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• Integration error in high velocity

  - by Elektito

  I've implemented a simple simulation of two planets (simple 2D disks really) in which the only force is gravity and there is also collision detection/response (collisions are completely elastic). I can launch one planet into orbit of the other just fine. The collision detection code though does not work so well. I noticed that when one planet hits the other in a free fall it speeds backward and goes much higher than its original position. Some poking around convinced me that the simplistic Euler integration is causing the error. Consider this case. One object has a mass of 1kg and the other has a mass equal to earth. Say the object is 10 meters above ground. Assume that our dt (delta t) is 1 second. The object goes to the height of 9 meters at the end of the first iteration, 7 at the end of the second, 4 at the end of the third and 0 at the end of the fourth iteration. At this points it hits the ground and bounces back with the speed of 10 meters per second. The problem is with dt=1, on the first iteration it bounces back to a height of 10. It takes several more steps to make the object change its course. So my question is, what integration method can I use which fixes this problem. Should I split dt to smaller pieces when velocity is high? Or should I use another method altogether? What method do you suggest? EDIT: You can see the source code here at github:https://github.com/elektito/diskworld/

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• What are the maths behind 'Raiden 2' purple laser?

  - by Aybe

  The path of the laser is affected by user input and enemies present on the screen. Here is a video, at 5:00 minutes the laser in question is shown : Raiden II (PS) - 1 Loop Clear - Part 2 UPDATE Here is a test using Inkscape, ship is at bottom, the first 4 enemies are targeted by the plasma. There seems to be a sort of pattern. I moved the ship first, then the handle from it to form a 45° angle, then while trying to fit the curve I found a pattern of parallel handles and continued so until I reached the last enemy. Update, 5/26/2012 : I started an XNA project using beziers, there is still some work needed, will update the question next week. Stay tuned ! Update : 5/30/2012 : It really seems that they are using Bézier curves, I think I will be able to replicate/imitate a plasma of such grade. There are two new topics I discovered since last time : Arc length, Runge's phenomenon, first one should help in having a linear movement possible over a Bézier curve, second should help in optimizing the number of vertices. Next time I will put a video so you can see the progress 8-)

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• Calculating collision force with AfterCollision/NormalImpulse is unreliable when IgnoreCCD = false?

  - by Michael

  I'm using Farseer Physics Engine 3.3.1 in a very simple XNA 4 test game. (Note: I'm also tagging this Box2D, because Farseer is a direct port of Box2D and I will happily accept Box2D answers that solve this problem.) In this game, I'm creating two bodies. The first body is created using BodyFactory.CreateCircle and BodyType.Dynamic. This body can be moved around using the keyboard (which sets Body.LinearVelocity). The second body is created using BodyFactory.CreateRectangle and BodyType.Static. This body is static and never moves. Then I'm using this code to calculate the force of collision when the two bodies collide: staticBody.FixtureList[0].AfterCollision += new AfterCollisionEventHandler(AfterCollision); protected void AfterCollision(Fixture fixtureA, Fixture fixtureB, Contact contact) { float maxImpulse = 0f; for (int i = 0; i < contact.Manifold.PointCount; i++) maxImpulse = Math.Max(maxImpulse, contact.Manifold.Points[i].NormalImpulse); // maxImpulse should contain the force of the collision } This code works great if both of these bodies are set to IgnoreCCD=true. I can calculate the force of collision between them 100% reliably. Perfect. But here's the problem: If I set the bodies to IgnoreCCD=false, that code becomes wildly unpredictable. AfterCollision is called reliably, but for some reason the NormalImpulse is 0 about 75% of the time, so only about one in four collisions is registered. Worse still, the NormalImpulse seems to be zero for completely random reasons. The dynamic body can collide with the static body 10 times in a row in virtually exactly the same way, and only 2 or 3 of the hits will register with a NormalImpulse greater than zero. Setting IgnoreCCD=true on both bodies instantly solves the problem, but then I lose continuous physics detection. Why is this happening and how can I fix it? Here's a link to a simple XNA 4 solution that demonstrates this problem in action: http://www.mediafire.com/?a1w242q9sna54j4

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• How to design a character animation system?

  - by Andrea Benedetti

  I'm searching for suggestions and resources on the possible ways to design a character animation system. I mean a system built on top of the graphics engine (as graphics engine I use Ogre3D, that provide an animation layer), and in strict contact with the logic of the game. It's for a sports title, so the question is not easy. Edit: What I'm searching for are suggestions and resources about the action state mechines (or animation state machines), that is build on top of the animation pipeline already provided by the graphics engine. So, a state-driver animation interface for use by virtually all higher-level game code.

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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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• Unity-Animation parameters are not being set

  - by user1814893

  I have the following animation controller: with two parameters of walkingSpeed and Jump. I have the following code which should change the values: animator.SetFloat("walkingSpeed",0.9f); animator.SetBool("Jump",true); and animator is the correctly referenced animator object. However the values that the parameters are set to do not appear to change in the animator window, nor do they appear to impact what is happening on the screen. However they do seem to impact the values obtained when doing the following: animator.GetFloat("walkingSpeed"); The animator consists of the shown blend tree, which works correctly and is always active, however due to the values not being changed it does not blends, and always acts as if the value with which it blends (walkingSpeed is 0). What is going on?

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• How can I test different TV display types for my XBLIG game?

  - by Steve Dunn

  The XBLIG submission check-list says to ensure that all important stuff critical to game-play be visible in the 'TitleSafeArea'. I've received a bug report during play-test of my game (Crazy Balloon Lite) that says parts of my scrolling 2D map are only half visible (i.e. chopped at the left of the screen). I've tested my game myself on a 47" TV and also a 19" VGA monitor, both of which look fine. The bug report says the issue occurs on a standard 20" TV. My question is: without buying different sizes of TVs, is there a way to test what my game will look like on different sized displays?

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• LWJGL - OpenGL - Texture shading

  - by Trixmix

  I want to use LWJGL to create a shader that all it does is change the color of the given texture. For example I tell it to draw the letter A using a sprite sheet then I can tell the shader to draw the letter in a certain color. How would you do something like this without needed to create different colored letter sprite sheets? Task for the shader: Simply change all pixels to a certain color in the texture. Input: Color , texture. Output: it draws onto the screen the new colored texture. How do i accomplish such a thing?

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• Isometric Movement in Javascript In the DOM

  - by deep

  I am creating a game using Javascript. I am not using the HTML5 Canvas Element. The game requires both side view controlles, and Isometric controls, hence the movementMode variable. I have got the specific angles, but I am stuck on an aspect of this. https://chillibyte.makes.org/thimble/movement function draw() { if (keyPressed) { if (whichKey == keys.left) { move(-1,0) } if (whichKey == keys.right) { move(1,0) } if (whichKey == keys.up) { move(0,-1) } if (whichKey == keys.down) { move(0,1) } } } This gives normal up, down , left, and right. i want to refactor this so that i can plugin two variables into the move() function, which will give the movement wanted. Now for the trig. /| / | / | y / | /a___| x Take This Right angled Triangle. given that x is 1, y must be equal to tan(a) That Seems right. However, when I do Math.tan(45), i get a number similar to 1.601. Why? To Sum up this question. I have a function, and i need a function which will converts an angle to a value, which will tell me the number of pixels that i need to go up by, if i only go across 1. Is it Math.tan that i want? or is it something else?

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• Time calculation between openGL update calls.

  - by Vijayendra

  In XNA, the system calls update and draw function with the time information. This contains information such as how much time has passed since last update was called. This makes easy to integrate time and do animation calculation accordingly. But I dont see any such mechanism in openGL. I see openGL requires programmers to have their own implementation which could be buggy or inefficient. Is there any standard (and efficient) code that demonstrate this practice in openGL?

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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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• Setting Anchor Point

  - by Siddharth

  I want to set anchor point for the sprite like cocos2d has done for their implementation. I do not found any thing like that in andengine so please provide guidance on that. I want to move the sprite on touch so I use following code but that does not work for me. super.setPosition(pX - this.getWidthScaled() / 2, pY - this.getHeightScaled() / 2); Because I touch on the corner of the image but automatically it comes at center of the image because of above code. I want to remain the touch at desire position and drag it. For me the anchor point became useful. But I don't found anything in andengine.

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• What is a currently a good game stack for simple Javascript 2D multiplatform game?

  - by JacobusR

  I'm looking for advice from someone can help me avoid common pitfalls in developing light weight, quick-to-market games. Yeah, I've heard of Google ;-), but a trip down Google lane does not beat solid experience from someone who has been down this path. I'm looking for advice from someone who works alone, or in a small team, and has developed some 2D games for mobile. My game ideas don't require intensive graphics, just simple arcade style glyphs and collision detection. My experience is mostly with Scala, Java and web technologies (Javascript, CSS, SVG, HTML, etc). My question is: Is there a nice stack that someone can suggest that will be a good fit for my skillset? I'm considering Javascript for simple 2D shooter games with simple multiplayer games being supported with a Scala server-side written on Spray. Is this silly? Should I rather look into things such as Unity 3D, and use it in 2D mode? For the actual game engine, something like the Sparrow Framework would be great, but it needs to be multiplatform.

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• High level project workflow

  - by user775060

  We are a small software company trying our hand at our second game. Since our first games' process was a living nightmare (since we used webdevelopment workflow) I have decided to educate myself on how to manage a game project on a high level. How does your process work, from idea to launch? Preferably in situations where you have a team that needs to cooperate. I've seen these 2 links, which are useful in a way, but was wondering if there are better/more comprehensive ways to do this? http://www.goodcontroller.com/blog/?p=136 http://gogogic.wordpress.com/2009/02/09/symbol6-how-we-created-an-iphone-game/ All input would be infinitely appreciated.

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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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• Drawing simple geometric figures with DrawUserPrimitives?

  - by Navy Seal

  I'm trying to draw a simple triangle based on an array of vertex. I've been searching for a tutorial and I found a simple example on riemers but I couldn't get it to work. I think it was made for XNA 3 and it seems there were some changes to XNA 4? Using this example: http://www.riemers.net/eng/Tutorials/XNA/Csharp/Series1/The_first_triangle.php I get this error: Additional information: The current vertex declaration does not include all the elements required by the current vertex shader. TextureCoordinate0 is missing. I'm not english so I'm having some trouble to understand everything. For what I understand error is confusing because I'm trying to draw a triangle color based and not texture based and it shouldn't need a texture. Also I saw some articles about dynamic shadows and lights and I would like to know if this is the kind of code used to do it with some tweaks like culling because I'm wondering if its heavy code for performance in real time.

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• Tool for creating complex paths?

  - by TerryB

  I want to create some fairly complex predefined paths for my AI sprites to follow. I'll need to use curves, splines etc to get the effect I want. Is there a drawing tool out there that will allow me to draw such curves, "mesh" them by placing lots of points along them at some defined density and then output the coordinates of all of those points for me? I could write this tool myself but hopefully one of the drawing packages can do this? Cheers!

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• Farseer: How can I crush Mario? [on hold]

  - by Homer_Simpson

  I want that Mario dies if the box is crushing him. My game has a similar level like this level from New Super Mario Bros. Wii: http://www.youtube.com/watch?v=tYyu6tFAa2M At the beginning of the level, you see some boxes falling to the ground. If a box crushes Mario, he dies. I want to do exactly the same in my game, but I don't know how to do that in Farseer. How can I do that in Farseer 3.3.1? Do you have any suggestions? I don't know how to do the collision detection. I use rectangles for the boxes and ground in Farseer. Mario is a polygon.

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• The technology behind 22can's curiosity

  - by Cameron Scully

  I don't have alot of experience with mobile apps and I definitely don't know much about MMO's but I was wondering what the basic architecture of a game like that would be (understandably some don't consider it a game, but it must use some game theory and implementation). Mainly, how are they able to send/recieve real time feed back of the cube being chipped away by thousands of players on their mobile devices? How is data of the cube's millions of pieces stored and accessed so quickly? Thanks

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• How to choose cell to put entity in in an uniform grid used for broad phase collision detection?

  - by nathan

  I'm trying to implement the broad phase of my collision detection algorithm. My game is an arcade game with lot of moving entities in an open space with relatively equivalent sizes. Regarding the above specifications, i decided to use an uniform grid for space partitioning. The problem i have right know is how to efficiently choose in which cells an entity should be added. ATM i'm doing something like this: for (int x = 0; x < gridSize; x++) { for (int y = 0; y < gridSize; y++) { GridCell cell = grid[x][y]; cell.clear(); //remove the previously added entities for (int i = 0; i < entities.size(); i++) { Entity e = entities.get(i); if (cell.isEntityOverlap(e)) { cell.add(e); } } } } The isEntityOverlap is a simple method i added my GridCell class. public boolean isEntityOverlap(Shape s) { return cellArea.intersects(s); } Where cellArea is a Rectangle. cellArea = new Rectangle(x, y, CollisionGrid.CELL_SIZE, CollisionGrid.CELL_SIZE); It works but it's damn slow. What would be a fast way to know all the cells an entity overlaps? Note: by "it works" i mean, the entities are contained in the good cells over the time after movements etc.

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• 2D pathfinding - finding smooth paths

  - by Kooi Nam Ng

  I was trying to implement a simple pathfinding, but the outcome is less satisfactory than what I intended to achieve. The thing is units in games like Starcraft 2 move in all directions whereas units in my case only move in at most 8 directions (Warcraft 1 style) as these 8 directions direct to next available nodes (they move from a tile to next neighboring tile). What should I do in order to achieve the result as in Starcraft 2? Shrink the tile size? On the picture you can see a horizontal line of rock tiles being obstacles, and the found path marked as green tiles. The red line is the path I want to achieve.

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• Recommended method towards making custom maps for a 2d game?

  - by Qasim

  I am planning on making a 2D game, however different from my last personal projects I want this one to have enhanced graphics, with custom-designed levels. My previous 2d platformers were tile-based, in which I made a map editor for to create levels. However, I am wondering the best way to implement custom designed maps? For say, some grass is a litter higher than others, flowers here and there, cool drawings and structures along the way, etc. instead of just the same old tiles over and over again. I am thinking but I just can't grasp the idea of how to implement it. I have seen it done in other games and am interested to see how they accomplish it, but can't get my hands on some source code. :(

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• Should I always be checking every neighbor when building voxel meshes?

  - by Raven Dreamer

  I've been playing around with Unity3d, seeing if I can make a voxel-based engine out of it (a la Castle Story, or Minecraft). I've dynamically built a mesh from a volume of cubes, and now I'm looking into reducing the number of vertices built into each mesh, as right now, I'm "rendering" vertices and triangles for cubes that are fully hidden within the larger voxel volume. The simple solution is to check each of the 6 directions for each cube, and only add the face to the mesh if the neighboring voxel in that direction is "empty". Parsing a voxel volume is BigO(N^3), and checking the 6 neighbors keeps it BigO(7*N^3)-BigO(N^3). The one thing this results in is a lot of redundant calls, as the same voxel will be polled up to 7 times, just to build the mesh. My question, then, is: Is there a way to parse a cubic volume (and find which faces have neighbors) with fewer redundant calls? And perhaps more importantly, does it matter (as BigO complexity is the same in both cases)?

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• Joystick example problem for android 2D

  - by iQue

  I've searched all over the web for an answer to this, and there are simular topics but nothing works for me, and I have no Idea why. I just want to move my sprite using a joystick, since I'm useless at math when it comes to angles etc I used an example, Ill post the code here: public float initx = 50; //og 425; public float inity = 300; //og 267; public Point _touchingPoint = new Point(50, 300); //og(425, 267); public Point _pointerPosition = new Point(100, 170); private Boolean _dragging = false; private MotionEvent lastEvent; @Override public boolean onTouchEvent(MotionEvent event) { if (event == null && lastEvent == null) { return _dragging; } else if (event == null && lastEvent != null) { event = lastEvent; } else { lastEvent = event; } // drag drop if (event.getAction() == MotionEvent.ACTION_DOWN) { _dragging = true; } else if (event.getAction() == MotionEvent.ACTION_UP) { _dragging = false; } if (_dragging) { // get the pos _touchingPoint.x = (int) event.getX(); _touchingPoint.y = (int) event.getY(); // bound to a box if (_touchingPoint.x < 25) { _touchingPoint.x = 25; //og 400 } if (_touchingPoint.x > 75) { _touchingPoint.x = 75; //og 450 } if (_touchingPoint.y < 275) { _touchingPoint.y = 275; //og 240 } if (_touchingPoint.y > 325) { _touchingPoint.y = 325; //og 290 } // get the angle double angle = Math.atan2(_touchingPoint.y - inity, _touchingPoint.x - initx) / (Math.PI / 180); // Move the beetle in proportion to how far // the joystick is dragged from its center _pointerPosition.y += Math.sin(angle * (Math.PI / 180)) * (_touchingPoint.x / 70); _pointerPosition.x += Math.cos(angle * (Math.PI / 180)) * (_touchingPoint.x / 70); // stop the sprite from goin thru if (_pointerPosition.x + happy.getWidth() >= getWidth()) { _pointerPosition.x = getWidth() - happy.getWidth(); } if (_pointerPosition.x < 0) { _pointerPosition.x = 0; } if (_pointerPosition.y + happy.getHeight() >= getHeight()) { _pointerPosition.y = getHeight() - happy.getHeight(); } if (_pointerPosition.y < 0) { _pointerPosition.y = 0; } } public void render(Canvas canvas) { canvas.drawColor(Color.BLUE); canvas.drawBitmap(joystick.get_joystickBg(), initx-45, inity-45, null); canvas.drawBitmap(happy, _pointerPosition.x, _pointerPosition.y, null); canvas.drawBitmap(joystick.get_joystick(), _touchingPoint.x - 26, _touchingPoint.y - 26, null); } public void update() { this.onTouchEvent(null); } og= original position. as you can see Im trying to move the joystick, but when I do it stops working correctly, I mean it still works like a joystick but the sprite dosnt move accordingly, if I for example push the joystick down, the sprite moves up, and if I push it up it moves left. can anyone PLEASE help me, I've been stuck here for sooo long and its really frustrating.

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• Calculating the position of an object with regards to current position using OpenGL like matrices

  - by spartan2417

  i have a 1st person camera that collides with walls, i also have a small sphere in front of my camera denoted by the camera position plus the distance ahead. I cannot get the postion of the sphere but i have the position of my camera. e.g. i need to find the position of the point or at the very least find away of calculating the position using the camera positions. code: static Float P_z = 0; P_z = -15; PushMatrix(); LoadMatrix(&Inv); Material(SCEGU_AMBIENT, 0x00000066); TranslateXYZ(0,0,P_z); ScaleXYZ(0.1f,0.1f,0.1f); pointer.Render(); PopMatrix(); where Inv is the camera positions (Inv.w.x,Inv.w.z), pointer is the sphere.

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