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  • How exactly to implement multiple threads in a game

    - by xerwin
    So I recently started learning Java, and having a interest in playing games as well as developing them, naturally I want to create game in Java. I have experience with games in C# and C++ but all of them were single-threaded simple games. But now, I learned how easy it is to make threads in Java, I want to take things to the next level. I started thinking about how would I actually implement threading in a game. I read couple of articles that say the same thing "Usually you have thread for rendering, for updating game logic, for AI, ..." but I haven't (or didn't look hard enough) found example of implementation. My idea how to make implementation is something like this (example for AI) public class AIThread implements Runnable{ private List<AI> ai; private Player player; /*...*/ public void run() { for (int i = 0; i < ai.size(); i++){ ai.get(i).update(player); } Thread.sleep(/* sleep until the next game "tick" */); } } I think this could work. If I also had a rendering and updating thread list of AI in both those threads, since I need to draw the AI and I need to calculate the logic between player and AI(But that could be moved to AIThread, but as an example) . Coming from C++ I'm used to do thing elegantly and efficiently, and this seems like neither of those. So what would be the correct way to handle this? Should I just keep multiple copies of resources in each thread or should I have the resources on one spot, declared with synchronized keyword? I'm afraid that could cause deadlocks, but I'm not yet qualified enough to know when a code will produce deadlock.

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  • Searching for entity awareness in 3D space algorithm and data structure

    - by Khanser
    I'm trying to do some huge AI system just for the fun and I've come to this problem. How can I let the AI entities know about each other without getting the CPU to perform redundant and costly work? Every entity has a spatial awareness zone and it has to know what's inside when it has to decide what to do. First thoughts, for every entity test if the other entities are inside the first's reach. Ok, so it was the first try and yep, that is redundant and costly. We are working with real time AI over 10000+ entities so this is not a solution. Second try, calculate some grid over the awareness zone of every entity and test whether in this zones are entities (we are working with 3D entities with float x,y,z location coordinates) testing every point in the grid with the indexed-by-coordinate entities. Well, I don't like this because is also costly, but not as the first one. Third, create some multi linked lists over the x's and y's indexed positions of the entities so when we search for an interval between x,y and z,w positions (this interval defines the square over the spatial awareness zone) over the multi linked list, we won't have 'voids'. This has the problem of finding the nearest proximity value if there isn't one at the position where we start the search. I'm not convinced with any of the ideas so I'm searching for some enlightening. Do you people have any better ideas?

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  • Business knowledge in a large financial org?

    - by Victor
    As a programmer working in the finance industry, I recently got a project that is a hedge fund adminsitrative application(used to calculate NAVs, allocate assets etc.) From a business point of view this is a good thing. When we think of our 'next' project, typically the impulse is to think in terms of technology. e.g: 'I want to work on a project that uses SOA/cloud etc etc.' I am interested to know if anyone while career planning also takes into account the business aspect of a future project. i.e. what the application does. So does anybody ever think like this : 'I wish to work on a trading system so I can understand capital markets better.' instead of 'I want to work on a project that uses SOA/cloud etc etc.' I say this because it appears to me in the finance domain, for senior position, good business knowledge pays well. So maybe a guy that knows more business but maybe not so much latest technologies is at an advantage? The rockstar programmer seems more suited for an aggressive startup. Particularly big old finance orgs rarely invest in tech just for the 'cool factor'. No?

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  • How to achieve selection of a tile from a tile sheet based on an ID?

    - by Bugster
    Let's say I have a tile sheet that contains 8 sprites per sheet. Each sprite is a tile of 30x30. I wrote my own custom map parser/map loader however I'm having trouble extracting a certain tile sprite from the file. I'll describe my problem better in order for everyone to understand. I wrote an enum of materials, each material has a value according to it's location relative to the tile sheet. For example void is 1, grass is 2, rock is 3, etc. So in my tile sheet they are represented as such: +---+---+---+---+---+ | 1 | 2 | 3 | 4 | 5 | +---+---+---+---+---+ Which is equivalent to: +------+-------+-------+ | void | grass | stone | +------+-------+-------+ Basically when rendering, I created a tile class, each tile has 2 coordinates: X and Y (They are calculated automatically) and a material which can be represented either as a number, either as a value (ID). When rendering, I have a vector of sprites which are all taken from 1 file called tilesheet.png, however each of them must only draw a certain portion of the tile sheet, for example say I have something like this: tile coordinateBounds(topLeftX, topLeftY, tileWidth, tileHeight); During the initialization of the map I calculate an array of tiles, and I give each of them their position, their materials based on the values in a map file and a few other variables such as collision. I need to apply the coordinateBounds to each of them according to their material value. For example if the material is grass it should only take the grass sprite from the tilesheet. I must also mention I'm using SFML, and there are no borders or spacing between the tiles.

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  • Coordinate and positioning problem on iOS with cocos2d-x

    - by Vexille
    I'm using cocos2d-x alongside with Marmalade and running some tests and tutorials before starting an actual project with them. So far things are working reasonably well on the windows simulator, Android and even on Blackberry's Playbook, but on iOS devices (iPhone and iPad) the positioning seems to be off. To make things clearer, I put together a scene that just draws an image in the middle of the screen. It worked as expected on everything else, but this is the result I got on an iPhone: To get the coordinates for the center of the screen I'm using the VisibleRect class from the TestCpp sample. It just uses sharedOpenGLView to get the visible size and visible origin, and calculate the center from that. CCSprite* test = CCSprite::create("Ball.png", CCRectMake(0, 0, 80, 80) ); test->setPosition( ccp(VisibleRect::center().x, VisibleRect::center().y) ); this->addChild(test); Also I have a noBorder policy set on AppDelegate: CCEGLView::sharedOpenGLView()->setDesignResolutionSize(designSize.width, designSize.height, kResolutionNoBorder); One funny thing is that I tried to deploy the TestCpp sample project to some iOS devices and it worked reasonably well on the iPhone, but on the iPad the application was only being drawn on a small portion of the screen - just like what happened on the iPhone when I tried using the ShowAll policy.

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  • Checking for collisions on a 3D heightmap

    - by Piku
    I have a 3D heightmap drawn using OpenGL (which isn't important). It's represented by a 2D array of height data. To draw this I go through the array using each point as a vertex. Three vertices are wound together to form a triangle, two triangles to make a quad. To stop the whole mesh being tiny I scale this by a certain amount called 'gridsize'. This produces a fairly nice and lumpy, angular terrain kind of similar to something you'd see in old Atari/Amiga or DOS '3D' games (think Virus/Zarch on the Atari ST). I'm now trying to work out how to do collision with the terrain, testing to see if the player is about to collide with a piece of scenery sticking upwards or fall into a hole. At the moment I am simply dividing the player's co-ordinates by the gridsize to find which vertex the player is on top of and it works well when the player is exactly over the corner of a triangle piece of terrain. However... How can I make it more accurate for the bits between the vertices? I get confused since they don't exist in my heightmap data, they're a product of the GPU trying to draw a triangle between three points. I can calculate the height of the point closest to the player, but not the space between them. I.e if the player is hovering over the centre of one of these 'quads', rather than over the corner vertex of one, how do I work out the height of the terrain below them? Later on I may want the player to slide down the slopes in the terrain.

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  • Dynamic Jump spot

    - by Pasquale Sada
    I have an initial velocity V(Vx,Vy,VZ) and a spot where he stands still at S(Sx,Sy,Sz). What I'm trying to achieve is a jump on a spot E(Ex,Ey,Ez) where you have clicked on(only lower or higher spot, because I've in place a simple steering behavior for even terrains). There are no obstacle around. I've implemented a formula that can make him jump in a precise way on a spot but you need to declare an angle: the problem arise when the selected spot is straight above your head. It' pretty lame that the char hang there and can reach a thing that is 1cm above is head. I'll share the code I'm using: Vector3 dir = target - transform.position; // get target direction float h = dir.y; // get height difference dir.y = 0; // retain only the horizontal direction float dist = dir.magnitude ; // get horizontal distance float a = angle * Mathf.Deg2Rad; // convert angle to radians dir.y = dist * Mathf.Tan(a); // set dir to the elevation angle dist += h / Mathf.Tan(a); // correct for small height differences // calculate the velocity magnitude float vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 *a)); return vel * dir.normalized;

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  • Generic rule parser for RPG board game rules - how to do it?

    - by burzum
    I want to build a generic rule parser for pen and paper style RPG systems. A rule can involve usually 1 to N entities 1 to N roles of a dice and calculating values based on multiple attributes of an entity. For example: Player has STR 18, his currently equipped weapon gives him a bonus of +1 STR but a malus of DEX -1. He attacks a monster entity and the game logic now is required to run a set of rules or actions: Player rolls the dice, if he gets for example 8 or more (base attack value he needs to pass is one of his base attributes!) his attack is successfully. The monster then rolls the dice to calculate if the attack goes through it's armor. If yes the damage is taken if not the attack was blocked. Besides simple math rules can also have constraints like applying only to a certain class of user (warrior vs wizzard for example) or any other attribute. So this is not just limited to mathematical operations. If you're familiar with RPG systems like Dungeon and Dragons you'll know what I'm up to. My issue is now that I have no clue how to exactly build this the best possible way. I want people to be able to set up any kind of rule and later simply do an action like selecting a player and a monster and run an action (set of rules like an attack). I'm asking less for help with the database side of things but more about how to come up with a structure and a parser for it to keep my rules flexible. The language of choice for this is php by the way.

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  • OOP implementation of BUFFS and Stats. Suggestion

    - by Mattia Manzo Manzati
    I am developing an MMORPG server using NodeJS. I am not sure how to implement Buffs, i mean, equipped objects or used skills have effects on the Player() which has many Stats(), some of them have a max cap... Effects can change the Stat value, increasing or decreasing it by a value, a percentage or completly rewrite the value of the stat. After a while I have decided to create a base class for buffs, which can be hidden (if they are casted from an equipped object) or shown if they came from an ability (Spell). Anyway I need suggestion how to implement it, use an array for all active buffs for a stat and have a function calculate the value of the stat affected by buffs each time I need the value of the stat or...? Other more OOP's ways to do it? I have read this What's a way to implement a flexible buff/debuff system? but this implements only a percentage system, which buffs can only say "+10%, +20%, etc...", but I would love to have an hybrid system, which can have percentage values or static values (like WoW does), and using modifiers it's hard to implement, because modifiers refers to the current value of stat :/ Thanks for suggestions :)

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  • Yelp, Google's API for restaurants help

    - by chris
    Ok I have looked into this, and I'm not sure if anyone else has experience with it. I'm having termendous difficulties with Yelp and Google's API. To help explain what I am trying to do here is the concept of the website. We would have to pull restaurants based on user distance, and then randomize them based on quality of restaurant based on feedback from review websites (Yelp, Google, urbanspoon, zagat, opentable, kudzu, yahoo - doesn't have to be from all), and feedback from our users (on results page for the random restaurant users can select good recommendation/bad recommendation). There’s a lot we could calculate for our formula. Things that will dictate your results will be based on if you’re at home or work. If you’re at home you will have more time to drive out to the city to grab some dinner or lunch. If you’re at work we would have to recommend restaurants nearby as lunch is typically 30 minutes to a hour. A 30 minute lunch would require take out most likely or quick service. A hour lunch break you could dine in at a local fine dining restaurant. So in a nutshell, user comes to website. Select if they're at home or work, click submit and we will have a random restaurant selected for them to go. If they don't like it they can click retry and a new restaurant can show. The issue I am having is using the API to gather all the restaurants in the US. I know it can be done because there are similiar websites/apps that pull restaurants that are closest to you such as Ness, Alfred, and I believe there's two more but I can't remember the names. Anyone know if this can be accomplish?

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  • Sorting Algorithm : output

    - by Aaditya
    I faced this problem on a website and I quite can't understand the output, please help me understand it :- Bogosort, is a dumb algorithm which shuffles the sequence randomly until it is sorted. But here we have tweaked it a little, so that if after the last shuffle several first elements end up in the right places we will fix them and don't shuffle those elements furthermore. We will do the same for the last elements if they are in the right places. For example, if the initial sequence is (3, 5, 1, 6, 4, 2) and after one shuffle we get (1, 2, 5, 4, 3, 6) we will keep 1, 2 and 6 and proceed with sorting (5, 4, 3) using the same algorithm. Calculate the expected amount of shuffles for the improved algorithm to sort the sequence of the first n natural numbers given that no elements are in the right places initially. Input: 2 6 10 Output: 2 1826/189 877318/35343 For each test case output the expected amount of shuffles needed for the improved algorithm to sort the sequence of first n natural numbers in the form of irreducible fractions. I just can't understand the output.

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  • Calculating the correct particle angle in an outwards explosion

    - by Sun
    I'm creating a simple particle explosion but am stuck in finding the correct angle to rotate my particle. The effect I'm going for is similar to this: Where each particle is going outwards from the point of origin and at the correct angle. This is what I currently have: As you can see, each particle is facing the same angle, but I'm having a little difficulty figuring out the correct angle. I have the vector for the point of emission and the new vector for each particle, how can I use this to calculate the angle? Some code for reference: private Particle CreateParticle() { ... Vector2 velocity = new Vector2(2.0f * (float)(random.NextDouble() * 2 - 1), 2.0f * (float)(random.NextDouble() * 2 - 1)); direction = velocity - ParticleLocation; float angle = (float)Math.Atan2(direction.Y, direction.X); ... return new Particle(texture, position, velocity, angle, angularVelocity, color, size, ttl, EmitterLocation); } I am then using the angle created as so in my particles Draw method: spriteBatch.Draw(Texture, Position, null, Color, Angle, origin, Size, SpriteEffects.None, 0f);

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  • How to prevent showing outside of world game in Cocos2D-x

    - by HRZ
    I'm trying to make a tower defense game and it can zoom in/out and scrolling over my world map. How to scroll over the game and how to restrict it not to show outside of my map(black area). At below I scroll over the map by using CCCamera but I don't know how I can restrict it. CCPoint tap = touch->getLocation(); CCPoint prev_tap = touch->getPreviousLocation(); CCPoint sub_point = tap - prev_tap; float xNewPos, yNewPos; float xEyePos, yEyePos, zEyePos; float cameraPosX, cameraPosY, cameraPosZ; // First we get the current camera position. GameLayer->getCamera()->getCenterXYZ(&cameraPosX, &cameraPosY, &cameraPosZ); GameLayer->getCamera()->getEyeXYZ(&xEyePos, &yEyePos, &zEyePos); // Calculate the new position xNewPos = cameraPosX - sub_point.x; yNewPos = cameraPosY - sub_point.y; GameLayer->getCamera()->setCenterXYZ(xNewPos, yNewPos, cameraPosZ); GameLayer->getCamera()->setEyeXYZ(xNewPos, yNewPos, zEyePos); And for zooming I used such code: GameLayer->setScale(GameLayer->getScale() + 0.002); //zooming in

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  • functional requirements - use wording based on verbs?

    - by yas
    Question: Should the functional requirements in a requirements doc use wording based on verbs? Context: School assignment, working in a team, working through the SDLC. The requirements doc has been done and we are now into design. Problem: The requirements doc has an enumerated list of what I'd call features of the app - the functional requirements. In that list are things that I'd think of as "how's" rather than "what's" and now, trying to work on design, I feel like a part of design has been prematurely dictated. I've not done this before! To me, I should be dealing strictly with things that describe "what." Example of current: Pretend that the job is to make an omelet. Listing: crack the egg, break into bowl, scramble, etc.; crosses over the line into the territory of how. Along that track, so does wording like: create, generate, list, calculate, determine, validate, etc. - verbs, basically. Right now, I have a list of requirements that are partially rooted in verbs. My idea of a requirements doc for an omelet would be more like: has two eggs, x ounces of ham, x ounces of bacon, x ounces of montery-jack cheese, x ounces of cilantro, etc. - nothing but what (nouns). I might have, and could have, spoken up before finalizing the requirements doc if I'd had any experience.

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  • Conventions for search result scoring

    - by DeaconDesperado
    I assume this type of question is more on-topic here than on regular SO. I have been working on a search feature for my team's web application and have had a lot of success building a multithreaded, "divide and conquer" processing system to work through a large amount of fulltext. Our problem domain is pretty specific. Users of the app generate posts, and as a general rule, posts that are more recent are considered to be of greater relevance. Some of the data we are trying to extract from search is very specific (user's feelings about specific items or things) and we are using python nltk to do named-entity extraction to find interesting likely query terms. Essentially we look for descriptive adjective-noun pairs and generate a general picture of a user's expressed sentiment as a list of tokens. This search is intended as an internal tool for our team to draw out a local picture of sentiments like "soggy pizza." There's some machine learning in there too to do entity resolution on terms like "soggy" to all manner of adjectives expressing nastiness. My problem is I am at a loss for how to go about scoring these results. The text being searched is split up into tokens in a list, so my initial approach would be to normalize a float score between 0.0-1.0 generated off of how far into the list the terms appear and how often they are repeated (a later mention of the term being worth less, earlier more, greater frequency-greater score, etc.) A certain amount of weight could be given to the timestamp as well, though I am not certain how to calculate this. I am curious if anyone has had to solve a similar problem in a search relevance grading between appreciable metrics (frequency, term location/colocation, recency) and if there are and guidelines for how to weight each. I should mention as well that the final fallback procedure in the search is to pipe the query to Sphinx, which has its own scoring practices. Sphinx operates as the last resort in case our application specific processing can't find any eligible candidates.

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  • XNA - 2D Rotation of an object to a selected direction

    - by lobsterhat
    I'm trying to figure out the best way of rotating an object towards the directional input of the user. I'm attempting to mimic making turns on ice skates. For instance, if the player is moving right and the input is down and left, the player should start rotating to the right a set amount each tick. I'll calculate a new vector based on current velocity and rotation and apply that to the current velocity. That should give me nice arcing turns, correct? At the moment I've got eight if/else statements for each key combination which in turn check the current rotation: // Rotate to 225 if (keyboardState.IsKeyDown(Keys.Up) && keyboardState.IsKeyDown(Keys.Left)) { // Rotate right if (rotation >= 45 || rotation < 225) { rotation += ROTATION_PER_TICK; } // Rotate left else if (rotation < 45 || rotation > 225) { rotation -= ROTATION_PER_TICK; } } This seems like a sloppy way to do this and eventually, I'll need to do this check about 10 times a tick. Any help toward a more efficient solution is appreciated.

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  • Points around a circumference C#

    - by Lautaro
    Im trying to get a list of vectors that go around a circle, but i keep getting the circle to go around several times. I want one circel and the dots to be placed along its circumference. I want the first dot to start at 0 and the last dot to end just before 360. Also i need to be able to calculate the spacing by the ammount of points. List<Vector2> pointsInPath = new List<Vector2>(); private int ammountOfPoints = 5; private int blobbSize = 200; private Vector2 topLeft = new Vector2(100, 100); private Vector2 blobbCenter; private int endAngle = 50; private int angleIncrementation; public Blobb() { blobbCenter = new Vector2(blobbSize / 2, blobbSize / 2) + topLeft; angleIncrementation = endAngle / ammountOfPoints; for (int i = 0; i < ammountOfPoints; i++) { pointsInPath.Add(getPointByAngle(i * angleIncrementation, 100, blobbCenter)); // pointsInPath.Add(getPointByAngle(i * angleIncrementation, blobbSize / 2, blobbCenter)); } } private Vector2 getPointByAngle(float angle, float distance, Vector2 centre) { return new Vector2((float)(distance * Math.Cos(angle) ), (float)(distance * Math.Sin(angle))) + centre ; }

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  • Is this high coupling?

    - by Bono
    Question I'm currently working a on an assignment for school. The assignment is to create a puzzle/calculator program in which you learn how to work with different datastructures (such as Stacks). We have generate infix math strings suchs as "1 + 2 * 3 - 4" and then turn them in to postfix math strings such as "1 2 + 3 * 4 -". In my book the author creates a special class for converting the infix notation to postfix. I was planning on using this but whilst I was about to implement it I was wondering if the following is what you would call "high coupling". I have read something about this (nothing that is taught in the book or anything) and was wondering about the aspect (since I still have to grasp it). Problem I have created a PuzzleGenerator class which generates the infix notation of the puzzle (or math string, whatever you want to call it) when it's instantiated. I was going to make a method getAnswer() in which I would instantiate the InToPost class (the class from the book) to convert the infix to postfox notation and then calculate the answer. But whilst doing this I thought: "Is using the InToPost class inside this method a form a high coupling, and would it be better to place this in a different method?" (such as a "convertPostfixToInfix" method, inside the PuzzleGenerator class) Thanks in advance.

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  • What sort of data should be sent for mouse-based movement in a multiplayer game?

    - by Daniel
    I'm new to the Multiplayer Rodeo here so please bear with me... I am just getting started and I'm trying to figure out how to deal with movement. I've looked at the question Best way to implement mouse-based movement in MMOG which gives me a pretty good idea, but I'm still struggling with what kind of data should be sent to the server. If a player is on position [x:0, y:0] and I click with the mouse on [x:40, y:40] to start movement, what information should I send to the server? Should I calculate the position based on velocity on client side and just send the expected location? Or should I send current location and velocity and direction? When the server is updating the clients on the players' whereabouts, should the position be sent only, and the clients expected to interpolate/predict movement, or can the direction sent from the client (instead of just coordinates) be used. My concern(or confusion) is regarding the ping/lag frequency of data update and use of a predictive algorithm, as I'd like the movement to be smooth even with a high latency, and prevent ability to cheat(though that's not the top priority).

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  • More efficient in range checking

    - by Mob
    I am going to use a specific example in my question, but overall it is pretty general. I use java and libgdx. I have a ship that moves through space. In space there is debris that the ship can tractor beam in and and harvest. Debris is stored in a list, and the object contains it own x and y values. So currently there is no way to to find the debris's location without first looking at the debris object. Now at any given time there can be a huge (1000+) amount of debris in space, and I figure that calculating the distance between the ship and every single piece of debris and comparing it to maximum tractor beam length is rather inefficient. I have thought of dividing space into sectors, and have each sector contain a list of every object in it. This way I could only check nearby sectors. However this essentially doubles memory for the list. (I would reference the same object so it wouldn't double overall. I am not CS major, but I doubt this would be hugely significant.) This also means anytime an object moves it has to calculate which sector it is in, again not a huge problem. I also don't know if I can use some sort of 2D MAP that uses x and y values as keys. But since I am using float locations this sounds more trouble than its worth. I am kind of new to programming games, and I imagined there would be some eloquent solution to this issue.

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  • How to perform game object smoothing in multiplayer games

    - by spaceOwl
    We're developing an infrastructure to support multiplayer games for our game engine. In simple terms, each client (player) engine sends some pieces of data regarding the relevant game objects at a given time interval. On the receiving end, we step the incoming data to current time (to compensate for latency), followed by a smoothing step (which is the subject of this question). I was wondering how smoothing should be performed ? Currently the algorithm is similar to this: Receive incoming state for an object (position, velocity, acceleration, rotation, custom data like visual properties, etc). Calculate a diff between local object position and the position we have after previous prediction steps. If diff doesn't exceed some threshold value, start a smoothing step: Mark the object's CURRENT POSITION and the TARGET POSITION. Linear interpolate between these values for 0.3 seconds. I wonder if this scheme is any good, or if there is any other common implementation or algorithm that should be used? (For example - should i only smooth out the position? or other values, such as speed, etc) any help will be appreciated.

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  • Calculating distance from viewer to object in a shader

    - by Jay
    Good morning, I'm working through creating the spherical billboards technique outlined in this paper. I'm trying to create a shader that calculates the distance from the camera to all objects in the scene and stores the results in a texture. I keep getting either a completely black or white texture. Here are my questions: I assume the position that's automatically sent to the vertex shader from ogre is in object space? The gpu interpolates the output position from the vertex shader when it sends it to the fragment shader. Does it do the same for my depth calculation or do I need to move that calculation to the fragment shader? Is there a way to debug shaders? I have no errors but I'm not sure I'm getting my parameters passed into the shaders correctly. Here's my shader code: void DepthVertexShader( float4 position : POSITION, uniform float4x4 worldViewProjMatrix, uniform float3 eyePosition, out float4 outPosition : POSITION, out float Depth ) { // position is in object space // outPosition is in camera space outPosition = mul( worldViewProjMatrix, position ); // calculate distance from camera to vertex Depth = length( eyePosition - position ); } void DepthFragmentShader( float Depth : TEXCOORD0, uniform float fNear, uniform float fFar, out float4 outColor : COLOR ) { // clamp output using clip planes float fColor = 1.0 - smoothstep( fNear, fFar, Depth ); outColor = float4( fColor, fColor, fColor, 1.0 ); } fNear is the near clip plane for the scene fFar is the far clip plane for the scene

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  • How do I interpolate air drag with a variable time step?

    - by Valentin Krummenacher
    So I have a little game which works with small steps, however those steps vary in time, so for example I sometimes have 10 Steps/second and then I have 20 Steps/second. This changes automatically depending on how many steps the user's computer can take. To avoid inaccurate positioning of the game's player object I use y=v0*dt+g*dt^2/2 to determine my objects y-position, where dt is the time since the last step, v0 is the velocity of my object in the beginning of my step and g is the gravity. To calculate the velocity in the end of a step I use v=v0+g*dt what also gives me correct results, independent of whether I use 2 steps with a dt of for example 20ms or one step with a dt of 40ms. Now I would like to introduce air drag. For simplicity's sake I use a=k*v^2 where a is the air drag's acceleration (I am aware that it would usually result in a force, but since I assume 1kg for my object's mass the force is the same as the resulting acceleration), k is a constant (in this case I'm using 0.001) and v is the speed. Now in an infinitely small time interval a is k multiplied by the velocity in this small time interval powered by 2. The problem is that v in the next time interval would depend on the drag of the last which again depends on the v of the last interval and so on... In other words: If I use a=k*v^2 I get different results for my position/velocity when I use 2 steps of 20ms than when I use one step of 40ms. I used to have this problem for my position too, but adding +g*dt^2/2 to the formula for my position fixed the problem since it takes into account that the position depends on the velocity which changes slightly in every infinitely small time interval. Does something like that exist for air drag too? And no, I dont mean anything like Adding air drag to a golf ball trajectory equation or similar, for that kind of method only gives correct results when all my steps are the same. (I hope you can understand my intermediate english, it's not my main language so I would like to say sorry for all the silly mistakes I might have made in my question)

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  • Reflection velocity

    - by MindSeeker
    I'm trying to get a moving circular object to bounce (elastically) off of an immovable circular object. Am I doing this right? (The results look right, but I hate to trust that alone, and I can't find a tutorial that tackles this problem and includes the nitty gritty math/code to verify what I'm doing). If it is right, is there a better/faster/more elegant way to do this? Note that the object (this) is the moving circle, and the EntPointer object is the immovable circle. //take vector separating the two centers <x, y>, and then get unit vector of the result: MathVector2d unitnormal = MathVector2d(this -> Retxpos() - EntPointer -> Retxpos(), this -> Retypos() - EntPointer -> Retypos()).UnitVector(); //take tangent <-y, x> of the unitnormal: MathVector2d unittangent = MathVector2d(-unitnormal.ycomp, unitnormal.xcomp); MathVector2d V1 = MathVector2d(this -> Retxvel(), this -> Retyvel()); //Calculate the normal and tangent vector lengths of the velocity: (the normal changes, the tangent stays the same) double LengthNormal = DotProduct(unitnormal, V1); double LengthTangent = DotProduct(unittangent, V1); MathVector2d VelVecNewNormal = unitnormal.ScalarMultiplication(-LengthNormal); //the negative of what it was before MathVector2d VelVecNewTangent = unittangent.ScalarMultiplication(LengthTangent); //this stays the same MathVector2d NewVel = VectorAddition(VelVecNewNormal, VelVecNewTangent); //combine them xvel = NewVel.xcomp; //and then apply them yvel = NewVel.ycomp; Note also that this question is just about velocity, the position code is handled elsewhere (in other words, assume that this code is implemented at the exact moment that the circles begin to overlap). Thanks in advance for your help and time!

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  • Separate collision mesh model?

    - by Menno Gouw
    I want to have another go at 3D within XNA. What I have seen from some other games that they just have a separate very low poly model "cage" around the environment model. However I can not find any reference to this. I have not that much experience with XNA 3D either. Is it possible to have this cage within each of my environmental models already? Lets just say I call the mesh within the .FBX wall and col_wall. How would I call to these different meshes within XNA? The player would just have a tight collision cube around. To make it a bit more efficient I will be making divide the map up by cubes and only calculate collision if the player is in it. Question two: I can't find anywhere to do cube vs mesh collision. Is there a method for this? Or perhaps it is possible to build my collision cage out of cubes in the 3D app and on loading of the models in XNA replace them directly by cubes? So I could just do box to box collision which should be very cheap and still give the player the ability to move over ledges on the static models.

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