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• Box2D Bicycle Wheels Motor Problem - Flash 2.1a

  - by Craig

  I have made a bicycle with Box2D using several polygons for the frame at different angles connected using weld joints, and I have revolute joints on the wheels with a motor. I have made some basic terrain (straight ground and a small ramp) and added keyboard input to control the bicycle with torque to balance it. All of this is done in with Box2D's Debug Draw. When the bicycle is on its back wheel but diagonally forward (kinda like this position - /) the motors just cause it go spinning backwards over when in reality it should either stay on its back wheel or go down onto both wheels. Here's my code the revolute joints: //Front Wheel Joint var frontWheelJointDef:b2RevoluteJointDef = new b2RevoluteJointDef(); frontWheelJointDef.Initialize(frontWheelBody, secondFrameBody, frontWheelBody.GetWorldCenter()); frontWheelJointDef.enableMotor=true; frontWheelJointDef.maxMotorTorque=10000; frontWheelJoint = _world.CreateJoint(frontWheelJointDef) as b2RevoluteJoint; //Rear Wheel Joint var rearWheelJointDef:b2RevoluteJointDef = new b2RevoluteJointDef(); rearWheelJointDef.Initialize(rearWheelBody, firstFrameBody, rearWheelBody.GetWorldCenter()); rearWheelJointDef.enableMotor=true; rearWheelJointDef.maxMotorTorque=10000; rearWheelJoint = _world.CreateJoint(rearWheelJointDef) as b2RevoluteJoint; And here's the relevant part of my update function: // up and down control wheels motor if (up) { motorSpeed-=0.5; } if (down) { motorSpeed += 0.5; } // left and right control cart torque if (left) { middleCentreFrameBody.ApplyTorque( -3); gearBody.ApplyTorque( -3); firstFrameBody.ApplyTorque( -3); secondFrameBody.ApplyTorque( -3); rearWheelToChainBody.ApplyTorque( -3); chainToFrontFrameBody.ApplyTorque( -3); topMiddleFrameBody.ApplyTorque( -3); } if (right) { middleCentreFrameBody.ApplyTorque( 3); gearBody.ApplyTorque( 3); firstFrameBody.ApplyTorque( 3); secondFrameBody.ApplyTorque( 3); rearWheelToChainBody.ApplyTorque( 3); chainToFrontFrameBody.ApplyTorque( 3); topMiddleFrameBody.ApplyTorque( 3); } // motor friction motorSpeed*=0.99; // motor max speed if (motorSpeed>100) { motorSpeed=100; } rearWheelJoint.SetMotorSpeed(motorSpeed); frontWheelJoint.SetMotorSpeed(motorSpeed); Any ideas what might be causing this? Thanks

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• How does flash store (represent) movieclips and sprites?

  - by humbleBee

  When we draw any object in flash and convert it into a movieclip or a sprite, how is it stored or represented in flash. I know in vector art it is stored or represented as line segments using formulae. Is there any way to get the vertices of the shape that was drawn? For example, lets say a simple rectangle is drawn and is converted to a movieclip. Is there anyway to obtain the vertices and the line segments from the sprite? So that its shape is obtained. Enough information should be obtained so that the shape can be replicated. That's the key - replication. In simple terms, where does flash store information about a shape that has been drawn so that we can obtain it and attempt to replicate the shape ourselves?

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• Making game constants/tables available to game logic classes/routines in a modular manner

  - by Extrakun

  Suppose I have a game where there are several predefined constants and charts (a XP chart, cost of goods and so on). Those could be defined at runtime, or load from files at start-up. The question is how should those logic routines access the constants and charts? For example, I could try using global variables, but that cause all classes relying on the variables to be tightly coupled with them.

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• 3Ds Max is exporting model with more normals than vertices

  - by Delta

  I made a simple teapot with the "Create Standard Primitives" option and exported it as a collada file, ended up with this: < float_array id="Teapot001-POSITION-array" count="1590" < float_array id="Teapot001-Normal0-array" count="9216" For what I know there should be only one normal per vertex, am I wrong? What am I supposed to do with that much normals? Just put them on the normal buffer all at once normally?

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• Why is Spritebatch drawing my Textures out of order?

  - by Andrew

  I just started working with XNA Studio after programming 2D games in java. Because of this, I have absolutely no experience with Spritebatch and sprite sorting. In java, I could just layer the images by calling the draw methods in order. For a while, my Spritebatch was working fine in deferred sorting mode, but when I made a change to one of my textures, it suddenly started drawing them out of order. I have searched for a solution to this problem, but nothing seems to work. I have tried adding layer depths to the sprites and changing the sort mode to BackToFront or FrontToBack or even immediate, but nothing seems to work. Here is my drawing code: protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(Color.Gray); Game1.spriteBatch.Begin(SpriteSortMode.Deferred, BlendState.AlphaBlend, SamplerState.PointClamp, null, null); for (int x = 0; x < 5; x++) { for (int y = 0; y < 5; y++) { region[x, y].draw(((float)w / aw)); // Draws the Tile-Based background } } player.draw(spriteBatch, ((float)w / aw));//draws the character (This method is where the problem occurs) enemy.draw(spriteBatch, (float)w/aw); // draws a basic enemy Game1.spriteBatch.End(); base.Draw(gameTime); } player.draw method: public void draw(SpriteBatch sb, float ratio){ //draws the player base (The character without hair or equipment) sb.Draw(playerbase[0], new Rectangle((int)(pos.X - (24 * ratio)), (int)(pos.Y - (48 * ratio)), (int)(48 * ratio), (int)(48 * ratio)), new Rectangle(orientation * 48, animFrame * 48, 48, 48), Color.White,0,Vector2.Zero,SpriteEffects.None,0); //draws the player's hair sb.Draw(playerbase[3], new Rectangle((int)(pos.X - (24 * ratio)), (int)(pos.Y - (48 * ratio)), (int)(48 * ratio), (int)(48 * ratio)), new Rectangle(orientation * 48, animFrame * 48, 48, 48), Color.White, 0, Vector2.Zero, SpriteEffects.None, 0); //draws the player's shirt sb.Draw(equipment[0], new Rectangle((int)(pos.X - (24 * ratio)), (int)(pos.Y - (48 * ratio)), (int)(48 * ratio), (int)(48 * ratio)), new Rectangle(orientation * 48, animFrame * 48, 48, 48), Color.White, 0, Vector2.Zero, SpriteEffects.None, 0); //draws the player's pants sb.Draw(equipment[1], new Rectangle((int)(pos.X - (24 * ratio)), (int)(pos.Y - (48 * ratio)), (int)(48 * ratio), (int)(48 * ratio)), new Rectangle(orientation * 48, animFrame * 48, 48, 48), Color.White, 0, Vector2.Zero, SpriteEffects.None, 0); //draws the player's shoes sb.Draw(equipment[2], new Rectangle((int)(pos.X - (24 * ratio)), (int)(pos.Y - (48 * ratio)), (int)(48 * ratio), (int)(48 * ratio)), new Rectangle(orientation * 48, animFrame * 48, 48, 48), Color.White, 0, Vector2.Zero, SpriteEffects.None, 0); } the game has a top-down perspective much like the early legend of zelda games. It draws sections of the texture depending on which direction the character is facing and the animation frame. However, instead of drawing the character in the order the draw methods are called, it ends up drawing the character out of order. Please help me with this problem.

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• Has anyone else read "Programming video games for the Evil Genius"

  - by Martin

  I bought this book called "Programming Video Games for the Evil Genius" by Ian Cinnamon. If there is anyone who has read or is familiar with this book I am wondering if they think it is worth reading. I am interested in making video games. I have already taken intro courses in C++, Java and Python and got through okay. I've been going through this book for about a month now(SLOWLY). All I have to do is type the code exactly in the book, BUT a lot of the code is not clearly explained. I do some research online but I usually still have some trouble answering my questions. Then I found stack overflow. It's been a ton of help. Right now I am trying to make a racing game right out of this book and I got to a point where the author left a bunch of errors in his code. One of the members of this website fixed it up for me, but added some stuff that I'm having trouble understanding. I spend more time trying to figure out the authors errors and fix them or get someone to help me fix them than I actually do learning code. I REALLY want to learn how to do this and I am ready and willing to put in the time, but I'm not sure if my time would be better spent learning from a different source. Are there any veterans out there that are familiar with this book and think it's worth it/not worth it? Should I try to move onto another book? Any advice for a fresh start for someone who wants to learn some video game programming?

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• Producing a smooth mesh from density cloud and marching cubes

  - by Wardy

  Based on my results from this question I decided to build myself a 3D noise map containing float values in place of my existing boolean point values. The effect I'm trying to produce is something like this, rather than typical rolling hills; which should explain the "missing cubes" in the image below. If I render my density map in normal "minecraft mode" (1 block per point in the density map) varying the size of the cube based on the value in my density map (floats in the range 0 to 1) I get something like this: I'm now happy that I can produce a density map for the marching cubes algorithm (which will need a little tweaking) but for some reason when I run it through my implementation it's not producing what I expect. My problem is that I'm getting something like the first image in this answer to my previous question, when I want to achieve the effect in the second image. Upon further investigation I can't see how marching cubes does the "move vertex along the edge" type logic (i.e. the difference between the two images on my previous link). I see that it does do some interpolation, but I'm not convinced I have the correct understanding of what I think it should do, because the code in question appears to give the same result regardless of whether I use boolean or float values. I took the code from here which is a C# implementation of marching cubes, but instead of using the MarchingCubesPrimitive I modified it to accept an object of type IDrawable, containing lists for the various collections (vertices, normals, UVs, indices), the logic was otherwise untouched. My understanding is that given a very low isovalue the accuracy level of the surface being rendered should increase, so in short "less 45 degree slows more rolling hills" type mesh output. However this isn't what I'm seeing. Have I missed something or is the implementation flawed and need to be fixed? EDIT: A little more detail on what I am seeing when I "marching cube" the data. Ok so firstly, ignore the fact that the meshes created by the chunks don't "connect" (i'll probably raise another question about this later). Then look at the shaping of the island, it's too ... square, from the voxels rendered as boxes you get the impression there's a clean soft gradual hill and yet from the image there are sharp falling edges even in the most central areas where the gradient in the first image looks the most smooth. The data is "regenerated" each time I run this so no 2 islands come out the same, and it's purely random so not based on noise, but still, how can it look so smooth in 1 image and so not smooth in the other?

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• Low coupling and tight cohesion

  - by hidayat

  Of course it depends on the situation. But when a lower lever object or system communicate with an higher level system, should callbacks or events be preferred to keeping a pointer to higher level object? For example, we have a world class that has a member variable vector<monster> monsters. When the monster class is going to communicate with the world class, should I prefer using a callback function then or should I have a pointer to the world class inside the monster class?

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• Technique to have screen independent grid based puzzle with sprite animation

  - by Yan Cheng CHEOK

  Hello all, let's say I have a fixed size grid puzzle game (8 x 10). I will be using sprites animation, when the "pieces" in the puzzle is moving from one grid to another grid. I was wondering, what is the technique to have this game being implemented as screen resolution independent. Here is what I plan to do. 1) The data structure coordinate will be represented using double, with 1.0 as max value. // Puzzle grid of 8 x 10 Environment { double width = 0.8; double height = 1.0; } // Location of Sprite at coordinate (1, 1) Sprite { double posX = 0.1; double posY = 0.1; double width = 0.1; double height = 0.1; } // scale = PYSICAL_SCREEN_SIZE drawBitmap ( sprite_image, sprite_image_rect, new Rect(sprite.posX * Scale, sprite.posY * Scale, (sprite.posX + sprite.width) * Scale, (sprite.posY + sprite.Height) * Scale), paint ); 2) A large size sprite image will be used (128x128). As sprite image shall look fine if we scale from large size down to small size, but not vice versa. Besides the above mentioned technique, is there any other consideration I had missed out?

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• LibGdx efficient data saving/loading?

  - by grimrader22

  Currently, my LibGDX game consists of a 512 x 512 map of Tiles and entities such as players and monsters. I am wondering how to efficiently save and load the data of my levels. At the moment I am using JSON serialization for each class I want to save. I implement the Json.Serializable interface for all of these classes and write only the variables that are necessary. So my map consists of 512 x 512 tiles, that's 260,000 tiles. Each tile on the map consists of a Tile object, which points to some final Tile object like a GRASS_TILE or a STONE_TILE. When I serialize each level tile, the final Tile that it points to is re-serialized over and over again, so if I have 100 Tiles all pointing to GRASS_TILE, the data of GRASS_TILE is written 100 times over. When I go to load/deserialize my objects, 100 GrassTile objects are created, but they are each their own object. They no longer point to the final tile object. I feel like this reading/writing files very slow. If I were to abandon JSON serialization, to my knowledge my next best option would be saving the level data to a sql database. Unless there is a way to speed up serializing/deserializing 260,000 tiles I may have to do this. Is this a good idea? Could I really write that many tiles to the database efficiently? To sum all this up, I am trying to save my levels using JSON serialization, but it is VERY slow. What other options do I have for saving the data of so many tiles. I also must note that the JSON serialization is not slow on a PC, it is only VERY slow on a mobile device. Since file writing/reading is so slow on mobile devices, what can I do?

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• Problems implementing a screen space shadow ray tracing shader

  - by Grieverheart

  Here I previously asked for the possibility of ray tracing shadows in screen space in a deferred shader. Several problems were pointed out. One of the most important problem is that only visible objects can cast shadows and objects between the camera and the shadow caster can interfere. Still I thought it'd be a fun experiment. The idea is to calculate the view coordinates of pixels and cast a ray to the light. The ray is then traced pixel by pixel to the light and its depth is compared with the depth at the pixel. If a pixel is in front of the ray, a shadow is casted at the original pixel. At first I thought that I could use the DDA algorithm in 2D to calculate the distance 't' (in p = o + t d, where o origin, d direction) to the next pixel and use it in the 3D ray equation to find the ray's z coordinate at that pixel's position. For the 2D ray, I would use the projected and biased 3D ray direction and origin. The idea was that 't' would be the same in both 2D and 3D equations. Unfortunately, this is not the case since the projection matrix is 4D. Thus, some tweak needs to be done to make this work this way. I would like to ask if someone knows of a way to do what I described above, i.e. from a 2D ray in texture coordinate space to get the 3D ray in screen space. I did implement a simple version of the idea which you can see in the following video: video here Shadows may seem a bit pixelated, but that's mostly because of the size of the step in 't' I chose. And here is the shader: #version 330 core uniform sampler2D DepthMap; uniform vec2 projAB; uniform mat4 projectionMatrix; const vec3 light_p = vec3(-30.0, 30.0, -10.0); noperspective in vec2 pass_TexCoord; smooth in vec3 viewRay; layout(location = 0) out float out_AO; vec3 CalcPosition(void){ float depth = texture(DepthMap, pass_TexCoord).r; float linearDepth = projAB.y / (depth - projAB.x); vec3 ray = normalize(viewRay); ray = ray / ray.z; return linearDepth * ray; } void main(void){ vec3 origin = CalcPosition(); if(origin.z < -60) discard; vec2 pixOrigin = pass_TexCoord; //tex coords vec3 dir = normalize(light_p - origin); vec2 texel_size = vec2(1.0 / 600.0); float t = 0.1; ivec2 pixIndex = ivec2(pixOrigin / texel_size); out_AO = 1.0; while(true){ vec3 ray = origin + t * dir; vec4 temp = projectionMatrix * vec4(ray, 1.0); vec2 texCoord = (temp.xy / temp.w) * 0.5 + 0.5; ivec2 newIndex = ivec2(texCoord / texel_size); if(newIndex != pixIndex){ float depth = texture(DepthMap, texCoord).r; float linearDepth = projAB.y / (depth - projAB.x); if(linearDepth > ray.z + 0.1){ out_AO = 0.2; break; } pixIndex = newIndex; } t += 0.5; if(texCoord.x < 0 || texCoord.x > 1.0 || texCoord.y < 0 || texCoord.y > 1.0) break; } } As you can see, here I just increment 't' by some arbitrary factor, calculate the 3D ray and project it to get the pixel coordinates, which is not really optimal. Hopefully, I would like to optimize the code as much as possible and compare it with shadow mapping and how it scales with the number of lights. PS: Keep in mind that I reconstruct position from depth by interpolating rays through a full screen quad.

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• Typical Applications of Linear System Solver in Game Developemnt

  - by craftsman.don

  I am going to write a custom solver for linear system. I would like to survey the typical problems involved the linear system solving in games. So that I can custom optimization on these problems based on the shape of the matrix. currently I am focus on these problems: B-Spline editing (I use a linear solve to resolve the C0, C1, C2 continuity) Constraint in Simulation (especially Position-Constraint, cloth) Both of them are Banded Matrix. I want to hear about some other applications of a linear system in games. Thank you.

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• isometric drawing order with larger than single tile images - drawing order algorithm?

  - by Roger Smith

  I have an isometric map over which I place various images. Most images will fit over a single tile, but some images are slightly larger. For example, I have a bed of size 2x3 tiles. This creates a problem when drawing my objects to the screen as I get some tiles erroneously overlapping other tiles. The two solutions that I know of are either splitting the image into 1x1 tile segments or implementing my own draw order algorithm, for example by assigning each image a number. The image with number 1 is drawn first, then 2, 3 etc. Does anyone have advice on what I should do? It seems to me like splitting an isometric image is very non obvious. How do you decide which parts of the image are 'in' a particular tile? I can't afford to split up all of my images manually either. The draw order algorithm seems like a nicer choice but I am not sure if it's going to be easy to implement. I can't solve, in my head, how to deal with situations whereby you change the index of one image, which causes a knock on effect to many other images. If anyone has an resources/tutorials on this I would be most grateful.

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• MiniMax function throws null pointer exception

  - by Sven

  I'm working on a school project, I have to build a tic tac toe game with the AI based on the MiniMax algorithm. The two player mode works like it should. I followed the code example on http://ethangunderson.com/blog/minimax-algorithm-in-c/. The only thing is that I get a NullPointer Exception when I run the code. And I can't wrap my finger around it. I placed a comment in the code where the exception is thrown. The recursive call is returning a null pointer, what is very strange because it can't.. When I place a breakpoint on the null return with the help of a if statement, then I see that there ARE still 2 to 3 empty places.. I probably overlooking something. Hope someone can tell me what I'm doing wrong. Here is the MiniMax code (the tic tac toe code is not important): /* * To change this template, choose Tools | Templates * and open the template in the editor. */ package MiniMax; import Game.Block; import Game.Board; import java.util.ArrayList; public class MiniMax { public static Place getBestMove(Board gameBoard, Block.TYPE player) { Place bestPlace = null; ArrayList<Place> emptyPlaces = gameBoard.getEmptyPlaces(); Board newBoard; //loop trough all the empty places for(Place emptyPlace : emptyPlaces) { newBoard = gameBoard.clone(); newBoard.setBlock(emptyPlace.getRow(), emptyPlace.getCell(), player); //no game won and still room to move if(newBoard.getWinner() == Block.TYPE.NONE && newBoard.getEmptyPlaces().size() > 0) { //is an node (has children) Place tempPlace = getBestMove(newBoard, invertPlayer(player)); //ERROR is thrown here! tempPlace is null. emptyPlace.setScore(tempPlace.getScore()); } else { //is an leaf if(newBoard.getWinner() == Block.TYPE.NONE) { emptyPlace.setScore(0); } else if(newBoard.getWinner() == Block.TYPE.X) { emptyPlace.setScore(-1); } else if(newBoard.getWinner() == Block.TYPE.O) { emptyPlace.setScore(1); } //if this move is better then our prev move, take it! if((bestPlace == null) || (player == Block.TYPE.X && emptyPlace.getScore() < bestPlace.getScore()) || (player == Block.TYPE.O && emptyPlace.getScore() > bestPlace.getScore())) { bestPlace = emptyPlace; } } } //This should never be null, but it does.. return bestPlace; } private static Block.TYPE invertPlayer(Block.TYPE player) { if(player == Block.TYPE.X) { return Block.TYPE.O; } return Block.TYPE.X; } }

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• What's a good data structure solution for a scene manager in XNA?

  - by tunnuz

  Hello, I'm playing with XNA for a game project of myself, I had previous exposure to OpenGL and worked a bit with Ogre, so I'm trying to get the same concepts working on XNA. Specifically I'm trying to add to XNA a scene manager to handle hierarchical transforms, frustum (maybe even occlusion) culling and transparency object sorting. My plan was to build a tree scene manager to handle hierarchical transforms and lighting, and then use an Octree for frustum culling and object sorting. The problem is how to do geometry sorting to support transparencies correctly. I know that sorting is very expensive if done on a per-polygon basis, so expensive that it is not even managed by Ogre. But still images from Ogre look right. Any ideas on how to do it and which data structures to use and their capabilities? I know people around is using: Octrees Kd-trees (someone on GameDev forum said that these are far better than Octrees) BSP (which should handle per-polygon ordering but are very expensive) BVH (but just for frustum and occlusion culling) Thank you Tunnuz

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• Eculidean space and vector magnitude

  - by Starkers

  Below we have distances from the origin calculated in two different ways, giving the Euclidean distance, the Manhattan distance and the Chebyshev distance. Euclidean distance is what we use to calculate the magnitude of vectors in 2D/3D games, and that makes sense to me: Let's say we have a vector that gives us the range a spaceship with limited fuel can travel. If we calculated this with Manhattan metric, our ship could travel a distance of X if it were travelling horizontally or vertically, however the second it attempted to travel diagonally it could only tavel X/2! So like I say, Euclidean distance does make sense. However, I still don't quite get how we calculate 'real' distances from the vector's magnitude. Here are two points, purple at (2,2) and green at (3,3). We can take two points away from each other to derive a vector. Let's create a vector to describe the magnitude and direction of purple from green: |d| = purple - green |d| = (purple.x, purple.y) - (green.x, green.y) |d| = (2, 2) - (3, 3) |d| = <-1,-1> Let's derive the magnitude of the vector via Pythagoras to get a Euclidean measurement: euc_magnitude = sqrt((x*x)+(y*y)) euc_magnitude = sqrt((-1*-1)+(-1*-1)) euc_magnitude = sqrt((1)+(1)) euc_magnitude = sqrt(2) euc_magnitude = 1.41 Now, if the answer had been 1, that would make sense to me, because 1 unit (in the direction described by the vector) from the green is bang on the purple. But it's not. It's 1.41. 1.41 units is the direction described, to me at least, makes us overshoot the purple by almost half a unit: So what do we do to the magnitude to allow us to calculate real distances on our point graph? Worth noting I'm a beginner just working my way through theory. Haven't programmed a game in my life!

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• XNA Quadtree with LOD

  - by Byron Cobb

  I'm looking to create a fairly large environment, and as such would like to implement a quadtree and use LOD on it. I've looked through numerous examples and I get the basic idea of a quadtree. Start with a root node with 4 vertices covering the whole map and divide into 4 children nodes until I meet some criteria(max number of triangles) I'm looking for some very very basic algorithm or explanation with respect to drawing the quadtree. What vertices need to be stored per iteration? When do I determine what vertices to draw? When to update indices and vertices? Hope to integrate the bounding frustrum? Do I include parent and child vertices? I'm looking for very simple instruction on what to do. I've scoured the internet for days now looking, but everyone adds extra code and a different spin without explanation. I understand quadtrees, but not with respect to 3d rendering and lod. A link to an outside source will probably have been read by myself already and won't help. Regards, Byron.

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• My first animation - Using SDL.NET C#

  - by Mark

  Hi all! I'm trying to animate a player object in my 2D grid when the user clicks somewhere in the screen. I got the following 4 variables: oX (Current player position X) oY (Current player position Y) dX (Destination X) dY (Destination Y) How can I make sure the player moves in a straight line to the new XY coordinates. The way I'm doing it now is really awfull and causes the player to first move along x axis, and finally in y axis. Can someone give me some guidance with the involved math cause I'm really not sure on how to accomplish this. Thank you for your time. Kind regards, Mark Update: It's working now but whats the right way to check if the current positions are equal to the target position? private static void MovePlayer(double x2, double y2, int duration) { double hX = x2 - m_PlayerPosition.X; double hY = y2 - m_PlayerPosition.Y; double Length = Math.Sqrt(Math.Pow(hX, 2) + Math.Pow(hY, 2)); hX = hX / Length; hY = hY / Length; while (m_PlayerPosition.X != Convert.ToInt32(x2) || m_PlayerPosition.Y != Convert.ToInt32(y2)) { m_PlayerPosition.X += Convert.ToInt32(hX * 1); m_PlayerPosition.Y += Convert.ToInt32(hY * 1); UpdatePlayerLocation(); } }

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• Quaternion Camera Orbiting around a Sphere

  - by jessejuicer

  Background: I'm trying to create a game where the camera is always rotating around a single sphere. I'm using the DirectX D3DX math functions in C++ on Windows. The Problem: I cannot get both the camera position and orientation both working properly at the same time. Either one works but not both together. Here's the code for my quaternion camera that revolves around a sphere, always looking at the centerpoint of the sphere, ... as far as I understand it (but which isn't working properly): (I'm only going to present rotation around the X axis here, to simplify this post) Whenever the UP key is pressed or held down, the camera should rotate around the X axis, while looking at the centerpoint of the sphere (which is at 0,0,0 in the world). So, I build a quaternion that represents a small angle of rotation around the x axis like this (where 'deltaAngle' is a small enough number for a slow rotation): D3DXVECTOR3 rotAxis; D3DXQUATERNION tempQuat; tempQuat.x = 0.0f; tempQuat.y = 0.0f; tempQuat.z = 0.0f; tempQuat.w = 1.0f; rotAxis.x = 1.0f; rotAxis.y = 0.0f; rotAxis.z = 0.0f; D3DXQuaternionRotationAxis(&tempQuat, &rotAxis, deltaAngle); ...and I accumulate the result into the camera's current orientation quat, like this: D3DXQuaternionMultiply(&cameraOrientationQuat, &cameraOrientationQuat, &tempQuat); ...which all works fine. Now I need to build a view matrix to pass to DirectX SetTransform function. So I build a rotation matrix from the camera orientation quat as follows: D3DXMATRIXA16 rotationMatrix; D3DXMatrixIdentity(&rotationMatrix); D3DXMatrixRotationQuaternion(&rotationMatrix, &cameraOrientationQuat); ...Now (as seen below) if I just transpose that rotationMatrix and plug it into the 3x3 section of the view matrix, then negate the camera's position and plug it into the translation section of the view matrix, the rotation magically works. Perfectly. (even when I add in rotations for all three axes). There's no gimbal lock, just a smooth rotation all around in any direction. BUT- this works even though I never change the camera's position. At all. Which sorta blows my mind. I even display the camera position and can watch it stay constant at it's starting point (0.0, 0.0, -4000.0). It never moves, but the rotation around the sphere is perfect. I don't understand that. For proper view rotation, the camera position should be revolving around the sphere. Here's the rest of building the view matrix (I'll talk about the commented code below). Note that the camera starts out at (0.0, 0.0, -4000.0) and m_camDistToTarget is 4000.0: /* D3DXVECTOR3 vec1; D3DXVECTOR4 vec2; vec1.x = 0.0f; vec1.y = 0.0f; vec1.z = -1.0f; D3DXVec3Transform(&vec2, &vec1, &rotationMatrix); g_cameraActor->pos.x = vec2.x * g_cameraActor->m_camDistToTarget; g_cameraActor->pos.y = vec2.y * g_cameraActor->m_camDistToTarget; g_cameraActor->pos.z = vec2.z * g_cameraActor->m_camDistToTarget; */ D3DXMatrixTranspose(&g_viewMatrix, &rotationMatrix); g_viewMatrix._41 = -g_cameraActor->pos.x; g_viewMatrix._42 = -g_cameraActor->pos.y; g_viewMatrix._43 = -g_cameraActor->pos.z; g_viewMatrix._44 = 1.0f; g_direct3DDevice9->SetTransform( D3DTS_VIEW, &g_viewMatrix ); ...(The world matrix is always an identity, and the perspective projection works fine). ...So, without the commented code being compiled, the rotation works fine. But to be proper, for obvious reasons, the camera position should be rotating around the sphere, which it currently is not. That's what the commented code is supposed to do. And when I add in that chunk of code to do that, and look at all the data as I hold the keys down (using UP, DOWN, LEFT, RIGHT to rotate different directions) all the values look correct! The camera position is rotating around the sphere just fine, and I can watch that happen visually too. The problem is that the camera orientation does not lookat the center of the sphere. It always looks straight forward down the z axis (toward positive z) as it revolves around the sphere. Yet the values of both the rotation matrix and the view matrix seem to be behaving correctly. (The view matrix orientation is the same as the rotation matrix, just transposed). For instance if I just hold down the key to spin around the x axis, I can watch the values of the three axes represented in the view matrix (x, y, and z axes)... view x-axis stays at (1.0, 0.0, 0.0), and view y-axis and z-axis both spin around the x axis just fine. All the numbers are changing as they should be... well, almost. As far as I can tell, the position of the view matrix is spinning around the sphere one direction (like clockwise), and the orientation (the axes in the view matrix) are spinning the opposite direction (like counter-clockwise). Which I guess explains why the orientation appears to stay straight ahead. I know the position is correct. It revolves properly. It's the orientation that's wrong. Can anyone see what am I doing wrong? Am I using these functions incorrectly? Or is my algorithm flawed? As usual I've been combing my code for simple mistakes for many hours. I'm willing to post the actual code, and a video of the behavior, but that will take much more effort. Thought I'd ask this way first.

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• How should I invoke a physics engine?

  - by ymfoi

  I'm new to writing games. I'm planning to write a 2D battle game which may require an physics engine. Suppose I've written one, but how can I combine it with the main routine of my game? Should I attach it directly to the graphics render routine or put it in an individual thread? I've spent much time looking for some common approach, but found nothing. So can you reveal some basics idea for me, a newbie? Thanks! P.S. There're many other problems I have to deal with if I choose to start a separate thread for the physics engine, for example, the lock problem, while from my intuition, I guess I'd better separate the render and the physics engine.

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• Is it important for reflection-based serialization maintain consistent field ordering?

  - by Matchlighter

  I just finished writing a packet builder that dynamically loads data into a data stream for eventual network transmission. Each builder operates by finding fields in a given class (and its superclasses) that are marked with a @data annotation. When I finishing my implementation, I remembered that getFields() does not return results in any specific order. Should reflection-based methods for serializing arbitrary data (like my packets) attempt to preserve a specific field ordering (such as alphabetical), and if so, how?

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• libgdx intersection problem between rectangle and circle

  - by Chris

  My collision detection in libgdx is somehow buggy. player.png is 20*80px and ball.png 25*25px. Code: @Override public void create() { // ... batch = new SpriteBatch(); playerTex = new Texture(Gdx.files.internal("data/player.png")); ballTex = new Texture(Gdx.files.internal("data/ball.png")); player = new Rectangle(); player.width = 20; player.height = 80; player.x = Gdx.graphics.getWidth() - player.width - 10; player.y = 300; ball = new Circle(); ball.x = Gdx.graphics.getWidth() / 2; ball.y = Gdx.graphics.getHeight() / 2; ball.radius = ballTex.getWidth() / 2; } @Override public void render() { Gdx.gl.glClearColor(1, 1, 1, 1); Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT); camera.update(); // draw player, ball batch.setProjectionMatrix(camera.combined); batch.begin(); batch.draw(ballTex, ball.x, ball.y); batch.draw(playerTex, player.x, player.y); batch.end(); // update player position if(Gdx.input.isKeyPressed(Keys.DOWN)) player.y -= 250 * Gdx.graphics.getDeltaTime(); if(Gdx.input.isKeyPressed(Keys.UP)) player.y += 250 * Gdx.graphics.getDeltaTime(); if(Gdx.input.isKeyPressed(Keys.LEFT)) player.x -= 250 * Gdx.graphics.getDeltaTime(); if(Gdx.input.isKeyPressed(Keys.RIGHT)) player.x += 250 * Gdx.graphics.getDeltaTime(); // don't let the player leave the field if(player.y < 0) player.y = 0; if(player.y > 600 - 80) player.y = 600 - 80; // check collision if (Intersector.overlaps(ball, player)) Gdx.app.log("overlaps", "yes"); }

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• What is involved for a simple UDP game?

  - by acidzombie24

  I once tried to write a simple game with UDP in a week as a throwaway test. It went horribly. I threw it away early. The main problem i had was restoring the game state of all players/enemies/objects to an old state and fast forward the game to the point of time the player is playing (ie half a second before a jump. A little early or late can make the player miss the jump) Maybe this method is not the easiest way? i suspect it to be but i designed it wrong from the beginning and realized at the end of 2nd day. (so i didnt learn too much or wasted that much time) For myself and others, What is involved for a simple UDP game and how do i write one? Or how do i solve the prediction problem restoring to state properly. I'll mark this as CW bc i know there will be lots of helpful answers.

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• openfeint or gamecenter?

  - by Gajet

  which one has more potential customers, easier API, and wider feature list? i'm going to develop implement one of those two for highscore recording in my game which ones gives more advantages? and by the way I might be going to port my game to android, so if you know any thing that can help me not to rewrite my code (for example a C++ wrapper for both of them) that would mean a greate plus for openfeint in my point of veiw.

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• Rendering performance in FlasCC + UDK when compared to Stage3d and UDK on Windows?

  - by Arthur Wulf White

  Adobe recently released the Flash C++ Compiler, which UDK uses to target Flash Player. Developers can now access UDK for browser applications. Does this mean greater performance than using a Stage3D engine (Away3D 4) and how much of a noticeable difference in performance would it make in rendering speeds? Is there any benchmark you could propose that would allow to compare them fairly? I am asking this to help myself understand the consequences in performance for deciding to use UDK in a browser based game. I would also like to know how it compares with UDK running natively in Windows? I am not asking which technology to use or which is better. Only interested in optimizing rendering speed in a 3d browser game with flash.

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