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• What are the semantics of glRotate and glTranslate's parameters?

  - by Zarkopafilis

  I have been trying to play with OpenGL after watching some tutorials and I don't understand how the glTranslatef and glRotatef functions work. I believe a simple picture would help me. I understand that glTranslatef changes the position of the "camera" (but does it change the position in wich the shapes are getting drawn)? However, I don't understand the rotation concept at all. If I do glRotatef(1,0,0,1) it makes my quad spin around. If I just do glRotatef(1,0,0,0) it makes the quad smaller (further away) but if I try to rotate around the X or Y axis, I get a black screen. I don't understand the angle either. Help would be appreciated.

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• Accounting for waves when doing planar reflections

  - by CloseReflector

  I've been studying Nvidia's examples from the SDK, in particular the Island11 project and I've found something curious about a piece of HLSL code which corrects the reflections up and down depending on the state of the wave's height. Naturally, after examining the brief paragraph of code: // calculating correction that shifts reflection up/down according to water wave Y position float4 projected_waveheight = mul(float4(input.positionWS.x,input.positionWS.y,input.positionWS.z,1),g_ModelViewProjectionMatrix); float waveheight_correction=-0.5*projected_waveheight.y/projected_waveheight.w; projected_waveheight = mul(float4(input.positionWS.x,-0.8,input.positionWS.z,1),g_ModelViewProjectionMatrix); waveheight_correction+=0.5*projected_waveheight.y/projected_waveheight.w; reflection_disturbance.y=max(-0.15,waveheight_correction+reflection_disturbance.y); My first guess was that it compensates for the planar reflection when it is subjected to vertical perturbation (the waves), shifting the reflected geometry to a point where is nothing and the water is just rendered as if there is nothing there or just the sky: Now, that's the sky reflecting where we should see the terrain's green/grey/yellowish reflection lerped with the water's baseline. My problem is now that I cannot really pinpoint what is the logic behind it. Projecting the actual world space position of a point of the wave/water geometry and then multiplying by -.5f, only to take another projection of the same point, this time with its y coordinate changed to -0.8 (why -0.8?). Clues in the code seem to indicate it was derived with trial and error because there is redundancy. For example, the author takes the negative half of the projected y coordinate (after the w divide): float waveheight_correction=-0.5*projected_waveheight.y/projected_waveheight.w; And then does the same for the second point (only positive, to get a difference of some sort, I presume) and combines them: waveheight_correction+=0.5*projected_waveheight.y/projected_waveheight.w; By removing the divide by 2, I see no difference in quality improvement (if someone cares to correct me, please do). The crux of it seems to be the difference in the projected y, why is that? This redundancy and the seemingly arbitrary selection of -.8f and -0.15f lead me to conclude that this might be a combination of heuristics/guess work. Is there a logical underpinning to this or is it just a desperate hack? Here is an exaggeration of the initial problem which the code fragment fixes, observe on the lowest tessellation level. Hopefully, it might spark an idea I'm missing. The -.8f might be a reference height from which to deduce how much to disturb the texture coordinate sampling the planarly reflected geometry render and -.15f might be the lower bound, a security measure.

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• Creating meaningful and engaging quests

  - by user384918

  Kill X number of monsters. Gather Y number of items (usually by killing X number of monsters). Deliver this NPC's package to this other NPC who is far far away. etc. Yeah. These quests are easy to implement, easy to complete, but also very boring after the first few times. It's kind of disingenuous to call them quests really; they're more like chores or errands. What ideas for quests have people seen that were well designed, immersive, and rewarding? What specific things did the developers do that made it so? What are some ideas you would use (or have used) to make quests more interesting?

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• rotate opengl mesh relative to camera

  - by shuall

  I have a cube in opengl. It's position is determined by multiplying it's specific model matrix, the view matrix, and the projection matrix and then passing that to the shader as per this tutorial (http://www.opengl-tutorial.org/beginners-tutorials/tutorial-3-matrices/). I want to rotate it relative to the camera. The only way I can think of getting the correct axis is by multiplying the inverse of the model matrix (because that's where all the previous rotations and tranforms are stored) times the view matrix times the axis of rotation (x or y). I feel like there's got to be a better way to do this like use something other than model, view and projection matrices, or maybe I'm doing something wrong. That's what all the tutorials I've seen use. PS I'm also trying to keep with opengl 4 core stuff. edit: If quaternions would fix my problems, could someone point me to a good tutorial/example for switching from 4x4 matrices to quaternions. I'm a little daunted by the task.

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• how get collision callback of two specific objects using bullet physics?

  - by sebap123

  I have got problem implementing collision callback into my project. I would like to have detection between two specific objects. I have got normall collision but I want one object to stop or change color or whatever when colides with another. I wrote code from bullet wiki: int numManifolds = dynamicsWorld->getDispatcher()->getNumManifolds(); for (int i=0;i<numManifolds;i++) { btPersistentManifold* contactManifold = dynamicsWorld->getDispatcher()->getManifoldByIndexInternal(i); btCollisionObject* obA = static_cast<btCollisionObject*>(contactManifold->getBody0()); btCollisionObject* obB = static_cast<btCollisionObject*>(contactManifold->getBody1()); int numContacts = contactManifold->getNumContacts(); for (int j=0;j<numContacts;j++) { btManifoldPoint& pt = contactManifold->getContactPoint(j); if (pt.getDistance()<0.f) { const btVector3& ptA = pt.getPositionWorldOnA(); const btVector3& ptB = pt.getPositionWorldOnB(); const btVector3& normalOnB = pt.m_normalWorldOnB; bool x = (ContactProcessedCallback)(pt,fallRigidBody,earthRigidBody); if(x) printf("collision\n"); } } } where fallRigidBody is a dynamic body - a sphere and earthRigiBody is static body - StaticPlaneShape and sphere isn't touching earthRigidBody all the time. I have got also other objects that are colliding with sphere and it works fine. But the program detects collision all the time. It doesn't matter if the objects are or aren't colliding. I have also added after declarations of rigid body: earthRigidBody->setCollisionFlags(earthRigidBody->getCollisionFlags() | btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK); fallRigidBody->setCollisionFlags(fallRigidBody->getCollisionFlags() | btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK); So can someone tell me what I am doing wrong? Maybe it is something simple?

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• 2D Camera Acceleration/Lag

  - by Cyral

  I have a nice camera set up for my 2D xna game. Im wondering how I should make the camera have 'acceleration' or 'lag' so it smoothly follows the player, instead of 'exactly' like mine does now. Im thinking somehow I need to Lerp the values when I set CameraPosition. Heres my code private void ScrollCamera(Viewport viewport) { float ViewMargin = .35f; float marginWidth = viewport.Width * ViewMargin; float marginLeft = cameraPosition.X + marginWidth; float marginRight = cameraPosition.X + viewport.Width - marginWidth; float TopMargin = .3f; float BottomMargin = .1f; float marginTop = cameraPosition.Y + viewport.Height * TopMargin; float marginBottom = cameraPosition.Y + viewport.Height - viewport.Height * BottomMargin; Vector2 CameraMovement; Vector2 maxCameraPosition; CameraMovement.X = 0.0f; if (Player.Position.X < marginLeft) CameraMovement.X = Player.Position.X - marginLeft; else if (Player.Position.X > marginRight) CameraMovement.X = Player.Position.X - marginRight; maxCameraPosition.X = 16 * Width - viewport.Width; cameraPosition.X = MathHelper.Clamp(cameraPosition.X + CameraMovement.X, 0.0f, maxCameraPosition.X); CameraMovement.Y = 0.0f; if (Player.Position.Y < marginTop) //above the top margin CameraMovement.Y = Player.Position.Y - marginTop; else if (Player.Position.Y > marginBottom) //below the bottom margin CameraMovement.Y = Player.Position.Y - marginBottom; maxCameraPosition.Y = 16 * Height - viewport.Height; cameraPosition.Y = MathHelper.Clamp(cameraPosition.Y + CameraMovement.Y, 0.0f, maxCameraPosition.Y); }

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• External classes positions don't work?

  - by SystemNetworks

  I have an external class which reads the user's mouse clicks. I gave a position where the user have to click, and when the user clicks on that position, it would turn my boolean "mouse" to true. But when I connect that to my game(state based) class, it does not work. Here's the code: External class public void UI(Input input, GameContainer gc, float posX, float posY) { int x = Mouse.getX(); int y = Mouse.getY(); if(posX<=100 && posY<=100) { if(Mouse.isButtonDown(1)) { mouse = true; } } } Game class(main) public void update(GameContainer gc, StateBasedGame sbg, int delta) throws SlickException { int x = Mouse.getX(); int y = Mouse.getY(); civ.UI(input, gc, x,y); } The problem is when I click my mouse at posX<=100 && posY<=100. It does not work.

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• Possible to pass pygame data to memory map block?

  - by toozie21

  I am building a matrix out of addressable pixels and it will be run by a Pi (over the ethernet bus). The matrix will be 75 pixels wide and 20 pixels tall. As a side project, I thought it would be neat to run pong on it. I've seen some python based pong tutorials for Pi, but the problem is that they want to pass the data out to a screen via pygame.display function. I have access to pass pixel information using a memory map block, so is there anyway to do that with pygame instead of passing it out the video port? In case anyone is curious, this was the pong tutorial I was looking at: Pong Tutorial

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• I don't understand why one of my vbo is overwritten by another

  - by Alays

  to create a vbo I use this function: public void loadVBO(){ vboID = GL15.glGenBuffers(); GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, vboID); GL15.glBufferData(GL15.GL_ARRAY_BUFFER, buf, GL15.GL_STATIC_DRAW); // Put the position coordinates in attribute list 0 GL20.glVertexAttribPointer(0, 4, GL11.GL_FLOAT, false,4*4+4*4+4*4+2*4 , 0); // Put the color components in attribute list 1 GL20.glVertexAttribPointer(1, 4, GL11.GL_FLOAT, false,4*4+4*4+4*4+2*4 , 4*4); GL20.glVertexAttribPointer(2, 4, GL11.GL_FLOAT, false,4*4+4*4+4*4+2*4 , 4*4+4*4); // Put the texture coordinates in attribute list 2 GL20.glVertexAttribPointer(3, 4, GL11.GL_FLOAT, false,4*4+4*4+4*4+2*4 , 4*4+4*4+4*4); GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, 0); } to display a vbo I use this function: public void displayVBO(){ GL15.glBindBuffer(GL15.GL_ELEMENT_ARRAY_BUFFER, vboID); GL20.glEnableVertexAttribArray(0); GL20.glEnableVertexAttribArray(1); GL20.glEnableVertexAttribArray(2); GL20.glEnableVertexAttribArray(3); GL11.glDrawArrays(GL_TRIANGLES, 0, buf.capacity()); GL20.glDisableVertexAttribArray(0); GL20.glDisableVertexAttribArray(1); GL20.glDisableVertexAttribArray(2); GL20.glDisableVertexAttribArray(3); GL15.glBindBuffer(GL15.GL_ARRAY_BUFFER, 0); } So when I call map.loadVBO() and then ocean.loadVBO(), I think the second call overwrite the first vbo I don't know how ... When I call map.display() and ocean.display(), I have the ocean draw 2 times .... Thanks.

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• Edge flicker when moving Camera (2D)

  - by Matthias Reisner

  I have a Orthographic camera. I have a fixed landscape texture and a texture for a moveable object. If the object moves to the right the camera will also move with the object. When I also draw an score text that should have fixed position on the screen, that score text position will be update too if the camera's position gets updated so that it looks like that it is fixed on the screen. But if I do that, I have some edge flickering at the text object. I'am using SpriteBatch! Is there another approach to implement a fixed positioned object on the screen?

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• non randomic enemy movement implementation

  - by user601836

  I would like to implement enemy movement on a X-Y grid. Would it be a good idea to have a predefined table with an initial X-Y position and a predefined "surveillance path"? Each enemy will follow its path until it detects a player, at this point it will start chasing it using a chasing algorithm. According to a friend of mine this implementation is good because the design of a good path will provide to the user a sort of reality sensation.

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• specifying an object type at runtime

  - by lapin

  I've written a Vbo template class to work with opengl. I'd like to set the type from a config file at runtime. e.g. <vbo type="bump_vt" ... /> Vbo* pVbo = new Vbo(bump_vt, ...); Is there some way I can do this without a large if else block e.g. if( sType.compareTo("bump_vt") == 0 ) Vbo* pVbo = new Vbo(bump_vt, ...); else if ... I'm writing for multiple platforms in c++. thanks

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• Component based design, but components rely on eatchother

  - by MintyAnt

  I've begun stabbing at a "Component Based" game system. Basically, each entity holds a list of components to update (and render) I inherit the "Component" class and break each game system into it. Examples: RenderComponent - Draws the entity MovementComponent - Moves the entity, deals with velocity and speed checks DamageComponent - Deals with how/if the entity gets damaged... So. My system has this: MovementComponent InputComponent Now maybe my design is off, but the InputComponent should say things like if (w key is down) add y speed to movement if (x key is down) Trigger primary attack This means that the InputComponent sort of relies on these other components. I have to do something alone the lines of: if (w key is down) { MovementComponent* entityMovement = mEntity->GetMovement(); if (entityMovement != NULL) add y speed to movement } which seems kinda crappy every update. Other options? Better design? Is this the best way? Thanks!

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• XNA- Texturing problem, exporting model

  - by user1806687

  How,can I disable coloring when texture is applied, because right now the texture is being colored over. foreach (BasicEffect effect in mesh.Effects) { effect.TextureEnabled = textureApplied; if(textureApplied) effect.Texture = Texture2D.FromStream(GraphicsDevice,System.IO.File.OpenRead(texturePath)); else { effect.DiffuseColor = ti.DiffuseColor; effect.EmissiveColor = ti.EmissiveColor; } ... } mesh.Draw(); Also, is there any easy way for xna to export models? Or do I have to write my own?

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• How can I locate the frames of a spritesheet PNG based on this PLIST data?

  - by kitsune

  Someone asked me to reskin a certain game. Now he only sent me the whole sprite PNG and PLIST files of the sprites. He instructed me to rename each sprite with the same name corresponding to each original sprite. The problem is, he gave me the whole sprite sheet instead of each individual sprite and the PLIST. Now yes, I can read the PNG filenames from the PLIST, but I cannot rename the reskin sprites I did because I'm not sure which sprite is boy_gun_3_3.png; there are multiple guns, I don't know which is which. Is there a way to extract individual accurately named individual PNG files from the single sprite sheet using the PLIST?

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• XNA When to call LoadContent

  - by Peteyslatts

  I have an enum in my game that denotes the game state ie MainMenu, InGame, GameOver, Exit and I was wondering if it would be advisable to add a new one in for PrepGame - in which the game creates viewports for however many players there are, creates the battlefield etc. I feel like this is a good idea except for one thing: should I make a call back to LoadContent() in this state? I could just put a switch statement in the LoadContent for my currentGameState. If it equals PrepGame load things like the skybox, ship models, texures, HUD graphics etc. Or is it a good idea to create an Asset Manager class in the first call to LoadContent() and load everything then. I feel like both approaches have different benefits: faster, but more load times vs slower initial load time, but then all my objects are referencing the same variables so I only have to load each on once. Any help is greatly appreciated. Thanks, Peter

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• Wall avoidance steering

  - by Vodemki

  I making a small steering simulator using the reynolds boid algorythm. Now I want to add a wall avoidance feature. My walls are in 3D and defined using two points like that: ---------. P2 | | P1 .--------- My agents have a velocity, a position, etc... Could you tell me how to make avoidance with my agents ? Vector2D ReynoldsSteeringModel::repulsionFromWalls() { Vector2D force; vector<Wall *> wallsList = walls(); Point2D pos = self()->position(); Vector2D velocity = self()->velocity(); for (unsigned i=0; i<wallsList.size(); i++) { //TODO } return force; } Then I use all the forces returned by my boid functions and I apply it to my agent. I just need to know how to do that with my walls ? Thanks for your help.

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• How do I create a big multiplayer world in UDK?

  - by Dorpe

  I want to create a big multiplayer world in UDK and I'm having a few difficulties. I created the biggest terrain possible but then any terrain related action I do takes forever. However, I've seen videos of people make same size terrain and working without a problem. My pc is strong enough, so maybe someone can tell me what I'm doing wrong. I want to make it even bigger then the biggest terrain size, so I was thinking of doing level streaming but then I read that streaming is working server side which means if I have a player on every terrain all terrains will still be loaded and I want to save as much memory possible so it will work well online. Thanks for any help you can give.

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• game engine done, ideas missing

  - by Thoms

  I read at many places how people have this GREAT ideas but are not able to program themselves. I have quite the opposite problem. I have developed game engine, level editor, embedded Lua scripting language, I have even made wrapper for Android and it all works well. But I have no good idea about how to proceed with actual levels; I have no good ideas. The engine itself is very generic and can be used in many game concepts, but I just cannot think of anything useful. Do you have any thoughts on how to proceed? Where should I seek ideas? Who should I ask? I am sorry if this question is a duplicate.

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• How do I properly center Nifty GUI elements on screen?

  - by Jason Crosby

  I am new to JME3 game engine but I know Android XML GUI layouts pretty good. I have a simple layout here and I cant figure out what is wrong. Here is my XML code: <?xml version="1.0" encoding="UTF-8"?> <nifty xmlns="http://nifty-gui.sourceforge.net/nifty-1.3.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://nifty-gui.sourceforge.net/nifty-1.3.xsd http://nifty-gui.sourceforge.net/nifty-1.3.xsd"> <useControls filename="nifty-default-controls.xml" /> <useStyles filename="nifty-default-styles.xml" /> <screen id="start" controller="com.jasoncrosby.game.farkle.gui.MenuScreenGui"> <layer id="layer" backgroundColor="#66CD00" childLayout="center"> <panel id="panel" align="center" valign="center" childLayout="center" visibleToMouse="true"> <image filename="Textures/wood_floor.png" height="95%" width="95%"/> <panel id="panel" align="center" valign="center" childLayout="center" visibleToMouse="true"> <text text="test" font="Interface/Fonts/Eraser.fnt"></text> </panel> </panel> </layer> </screen> Everything works well until I get to displaying the text. I have tried different alignments and tried moving the text into different panels but no matter what I do the text is never in the center of the screen. It's always in the upper left corner, so far I can only see the lower right part of the text. How can I center the text element in the center of the screen?

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• Moving an object using its velocity on a closed curve

  - by Futaro

  I want that an object follows a path, in Peggle game there are some pegs that have movement in a closed path. How can i get the same result? I guess that I can use parametric curve but I need use the velocity and not the position (x, y). I use NAPE and I have this in my gameloop: //circunference angle = angle + 1*(Math.PI / 180); movableBall.position.x = radius * Math.cos(angle)+ h; movableBall.position.y = radius * Math.sin(angle)+ k; it's works but I can not control the velocity, each movableBall must have its own velocity. Besides, from docs of NAPE:"Setting the position of a body is equivalent to simply teleporting the body; for instance moving a kinematic body by position is not the way to go about things.." I want to use: movableBall.velocity.x =?? movableBall.velocity.y = ?? The final idea is to follow others paths like the Lemniscate of Bernoulli. Thanks!

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• Realistic Jumping

  - by Seth Taddiken

  I want to make the jumping that my character does more realistic. This is what I've tried so far but it doesn't seem very realistic when the player jumps. I want it to jump up at a certain speed then slow down as it gets to the top then eventually stopping (for about one frame) and then slowly going back down but going faster and faster as it goes back down. I've been trying to make the speed at which the player jumps up slow down by one each frame then become negative and go down faster... but it doesn't work very well public bool isPlayerDown = true; public bool maxJumpLimit = false; public bool gravityReality = false; public bool leftWall = false; public bool rightWall = false; public float x = 76f; public float y = 405f; if (Keyboard.GetState().IsKeyDown(up) && this.isPlayerDown == true && this.y <= 405f) { this.isPlayerDown = false; } if (this.isPlayerDown == false && this.maxJumpLimit == false) { this.y = this.y - 6; } if (this.y <= 200) { this.maxJumpLimit = true; } if (this.isPlayerDown == true) { this.y = 405f; this.isPlayerDown = true; this.maxJumpLimit = false; } if (this.gravityReality == true) { this.y = this.y + 2f; this.gravityReality = false; } if (this.maxJumpLimit == true) { this.y = this.y + 2f; this.gravityReality = true; } if (this.y > 405f) { this.isPlayerDown = true; }

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• ScissorStack LIBGDX example?

  - by user36531

  I cant find a good resource/tutorial on how to do this. I would appreciate it if someone could provide a scissorstack example from an entity class. ie. using scissorstack on PlayerClass such that the map renders around the Player sprite, say 5 tiles. which would then allow me to create a Pawn class and apply same methodology to give a pawn sprite a lower number, like only rendering 1 tile around the location of the pawn.

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• Phone complains that identical GLSL struct definition differs in vert/frag programs

  - by stephelton

  When I provide the following struct definition in linked frag and vert shaders, my phone (Samsung Vibrant / Android 2.2) complains that the definition differs. struct Light { mediump vec3 _position; lowp vec4 _ambient; lowp vec4 _diffuse; lowp vec4 _specular; bool _isDirectional; mediump vec3 _attenuation; // constant, linear, and quadratic components }; uniform Light u_light; I know the struct is identical because its included from another file. These shaders work on a linux implementation and on my Android 3.0 tablet. Both shaders declare "precision mediump float;" The exact error is: Uniform variable u_light type/precision does not match in vertex and fragment shader Am I doing anything wrong here, or is my phone's implementation broken? Any advice (other than file a bug report?)

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• 3D collision physics. Response when hitting wall, floor or roof

  - by GlamCasvaluir

  I am having problem with the most basic physic response when the player collide with static wall, floor or roof. I have a simple 3D maze, true means solid while false means air: bool bMap[100][100][100]; The player is a sphere. I have keys for moving x++, x--, y++, y-- and diagonal at speed 0.1f (0.1 * ftime). The player can also jump. And there is gravity pulling the player down. Relative movement is saved in: relx, rely and relz. One solid cube on the map is exactly 1.0f width, height and depth. The problem I have is to adjust the player position when colliding with solids, I don't want it to bounce or anything like that, just stop. But if moving diagonal left/up and hitting solid up, the player should continue moving left, sliding along the wall. Before moving the player I save the old player position: oxpos = xpos; oypos = ypos; ozpos = zpos; vec3 direction; direction = vec3(relx, rely, relz); xpos += direction.x*ftime; ypos += direction.y*ftime; zpos += direction.z*ftime; gx = floor(xpos+0.25); gy = floor(ypos+0.25); gz = floor(zpos+0.25); if (bMap[gx][gy][gz] == true) { vec3 normal = vec3(0.0, 0.0, 1.0); // <- Problem. vec3 invNormal = vec3(-normal.x, -normal.y, -normal.z) * length(direction * normal); vec3 wallDir = direction - invNormal; xpos = oxpos + wallDir.x; ypos = oypos + wallDir.y; zpos = ozpos + wallDir.z; } The problem with my version is that I do not know how to chose the correct normal for the cube side. I only have the bool array to look at, nothing else. One theory I have is to use old values of gx, gy and gz, but I do not know have to use them to calculate the correct cube side normal.

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