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• Complete Math Library for use in OpenGL ES 2.0 Game?

  - by Bunkai.Satori

  Are you aware of a complete (or almost complete) cross platform math library for use in OpenGL ES 2.0 games? The library should contain: Matrix2x2, Matrix 3x3, Matrix4x4 classes Quaternions Vector2, Vector3, Vector4 Classes Euler Angle Class Operations amongh the above mentioned classes, conversions, etc.. Standardly used math operations in 3D graphics (Dot Product, Cross Product, SLERP, etc...) Is there such Math API available either standalone or as a part of any package? Programming Language: Visual C++ but planned to be ported to OS X and Android OS.

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• Recasting and Drawing in SDL

  - by user1078123

  I have some code that essentially draws a column on the screen of a wall in a raycasting-type 3d engine. I am trying to optimize it, as it takes about 10 milliseconds do draw a million pixels using this, and the vast majority of game time is spent in this loop. However, I don't quite understand what's occurring, particularly the recasting (I modified the "pixel manipulation" sample code from the SDL documentation). "canvas" is the surface I am drawing to, and "hello" is the surface containing the texture for the column. int c = (curcol)* canvas->format->BytesPerPixel; void *canvaspixels = canvas->pixels; Uint16 texpitch = hello->pitch; int lim = (drawheight +startdraw) * canvpitch +c + (int) canvaspixels; Uint8 *k = (Uint8 *)hello->pixels + (hit)* hello->format->BytesPerPixel; for (int j= (startdraw)*(canvpitch)+c + (int) canvaspixels; (j< lim); j+= canvpitch){ Uint8 *q = (Uint8 *) ((int(h))*(texpitch)+k); *(Uint32 *)j = *(Uint32 *)q; h += s; } We have void pointers (not sure how those are even represented), 8, 16, and 32 bit ints (h and s are floats), all being intermingled, and while it works, it is quite confusing.

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• Interesting 3d zooming technique

  - by stark

  Is it possible to zoom to a certain point on screen by modifying the field of view and rotating the camera as to keep that point/object in the same place on screen while zooming ? Changing the camera position is not allowed.. I projected the 3d pos of the object on screen and remembered it. Then on each frame I calculate the direction to it in camera space and then I construct a rotation matrix to align this direction to Z axis (in cam space). After this, I calculate the direction from the camera to the object in world space and transform this vector with the matrix I obtained earlier and then use this final vector as the camera's new direction. And it's actually "kinda working", the problem is that it is more/less off than the camera's rotation before starting to zoom depending on the area you are trying to zoom in (larger error on edges/corners). It looks acceptable, but I'm not settling for only this. Any suggestions/resources for doing this technique perfectly ? If some of you want to explain the math in detail, be my guests, I can understand these things well. Thanks. Edit: I'll check often for responses, I'm really curious about this :D

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• Behaviour Trees with irregular updates

  - by Robominister

  I'm interested in behaviour trees that aren't iterated every game tick, but every so often. (Edit: the tree could specify how many frames within the main game loop to wait before running its tick function again). Every theoretical implementation I have seen of behaviour trees talks of the tree search being carried out every game update - which seems necessary, because a leaf node (eg a behaviour, like 'return to base') needs to be constantly checked to see if is still running, failed or completed. Can anyone suggest how I might start implementing a tree that isnt run every tick, or point me in the direction of good material specific to this case (I am struggling to find anything)? My thoughts so far: action leaf nodes (when they start) must only push some kind of action object onto a list for an entity, rather than directly calling any code that makes the entity do something. The list of actions for the entity would be run every frame (update any that need to run, pop any that have completed from the list). the return state from a given action must be fed back into the tree, so that when we run the tree iteration again (and reach the same action leaf node - so the tree has so far determined that we ought to still be trying this action) - that the action has completed, or is still running etc. If my actual action code is running from an action list on an entity, then I possibly need to cancel previously running actions in the list - i am thinking that I can just delete the entire stack of queued up actions. I've seen the idea of ActionLists which block lower priority actions when a higher priority one is added, but this seems like very close logic to behaviour trees, and I dont want to be duplicating behaviour. This leaves me with some questions 1) How would I feed the action return state back into the tree? Its obvious I need to store some information relating to 'currently executing actions' on the entity, and check that in the tree tick, but I can't imagine how. 2) Does having a seperate behaviour tree (for deciding behaviour) and action list (for carrying out actual queued up actions) sound like a reasonable approach? 3) Is the approach of updating a behaviour tree irregularly actually used by anyone? It seems like a nice idea for budgeting ai search time when you have a lot of ai entities to process. (Edit) - I am also thinking about storing a single instance of a given behaviour tree in memory, and providing it by reference to any entity that uses it. So any information about what action was last selected for execution on an entity must be stored in a data context relative to the entity (which the tree can check). (I am probably answering my own questions as i go!) I hope I have expressed my questions adequately! Thanks in advance for any help :)

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• Resolving a collision between point and moving line

  - by Conundrumer

  I am designing a 2d physics engine that uses Verlet integration for moving points (velocities mentioned below can be derived), constraints to represent moving line segments, and continuous collision detection to resolve collisions between moving points and static lines, and collisions between moving/static points and moving lines. I already know how to calculate the Time of Impact for both types of collision events, and how to resolve moving point static line collisions. However, I can't figure out how to resolve moving/static point moving line collisions. Here are the initial conditions in a point and moving line collision event. We have a line segment joined by two points, A and B. At this instant, point P is touching/colliding with line AB. These points have unit mass and some might have an initial velocity, unless point P is static. The line is massless and has no explicit rotational component, since points A and B could freely move around, extending or contracting the line as a result (which will be fixed later by the constraint solver). Collision is inelastic. What are the final velocities of the points after collision?

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• Adding 'swerve' to a direction

  - by Skoder

  Hey. I'm not much of a maths expert, so this is probably quite straight forward. I was playing a soccer flash game where you take free kicks. You provide Power, Swerve and Direction. I'm reading up on vectors and such so I can use the direction and power information to shoot the ball with the correct velocity. What I don't understand is how the 'Swerve' information is used. What formula connects the Swerve information with the Direction and Power? (This is all in 2D) Thanks for any advice.

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• Reversi/Othello early-game evaluation function

  - by Vladislav Il'ushin

  I've written my own Reversi player, based on the MiniMax algorithm, with Alpha-Beta pruning, but in the first 10 moves my evaluation function is too slow. I need a good early-game evaluation function. I'm trying to do it with this matrix (corresponding to the board) which determines how favourable that square is to have: { 30, -25, 10, 5, 5, 10, -25, 30,}, {-25, -25, 1, 1, 1, 1, -25, -25,}, { 10, 1, 5, 2, 2, 5, 1, 10,}, { 5, 1, 2, 1, 1, 2, 1, 5,}, { 5, 1, 2, 1, 1, 2, 1, 5,}, { 10, 1, 5, 2, 2, 5, 1, 10,}, {-25, -25, 1, 1, 1, 1, -25, -25,}, { 30, -25, 10, 5, 5, 10, -25, 30,},}; But it doesn't work well. Have you even written an early-game evaluation function for Reversi?

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• Drawing 2D Grid in 3D View - Need help with method

  - by Deukalion

  I'm trying to draw a simple 2D grid for an editor, to able to navigate more clearly around the 3D space, but I can't render it: Grid2D class, creates a grid of a certain size at a location and should just draw lines. public class Grid2D : IShape { private VertexPositionColor[] _vertices; private Vector2 _size; private Vector3 _location; private int _faces; public Grid2D(Vector2 size, Vector3 location, Color color) { float x = 0, y = 0; if (size.X < 1f) { size.X = 1f; } if (size.Y < 1f) { size.Y = 1f; } _size = size; _location = location; List<VertexPositionColor> vertices = new List<VertexPositionColor>(); _faces = 0; for (y = -size.Y; y <= size.Y; y++) { vertices.Add(new VertexPositionColor(location + new Vector3(-size.X, y, 0), color)); vertices.Add(new VertexPositionColor(location + new Vector3(size.X, y, 0), color)); _faces++; } for (x = -size.X; x <= size.X; x++) { vertices.Add(new VertexPositionColor(location + new Vector3(x, -size.Y, 0), color)); vertices.Add(new VertexPositionColor(location + new Vector3(x, size.Y, 0), color)); _faces++; } _vertices = vertices.ToArray(); } public void Render(GraphicsDevice device) { device.DrawUserPrimitives<VertexPositionColor>(PrimitiveType.LineList, _vertices, 0, _faces); } } Like this: +----+----+----+----+ | | | | | +----+----+----+----+ | | | | | +----+----+----+----+ | | | | | +----+----+----+----+ | | | | | +----+----+----+----+ Anyone knows what I'm doing wrong? If I add a Shape without texture, it's set automatically to VertexColorEnabled and TextureEnabled = false. This is how I render it: foreach (RenderObject render in _renderObjects) { render.Effect.Projection = projection; render.Effect.View = view; render.Effect.World = world; foreach (EffectPass pass in render.Effect.CurrentTechnique.Passes) { pass.Apply(); try { // Could be a Grid2D render.Shape.Render(_device); } catch { throw; } } } Exception is thrown: The current vertex shader declaration does not include all the elements required by the current Vertex Shader. Normal0 is missing. Simply put, I can't figure out how to draw a few lines. I want to draw them one at a time and I guess that's the problem I haven't figured out, and even when I tried rendering vertices[i], vertices[i+1] and primitiveCount = 1, vertices = 2, and so on it didn't work either. Any suggestions?

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• Collision Detection problems in Voxel Engine (XNA)

  - by Darestium

  I am creating a minecraft like terrain engine in XNA and have had some collision problems for quite some time. I have checked and changed my code based on other peoples collision code and I still have the same problem. It always seems to be off by about a block. for instance, if I walk across a bridge which is one block high I fall through it. Also, if you walk towards a "row" of blocks like this: You are able to stand "inside" the left most one, and you collide with nothing in the right most side (where there is no block and is not visible on this image). Here is all my collision code: private void Move(GameTime gameTime, Vector3 direction) { float speed = playermovespeed * (float)gameTime.ElapsedGameTime.TotalSeconds; Matrix rotationMatrix = Matrix.CreateRotationY(player.Camera.LeftRightRotation); Vector3 rotatedVector = Vector3.Transform(direction, rotationMatrix); rotatedVector.Normalize(); Vector3 testVector = rotatedVector; testVector.Normalize(); Vector3 movePosition = player.position + testVector * speed; Vector3 midBodyPoint = movePosition + new Vector3(0, -0.7f, 0); Vector3 headPosition = movePosition + new Vector3(0, 0.1f, 0); if (!world.GetBlock(movePosition).IsSolid && !world.GetBlock(midBodyPoint).IsSolid && !world.GetBlock(headPosition).IsSolid) { player.position += rotatedVector * speed; } //player.position += rotatedVector * speed; } ... public void UpdatePosition(GameTime gameTime) { player.velocity.Y += playergravity * (float)gameTime.ElapsedGameTime.TotalSeconds; Vector3 footPosition = player.Position + new Vector3(0f, -1.5f, 0f); Vector3 headPosition = player.Position + new Vector3(0f, 0.1f, 0f); // If the block below the player is solid the Y velocity should be zero if (world.GetBlock(footPosition).IsSolid || world.GetBlock(headPosition).IsSolid) { player.velocity.Y = 0; } UpdateJump(gameTime); UpdateCounter(gameTime); ProcessInput(gameTime); player.Position = player.Position + player.velocity * (float)gameTime.ElapsedGameTime.TotalSeconds; velocity = Vector3.Zero; } and the one and only function in the camera class: protected void CalculateView() { Matrix rotationMatrix = Matrix.CreateRotationX(upDownRotation) * Matrix.CreateRotationY(leftRightRotation); lookVector = Vector3.Transform(Vector3.Forward, rotationMatrix); cameraFinalTarget = Position + lookVector; Vector3 cameraRotatedUpVector = Vector3.Transform(Vector3.Up, rotationMatrix); viewMatrix = Matrix.CreateLookAt(Position, cameraFinalTarget, cameraRotatedUpVector); } which is called when the rotation variables are changed: public float LeftRightRotation { get { return leftRightRotation; } set { leftRightRotation = value; CalculateView(); } } public float UpDownRotation { get { return upDownRotation; } set { upDownRotation = value; CalculateView(); } } World class: public Block GetBlock(int x, int y, int z) { if (InBounds(x, y, z)) { Vector3i regionalPosition = GetRegionalPosition(x, y, z); Vector3i region = GetRegionPosition(x, y, z); return regions[region.X, region.Y, region.Z].Blocks[regionalPosition.X, regionalPosition.Y, regionalPosition.Z]; } return new Block(BlockType.none); } public Vector3i GetRegionPosition(int x, int y, int z) { int regionx = x == 0 ? 0 : x / Variables.REGION_SIZE_X; int regiony = y == 0 ? 0 : y / Variables.REGION_SIZE_Y; int regionz = z == 0 ? 0 : z / Variables.REGION_SIZE_Z; return new Vector3i(regionx, regiony, regionz); } public Vector3i GetRegionalPosition(int x, int y, int z) { int regionx = x == 0 ? 0 : x / Variables.REGION_SIZE_X; int X = x % Variables.REGION_SIZE_X; int regiony = y == 0 ? 0 : y / Variables.REGION_SIZE_Y; int Y = y % Variables.REGION_SIZE_Y; int regionz = z == 0 ? 0 : z / Variables.REGION_SIZE_Z; int Z = z % Variables.REGION_SIZE_Z; return new Vector3i(X, Y, Z); } Any ideas how to fix this problem? EDIT 1: Graphic of the problem: EDIT 2 GetBlock, Vector3 version: public Block GetBlock(Vector3 position) { int x = (int)Math.Floor(position.X); int y = (int)Math.Floor(position.Y); int z = (int)Math.Ceiling(position.Z); Block block = GetBlock(x, y, z); return block; } Now, the thing is I tested the theroy that the Z is always "off by one" and by ceiling the value it actually works as intended. Altough it still could be greatly more accurate (when you go down holes you can see through the sides, and I doubt it will work with negitive positions). I also does not feel clean Flooring the X and Y values and just Ceiling the Z. I am surely not doing something correctly still.

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• Ignore collisions with some objects in certain contexts

  - by Paul Manta

  I'm making a racing game with cars in Unity. The car has a boost/nitro powerup. While boosting, I wouldn't want to be deviated when colliding with zombies, but I do want to be deviated when colliding with walls. On the other hand, I don't want to ignore collision with zombies, because I still want to hit them on impact. How should I handle this? Basically, what I want is for the car to not rotate when colliding with certain objects.

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• How does one specify raster operations in XNA?

  - by Corey Ogburn

  I'm looking for a way to add a sprite using a particular logic operation (like XOR). I can't find anything on Google and I'm not sure where to look in the documentation. I've looked into SpriteBatch.Begin(...) and its Draw method and several options in the GraphicsDevice class, but I'm not recognizing anything capable of this. I'm still pretty new to XNA so I may just not have recognized the terminology to do this.

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• Game has noticeable frame drops but when through a profiler it always runs smooth

  - by felipedrl

  I'm trying to optimize my PC game but I can find the bottleneck since every time I run it through a profiler (gDEBugger) it runs smooths. When running outside gDEBugger I get these annoying hiccups. It's not just the graphics, the sound also gets choppy. The drops are inconsistent across runs, i.e, sometimes I run the same scenario and get no drops at all, sometimes I get a few drops, and others the game is consistently slow. The only constant is: when running through gDEBugger I ALWAYS get a smooth run. I'm suspecting something outside my game is interfering and causing these drops, but what in the hell does gDEBugger do that nullifies these drops? A higher process priority? Any ideas? Thanks in advance.

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• Using two joysticks in Cocos2D

  - by Blade

  Here is what I am trying to do: With the left joystick the player can steer the figure and with the right joystick it can attack. Problem is that the left joystick seems to get all the input, the right one does not even register anything. I enabled multipletouch after the eagleView and gone thoroughly over the code. But I seem to miss something. I initiliaze both sticks and it shows me both of them in game, but like I said, only the left one works. I initialize them both. From the h. file: SneakyJoystick *joystick; SneakyJoystick *joystickRight; And in m.file I synthesize, deallocate and initialize them. In order to use one for controlling and the other for attacking I put this: -(void)updateStateWithDeltaTime:(ccTime)deltaTime andListOfGameObjects:(CCArray*)listOfGameObjects { if ((self.characterState == kStateIdle) || (self.characterState == kStateWalkingBack) || (self.characterState == kStateWalkingLeft) || (self.characterState == kStateWalkingRight)|| (self.characterState == kStateWalkingFront) || (self.characterState == kStateAttackingFront) || (self.characterState == kStateAttackingBack)|| (self.characterState == kStateAttackingRight)|| (self.characterState == kStateAttackingLeft)) { if (joystick.degrees > 60 && joystick.degrees < 120) { if (self.characterState != kStateWalkingBack) [self changeState:kStateWalkingBack]; }else if (joystick.degrees > 1 && joystick.degrees < 59) { if (self.characterState != kStateWalkingRight) [self changeState:kStateWalkingRight]; } else if (joystick.degrees > 211 && joystick.degrees < 300) { if (self.characterState != kStateWalkingFront) [self changeState:kStateWalkingFront]; } else if (joystick.degrees > 301 && joystick.degrees < 360){ if (self.characterState != kStateWalkingRight) [self changeState:kStateWalkingRight]; } else if (joystick.degrees > 121 && joystick.degrees < 210) { if (self.characterState != kStateWalkingLeft) [self changeState:kStateWalkingLeft]; } if (joystickRight.degrees > 60 && joystickRight.degrees < 120) { if (self.characterState != kStateAttackingBack) [self changeState:kStateAttackingBack]; }else if (joystickRight.degrees > 1 && joystickRight.degrees < 59) { if (self.characterState != kStateAttackingRight) [self changeState:kStateAttackingRight]; } else if (joystickRight.degrees > 211 && joystickRight.degrees < 300) { if (self.characterState != kStateAttackingFront) [self changeState:kStateAttackingFront]; } else if (joystickRight.degrees > 301 && joystickRight.degrees < 360){ if (self.characterState != kStateAttackingRight) [self changeState:kStateAttackingRight]; } else if (joystickRight.degrees > 121 && joystickRight.degrees < 210) { if (self.characterState != kStateAttackingLeft) [self changeState:kStateAttackingLeft]; } [self applyJoystick:joystick forTimeDelta:deltaTime]; [self applyJoystick:joystickRight forTimeDelta:deltaTime]; } Maybe it has something to do with putting them both to time delta? I tried working around it, but it did not work. So I am thankful for any input you guys can give me :)

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• Import FBX with multiple meshes into UDK

  - by Tom

  I used this script to generate a few buildings that I was hoping to import into UDK. Each building is made of about 1000 separate objects. When I export a building as FBX and import the file into UDK it breaks it up into its individual objects again, so I was wondering how I would avoid this. Whether there was a tool to combine all of the objects into one mesh automatically before exporting or if I could prevent UDK from breaking them upon import.

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• Linear search vs Octree (Frustum cull)

  - by Dave

  I am wondering whether I should look into implementing an octree of some kind. I have a very simple game which consists of a 3d plane for the floor. There are multiple objects scattered around on the ground, each one has an aabb in world space. Currently I just do a loop through the list of all these objects and check if its bounding box intersects with the frustum, it works great but I am wondering if if it would be a good investment in an octree. I only have max 512 of these objects on the map and they all contain bounding boxes. I am not sure if an octree would make it faster since I have so little objects in the scene.

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• How i can sign and/or group a specific set of vertices in a 3D file container like OBJ ? - in Blender

  - by user827992

  I would like to export a 3D model with each part having a name or a label if you will. For example i would like to export a model of an human body and name each part in specifics vertex groups like: left hand, right hand, right foot, head, ears, ... and you got the idea; so i can have a single 3D model that i can explode in various parts if needed. If there is a better technique about how to mark vertex groups in a 3D file please share your solution. As 3D editor i use Blender.

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• Creating my own kill cam

  - by DalexL

  I plan on creating my own kill cam system for a sandbox tool set. After thinking about the mechanics of the kill cam itself, however, I'm quite lost. I'm trying to recreate the ones commonly seen in call of duty games that show, from the view of the killer, the actual killing scene. My Thoughts: -I can't just keep in memory when people kill others because I wouldn't know when to start the 'recording process'. There is on way for me to accurately determine when somebody is 'about' to kill someone. -My only real idea so far is to have a complete duplicate of everything loaded off to the side copying all the movement from the original world but with a 10 second delay. That way, all the kill cams would be 10 seconds long and the persons camera would just be moved to the second world of their killer. My Questions: Is there already an accepted way to do this? Does anybody have any good ideas for something like this? Thanks if you can!

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• Posting to facebook from unity3d on iOS and android

  - by Guye Incognito

  I've made a game in unity3d for iOS and android. We have our own server to manage high scores and stuff like that. We'd also like to have the possibility post high scores to facebook, and also do things like this.. If you and your friend are have both posted a score for our game to facebook and you post a better score then you can send them a notification. I'm reading around about this now, but I'm wondering whats the normal way people do this? Possible ways.. Use the unity facebook SDK Looks like it would work but there are different versions for iOS and android. Call the facebook graph API directly from our server. This would unify the iOS and android versions and also it makes sense as our server holds / deals with all the highscore info. I can just imagine difficulties with logging in / authentication

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• Continuous Collision Detection Techniques

  - by Griffin

  I know there are quite a few continuous collision detection algorithms out there , but I can't find a list or summary of different 2D techniques; only tutorials on specific algorithms. What techniques are out there for calculating when different 2D bodies will collide and what are the advantages / disadvantages of each? I say techniques and not algorithms because I have not yet decided on how I will store different polygons which might be concave or even have holes. I plan to make a decision on this based on what the algorithm requires (for instance if an algorithm breaks down a polygon into triangles or convex shapes I will simply store the polygon data in this form).

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• relationship between the model and the renderer

  - by acrilige

  I tried to build a simple graphics engine, and faced with this problems: i have a list of models that i need to draw, and object (renderer) that implements IRenderer interface with method DrawObject(Object* obj). Implementation of renderer depends on using graphics library (opengl/directx). 1st question: model should not know nothing about renderer implementation, but in this case where can i hold (cache) information that depends on renderer implementation? For example, if model have this definition: class Model { public: Model(); Vertex* GetVertices() const; private: Vertex* m_vertices; }; what is the best way to cache, for example, vertex buffer of this model for dx11? Hold it in renderer object? 2nd question: what is the best way for model to say renderer HOW it must be rendered (for example with texture, bump mapping, or may be just in one color). I thought it can be done with flags, like this: model-SetRenderOptions(RENDER_TEXTURE | RENDER_BUMPMAPPING | RENDER_LIGHTING); and in Renderer::DrawModel method check for each flag. But looks like it will become uncomfortable with the options count growth...

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• Render 3d object to 2d surface (embedded system)

  - by Martin Berger

  i am working on an embedded system of a sort, and in some free time i would like to test its drawing capabilities. System in question is ARM Cortex M3 microcontroller attached to EasyMX Stellaris board. And i have a small 320x240 TFT screen :) Now, i have some free time each day and i want to create rotating cube. Micro C PRO for ARM doesnt have 3d drawing capabilities, which means it must be done in software. From the book Introduction to 3D Game Programming with DirectX 10 i know matrix algebra for transformations but that is cool when you have DirectX to set camera right. I gues i could make 2d object to rotate, but how would i go with 3d one? Any ideas and examples are welcome. Although i would prefer advices. I'd like to understand this.

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• Calculating up-vector to avoid gimbal lock using euler angles

  - by jessejuicer

  I wish to orbit a camera around a sphere, yet the problem is that when the camera rotates so that it is at the north pole (and pointing down) or the south pole (and pointing up) of the sphere the camera doesn't handle itself very well. It spins rapidly until arriving 180 degrees in the opposite direction. I believe this is known as gimbal lock. I understand you can avoid this problem using quaternions. But I also read in another forum that it's possible to avoid this easily using euler angles as well. Which I would prefer to do. It was said that all you need to do is "calculate a proper up-vector every frame, and that avoids the problem entirely." Well, I tried aligning the up-vector with the vertical axis of the camera whenever the camera changed orientation, but this didn't seem to work. Meaning that the up-vector followed exactly the orientation of the camera's y-axis (or it's up vector), instead of using a constant up-vector aligned to the up-vector of the world (0, 1, 0). How exactly do I go about calculating a proper up-vector as my camera orientation changes to avoid the gimbal lock problem mentioned above?

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• what's wrong with this Lua code (creating text inside listener in Corona)

  - by Greg

  If you double/triple click on the myObject here the text does NOT disappear. Why is this not working when there are multiple events being fired? That is, are there actually multiple "text" objects, with some existing but no longer having a reference to them held by the local "myText" variable? Do I have to manually removeSelf() on the local "myText" field before assigning it another "display.newText(...)"? display.setStatusBar( display.HiddenStatusBar ) local myText local function hideMyText(event) print ("hideMyText") myText.isVisible = false end local function showTextListener(event) if event.phase == "began" then print("showTextListener") myText = display.newText("Hello World!", 0, 0, native.systemFont, 30) timer.performWithDelay(1000, hideMyText, 1 ) end end -- Display object to press to show text local myObject = display.newImage( "inventory_button.png", display.contentWidth/2, display.contentHeight/2) myObject:addEventListener("touch", showTextListener) Question 2 - Also why is it the case that if I add a line BEFORE "myText = ..." of: a) "if myText then myText:removeSelf() end" = THIS FIXES THINGS, whereas b) "if myText then myText=nil end" = DOES NOT FIX THINGS Interested in hearing how Lua works here re the answer...

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• Quaternion based rotation and pivot position

  - by Michael IV

  I can't figure out how to perform matrix rotation using Quaternion while taking into account pivot position in OpenGL.What I am currently getting is rotation of the object around some point in the space and not a local pivot which is what I want. Here is the code [Using Java] Quaternion rotation method: public void rotateTo3(float xr, float yr, float zr) { _rotation.x = xr; _rotation.y = yr; _rotation.z = zr; Quaternion xrotQ = Glm.angleAxis((xr), Vec3.X_AXIS); Quaternion yrotQ = Glm.angleAxis((yr), Vec3.Y_AXIS); Quaternion zrotQ = Glm.angleAxis((zr), Vec3.Z_AXIS); xrotQ = Glm.normalize(xrotQ); yrotQ = Glm.normalize(yrotQ); zrotQ = Glm.normalize(zrotQ); Quaternion acumQuat; acumQuat = Quaternion.mul(xrotQ, yrotQ); acumQuat = Quaternion.mul(acumQuat, zrotQ); Mat4 rotMat = Glm.matCast(acumQuat); _model = new Mat4(1); scaleTo(_scaleX, _scaleY, _scaleZ); _model = Glm.translate(_model, new Vec3(_pivot.x, _pivot.y, 0)); _model =rotMat.mul(_model);//_model.mul(rotMat); //rotMat.mul(_model); _model = Glm.translate(_model, new Vec3(-_pivot.x, -_pivot.y, 0)); translateTo(_x, _y, _z); notifyTranformChange(); } Model matrix scale method: public void scaleTo(float x, float y, float z) { _model.set(0, x); _model.set(5, y); _model.set(10, z); _scaleX = x; _scaleY = y; _scaleZ = z; notifyTranformChange(); } Translate method: public void translateTo(float x, float y, float z) { _x = x - _pivot.x; _y = y - _pivot.y; _z = z; _position.x = _x; _position.y = _y; _position.z = _z; _model.set(12, _x); _model.set(13, _y); _model.set(14, _z); notifyTranformChange(); } But this method in which I don't use Quaternion works fine: public void rotate(Vec3 axis, float angleDegr) { _rotation.add(axis.scale(angleDegr)); // change to GLM: Mat4 backTr = new Mat4(1.0f); backTr = Glm.translate(backTr, new Vec3(_pivot.x, _pivot.y, 0)); backTr = Glm.rotate(backTr, angleDegr, axis); backTr = Glm.translate(backTr, new Vec3(-_pivot.x, -_pivot.y, 0)); _model =_model.mul(backTr);///backTr.mul(_model); notifyTranformChange(); }

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• Question about JPanel "transition" for Java Swing

  - by user16778

  I want to make like a sort of main menu (in GUI). When the user clicks the start button, the screen transition into another "screen" (JPanel). This image will make it easier to understand. http://i.imgur.com/Cfdry.png Currently, I have a MainMenu extends JPanel and that gets added into a driver class with a JFrame. I can't figure how to switch to another class like Game extends JPanel. So when the user clicks the start button in MainMenu, I want it to somehow hide itself and the Game to show itself. Thanks.

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