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• Biome Transition in a Grid & Borderless World

  - by API-Beast

  I have a universe: a list of "Systems", each with their own center, type and radius. A small part of such a universe could look like this: Systems: Can be very close to a different system, e.g. overlap Can be inside another, much bigger system Can be very far away from any other systems Spawn system specific entities and particles inside the system radius Have some properties like background color So far so good. However, the player can fly around freely, inside and outside of systems, in real time. How do I interpolate and determine things like the background color now, depending on camera position? E.g. if you are halfway between a green and a red system you should see a background halfway between red and green, or if you are inside a lilac system near the center and at the border of a green system you should get a mostly lilac background etc.

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• scaling point sprites with distance

  - by Will

  How can you scale a point sprite by its distance from the camera? GLSL fragment shader: gl_PointSize = size / gl_Position.w; seems along the right tracks; for any given scene all sprites seem nicely scaled by distance. Is this correct? How do you compute the proper scaling for my vertex attribute size? I want each sprite to be scaled by the modelview matrix. I had played with arbitrary values and it seems that size is the radius in pixels at the camera, and is not in modelview scale. I've also tried: gl_Position = pMatrix * mvMatrix * vec4(vertex,1.0); vec4 v2 = pMatrix * mvMatrix * vec4(vertex.x,vertex.y+0.5*size,vertex.z,1.0); gl_PointSize = length(gl_Position.xyz-v2.xyz) * gl_Position.w; But this makes the sprites be bigger in the distance, rather than smaller:

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• [JOGL] my program is too slow, ho can i profile with Eclipse?

  - by nkint

  hi juys my simple opengl program is really toooo slow and not fluid i'm rendering 30 sphere with simple illumination and simple material. the only hard(?) computing stuffs i do is a collision detection between ray-mouse and spheres (that works ok and i do it only in mouseMoved) i have no thread only animator to move spheres how can i profile my jogl project? or mayebe (most probable..) i have some opengl instruction that i don't understand and make render particular accurate (or back face rendering that i don't need or whatever i don't know exctly i'm just entered in opengl world)

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• Collision within a poly

  - by G1i1ch

  For an html5 engine I'm making, for speed I'm using a path poly. I'm having trouble trying to find ways to get collision with the walls of the poly. To make it simple I just have a vector for the object and an array of vectors for the poly. I'm using Cartesian vectors and they're 2d. Say poly = [[550,0],[169,523],[-444,323],[-444,-323],[169,-523]], it's just a pentagon I generated. The object that will collide is object, object.pos is it's position and object.vel is it's velocity. They're both 2d vectors too. I've had some success to get it to find a collision, but it's just black box code I ripped from a c++ example. It's very obscure inside and all it does though is return true/false and doesn't return what vertices are collided or collision point, I'd really like to be able to understand this and make my own so I can have more meaningful collision. I'll tackle that later though. Again the question is just how does one find a collision to walls of a poly given you know the poly vertices and the object's position + velocity? If more info is needed please let me know. And if all anyone can do is point me to the right direction that's great.

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• Character Jump Control

  - by Abdullah Sorathia

  I would like to know how can I control the jump movement of a character in Unity3D. Basically I am trying to program the jump in such a way that while a jump is in progress the character is allowed to move either left or right in mid-air when the corresponding keys are pressed. With my script the character will correctly move to the left when, for example, the left key is pressed, but when the right key is pressed afterwards, the character moves to the right before the movement to the left is completed. Following is the script: void Update () { if(touchingPlatform && Input.GetButtonDown("Jump")){ rigidbody.AddForce(jumpVelocity, ForceMode.VelocityChange); touchingPlatform = false; isJump=true; } //left & right movement Vector3 moveDir = Vector3.zero; if(Input.GetKey ("right")||Input.GetKey ("left")){ moveDir.x = Input.GetAxis("Horizontal"); // get result of AD keys in X if(ShipCurrentSpeed==0) { transform.position += moveDir * 3f * Time.deltaTime; }else if(ShipCurrentSpeed<=15) { transform.position += moveDir * ShipCurrentSpeed * 2f * Time.deltaTime; }else { transform.position += moveDir * 30f * Time.deltaTime; } }

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• SFX Played Once per Collision or Hit

  - by David Dimalanta

  I have a question about using Box2D (engine for LibGDX used to make realistic physics). I observed on the code that I've made for the physics here below: @Override public boolean touchUp(int screenX, int screenY, int pointer, int button) { // TODO Touch Up Event if(is_Next_Fruit_Touched) { BodyEditorLoader Fruit_Loader = new BodyEditorLoader(Gdx.files.internal("Shape_Physics/Fruity Physics.json")); Fruit_BD.type = BodyType.DynamicBody; Fruit_BD.position.set(x, y); FixtureDef Fruit_FD = new FixtureDef(); // --> Allows you to make the object's physics. Fruit_FD.density = 1.0f; Fruit_FD.friction = 0.7f; Fruit_FD.restitution = 0.2f; MassData mass = new MassData(); mass.mass = 5f; Fruit_Body[n] = world.createBody(Fruit_BD); Fruit_Body[n].setActive(true); // --> Let your dragon fall. Fruit_Body[n].setMassData(mass); Fruit_Body[n].setGravityScale(1.0f); System.out.println("Eggs... " + n); Fruit_Loader.attachFixture(Fruit_Body[n], Body, Fruit_FD, Fruit_IMG.getWidth()); Fruit_Origin = Fruit_Loader.getOrigin(Body, Fruit_IMG.getWidth()).cpy(); is_Next_Fruit_Touched = false; up = y; Gdx.app.log("Initial Y-coordinate", "Y at " + up); //Once it's touched, the next fruit will set to drag. if(n < 50) { n++; }else{ System.exit(0); } } return true; } Now, I'm thinking which part o line should I implement for the sound effects. My objectives to make SFX played once for every collision (Or should I say "SFX played once per collision"?) on the following: SFX played once if they hit on the objects of its kind. (e.g. apple vs. apple) SFX played once on a different sound when it hit on the ground. (e.g. apple land on the mud) Take note that I'm using Box2D for the Java programming version thanks to LibGDX via Box2D engine and I edited the physics body using Physics Body Editor before I implement it to code. I tried to check every available methods for body, fixture definition, or body definition to code for the SFX when hit but it seems only for the gravity and weight. Is there possibly available on the document for SFX played when collision happens if possible?

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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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• How to handle animations?

  - by Bane

  I am coding a simple 2D engine to be used with HTML5. I already have classes such as Picture, Scene, Camera and Renderer, but now I need to work on Animations. Picture is basocally a wrapper for a normal image object, with it's own draw method, but this is unrelated, I'm interested in how animation in 2D games is usually done. What I planned to do, is to have the Animation class as well act like a wrapper for a few image objects, and then have methods such as getCurrentImage, next and animate (which would use intervals to quickly change the current image). I meant to feed the animation a couple of PNG's at inicialisation. Is quickly swapping PNG images acceptable for 2D animation? Are there some standard ways of doing this, or are there flaws in my ways?

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• Projective texture and deferred lighting

  - by Vodácek

  In my previous question, I asked whether it is possible to do projective texturing with deferred lighting. Now (more than half a year later) I have a problem with my implementation of the same thing. I am trying to apply this technique in light pass. (my projector doesn't affect albedo). I have this projector View a Projection matrix: Matrix projection = Matrix.CreateOrthographicOffCenter(-halfWidth * Scale, halfWidth * Scale, -halfHeight * Scale, halfHeight * Scale, 1, 100000); Matrix view = Matrix.CreateLookAt(Position, Target, Vector3.Up); Where halfWidth and halfHeight is are half of the texture's width and height, Position is the Projector's position and target is the projector's target. This seems to be ok. I am drawing full screen quad with this shader: float4x4 InvViewProjection; texture2D DepthTexture; texture2D NormalTexture; texture2D ProjectorTexture; float4x4 ProjectorViewProjection; sampler2D depthSampler = sampler_state { texture = <DepthTexture>; minfilter = point; magfilter = point; mipfilter = point; }; sampler2D normalSampler = sampler_state { texture = <NormalTexture>; minfilter = point; magfilter = point; mipfilter = point; }; sampler2D projectorSampler = sampler_state { texture = <ProjectorTexture>; AddressU = Clamp; AddressV = Clamp; }; float viewportWidth; float viewportHeight; // Calculate the 2D screen position of a 3D position float2 postProjToScreen(float4 position) { float2 screenPos = position.xy / position.w; return 0.5f * (float2(screenPos.x, -screenPos.y) + 1); } // Calculate the size of one half of a pixel, to convert // between texels and pixels float2 halfPixel() { return 0.5f / float2(viewportWidth, viewportHeight); } struct VertexShaderInput { float4 Position : POSITION0; }; struct VertexShaderOutput { float4 Position :POSITION0; float4 PositionCopy : TEXCOORD1; }; VertexShaderOutput VertexShaderFunction(VertexShaderInput input) { VertexShaderOutput output; output.Position = input.Position; output.PositionCopy=output.Position; return output; } float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 { float2 texCoord =postProjToScreen(input.PositionCopy) + halfPixel(); // Extract the depth for this pixel from the depth map float4 depth = tex2D(depthSampler, texCoord); //return float4(depth.r,0,0,1); // Recreate the position with the UV coordinates and depth value float4 position; position.x = texCoord.x * 2 - 1; position.y = (1 - texCoord.y) * 2 - 1; position.z = depth.r; position.w = 1.0f; // Transform position from screen space to world space position = mul(position, InvViewProjection); position.xyz /= position.w; //compute projection float3 projection=tex2D(projectorSampler,postProjToScreen(mul(position,ProjectorViewProjection)) + halfPixel()); return float4(projection,1); } In first part of pixel shader is recovered position from G-buffer (this code I am using in other shaders without any problem) and then is tranformed to projector viewprojection space. Problem is that projection doesn't appear. Here is an image of my situation: The green lines are the rendered projector frustum. Where is my mistake hidden? I am using XNA 4. Thanks for advice and sorry for my English. EDIT: Shader above is working but projection was too small. When I changed the Scale property to a large value (e.g. 100), the projection appears. But when the camera moves toward the projection, the projection expands, as can bee seen on this YouTube video.

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• How to remove a box2d body when collision happens?

  - by Ayham

  I’m still new to java and android programming and I am having so much trouble Removing an object when collision happens. I looked around the web and found that I should never handle removing BOX2D bodies during collision detection (a contact listener) and I should add my objects to an arraylist and set a variable in the User Data section of the body to delete or not and handle the removing action in an update handler. So I did this: First I define two ArrayLists one for the faces and one for the bodies: ArrayList<Sprite> myFaces = new ArrayList<Sprite>(); ArrayList<Body> myBodies = new ArrayList<Body>(); Then when I create a face and connect that face to its body I add them to their ArrayLists like this: face = new AnimatedSprite(pX, pY, pWidth, pHeight, this.mBoxFaceTextureRegion); Body BoxBody = PhysicsFactory.createBoxBody(mPhysicsWorld, face, BodyType.DynamicBody, objectFixtureDef); mPhysicsWorld.registerPhysicsConnector(new PhysicsConnector(face, BoxBody, true, true)); myFaces.add(face); myBodies.add(BoxBody); now I add a contact listener and an update handler in the onloadscene like this: this.mPhysicsWorld.setContactListener(new ContactListener() { private AnimatedSprite face2; @Override public void beginContact(final Contact pContact) { } @Override public void endContact(final Contact pContact) { } @Override public void preSolve(Contact contact,Manifold oldManifold) { } @Override public void postSolve(Contact contact,ContactImpulse impulse) { } }); scene.registerUpdateHandler(new IUpdateHandler() { @Override public void reset() { } @Override public void onUpdate(final float pSecondsElapsed) { } }); My plan is to detect which two bodies collided in the contact listener by checking a variable from the user data section of the body, get their numbers in the array list and finally use the update handler to remove these bodies. The questions are: Am I using the arraylist correctly? How to add a variable to the User Data (the code please). I tried removing a body in this update handler but it still throws me NullPointerException , so what is the right way to add an update handler and where should I add it. Any other advices to do this would be great. Thanks in advance.

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• Balancing Player vs. Monsters: Level-Up Curves

  - by ashes999

  I've written a fair number of games that have RPG-like "levelling up," where the player gains experience for killing monsters/enemies, and eventually, reaches a new level, where their stats increase. How do you find a balance between player growth, monster strength, and difficulty? The extreme ends of this spectrum are: Player levels up really fast and blows away monsters without much effort Monsters are incredibly strong and even at low levels, are very difficult to beat I've also tried a strange situation of making enemies relative to players, i.e. an enemy will always be at 50% or 100% or 150% of player stats (thus requiring the player to use other techniques instead of brute strength to succeeed). But where's the balance, and how do you find it? Edit: For example, I am expecting to hear things like: Balance high instead of balance low (200 HP and 20 str is easier to balance than 20 HP and 2 str) Look at easiest vs. hardest monsters, and see what you have in terms of a range

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• Generating triangles from a square grid

  - by vivi

  I have a 2D square grid of values representing terrain elevations, and I want to generate triangles from that grid to make a 3D view of the terrain. My first thought was to split each square diagonally into 2 triangles, however the split diagonal can clearly be seen, especially from the top : [Sorry, as a new user I can't post images, please see here : imgur] Is there a recommended way to generate triangles to remove/reduce this effect ?

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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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• Simple 3D Physics engine as a part of graduation project [on hold]

  - by Eugene Kolesnikov

  I am working on my graduation project and one part of it is to simulate the motion of a rigid body in 3D space. I can use either already written physics engine or to write it myself. It's quite an interesting challenge for me, so I would like to do it myself. I am able to use either C++ or Java for programming (prefer C++). I am using Mac OS X and Debian 7. Could you suggest any guides or tutorials how to do it, can't find it anywhere... More precisely, I need a very simple engine, without collision detection, and many other things that I do not know, I just need to calculate the forces and move my body, depending on the resultant force. If you think that this task is still very difficult or there is no such tutorial, please suggest me some good and simple engine.

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• 2D Animation Smoothness - Delta time vs. Kinematics

  - by viperld002

  I'm animating a sprite in 2D with key frames of rotation and xy-positions. I've recently had a discussion with someone saying that when the device (happens to be an iPad using cocos2D) hits a performance bump due to whatever else the user may be doing, lag will arise and that the best way to fight it is to not use actual positions, but velocities, accelerations and torques with kinematics. His message is to evaluate the positions and rotations from these speeds at the current point in time. I've never experienced a situation where I've heard of using kinematics to stem lag in 2D animations and am not sure of how effective it could be. Also, it seems to be overkill. The application is not networked so it's all running on a local device. The desired effect is that the animation always plays as closely as it can to the target frame rate. Wouldn't the technique suffer the same problems as just using the time since the last frame or a fixed time step since the kinematics would also require some time value to perform the calculation? What techniques could you suggest to best achieve the desired effect? EDIT 1 Thank you for your responses, they are very illuminating. I want to clarify my question before choosing an answer however, to make sure that this post really serves it's purpose. I have a sprite of a ball, and a text file with 3 arrays worth of information (rotation,translations x, translations y) with each unit of information existing as a key frame to be stepped through (0 to 49 and back to 0 to replay it again). I have this playing by interpolating from the current key frame to the next, every n-units of time. The animation is visibly correct when compared to a video I was given of it, and it is smooth because of the interpolations between the key frames. This is the existing state of the project. There are no physics simulated, only a static animation of a ball moving in a way an artist specifically designed. Should I, instead of rotation in degrees and translations by positions in space, derive velocities, accelerations and torques to express this static animation as a function of time? As in, position now = foo(time now), where foo uses kinematics.

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• OpenGL setup on Windows

  - by kevin james

  I have been trying to use OpenGL for two days now. First on Mac, then on Windows. The problem with Mac is that it doesn't support the newer versions of OpenGL. I ran a tutorial that actually did get some things working, but it only works in XCode (i.e., I can't create a new file, paste in the same code, and get it to work). Because of these issues, I moved to Windows. My Windows 7 has OpenGL 4.3, which is the same that is used in alot of other tutorials. However, not one of these tutorials gives any instruction on how to set it up for the first time. I have come across some vague posts saying that some libraries need to be linked. But WHAT libraries, and HOW do I link them? Please help. I am pretty desperate to set this up as this project is due for work soon. I have actually used OpenGL before at my university, but the computers already had everything set up. The project itself is very easy, but setting up OpenGL is not something I know how to do.

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• Why does my program stutter so much?

  - by user36322

  I've been very frustrated trying to solve this. I've looked it up, and all the answers are the same: set IsFixedTimeStep = false. This doesn't help me at all, the program is still jittery and stutters. I have absolutely no idea what is going on, can you guys help? Code for movement (objects is a list): speed = Math.Min(speed + (speedIncrement * gameTime.ElapsedGameTime.Milliseconds / 200), maxSpeed); for (int i = objects.Count - 1; i >= 0; i--) { objects[i].rect.Y += (int)(speed * gameTime.ElapsedGameTime.Milliseconds); //Check if the object is past the screen. If it is, remove it if (objects[i].rect.Y > screenHeight) { objects.Remove(objects[i]); } }

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• Java Slick2d - Mouse picking how to take into account camera

  - by Corey

  When I move it it obviously changes the viewport so my mouse picking is off. My camera is just a float x and y and I use g.translate(-cam.cameraX+400, -cam.cameraY+300); to translate the graphics. I have the numbers hard coded just for testing purposes. How would I take into account the camera so my mouse picking works correctly. double mousetileX = Math.floor((double)mouseX/tiles.tileWidth); double mousetileY = Math.floor((double)mouseY/tiles.tileHeight); double playertileX = Math.floor(playerX/tiles.tileWidth); double playertileY = Math.floor(playerY/tiles.tileHeight); double lengthX = Math.abs((float)playertileX - mousetileX); double lengthY = Math.abs((float)playertileY - mousetileY); double distance = Math.sqrt((lengthX*lengthX)+(lengthY*lengthY)); if(input.isMousePressed(Input.MOUSE_LEFT_BUTTON) && distance < 4) { if(tiles.map[(int)mousetileX][(int)mousetileY] == 1) { tiles.map[(int)mousetileX][(int)mousetileY] = 0; } } That is my mouse picking code

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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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• samplerCubeShadow and texture offset

  - by Irbis

  I use sampler2DShadow when accessing a single shadow map. I create PCF in this way: result += textureProjOffset(ShadowSampler, ShadowCoord, ivec2(-1,-1)); result += textureProjOffset(ShadowSampler, ShadowCoord, ivec2(-1,1)); result += textureProjOffset(ShadowSampler, ShadowCoord, ivec2(1,1)); result += textureProjOffset(ShadowSampler, ShadowCoord, ivec2(1,-1)); result = result * 0.25; For a cube map I use samplerCubeShadow: result = texture(ShadowCubeSampler, vec4(normalize(position), depth)); How to adopt above PCF when accessing a cube map ?

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• Where to start? (3D Modeling)

  - by herfus

  I'm looking for a good resource to start learning 3d modeling. I'm looking for something that starts with the basics (e.g. terminology; what are quads, triangles etc.) before/while going into the actual modeling. Book, website, video, anything will do. I'm only concerned with the quality of the tutorials, how thorough they are. I have experience with texturing, level design and so on - but I've never created anything more than simple shapes/editing existing assets.

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• How to calculate vertext normals for a mesh in Java in OpenGL ES application?

  - by alan mc

  Can some one point me to Java code ( in Java not C or C++) that calculates all the normals for all the vertices of a mesh for OpenGL ES application. I need this for lighting. Lets say I have a cube with following vertices and indices: float vertices[] = { -width, -height, -depth, // 0 width, -height, -depth, // 1 width, height, -depth, // 2 -width, height, -depth, // 3 -width, -height, depth, // 4 width, -height, depth, // 5 width, height, depth, // 6 -width, height, depth // 7 }; short indices[] = { 0, 2, 1, 0, 3, 2, 1,2,6, 6,5,1, 4,5,6, 6,7,4, 2,3,6, 6,3,7, 0,7,3, 0,4,7, 0,1,5, 0,5,4 }; In above specific example how many normals we need ?

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• Checking if an int is prime more efficiently

  - by SipSop

  I recently was part of a small java programming competition at my school. My partner and I have just finished our first pure oop class and most of the questions were out of our league so we settled on this one (and I am paraphrasing somewhat): "given an input integer n return the next int that is prime and its reverse is also prime for example if n = 18 your program should print 31" because 31 and 13 are both prime. Your .class file would then have a test case of all the possible numbers from 1-2,000,000,000 passed to it and it had to return the correct answer within 10 seconds to be considered valid. We found a solution but with larger test cases it would take longer than 10 seconds. I am fairly certain there is a way to move the range of looping from n,..2,000,000,000 down as the likely hood of needing to loop that far when n is a low number is small, but either way we broke the loop when a number is prime under both conditions is found. At first we were looping from 2,..n no matter how large it was then i remembered the rule about only looping to the square root of n. Any suggestions on how to make my program more efficient? I have had no classes dealing with complexity analysis of algorithms. Here is our attempt. public class P3 { public static void main(String[] args){ long loop = 2000000000; long n = Integer.parseInt(args[0]); for(long i = n; i<loop; i++) { String s = i +""; String r = ""; for(int j = s.length()-1; j>=0; j--) r = r + s.charAt(j); if(prime(i) && prime(Long.parseLong(r))) { System.out.println(i); break; } } System.out.println("#"); } public static boolean prime(long p){ for(int i = 2; i<(int)Math.sqrt(p); i++) { if(p%i==0) return false; } return true; } } ps sorry if i did the formatting for code wrong this is my first time posting here. Also the output had to have a '#' after each line thats what the line after the loop is about Thanks for any help you guys offer!!!

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• Sorting objects before rendering

  - by dreta

  I'm trying to implement a scene graph and in all the articles i've come across there is talk about object sorting. So you'd sort your objects by "material" for example. Now untill i sat down and started implementing it, i kind of took this for granted, because it made sense. But now i'm wondering what does sorting actually change? In my engine, i have a manager for UBOs, i use those to store data that'll be shared between programs, at the moment that only involves time, camera and projection matrices and lights (i'm not worrying about managing which lights affect which objects ATM). Now for each model i have to change the model to world matrix uniform, no sorting is going to change that. So is the jump from changing this matrix to also setting a material for each object that bad? I vaguely remember reading somewhere that each time you change something in the pipeline, it has to get flushed and that can cause performance issues. But for each drawing call i'm setting up a model to world matrix anyway, so what sense does it make to ever be concerned about this? BTW is there any information about whether changing a uniform and calling glBufferSubData is more (or less) expensive.

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• Permanently Sync a wiimote with a computer

  - by Adam Geisweit

  i have tried to look up many ways to sync up my wiimotes to my computer so that i can program games with it, but every time it only syncs them up temporarily, or if it says it can permanently sync it, it doesn't actually do it. it gets tiresome when i have to keep on reconnecting it every time i want to save battery life. how would i be able to sync up my wiimote to my computer so that if i turn off my wiimote, i can just hit any button and it will automatically sync it up?

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