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• Draw depth works on WP7 emulator but not device

  - by Luke

  I am making a game on a WP7 device using C# and XNA. I have a system where I always want the object the user is touching to be brought to the top, so every time it is touched I add float.Epsilon to its draw depth (I have it set so that 0 is the back and 1 is the front). On the Emulator that all works fine, but when I run it on my device the draw depths seem to be completely random. I am hoping that anybody knows a way to fix this. I have tried doing a Clean & Rebuild and uninstalling from the device but that is no luck. My call to spritebatch.Begin is: spriteBatch.Begin(SpriteSortMode.FrontToBack, BlendState.AlphaBlend); and to draw I use spriteBatch.Draw(Texture, new Rectangle((int)X, (int)Y, (int)Width, (int)Height), null, Color.White, 0, Vector2.Zero, SpriteEffects.None, mDrawDepth); Where mDrawDepth is a float value of the draw depth (likely to be a very small number; a small multiple of float.Epsilon. Any help much appreciated, thanks!

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• What's the proper way to calculate probability for a card game?

  - by Milan Babuškov

  I'm creating AI for a card game, and I run into problem calculating the probability of passing/failing the hand when AI needs to start the hand. Cards are A, K, Q, J, 10, 9, 8, 7 (with A being the strongest) and AI needs to play to not take the hand. Assuming there are 4 cards of the suit left in the game and one is in AI's hand, I need to calculate probability that one of the other players would take the hand. Here's an example: AI player has: J Other 2 players have: A, K, 7 If a single opponent has AK7 then AI would lose. However, if one of the players has A or K without 7, AI would survive. Now, looking at possible distribution, I have: P1 P2 AI --- --- --- AK7 loses AK 7 survives A7 K survives K7 A survives A 7K survives K 7A survives 7 KA survives AK7 loses Looking at this, it seems that there is 75% chance of survival. However, I skipped the permutations that mirror the ones from above. It should be the same, but somehow when I write them all down, it seems that chance is only 50%: P1 P2 AI --- --- --- AK7 loses A7K loses K7A loses KA7 loses 7AK loses 7KA loses AK 7 survives A7 K survives K7 A survives KA 7 survives 7A K survives 7K A survives A K7 survives A 7K survives K 7A survives K A7 survives 7 AK survives 7 KA survives AK7 loses A7K loses K7A loses KA7 loses 7AK loses 7KA loses 12 loses, 12 survivals = 50% chance. Obviously, it should be the same (shouldn't it?) and I'm missing something in one of the ways to calculate. Which one is correct?

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• Moving camera, or camera with discrete "screens"?

  - by Jacob Millward

  I'm making a game with a friend, but having trouble deciding on a camera style. The basic idea for the game, is having a randomly generated 2-dimensional world, with settlements in it. These settlements would have access to different resources, and it would be the job of the player to create bridges and ladders and links between these villages so they can trade. The player would advance personally by getting better gear, fighting monsters and looking for materials in the world, in order to craft and trade them at the settlements. My friend wants to use an old-style camera, where the world is split into a discrete number of screens that the player moves between. Similar to early Zelda dungeons, or Knytt Stories. This is opposite to me, as I want a standard camera that follows the player around as I feel the split-screen style camera limits the game. Can anyone argue the case either way? We've hit a massive roadblock here and can't seem to get past it.

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• Android/Java AI agent framework/middleware

  - by corneliu

  I am looking for an AI agent framework to use as a starting point in an Android game I have to create for a university research project. It has been suggested to me to use JADE, but, as far as I can tell, it's not a suitable framework for games (at least for my game idea) because it runs in a split-execution mode, and it needs an always-active network connection to a main host. What I want is just a little something to give me a headstart. I am willing to adjust the game's features to the framework because it's more of a mockup game, and the purpose is to compare the performance of a couple of agents in the game world. The game will be very simplistic, with a minimal UI that displays various stats about the characters in the game (so no graphics, no pathfinding). Thank you.

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• How to create Executable Jar

  - by Siddharth

  When I try to create a jar file i found the following error, so please someone help me to out of this. Exception in thread "LWJGL Application" com.badlogic.gdx.utils.GdxRuntimeException: Couldn't load file: img/black_ring.png at com.badlogic.gdx.graphics.Pixmap.(Pixmap.java:137) at com.badlogic.gdx.graphics.glutils.FileTextureData.prepare(FileTextureData.java:55) at com.badlogic.gdx.graphics.Texture.load(Texture.java:175) at com.badlogic.gdx.graphics.Texture.create(Texture.java:159) at com.badlogic.gdx.graphics.Texture.(Texture.java:133) at com.badlogic.gdx.graphics.Texture.(Texture.java:122) at com.badlogic.runningball.UserBall.(UserBall.java:19) at com.badlogic.runningball.GameScreen.(GameScreen.java:25) at com.badlogic.runningball.RunningBall.create(RunningBall.java:12) at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:126) at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:113) Caused by: com.badlogic.gdx.utils.GdxRuntimeException: File not found: img/black_ring.png (Internal) at com.badlogic.gdx.files.FileHandle.read(FileHandle.java:108) at com.badlogic.gdx.files.FileHandle.length(FileHandle.java:364) at com.badlogic.gdx.files.FileHandle.readBytes(FileHandle.java:156) at com.badlogic.gdx.graphics.Pixmap.(Pixmap.java:134) ... 10 more

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• UDK ParticleSystem Problem

  - by EmAdpres

  I use below code to create my particles ( in fact, I don't know any other way.) spawnedParticleComponents = WorldInfo.MyEmitterPool.SpawnEmitter(ParticleSystem'ParticleName', Location, Rotator ); spawnedParticleComponents.setTranslation(newLocation); ... And unfortunately, I spawn many particles in game. When I play my game, after some time, I see Exceeded max active pooled emitters! Warning in console . To solve the problem, first, I tried spawnedParticleComponents.DeactivateSystem();, But it doesn't help. Then I try WorldInfo.MyEmitterPool.ClearPoolComponents(false);, But it doesn't either . :( How can I destroy many spawned particles and avoid this warning ?

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• Collisions between moving ball and polygons

  - by miguelSantirso

  I know this is a very typical problem and that there area a lot of similar questions, but I have been looking for a while and I have not found anything that fits what I want. I am developing a 2D game in which I need to perform collisions between a ball and simple polygons. The polygons are defined as an array of vertices. I have implemented the collisions with the bounding boxes of the polygons (that was easy) and I need to refine that collision in the cases where the ball collides with the bounding box. The ball can move quite fast and the polygons are not too big so I need to perform continuous collisions. I am looking for a method that allows me to detect if the ball collides with a polygon and, at the same time, calculate the new direction for the ball after bouncing in the polygon. (I am using XNA, in case that helps)

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• Sounds to describe the weather?

  - by Matthew

  I'm trying to think of sounds that will help convey the time of day and weather condition. I'm not even sure of all the weather conditions I would consider, and some are obvious. Like if it's raining, the sound of rain. But then I'm thinking, what about for a calm day? If it's morning time, I could do birds chirping or something. Night time could be an owl or something. What are some good combinations of sounds/weather/time to have a good effect?

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• Updating scene graph in multithreaded game

  - by user782220

  In a game with a render thread and a game logic thread the game logic thread needs to update the scene graph used by the render thread. I've read about ideas such as a queue of updates. Can someone describe to a newbie at scene graphs what kind of interface the scene graph exports. Presumably it would be rather complicated. So then how does a queue of updates get implemented in C++ in a way that can handle the complexity of the interface of the scene graph while also being type safe and efficient. Again I'm a newbie at scene graphs and C++.

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• D3D11 how to simulate multiple depth channels

  - by Nock

  Here's what I'd like to achieve: Rendering a first pass of objects in my scene, using standard depth comparison Rendering another pass of objects in the same scene, but with the following rules: A Pixel of the 2nd pass always override the first pass (no depth compare between them) Use Depth comparison between pixels written from the second pass. In English I want depth comparison made inside each pass but I always want the second pass pixels to override the first pass ones. Some things I've thought: I tried to think about using stencil to solve this, but I couldn't find a way. I know I could render into a separate target the second pass then composite the result into the first, but I'd like to avoid that. I could use two separate Depth Buffer, one dedicated to each pass. (I never tried, but I figure it's possible to switch the depth buffer in a Render Target "on the fly") Any idea of the best solution? Thanks

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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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• Handling early/late/dropped packets for interpolation in a 3D multiplayer game

  - by Ben Cracknell

  I'm working on a multiplayer game that for the purposes of this question, is most similar to Team Fortress. Each network data packet will contain the 3D position of the target moving object. (this object could be another player) The packets are sent on a fixed interval, and linear interpolation will be used to smooth the transition between packets. Under normal circumstances, interpolation will occur between the second-to-last packet, and the last packet received. The linear interpolation algorithm is the same as this post: Interpolating positions in a multiplayer game I have the same issue as in that post, but the answers don't seem like they will work in my situation. Consider the following scenario: Normal packet timing, everything is okay The next expected packet is late. That's okay, we'll just extrapolate based on previous positions The late packet eventually arrives with corrections to our extrapolation. Now what do we do with its information? The answers on the above post suggest we should just interpolate to this new packet's position, but that would not work at all. If we have already extrapolated past that point in time, moving back would cause rubber-banding. The issue is similar in the case of an early or dropped packet. So I believe what I am looking for is some way to smoothly deal with new information in an ongoing interpolation/extrapolation process. Since I might be moving on to quadratic or even cubic interpolation, it would be great if the same solutiuon could be applied to those as well.

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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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• How do game engines implement certain features?

  - by Milo

  I have always wondered how modern game engines do things such as realistic water, ambient occluded lighting, eye adaptation, global illumination, etc. I'm not so much interested in the implementation details, but more on what part of the graphics API such as D3D or OpenGL allow adding such functionality. The only thing I can think of is shaders, but I do not think just shaders can do all that. So really what I'm asking is, what functions or capabilities of graphics APIs enable developers to implement these types of features into their engines? Thanks

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• Pathfinding results in false path costs that are too high

  - by user2144536

  I'm trying to implement pathfinding in a game I'm programming using this method. I'm implementing it with recursion but some of the values after the immediate circle of tiles around the player are way off. For some reason I cannot find the problem with it. This is a screen cap of the problem: The pathfinding values are displayed in the center of every tile. Clipped blocks are displayed with the value of 'c' because the values were too high and were covering up the next value. The red circle is the first value that is incorrect. The code below is the recursive method. //tileX is the coordinates of the current tile, val is the current pathfinding value, used[][] is a boolean //array to keep track of which tiles' values have already been assigned public void pathFind(int tileX, int tileY, int val, boolean[][] used) { //increment pathfinding value int curVal = val + 1; //set current tile to true if it hasn't been already used[tileX][tileY] = true; //booleans to know which tiles the recursive call needs to be used on boolean topLeftUsed = false, topUsed = false, topRightUsed = false, leftUsed = false, rightUsed = false, botomLeftUsed = false, botomUsed = false, botomRightUsed = false; //set value of top left tile if necessary if(tileX - 1 >= 0 && tileY - 1 >= 0) { //isClipped(int x, int y) returns true if the coordinates givin are in a tile that can't be walked through (IE walls) //occupied[][] is an array that keeps track of which tiles have an enemy in them // //if the tile is not clipped and not occupied set the pathfinding value if(isClipped((tileX - 1) * 50 + 25, (tileY - 1) * 50 + 25) == false && occupied[tileX - 1][tileY - 1] == false && !(used[tileX - 1][tileY - 1])) { pathFindingValues[tileX - 1][tileY - 1] = curVal; topLeftUsed = true; used[tileX - 1][tileY - 1] = true; } //if it is occupied set it to an arbitrary high number so enemies find alternate routes if the best is clogged if(occupied[tileX - 1][tileY - 1] == true) pathFindingValues[tileX - 1][tileY - 1] = 1000000000; //if it is clipped set it to an arbitrary higher number so enemies don't travel through walls if(isClipped((tileX - 1) * 50 + 25, (tileY - 1) * 50 + 25) == true) pathFindingValues[tileX - 1][tileY - 1] = 2000000000; } //top middle if(tileY - 1 >= 0 ) { if(isClipped(tileX * 50 + 25, (tileY - 1) * 50 + 25) == false && occupied[tileX][tileY - 1] == false && !(used[tileX][tileY - 1])) { pathFindingValues[tileX][tileY - 1] = curVal; topUsed = true; used[tileX][tileY - 1] = true; } if(occupied[tileX][tileY - 1] == true) pathFindingValues[tileX][tileY - 1] = 1000000000; if(isClipped(tileX * 50 + 25, (tileY - 1) * 50 + 25) == true) pathFindingValues[tileX][tileY - 1] = 2000000000; } //top right if(tileX + 1 <= used.length && tileY - 1 >= 0) { if(isClipped((tileX + 1) * 50 + 25, (tileY - 1) * 50 + 25) == false && occupied[tileX + 1][tileY - 1] == false && !(used[tileX + 1][tileY - 1])) { pathFindingValues[tileX + 1][tileY - 1] = curVal; topRightUsed = true; used[tileX + 1][tileY - 1] = true; } if(occupied[tileX + 1][tileY - 1] == true) pathFindingValues[tileX + 1][tileY - 1] = 1000000000; if(isClipped((tileX + 1) * 50 + 25, (tileY - 1) * 50 + 25) == true) pathFindingValues[tileX + 1][tileY - 1] = 2000000000; } //left if(tileX - 1 >= 0) { if(isClipped((tileX - 1) * 50 + 25, (tileY) * 50 + 25) == false && occupied[tileX - 1][tileY] == false && !(used[tileX - 1][tileY])) { pathFindingValues[tileX - 1][tileY] = curVal; leftUsed = true; used[tileX - 1][tileY] = true; } if(occupied[tileX - 1][tileY] == true) pathFindingValues[tileX - 1][tileY] = 1000000000; if(isClipped((tileX - 1) * 50 + 25, (tileY) * 50 + 25) == true) pathFindingValues[tileX - 1][tileY] = 2000000000; } //right if(tileX + 1 <= used.length) { if(isClipped((tileX + 1) * 50 + 25, (tileY) * 50 + 25) == false && occupied[tileX + 1][tileY] == false && !(used[tileX + 1][tileY])) { pathFindingValues[tileX + 1][tileY] = curVal; rightUsed = true; used[tileX + 1][tileY] = true; } if(occupied[tileX + 1][tileY] == true) pathFindingValues[tileX + 1][tileY] = 1000000000; if(isClipped((tileX + 1) * 50 + 25, (tileY) * 50 + 25) == true) pathFindingValues[tileX + 1][tileY] = 2000000000; } //botom left if(tileX - 1 >= 0 && tileY + 1 <= used[0].length) { if(isClipped((tileX - 1) * 50 + 25, (tileY + 1) * 50 + 25) == false && occupied[tileX - 1][tileY + 1] == false && !(used[tileX - 1][tileY + 1])) { pathFindingValues[tileX - 1][tileY + 1] = curVal; botomLeftUsed = true; used[tileX - 1][tileY + 1] = true; } if(occupied[tileX - 1][tileY + 1] == true) pathFindingValues[tileX - 1][tileY + 1] = 1000000000; if(isClipped((tileX - 1) * 50 + 25, (tileY + 1) * 50 + 25) == true) pathFindingValues[tileX - 1][tileY + 1] = 2000000000; } //botom middle if(tileY + 1 <= used[0].length) { if(isClipped((tileX) * 50 + 25, (tileY + 1) * 50 + 25) == false && occupied[tileX][tileY + 1] == false && !(used[tileX][tileY + 1])) { pathFindingValues[tileX][tileY + 1] = curVal; botomUsed = true; used[tileX][tileY + 1] = true; } if(occupied[tileX][tileY + 1] == true) pathFindingValues[tileX][tileY + 1] = 1000000000; if(isClipped((tileX) * 50 + 25, (tileY + 1) * 50 + 25) == true) pathFindingValues[tileX][tileY + 1] = 2000000000; } //botom right if(tileX + 1 <= used.length && tileY + 1 <= used[0].length) { if(isClipped((tileX + 1) * 50 + 25, (tileY + 1) * 50 + 25) == false && occupied[tileX + 1][tileY + 1] == false && !(used[tileX + 1][tileY + 1])) { pathFindingValues[tileX + 1][tileY + 1] = curVal; botomRightUsed = true; used[tileX + 1][tileY + 1] = true; } if(occupied[tileX + 1][tileY + 1] == true) pathFindingValues[tileX + 1][tileY + 1] = 1000000000; if(isClipped((tileX + 1) * 50 + 25, (tileY + 1) * 50 + 25) == true) pathFindingValues[tileX + 1][tileY + 1] = 2000000000; } //call the method on the tiles that need it if(tileX - 1 >= 0 && tileY - 1 >= 0 && topLeftUsed) pathFind(tileX - 1, tileY - 1, curVal, used); if(tileY - 1 >= 0 && topUsed) pathFind(tileX , tileY - 1, curVal, used); if(tileX + 1 <= used.length && tileY - 1 >= 0 && topRightUsed) pathFind(tileX + 1, tileY - 1, curVal, used); if(tileX - 1 >= 0 && leftUsed) pathFind(tileX - 1, tileY, curVal, used); if(tileX + 1 <= used.length && rightUsed) pathFind(tileX + 1, tileY, curVal, used); if(tileX - 1 >= 0 && tileY + 1 <= used[0].length && botomLeftUsed) pathFind(tileX - 1, tileY + 1, curVal, used); if(tileY + 1 <= used[0].length && botomUsed) pathFind(tileX, tileY + 1, curVal, used); if(tileX + 1 <= used.length && tileY + 1 <= used[0].length && botomRightUsed) pathFind(tileX + 1, tileY + 1, curVal, used); }

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• Fitting a rectangle into screen with XNA

  - by alecnash

  I am drawing a rectangle with primitives in XNA. The width is: width = GraphicsDevice.Viewport.Width and the height is height = GraphicsDevice.Viewport.Height I am trying to fit this rectangle in the screen (using different screens and devices) but I am not sure where to put the camera on the Z-axis. Sometimes the camera is too close and sometimes to far. This is what I am using to get the camera distance: //Height of piramid float alpha = 0; float beta = 0; float gamma = 0; alpha = (float)Math.Sqrt((width / 2 * width/2) + (height / 2 * height / 2)); beta = height / ((float)Math.Cos(MathHelper.ToRadians(67.5f)) * 2); gamma = (float)Math.Sqrt(beta*beta - alpha*alpha); position = new Vector3(0, 0, gamma); Any idea where to put the camera on the Z-axis?

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• Is it possible to construct a cube with fewer than 24 vertices

  - by Telanor

  I have a cube-based world like Minecraft and I'm wondering if there's a way to construct a cube with fewer than 24 vertices so I can reduce memory usage. It doesn't seem possible to me for 2 reasons: the normals wouldn't come out right and per-face textures wouldn't work. Is this the case or am I wrong? Maybe there's some fancy new DX11 tech that can help? Edit: Just to clarify, I have 2 requirements: I need surface normals for each cube face in order to do proper lighting and I need a way to address a different indexes in a texture array for each cube face

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• can't spot the error. Trying to increment

  - by Kevin Jensen Petersen

  I really can't spot the error, or the misspelling. This script should increase the variable currentTime with 1 every second, as long as i am holding the Space button down. This is Unity C#. using UnityEngine; using System.Collections; public class GameTimer : MonoBehaviour { //Timer private bool isTimeDone; public GUIText counter; public int currentTime; private bool starting; //Each message will be shown random each 20 seconds. public string[] messages; public GUIText msg; //To check if this is the end private bool end; void Update () { counter.guiText.text = currentTime.ToString(); if(Input.GetKey(KeyCode.Space)) { if(starting == false) { starting = true; } if(end == false) { if(isTimeDone) { StartCoroutine(timer()); } } else { msg.guiText.text = "You think you can do better? Press 'R' to Try again!"; if(Input.GetKeyDown(KeyCode.R)) { Application.LoadLevel(Application.loadedLevel); } } } if(!Input.GetKey(KeyCode.Space) & starting) { end = true; } } IEnumerator timer() { isTimeDone = false; yield return new WaitForSeconds(1); currentTime++; isTimeDone = true; } }

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• Seek Steering Behavior with Target Direction for Group of Fighters

  - by SebastianStehle

  I am implementing steering algorithms with group management for spaceships (fighters). I select a leader and assign the target positions for the other spaceships based on the target position of the leader and an offset. This works well. But when my spaceships arrive they all have a different direction. I want them to keep to look in the same direction (target - start). I also want to combine this behavior with a minimum turning radius that is based on the speed. The only idea I have is to calculate a path for each spaceship with an point before the target position, so the ships have some time left to turn into the right position. But I dont know if this is a good idea. I guess there will be a lot of rare cases where this can cause a problem. So the question is, if anybody knows how to solve this problem and has some (simple code) or pseudocode for me or at least some good explanation.

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• Circular motion on low powered hardware

  - by Akroy

  I was thinking about platforms and enemies moving in circles in old 2D games, and I was wondering how that was done. I understand parametric equations, and it's trivial to use sin and cos to do it, but could an NES or SNES make real time trig calls? I admit heavy ignorance, but I thought those were expensive operations. Is there some clever way to calculate that motion more cheaply? I've been working on deriving an algorithm from trig sum identities that would only use precalculated trig, but that seems convoluted.

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• Do Apple and Google ask for a share if custom payment is done in a free app?

  - by user1590354

  I have a multiplatform game (web/iOS/Android) in the making. In the free version the core game is still fully playable but people who choose to pay will get more social features (and no ads, of course). I was thinking that rather than having a free and a paid version for all the platforms I may release the apps just for free and if the users want more, they have to register and pay a one-time fee (through a payment gateway or PayPal). The extra content would then be available in all the clients they have access to. Theoretically, this means a better value for the players and less maintenance and headache for me (obviously I have to handle all the payment troubles myself). Does it fit into the business model of Apple/Google? Or will they still claim their share of the registration fee?

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• Why can we recognize game engines?

  - by Bart van Heukelom

  About many games you can say "oh that's the Unreal engine for sure", "this was made by upgrading GTA 4", etc. We can often recognize the engine used for a game just by looking at its graphics (disregarding menus and such). I'm wondering, why is this? All game engines use the same 3D rendering technology that we all use, and the different games usually have a distinct art style, so what's left to recognize?

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• Are there existing FOSS component-based frameworks?

  - by Tesserex

  The component based game programming paradigm is becoming much more popular. I was wondering, are there any projects out there that offer a reusable component framework? In any language, I guess I don't care about that. It's not for my own project, I'm just curious. Specifically I mean are there projects that include a base Entity class, a base Component class, and maybe some standard components? It would then be much easier starting a game if you didn't want to reinvent the wheel, or maybe you want a GraphicsComponent that does sprites with Direct3D, but you figure it's already been done a dozen times. A quick Googling turns up Rusher. Has anyone heard of this / does anyone use it? If there are no popular ones, then why not? Is it too difficult to make something like this reusable, and they need heavy customization? In my own implementation I found a lot of boilerplate that could be shoved into a framework.

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• how can I specify interleaved vertex attributes and vertex indices

  - by freefallr

  I'm writing a generic ShaderProgram class that compiles a set of Shader objects, passes args to the shader (like vertex position, vertex normal, tex coords etc), then links the shader components into a shader program, for use with glDrawArrays. My vertex data already exists in a VertexBufferObject that uses the following data structure to create a vertex buffer: class CustomVertex { public: float m_Position[3]; // x, y, z // offset 0, size = 3*sizeof(float) float m_TexCoords[2]; // u, v // offset 3*sizeof(float), size = 2*sizeof(float) float m_Normal[3]; // nx, ny, nz; float colour[4]; // r, g, b, a float padding[20]; // padded for performance }; I've already written a working VertexBufferObject class that creates a vertex buffer object from an array of CustomVertex objects. This array is said to be interleaved. It renders successfully with the following code: void VertexBufferObject::Draw() { if( ! m_bInitialized ) return; glBindBuffer( GL_ARRAY_BUFFER, m_nVboId ); glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, m_nVboIdIndex ); glEnableClientState( GL_VERTEX_ARRAY ); glEnableClientState( GL_TEXTURE_COORD_ARRAY ); glEnableClientState( GL_NORMAL_ARRAY ); glEnableClientState( GL_COLOR_ARRAY ); glVertexPointer( 3, GL_FLOAT, sizeof(CustomVertex), ((char*)NULL + 0) ); glTexCoordPointer(3, GL_FLOAT, sizeof(CustomVertex), ((char*)NULL + 12)); glNormalPointer(GL_FLOAT, sizeof(CustomVertex), ((char*)NULL + 20)); glColorPointer(3, GL_FLOAT, sizeof(CustomVertex), ((char*)NULL + 32)); glDrawElements( GL_TRIANGLES, m_nNumIndices, GL_UNSIGNED_INT, ((char*)NULL + 0) ); glDisableClientState( GL_VERTEX_ARRAY ); glDisableClientState( GL_TEXTURE_COORD_ARRAY ); glDisableClientState( GL_NORMAL_ARRAY ); glDisableClientState( GL_COLOR_ARRAY ); glBindBuffer( GL_ARRAY_BUFFER, 0 ); glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, 0 ); } Back to the Vertex Array Object though. My code for creating the Vertex Array object is as follows. This is performed before the ShaderProgram runtime linking stage, and no glErrors are reported after its steps. // Specify the shader arg locations (e.g. their order in the shader code) for( int n = 0; n < vShaderArgs.size(); n ++) glBindAttribLocation( m_nProgramId, n, vShaderArgs[n].sFieldName.c_str() ); // Create and bind to a vertex array object, which stores the relationship between // the buffer and the input attributes glGenVertexArrays( 1, &m_nVaoHandle ); glBindVertexArray( m_nVaoHandle ); // Enable the vertex attribute array (we're using interleaved array, since its faster) glBindBuffer( GL_ARRAY_BUFFER, vShaderArgs[0].nVboId ); glBindBuffer( GL_ELEMENT_ARRAY_BUFFER, vShaderArgs[0].nVboIndexId ); // vertex data for( int n = 0; n < vShaderArgs.size(); n ++ ) { glEnableVertexAttribArray(n); glVertexAttribPointer( n, vShaderArgs[n].nFieldSize, GL_FLOAT, GL_FALSE, vShaderArgs[n].nStride, (GLubyte *) NULL + vShaderArgs[n].nFieldOffset ); AppLog::Ref().OutputGlErrors(); } This doesn't render correctly at all. I get a pattern of white specks onscreen, in the shape of the terrain rectangle, but there are no regular lines etc. Here's the code I use for rendering: void ShaderProgram::Draw() { using namespace AntiMatter; if( ! m_nShaderProgramId || ! m_nVaoHandle ) { AppLog::Ref().LogMsg("ShaderProgram::Draw() Couldn't draw object, as initialization of ShaderProgram is incomplete"); return; } glUseProgram( m_nShaderProgramId ); glBindVertexArray( m_nVaoHandle ); glDrawArrays( GL_TRIANGLES, 0, m_nNumTris ); glBindVertexArray(0); glUseProgram(0); } Can anyone see errors or omissions in either the VAO creation code or rendering code? thanks!

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• 3D Ball Physics Theory: collision response on ground and against walls?

  - by David

  I'm really struggling to get a strong grasp on how I should be handling collision response in a game engine I'm building around a 3D ball physics concept. Think Monkey Ball as an example of the type of gameplay. I am currently using sphere-to-sphere broad phase, then AABB to OBB testing (the final test I am using right now is one that checks if one of the 8 OBB points crosses the planes of the object it is testing against). This seems to work pretty well, and I am getting back: Plane that object is colliding against (with a point on the plane, the plane's normal, and the exact point of intersection. I've tried what feels like dozens of different high-level strategies for handling these collisions, without any real success. I think my biggest problem is understanding how to handle collisions against walls in the x-y axes (left/right, front/back), which I want to have elasticity, and the ground (z-axis) where I want an elastic reaction if the ball drops down, but then for it to eventually normalize and be kept "on the ground" (not go into the ground, but also not continue bouncing). Without kluging something together, I'm positive there is a good way to handle this, my theories just aren't getting me all the way there. For physics modeling and movement, I am trying to use a Euler based setup with each object maintaining a position (and destination position prior to collision detection), a velocity (which is added onto the position to determine the destination position), and an acceleration (which I use to store any player input being put on the ball, as well as gravity in the z coord). Starting from when I detect a collision, what is a good way to approach the response to get the expected behavior in all cases? Thanks in advance to anyone taking the time to assist... I am grateful for any pointers, and happy to post any additional info or code if it is useful. UPDATE Based on Steve H's and eBusiness' responses below, I have adapted my collision response to what makes a lot more sense now. It was close to right before, but I didn't have all the right pieces together at the right time! I have one problem left to solve, and that is what is causing the floor collision to hit every frame. Here's the collision response code I have now for the ball, then I'll describe the last bit I'm still struggling to understand. // if we are moving in the direction of the plane (against the normal)... if (m_velocity.dot(intersection.plane.normal) <= 0.0f) { float dampeningForce = 1.8f; // eventually create this value based on mass and acceleration // Calculate the projection velocity PVRTVec3 actingVelocity = m_velocity.project(intersection.plane.normal); m_velocity -= actingVelocity * dampeningForce; } // Clamp z-velocity to zero if we are within a certain threshold // -- NOTE: this was an experimental idea I had to solve the "jitter" bug I'll describe below float diff = 0.2f - abs(m_velocity.z); if (diff > 0.0f && diff <= 0.2f) { m_velocity.z = 0.0f; } // Take this object to its new destination position based on... // -- our pre-collision position + vector to the collision point + our new velocity after collision * time // -- remaining after the collision to finish the movement m_destPosition = m_position + intersection.diff + (m_velocity * intersection.tRemaining * GAMESTATE->dt); The above snippet is run after a collision is detected on the ball (collider) with a collidee (floor in this case). With a dampening force of 1.8f, the ball's reflected "upward" velocity will eventually be overcome by gravity, so the ball will essentially be stuck on the floor. THIS is the problem I have now... the collision code is running every frame (since the ball's z-velocity is constantly pushing it a collision with the floor below it). The ball is not technically stuck, I can move it around still, but the movement is really goofy because the velocity and position keep getting affected adversely by the above snippet. I was experimenting with an idea to clamp the z-velocity to zero if it was "close to zero", but this didn't do what I think... probably because the very next frame the ball gets a new gravity acceleration applied to its velocity regardless (which I think is good, right?). Collisions with walls are as they used to be and work very well. It's just this last bit of "stickiness" to deal with. The camera is constantly jittering up and down by extremely small fractions too when the ball is "at rest". I'll keep playing with it... I like puzzles like this, especially when I think I'm close. Any final ideas on what I could be doing wrong here? UPDATE 2 Good news - I discovered I should be subtracting the intersection.diff from the m_position (position prior to collision). The intersection.diff is my calculation of the difference in the vector of position to destPosition from the intersection point to the position. In this case, adding it was causing my ball to always go "up" just a little bit, causing the jitter. By subtracting it, and moving that clamper for the velocity.z when close to zero to being above the dot product (and changing the test from <= 0 to < 0), I now have the following: // Clamp z-velocity to zero if we are within a certain threshold float diff = 0.2f - abs(m_velocity.z); if (diff > 0.0f && diff <= 0.2f) { m_velocity.z = 0.0f; } // if we are moving in the direction of the plane (against the normal)... float dotprod = m_velocity.dot(intersection.plane.normal); if (dotprod < 0.0f) { float dampeningForce = 1.8f; // eventually create this value based on mass and acceleration? // Calculate the projection velocity PVRTVec3 actingVelocity = m_velocity.project(intersection.plane.normal); m_velocity -= actingVelocity * dampeningForce; } // Take this object to its new destination position based on... // -- our pre-collision position + vector to the collision point + our new velocity after collision * time // -- remaining after the collision to finish the movement m_destPosition = m_position - intersection.diff + (m_velocity * intersection.tRemaining * GAMESTATE->dt); UpdateWorldMatrix(m_destWorldMatrix, m_destOBB, m_destPosition, false); This is MUCH better. No jitter, and the ball now "rests" at the floor, while still bouncing off the floor and walls. The ONLY thing left is that the ball is now virtually "stuck". He can move but at a much slower rate, likely because the else of my dot product test is only letting the ball move at a rate multiplied against the tRemaining... I think this is a better solution than I had previously, but still somehow not the right idea. BTW, I'm trying to journal my progress through this problem for anyone else with a similar situation - hopefully it will serve as some help, as many similar posts have for me over the years.

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