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• Solaris X86 AESNI OpenSSL Engine

  - by danx

  Solaris X86 AESNI OpenSSL Engine Cryptography is a major component of secure e-commerce. Since cryptography is compute intensive and adds a significant load to applications, such as SSL web servers (https), crypto performance is an important factor. Providing accelerated crypto hardware greatly helps these applications and will help lead to a wider adoption of cryptography, and lower cost, in e-commerce and other applications. The Intel Westmere microprocessor has six new instructions to acclerate AES encryption. They are called "AESNI" for "AES New Instructions". These are unprivileged instructions, so no "root", other elevated access, or context switch is required to execute these instructions. These instructions are used in a new built-in OpenSSL 1.0 engine available in Solaris 11, the aesni engine. Previous Work Previously, AESNI instructions were introduced into the Solaris x86 kernel and libraries. That is, the "aes" kernel module (used by IPsec and other kernel modules) and the Solaris pkcs11 library (for user applications). These are available in Solaris 10 10/09 (update 8) and above, and Solaris 11. The work here is to add the aesni engine to OpenSSL. X86 AESNI Instructions Intel's Xeon 5600 is one of the processors that support AESNI. This processor is used in the Sun Fire X4170 M2 As mentioned above, six new instructions acclerate AES encryption in processor silicon. The new instructions are: aesenc performs one round of AES encryption. One encryption round is composed of these steps: substitute bytes, shift rows, mix columns, and xor the round key. aesenclast performs the final encryption round, which is the same as above, except omitting the mix columns (which is only needed for the next encryption round). aesdec performs one round of AES decryption aesdeclast performs the final AES decryption round aeskeygenassist Helps expand the user-provided key into a "key schedule" of keys, one per round aesimc performs an "inverse mixed columns" operation to convert the encryption key schedule into a decryption key schedule pclmulqdq Not a AESNI instruction, but performs "carryless multiply" operations to acclerate AES GCM mode. Since the AESNI instructions are implemented in hardware, they take a constant number of cycles and are not vulnerable to side-channel timing attacks that attempt to discern some bits of data from the time taken to encrypt or decrypt the data. Solaris x86 and OpenSSL Software Optimizations Having X86 AESNI hardware crypto instructions is all well and good, but how do we access it? The software is available with Solaris 11 and is used automatically if you are running Solaris x86 on a AESNI-capable processor. AESNI is used internally in the kernel through kernel crypto modules and is available in user space through the PKCS#11 library. For OpenSSL on Solaris 11, AESNI crypto is available directly with a new built-in OpenSSL 1.0 engine, called the "aesni engine." This is in lieu of the extra overhead of going through the Solaris OpenSSL pkcs11 engine, which accesses Solaris crypto and digest operations. Instead, AESNI assembly is included directly in the new aesni engine. Instead of including the aesni engine in a separate library in /lib/openssl/engines/, the aesni engine is "built-in", meaning it is included directly in OpenSSL's libcrypto.so.1.0.0 library. This reduces overhead and the need to manually specify the aesni engine. Since the engine is built-in (that is, in libcrypto.so.1.0.0), the openssl -engine command line flag or API call is not needed to access the engine—the aesni engine is used automatically on AESNI hardware. Ciphers and Digests supported by OpenSSL aesni engine The Openssl aesni engine auto-detects if it's running on AESNI hardware and uses AESNI encryption instructions for these ciphers: AES-128-CBC, AES-192-CBC, AES-256-CBC, AES-128-CFB128, AES-192-CFB128, AES-256-CFB128, AES-128-CTR, AES-192-CTR, AES-256-CTR, AES-128-ECB, AES-192-ECB, AES-256-ECB, AES-128-OFB, AES-192-OFB, and AES-256-OFB. Implementation of the OpenSSL aesni engine The AESNI assembly language routines are not a part of the regular Openssl 1.0.0 release. AESNI is a part of the "HEAD" ("development" or "unstable") branch of OpenSSL, for future release. But AESNI is also available as a separate patch provided by Intel to the OpenSSL project for OpenSSL 1.0.0. A minimal amount of "glue" code in the aesni engine works between the OpenSSL libcrypto.so.1.0.0 library and the assembly functions. The aesni engine code is separate from the base OpenSSL code and requires patching only a few source files to use it. That means OpenSSL can be more easily updated to future versions without losing the performance from the built-in aesni engine. OpenSSL aesni engine Performance Here's some graphs of aesni engine performance I measured by running openssl speed -evp $algorithm where $algorithm is aes-128-cbc, aes-192-cbc, and aes-256-cbc. These are using the 64-bit version of openssl on the same AESNI hardware, a Sun Fire X4170 M2 with a Intel Xeon E5620 @2.40GHz, running Solaris 11 FCS. "Before" is openssl without the aesni engine and "after" is openssl with the aesni engine. The numbers are MBytes/second. OpenSSL aesni engine performance on Sun Fire X4170 M2 (Xeon E5620 @2.40GHz) (Higher is better; "before"=OpenSSL on AESNI without AESNI engine software, "after"=OpenSSL AESNI engine) As you can see the speedup is dramatic for all 3 key lengths and for data sizes from 16 bytes to 8 Kbytes—AESNI is about 7.5-8x faster over hand-coded amd64 assembly (without aesni instructions). Verifying the OpenSSL aesni engine is present The easiest way to determine if you are running the aesni engine is to type "openssl engine" on the command line. No configuration, API, or command line options are needed to use the OpenSSL aesni engine. If you are running on Intel AESNI hardware with Solaris 11 FCS, you'll see this output indicating you are using the aesni engine: intel-westmere $ openssl engine (aesni) Intel AES-NI engine (no-aesni) (dynamic) Dynamic engine loading support (pkcs11) PKCS #11 engine support If you are running on Intel without AESNI hardware you'll see this output indicating the hardware can't support the aesni engine: intel-nehalem $ openssl engine (aesni) Intel AES-NI engine (no-aesni) (dynamic) Dynamic engine loading support (pkcs11) PKCS #11 engine support For Solaris on SPARC or older Solaris OpenSSL software, you won't see any aesni engine line at all. Third-party OpenSSL software (built yourself or from outside Oracle) will not have the aesni engine either. Solaris 11 FCS comes with OpenSSL version 1.0.0e. The output of typing "openssl version" should be "OpenSSL 1.0.0e 6 Sep 2011". 64- and 32-bit OpenSSL OpenSSL comes in both 32- and 64-bit binaries. 64-bit executable is now the default, at /usr/bin/openssl, and OpenSSL 64-bit libraries at /lib/amd64/libcrypto.so.1.0.0 and libssl.so.1.0.0 The 32-bit executable is at /usr/bin/i86/openssl and the libraries are at /lib/libcrytpo.so.1.0.0 and libssl.so.1.0.0. Availability The OpenSSL AESNI engine is available in Solaris 11 x86 for both the 64- and 32-bit versions of OpenSSL. It is not available with Solaris 10. You must have a processor that supports AESNI instructions, otherwise OpenSSL will fallback to the older, slower AES implementation without AESNI. Processors that support AESNI include most Westmere and Sandy Bridge class processor architectures. Some low-end processors (such as for mobile/laptop platforms) do not support AESNI. The easiest way to determine if the processor supports AESNI is with the isainfo -v command—look for "amd64" and "aes" in the output: $ isainfo -v 64-bit amd64 applications pclmulqdq aes sse4.2 sse4.1 ssse3 popcnt tscp ahf cx16 sse3 sse2 sse fxsr mmx cmov amd_sysc cx8 tsc fpu Conclusion The Solaris 11 OpenSSL aesni engine provides easy access to powerful Intel AESNI hardware cryptography, in addition to Solaris userland PKCS#11 libraries and Solaris crypto kernel modules.

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• How can I make my main character move in a parabolic arc when jumping?

  - by user1276078

  I'm entering Android game development, and I already have a computer version of a game I want to publish. The thing is, I want to make this as good as it can be. With that said, I need a physics engine, really to only do one thing: make a parabolic movement of my main character as he's jumping in the air. Currently, my computer version simply makes the guy move up at a 45 degree angle, and as soon as it hits the ceiling, down at a 45 degree angle. I need a physics engine/library that would accomplish that, it has to be in java since that's my best language, it has to be 2D, and it has to be able to work on Android. Which physics engine/library could accomplish all of that?

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• Particle and Physics problem.

  - by Quincy

  This was originally a forum post so I hope you guys don't mind it being 2 questions in one. I am making a game and I got some basic physics implemented. I have 2 problems, 1 with particles being drawn in the wrong place and one with going through walls while jumping in corners. Skip over to about 15 sec video showing the 2 problems : http://youtube.com/watch?v=Tm9nfWsWfiM So the problem with the particles seems to be coming from the removal, as soon as I remove that piece of code it instantly works, but there shouldn't be a problem since they shouldn't even draw when their energy gets to 0 (and then they get removed) So my first question is, how are these particles getting warped all over the screen ? Relevant code : Particle class : class Particle { //Physics public Vector2 position = new Vector2(0,0); public float direction = 180; public float speed = 100; public float energy = 1; protected float startEnergy = 1; //Visual public Sprite sprite; public float rotation = 0; public float scale = 1; public byte alpha = 255; public BlendMode blendMode { get { return sprite.BlendMode; } set { sprite.BlendMode = value; } } public Particle() { } public virtual void Think(float frameTime) { if (energy - frameTime < 0) energy = 0; else energy -= frameTime; position += new Vector2((float)Math.Cos(MathHelper.DegToRad(direction)), (float)Math.Sin(MathHelper.DegToRad(direction))) * speed * frameTime; alpha = (byte)(255 * energy / startEnergy); sprite.Rotation = rotation; sprite.Position = position; sprite.Color = new Color(sprite.Color.R, sprite.Color.G, sprite.Color.B, alpha); } public virtual void Draw(float frameTime) { if (energy > 0) { World.camera.DrawSprite(sprite); } } // Basic particle implementation class BasicSprite : Particle { public BasicSprite(Sprite _sprite) { sprite = _sprite; } } Emitter : class Emitter { protected static Random rand = new Random(); protected List<Particle> particles = new List<Particle>(); public BaseEntity target = null; public Vector2 position = new Vector2(0, 0); public bool Active = true; public float timeAlive = 0; public int particleCount = 0; public int ParticlesPerSeccond { get { return (int)(1 / particleSpawnTime); } set { particleSpawnTime = 1 / (float)value; } } public float dieTime = float.MaxValue; float particleSpawnTime = 0.05f; float spawnTime = 0; public Emitter() { } public virtual void Think(float frametime) { spawnTime += frametime; if (dieTime != float.MaxValue) { timeAlive += frametime; if (timeAlive >= dieTime) Active = false; } if (Active) { if (target != null) position = target.Position; while (spawnTime > particleSpawnTime) { spawnTime -= particleSpawnTime; AddParticle(); particleCount++; } } for (int i = 0; i < particles.Count; i++) { particles[i].Think(frametime); if (particles[i].energy <= 0) { particles.Remove(particles[i]); // As soon as this is removed, it works particleCount--; } } } public virtual void AddParticle() { } public virtual void Draw(float frametime) { foreach (Particle particle in particles) { particle.Draw(frametime); } } } class BloodEmitter : Emitter { Image image; public BloodEmitter() { image = new Image(@"Content/Particles/TinyCircle.png"); image.CreateMaskFromColor(new Color(255, 0, 255, 255)); this.dieTime = 0.5f; this.ParticlesPerSeccond = 100; } public override void AddParticle() { Sprite sprite = new Sprite(image); sprite.Color = new Color((byte)(rand.NextDouble() * 255), (byte)(rand.NextDouble() * 255), (byte)(rand.NextDouble() * 255)); BasicSprite particle = new BasicSprite(sprite); particle.direction = (float)rand.NextDouble() * 360; particle.position = position; particle.blendMode = BlendMode.Alpha; particles.Add(particle); } } The seccond problem is the physics problem, for some reason I can get through the right bottom corner while jumping. I think this is coming from me switching animations but I thought I made it compensate for that. Relevant code : PhysicsEntity : class PhysicsEntity : BaseEntity { // Horizontal movement constants protected const float maxHorizontalSpeed = 1000; protected const float horizontalAcceleration = 15; protected const float horizontalDragAir = 0.95f; protected const float horizontalDragGround = 0.95f; // Vertical movement constants protected const float maxVerticalSpeed = 1000; protected const float verticalAcceleration = 20; // Everything needed for movement and correct animations protected float movement = 0; protected bool onGround = false; protected Vector2 Velocity = new Vector2(0, 0); protected float maxSpeed = 0; float lastThink = 0; float thinkTime = 1f/60f; public PhysicsEntity(Vector2 position, Sprite sprite) : base(position, sprite) { } public override void Draw(float frameTime) { base.Draw(frameTime); } public override void Think(float frameTime) { CalculateMovement(frameTime); base.Think(frameTime); } protected void CalculateMovement(float frameTime) { lastThink += frameTime; while (lastThink > thinkTime) { onGround = false; Velocity.X = MathHelper.Clamp(Velocity.X + horizontalAcceleration * movement, -maxHorizontalSpeed, maxHorizontalSpeed); if (onGround) Velocity.X *= horizontalDragGround; else Velocity.X *= horizontalDragAir; if (maxSpeed < Velocity.X) maxSpeed = Velocity.X; Velocity.Y = MathHelper.Clamp(Velocity.Y + verticalAcceleration, -maxVerticalSpeed, maxVerticalSpeed); lastThink -= thinkTime; DoCollisions(thinkTime); DoAnimations(thinkTime); } } public virtual void DoAnimations(float frameTime) { } public void DoCollisions(float frameTime) { Position.Y += Velocity.Y * frameTime; Vector2 tileCollision = GetTileCollision(); if (tileCollision.X != -1 || tileCollision.Y != -1) { Vector2 collisionDepth = CollisionRectangle.DepthIntersection( new Rectangle( tileCollision.X * World.tileEngine.TileWidth, tileCollision.Y * World.tileEngine.TileHeight, World.tileEngine.TileWidth, World.tileEngine.TileHeight ) ); Position.Y += collisionDepth.Y; if (collisionDepth.Y < 0) onGround = true; Velocity.Y = 0; } Position.X += Velocity.X * frameTime; tileCollision = GetTileCollision(); if (tileCollision.X != -1 || tileCollision.Y != -1) { Vector2 collisionDepth = CollisionRectangle.DepthIntersection( new Rectangle( tileCollision.X * World.tileEngine.TileWidth, tileCollision.Y * World.tileEngine.TileHeight, World.tileEngine.TileWidth, World.tileEngine.TileHeight ) ); Position.X += collisionDepth.X; Velocity.X = 0; } } public void DoCollisions(Vector2 difference) { CollisionRectangle.Y = Position.Y - difference.Y; CollisionRectangle.Height += difference.Y; Vector2 tileCollision = GetTileCollision(); if (tileCollision.X != -1 || tileCollision.Y != -1) { Vector2 collisionDepth = CollisionRectangle.DepthIntersection( new Rectangle( tileCollision.X * World.tileEngine.TileWidth, tileCollision.Y * World.tileEngine.TileHeight, World.tileEngine.TileWidth, World.tileEngine.TileHeight ) ); Position.Y += collisionDepth.Y; if (collisionDepth.Y < 0) onGround = true; Velocity.Y = 0; } CollisionRectangle.X = Position.X - difference.X; CollisionRectangle.Width += difference.X; tileCollision = GetTileCollision(); if (tileCollision.X != -1 || tileCollision.Y != -1) { Vector2 collisionDepth = CollisionRectangle.DepthIntersection( new Rectangle( tileCollision.X * World.tileEngine.TileWidth, tileCollision.Y * World.tileEngine.TileHeight, World.tileEngine.TileWidth, World.tileEngine.TileHeight ) ); Position.X += collisionDepth.X; Velocity.X = 0; } } Vector2 GetTileCollision() { int topLeftTileX = (int)(CollisionRectangle.TopLeft.X / World.tileEngine.TileWidth); int topLeftTileY = (int)(CollisionRectangle.TopLeft.Y / World.tileEngine.TileHeight); int BottomRightTileX = (int)(CollisionRectangle.DownRight.X / World.tileEngine.TileWidth); int BottomRightTileY = (int)(CollisionRectangle.DownRight.Y / World.tileEngine.TileHeight); if (CollisionRectangle.DownRight.Y % World.tileEngine.TileHeight == 0) // If your exactly against the tile don't count that as being inside the tile BottomRightTileY -= 1; if (CollisionRectangle.DownRight.X % World.tileEngine.TileWidth == 0) // If your exactly against the tile don't count that as being inside the tile BottomRightTileX -= 1; for (int i = topLeftTileX; i <= BottomRightTileX; i++) { for (int j = topLeftTileY; j <= BottomRightTileY; j++) { if (World.tileEngine.TileIsSolid(i, j)) { return new Vector2(i, j); } } } return new Vector2(-1, -1); } } Player : enum State { Standing, Running, Jumping, Falling, Sliding, WallSlide } class Player : PhysicsEntity { private State state { get { return currentState; } set { if (currentState != value) { currentState = value; animationChanged = true; } } } private State currentState = State.Standing; private BasicEmitter basicEmitter = new BasicEmitter(); public bool flipped; public bool animationChanged = false; protected const float jumpPower = 600; AnimationManager animationManager; Rectangle DrawRectangle; public override Rectangle CollisionRectangle { get { return new Rectangle( Position.X - DrawRectangle.Width / 2f, Position.Y - DrawRectangle.Height / 2f, DrawRectangle.Width, DrawRectangle.Height ); } } public Player(Vector2 position, Sprite sprite) : base(position, sprite) { // Only posted the relevant bit DrawRectangle = animationManager.currentAnimation.drawingRectangle; } public override void Draw(float frameTime) { World.camera.DrawSprite( Sprite, Position + new Vector2(DrawRectangle.X, DrawRectangle.Y), animationManager.currentAnimation.drawingRectangle ); } public override void Think(float frameTime) { //I only posted the relevant stuff if (animationChanged) { // if the animation has changed make sure we compensate for the change in with and height animationChanged = false; DoCollisions(animationManager.getSizeDifference()); } DoCustomMovement(); base.Think(frameTime); if (!onGround && Velocity.Y > 0) { state = State.Falling; } } void DoCustomMovement() { if (onGround) { if (World.renderWindow.Input.IsKeyDown(KeyCode.W)) { Velocity.Y = -jumpPower; state = State.Jumping; } } } public override void DoAnimations(float frameTime) { string stateName = Enum.GetName(typeof(State), state); if (!animationManager.currentAnimationIs(stateName)) { animationManager.PlayAnimation(stateName); } animationManager.Think(frameTime); DrawRectangle = animationManager.currentAnimation.drawingRectangle; Sprite.Center = new Vector2( DrawRectangle.X + DrawRectangle.Width / 2, DrawRectangle.Y + DrawRectangle.Height / 2 ); Sprite.FlipX(flipped); } So why am I warping through walls ? I have given this some thought but I just can't seem to find out why this is happening. Full source if needed : source : http://www.mediafire.com/?rc7ddo09gnr68zd (download link)

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• How to ‘Bounce’ Drops of Water on Top of a Pool of Water Indefinitely [Physics Video]

  - by Asian Angel

  Normally drops of water are automatically ‘absorbed’ into a larger pool of water when contact is made, but there is one way to stop those water drops from coalescing with the rest: vibration. This awesome video shows the process in action as drops of water remain on top of the pool of water and even form groups of drops! Drops on Drops on Drops Article [Physics Buzz Blog] Drops on Drops on Drops Video [YouTube] [via Neatorama] How Hackers Can Disguise Malicious Programs With Fake File Extensions Can Dust Actually Damage My Computer? What To Do If You Get a Virus on Your Computer

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• Bullet physics debug drawing not working

  - by Krishnabhadra

  Background I am following on from this question, which isn't answered yet. Basically I have a cube and a UVSphere in my scene, with UVSphere on the top of the cube without touching the cube. Both exported from blender. When I run the app The UVSphere does circle around the cube for 3 or 4 times and jump out of the scene. What I actually expect was the sphere to fall on top of the cube. What this question about From the comment to the linked question, I got to know about bullet debug drawing, which helps in debugging by drawing outline of physics bodies which are normally invisible. I did some research on that and came up with the code given below. From whatever I have read, below code should work, but it doesn't. My Code My bullet initialization code. -(void) initializeScene { /*Setup physics world*/ _physicsWorld = [[CC3PhysicsWorld alloc] init]; [_physicsWorld setGravity:0 y:-9.8 z:0]; /*Setting up debug draw*/ MyDebugDraw *draw = new MyDebugDraw; draw->setDebugMode(draw->getDebugMode() | btIDebugDraw::DBG_DrawWireframe ); _physicsWorld._discreteDynamicsWorld->setDebugDrawer(draw); /*Setup camera and lamb*/ ………….. //This simpleCube.pod contains the cube [self addContentFromPODFile: @"simpleCube.pod"]; //This file contains sphere [self addContentFromPODFile: @"SimpleSphere.pod"]; [self createGLBuffers]; CC3MeshNode* cubeNode = (CC3MeshNode*)[self getNodeNamed:@"Cube"]; CC3MeshNode* sphereNode = (CC3MeshNode*)[self getNodeNamed:@"Sphere"]; // both cubeNode and sphereNode are not nil from this point float *cVertexData = (float*)((CC3VertexArrayMesh*)cubeNode.mesh) .vertexLocations.vertices; int cVertexCount = ((CC3VertexArrayMesh*)cubeNode.mesh) .vertexLocations.vertexCount; btTriangleMesh* cTriangleMesh = new btTriangleMesh(); int offset = 0; for (int i = 0; i < (cVertexCount / 3); i++) { unsigned int index1 = offset; unsigned int index2 = offset+6; unsigned int index3 = offset+12; cTriangleMesh->addTriangle( btVector3(cVertexData[index1], cVertexData[index1+1], cVertexData[index1+2]), btVector3(cVertexData[index2], cVertexData[index2+1], cVertexData[index2+2]), btVector3(cVertexData[index3], cVertexData[index3+1], cVertexData[index3+2])); offset += 18; } [self releaseRedundantData]; /*Create a triangle mesh from the vertices*/ btBvhTriangleMeshShape* cTriMeshShape = new btBvhTriangleMeshShape(cTriangleMesh,true); btCollisionShape *sphereShape = new btSphereShape(1); gTriMeshObject = [_physicsWorld createPhysicsObjectTrimesh:cubeNode shape:cTriMeshShape mass:0 restitution:1.0 position:cubeNode.location]; sphereObject = [_physicsWorld createPhysicsObject:sphereNode shape:sphereShape mass:1 restitution:0.1 position:sphereNode.location]; sphereObject.rigidBody->setDamping(0.1,0.8); /*Enable debug drawing*/ _physicsWorld._discreteDynamicsWorld->debugDrawWorld(); } And My btIDebugDraw implementation (MyDebugDraw.h) //MyDebugDraw.h class MyDebugDraw: public btIDebugDraw{ int m_debugMode; public: virtual void drawLine(const btVector3& from,const btVector3& to ,const btVector3& color); virtual void drawContactPoint(const btVector3& PointOnB ,const btVector3& normalOnB,btScalar distance ,int lifeTime,const btVector3& color); virtual void reportErrorWarning(const char* warningString); virtual void draw3dText(const btVector3& location ,const char* textString); virtual void setDebugMode(int debugMode); virtual int getDebugMode() const; }; void MyDebugDraw::drawLine(const btVector3& from,const btVector3& to ,const btVector3& color){ LogInfo(@"Works!!"); glPushMatrix(); glColor4f(color.getX(), color.getY(), color.getZ(), 1.0); const GLfloat line[] = { from.getX()*1, from.getY()*1, from.getZ()*1, //point A to.getX()*1, to.getY()*1,to.getZ()*1 //point B }; glVertexPointer( 3, GL_FLOAT, 0, &line ); glPointSize( 5.0f ); glDrawArrays( GL_POINTS, 0, 2 ); glDrawArrays( GL_LINES, 0, 2 ); glPopMatrix(); } void MyDebugDraw::drawContactPoint(const btVector3 &PointOnB ,const btVector3 &normalOnB, btScalar distance ,int lifeTime, const btVector3 &color){ } void MyDebugDraw::reportErrorWarning(const char *warningString){ } void MyDebugDraw::draw3dText(const btVector3 &location , const char *textString){ } void MyDebugDraw::setDebugMode(int debugMode){ } int MyDebugDraw::getDebugMode() const{ return DBG_DrawWireframe; } My Problem The drawLine method is getting called. I can see the cube and sphere in place. Sphere again does some circling around the cube before jumping off. No debug lines are getting drawn.

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• farseer physics xbox samples not working

  - by Hugh

  I have downloaded a few of the sample projects from the official farseer physics website and i just cant get them to run on my xbox. -My connection to the xbox is fine, other xbox projects debug fine on my xbox -I have tried running both the xbox versions of the samples (for example the farseer hello world sample project) and the windows version by right-clicking the project and making a copy for xbox. I get a bunch of errors but what i always get is "unreachable code detected" referring to code in the farseer library, it seems to be a problem to do with referencing/linking the farseer library to the main game project. Help please!

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• Physics timestep questions

  - by SSL

  I've got a projectile working perfectly using the code below: //initialised in loading screen 60 is the FPS - projectilEposition and velocity are Vector3 types gravity = new Vector3(0, -(float)9.81 / 60, 0); //called every frame projectilePosition += projectileVelocity; This seems to work fine but I've noticed in various projectile examples I've seen that the elapsedtime per update is taken into account. What's the difference between the two and how can I convert the above to take into account the elapsedtime? (I'm using XNA - do I use ElapsedTime.TotalSeconds or TotalMilliseconds)? Edit: Forgot to add my attempt at using elapsedtime, which seemed to break the physics: projectileVelocity.Y += -(float)((9.81 * gameTime.ElapsedGameTime.TotalSeconds * gameTime.ElapsedGameTime.TotalSeconds) * 0.5f); Thanks for the help

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• Correct order of tasks in each frame for a Physics simulation

  - by Johny

  I'm playing a bit around with 2D physics. I created now some physic blocks which should collide with each other. This works fine "mostly" but sometimes one of the blocks does not react to a collision and i think that's because of my order of tasks done in each frame. At the moment it looks something like this: function GameFrame(){ foreach physicObject do AddVelocityToPosition(); DoCollisionStuff(); // Only for this object not to forget! AddGravitationToVelocity(); end RedrawScene(); } Is this the correct order of tasks in each frame?

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• Numerical stability in continuous physics simulation

  - by Panda Pajama

  Pretty much all of the game development I have been involved with runs afoul of simulating a physical world in discrete time steps. This is of course very simple, but hardly elegant (not to mention mathematically inaccurate). It also has severe disadvantages when large values are involved (either very large speeds, or very large time intervals). I'm trying to make a continuous physics simulation, just for learning, which goes like this: time = get_time() while true do new_time = get_time() update_world(new_time - time) render() time = new_time end And update_world() is a continuous physical simulation. Meaning that for example, for an accelerated object, instead of doing object.x = object.x + object.vx * timestep object.vx = object.vx + object.ax * timestep -- timestep is fixed I'm doing something like object.x = object.x + object.vx * deltatime + object.ax * ((deltatime ^ 2) / 2) object.vx = object.vx + object.ax * deltatime However, I'm having a hard time with the numerical stability of my solutions, especially for very large time intervals (think of simulating a physical world for hundreds of thousands of virtual years). Depending on the framerate, I get wildly different solutions. How can I improve the numerical stability of my continuous physical simulations?

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• Understanding Unity3d physics: where is the force applied?

  - by Heisenbug

  I'm trying to understand which is the right way to apply forces to a RigidBody. I noticed that there are AddForce and AddRelativeForce methods, one applied in world space coordinate system meanwhile the other in the local space. The thing that I do not understand is the following: usually in physics library (es. Bullet) we can specify the force vector and also the force application point. How can I do this in Unity? Is it possible to apply a force vector in a specific point relative to the given RigidBody coordinate system? Where does AddForce apply the force?

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• writing an autopilot for a 2d game with newtonian physics

  - by Jargo

  The subject says it all. I am making a 2d space game with newtonian physics and I need pointers on how to write an autopilot for it. The requirements are best explained by an example. There is a target object which has speed- and position-vectors and there a spaceship that is controlled by the autopilot. This spaceship also have speed, position and maximum acceleration. The autopilot needs to control the ship that it either collides with the target, Or intercepts the target so that the ship has matching speed and position with the target. Could someone give me some pointers how to achieve this behavior or perhaps even an ready implementation? I am sure someone has written something like this before and there is no point in reinventing the wheel.

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• 3D physics engine for accurate collision handling on desktop/laptop computers (non-console)

  - by Georges Oates Larsen

  What are your suggestions for a physics engine that satisfies the following criteria? Capable of calculating collisions between multiple concave mesh-based colliders Handles many collisions going on at once (for instance one mesh being wedged between two others, which themselves may be wedged between two meshes) Does not allow for collider passthrough, even at high speeds. For instance, if I am applying force to a programmatically hinged object that makes it spin, I do not want it to pass through another rigidbody that it collides with while spinning. I have this problem using PhysX As implied before, reacts well to hinged objects, preferably has its own implementation of a hinge, but I am willing to program my own. The important part is that it has some sort of interface that guarantees accurate collision tracking even when dealing with these things Platform independent -- runs on mac as well as PC, also not tied down to specific graphics cards I think that's the best way to explain what I am looking for. Basically, I need SUPER reliable collisions. Something that can't be accomplished with a simple ray casting approach that sends a ray from the last position of the object to the current position (as this object may be potentially large and colliding with small objects via rotation) Bonus points for also including an OPEN SOURCE engine.

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• jBullet Collision/Physics not working correctly

  - by Kenneth Bray

  Below is the code for one of my objects in the game I am creating (yes although this is a cube, I am not making anything remotely like MineCraft), and my issue is I while the cube will display and is does follow the physics if the cube falls, it does not interact with any other objects in the game. If I was to have multiple cubes in screen at once they all just sit there, or shoot off in all directions never stopping. Anyway, I am new to jBullet, and any help would be appreciated. package Object; import static org.lwjgl.opengl.GL11.GL_QUADS; import static org.lwjgl.opengl.GL11.glBegin; import static org.lwjgl.opengl.GL11.glColor3f; import static org.lwjgl.opengl.GL11.glEnd; import static org.lwjgl.opengl.GL11.glPopMatrix; import static org.lwjgl.opengl.GL11.glPushMatrix; import static org.lwjgl.opengl.GL11.glVertex3f; import javax.vecmath.Matrix4f; import javax.vecmath.Quat4f; import javax.vecmath.Vector3f; import com.bulletphysics.collision.shapes.BoxShape; import com.bulletphysics.collision.shapes.CollisionShape; import com.bulletphysics.dynamics.RigidBody; import com.bulletphysics.dynamics.RigidBodyConstructionInfo; import com.bulletphysics.linearmath.DefaultMotionState; import com.bulletphysics.linearmath.Transform; public class Cube { // Cube size/shape variables private float size; boolean cubeCollidable; boolean cubeDestroyable; // Position variables - currently this defines the center of the cube private float posX; private float posY; private float posZ; // Rotation variables - should be between 0 and 359, might consider letting rotation go higher though I can't think of a purpose currently private float rotX; private float rotY; private float rotZ; //collision shape is a box shape CollisionShape fallShape; // setup the motion state for the ball DefaultMotionState fallMotionState; Vector3f fallInertia = new Vector3f(0, 1, 0); RigidBodyConstructionInfo fallRigidBodyCI; public RigidBody fallRigidBody; int mass = 1; // Constructor public Cube(float pX, float pY, float pZ, float pSize) { posX = pX; posY = pY; posZ = pZ; size = pSize; rotX = 0; rotY = 0; rotZ = 0; // define the physics based on the values passed in fallShape = new BoxShape(new Vector3f(size, size, size)); fallMotionState = new DefaultMotionState(new Transform(new Matrix4f(new Quat4f(0, 0, 0, 1), new Vector3f(0, 50, 0), 1f))); fallRigidBodyCI = new RigidBodyConstructionInfo(mass, fallMotionState, fallShape, fallInertia); fallRigidBody = new RigidBody(fallRigidBodyCI); } public void Update() { Transform trans = new Transform(); fallRigidBody.getMotionState().getWorldTransform(trans); posY = trans.origin.x; posX = trans.origin.y; posZ = trans.origin.z; } public void Draw() { fallShape.calculateLocalInertia(mass, fallInertia); // center point posX, posY, posZ float radius = size / 2; //top glPushMatrix(); glBegin(GL_QUADS); { glColor3f(1.0f,0.0f,0.0f); // red glVertex3f(posX + radius, posY + radius, posZ - radius); glVertex3f(posX - radius, posY + radius, posZ - radius); glVertex3f(posX - radius, posY + radius, posZ + radius); glVertex3f(posX + radius, posY + radius, posZ + radius); } glEnd(); glPopMatrix(); //bottom glPushMatrix(); glBegin(GL_QUADS); { glColor3f(1.0f,1.0f,0.0f); // ?? color glVertex3f(posX + radius, posY - radius, posZ + radius); glVertex3f(posX - radius, posY - radius, posZ + radius); glVertex3f(posX - radius, posY - radius, posZ - radius); glVertex3f(posX + radius, posY - radius, posZ - radius); } glEnd(); glPopMatrix(); //right side glPushMatrix(); glBegin(GL_QUADS); { glColor3f(1.0f,0.0f,1.0f); // ?? color glVertex3f(posX + radius, posY + radius, posZ + radius); glVertex3f(posX + radius, posY - radius, posZ + radius); glVertex3f(posX + radius, posY - radius, posZ - radius); glVertex3f(posX + radius, posY + radius, posZ - radius); } glEnd(); glPopMatrix(); //left side glPushMatrix(); glBegin(GL_QUADS); { glColor3f(0.0f,1.0f,1.0f); // ?? color glVertex3f(posX - radius, posY + radius, posZ - radius); glVertex3f(posX - radius, posY - radius, posZ - radius); glVertex3f(posX - radius, posY - radius, posZ + radius); glVertex3f(posX - radius, posY + radius, posZ + radius); } glEnd(); glPopMatrix(); //front side glPushMatrix(); glBegin(GL_QUADS); { glColor3f(0.0f,0.0f,1.0f); //blue glVertex3f(posX + radius, posY + radius, posZ + radius); glVertex3f(posX - radius, posY + radius, posZ + radius); glVertex3f(posX - radius, posY - radius, posZ + radius); glVertex3f(posX + radius, posY - radius, posZ + radius); } glEnd(); glPopMatrix(); //back side glPushMatrix(); glBegin(GL_QUADS); { glColor3f(0.0f,1.0f,0.0f); // green glVertex3f(posX + radius, posY - radius, posZ - radius); glVertex3f(posX - radius, posY - radius, posZ - radius); glVertex3f(posX - radius, posY + radius, posZ - radius); glVertex3f(posX + radius, posY + radius, posZ - radius); } glEnd(); glPopMatrix(); } }

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• Detect two specific objects collision with bullet physics

  - by sebap123

  I have got some problem with defining collision between objects in my game using bullet physics. I know that objects are colliding with each other simultaneously and I don't have to do anything more. However I need to be noticed when one object collides with one of the rest. It is quite awkward written so I will tell what I want to achive. I have got ball which hits wall from tubes. Everything is on the floor. When ball hits wall some fragments fall down to infinity. So I have got bellow floor btStaticPlaneShape. This is place where most of objects is stoping and then I can start another action. But not all of them. So I've been trying to use function checkCollideWith but it isn't good method as it was said in reference and wiki. So I've checked method described in wiki http://bulletphysics.org/mediawiki-1.5.8/index.php/Collision_Callbacks_and_Triggers called contact information. This isn't good method either because it is extremly hard to identify what is what when colliding. You have to also remember that ball is almost all the time colliding with something - floor, wall or eart level. So is there any other method to check what is colliding with what?

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• Updating physics for animated models

  - by Mathias Hölzl

  For a new game we have do set up a scene with a minimum of 30 bone animated models.(shooter) The problem is that the update process for the animated models takes too long. Thats what I do: Each character has ~30 bones and for every update tick the animation gets calculated and every bone fires a event with the new matrix. The physics receives the event with the new matrix and updates the collision shape for that bone. The time that it takes to build the animation isn't that bad (0.2ms for 30 Bones - 6ms for 30 models). But the main problem is that the physic engine (Bullet) uses a diffrent matrix for transformation and so its necessary to convert it. Code for matrix conversion: (~0.005ms) btTransform CLEAR_PHYSICS_API Mat_to_btTransform( Mat mat ) { btMatrix3x3 bulletRotation; btVector3 bulletPosition; XMFLOAT4X4 matData = mat.GetStorage(); // copy rotation matrix for ( int row=0; row<3; ++row ) for ( int column=0; column<3; ++column ) bulletRotation[row][column] = matData.m[column][row]; for ( int column=0; column<3; ++column ) bulletPosition[column] = matData.m[3][column]; return btTransform( bulletRotation, bulletPosition ); } The function for updating the transform(Physic): void CLEAR_PHYSICS_API BulletPhysics::VKinematicMove(Mat mat, ActorId aid) { if ( btRigidBody * const body = FindActorBody( aid ) ) { btTransform tmp = Mat_to_btTransform( mat ); body->setWorldTransform( tmp ); } } The real problem is the function FindActorBody(id): ActorIDToBulletActorMap::const_iterator found = m_actorBodies.find( id ); if ( found != m_actorBodies.end() ) return found->second; All physic actors are stored in m_actorBodies and thats why the updating process takes to long. But I have no idea how I could avoid this. Friendly greedings, Mathias

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• Implementing Circle Physics in Java

  - by Shijima

  I am working on a simple physics based game where 2 balls bounce off each other. I am following a tutorial, 2-Dimensional Elastic Collisions Without Trigonometry, for the collision reactions. I am using Vector2 from the LIBGDX library to handle vectors. I am a bit confused on how to implement step 6 in Java from the tutorial. Below is my current code, please note that the code strictly follows the tutorial and there are redundant pieces of code which I plan to refactor later. Note: refrences to this refer to ball 1, and ball refers to ball 2. /* * Step 1 * * Find the Normal, Unit Normal and Unit Tangential vectors */ Vector2 n = new Vector2(this.position[0] - ball.position[0], this.position[1] - ball.position[1]); Vector2 un = n.normalize(); Vector2 ut = new Vector2(-un.y, un.x); /* * Step 2 * * Create the initial (before collision) velocity vectors */ Vector2 v1 = this.velocity; Vector2 v2 = ball.velocity; /* * Step 3 * * Resolve the velocity vectors into normal and tangential components */ float v1n = un.dot(v1); float v1t = ut.dot(v1); float v2n = un.dot(v2); float v2t = ut.dot(v2); /* * Step 4 * * Find the new tangential Velocities after collision */ float v1tPrime = v1t; float v2tPrime = v2t; /* * Step 5 * * Find the new normal velocities */ float v1nPrime = v1n * (this.mass - ball.mass) + (2 * ball.mass * v2n) / (this.mass + ball.mass); float v2nPrime = v2n * (ball.mass - this.mass) + (2 * this.mass * v1n) / (this.mass + ball.mass); /* * Step 6 * * Convert the scalar normal and tangential velocities into vectors??? */

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• Create indefinitely oscillating pendulum in Farseer Physics 3.3.1/Box2d

  - by GONeale

  I am new to Farseer Physics and using version 3.3.1. I am after some help and would even be happy to receive Box2d answers just to ensure I get a response as I should then be able to convert it! -- Thanks ...After a lot of tinkering around I have managed to produce a thin vertical rectangle shape on the screen and I wish this to swing back and forth pinned at the top up to an angle I set (90 degrees would be fine for this sample). When it is approaching the top I wish it to slow down, then fall back the way it just came, increase speed then obviously slow to a stop at the top again. Almost how a swinging pirate ship would work at a theme park. This is the code I have so far which swings the shape, but it is seeming to lose speed on each swing eventually grinding to a halt: float playerWidth = ConvertUnits.ToSimUnits(5), playerHeight = ConvertUnits.ToSimUnits(68); playerPosition = ConvertUnits.ToSimUnits(-350, 0); playerBody = BodyFactory.CreateRectangle(World, playerWidth, playerHeight, 2f, playerPosition); playerBody.BodyType = BodyType.Dynamic; // create player sprite based on player body _rectangleSprite = new Sprite(ScreenManager.Assets.TextureFromShape(playerBody.FixtureList[0].Shape, MaterialType.Player, Color.Orange, 1f)); // Create swinging joint var joint = JointFactory.CreateFixedRevoluteJoint(World, playerBody, ConvertUnits.ToSimUnits(0, -34), playerBody.Position); If somebody could also provide the command I would need to pause the shape on a mouse click or keyboard command at it's current angle and then continue when I let go of the mouse click that would be super fantastic! (I actually posted this on StackOverflow as well before I realised there was a dedicated game development forum) Cheers

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• Correct way to use Farseer Physics in XNA

  - by user1640602

  I am using Farseer Physics for my 2D sidescroller game and I'm not sure how to proceed with it. I currently have a Sprite class (handles nothing but graphics), a GameObject class (contains specific object info like hit points), a World object which contains the list of Bodies, and a Level object which contains all of these objects. Originally I was trying to keep track of the Sprites, GameObjects, and Bodies separately because I felt that would provide loose coupling but it quickly became a headache. So my new idea was to add a Sprite member to the GameObject class but I'm still not sure how to maintain the Bodies because they have to communicate with GameObject. Specifically, my issue is this: The position of the Body is used to draw the Sprite inside of the Level. In order to do that I would have to maintain a link between GameObjects and Bodies. Is this correct or is there a better way to architect my game? If any of this is unclear please ask and I'll try to clarify. Thank you in advance for any help.

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• Using Bullet physics engine to find the moment of object contact before penetration

  - by MooMoo

  I would like to use Bullet Physics engine to simulate the objects in 3D world. One of the objects in the world will move using the position from 3D mouse control. I will call it "Mouse Object" and any object in the world as "Object A" I define the time before "mouse object" and "Object A" collide as t-1 The time "mouse object" penetrate "Object A" as t Now there is a problem about rendering the scene because when I move the mouse very fast, "Mouse object" will reside in "Object A" before "Object A" start to move. I would like the "Mouse Object" to stop right away attach to the "Object A". Also If the "Object A" move, the "Mouse object" should move following (attach) the "Object A" without stop at the first collision take place. This is what i did I find the position of the "Mouse Object" at time t-1 and time t. I will name it as pos(t-1) and pos(t) The contact time will be sometime between t-1 to t, which the time of contact I name it as t_contact, therefore the contact position (without penetration) between "Mouse object" and "Object A" will be pos(t_contact) then I create multiple "Mouse object"s using this equation pos[n] = pos(t-1) * C * ( pos(t) - pos(t-1) ) where 0 <= C <= 1 if I choose C = 0.1, 0.2, 0.3,0.4..... 1.0, I will get pos[n] for 10 values Then I test collision for all of these 10 "Mouse Objects" and choose the one that seperate between "no collision" and "collision". I feel this method is super non-efficient. I am not sure the way other people find the time-of-contact or the position-of-contact when "Object A" can move.

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• Bullet Physics - Casting a ray straight down from a rigid body (first person camera)

  - by Hydrocity

  I've implemented a first person camera using Bullet--it's a rigid body with a capsule shape. I've only been using Bullet for a few days and physics engines are new to me. I use btRigidBody::setLinearVelocity() to move it and it collides perfectly with the world. The only problem is the Y-value moves freely, which I temporarily solved by setting the Y-value of the translation vector to zero before the body is moved. This works for all cases except when falling from a height. When the body drops off a tall object, you can still glide around since the translate vector's Y-value is being set to zero, until you stop moving and fall to the ground (the velocity is only set when moving). So to solve this I would like to try casting a ray down from the body to determine the Y-value of the world, and checking the difference between that value and the Y-value of the camera body, and disable or slow down movement if the difference is large enough. I'm a bit stuck on simply casting a ray and determining the Y-value of the world where it struck. I've implemented this callback: struct AllRayResultCallback : public btCollisionWorld::RayResultCallback{ AllRayResultCallback(const btVector3& rayFromWorld, const btVector3& rayToWorld) : m_rayFromWorld(rayFromWorld), m_rayToWorld(rayToWorld), m_closestHitFraction(1.0){} btVector3 m_rayFromWorld; btVector3 m_rayToWorld; btVector3 m_hitNormalWorld; btVector3 m_hitPointWorld; float m_closestHitFraction; virtual btScalar addSingleResult(btCollisionWorld::LocalRayResult& rayResult, bool normalInWorldSpace) { if(rayResult.m_hitFraction < m_closestHitFraction) m_closestHitFraction = rayResult.m_hitFraction; m_collisionObject = rayResult.m_collisionObject; if(normalInWorldSpace){ m_hitNormalWorld = rayResult.m_hitNormalLocal; } else{ m_hitNormalWorld = m_collisionObject->getWorldTransform().getBasis() * rayResult.m_hitNormalLocal; } m_hitPointWorld.setInterpolate3(m_rayFromWorld, m_rayToWorld, m_closestHitFraction); return 1.0f; } }; And in the movement function, I have this code: btVector3 from(pos.x, pos.y + 1000, pos.z); // pos is the camera's rigid body position btVector3 to(pos.x, 0, pos.z); // not sure if 0 is correct for Y AllRayResultCallback callback(from, to); Base::getSingletonPtr()->m_btWorld->rayTest(from, to, callback); So I have the callback.m_hitPointWorld vector, which seems to just show the position of the camera each frame. I've searched Google for examples of casting rays, as well as the Bullet documentation, and it's been hard to just find an example. An example is really all I need. Or perhaps there is some method in Bullet to keep the rigid body on the ground? I'm using Ogre3D as a rendering engine, and casting a ray down is quite straightforward with that, however I want to keep all the ray casting within Bullet for simplicity. Could anyone point me in the right direction? Thanks.

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• Bullet Physics implementing custom MotionState class

  - by Arosboro

  I'm trying to make my engine's camera a kinematic rigid body that can collide into other rigid bodies. I've overridden the btMotionState class and implemented setKinematicPos which updates the motion state's tranform. I use the overridden class when creating my kinematic body, but the collision detection fails. I'm doing this for fun trying to add collision detection and physics to Sean O' Neil's Procedural Universe I referred to the bullet wiki on MotionStates for my CPhysicsMotionState class. If it helps I can add the code for the Planetary rigid bodies, but I didn't want to clutter the post. Here is my motion state class: class CPhysicsMotionState: public btMotionState { protected: // This is the transform with position and rotation of the camera CSRTTransform* m_srtTransform; btTransform m_btPos1; public: CPhysicsMotionState(const btTransform &initialpos, CSRTTransform* srtTransform) { m_srtTransform = srtTransform; m_btPos1 = initialpos; } virtual ~CPhysicsMotionState() { // TODO Auto-generated destructor stub } virtual void getWorldTransform(btTransform &worldTrans) const { worldTrans = m_btPos1; } void setKinematicPos(btQuaternion &rot, btVector3 &pos) { m_btPos1.setRotation(rot); m_btPos1.setOrigin(pos); } virtual void setWorldTransform(const btTransform &worldTrans) { btQuaternion rot = worldTrans.getRotation(); btVector3 pos = worldTrans.getOrigin(); m_srtTransform->m_qRotate = CQuaternion(rot.x(), rot.y(), rot.z(), rot.w()); m_srtTransform->SetPosition(CVector(pos.x(), pos.y(), pos.z())); m_btPos1 = worldTrans; } }; I add a rigid body for the camera: // Create rigid body for camera btCollisionShape* cameraShape = new btSphereShape(btScalar(5.0f)); btTransform startTransform; startTransform.setIdentity(); // forgot to add this line CVector vCamera = m_srtCamera.GetPosition(); startTransform.setOrigin(btVector3(vCamera.x, vCamera.y, vCamera.z)); m_msCamera = new CPhysicsMotionState(startTransform, &m_srtCamera); btScalar tMass(80.7f); bool isDynamic = (tMass != 0.f); btVector3 localInertia(0,0,0); if (isDynamic) cameraShape->calculateLocalInertia(tMass,localInertia); btRigidBody::btRigidBodyConstructionInfo rbInfo(tMass, m_msCamera, cameraShape, localInertia); m_rigidBody = new btRigidBody(rbInfo); m_rigidBody->setCollisionFlags(m_rigidBody->getCollisionFlags() | btCollisionObject::CF_KINEMATIC_OBJECT); m_rigidBody->setActivationState(DISABLE_DEACTIVATION); This is the code in Update() that runs each frame: CSRTTransform srtCamera = CCameraTask::GetPtr()->GetCamera(); Quaternion qRotate = srtCamera.m_qRotate; btQuaternion rot = btQuaternion(qRotate.x, qRotate.y, qRotate.z, qRotate.w); CVector vCamera = CCameraTask::GetPtr()->GetPosition(); btVector3 pos = btVector3(vCamera.x, vCamera.y, vCamera.z); CPhysicsMotionState* cameraMotionState = CCameraTask::GetPtr()->GetMotionState(); cameraMotionState->setKinematicPos(rot, pos);

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• Farseer Physics Engine and the Ms-PL License

  - by Stephen Tierney

  Am I able to produce code for a game which uses the Farseer engine and release my code under an open source license other than the Ms-PL? My concern is with the following section from the license: If you distribute any portion of the software in source code form, you may do so only under this license by including a complete copy of this license with your distribution. If you distribute any portion of the software in compiled or object code form, you may only do so under a license that complies with this license. If I do not include Farseer in my source code distribution does this give me an exemption from this clause as I am not distributing the software? My code merely uses its functions. No where in the license does it force you to provide source code for derivative works or linking works, it simply gives you the option of "if you distribute".

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• Box2D physics editor for complex bodies

  - by Paul Manta

  Is there any editor out there that would allow me to define complex entities, with joins connecting their multiple bodies, instead of regular single body entities? For example, an editor that would allow me to 'define' a car as having a main body with two circles as wheels, connected through joints. Clarification: I realize I haven't been clear enough about what I need. I'd like to make my engine data-driven, so all entities (and therefore their Box2D bodies) should be defined externally, not in code. I'm looking for a program like Code 'N' Web's PhysicsEditor, except that one only handles single body entities, no joints or anything like that. Like PhysicsEditor, the program should be configurable so that I can save the data in whatever format I want to. Does anyone know of any such software?

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• Physics-perfect (or somewhere near) 3d sound engine

  - by passcod

  I'm new to game programming, although I have some years of experience in console/web development. My problem is not so much that I can't find what I'm looking for, it's just that I don't have the terminology to actually perform a successful search. I am looking for a physics engine which has great focus on sounds. In fact, I do not care at all for anything else. What I mean is better explained by an example: Suppose a 1st person type game. You are facing North, and someone somewhere around you throws a flute at you (nevermind the absurdity of the situation). The flute spins while it is on its way, making sounds through its holes. There is a wind of say, 5 knots South. I imagine a physics engine will be capable of calculating the trajectory of the flute, as well as the direction it takes after it hits. What I want is for the physics engine to calculate the precise sounds it will make, from any listener's perspective. Does any such engine exists? If there are several, which one would be best for the example above?

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• Why do we use Pythagoras in game physics?

  - by Starkers

  I've recently learned that we use Pythagoras a lot in our physics calculations and I'm afraid I don't really get the point. Here's an example from a book to make sure an object doesn't travel faster than a MAXIMUM_VELOCITY constant in the horizontal plane: MAXIMUM_VELOCITY = <any number>; SQUARED_MAXIMUM_VELOCITY = MAXIMUM_VELOCITY * MAXIMUM_VELOCITY; function animate(){ var squared_horizontal_velocity = (x_velocity * x_velocity) + (z_velocity * z_velocity); if( squared_horizontal_velocity <= SQUARED_MAXIMUM_VELOCITY ){ scalar = squared_horizontal_velocity / SQUARED_MAXIMUM_VELOCITY; x_velocity = x_velocity / scalar; z_velocity = x_velocity / scalar; } } Let's try this with some numbers: An object is attempting to move 5 units in x and 5 units in z. It should only be able to move 5 units horizontally in total! MAXIMUM_VELOCITY = 5; SQUARED_MAXIMUM_VELOCITY = 5 * 5; SQUARED_MAXIMUM_VELOCITY = 25; function animate(){ var x_velocity = 5; var z_velocity = 5; var squared_horizontal_velocity = (x_velocity * x_velocity) + (z_velocity * z_velocity); var squared_horizontal_velocity = 5 * 5 + 5 * 5; var squared_horizontal_velocity = 25 + 25; var squared_horizontal_velocity = 50; // if( squared_horizontal_velocity <= SQUARED_MAXIMUM_VELOCITY ){ if( 50 <= 25 ){ scalar = squared_horizontal_velocity / SQUARED_MAXIMUM_VELOCITY; scalar = 50 / 25; scalar = 2.0; x_velocity = x_velocity / scalar; x_velocity = 5 / 2.0; x_velocity = 2.5; z_velocity = z_velocity / scalar; z_velocity = 5 / 2.0; z_velocity = 2.5; // new_horizontal_velocity = x_velocity + z_velocity // new_horizontal_velocity = 2.5 + 2.5 // new_horizontal_velocity = 5 } } Now this works well, but we can do the same thing without Pythagoras: MAXIMUM_VELOCITY = 5; function animate(){ var x_velocity = 5; var z_velocity = 5; var horizontal_velocity = x_velocity + z_velocity; var horizontal_velocity = 5 + 5; var horizontal_velocity = 10; // if( horizontal_velocity >= MAXIMUM_VELOCITY ){ if( 10 >= 5 ){ scalar = horizontal_velocity / MAXIMUM_VELOCITY; scalar = 10 / 5; scalar = 2.0; x_velocity = x_velocity / scalar; x_velocity = 5 / 2.0; x_velocity = 2.5; z_velocity = z_velocity / scalar; z_velocity = 5 / 2.0; z_velocity = 2.5; // new_horizontal_velocity = x_velocity + z_velocity // new_horizontal_velocity = 2.5 + 2.5 // new_horizontal_velocity = 5 } } Benefits of doing it without Pythagoras: Less lines Within those lines, it's easier to read what's going on ...and it takes less time to compute, as there are less multiplications Seems to me like computers and humans get a better deal without Pythagoras! However, I'm sure I'm wrong as I've seen Pythagoras' theorem in a number of reputable places, so I'd like someone to explain me the benefit of using Pythagoras to a maths newbie. Does this have anything to do with unit vectors? To me a unit vector is when we normalize a vector and turn it into a fraction. We do this by dividing the vector by a larger constant. I'm not sure what constant it is. The total size of the graph? Anyway, because it's a fraction, I take it, a unit vector is basically a graph that can fit inside a 3D grid with the x-axis running from -1 to 1, z-axis running from -1 to 1, and the y-axis running from -1 to 1. That's literally everything I know about unit vectors... not much :P And I fail to see their usefulness. Also, we're not really creating a unit vector in the above examples. Should I be determining the scalar like this: // a mathematical work-around of my own invention. There may be a cleverer way to do this! I've also made up my own terms such as 'divisive_scalar' so don't bother googling var divisive_scalar = (squared_horizontal_velocity / SQUARED_MAXIMUM_VELOCITY); var divisive_scalar = ( 50 / 25 ); var divisive_scalar = 2; var multiplicative_scalar = (divisive_scalar / (2*divisive_scalar)); var multiplicative_scalar = (2 / (2*2)); var multiplicative_scalar = (2 / 4); var multiplicative_scalar = 0.5; x_velocity = x_velocity * multiplicative_scalar x_velocity = 5 * 0.5 x_velocity = 2.5 Again, I can't see why this is better, but it's more "unit-vector-y" because the multiplicative_scalar is a unit_vector? As you can see, I use words such as "unit-vector-y" so I'm really not a maths whiz! Also aware that unit vectors might have nothing to do with Pythagoras so ignore all of this if I'm barking up the wrong tree. I'm a very visual person (3D modeller and concept artist by trade!) and I find diagrams and graphs really, really helpful so as many as humanely possible please!

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