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• AndEngine player, background and camera

  - by valdemar593

  I'm developing a 2D shooter using AndEngine. At the moment I'm trying to make the camera follow the player. As I've understood the common approach is to use the SmoothCamera zooming it and setting the chased entity. The problem is that the camera follows the player WITH background moving also (RepeatingSpriteBackground), so it looks like the player doesn't move at all though the actual position changes. So I don't really get how to make the camera follow the player and have the background not moving. Thanks in advance.

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• The input doesn't recognize that I release the key?

  - by joapet99

  I'm creating a window (JOptionPane), in response to a collision. However, if the player is holding a key down when the window pops up, the input doesn't trigger a key release when the key is released. I don't think you can just check it with a isRelease function in the input, since the input is kind of corrupt. Can you help me? The way I check if the key is down: if(input.isKeyDown(Input.KEY_A)&& TestLevel.isFighting == false){ if(owner.canMoveLeft){ position.x -= speed * delta; } } I am not handling the key release by myself, but if I check if the key is down it should work. But it doesn't.

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• How can I keep the correct alpha during rendering particles?

  - by April

  Rencently,I was trying to save textures of 3D particles so that I can reuse the in 2D rendering.Now I had some problem with alpha channel.Some artist told me I that my textures should have unpremultiplied alpha channel.When I try to get the rgb value back,I got strange result.Some area went lighter and even totally white.I mainly focus on additive and blend mode,that is: ADDITIVE: srcAlpha VS 1 BLEND: srcAlpha VS 1-srcAlpha I tried a technique called premultiplied alpha.This technique just got you the right rgb value,its all you need on screen.As for alpha value,it worked well with BLEND mode,but not ADDITIVE mode.As you can see in parameters,BLEND mode always controlled its value within 1.While ADDITIVE mode cannot guarantee. I want proper alpha,but it just got too big or too small consider to rgb.Now what can I do?Any help will be great thankful. PS:If you don't understand what I am trying to do,there is a commercial software called "Particle Illusion".You can create various particles and then save the scene to texture,where you can choose to remove background of particles.

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• Blender 2.6: How to Merge the Pros of Meshes and Surfaces

  - by fridojet

  there are two interesting kinds of objects: Meshes and Surfaces. Each of them offers very cool features. Object Type Specific Features Nice Features of Surfaces: (for example) They're as scalable as vector graphics (really nice!) You can build winding things real simply. Nice Features of Meshes: (for example) You can build organic things really good using the Sculpt Mode and a graphic tablet. You can use some special things like Physics. My Question There are things for which Surfaces are better and things for which Meshes are better. But how can I use both the best features of Surfaces and the best features of Meshes on one object at once? For example: How can I use Physics (like on Meshes) on lossless scalable objects (like Surfaces)? Thanks.

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• Simulate 'Shock absorbtion' with tire rubber in PhysX (2.8.x)

  - by Mungoid

  This is a kinda tricky question and I fear there is no easy enough solution, but I figured I'd hit SE up before giving up on it and just doing what I can. A machine I am working on has no suspension or shocks or springs of any sort in the real machine, so you would think that when it drives over bumps, it would shake like crazy but because its tires (6 of them) are quite large they seem to absorb a lot of shock from the bumps. Part of this is because the machine is around 30k lbs and it just smashes/compresses any bumps in the ground down (This is another issue im still working on) and the other part is that the tires seem to have a lot of flex to them with a lot of air as well. So my current task is to simulate shock absorption in physx without visibly separating the tires from the spindle/axle.. I have been messing with all kinds of NxMaterial, NxSpring, Joints, etc. and have had no luck getting this to work. The main problem is that the spindle attached to the tire is directly in the center and the axle is basically solidly attached to the chassis, so if i give it any spring or suspension travel, that spindle on the tires will move upwards or downwards, looking very odd because now its not any longer in the center of the tire. I tried giving it a higher restitution but that just makes it bouncy without any shock absorption. Another avenue I am messing with is to actively smooth the terrain in front of the tires so that before it hits a bumpy patch, that patch is smoothed and it doesn't bounce. The only issue with this is that it is pretty expensive to do with 6 tires, high tesselation of the terrain and other complex things going on at the same time in this simulation. I am still working on this but I am hoping to mix and match a few different aspects to get the best possible outcome. This is a bit of a complex issue so I'm not expecting anyone to have a definitive answer, just hoping someone may think of something I haven't =-) -Side note: Yes i know PhysX 2.8.x is quite outdated but we have to stick with it for this implementation. We are in the process of going to another physics engine but it is out of scope to apply that engine to this project.

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• TGA loader: reverse y-axis

  - by aVoX

  I've written a TGA image loader in Java which is working perfectly for files created with GIMP as long as they are saved with the option origin set to Top Left (Note: Actually TGA files are meant to be stored upside down - Bottom Left in GIMP). My problem is that I want my image loader to be capable of reading all different kinds of TGA, so my question is: How do I flip the image upside down? Note that I store all image data inside a one-dimensional byte array, because OpenGL (glTexImage2D to be specific) requires it that way. Thanks in advance.

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• C# Collision Math Help

  - by user36037

  I am making my own collision detection in MonoGame. I have a PolyLine class That has a property to return the normal of that PolyLine instance. I have a ConvexPolySprite class that has a List LineSegments. I hav a CircleSprite class that has a Center Property and a Radius Property. I am using a static class for the collision detection method. I am testing it on a single line segment. Vector2(200,0) = Vector2(300, 200) The problem is it detects the collision anywhere along the path of line out into space. I cannot figure out why. Thanks in advance; public class PolyLine { //--------------------------------------------------------------------------------------------------------------------------- // Class Properties /// <summary> /// Property for the upper left-hand corner of the owner of this instance /// </summary> public Vector2 ParentPosition { get; set; } /// <summary> /// Relative start point of the line segment /// </summary> public Vector2 RelativeStartPoint { get; set; } /// <summary> /// Relative end point of the line segment /// </summary> public Vector2 RelativeEndPoint { get; set; } /// <summary> /// Property that gets the absolute position of the starting point of the line segment /// </summary> public Vector2 AbsoluteStartPoint { get { return ParentPosition + RelativeStartPoint; } }//end of AbsoluteStartPoint /// <summary> /// Gets the absolute position of the end point of the line segment /// </summary> public Vector2 AbsoluteEndPoint { get { return ParentPosition + RelativeEndPoint; } }//end of AbsoluteEndPoint public Vector2 NormalizedLeftNormal { get { Vector2 P = AbsoluteEndPoint - AbsoluteStartPoint; P.Normalize(); float x = P.X; float y = P.Y; return new Vector2(-y, x); } }//end of NormalizedLeftNormal //--------------------------------------------------------------------------------------------------------------------------- // Class Constructors /// <summary> /// Sole ctor /// </summary> /// <param name="parentPosition"></param> /// <param name="relStart"></param> /// <param name="relEnd"></param> public PolyLine(Vector2 parentPosition, Vector2 relStart, Vector2 relEnd) { ParentPosition = parentPosition; RelativeEndPoint = relEnd; RelativeStartPoint = relStart; }//end of ctor }//end of PolyLine class public static bool Collided(CircleSprite circle, ConvexPolygonSprite poly) { var distance = Vector2.Dot(circle.Position - poly.LineSegments[0].AbsoluteEndPoint, poly.LineSegments[0].NormalizedLeftNormal) + circle.Radius; if (distance <= 0) { return false; } else { return true; } }//end of collided

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• Collision rectangle response

  - by dotty

  I'm having difficulties getting a moveable rectangle to collide with more than one rectangle. I'm using SFML and it has a handy function called Intersect() which takes 2 rectangles and returns the intersections. I have a vector full of rectangles which I want my moveable rectangle to collide with. I'm looping through this using the following code (p is the moveble rectangle). IsCollidingWith returns a bool but also uses SFML's Interesect to work out the intersections. while(unsigned i = 0; i!= testRects.size(); i++){ if(p.IsCollidingWith(testRects[i]){ p.Collide(testRects[i]); } } and the actual Collide() code void gameObj::collide( gameObj collidingObject ){ printf("%f %f\n", this->colliderResult.width, this->colliderResult.height); if (this->colliderResult.width < this->colliderResult.height) { // collided on X if (this->getCollider().left < collidingObject.getCollider().left ) { this->move( -this->colliderResult.width , 0); }else { this->move( this->colliderResult.width, 0 ); } } if(this->colliderResult.width > this->colliderResult.height){ if (this->getCollider().top < collidingObject.getCollider().top ) { this->move( 0, -this->colliderResult.height); }else { this->move( 0, this->colliderResult.height ); } } } and the IsCollidingWith() code is bool gameObj::isCollidingWith( gameObj testObject ){ if (this->getCollider().intersects( testObject.getCollider(), this->colliderResult )) { return true; }else { return false; } } This works fine when there's only 1 Rect in the scene. However, when there's move than one Rect it causes issue when working out 2 collisions at once. Any idea how to deal with this correctly? I have uploaded a video to youtube to show my problem. The console on the far-right shows the width and height of the intersections. You can see on the console that it's trying to calculate 2 collisions at once, I think this is where the problem is being caused. The youtube video is at http://www.youtube.com/watch?v=fA2gflOMcAk also , this image also seems to illustrate the problem nicely. Can someone please help, I've been stuck on this all weekend!

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• Cross-platform builds with OGRE3D via CMake. Any tips?

  - by frarees

  I've been trying to compile a simple project for both OSX and Windows platforms, using OGRE3D, but I've got some problems on the way. I'm using CMake to create my platform specific project files (VS solution & Xcode project). Some problems I found are: OGRE3D source is distributed in 2 flavors, Windows sources and UNIX/OSX sources. In OSX, compiling dependencies (freetype, FreeImage and specially OIS) is such a pain. I don't know how to handle precompiled dependencies (they exist for both Win & Mac). May sound like a noob question, but I would appreciate some tips on this. Resources, forum posts, anything. There exists any "cross-platform base project for OGRE3D" on the net? Would be really helpful if someone who already managed to do this can bring some light. Btw, I'm not basing the project on OGRE3D, it's just that is the biggest library I'm probably using, so I depend a lot on it. Thanks in advantage!

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• XNA Octree with batching

  - by Alex

  I'm integrating batching in my engine. However I'm using an octree which is auto generated around my scene. Now batching renders a hole group at ones while an octree sorts out which objects that should be rendered within the camera frustum, therefore dividing the group. Batching and octree doesn't go along very well, right? Problem: The way I see it I have two options, either create batch groups based on objects who are close to one another within the octree or I can rebuild the batching matrixbuffer for the instances visible each frame. Which approach should I go with or does there exist another solution?

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• forward rendering and multiple shadow maps

  - by Irbis

  I have two light sources on my scene. I created two fbo's which store depth textures for these lights. A render loop looks like this: bind fbo1 save depth values for first light unbind fbo1 bind fbo2 save depth values for second light unbind fbo2 enable additive blending bind first depth texture render scene bind second depth texture render scene disable additive blending For one light source the program works fine. For many light sources I use an additive blending to acumulate lighting results but then some objects become transparent (for example when an object which is further away from the camera is drawn before an object which is closer to the camera). How to resolve that problem ? How should I accumulate lighting effects for many light sources (many shadow maps) ? P.S. I use OpenGL/GLSL 3.3+

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• How Would I create alternate players (Turn base Event)

  - by Blue

  The picture above shows 2 players. Each containing 3 characters. I want to know how to make a Turn based event starting with player 1 alternating turns with player 2. And in every alternation each character gets a turn. If a character dies, the next character on the same team goes, and so on. How would I create this? Is there a tutorial? I haven't made any turn-based games so I don't know how to program these kinds of stuff.

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• How to do proper Alpha in XNA?

  - by Soshimo

  Okay, I've read several articles, tutorials, and questions regarding this. Most point to the same technique which doesn't solve my problem. I need the ability to create semi-transparent sprites (texture2D's really) and have them overlay another sprite. I can achieve that somewhat with the code samples I've found but I'm not satisfied with the results and I know there is a way to do this. In mobile programming (BREW) we did it old school and actually checked each pixel for transparency before rendering. In this case it seems to render the sprite below it blended with the alpha above it. This may be an artifact of how I'm rendering the texture but, as I said before, all examples point to this one technique. Before I go any further I'll go ahead and paste my example code. public void Draw(SpriteBatch batch, Camera camera, float alpha) { int tileMapWidth = Width; int tileMapHeight = Height; batch.Begin(SpriteSortMode.Texture, BlendState.AlphaBlend, SamplerState.PointWrap, DepthStencilState.Default, RasterizerState.CullNone, null, camera.TransformMatrix); for (int x = 0; x < tileMapWidth; x++) { for (int y = 0; y < tileMapHeight; y++) { int tileIndex = _map[y, x]; if (tileIndex != -1) { Texture2D texture = _tileTextures[tileIndex]; batch.Draw( texture, new Rectangle( (x * Engine.TileWidth), (y * Engine.TileHeight), Engine.TileWidth, Engine.TileHeight), new Color(new Vector4(1f, 1f, 1f, alpha ))); } } } batch.End(); } As you can see, in this code I'm using the overloaded SpriteBatch.Begin method which takes, among other things, a blend state. I'm almost positive that's my problem. I don't want to BLEND the sprites, I want them to be transparent when alpha is 0. In this example I can set alpha to 0 but it still renders both tiles, with the lower z ordered sprite showing through, discolored because of the blending. This is not a desired effect, I want the higher z-ordered sprite to fade out and not effect the color beneath it in such a manner. I might be way off here as I'm fairly new to XNA development so feel free to steer me in the correct direction in the event I'm going down the wrong rabbit hole. TIA

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• Movement on the X an Z axis are combined?

  - by Magicaxis

  This is probably a stupid question, but I'm trying to simply move a 3D object up, down, left, and right (Not forward or backward). The Y axis works fine, but when I increment the object's X position, the object moves BOTH right and backwards! when I decrement X, left and forwards! setPosition(getPosition().X + 2/*times deltatime*/, getPosition().Y, getPosition().Z); I was astonished that XNA doesnt have its own setPosition function, so I made a parent class for all objects with a setPosition and Draw function. Setposition simply edits a variable "mPosition" and passes it to the common draw function: // Copy any parent transforms. Matrix[] transforms = new Matrix[block.Bones.Count]; block.CopyAbsoluteBoneTransformsTo(transforms); // Draw the model. A model can have multiple meshes, so loop. foreach (ModelMesh mesh in block.Meshes) { // This is where the mesh orientation is set, as well // as our camera and projection. foreach (BasicEffect effect in mesh.Effects) { effect.EnableDefaultLighting(); effect.World = transforms[mesh.ParentBone.Index] * Matrix.CreateRotationY(MathHelper.ToRadians(mOrientation.Y)) * Matrix.CreateTranslation(mPosition); effect.View = game1.getView(); effect.Projection = game1.getProjection(); } // Draw the mesh, using the effects set above. mesh.Draw(); } I tried to work it out by attempting to increment and decrement the Z axis, but nothing happens?! So using the X axis changes the objects x and z axis', but changing the Z does nothing. Great. So how do I seperate the X and Z axis movement?

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• How to create a script for moving a 3rd person controller in an iOS device by using Javascript in Unity3D?

  - by user36563

  I've a code but I'm not sure about the steps, so what I should do after the script? pragma strict public var horizontalSpeed : float = 1.0; public var verticalSpeed : float = 1.0; private var h : float = 0.0; private var v : float = 0.0; private var lastPos : Vector3 = Vector3.zero; function Update() { if UNITY_EDITOR if ( Input.GetMouseButtonDown(0) ) { lastPos = Input.mousePosition; } else if ( Input.GetMouseButton(0) ) { var delta = Input.mousePosition - lastPos; h = horizontalSpeed * delta.x ; transform.Rotate( 0, -h, 0, Space.World ); v = verticalSpeed * delta.y ; transform.position += transform.forward * v * Time.deltaTime; lastPos = Input.mousePosition; } else if (Input.touchCount == 1) { var touch : Touch = Input.GetTouch(0); if (touch.phase == TouchPhase.Moved) { h = horizontalSpeed * touch.deltaPosition.x ; transform.Rotate( 0, -h, 0, Space.World ); v = verticalSpeed * touch.deltaPosition.y ; transform.position += transform.forward * v * Time.deltaTime; } } endif }

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• Vector reflect problem

  - by xdevel2000

  I'm testing some vector reflection and I want to check what happens when a ball collides with a paddle. So if I have: Vector2 velocity = new Vector2(-5, 2); position_ball += velocity; if (position_ball.X < 10) { Vector2 v = new Vector2(1,0); // or Vector2.UnitX velocity = Vector2.Reflect(velocity, v); } then, correctly, velocity is (5,2) after Reflect, but if I do: if (position_ball.X < 10) { Vector2 v = new Vector2(1,1); velocity = Vector2.Reflect(velocity, v); } then velocity is (1,8) and not (5, -2) that is the solution of reflection equation R = V - 2 * (V . N) Why is that?

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• OpenGL : sluggish performance in extracting texture from GPU

  - by Cyan

  I'm currently working on an algorithm which creates a texture within a render buffer. The operations are pretty complex, but for the GPU this is a simple task, done very quickly. The problem is that, after creating the texture, i would like to save it. This requires to extract it from GPU memory. For this operation, i'm using glGetTexImage(). It works, but the performance is sluggish. No, i mean even slower than that. For example, an 8MB texture (uncompressed) requires 3 seconds (yes, seconds) to be extracted. That's mind puzzling. I'm almost wondering if my graphic card is connected by a serial link... Well, anyway, i've looked around, and found some people complaining about the same, but no working solution so far. The most promising advise was to "extract data in the native format of the GPU". Which i've tried and tried, but failed so far. Edit : by moving the call to glGetTexImage() in a different place, the speed has been a bit improved for the most dramatic samples : looking again at the 8MB texture, it knows requires 500ms, instead of 3sec. It's better, but still much too slow. Smaller texture sizes were not affected by the change (typical timing remained into the 60-80ms range). Using glFinish() didn't help either. Note that, if i call glFinish() (without glGetTexImage), i'm getting a fixed 16ms result, whatever the texture size or complexity. It really looks like the timing for a frame at 60fps. The timing is measured for the full rendering + saving sequence. The call to glGetTexImage() alone does not really matter. That being said, it is this call which changes the performance. And yes, of course, as stated at the beginning, the texture is "created into the GPU", hence the need to save it.

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• How to configure Bullet for LookAt?

  - by AllCoder

  I'm having problems positioning Bullet objects. I am doing: ToolVec3 origin = ToolVec3( obj_posx, obj_posy, obj_posz ); ToolVec3 vmod = ToolVec3( object_sizex / 2.0f, object_sizey / 2.0f, object_sizez / 2.0f ); btTransform shapeTransform = btTransform::getIdentity(); shapeTransform.setOrigin( btVector3(origin.x+vmod.x, origin.y+vmod.y, origin.z+vmod.z) ); btDefaultMotionState* myMotionState = new btDefaultMotionState(shapeTransform); btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,m_collisionShapes[2],localInertia); btRigidBody* body = new btRigidBody(rbInfo); I then do: btCollisionObject* colObj = m_dynamicsWorld->getCollisionObjectArray()[i]; btRigidBody* body = btRigidBody::upcast(colObj); if(body && body->getMotionState()) { btDefaultMotionState* myMotionState = (btDefaultMotionState*)body->getMotionState(); myMotionState->m_graphicsWorldTrans.getOpenGLMatrix(m); } else { colObj->getWorldTransform().getOpenGLMatrix(m); } And after obtaining the matrix m, I paste it as model matrix. I am observing few things: I must add some weird "size / 2" to object's position, to have it drawed normally, I have following "up" look at vector defined: "0.0f, -1.0f, 0.0f" – basically, Y grows up, Z grows forward (to monitor), BUT – x grows LEFT, I think there is some conflict with the X direction.. I cannot obtain consistent positioning having world setup like this How to configure this in Bullet? Why the weird + size/2 requirement?

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• What techniques can I use to render very large numbers of objects more efficiently in OpenGL?

  - by Luke

  You can think of my application as drawing a very large ball-and-stick diagram (or graph). At times, this graph can get very large, where the number of elements even outnumbers the pixels on the screen. Currently I am simply passing all of my textures (as GL_POINTS) and lines to the graphics card using VBO's. When the number of elements outnumbers the number of pixels, is this the most efficient way to do this? Or should I do some calculations on the CPU side before handing everything over to the GPU? If it matters, I do use GL_DEPTH_TEST and GL_ALPHA_TEST. I do some alpha blending, but probably not enough to make a huge performance difference. My scene can be static at times, but the user has control over a typical arc-ball camera and can pan, rotate, or zoom. It is during these operations that performance degradation is noticeable.

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• glTexImage2D not loading my data

  - by Clyde

  Can anyone suggest why this code doesn't work? When I draw using this texture all I get is black. If I use GLUtils.texImage2D() to load a png file, it works correctly. ByteBuffer bb = ByteBuffer.allocateDirect(128*128*4).order(ByteOrder.nativeOrder()); bb.position(0); for(int row = 0; row != 128; row++) { for(int i = 0 ; i != 128 ; i++) { bb.put((byte)0x80); bb.put((byte)0xFF); bb.put((byte)0xFF); bb.put((byte)i); } } int[] handle = new int[1]; GLES20.glEnable(GLES20.GL_TEXTURE_2D); GLES20.glGenTextures(1, handle, 0); DrawAdapter.checkGlError("Gen textures"); GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, handle[0]); DrawAdapter.checkGlError("Bind textures"); bb.position(0); GLES20.glTexImage2D(GLES20.GL_TEXTURE_2D, 0, GLES20.GL_RGBA, 128, 128, 0, GLES20.GL_RGBA, GLES20.GL_UNSIGNED_BYTE, bb); DrawAdapter.checkGlError("glTexImage2D"); return handle[0];

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• Parsing glGetShaderInfoLog() to get error info. Is this reliable, or is there a better way?

  - by m4ttbush

  I want to get a list of errors and their line numbers so I can display the error information different to how it's formatted in the error string, and also show the line in error. It looks easy enough to just parse the result of glGetShaderInfoLog(), look for "ERROR:" then read the next number up to : and then the next, and then the error description up to the next newline. But the OpenGL docs say "Application developers should not expect different OpenGL implementations to produce identical information logs." Which makes me worry that my code may behave incorrectly on different systems. I don't need them to be identical, I just need them to follow the same format. So is there a better way to get a list of errors with line number separate, is it safe to assume that they'll always follow the "ERROR: 0:123:" format, or is there simply no reliable way to do this? Thanks!

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• Achieve anisotropic filtering

  - by fedab

  I want to set anisotropic filtering to my scene. I use SharpDX (DirectX 11) and C#. How do i set up anisotropic filtering in my shader? Currently i try that in the shader: Texture2D tex; sampler textureSampler = sampler_state { Texture = (tex); MipFilter = Anisotropic; MagFilter = Anisotropic; MinFilter = Anisotropic; MaxAnisotropy = 16; }; float4 PShader(float4 position : SV_POSITION, float4 color:COLOR, float2 tex0 : TEXCOORD0) : SV_TARGET { float4 textureColor; textureColor = tex.Sample(textureSampler, tex0) * color; return textureColor; } I get my object, textured, but it is not filtered anisotropic. I can write everything in the Parameters, even invalid things and i don't get any errors. The result is the same, objects without applied anisotropic filtering. Do i have to set that in the shader? Can i do that also with SamplerState? I tested that but i didn't get a result too. Some steps what i have to set would be helpful.

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• Android Dynamic 2D Map

  - by Deltharis

  My problem is, I want to create a 2D tiled map. Yes, I know it's been asked a lot. I've seen answers that propose the use of tiled however it only allows (or so it seems to me) to generate static maps that do not change once generated. And I need a large empty uniform space of empty tiles, upon which players may place various buildings (some spanning more than one tile and logically being the same one). How to approach this in Android? Do I make some kind of TableLayout, use arbitrarly large amount of rows and imageviews (with my emptyTile), than somehow work event-based changing of image ids from there? I'd think that only a portion of that map should be visible at a time, but I don't see how scrolling around could be the part of that structure.

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• How to make a stack stable? Need help for an explicit resting contact scheme (2-dimensional)

  - by Register Sole

  Previously, I struggle with the sequential impulse-based method I developed. Thanks to jedediah referring me to this paper, I managed to rebuild the codes and implement the simultaneous impulse based method with Projected-Gauss-Seidel (PGS) iterative solver as described by Erin Catto (mentioned in the reference of the paper as [Catt05]). So here's how it currently is: The simulation handles 2-dimensional rotating convex polygons. Detection is using separating-axis test, with a SKIN, meaning closest points between two polygons is detected and determined if their distance is less than SKIN. To resolve collision, simultaneous impulse-based method is used. It is solved using iterative solver (PGS-solver) as in Erin Catto's paper. Error-correction is implemented using Baumgarte's stabilization (you can refer to either paper for this) using J V = beta/dt*overlap, J is the Jacobian for the constraints, V the matrix containing the velocities of the bodies, beta an error-correction parameter that is better be < 1, dt the time-step taken by the engine, and overlap, the overlap between the bodies (true overlap, so SKIN is ignored). However, it is still less stable than I expected :s I tried to stack hexagons (or squares, doesn't really matter), and even with only 4 to 5 of them, they would swing! Also note that I am not looking for a sleeping scheme. But I would settle if you have any explicit scheme to handle resting contacts. That said, I would be more than happy if you have a way of treating it generally (as continuous collision, instead of explicitly as a special state). Ideas I have tried: Using simultaneous position based error correction as described in the paper in section 5.3.2, turned out to be worse than the current scheme. If you want to know the parameters I used: Hexagons, side 50 (pixels) gravity 2400 (pixels/sec^2) time-step 1/60 (sec) beta 0.1 restitution 0 to 0.2 coeff. of friction 0.2 PGS iteration 10 initial separation 10 (pixels) mass 1 (unit is irrelevant for now, i modified velocity directly<-impulse method) inertia 1/1000 Thanks in advance! I really appreciate any help from you guys!! :) EDIT In response to Cholesky's comment about warm starting the solver and Baumgarte: Oh right, I forgot to mention! I do save the contact history and the impulse determined in this time step to be used as initial guess in the next time step. As for the Baumgarte, here's what actually happens in the code. Collision is detected when the bodies' closest distance is less than SKIN, meaning they are actually still separated. If at this moment, I used the PGS solver without Baumgarte, restitution of 0 alone would be able to stop the bodies, separated by a distance of ~SKIN, in mid-air! So this isn't right, I want to have the bodies touching each other. So I turn on the Baumgarte, where its role is actually to pull the bodies together! Weird I know, a scheme intended to push the body apart becomes useful for the reverse. Also, I found that if I increase the number of iteration to 100, stacks become much more stable, though the program becomes so slow. UPDATE Since the stack swings left and right, could it be something is wrong with my friction model? Current friction constraint: relative_tangential_velocity = 0

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• Particles are not moving correctly [closed]

  - by cr33p

  I want to make a particle explosion, after something gets destroyed, but somehow only one line of mixed colors show up on the screen. Here's the header: http://pastebin.com/JW5bPLj2 Here's the source: http://pastebin.com/KHmFqytD I don't get what's wrong, as it's nearly the same as in "Programming Linux Games" Can somebody help me fix that? PS: "Uint32 delta" is needed to update the pixels based on time. PSS: Maybe I should add that it's programmed in C and includes SDL. EDIT: Found the problem. It was the "drawParticles" function. The problem was, that I passed a double to "offset" (as particles[i].x, etc are all doubles). So I ended up with values like ~MAX_INT because I didn't cast the doubles properly to ints.

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