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• About floating point precision and why do we still use it

  - by system_is_b0rken

  Floating point has always been troublesome for precision on large worlds. This article explains behind-the-scenes and offers the obvious alternative - fixed point numbers. Some facts are really impressive, like: "Well 64 bits of precision gets you to the furthest distance of Pluto from the Sun (7.4 billion km) with sub-micrometer precision. " Well sub-micrometer precision is more than any fps needs (for positions and even velocities), and it would enable you to build really big worlds. My question is, why do we still use floating point if fixed point has such advantages? Most rendering APIs and physics libraries use floating point (and suffer it's disadvantages, so developers need to get around them). Are they so much slower? Additionally, how do you think scalable planetary engines like outerra or infinity handle the large scale? Do they use fixed point for positions or do they have some space dividing algorithm?

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• How do I prevent a KActor from changing the orientation of its Z-Axis?

  - by Almo

  So I have an object that inherits from KActor that I would like to behave as a dynamic physics object, but I want its Z-Axis to remain upright, but very stiffly. I've tried the bStayUpright that triggers the "Stay Upright Spring". The problem is, it's a spring, and the object in question oscillates into position when I want it to remain oriented properly without wobbling. In the image above, the yellow block has fallen onto the gray box, and it is currently pivoting about the contact point as it tries to right itself. Should I be tweaking the StayUprightMaxTorque and StayUprightTorqueFactor parameters, or should I be using a Constraint of some sort?

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• what is the easiest way to make a hitbox that rotates with it's texture

  - by Matthew Optional Meehan

  In xna when you have a sprite that doesnt rotate it's very easy to get the four corner of a sprite to make a hitbox, but when you do a rotation the points get moved and I assume there is some kind of math that I can use to aquire them. I am using the four points to draw a rectangle that visually represents the hitboxes. I have seen some per-pixel collission examples but I can forsee they would be hard to draw a box/'convex hull' around. I have also seen physics like farseer but I'm not sure if there is a quick tutorial to do what I want. What do you guys think is the best approach becuase I am looking to complete this work by the end of the week.

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• Who should respond to collision: Unit or projectile?

  - by aleguna

  In an RTS if a projectile hits a unit. Who should handle the collision? If projectile handles the collision, it must be aware of all possible types of units, to know what damage to inflict. For example a bullet will likely kill a human, but it will do nothing to a tank. The same goes if unit handles a collision. So either way one of them should be aware of all possible types of the other. Of course the 'true' way would be to do full physics simulation, but that's not an option for an RTS with 1000s of units and projectiles... So what are the common practicies in this regards?

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• How do I convert matrices intended for OpenGL to be compatible for DirectX?

  - by gardian06

  I have finished working through the book "Game Physics Engine Development 2nd Ed" by Millington, and have got it working, but I want to adapt it to work with DirectX. I understand that D3D9+ has the option to use either left handed, or right handed convention, but I am unsure about how to return my matrices to be usable by D3D. The source code gives returning OpenGL column major matrices (the transpose of the working transform matrix shown below), but DirectX is row major. For those unfamiliar for the organization of the matrices used in the book: [r11 r12 r13 t1] [r21 r22 r23 t2] [r31 r32 r33 t3] [ 0 0 0 1] r## meaning the value of that element in the rotation matrix, and t# meaning the translation value. So the question in short is: How do I convert the matrix above to be easily usable by D3D? All of the documentation that I have found simply states that D3D is row major, but not where to put what elements so that it is usable by D3D in terms of rotation, and translation elements.

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• How do I transition from physics and math to programming?

  - by inovaovao

  I'm a physics PhD with little actual programming experience. I've always liked programming and played around with BASIC, Pascal as a teen, but the extent of my experience writing complex programs comes from an introductory course in computer science. Now I've decided that I'm more interested in programming than in physics and started to learn Java. Coming from a physics or math-heavy background, what would be the best strategy to maximize my value in the field?

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• BOX2D Kinematic Platform with parallax layer

  - by Marcell

  I am using a kinematic body for my moving platform on x-axis, so I set the linear velocity to b2vec2(5,0). When the player jump on the platform, it works like it is suppose to. But the thing is that my platform is on the obstacle layer and I am moving it with the parallax layer. So if I setTransform the kinematic platform to follow the obstacle layer than it's physics will not work and the player will slip-off the platform. I'm developing for iOS and using cocos2d api. Anyway around this?

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• Calculating the force of an impact?

  - by meds

  I'm trying to figure out a way to determine the force two objects collide in. I have two vectors defining their linear velocity at the time of impact, their mass and their angular velocity. Keep in mind this is all for a 2D physics engine. I don't think it's as simple as adding up these values and figuring out if it's large enogh it makes a large impact since that doesn't take into account if the two objects are travelling in the same direction (as an example). Any ideas?

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• Studying Quantum Computing?

  - by The_Neo

  Hi I am a computer science student currently on an internship and I have been thinking more and more about looking into working for a company / places that is developing quantum computers/ing when I graduate. Here is my problem, I have a pretty solid grasp of mathematics involved in Comp Sci and enjoy learning about more Comp Sci theory but in doing some minor research about Quantum Computing it seems to me to be more about hardware and I have always leant more to the software side of things. I haven't studied any physics since high school so I am wondering if I would be suitable to work in such a field with a Comp Sci degree, is it a field more aimed at physicists?

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• What's the best way to handle slopes for a platfomer game using Box2D

  - by songokuhd

  I would like to know if there is any known solution for handling the player's movement on slopes using Box2D engine. I tried to do it using a circle as the player. Everything was fine until I tried to walk on slopes, the main problem is that due to gravity, the circle does not stop on the slope. Please if somebody has tried this before I'll appreciate it. If you have a better solution without the physics engine would be fine for me too. Thank you.

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• Unity, Unrealistic Sphere On Inclined Plane

  - by user1086516

  So I am trying to model a ball rolling down an inclined surface in Unity based on what I am observing in real life but it is still quite off. In Unity it takes the ball about 3 seconds to travel from a place to another specified place where in real life it only takes 1 second. The ball isn't as fast to react to the incline as in real life (even though I have tried giving the ball and surface low or zero friction values) The ball does not accelerate as nearly as fast as it does in real life What do I do to give the ball more realistic behavior ? I have tried messing around with mass, physics materials, drag, and angular drag on the ball and surface but it doesn't seem to be helping.

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• Inverted textures

  - by brainydexter

  I'm trying to draw textures aligned with this physics body whose coordinate system's origin is at the center of the screen. (XNA)Spritebatch has its default origin set to top-left corner. I got the textures to be positioned correctly, but I noticed my textures are vertically inverted. That is, an arrow texture pointing Up , when rendered points down. I'm not sure where I am going wrong with the math. My approach is to convert everything in physic's meter units and draw accordingly. Matrix proj = Matrix.CreateOrthographic(scale * graphics.GraphicsDevice.Viewport.AspectRatio, scale, 0, 1); Matrix view = Matrix.Identity; effect.World = Matrix.Identity; effect.View = view; effect.Projection = proj; effect.TextureEnabled = true; effect.VertexColorEnabled = true; effect.Techniques[0].Passes[0].Apply(); SpriteBatch.Begin(SpriteSortMode.BackToFront, BlendState.AlphaBlend, null, DepthStencilState.Default, RasterizerState.CullNone, effect); m_Paddles[1].Draw(gameTime); SpriteBatch.End(); where Paddle::Draw looks like: SpriteBatch.Draw(paddleTexture, mBody.Position, null, Color.White, 0f, new Vector2(16f, 16f), // origin of the texture 0.1875f, SpriteEffects.None, // width of box is 3*2 = 6 meters. texture is 32 pixels wide. to make it 6 meters wide in world space: 6/32 = 0.1875f 0); The orthographic projection matrix seem fine to me, but I am obviously doing something wrong somewhere! Can someone please help me figure out what am i doing wrong here ? Thanks

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• CERN Announces the Discovery of a Higgs-Boson-like Particle

  - by Jason Fitzpatrick

  CERN scientists dropped a press release today indicating they’ve found a particle consistent with the long sought after Higgs Boson particle–the “God” particle, that could help radically refine our understanding of Standard Model of Particle Physics. For years scientists at CERN have been harnessing the power of the Large Hadron Collider to answer fundamental questions about the nature of particles and the universe around us. In the above video John Ellis, a theoretical physicist, answers the question “What is the Higgs Boson?” The video pairs nicely with the CERN press release: “We observe in our data clear signs of a new particle, at the level of 5 sigma, in the mass region around 126 GeV. The outstanding performance of the LHC and ATLAS and the huge efforts of many people have brought us to this exciting stage,” said ATLAS experiment spokesperson Fabiola Gianotti, “but a little more time is needed to prepare these results for publication.” “The results are preliminary but the 5 sigma signal at around 125 GeV we’re seeing is dramatic. This is indeed a new particle. We know it must be a boson and it’s the heaviest boson ever found,” said CMS experiment spokesperson Joe Incandela. “The implications are very significant and it is precisely for this reason that we must be extremely diligent in all of our studies and cross-checks.” “It’s hard not to get excited by these results,” said CERN Research Director Sergio Bertolucci. “ We stated last year that in 2012 we would either find a new Higgs-like particle or exclude the existence of the Standard Model Higgs. With all the necessary caution, it looks to me that we are at a branching point: the observation of this new particle indicates the path for the future towards a more detailed understanding of what we’re seeing in the data.” How to Use an Xbox 360 Controller On Your Windows PC Download the Official How-To Geek Trivia App for Windows 8 How to Banish Duplicate Photos with VisiPic

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• Why does Farseer 2.x store temporaries as members and not on the stack? (.NET)

  - by Andrew Russell

  UPDATE: This question refers to Farseer 2.x. The newer 3.x doesn't seem to do this. I'm using Farseer Physics Engine quite extensively at the moment, and I've noticed that it seems to store a lot of temporary value types as members of the class, and not on the stack as one might expect. Here is an example from the Body class: private Vector2 _worldPositionTemp = Vector2.Zero; private Matrix _bodyMatrixTemp = Matrix.Identity; private Matrix _rotationMatrixTemp = Matrix.Identity; private Matrix _translationMatrixTemp = Matrix.Identity; public void GetBodyMatrix(out Matrix bodyMatrix) { Matrix.CreateTranslation(position.X, position.Y, 0, out _translationMatrixTemp); Matrix.CreateRotationZ(rotation, out _rotationMatrixTemp); Matrix.Multiply(ref _rotationMatrixTemp, ref _translationMatrixTemp, out bodyMatrix); } public Vector2 GetWorldPosition(Vector2 localPosition) { GetBodyMatrix(out _bodyMatrixTemp); Vector2.Transform(ref localPosition, ref _bodyMatrixTemp, out _worldPositionTemp); return _worldPositionTemp; } It looks like its a by-hand performance optimisation. But I don't see how this could possibly help performance? (If anything I think it would hurt by making objects much larger).

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• Getting into game/game engine programming

  - by Darkslash

  So I am interested in learning game programming, but I really have an interest in the lower level engineering in games. I have openGL experience, and I am really interested in learning more about implementing AI, Physics, etc. I have a computer science degree, so I really like getting into technical stuff. Many times when I ask about this sort of thing, I get a lot of "Use an engine", "Use Unity3d", "Why waste your time writing code that already exists", etc etc. My idea was to use simpler libraries such as SFML or XNA so that I could learn how to implement the more complex systems. The thing is, although I do want to write games, I want to learn things that using something like Unity simply doesnt teach you. My goal is not to make a current generation quality 3D game to sell, I just want to make some cool smaller games and learn all I can about the programming side of game development. Is this something that people just do not do anymore? It seems like everywhere I turn people are using Unity or UDK or GameMaker. I fully understand why you would use a tool like these, but I cant see how they would suit my purposes. So where does someone like myself turn? Am I trying to learn something that people just do not bother doing anymore? Is the innovation in this area gone and just all about gameplay now? Im sorry if this question seems silly, but I am genuinely interested in knowing more about this and meeting more people who are interested in this sort of thing.

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• Semi Fixed-timestep ported to javascript

  - by abernier

  In Gaffer's "Fix Your Timestep!" article, the author explains how to free your physics' loop from the paint one. Here is the final code, written in C: double t = 0.0; const double dt = 0.01; double currentTime = hires_time_in_seconds(); double accumulator = 0.0; State previous; State current; while ( !quit ) { double newTime = time(); double frameTime = newTime - currentTime; if ( frameTime > 0.25 ) frameTime = 0.25; // note: max frame time to avoid spiral of death currentTime = newTime; accumulator += frameTime; while ( accumulator >= dt ) { previousState = currentState; integrate( currentState, t, dt ); t += dt; accumulator -= dt; } const double alpha = accumulator / dt; State state = currentState*alpha + previousState * ( 1.0 - alpha ); render( state ); } I'm trying to implement this in JavaScript but I'm quite confused about the second while loop... Here is what I have for now (simplified): ... (function animLoop(){ ... while (accumulator >= dt) { // While? In a requestAnimation loop? Maybe if? ... } ... // render requestAnimationFrame(animLoop); // stand for the 1st while loop [OK] }()) As you can see, I'm not sure about the while loop inside the requestAnimation one... I thought replacing it with a if but I'm not sure it will be equivalent... Maybe some can help me.

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• What is a simple deformer in which vertices deform linearly with control points?

  - by sebf

  In my project I want to deform a complex mesh, using a simpler 'proxy' mesh. In effect, each vertex of the proxy/collision mesh will be a control point/bone, which should deform the vertices of the main mesh attached to it depending on weight, but where the weight is not dependant on the absolute distance from the control point but rather distance relative to the other affecting control points. The point of this is to preserve complex three dimensional features of the main mesh while using physics implementations which expect something far simpler, low resolution, single surface, etc. Therefore, the vertices must deform linearly with their respective weighted control points (i.e. no falloff fields or all the mesh features will end up collapsed) - as if each vertex was linked to a point on the plane created by the attached control points and deformed with it. I have tried implementing the weight computation algorithm in this paper (page 4) but it is not working as expected and I am wondering if it is really the best way to do what I want. What is the simplest way to 'skin'* an arbitrary mesh, to another arbitrary mesh? *By skin I mean I need an algorithm to determine the best control points for a vertex, and their weights.

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• Coarse Collision Detection in highly dynamic environment

  - by Millianz

  I'm currently working a 3D space game with A LOT of dynamic objects that are all moving (there is pretty much no static environment). I have the collision detection and resolution working just fine, but I am now trying to optimize the collision detection (which is currently O(N^2) -- linear search). I thought about multiple options, a bounding volume hierarchy, a Binary Spatial Partitioning tree, an Octree or a Grid. I however need some help with deciding what's best for my situation. A grid seems unfeasible simply due to the space requirements and cache coherence problems. Since everything is so dynamic however, it seems to be that trees aren't ideal either, since they would have to be completely rebuilt every frame. I must admit I never implemented a physics engine that required spatial partitioning, do I indeed need to rebuild the tree every frame (assuming that everything is constantly moving) or can I update the trees after integrating? Advice is much appreciated - to give some more background: You're flying a space ship in an asteroid field, and there are lots and lots of asteroids and some enemy ships, all of which shoot bullets. EDIT: I came across the "Sweep an Prune" algorithm, which seems like the right thing for my purposes. It appears like the right mixture of fast building of the data structures involved and detailed enough partitioning. This is the best resource I can find: http://www.codercorner.com/SAP.pdf If anyone has any suggestions whether or not I'm going in the right direction, please let me know.

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• In a 2D platform game, how to ensure the player moves smoothly over sloping ground?

  - by Kovsa

  See image: http://i41.tinypic.com/huis13.jpg I'm developing a physics engine for a 2D platform game. I'm using the separating axis theorem for collision detection. The ground surface is constructed from oriented bounding boxes, with the player as an axis aligned bounding box. (Specifically, I'm using the algorithm from the book "Realtime Collision Detection" which performs swept collision detection for OBBs using SAT). I'm using a fairly small (close to zero) restitution coefficient in the collision response, to ensure that the dynamic objects don't penetrate the environment. The engine mostly works fine, it's just that I'm concerned about some edge cases that could possibly occur. For example, in the diagram, A, B and C are the ground surface. The player is heading left along B towards A. It seems to me that due to inaccuracy, the player box could be slightly below the box B as it continues up and left. When it reaches A, therefore, the bottom left corner of the player might then collide with the right side of A, which would be undesirable (as the intention is for the player to move smoothly over the top of A). It seems like a similar problem could happen when the player is on top of box C, moving left towards B - the most extreme point of B could collide with the left side of the player, instead of the player's bottom left corner sliding up and left above B. Box2D seems to handle this problem by storing connectivity information for its edge shapes, but I'm not really sure how it uses this information to solve the problem, and after looking at the code I don't really grasp what it's doing. Any suggestions would be greatly appreciated.

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• Need Guidance Making HTML5 Canvas Game Engine

  - by Scriptonaut

  So I have some free time this winter break and want to build a simple 2d HTML5 canvas game engine. Mostly a physics engine that will dictate the way objects move and interact(collisions, etc). I made a basic game here: http://caidenhome.com/HTML%205/pong.html and would like to make more, and thought that this would be a good reason to make a simple framework for this stuff. Here are some questions: Does the scripting language have to be Javascript? What about Ruby? I will probably write it with jQuery because of the selecting powers, but I'm curious either way. Are there any great guides you guys know of? I want a fast guide that will help me bust out this engine sometime in the next 2 weeks, hopefully sooner. What are some good conventions I should be aware of? What's the best way to get sound? At the moment I'm using something like this: var audioElement = document.createElement('audio'); audioElement.setAttribute('src', 'paddle_col.wav'); audioElement.load(); I'm interested in making this engine lightweight and extremely efficient, I will do whatever it takes to get great speeds and processing power. I know this question is fairly vague, but I just need a push in the right direction. Thanks :)

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• Find meeting point of 2 objects in 2D, knowing (constant) speed and slope

  - by Axonn

  I have a gun which fires a projectile which has to hit an enemy. The problem is that the gun has to be automatic, i.e. - choose the angle in which it has to shoot so that the projectile hits the enemy dead in the center. It's been a looooong time since school, and my physics skills are a bit rusty, but they're there. I've been thinking to somehow apply the v = d/t formula to find the time needed for the projectile or enemy to reach a certain point. But the problem is that I can't find the common point for both the projectile and enemy. Yes, I can find a certain point for the projectile, and another for the enemy, but I would need lots of tries to find where the point coincides, which is stupid. There has to be a way to link them together but I can't figure it out. I prepared some drawings and samples: A simple version of my Flash game, dumbed down to the basics, just some shapes: http://axonnsd.org/W/P001/MathSandBox.swf - click the mouse anywhere to fire a projectile. Or, here is an image which describes my problem: So... who has any ideas about how to find x3/y3 - thus leading me to find the angle in which the weapon has to tilt in order to fire a projectile to meet the enemy? EDIT I think it would be clearer if I also mention that I know: the speed of both Enemy and Projectile and the Enemy travels on a straight vertical line.

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• Hydraulics in game

  - by Mungoid

  I'm not completely sure if this would be better in the Physics site or not as this question is more about how hydraulics should work in game as opposed to how they really work (although that is taken into account) - So I apologize if this is in the wrong place. A project we are on, we have a machine with hydraulics that are powered (They don't just look like they move something, they are the only thing moving/turning/lifting something) - However, the hydraulic extends the same speed no matter what it is pushing. So, say there is a 10 ton object attached to one end of the hydraulic and the other end is attached to a plate on the ground. In real life it takes a few seconds to build up pressure depending on how heavy the object is, but in our project the hydraulics don't care about that. It will lift a 100 ton object the same speed as a 10 ton object. We have a way to fake the hydraulic pressurizing by reducing the 'drive amount' (how fast or slow the hydraulic extends) when we sense that it is touching the ground and that does a relatively decent job but we would like to be able to take other things into account like engine speed, ratios, loads, etc. but we aren't too sure what we need to think about. I'm kinda wondering if anyone here has any experience with this and could offer some suggestions on what to take into account?

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• Strange behavior of RigidBody with gravity and impulse applied

  - by Heisenbug

  I'm doing some experiments trying to figure out how physics works in Unity. I created a cube mesh with a BoxCollider and a RigidBody. The cuve is laying on a mesh plane with a BoxCollider. I'm trying to update the object position applying a force on its RigidBody. Inside script FixedUpdate function I'm doing the following: public void FixedUpdate() { if (leftButtonPressed()) this.rigidbody.AddForce( this.transform.forward * this.forceStrength, ForceMode.Impulse); } Despite the object is aligned with the world axis and the force is applied along Z axis, it performs a quite big rotation movement around its y axis. Since I didn't modify the center of mass and the BoxCollider position and dimension, all values should be fine. Removing gravity and letting the object flying without touching the plane, the problem doesn't show. So I suppose it's related to the friction between objects, but I can't understand exactly which is the problem. Why this? What's my mistake? How can I fix this, or what's the right way to do such a moving an object on a plane through a force impulse?

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• Making particle bounce off a line with friction

  - by Dlaor

  So I'm making a game and I need a particle to bounce off a line. I've got this so far: public static Vector2f Reflect(this Vector2f vec, Vector2f axis) //vec is velocity { Vector2f result = vec - 2f * axis * axis.Dot(vec); return result; } Which works fine, but then I decided I wanted to be able to change the bounciness and friction of the bounce. I got bounciness down... public static Vector2f Reflect(this Vector2f vec, Vector2f axis, float bounciness) //Bounciness goes from 0 to 1, 0 being not bouncy and 1 being perfectly bouncy { var reflect = (1 + bounciness); //2f Vector2f result = vec - reflect * axis * axis.Dot(vec); return result; } But when I tried to add friction, everything went to hell and back... public static Vector2f Reflect(this Vector2f vec, Vector2f axis, float bounciness, float friction) //Does not work at all! { var reflect = (1 + bounciness); //2f Vector2f subtract = reflect * axis * axis.Dot(vec); Vector2f subtract2 = axis * axis.Dot(vec); Vector2f result = vec - subtract; result -= axis.PerpendicularLeft() * subtract2.Length() * friction; return result; } Any physics guys willing to help me out with this? (if you're not sure what I mean with the friction of a bounce see this: http://www.metanetsoftware.com/technique/diagrams/A-1_particle_collision.swf)

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• Dynamic Jump spot

  - by Pasquale Sada

  I have an initial velocity V(Vx,Vy,VZ) and a spot where he stands still at S(Sx,Sy,Sz). What I'm trying to achieve is a jump on a spot E(Ex,Ey,Ez) where you have clicked on(only lower or higher spot, because I've in place a simple steering behavior for even terrains). There are no obstacle around. I've implemented a formula that can make him jump in a precise way on a spot but you need to declare an angle: the problem arise when the selected spot is straight above your head. It' pretty lame that the char hang there and can reach a thing that is 1cm above is head. I'll share the code I'm using: Vector3 dir = target - transform.position; // get target direction float h = dir.y; // get height difference dir.y = 0; // retain only the horizontal direction float dist = dir.magnitude ; // get horizontal distance float a = angle * Mathf.Deg2Rad; // convert angle to radians dir.y = dist * Mathf.Tan(a); // set dir to the elevation angle dist += h / Mathf.Tan(a); // correct for small height differences // calculate the velocity magnitude float vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 *a)); return vel * dir.normalized;

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