an expert (obviously), I don't even know if I can consider myself an average programmer. In short, I am simply curious about my thoughts and my past experience when programming the game. I may come back to it when my PC is fixed, I'm already filling a note about these things.

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• Actually utilizing relational databases for entity systems

  - by Marc Müller

  Recently I was researching several entity systems and obviously I came across T=Machine's fantastic articles on the subject. In Part 5 of the series the author uses a relational schema to explain how an entity system is built and works. Since reading this, I have been wondering whether or not actually using a compact SQL library would be fast enough for real-time usage in video games. Performance seems to be the main issue with a full blown SQL database for management of all entities and components. However, as mentioned in T=Machine's post, basically all access to data inside the SQLDB is done sequentlially by each system over each component. Additionally, using a library like SQLite, one could easily improve performance by storing the entity data exclusively in RAM to increase access speeds. Disregarding possible performance issues, using a SQL database, in my opinion, would allow for a very intuitive implementation of entity systems and bring a long certain other benefits like easy de/serialization of game states and consistency checks like the uniqueness of entity IDs. Edit for clarification: The main question was whether using a SQL database for the actual entity management (not just storing the game state on the disk) in a real-time game would still yield a framerate appropriate for a game or even if someone is aware of projects that demonstrate SQL in a video game.

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• Mesh with quads to triangle mesh

  - by scape

  I want to use Blender for making models yet realize some of the polygons are not triangles but contain quads or more (example: cylinder top and bottom). I could export the the mesh as a basic mesh file and import it in to an openGL application and workout rendering the quads as tris, but anything with more than 4 vert indices is beyond me. Is it typical to convert the mesh to a triangle-based mesh inside blender before exporting it? I actually tried this through the quads_convert_to_tris method within a blender py script and the top of the cylinder does not look symmetrical. What is typically done to render a loaded mesh as a tri?

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• Html 5 ping pong game side collision problem

  - by Gurjit

  I am making a simple ping pong game where I am facing a side collision problem means when the ball collides with the either side of the paddle . Although I have written code for making it works but something is failing....I want plz someone to give suggestions and tell how to avoid it. Means while trying to hit the ball with side face of the paddle poses a problem.!! Here is the main part of the code causing problem function checkCollision(){ ///// This is collision detection for the upper part ///// if( cy + radius >= paddleTop && cx + radius > paddleLeft && cy + radius >= paddleTop + 5 && cx - radius <= paddleLeft + paddleWidth ) { dy = -dy; ++hits; /// On collision we are increasing the Score playSound(); } else if( cy + radius >= paddleTop && cy + radius <= paddleTop + paddleHeight && cx + radius >= paddleLeft && cy - radius <= paddleLeft - (radius + 1) ) { dx = -dx; } } here is working fiddle for it :- http://jsfiddle.net/gurjitmehta/orzpzf69/

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• Skanska Builds Global Workforce Insight with Cloud-Based HCM System

  - by HCM-Oracle

  By David Baum - Originally posted on Profit Peter Bjork grew up building things. He started his work life learning all sorts of trades at his father’s construction company in the northern part of Sweden. So in college, it was natural for him to pursue a bachelor’s degree in construction engineering—but he broke new ground when he added a master’s degree in finance to his curriculum vitae. Written on a traditional résumé, Bjork’s current title (vice president of information systems strategies) doesn’t reveal the diversity of his experience—that he’s adept with hammer and nails as well as rows and columns. But a big part of his current job is to work with his counterparts in human resources (HR) designing, building, and deploying the systems needed to get a complete view of the skills and potential of Skanska’s 22,000-strong white-collar workforce. And Bjork believes that complete view is essential to Skanska’s success. “Our business is really all about people,” says Bjork, who has worked with Skanska for 16 years. “You can have equipment and financial resources, but to truly succeed in a business like ours you need to have the right people in the right places. That’s what this system is helping us accomplish.” In a global HR environment that suffers from a paradox of high unemployment and a scarcity of skilled labor, managers need to have a complete understanding of workforce capabilities to develop management skills, recruit for open positions, ensure that staff is getting the training they need, and reduce attrition. Skanska’s human capital management (HCM) systems, based on Oracle Talent Management Cloud, play a critical role delivering that understanding. “Skanska’s philosophy of having great people, encouraging their development, and giving them the chance to move across business units has nurtured a culture of collaboration, but managing a diverse workforce spread across the globe is a monumental challenge,” says Annika Lindholm, global human resources system owner in the HR department at Skanska’s headquarters just outside of Stockholm, Sweden. “We depend heavily on Oracle’s cloud technology to support our HCM function.” Construction, Workers For Skanska’s more than 60,000 employees and contractors, managing huge construction projects is an everyday job. Beyond erecting signature buildings, management’s goal is to build a corporate culture where valuable talent can be sought out and developed, bringing in the right mix of people to support and grow the business. “Of all the companies in our space, Skanska is probably one of the strongest ones, with a laser focus on people and people development,” notes Tom Crane, chief HR and communications officer for Skanska in the United States. “Our business looks like equipment and material, but all we really have at the end of the day are people and their intellectual capital. Without them, second only to clients, of course, you really can’t achieve great things in the high-profile environment in which we work.” During the 1990s, Skanska entered an expansive growth phase. A string of successful acquisitions paved the way for the company’s transformation into a global enterprise. “Today the company’s focus is on profitable growth,” continues Crane. “But you can’t really achieve growth unless you are doing a very good job of developing your people and having the right people in the right places and driving a culture of growth.” In the United States alone, Skanska has more than 8,000 employees in four distinct business units: Skanska USA Building, also known as the Construction Manager, builds everything at ground level and above—hospitals, educational facilities, stadiums, airport terminals, and other massive projects. Skanska USA Civil does everything at ground level and below, such as light rail, water treatment facilities, power plants or power industry facilities, highways, and bridges. Skanska Infrastructure Development develops public-private partnerships—projects in which Skanska adds equity and also arranges for outside financing. Skanska Commercial Development acts like a commercial real estate developer, acquiring land and building offices on spec or build-to-suit for its clients. Skanska's international portfolio includes construction of the new Meadowlands Stadium. Getting the various units to operate collaboratatively helps Skanska deliver high value to clients and shareholders. “When we have this collaboration among units, it allows us to enrich each of the business units and, at the same time, develop our future leaders to be more facile in operating across business units—more accepting of a ‘one Skanska’ approach,” explains Crane. Workforce Worldwide But HR needs processes and tools to support managers who face such business dynamics. Oracle Talent Management Cloud is helping Skanska implement world-class recruiting strategies and generate the insights needed to drive quality hiring practices, internal mobility, and a proactive approach to building talent pipelines. With their new cloud system in place, Skanska HR leaders can manage everything from recruiting, compensation, and goal and performance management to employee learning and talent review—all as part of a single, cohesive software-as-a-service (SaaS) environment. Skanska has successfully implemented two modules from Oracle Talent Management Cloud—the recruiting and performance management modules—and is in the process of implementing the learn module. Internally, they call the systems Skanska Recruit, Skanska Talent, and Skanska Learn. The timing is apropos. With high rates of unemployment in recent years, there have been many job candidates on the market. However, talent scarcity continues to frustrate recruiters. Oracle Taleo Recruiting Cloud Service, one of the applications in the Oracle Talent Management cloud portfolio, enables Skanska managers to create more-intelligent recruiting strategies, pulling high-performer profile statistics to create new candidate profiles and using multitiered screening and assessments to ensure that only the best-suited candidate applications make it to the recruiter’s desk. Tools such as applicant tracking, interview management, and requisition management help recruiters and hiring managers streamline the hiring process. Oracle’s cloud-based software system automates and streamlines many other HR processes for Skanska’s multinational organization and delivers insight into the success of recruiting and talent-management efforts. “The Oracle system is definitely helping us to construct global HR processes,” adds Bjork. “It is really important that we have a business model that is decentralized, so we can effectively serve our local markets, and interact with our global ERP [enterprise resource planning] systems as well. We would not be able to do this without a really good, well-integrated HCM system that could support these efforts.” A key piece of this effort is something Skanska has developed internally called the Skanska Leadership Profile. Core competencies, on which all employees are measured, are used in performance reviews to determine weak areas but also to discover talent, such as those who will be promoted or need succession plans. This global profiling system brings consistency to the way HR professionals evaluate and review talent across the company, with a consistent set of ratings and a consistent definition of competencies. All salaried employees in Skanska are tied to a talent management process that gives opportunity for midyear and year-end reviews. Using the performance management module, managers can align individual goals with corporate goals; provide clear visibility into how each employee contributes to the success of the organization; and drive a strategic, end-to-end talent management strategy with a single, integrated system for all talent-related activities. This is critical to a company that is highly focused on ensuring that every employee has a development plan linked to his or her succession potential. “Our approach all along has been to deploy software applications that are seamless to end users,” says Crane. “The beauty of a cloud-based system is that much of the functionality takes place behind the scenes so we can focus on making sure users can access the data when they need it. This model greatly improves their efficiency.” The employee profile not only sets a competency baseline for new employees but is also integrated with Skanska’s other back-office Oracle systems to ensure consistency in the way information is used to support other business functions. “Since we have about a dozen different HR systems that are providing us with information, we built a master database that collects all the information,” explains Lindholm. “That data is sent not only to Oracle Talent Management Cloud, but also to other systems that are dependent on this information.” Collaboration to Scale Skanska is poised to launch a new Oracle module to link employee learning plans to the review process and recruitment assessments. According to Crane, connecting these processes allows Skanska managers to see employees’ progress and produce an updated learning program. For example, as employees take classes, supervisors can consult the Oracle Talent Management Cloud portal to monitor progress and align it to each individual’s training and development plan. “That’s a pretty compelling solution for an organization that wants to manage its talent on a real-time basis and see how the training is working,” Crane says. Rolling out Oracle Talent Management Cloud was a joint effort among HR, IT, and a global group that oversaw the worldwide implementation. Skanska deployed the solution quickly across all markets at once. In the United States, for example, more than 35 offices quickly got up to speed on the new system via webinars for employees and face-to-face training for the HR group. “With any migration, there are moments when you hold your breath, but in this case, we had very few problems getting the system up and running,” says Crane. Lindholm adds, “There has been very little resistance to the system as users recognize its potential. Customizations are easy, and a lasting partnership has developed between Skanska and Oracle when help is needed. They listen to us.” Bjork elaborates on the implementation process from an IT perspective. “Deploying a SaaS system removes a lot of the complexity,” he says. “You can downsize the IT part and focus on the business part, which increases the probability of a successful implementation. If you want to scale the system, you make a quick phone call. That’s all it took recently when we added 4,000 users. We didn’t have to think about resizing the servers or hiring more IT people. Oracle does that for us, and they have provided very good support.” As a result, Skanska has been able to implement a single, cost-effective talent management solution across the organization to support its strategy to recruit and develop a world-class staff. Stakeholders are confident that they are providing the most efficient recruitment system possible for competent personnel at all levels within the company—from skilled workers at construction sites to top management at headquarters. And Skanska can retain skilled employees and ensure that they receive the development opportunities they need to grow and advance.

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• Illumination and Shading for computer graphics class

  - by Sam I Am

  I am preparing for my test tomorrow and this is one of the practice questions. I solved it partially but I am confused with the rest. Here is the problem: Consider a gray world with no ambient and specular lighting ( only diffuse lighting). The screen coordinates of a triangle P1,P2,P3, are P1=(100,100), P2= (300,150), P3 = (200, 200). The gray values at P!,P2,P3 are 1/2, 3/4, and 1/4 respectively. The light is at infinity and its direction and gray color are (1,1,1) and 1.0 respectively. The coefficients of diffused reflection is 1/2. The normals of P1,P2,P3 are N1= (0,0,1), N2 = (1,0,0), and N3 = (0,1,0) respectively. Consider the coordinates of three points P1,P2,P3 to be 0. Do not normalize the normals. I have computed that the illumination at the 3 vertices P1,P2,P3 is (1/4,3/8,1/8). Also I computed that interpolation coefficients of a point P inside the triangle whose coordinates are (220, 160) are given by (1/5,2/5,2/5). Now I have 4 more questions regarding this problem. 1) The illumination at P using Gouraud Shading is: i) 1/2 The answer is 1/2, but I have no idea how to compute it.. 2) The interpolated normal at P is given by i) (2/5, 2/5,1/5) ii) (1/2, 1/4, 1/4) iii) (3/5, 1/5, 1/5) 3) The interpolated color at P is given by: i) 1/2 Again, I know the correct answer but no idea how to solve it 4) The illumination at P using Phong Shading is i) 1/4 ii) 9/40 iii) 1/2

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• How to calculate turn heading to a missile?

  - by Tony

  I have a missile that is shot from a ship at an angle, the missile then turns towards the target in an arc with a given turn radius. How do I determine the point on the arc when I need to start turning so the missile is heading straight for the target? EDIT What I need to do before I launch the missiles is calculate and draw the flight paths. So in the attached example the launch vehicle has a heading of 90 deg and the targets are behind it. Both missiles are launched at a relative heading of -45deg or + 45 deg to the launch vehicle's heading. The missiles initially turn towards the target with a known turn radius. I have to calculate the point at which the turn takes the missile to heading at which it will turn to directly attack the target. Obviously if the target is at or near 45 degrees then there is no initial turn the missile just goes straight for the target. After the missile is launched the map will also show the missile tracking on this line as indication of its flight path. What I am doing is working on a simulator which mimics operational software. So I need to draw the calculated flight path before I allow the missile to be launched. In this example the targets are behind the launch vehicle but the precalculated paths are drawn.

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• Platformer Starter Kit - Collision Issues

  - by Cyral

  I'm having trouble with my game that is based off the XNA Platformer starter kit. My game uses smaller tiles (16x16) then the original (32x40) which I'm thinking may be having an effect on collision (Being it needs to be more precise). Standing on the edge of a tile and jumping causes the player to move off the the tile when he lands. And 80% of the time, when the player lands, he goes flying though SOLID tiles in a diagonal fashion. This is very annoying as it is almost impossible to test other features, when spawning and jumping will result in the player landing in another part of the level or falling off the edge completely. The code is as follows: /// <summary> /// Updates the player's velocity and position based on input, gravity, etc. /// </summary> public void ApplyPhysics(GameTime gameTime) { float elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds; Vector2 previousPosition = Position; // Base velocity is a combination of horizontal movement control and // acceleration downward due to gravity. velocity.X += movement * MoveAcceleration * elapsed; velocity.Y = MathHelper.Clamp(velocity.Y + GravityAcceleration * elapsed, -MaxFallSpeed, MaxFallSpeed); velocity.Y = DoJump(velocity.Y, gameTime); // Apply pseudo-drag horizontally. if (IsOnGround) velocity.X *= GroundDragFactor; else velocity.X *= AirDragFactor; // Prevent the player from running faster than his top speed. velocity.X = MathHelper.Clamp(velocity.X, -MaxMoveSpeed, MaxMoveSpeed); // Apply velocity. Position += velocity * elapsed; Position = new Vector2((float)Math.Round(Position.X), (float)Math.Round(Position.Y)); // If the player is now colliding with the level, separate them. HandleCollisions(); // If the collision stopped us from moving, reset the velocity to zero. if (Position.X == previousPosition.X) velocity.X = 0; if (Position.Y == previousPosition.Y) velocity.Y = 0; } /// <summary> /// Detects and resolves all collisions between the player and his neighboring /// tiles. When a collision is detected, the player is pushed away along one /// axis to prevent overlapping. There is some special logic for the Y axis to /// handle platforms which behave differently depending on direction of movement. /// </summary> private void HandleCollisions() { // Get the player's bounding rectangle and find neighboring tiles. Rectangle bounds = BoundingRectangle; int leftTile = (int)Math.Floor((float)bounds.Left / Tile.Width); int rightTile = (int)Math.Ceiling(((float)bounds.Right / Tile.Width)) - 1; int topTile = (int)Math.Floor((float)bounds.Top / Tile.Height); int bottomTile = (int)Math.Ceiling(((float)bounds.Bottom / Tile.Height)) - 1; // Reset flag to search for ground collision. isOnGround = false; // For each potentially colliding tile, for (int y = topTile; y <= bottomTile; ++y) { for (int x = leftTile; x <= rightTile; ++x) { // If this tile is collidable, ItemCollision collision = Level.GetCollision(x, y); if (collision != ItemCollision.Passable) { // Determine collision depth (with direction) and magnitude. Rectangle tileBounds = Level.GetBounds(x, y); Vector2 depth = RectangleExtensions.GetIntersectionDepth(bounds, tileBounds); if (depth != Vector2.Zero) { float absDepthX = Math.Abs(depth.X); float absDepthY = Math.Abs(depth.Y); // Resolve the collision along the shallow axis. if (absDepthY < absDepthX || collision == ItemCollision.Platform) { // If we crossed the top of a tile, we are on the ground. if (previousBottom <= tileBounds.Top) isOnGround = true; // Ignore platforms, unless we are on the ground. if (collision == ItemCollision.Impassable || IsOnGround) { // Resolve the collision along the Y axis. Position = new Vector2(Position.X, Position.Y + depth.Y); // Perform further collisions with the new bounds. bounds = BoundingRectangle; } } else if (collision == ItemCollision.Impassable) // Ignore platforms. { // Resolve the collision along the X axis. Position = new Vector2(Position.X + depth.X, Position.Y); // Perform further collisions with the new bounds. bounds = BoundingRectangle; } } } } } // Save the new bounds bottom. previousBottom = bounds.Bottom; } It also tends to jitter a little bit sometimes, I'm solved some of this with some fixes I found here on stackexchange, But Ive only seen one other case of the flying though blocks problem. This question seems to have a similar problem in the video, but mine is more crazy. Again this is a very annoying bug! Any help would be greatly appreciated! EDIT: Speed stuff // Constants for controling horizontal movement private const float MoveAcceleration = 13000.0f; private const float MaxMoveSpeed = 1750.0f; private const float GroundDragFactor = 0.48f; private const float AirDragFactor = 0.58f; // Constants for controlling vertical movement private const float MaxJumpTime = 0.35f; private const float JumpLaunchVelocity = -3500.0f; private const float GravityAcceleration = 3400.0f; private const float MaxFallSpeed = 550.0f; private const float JumpControlPower = 0.14f;

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