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• Why doesn't it seem to be any development in the field of 3D VR gear, especially with regard to gaming?

  - by neuviemeporte

  I remember that way back around 1995, there was this big craze with VR in the media, a whole bunch of (mostly mediocre) games labeled as "virtual-reality-interactive-movie (...)" were published. If I recall correctly, the first 3D VR helmet was called VFX-1 and was sold bundled with Descent and some dedicated joystick. I never owned one, and I read just one review which was mostly enthusiastic, but pointed to some weak points, like the eyes getting tired after an hour or so of playing. Then the whole thing basically flickered down and died. I suppose the main reason it wasn't successful was that the hardware of the day was not powerful enough, the VR gear's design wasn't perfected to make it comfortable and natural to use, and the companies that made it failed to market it successfully. What I can't understand is why isn't there any development in the field today. There is some vr-ish hardware mostly targeted at the consoles (Kinect, Wii remote, TrackIR), but all projects of creating some 3d head-mounted display system seem to be in early infancy, appear once in a trade show somewhere and aren't heard of again. I think it could work great with head tracking and some of today's shooters, flight sims (trackIR is nice but the movement scale translation is awkward) and other games with an FPP POV. Is there any technological reason why decent vr headgear can't be made today, or is it just that nobody really cares/everyone is scared to repeat the '90s failure?

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• ssao implementation

  - by Irbis

  I try to implement a ssao based on this tutorial: link I use a deferred rendering and world coordinates for shading calculations. When saving gbuffer a vertex shader output looks like this: worldPosition = vec3(ModelMatrix * vec4(inPosition, 1.0)); normal = normalize(normalModelMatrix * inNormal); gl_Position = ProjectionMatrix * ViewMatrix * ModelMatrix * vec4(inPosition, 1.0); Next for a ssao calculations I render a scene as a full screen quad and I save an occlusion parameter in a texture. (Vertex positions in the world space: link Normals in the world space: link) SSAO implementation: subroutine (RenderPassType) void ssao() { vec2 texCoord = CalcTexCoord(); vec3 worldPos = texture(texture0, texCoord).xyz; vec3 normal = normalize(texture(texture1, texCoord).xyz); vec2 noiseScale = vec2(screenSize.x / 4, screenSize.y / 4); vec3 rvec = texture(texture2, texCoord * noiseScale).xyz; vec3 tangent = normalize(rvec - normal * dot(rvec, normal)); vec3 bitangent = cross(normal, tangent); mat3 tbn = mat3(tangent, bitangent, normal); float occlusion = 0.0; float radius = 4.0; for (int i = 0; i < kernelSize; ++i) { vec3 pix = tbn * kernel[i]; pix = pix * radius + worldPos; vec4 offset = vec4(pix, 1.0); offset = ProjectionMatrix * ViewMatrix * offset; offset.xy /= offset.w; offset.xy = offset.xy * 0.5 + 0.5; float sample_depth = texture(texture0, offset.xy).z; float range_check = abs(worldPos.z - sample_depth) < radius ? 1.0 : 0.0; occlusion += (sample_depth <= pix.z ? 1.0 : 0.0); } outputColor = vec4(occlusion, occlusion, occlusion, 1); } That code gives following results: camera looking towards -z world space: link camera looking towards +z world space: link I wonder if it is possible to use world coordinates in the above code ? When I move camera I get different results because world space positions don't change. Can I treat worldPos.z as a linear depth ? What should I change to get a correct results ? I except the white areas in place of occlusion, so the ground should has the white areas only near to the object.

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• What is the difference between Constant Vertex Attributes and Uniforms?

  - by Samaursa

  According to the OpenGL ES 2.0 Programming Guide: A constant vertex attribute is the same for all vertices of a primitive, and therefore only one value needs to be specified for all the vertices of a primitive. For uniforms the book states: ...any parameter to a shader that is constant across either all vertices or fragments (but that is not known at compile time) should be passed in as a uniform. I've always used uniforms for data that is constant for a primitive but now it appears that attributes can also be used in the same way. Is there more to constant vertex attribute than simply 'they are the same as uniforms'?

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• Determining relative velocities on impact?

  - by meds

  I'm trying to figure out a way to determine the relative velocity of a body colliding with another in a 2D environment. For example if one body is moving at (1,0) and another traveling behind it collides with it from behind at (2,0) the velocity of the impact relative to the first body was (1,0). I need a method which takes in two velocities, one velocity belonging to the body the velocity is being measured against, and the other for the impacting body and return the relative velocity.

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• Nifty popup fails to register

  - by Snailer

  I'm new to Nifty GUI, so I'm following a tutorial here for making popups. For now, I'm just trying to get a very basic "test" popup to show, but I get multiple errors and none of them make much sense. To show a popup, I believe it is necessary to first have a Nifty Screen already showing, which I do. So here is the ScreenController for the working Nifty Screen: public class WorkingScreen extends AbstractAppState implements ScreenController { //Main is my jme SimpleApplication private Main app; private Nifty nifty; private Screen screen; public WorkingScreen() {} public void equip(String slotstr) { int slot = Integer.valueOf(slotstr); System.out.println("Equipping item in slot "+slot); //Here's where it STOPS working. app.getPlayer().registerPopupScreen(nifty); System.out.println("Registered new popup"); Element ele = nifty.createPopup(app.getPlayer().POPUP); System.out.println("popup is " +ele); nifty.showPopup(nifty.getCurrentScreen(), ele.getId(), null); } @Override public void initialize(AppStateManager stateManager, Application app) { super.initialize(stateManager, app); this.app = (Main)app; } @Override public void update(float tpf) { /** jME update loop! */ } public void bind(Nifty nifty, Screen screen) { this.nifty = nifty; this.screen = screen; } When I call equip(0) the system prints Equipping item in slot 0, then a lot of errors and none of the subsequent println()'s. Clearly it botches somewhere in Player.registerPopupScreen(Nifty nifty). Here's the method: public final String POPUP = "Test Popup"; public void registerPopupScreen(Nifty nifty) { System.out.println("Attempting new popup"); PopupBuilder b = new PopupBuilder(POPUP) {{ childLayoutCenter(); backgroundColor("#000a"); panel(new PanelBuilder() {{ id("List"); childLayoutCenter(); height(percentage(75)); width(percentage(50)); control(new ButtonBuilder("TestButton") {{ label("TestButton"); width("120px"); height("40px"); align(Align.Center); }}); }}); }}; System.out.println("PopupBuilder success."); b.registerPopup(nifty); System.out.println("Registerpopup success."); } Because that first println() doesn't show, it looks like this method isn't even called at all! Edit After removing all calls on the Player object, the popup works. It seems I'm not "allowed" to access the player from the ScreenController. Unfortunate, since I need information on the player for the popup. Is there a workaround?

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• Basic 3D Collision detection in XNA 4.0

  - by NDraskovic

  I have a problem with detecting collision between 2 models using BoundingSpheres in XNA 4.0. The code I'm using i very simple: private bool IsCollision(Model model1, Matrix world1, Model model2, Matrix world2) { for (int meshIndex1 = 0; meshIndex1 < model1.Meshes.Count; meshIndex1++) { BoundingSphere sphere1 = model1.Meshes[meshIndex1].BoundingSphere; sphere1 = sphere1.Transform(world1); for (int meshIndex2 = 0; meshIndex2 < model2.Meshes.Count; meshIndex2++) { BoundingSphere sphere2 = model2.Meshes[meshIndex2].BoundingSphere; sphere2 = sphere2.Transform(world2); if (sphere1.Intersects(sphere2)) return true; } } return false; } The problem I'm getting is that when I call this method from the Update method, the program behaves as if this method always returns true value (which of course is not correct). The code for calling is very simple (although this is only the test code): if (IsCollision(model1, worldModel1, model2, worldModel2)) { Window.Title = "Intersects"; } What is causing this?

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• Problem animating in Unity/Orthello 2D. Can't move gameObject

  - by Nelson Gregório

  I have a enemy npc that moves left and right in a corridor. It's animated with 2 sprites using Orthello 2D Framework. If I untick the animation's play on start and looping, the npc moves correctly. If I turn it on, the npc tries to move but is pulled back to his starting position again and again because of the animation loop. If I turn looping off during runtime, the npc moves correctly again. What did I do wrong? Here's the npc code if needed. using UnityEngine; using System.Collections; public class Enemies : MonoBehaviour { private Vector2 movement; public float moveSpeed = 200; public bool started = true; public bool blockedRight = false; public bool blockedLeft = false; public GameObject BorderL; public GameObject BorderR; void Update () { if (gameObject.transform.position.x < BorderL.transform.position.x) { started = false; blockedRight = false; blockedLeft = true; } if (gameObject.transform.position.x > BorderR.transform.position.x) { started = false; blockedLeft = false; blockedRight = true; } if(started) { movement = new Vector2(1, 0f); movement *= Time.deltaTime*moveSpeed; gameObject.transform.Translate(movement.x,movement.y, 0f); } if(!blockedRight && !started && blockedLeft) { movement = new Vector2(1, 0f); movement *= Time.deltaTime*moveSpeed; gameObject.transform.Translate(movement.x,movement.y, 0f); } if(!blockedLeft && !started && blockedRight) { movement = new Vector2(-1, 0f); movement *= Time.deltaTime*moveSpeed; gameObject.transform.Translate(movement.x,movement.y, 0f); } } }

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• why would you use textures that are not a power of 2?

  - by Will

  In the early days of OpenGL and DirectX, it was required that textures were powers of two. This meant that interpolation of float values could be done very quickly using shifting and such. Since OpenGL 2.0, and preceding that via an extension, non-power-of-two texture dimensions has been supported. Are there performance advantages to sticking to power-of-two textures on modern integrated and discrete GPUs? What advantages do non-power-of-two textures have, if any? Are there large populations of desktop users who don't have cards that support non-power-of-two textures?

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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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• Best way to load rigid bodies from file

  - by Mel

  I'm trying to switch to bullet for physics simulation. Lemme just say first that I am so pleased with bullet's accuracy and performance. After messing around it for a bit, I'm now trying to load rigid bodies from files. Most of my models are in blender and with some searching, I was able to export them in .bullet format. However, loading the files into bullet doesn't look like an easy task. I've come across this page that points me to a sample application that loads bullet files. But then it goes and says that this loader is just a starting point. Is there any open source library out there that will allow me to load rigid bodies from a file? I don't really wanna spend that much time trying to create my own loader.

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• Build a view frustum from angles

  - by MulletDevil

  I have 4 angles, left, right, top & bottom. These angles are in degrees. They define the angle between the forward vector and the corresponding side. I am trying to use these to calculate the required values for Perseective Off Centre function found here http://docs.unity3d.com/Documentation/ScriptReference/Camera-projectionMatrix.html I tried doing (near plane-far plane) * Tan(angle) But that didn't give the correct results.

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• Getting isometric grid coordinates from standard X,Y coordinates

  - by RoryHarvey

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

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• How can I convert an image from raw data in Android without any munging?

  - by stephelton

  I have raw image data (may be .png, .jpg, ...) and I want it converted in Android without changing its pixel depth (bpp). In particular, when I load a grayscale (8 bpp) image that I want to use as alpha (glTexImage() with GL_ALPHA), it converts it to 16 bpp (presumably 5_6_5). While I do have a plan B (actually, I'm probably on plan 'E' by now, this is really becoming annoying) I would really like to discover an easy way to do this using what is readily available in the API. So far, I'm using BitmapFactory.decodeByteArray(). While I'm at it. I'm doing this from a native environment via JNI (passing the buffer in from C, and a new buffer back to C from Java). Any portable solution in C/C++ would be preferable, but I don't want to introduce anything that might break in future versions of Android, etc.

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• 2D scene graph not transforming relative to parent

  - by Dr.Denis McCracleJizz

  I am currently in the process of coding my own 2D Scene graph, which is basically a port of flash's render engine. The problem I have right now is my rendering doesn't seem to be working properly. This code creates the localTransform property for each DisplayObject. Matrix m_transform = Matrix.CreateRotationZ(rotation) * Matrix.CreateScale(scaleX, scaleY, 1) * Matrix.CreateTranslation(new Vector3(x, y, z)); This is my render code. float dRotation; Vector2 dPosition, dScale; Matrix transform; transform = this.localTransform; if (parent != null) transform = localTransform * parent.localTransform; DecomposeMatrix(ref transform, out dPosition, out dRotation, out dScale); spriteBatch.Draw(this.texture, dPosition, null, Color.White, dRotation, new Vector2(originX, originY), dScale, SpriteEffects.None, 0.0f); Here is the result when I try to add the Stage then to the stage a First DisplayObjectContainer and then a second one. It may look fine but the problem lies in the fact that I add a first DisplayObjectContainer at (400,400) and the second one within it (that's the smallest one) at position (0,0). So he should be right over its parent but he gets render within the parent at the same position the parent has (400, 400) for some reason. It's just as if I double the parent's localMatrix and then render the second cat there. This is the code i use to loop through every childs. base.Draw(spriteBatch); foreach (DisplayObject childs in _childs) { childs.Draw(spriteBatch); }

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• Bullet pattern isn't behaving as expected

  - by Fibericon

  I have a boss that's supposed to continuously shoot five streams of bullets, each at a different angle. It starts off just fine, but doesn't seem to want to use its entire array of bullets. No matter how large I set the length of bulletList, the boss simply stops shooting after a couple of seconds, then pick up again shortly. Here's what I'm using to generate the pattern: Vector3 direction = new Vector3(0.5f, -1, 0); for (int r = 0; r < boss.gun.bulletList.Length; r++) { if (!boss.gun.bulletList[r].isActive) { boss.gun.bulletList[r].direction = direction; boss.gun.bulletList[r].speed = boss.gun.BulletSpeedAdjustment; boss.gun.bulletList[r].position = boss.position; boss.gun.bulletList[r].isActive = true; break; } } direction = new Vector3(-0.5f, -1, 0); //Repeat with four similar for loops, to place a bullet in each direction It doesn't seem to matter if the bulletList length is 1000 or 100000. What could be the issue here?

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• libgdx draw issue and animation

  - by johnny-b

  it seems as though i cannot get the draw method to work??? it seems as though the bullet.draw(batcher) does not work and i cannot understand why as the bullet is a sprite. i have made a Sprite[] and added them as animation. could that be it? i tried batcher.draw(AssetLoader.bulletAnimation.getKeyFrame(runTime), bullet.getX(), bullet.getY(), bullet.getOriginX() / 2, bullet.getOriginY() / 2, bullet.getWidth(), bullet.getHeight(), 1, 1, bullet.getRotation()); but that dont work, the only way it draws is this batcher.draw(AssetLoader.bulletAnimation.getKeyFrame(runTime), bullet.getX(), bullet.getY()); below is the code. // this is in a Asset Class texture = new Texture(Gdx.files.internal("SpriteN1.png")); texture.setFilter(TextureFilter.Nearest, TextureFilter.Nearest); bullet1 = new Sprite(texture, 380, 350, 45, 20); bullet1.flip(false, true); bullet2 = new Sprite(texture, 425, 350, 45, 20); bullet2.flip(false, true); Sprite[] bullets = { bullet1, bullet2 }; bulletAnimation = new Animation(0.06f, bullets); bulletAnimation.setPlayMode(Animation.PlayMode.LOOP); // this is the GameRender class public class GameRender() { private Bullet bullet; private Ball ball; public GameRenderer(GameWorld world) { myWorld = world; cam = new OrthographicCamera(); cam.setToOrtho(true, 480, 320); batcher = new SpriteBatch(); // Attach batcher to camera batcher.setProjectionMatrix(cam.combined); shapeRenderer = new ShapeRenderer(); shapeRenderer.setProjectionMatrix(cam.combined); // Call helper methods to initialize instance variables initGameObjects(); initAssets(); } private void initGameObjects() { ball = GameWorld.getBall(); bullet = myWorld.getBullet(); scroller = myWorld.getScroller(); } private void initAssets() { ballAnimation = AssetLoader.ballAnimation; bulletAnimation = AssetLoader.bulletAnimation; } public void render(float runTime) { Gdx.gl.glClearColor(0, 0, 0, 1); Gdx.gl.glClear(GL30.GL_COLOR_BUFFER_BIT); batcher.begin(); // Disable transparency // This is good for performance when drawing images that do not require // transparency. batcher.disableBlending(); // The ball needs transparency, so we enable that again. batcher.enableBlending(); batcher.draw(AssetLoader.ballAnimation.getKeyFrame(runTime), ball.getX(), ball.getY(), ball.getWidth(), ball.getHeight()); batcher.draw(AssetLoader.bulletAnimation.getKeyFrame(runTime), bullet.getX(), bullet.getY()); // End SpriteBatch batcher.end(); } } // this is the gameworld class public class GameWorld { public static Ball ball; private Bullet bullet; private ScrollHandler scroller; public GameWorld() { ball = new Ball(480, 273, 32, 32); bullet = new Bullet(10, 10); scroller = new ScrollHandler(0); } public void update(float delta) { ball.update(delta); bullet.update(delta); scroller.update(delta); } public static Ball getBall() { return ball; } public ScrollHandler getScroller() { return scroller; } public Bullet getBullet() { return bullet; } } is there anyway so make the sprite work?

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• Confusion with floats converted into ints during collision detection

  - by TheBroodian

  So in designing a 2D platformer, I decided that I should be using a Vector2 to track the world location of my world objects to retain some sub-pixel precision for slow-moving objects and other such subtle nuances, yet representing their bodies with Rectangles, because as far as collision detection and resolution is concerned, I don't need sub-pixel precision. I thought that the following line of thought would work smoothly... Vector2 wrldLocation; Point WorldLocation; Rectangle collisionRectangle; public void Update(GameTime gameTime) { Vector2 moveAmount = velocity * (float)gameTime.ElapsedGameTime.TotalSeconds wrldLocation += moveAmount; WorldLocation = new Point((int)wrldLocation.X, (int)wrldLocation.Y); collisionRectangle = new Rectangle(WorldLocation.X, WorldLocation.Y, genericWidth, genericHeight); } and I guess in theory it sort of works, until I try to use it in conjunction with my collision detection, which works by using Rectangle.Offset() to project where collisionRectangle would supposedly end up after applying moveAmount to it, and if a collision is found, finding the intersection and subtracting the difference between the two intersecting sides to the given moveAmount, which would theoretically give a corrected moveAmount to apply to the object's world location that would prevent it from passing through walls and such. The issue here is that Rectangle.Offset() only accepts ints, and so I'm not really receiving an accurate adjustment to moveAmount for a Vector2. If I leave out wrldLocation from my previous example, and just use WorldLocation to keep track of my object's location, everything works smoothly, but then obviously if my object is being given velocities less than 1 pixel per update, then the velocity value may as well be 0, which I feel further down the line I may regret. Does anybody have any suggestions about how I might go about resolving this?

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• XNA 4.0 Refresh AudioEngine, WaveBank and Others Not Found

  - by Peteyslatts

  I'm going through the Learning XNA 4.0 book, and unfortunately I installed XNA 4.0 refresh. All the code up until now has worked, with the exception of me needing to remove the Framework.Net and Framework.Storage. (As a side question, will this be problematic later?) The problem I'm having now is that in my Game1.cs file, I have imported all of the XNA.Framework libraries, and when I try and create instances of any of the following classes, an error pops up saying VisualStudio can't find them: AudiEngine, WaveBank, SoundBank, and Cue. I have googled around for a while, and the only solution I saw was to import Microsoft.Xna.Framework.Xact, but this doesn't seem to exist for me. Any help is much appreciated, Thanks Peter.

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• What has the most efficient intersection test against an AABB tree - OBB, Cylinder or Capsule?

  - by identitycrisisuk

  I'm currently trying to find collisions in 3D between a tighter volume than an AABB and a tree of AABB volumes. I just need to know whether they are intersecting, no closest distance or collision response. An OBB, Cylinder or Capsule would all roughly fit these purposes but Cylinder and Capsule were the first thing I thought of, which I have found little information about detecting intersections online. Am I right in thinking that they would always be more complex to perform Separating Axis Tests on even though they might seem like simpler shapes? I figure by the time I get my head around SAT for curved shapes I could have done the thing with OBBs but I wanted to find out for sure.

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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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• 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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• Alternative to NV Occlusion Query - getting the number of fragments which passed the depth test

  - by Etan

  In "modern" environments, the "NV Occlusion Query" extension provide a method to get the number of fragments which passed the depth test. However, on the iPad / iPhone using OpenGL ES, the extension is not available. What is the most performant approach to implement a similar behaviour in the fragment shader? Some of my ideas: Render the object completely in white, then count all the colors together using a two-pass shader where first a vertical line is rendered and for each fragment the shader computes the sum over the whole row. Then, a single vertex is rendered whose fragment sums all the partial sums of the first pass. Doesn't seem to be very efficient. Render the object completely in white over a black background. Downsample recursively, abusing the hardware linear interpolation between textures until being at a reasonably small resolution. This leads to fragments which have a greyscale level depending on the number of white pixels where in their corresponding region. Is this even accurate enough? ... ?

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• Why the clip space in OpenGL has 4 dimensions?

  - by user827992

  I will use this as a generic reference, but the more i browser online docs and books, the less i understand about this. const float vertexPositions[] = { 0.75f, 0.75f, 0.0f, 1.0f, 0.75f, -0.75f, 0.0f, 1.0f, -0.75f, -0.75f, 0.0f, 1.0f, }; in this online book there is an example about how to draw the first and classic hello world for OpenGL about making a triangle. The vertex structure for the triangle is declared as stated in the code above. The book, as all the other sources about this, stress the point that the Clip Space is a 4D structure that is used to basically decide what will be rasterized and rendered to the screen. Here I have my questions: i can't imagine something in 4D, i don't think that a human can do that, what is a 4D for this Clip space ? the most human-readable doc that i have read speaks about a camera, which is just an abstraction over the clipping concept, and i get that, the problem is, why not using the concept of a camera in the first place which is a more familiar 3D structure? The only problem with the concept of a camera is that you need to define the prospective in other way and so you basically have to add another statement about what kind of camera you wish to have. How i'm supposed to read this 0.75f, 0.75f, 0.0f, 1.0f ? All i get is that they are all float values and i get the meaning of the first 3 values, what does it mean the last one?

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• Trouble with SAT style vector projection in C#/XNA

  - by ssb

  Simply put I'm having a hard time working out how to work with XNA's Vector2 types while maintaining spatial considerations. I'm working with separating axis theorem and trying to project vectors onto an arbitrary axis to check if those projections overlap, but the severe lack of XNA-specific help online combined with pseudo code everywhere that omits key parts of the algorithm, googling has left me little help. I'm aware of HOW to project a vector, but the way that I know of doing it involves the two vectors starting from the same point. Particularly here: http://www.metanetsoftware.com/technique/tutorialA.html So let's say I have a simple rectangle, and I store each of its corners in a list of Vector2s. How would I go about projecting that onto an arbitrary axis? The crux of my problem is that taking the dot product of say, a vector2 of (1, 0) and a vector2 of (50, 50) won't get me the dot product I'm looking for.. or will it? Because that (50, 50) won't be the vector of the polygon's vertex but from whatever XNA calculates. It's getting the calculation from the right starting point that's throwing me off. I'm sorry if this is unclear, but my brain is fried from trying to think about this. I need a better understanding of how XNA calculates Vector2s as actual vectors and not just as random points.

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• How can I clear explosions in my function?

  - by hustlerinc

  Hi I have a function to place bombs, and a for loop that places explosions on the tiles where possible. My problem is that I can't remove the explosions after a while. I've tried everything I can come up with so now I turn here as a last resort. The function looks like this: function Bomb(){ var placebomb = false; if(placeBomb && player.bombs != 0){ map[player.Y][player.X].object = 2; var bombX = player.X; var bombY = player.Y; placeBomb = false; player.bombs--; setTimeout(explode, 3000); } function explode(){ var explodeNorth = true; var explodeEast = true; var explodeSouth = true; var explodeWest = true; map[bombY][bombX].explosion = 1; delete map[bombY][bombX].object; for(i=0;i<=player.bombRadius;i++){ if(explodeNorth && map[bombY-i][bombX]){ if(!map[bombY-i][bombX].wall){ if(!map[bombY-i][bombX].object){ map[bombY-i][bombX].explosion = 1; } else var explodeNorth = false; delete map[bombY-i][bombX].object; map[bombY-i][bombX].explosion = 1; } else var explodeNorth = false; } if(explodeEast && map[bombY][bombX+i]){ if(!map[bombY][bombX+i].wall){ if(!map[bombY][bombX+i].object){ map[bombY][bombX+i].explosion = 1; } else var explodeEast = false; delete map[bombY][bombX+i].object; map[bombY][bombX+i].explosion = 1; } else var explodeEast = false; } if(explodeSouth && map[bombY+i][bombX]){ if(!map[bombY+i][bombX].wall){ if(!map[bombY+i][bombX].object){ map[bombY+i][bombX].explosion = 1; } else var explodeSouth = false; delete map[bombY+i][bombX].object; map[bombY+i][bombX].explosion = 1; } else var explodeSouth = false; } if(explodeWest && map[bombY][bombX-i]){ if(!map[bombY][bombX-i].wall){ if(!map[bombY][bombX-i].object){ map[bombY][bombX-i].explosion = 1; } else var explodeWest = false; delete map[bombY][bombX-i].object; map[bombY][bombX-i].explosion = 1; } else var explodeWest = false; } } player.bombs++; } } If anyone can think of a good way to remove the explosion after a delay please help.

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