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• Wrong faces culled in OpenGL when drawing a rectangular prism

  - by BadSniper

  I'm trying to learn opengl. I did some code for building a rectangular prism. I don't want to draw back faces so I used glCullFace(GL_BACK), glEnable(GL_CULL_FACE);. But I keep getting back faces also when viewing from front and also sometimes when rotating sides are vanishing. Can someone point me in right direction? glPolygonMode(GL_FRONT,GL_LINE); // draw wireframe polygons glColor3f(0,1,0); // set color green glCullFace(GL_BACK); // don't draw back faces glEnable(GL_CULL_FACE); // don't draw back faces glTranslatef(-10, 1, 0); // position glBegin(GL_QUADS); // face 1 glVertex3f(0,-1,0); glVertex3f(0,-1,2); glVertex3f(2,-1,2); glVertex3f(2,-1,0); // face 2 glVertex3f(2,-1,2); glVertex3f(2,-1,0); glVertex3f(2,5,0); glVertex3f(2,5,2); // face 3 glVertex3f(0,5,0); glVertex3f(0,5,2); glVertex3f(2,5,2); glVertex3f(2,5,0); // face 4 glVertex3f(0,-1,2); glVertex3f(2,-1,2); glVertex3f(2,5,2); glVertex3f(0,5,2); // face 5 glVertex3f(0,-1,2); glVertex3f(0,-1,0); glVertex3f(0,5,0); glVertex3f(0,5,2); // face 6 glVertex3f(0,-1,0); glVertex3f(2,-1,0); glVertex3f(2,5,0); glVertex3f(0,5,0); glEnd();

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• Are there any good guides for making mods for Minecraft?

  - by Pureferret

  I've been coding in Java for 5 months at work now, and having past experience with programming in other languages, modifying existing code at Uni etc. I feel like I want to get started on (read: continue learning to program by) modding with minecraft. I know what I need, but not exactly how to do so. I once saw some good guides on the minecraft forum, but they all explained how to write in java, hows different classes in the code work etc. I'm more interested in how you decompile the code, write your own separate from the main 'trunk' of minecraft and then package it to install with a tool like 'Magic Loader'. My issue with these guides is that they always relied on being in windows, but I'm primarily a linux user, and the guides on the forums only seemed to assume you were on a Windows box. So is there a good 'walkthrough' for modding for Minecraft? Especially one where it assumes or at least allows for the fact you are in linux?

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• Does SFML render graphics outside the window?

  - by ThePlan

  While working on a tile-based map I figured it would be a good idea if I would only render what the player sees on the game window, but then it occurred to me that SFML could already be optimized enough to know when it doesn't have to render those things. Let's say I draw a 30x30 squared maps (A medium one) but the player only sees a bunch of them, not entirely. Would SFML automatically hide what the player doesn't see, or should I hide it myself?

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• Using SQL tables for storing user created level stats. Is there a better way?

  - by Ivan

  I am developing a racing game in which players can create their own tracks and upload them to a server. Players will be able to compare their best track times to their friends and see world records. I was going to generate a table for each track submitted to store the best times of each player who plays the track. However, I can't predict how many will be uploaded and I imagine too many tables might cause problems, or is this a valid method? I considered saving each player's best times in a string in a single table field like so: level1:00.45;level2:00.43;level3:00.12 If I did this I wouldn't need a separate table for each level (each level could just have a row in a 'WorldRecords' table). However, this just causes another problem because the text would eventually reach the limit for varchar length. I also considered storing the times data in XML files. This would avoid database issues and server disk space can be increased if needed. But I imagine this would be very slow. To update one players best time on one level, I would have to check every node in the file to find their time record to update. Apologies for the wall of text. Any suggestions would be appreciated.

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• Which game logic should run when doing prediction for PNP state updates

  - by spaceOwl

  We are writing a multiplayer game, where each game client (player) is responsible for sending state updates regarding its "owned" objects to other players. Each message that arrives to other (remote) clients is processed as such: Figure out when the message was sent. Create a diff between NOW and that time. Run game specific logic to bring the received state to "current" time. I am wondering which sort of logic should execute as part of step #3 ? Our game is composed of a physical update (position, speed, acceleration, etc) and many other components that can update an object's state and occur regularly (locally). There's a trade off here - Getting the new state quickly or remaining "faithful" to the true state representation and executing the whole thing to predict the "true" state when receiving state updates from remote clients. Which one is recommended to be used? and why?

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• Setting Krypton Light to Screen Pixels

  - by Adam Jerrett

  So a few days back, I started playing around with Krypton XNA for 2D lighting in my game. I noticed in general, that spawning a light at (0,0) with Krypton causes the light to appear in, pretty much, the centre of the game screen. Is there any way to change this so a Krypton light's "starting point" at [0,0] would spawn at the top left of the screen, and thus follow the standard screen co-ordinates for position? I ask because currently I'm busy working on my game where my spawn point is [512,512]. With hard code, the closest I've got to the light being "central" to this point is the vector position [12,-20], which makes no sense and is impossible to craft, mathematically, if I want the light to move with the camera (the position [480,512] maps roughly to [10,-20]). So, is there any way to "normalise" the krypton lights to use standard screen co-ordinates? If you guys can, play around with the demo from the site and please see if you can find anything out about it. Documentation on the engine is rather scarce, so it's difficult to find anything relevant to my "pixel-perfect" need. It might just also be something in the code with regards to the matrices that I'm not fully understanding. Any help would be useful. Thanks.

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• UDK/ UnrealScript class interaction? HUD advice?

  - by Holly

  Beginner basics requested here, While i'm familiar with the basics of OOP programming i've just started looking as UnrealScript for a game i had made in the UDK editor up to now. I have a class that extends UTHUD and another that extends UDKPAWN. I have the pawn destroyed when its been shot 3 times and some basic helloworld text displaying in my HUD but i'm completely lost as to how one would get some sort of feedback between the two classes going on? What i would like to do to start off, is have some text that says something like "Amount of baddies killed: 0" Displayed on the HUD which would then increment each time the player destroyed one of my pawns. I'm sorry if this is an inappropriate question but i've never really worked within a framework like this before and wasn't sure where to go for help to get my footing. All advice appreciated!

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• Slick & NiftyGUI. Nifty initialize exception

  - by Romeo

  I found my self into trouble when trying to run a Slick game with a Nifty Game State. This is the code: @Override protected void initGameAndGUI(GameContainer container, StateBasedGame game) throws SlickException { initNifty(container, game); } If i run this i get: java.lang.IllegalStateException: The NiftyGUI was already initialized. Its illegal to do so twice. If i delete the call to initNifty() i get another exception:java.lang.IllegalStateException: NiftyGUI was not initialized.

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• Which will be faster? Switching shaders or ignore that some cases don't need full code?

  - by PolGraphic

  I have two types of 2d objects: In first case (for about 70% of objects), I need that code in the shader: float2 texCoord = input.TexCoord + textureCoord.xy But in the second case I have to use: float2 texCoord = fmod(input.TexCoord, texCoordM.xy - textureCoord.xy) + textureCoord.xy I can use second code also for first case, but it will be a little slower (fmod is useless here, input.TexCoord will be always lower than textureCoord.xy - textureCoord.xy for sure). My question is, which way will be faster: Making two independent shaders for both types of rectangles, group rectangles by types and switch shaders during rendering. Make one shader and use some if statement. Make one shader and ignore that sometimes (70% of cases) I don't need to use fmod.

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• exact point on a rotating sphere

  - by nkint

  I have a sphere that represents the Earth textured with real pictures. It's rotating around the x axis, and when user click down it has to show me the exact place he clicked on. For example if he clicked on Singapore the system should be able to: understand that user clicked on the sphere (OK, I'll do it with unProject) understand where user clicked on the sphere (ray-sphere collision?) and take into account the rotation transform sphere-coordinate to some coordinate system good for some web-api service ask to api (OK, this is the simpler thing for me ;-) some advice?

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• Making AI jump on a spot effectively

  - by Pasquale Sada

  How to calculate, in 3D environment, the closest point, from which an AI character can jump onto a platform? Setup I have an initial velocity V(Vx,Vy,VZ) and a spot where the character stands still at S(Sx,Sy,Sz). What I'm trying to achieve is a successful jump on a spot E(Ex,Ey,Ez) where you have clicked on(only lower or higher spot, because I've in place a simple steering behavior for even terrains). There are no obstacles around. I've implemented a formula that can make him jump in a precise way on a spot but you need to declare an angle: the problem arise when the selected spot is straight above your head. It' pretty lame that the char hang there and can reach a thing that is 1cm above is head. I'll share the code I'm using: Vector3 dir = target - transform.position; // get target direction float h = dir.y; // get height difference dir.y = 0; // retain only the horizontal direction float dist = dir.magnitude ; // get horizontal distance float a = angle * Mathf.Deg2Rad; // convert angle to radians dir.y = dist * Mathf.Tan(a); // set dir to the elevation angle dist += h / Mathf.Tan(a); // correct for small height differences // calculate the velocity magnitude float vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 *a)); return vel * dir.normalized; Ended up using the lowest angle (20 degree) and checking for collision on the trajectory. If found any increase the angle. Here some code (to improve the code maybe must stop the check at the highest point of the curve): Vector3 BallisticVel(Vector3 target, float angle) { Vector3 dir = target - transform.position; // get target direction float h = dir.y; // get height difference dir.y = 0; // retain only the horizontal direction float dist = dir.magnitude ; // get horizontal distance float a = angle * Mathf.Deg2Rad; // convert angle to radians dir.y = dist * Mathf.Tan(a); // set dir to the elevation angle dist += h / Mathf.Tan(a); // correct for small height differences // calculate the velocity magnitude float vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 * a)); return vel * dir.normalized; } Vector3 TrajectoryPoint(Vector3 startingPosition, Vector3 startingVelocity, float n ) { float t = 1/60 ; // seconds per time step Vector3 stepVelocity = t * startingVelocity; // m/s Vector3 stepGravity = t * t * Physics.gravity; // m/s/s return startingPosition + n * stepVelocity + 0.5f * (n*n+n) * stepGravity; } bool CheckTrajectory(Vector3 startingPosition,Vector3 target, float angle_jump) { Debug.Log("checking"); if(angle_jump < 80f) { Debug.Log("if"); Vector3 startingVelocity = BallisticVel(target, angle_jump); for (int i = 0; i < 180; i++) { //Debug.Log(i); Vector3 trajectoryPosition = TrajectoryPoint( startingPosition, startingVelocity, i ); if(Physics.Raycast(trajectoryPosition,Vector3.forward,safeDistance)) { angle_jump += 10; break; // restart loop with the new angle } else continue; } return true; JumpVelocity = BallisticVel(target, angle_jump); } return false; }

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• Using glReadBuffer returns black image instead of the actual image only on Intel cards

  - by cloudraven

  I have this piece of code glReadBuffer( GL_FRONT ); glReadPixels( 0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, buffer ); Which works just perfectly in all the Nvidia and AMD GPUs I have tried, but it fails in almost every single Intel built-in video that I have tried. It actually works in a very old 945GME, but fails in all the others. Instead of getting a screenshot I am actually getting a black screen. If it helps, I am working with the Doom3 Engine, and that code is derived from the built-in screen capture code. By the way, even with the original game I cannot do screen capture on those intel devices anyway. My guess is that they are not implementing the standard correctly or something. Is there a workaround for this?

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• Particle effect after the bullet

  - by Siddharth

  In my game, I fire a bullet from the gun along with that I generate a particle behind the bullet so that I look like fire effect after the bullet. But my problem is that the position I got from the bullet was distance in place. So basically I want to say that the bullet speed was high for that reason I got coordinate for the particle generation was far from each other like dot dot effect. But I want continuous flow of particle behind the bullet. So please provide any guidance for my problem

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• When I shoot from a gun while walking, the bullet is off the center, but when stand still it's fine

  - by Vlad1k

  I am making a small project in Unity, and whenever I walk with the gun and shoot at the same time, the bullets seem to curve and shoot off 2-3 CMs from the center. When I stand still this doesn't happen. This is my main Javascript code: @script RequireComponent(AudioSource) var projectile : Rigidbody; var speed = 500; var ammo = 30; var fireRate = 0.1; private var nextFire = 0.0; function Update() { if(Input.GetButton ("Fire1") && Time.time > nextFire) { if(ammo != 0) { nextFire = Time.time + fireRate; var clone = Instantiate(projectile, transform.position, transform.root.rotation); clone.velocity = transform.TransformDirection(Vector3 (0, 0, speed)); ammo = ammo - 1; audio.Play(); } else { } } } I assume that these two lines need to be tweaked: var clone = Instantiate(projectile, transform.position, transform.root.rotation); clone.velocity = transform.TransformDirection(Vector3 (0, 0, speed)); Thanks in advanced, and please remember that I just started Unity, and I might have a difficult time understanding some things. Thanks!

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• ways to program glitch style effects

  - by okkk

  Most tutorials for generating glitch art usually has to do with some form of manipulation of the compression of files. Should my goal instead to replicate the look of these glitches in shaders or is it somehow possible to authentically generate the compression artifacts in real time? Example: This effect which I'm particularly interested is referred to as datamoshing. It does "things" using the p-frames of a video (frames that I think store just the change in pixels). I feel like I need a better understanding of both graphics programming and data-compression.

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• What data should be cached in a multiplayer server, relative to AI and players?

  - by DevilWithin

  In a virtual place, fully network driven, with an arbitrary number of players and an arbitrary number of enemies, what data should be cached in the server memory, in order to optimize smooth AI simulation? Trying to explain, lets say player A sees player B to E, and enemy A to G. Each of those players, see player A, but not necessarily each other. Same applies to enemies. Think of this question from a topdown perspective please. In many cases, for example, when a player shoots his gun, the server handles the sound as a radial "signal" that every other entity within reach "hear" and react upon. Doing these searches all the time for a whole area, containing possibly a lot of unrelated players and enemies, seems to be an issue, when the budget for each AI agent is so small. Should every entity cache whatever enters and exits from its radius of awareness? Is there a great way to trace the entities close by without flooding the memory with such caches? What about other AI related problems that may arise, after assuming the previous one works well? We're talking about environments with possibly hundreds of enemies, a swarm.

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• Minecraft style XNA game collision?

  - by Levi

  I've been trying to get this working for ages now, I can detect if there's a solid block at any place on the map and I can check how far something is inside of it, but I don't understand how to fix the collision. I've tried loads of ways and all of them end up by the player getting stuck, glitching around, incorrect responses and I really have no idea how to go about this :/. int Chnk = Utility.GetChunkFromPosition(origin); if (Chnk == -1) return; Vector3 Pos = Utility.GetCubeVectorFromPosition(origin); if (GlobalWorld.LoadedChunks[Chnk].Blocks[(byte)Pos.X, (byte)Pos.Y, (byte)Pos.Z] != 0) { isInIllegalState = true; if (velocity.Y < 0f) velocity.Y = 0f; } while (isInIllegalState) { if (GlobalWorld.LoadedChunks[Chnk].Blocks[(byte)Pos.X, (byte)origin.Y, (byte)Pos.Z] != 0) origin.Y = (int)(origin.Y + 1); else isInIllegalState = false; } if (origin.Y < Chunk.YSize - 2 && GlobalWorld.LoadedChunks[Chnk].Blocks[(byte)Pos.X, (byte)(origin.Y + playerHeight.Y), (byte)Pos.Z] != 0) { velocity.Y = 0f; //Acceleration.Y = 0f; origin.Y = (int)origin.Y;// -0.5f; } for (int x = -1; x <= 1; x+=2) { for (int z = -1; z <= 1; z += 2) { Vector3 CornerPosition = new Vector3(boundingSize * x, 0, boundingSize * z); bool CorrectX = false; bool CorrectZ = false; Vector3 RoundedOrigin = Utility.RoundVector(origin); Vector3 RoundedCorner = Utility.RoundVector(origin + CornerPosition); byte BlockAdjacent = Utility.GetCubeFromPosition(origin + CornerPosition); if (BlockAdjacent == 0) continue; if (RoundedCorner.X != RoundedOrigin.X && RoundedCorner.Z != RoundedOrigin.Z) { CorrectX = true; CorrectZ = true; } if (RoundedCorner.Z != RoundedOrigin.Z && RoundedCorner.X == RoundedOrigin.X) CorrectZ = true; if (RoundedCorner.X != RoundedOrigin.X && RoundedCorner.Z == RoundedOrigin.Z) CorrectX = true; if (CorrectX && CornerPosition.X > 0) { if (origin.X > 0f) origin.X = (int)(origin.X + 1) - boundingSize; else origin.X = (int)origin.X - boundingSize; } else if (CorrectX && CornerPosition.X < 0) { if (origin.X > 0f) origin.X = (int)(origin.X) + boundingSize; else origin.X = (int)(origin.X - 1) + boundingSize; } if (CorrectZ && CornerPosition.Z > 0) { if (origin.Z > 0f) origin.Z = (int)(origin.Z + 1) - boundingSize; else origin.Z = (int)origin.Z - boundingSize; } else if (CorrectZ && CornerPosition.Z < 0) { if (origin.Z > 0f) origin.Z = (int)(origin.Z) + boundingSize; else origin.Z = (int)(origin.Z - 1) + boundingSize; } } }

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• Numerically stable(ish) method of getting Y-intercept of mouse position?

  - by Fraser

  I'm trying to unproject the mouse position to get the position on the X-Z plane of a ray cast from the mouse. The camera is fully controllable by the user. Right now, the algorithm I'm using is... Unproject the mouse into the camera to get the ray: Vector3 p1 = Vector3.Unproject(new Vector3(x, y, 0), 0, 0, width, height, nearPlane, farPlane, viewProj; Vector3 p2 = Vector3.Unproject(new Vector3(x, y, 1), 0, 0, width, height, nearPlane, farPlane, viewProj); Vector3 dir = p2 - p1; dir.Normalize(); Ray ray = Ray(p1, dir); Then get the Y-intercept by using algebra: float t = -ray.Position.Y / ray.Direction.Y; Vector3 p = ray.Position + t * ray.Direction; The problem is that the projected position is "jumpy". As I make small adjustments to the mouse position, the projected point moves in strange ways. For example, if I move the mouse one pixel up, it will sometimes move the projected position down, but when I move it a second pixel, the project position will jump back to the mouse's location. The projected location is always close to where it should be, but it does not smoothly follow a moving mouse. The problem intensifies as I zoom the camera out. I believe the problem is caused by numeric instability. I can make minor improvements to this by doing some computations at double precision, and possibly abusing the fact that floating point calculations are done at 80-bit precision on x86, however before I start micro-optimizing this and getting deep into how the CLR handles floating point, I was wondering if there's an algorithmic change I can do to improve this? EDIT: A little snooping around in .NET Reflector on SlimDX.dll: public static Vector3 Unproject(Vector3 vector, float x, float y, float width, float height, float minZ, float maxZ, Matrix worldViewProjection) { Vector3 coordinate = new Vector3(); Matrix result = new Matrix(); Matrix.Invert(ref worldViewProjection, out result); coordinate.X = (float) ((((vector.X - x) / ((double) width)) * 2.0) - 1.0); coordinate.Y = (float) -((((vector.Y - y) / ((double) height)) * 2.0) - 1.0); coordinate.Z = (vector.Z - minZ) / (maxZ - minZ); TransformCoordinate(ref coordinate, ref result, out coordinate); return coordinate; } // ... public static void TransformCoordinate(ref Vector3 coordinate, ref Matrix transformation, out Vector3 result) { Vector3 vector; Vector4 vector2 = new Vector4 { X = (((coordinate.Y * transformation.M21) + (coordinate.X * transformation.M11)) + (coordinate.Z * transformation.M31)) + transformation.M41, Y = (((coordinate.Y * transformation.M22) + (coordinate.X * transformation.M12)) + (coordinate.Z * transformation.M32)) + transformation.M42, Z = (((coordinate.Y * transformation.M23) + (coordinate.X * transformation.M13)) + (coordinate.Z * transformation.M33)) + transformation.M43 }; float num = (float) (1.0 / ((((transformation.M24 * coordinate.Y) + (transformation.M14 * coordinate.X)) + (coordinate.Z * transformation.M34)) + transformation.M44)); vector2.W = num; vector.X = vector2.X * num; vector.Y = vector2.Y * num; vector.Z = vector2.Z * num; result = vector; } ...which seems to be a pretty standard method of unprojecting a point from a projection matrix, however this serves to introduce another point of possible instability. Still, I'd like to stick with the SlimDX Unproject routine rather than writing my own unless it's really necessary.

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• LWJGL - Mixing 2D and 3D

  - by nathan

  I'm trying to mix 2D and 3D using LWJGL. I have wrote 2D little method that allow me to easily switch between 2D and 3D. protected static void make2D() { glEnable(GL_BLEND); GL11.glMatrixMode(GL11.GL_PROJECTION); GL11.glLoadIdentity(); glOrtho(0.0f, SCREEN_WIDTH, SCREEN_HEIGHT, 0.0f, 0.0f, 1.0f); GL11.glMatrixMode(GL11.GL_MODELVIEW); GL11.glLoadIdentity(); } protected static void make3D() { glDisable(GL_BLEND); GL11.glMatrixMode(GL11.GL_PROJECTION); GL11.glLoadIdentity(); // Reset The Projection Matrix GLU.gluPerspective(45.0f, ((float) SCREEN_WIDTH / (float) SCREEN_HEIGHT), 0.1f, 100.0f); // Calculate The Aspect Ratio Of The Window GL11.glMatrixMode(GL11.GL_MODELVIEW); glLoadIdentity(); } The in my rendering code i would do something like: make2D(); //draw 2D stuffs here make3D(); //draw 3D stuffs here What i'm trying to do is to draw a 3D shape (in my case a quad) and i 2D image. I found this example and i took the code from TextureLoader, Texture and Sprite to load and render a 2D image. Here is how i load the image. TextureLoader loader = new TextureLoader(); Sprite s = new Sprite(loader, "player.png") And how i render it: make2D(); s.draw(0, 0); It works great. Here is how i render my quad: glTranslatef(0.0f, 0.0f, 30.0f); glScalef(12.0f, 9.0f, 1.0f); DrawUtils.drawQuad(); Once again, no problem, the quad is properly rendered. DrawUtils is a simple class i wrote containing utility method to draw primitives shapes. Now my problem is when i want to mix both of the above, loading/rendering the 2D image, rendering the quad. When i try to load my 2D image with the following: s = new Sprite(loader, "player.png); My quad is not rendered anymore (i'm not even trying to render the 2D image at this point). Only the fact of creating the texture create the issue. After looking a bit at the code of Sprite and TextureLoader i found that the problem appears after the call of the glTexImage2d. In the TextureLoader class: glTexImage2D(target, 0, dstPixelFormat, get2Fold(bufferedImage.getWidth()), get2Fold(bufferedImage.getHeight()), 0, srcPixelFormat, GL_UNSIGNED_BYTE, textureBuffer); Commenting this like make the problem disappear. My question is then why? Is there anything special to do after calling this function to do 3D? Does this function alter the render part, the projection matrix?

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• cocos2d event handler not fired when reentering scene

  - by Adam Freund

  I am encountering a very strange problem with my cocos2d app. I add a sprite to the page and have an event handler linked to it which replaces the scene with another scene. On that page I have another button to take me back to the original scene. When I am back on the original scene, the eventHandler doesn't get fired when I click on the sprite. Below is the relevant code. Thanks for any help! CCMenuItemImage *backBtnImg = [CCMenuItemImage itemWithNormalImage:@"btn_back.png" selectedImage:@"btn_back_pressed.png" target:self selector:@selector(backButtonTapped:)]; backBtnImg.position = ccp(45, 286); CCMenu *backBtn = [CCMenu menuWithItems:backBtnImg, nil]; backBtn.position = CGPointZero; [self addChild:backBtn]; EventHandler method (doesn't get called when the scene is re-entered). (void)backButtonTapped:(id)sender { NSLog(@"backButtonTapped\n"); CCMenuItemImage *backButton = (CCMenuItemImage *)sender; [backButton setNormalImage:[CCSprite spriteWithFile:@"btn_back_pressed.png"]]; [[CCDirector sharedDirector] replaceScene:[CCTransitionFade transitionWithDuration:.25 scene:[MenuView scene] withColor:ccBLACK]]; }

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• Getting isometric grid coordinates from standard X,Y coordinates

  - by RoryHarvey

  I'm currently trying to add sprites to an isometric Tiled TMX map using Objects in cocos2d. The problem is the X and Y metadata from TMX object are in standard 2d format (pixels x, pixels y), instead of isometric grid X and Y format. Usually you would just divide them by the tile size, but isometric needs some sort of transform. For example on a 64x32 isometric tilemap of size 40 tiles by 40 tiles an object at (20,21)'s coordinates come out as (640,584) So the question really is what formula gets (20,21) from (640,584)?

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• determine collision angle on a rotating body

  - by jorb

  update: new diagram and updated description I have a contact listener set up to try and determine the side that a collision happened at relative to the a bodies rotation. One way to solve this is to find the value of the yellow angle between the red and blue vectors drawn above. The angle can be found by taking the arc cosine of the dot product of the two vectors (Evan pointed this out). One of my points of confusion is the difference in domain of the atan2 function html canvas coordinates and the Box2d rotation information. I know I have to account for this somehow... SS below questions: Does Box2D provide these angles more directly in the collision information? Am I even on the right track? If so, any hints? I have the following javascript so far: Ship.prototype.onCollide = function (other_ent,cx,cy) { var pos = this.body.GetPosition(); //collision position relative to body var d_cx = pos.x - cx; var d_cy = pos.y - cy; //length of initial vector var len = Math.sqrt(Math.pow(pos.x -cx,2) + Math.pow(pos.y-cy,2)); //body angle - can over rotate hence mod 2*Pi var ang = this.body.GetAngle() % (Math.PI * 2); //vector representing body's angle - same magnitude as the first var b_vx = len * Math.cos(ang); var b_vy = len * Math.sin(ang); //dot product of the two vectors var dot_prod = d_cx * b_vx + d_cy * b_vy; //new calculation of difference in angle - NOT WORKING! var d_ang = Math.acos(dot_prod); var side; if (Math.abs(d_ang) < Math.PI/2 ) side = "front"; else side = "back"; console.log("length",len); console.log("pos:",pos.x,pos.y); console.log("offs:",d_cx,d_cy); console.log("body vec",b_vx,b_vy); console.log("body angle:",ang); console.log("dot product",dot_prod); console.log("result:",d_ang); console.log("side",side); console.log("------------------------"); }

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• OpenGL ES, orthopgraphics projection and viewport

  - by DarkDeny

  I want to make some simple 2D game on iOS to familiarize myself with OpenGL ES. I started with Ray Wenderlich tutorial (How To Create A Simple 2D iPhone Game with OpenGL ES 2.0 and GLKit). That tutorial is quite good, but I miss some parts of a puzzle. Ray creates orthographic projection using some magic numbers like 480 and 320. It is not clear to me why did he take these numbers, and as far as I can see - sprite is not mapped to the ipad simulator screen one-to-one pixel. I tried to play with parameters with which ortho matrix is created, but I cannot figure out what math is here. How can I calculate numbers (bottom, top, left, right, close, far) which will be parameters to orthographic projection matrix creation and have sprite on the screen shown in its original size?

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• How to mimic the same fixed-size horizon as in this racing game?

  - by Aybe

  I am trying to replicate the same horizon (buildings and sky) as in the image below: As you can see, the player has advanced in a straight line, yet the horizon has still the same size: This is my attempt using 3D, while it's okay when the player is on the start line: It's not so great when the player advanced as much as in the image no. 2: This is an overview of where the horizon buildings and sky are located: Obviously this won't achieve such effect when one is close to it, so I've tried to scale up the horizon on all axes but the problem is that the buildings are too small depending where you look at them from. How can one mimic such rendering ?

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• Adding 2D vector movement with rotation applied

  - by Michael Zehnich

  I am trying to apply a slight sine wave movement to objects that float around the screen to make them a little more interesting. I would like to apply this to the objects so that they oscillate from side to side, not front to back (so the oscillation does not affect their forward velocity). After reading various threads and tutorials, I have come to the conclusion that I need to create and add vectors, but I simply cannot come up with a solution that works. This is where I'm at right now, in the object's update method (updated based on comments): Vector2 oldPosition = new Vector2(spritePos.X, spritePos.Y); //note: newPosition is initially set in the constructor to spritePos.x/y Vector2 direction = newPosition - oldPosition; Vector2 perpendicular = new Vector2(direction.Y, -direction.X); perpendicular.Normalize(); sinePosAng += 0.1f; perpendicular.X += 2.5f * (float)Math.Sin(sinePosAng); spritePos.X += velocity * (float)Math.Cos(radians); spritePos.Y += velocity * (float)Math.Sin(radians); spritePos += perpendicular; newPosition = spritePos;

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