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  • Want to develop my own primitive physics engine, don't know how to start with it's high-level architecture. Suggestions?

    - by Violet Giraffe
    Few years ago I tried to make a simple 3D game - billiards. Completed like 50%, stuck with physics. Basically, I only need to calculate balls rolling over flat surface, but it would be nice to make something more flexible. I know all the formulas and laws (most of them, anyway). the problem is I have no idea of how to make good physics engine architecture-wise. I tried google and other forums but didn't find what I was looking for. The only suggestion was to look at open-source engine, but I'm not that good a programmer to make heads or tails out of it...

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  • List of header file locations for the Havok Physics Engine

    - by QAH
    Hello everyone! I am trying to integrate the Havok physics engine into my small game. It is a really nice SDK, but the header files are all over the place. Many headers are deeply nested in multiple directories. That gets confusing when you are trying to include headers for different important objects. I would like to know if there is a nice guide that will let you know where certian objects are and what headres they are in. I have already looked at Havok's documentation, and I also looked at the reference manual, but they don't give great detail as to where certain classes are located (header location). Also, is there any programs out there that can scan header files and create a list of where objects can be found? Thanks again

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  • Closest Approach question for math/physics heads

    - by Kyle
    I'm using a Segment to Segment closest approach method which will output the closest distance between two segments of length. These objects are moving at variable speed each, so even when it succeeds I'm currently using a 10-step method and calculating the distance between 2 spheres as they move along the two segments. So, basically the length of each segment is the object's traverse in the physics step, and the radius is the objects radius. By stepping, I can tell where they collide, and if they collide (Sort of; for the MOST part.).. I get the feeling that there could be something better. While I sort of believe that the first closest approach call is required, I think that the method immediately following it is a TAD weak. Can anyone help me out? I can illustrate this if needed. Thanks alot!

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  • Chipmunk Physics or Box2D for C++ 2D GameEngine ?

    - by Mr.Gando
    Hello, I'm developing what it's turning into a "cross-platform" 2D Game Engine, my initial platform target is iPhone OS, but could move on to Android or even some console like the PSP, or Nintendo DS, I want to keep my options open. My engine is developed in C++, and have been reading a lot about Box2D and Chipmunk but still I can't decide which one to use as my Physics Middleware. Chipmunk appears to have been made to be embedded easily, and Box2D seems to be widely used. Chipmunk is C , and Box2D is C++, but I've heard the API's of Box2D are much worse than chipmunk's API's. For now I will be using the engine shape creation and collision detection features for irregular polygons (not concave). I value: 1) Good API's 2) Easy to integrate. 3) Portability. And of course if you notice anything else, I would love to hear it. Which one do you think that would fit my needs better ?

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  • Game network physics collision

    - by Jonas Byström
    How to simulating two client-controlled vehicles colliding (sensibly) in a typical client/server setup for a network game? I did read this eminent blog post on how to do distributed network physics in general (without traditional client prediction), but this question is specifically on how to handle collisions of owned objects. Example Say client A is 20 ms ahead of server, client B 300 ms ahead of server (counting both latency and maximum jitter). This means that when the two vehicles collide, both clients will see the other as 320 ms behind - in the opposite direction of the velocity of the other vehicle. Head-to-head on a Swedish highway means a difference of 16 meters/17.5 yards! What not to try It is virtually impossible to extrapolate the positions, since I also have very complex vehicles with joints and bodies all over, which in turn have linear and angular positions, velocities and accelerations, not to mention states from user input.

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  • From physics to Java programmer?

    - by inovaovao
    I'm a physics phd with little actual programming experience. I've always liked programming and played around with Basic and Pascal (also VB and Delphi) as a teen, but the largest actual project I completed was an assignement for the introductory computer science class in university where I wrote a nice little program (about 1500 lines of pascal) to display functions of 2 variables in 3D. I've had also a couple other projects of a few hundred lines range, but during my phd I didn't have (or take) the time to program more (string theory is hard guys!), beside playing around with ruby. Now I've decided that I'm more interested in programming than in physics and started to learn Java (hoping to pass the certification exam next week) and OO design. Still, I have trouble deciding on what to focus next (Java EE? Web development? algorithms and C programming?) in order to maximize my employement chances. Bear in mind that I'm aiming (mostly) at the swedish job market and that I'm 30 years old. So for the questions: Do you think that I have any chances to start and make a career in IT and programming coming from physics? What would be the best strategy to maximize my value in the field? Do you have suggestions as to where my physics background might be useful?

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  • At the end of my rope

    - by hvgotcodes
    I am a contractor to a big company. Currently, there are three developers on the project, myself included. The problem is the other 2 developers don't really get it. By "it" i mean the following: They don't understand the best practices for the technology we are using. After 6 months of me and others giving them examples there are terrible anti-patterns being used. They are "copy and paste" programmers that produce primarily spaghetti code. They constantly break things, implementing changes but not doing a basic smoke test to see if all is good They refuse/rarely to ask for code-reviews. They refuse/rarely even do basic things like formatting code. No documentation on any classes (jsdocs) Afraid to delete code that doesn't do anything Leave commented code blocks everywhere even though we have version control. I find myself getting more and more frustrated as I format others code, fix bugs, discover functionality that is broken, and create abstractions to remove the spaghetti. I really don't know what to do. I try not to get to frustrated, but it's just a mess. I like these people as people, but I feel like the coding situation is so bad that I could move faster if they simply browsed the web all day. Would it be out of line to ask our manager to review the others svn commit access; commits can only be done after a review by someone who is knowledgeable in what we are doing? As a contractor, I'm not sure if that's the best move. Is there a subtle/not so subtle way of making it clear how many things I am fixing?

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  • iPhone shooter game bullet physics!

    - by user298261
    Hello, Making a new shooter game here in the vein of "Galaga" (my fav shooter game growing up). Here's the code I have for bullet physics: -(IBAction)shootBullet:(id)sender{ imgBullet.hidden = NO; timer = [NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:@selector(fireBullet) userInfo:Nil repeats:YES]; } -(void)fireBullet{ imgBullet.center = CGPointMake(imgBullet.center.x + bulletVelocity.x , imgBullet.center.y + bulletVelocity.y); if(imgBullet.center.y <= 0){ imgBullet.hidden = YES; imgBullet.center = self.view.center; [timer invalidate]; } } Anyway, the obvious issue is that once the bullet leaves the screen, its center is being reset, so I'm reusing the same bullet for each press of the "fire" button. Ideally, I would like the user to be able to spam the "fire" button without causing the program to crash. How would I tinker this existing code so that a bullet object would spawn on the button press each time, and then despawn after it exits the screen, or collides with an enemy? Thank you for any assistance you can offer!

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  • Simple Physics Simulation in java not working.

    - by Static Void Main
    Dear experts, I wanted to implement ball physics and as i m newbie, i adapt the code in tutorial http://adam21.web.officelive.com/Documents/JavaPhysicsTutorial.pdf . i try to follow that as i much as i can, but i m not able to apply all physical phenomenon in code, can somebody please tell me, where i m mistaken or i m still doing some silly programming mistake. The balls are moving when i m not calling bounce method and i m unable to avail the bounce method and ball are moving towards left side instead of falling/ending on floor**, Can some body recommend me some better way or similar easy compact way to accomplish this task of applying physics on two ball or more balls with interactivity. here is code ; import java.awt.*; public class AdobeBall { protected int radius = 20; protected Color color; // ... Constants final static int DIAMETER = 40; // ... Instance variables private int m_x; // x and y coordinates upper left private int m_y; private double dx = 3.0; // delta x and y private double dy = 6.0; private double m_velocityX; // Pixels to move each time move() is called. private double m_velocityY; private int m_rightBound; // Maximum permissible x, y values. private int m_bottomBound; public AdobeBall(int x, int y, double velocityX, double velocityY, Color color1) { super(); m_x = x; m_y = y; m_velocityX = velocityX; m_velocityY = velocityY; color = color1; } public double getSpeed() { return Math.sqrt((m_x + m_velocityX - m_x) * (m_x + m_velocityX - m_x) + (m_y + m_velocityY - m_y) * (m_y + m_velocityY - m_y)); } public void setSpeed(double speed) { double currentSpeed = Math.sqrt(dx * dx + dy * dy); dx = dx * speed / currentSpeed; dy = dy * speed / currentSpeed; } public void setDirection(double direction) { m_velocityX = (int) (Math.cos(direction) * getSpeed()); m_velocityY = (int) (Math.sin(direction) * getSpeed()); } public double getDirection() { double h = ((m_x + dx - m_x) * (m_x + dx - m_x)) + ((m_y + dy - m_y) * (m_y + dy - m_y)); double a = (m_x + dx - m_x) / h; return a; } // ======================================================== setBounds public void setBounds(int width, int height) { m_rightBound = width - DIAMETER; m_bottomBound = height - DIAMETER; } // ============================================================== move public void move() { double gravAmount = 0.02; double gravDir = 90; // The direction for the gravity to be in. // ... Move the ball at the give velocity. m_x += m_velocityX; m_y += m_velocityY; // ... Bounce the ball off the walls if necessary. if (m_x < 0) { // If at or beyond left side m_x = 0; // Place against edge and m_velocityX = -m_velocityX; } else if (m_x > m_rightBound) { // If at or beyond right side m_x = m_rightBound; // Place against right edge. m_velocityX = -m_velocityX; } if (m_y < 0) { // if we're at top m_y = 0; m_velocityY = -m_velocityY; } else if (m_y > m_bottomBound) { // if we're at bottom m_y = m_bottomBound; m_velocityY = -m_velocityY; } // double speed = Math.sqrt((m_velocityX * m_velocityX) // + (m_velocityY * m_velocityY)); // ...Friction stuff double fricMax = 0.02; // You can use any number, preferably less than 1 double friction = getSpeed(); if (friction > fricMax) friction = fricMax; if (m_velocityX >= 0) { m_velocityX -= friction; } if (m_velocityX <= 0) { m_velocityX += friction; } if (m_velocityY >= 0) { m_velocityY -= friction; } if (m_velocityY <= 0) { m_velocityY += friction; } // ...Gravity stuff m_velocityX += Math.cos(gravDir) * gravAmount; m_velocityY += Math.sin(gravDir) * gravAmount; } public Color getColor() { return color; } public void setColor(Color newColor) { color = newColor; } // ============================================= getDiameter, getX, getY public int getDiameter() { return DIAMETER; } public double getRadius() { return radius; // radius should be a local variable in Ball. } public int getX() { return m_x; } public int getY() { return m_y; } } using adobeBall: import java.awt.*; import java.awt.event.*; import javax.swing.*; public class AdobeBallImplementation implements Runnable { private static final long serialVersionUID = 1L; private volatile boolean Play; private long mFrameDelay; private JFrame frame; private MyKeyListener pit; /** true means mouse was pressed in ball and still in panel. */ private boolean _canDrag = false; private static final int MAX_BALLS = 50; // max number allowed private int currentNumBalls = 2; // number currently active private AdobeBall[] ball = new AdobeBall[MAX_BALLS]; public AdobeBallImplementation(Color ballColor) { frame = new JFrame("simple gaming loop in java"); frame.setSize(400, 400); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); pit = new MyKeyListener(); pit.setPreferredSize(new Dimension(400, 400)); frame.setContentPane(pit); ball[0] = new AdobeBall(34, 150, 7, 2, Color.YELLOW); ball[1] = new AdobeBall(50, 50, 5, 3, Color.BLUE); frame.pack(); frame.setVisible(true); frame.setBackground(Color.white); start(); frame.addMouseListener(pit); frame.addMouseMotionListener(pit); } public void start() { Play = true; Thread t = new Thread(this); t.start(); } public void stop() { Play = false; } public void run() { while (Play == true) { // bounce(ball[0],ball[1]); runball(); pit.repaint(); try { Thread.sleep(mFrameDelay); } catch (InterruptedException ie) { stop(); } } } public void drawworld(Graphics g) { for (int i = 0; i < currentNumBalls; i++) { g.setColor(ball[i].getColor()); g.fillOval(ball[i].getX(), ball[i].getY(), 40, 40); } } public double pointDistance (double x1, double y1, double x2, double y2) { return Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)); } public void runball() { while (Play == true) { try { for (int i = 0; i < currentNumBalls; i++) { for (int j = 0; j < currentNumBalls; j++) { if (pointDistance(ball[i].getX(), ball[i].getY(), ball[j].getX(), ball[j].getY()) < ball[i] .getRadius() + ball[j].getRadius() + 2) { // bounce(ball[i],ball[j]); ball[i].setBounds(pit.getWidth(), pit.getHeight()); ball[i].move(); pit.repaint(); } } } try { Thread.sleep(50); } catch (Exception e) { System.exit(0); } } catch (Exception e) { e.printStackTrace(); } } } public static double pointDirection(int x1, int y1, int x2, int y2) { double H = Math.sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)); // The // hypotenuse double x = x2 - x1; // The opposite double y = y2 - y1; // The adjacent double angle = Math.acos(x / H); angle = angle * 57.2960285258; if (y < 0) { angle = 360 - angle; } return angle; } public static void bounce(AdobeBall b1, AdobeBall b2) { if (b2.getSpeed() == 0 && b1.getSpeed() == 0) { // Both balls are stopped. b1.setDirection(pointDirection(b1.getX(), b1.getY(), b2.getX(), b2 .getY())); b2.setDirection(pointDirection(b2.getX(), b2.getY(), b1.getX(), b1 .getY())); b1.setSpeed(1); b2.setSpeed(1); } else if (b2.getSpeed() == 0 && b1.getSpeed() != 0) { // B1 is moving. B2 is stationary. double angle = pointDirection(b1.getX(), b1.getY(), b2.getX(), b2 .getY()); b2.setSpeed(b1.getSpeed()); b2.setDirection(angle); b1.setDirection(angle - 90); } else if (b1.getSpeed() == 0 && b2.getSpeed() != 0) { // B1 is moving. B2 is stationary. double angle = pointDirection(b2.getX(), b2.getY(), b1.getX(), b1 .getY()); b1.setSpeed(b2.getSpeed()); b1.setDirection(angle); b2.setDirection(angle - 90); } else { // Both balls are moving. AdobeBall tmp = b1; double angle = pointDirection(b2.getX(), b2.getY(), b1.getX(), b1 .getY()); double origangle = b1.getDirection(); b1.setDirection(angle + origangle); angle = pointDirection(tmp.getX(), tmp.getY(), b2.getX(), b2.getY()); origangle = b2.getDirection(); b2.setDirection(angle + origangle); } } public static void main(String[] args) { javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { new AdobeBallImplementation(Color.red); } }); } } *EDIT:*ok splitting the code using new approach for gravity from this forum: this code also not working the ball is not coming on floor: public void mymove() { m_x += m_velocityX; m_y += m_velocityY; if (m_y + m_bottomBound > 400) { m_velocityY *= -0.981; // setY(400 - m_bottomBound); m_y = 400 - m_bottomBound; } // ... Bounce the ball off the walls if necessary. if (m_x < 0) { // If at or beyond left side m_x = 0; // Place against edge and m_velocityX = -m_velocityX; } else if (m_x > m_rightBound) { // If at or beyond right side m_x = m_rightBound - 20; // Place against right edge. m_velocityX = -m_velocityX; } if (m_y < 0) { // if we're at top m_y = 1; m_velocityY = -m_velocityY; } else if (m_y > m_bottomBound) { // if we're at bottom m_y = m_bottomBound - 20; m_velocityY = -m_velocityY; } } thanks a lot for any correction and help. jibby

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  • Runge-Kutta (RK4) integration for game physics

    - by Kai
    Gaffer on Games has a great article about using RK4 integration for better game physics. The implementation is straightforward but the math behind it confuses me. I understand derivatives and integrals on a conceptual level but I haven't manipulated equations in a long time. Here's the brunt of Gaffer's implementation: void integrate(State &state, float t, float dt) { Derivative a = evaluate(state, t, 0.0f, Derivative()); Derivative b = evaluate(state, t+dt*0.5f, dt*0.5f, a); Derivative c = evaluate(state, t+dt*0.5f, dt*0.5f, b); Derivative d = evaluate(state, t+dt, dt, c); const float dxdt = 1.0f/6.0f * (a.dx + 2.0f*(b.dx + c.dx) + d.dx); const float dvdt = 1.0f/6.0f * (a.dv + 2.0f*(b.dv + c.dv) + d.dv) state.x = state.x + dxdt * dt; state.v = state.v + dvdt * dt; } Can anybody explain in simple terms how RK4 works? Specifically, why are we averaging the derivatives at 0.0f, 0.5f, 0.5f, and 1.0f? How is averaging derivatives up to the 4th order different from doing a simple euler integration with a smaller timestep? After reading the accepted answer below, and several other articles, I have a grasp on how RK4 works. To answer my own questions: Can anybody explain in simple terms how RK4 works? RK4 takes advantage of the fact that we can get a much better approximation of a function if we use its higher-order derivatives rather than just the first or second derivative. That's why the Taylor series converges much faster than Euler approximations. (take a look at the animation on the right side of that page) Specifically, why are we averaging the derivatives at 0.0f, 0.5f, 0.5f, and 1.0f? The Runge-Kutta method is an approximation of a function that samples derivatives of several points within a timestep, unlike the Taylor series which only samples derivatives of a single point. After sampling these derivatives we need to know how to weigh each sample to get the closest approximation possible. An easy way to do this is to pick constants that coincide with the Taylor series, which is how the constants of a Runge-Kutta equation are determined. This article made it clearer for me: http://web.mit.edu/10.001/Web/Course%5FNotes/Differential%5FEquations%5FNotes/node5.html. Notice how (15) is the Taylor series expansion while (17) is the Runge-Kutta derivation. How is averaging derivatives up to the 4th order different from doing a simple euler integration with a smaller timestep? Mathematically it converges much faster than doing many Euler approximations. Of course, with enough Euler approximations we can gain equal accuracy to RK4, but the computational power needed doesn't justify using Euler.

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  • 3D collision physics. Response when hitting wall, floor or roof

    - by GlamCasvaluir
    I am having problem with the most basic physic response when the player collide with static wall, floor or roof. I have a simple 3D maze, true means solid while false means air: bool bMap[100][100][100]; The player is a sphere. I have keys for moving x++, x--, y++, y-- and diagonal at speed 0.1f (0.1 * ftime). The player can also jump. And there is gravity pulling the player down. Relative movement is saved in: relx, rely and relz. One solid cube on the map is exactly 1.0f width, height and depth. The problem I have is to adjust the player position when colliding with solids, I don't want it to bounce or anything like that, just stop. But if moving diagonal left/up and hitting solid up, the player should continue moving left, sliding along the wall. Before moving the player I save the old player position: oxpos = xpos; oypos = ypos; ozpos = zpos; vec3 direction; direction = vec3(relx, rely, relz); xpos += direction.x*ftime; ypos += direction.y*ftime; zpos += direction.z*ftime; gx = floor(xpos+0.25); gy = floor(ypos+0.25); gz = floor(zpos+0.25); if (bMap[gx][gy][gz] == true) { vec3 normal = vec3(0.0, 0.0, 1.0); // <- Problem. vec3 invNormal = vec3(-normal.x, -normal.y, -normal.z) * length(direction * normal); vec3 wallDir = direction - invNormal; xpos = oxpos + wallDir.x; ypos = oypos + wallDir.y; zpos = ozpos + wallDir.z; } The problem with my version is that I do not know how to chose the correct normal for the cube side. I only have the bool array to look at, nothing else. One theory I have is to use old values of gx, gy and gz, but I do not know have to use them to calculate the correct cube side normal.

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  • how get collision callback of two specific objects using bullet physics?

    - by sebap123
    I have got problem implementing collision callback into my project. I would like to have detection between two specific objects. I have got normall collision but I want one object to stop or change color or whatever when colides with another. I wrote code from bullet wiki: int numManifolds = dynamicsWorld->getDispatcher()->getNumManifolds(); for (int i=0;i<numManifolds;i++) { btPersistentManifold* contactManifold = dynamicsWorld->getDispatcher()->getManifoldByIndexInternal(i); btCollisionObject* obA = static_cast<btCollisionObject*>(contactManifold->getBody0()); btCollisionObject* obB = static_cast<btCollisionObject*>(contactManifold->getBody1()); int numContacts = contactManifold->getNumContacts(); for (int j=0;j<numContacts;j++) { btManifoldPoint& pt = contactManifold->getContactPoint(j); if (pt.getDistance()<0.f) { const btVector3& ptA = pt.getPositionWorldOnA(); const btVector3& ptB = pt.getPositionWorldOnB(); const btVector3& normalOnB = pt.m_normalWorldOnB; bool x = (ContactProcessedCallback)(pt,fallRigidBody,earthRigidBody); if(x) printf("collision\n"); } } } where fallRigidBody is a dynamic body - a sphere and earthRigiBody is static body - StaticPlaneShape and sphere isn't touching earthRigidBody all the time. I have got also other objects that are colliding with sphere and it works fine. But the program detects collision all the time. It doesn't matter if the objects are or aren't colliding. I have also added after declarations of rigid body: earthRigidBody->setCollisionFlags(earthRigidBody->getCollisionFlags() | btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK); fallRigidBody->setCollisionFlags(fallRigidBody->getCollisionFlags() | btCollisionObject::CF_CUSTOM_MATERIAL_CALLBACK); So can someone tell me what I am doing wrong? Maybe it is something simple?

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  • Physics Engine [Collision Response, 2-dimensional] experts, help!! My stack is unstable!

    - 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 hardly stand still! 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: I would try adding a damping term (proportional to velocity) to the Baumgarte. Is this a good idea in general? If not I would not want to waste my time trying to tune the parameter hoping it magically works. 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!! :)

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  • Without using a pre-built physics engine, how can I implement 3-D collision detection from scratch?

    - by Andy Harglesis
    I want to tackle some basic 3-D collision detection and was wondering how engines handle this and give you a pretty interface and make it so easy ... I want to do it all myself, however. 2-D collision detection is extremely simple and can be done multiple ways that even beginner programmers could think up: 1.When the pixels touch; 2.when a rectangle range is exceeded; 3.when a pixel object is detected near another one in a pixel-based rendering engine. But 3-D is different with one dimension, but complex in many more so ... what are the general, basic understanding/examples on how 3-D collision detection can be implemented? Think two shaded, OpenGL cubes that are moved next to each other with a simple OpenGL rendering context and keyboard events.

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  • Physics Loop in a NodeJS/Socket.IO Environment

    - by Thomas Mosey
    I'm developing a 2D HTML5 Canvas Game, and I am trying to think of the most efficient way to implement a Physics Loop on the server-end of things, running NodeJS and Socket.IO. The only method I've thought of is using setTimeout/Interval, is there any better way? Any examples would be appreciated. EDIT: The Game is a top-down Game, like Zelda and older Pokemon Games. Most of the physics done in the loop will be simple intersects.

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  • physics game programming box2d - orientating a turret-like object using torques

    - by egarcia
    This is a problem I hit when trying to implement a game using the LÖVE engine, which covers box2d with Lua scripting. The objective is simple: A turret-like object (seen from the top, on a 2D environment) needs to orientate itself so it points to a target. The turret is on the x,y coordinates, and the target is on tx, ty. We can consider that x,y are fixed, but tx, ty tend to vary from one instant to the other (i.e. they would be the mouse cursor). The turret has a rotor that can apply a rotational force (torque) on any given moment, clockwise or counter-clockwise. The magnitude of that force has an upper limit called maxTorque. The turret also has certain rotational inertia, which acts for angular movement the same way mass acts for linear movement. There's no friction of any kind, so the turret will keep spinning if it has an angular velocity. The turret has a small AI function that re-evaluates its orientation to verify that it points to the right direction, and activates the rotator. This happens every dt (~60 times per second). It looks like this right now: function Turret:update(dt) local x,y = self:getPositon() local tx,ty = self:getTarget() local maxTorque = self:getMaxTorque() -- max force of the turret rotor local inertia = self:getInertia() -- the rotational inertia local w = self:getAngularVelocity() -- current angular velocity of the turret local angle = self:getAngle() -- the angle the turret is facing currently -- the angle of the like that links the turret center with the target local targetAngle = math.atan2(oy-y,ox-x) local differenceAngle = _normalizeAngle(targetAngle - angle) if(differenceAngle <= math.pi) then -- counter-clockwise is the shortest path self:applyTorque(maxTorque) else -- clockwise is the shortest path self:applyTorque(-maxTorque) end end ... it fails. Let me explain with two illustrative situations: The turret "oscillates" around the targetAngle. If the target is "right behind the turret, just a little clock-wise", the turret will start applying clockwise torques, and keep applying them until the instant in which it surpasses the target angle. At that moment it will start applying torques on the opposite direction. But it will have gained a significant angular velocity, so it will keep going clockwise for some time... until the target will be "just behind, but a bit counter-clockwise". And it will start again. So the turret will oscillate or even go in round circles. I think that my turret should start applying torques in the "opposite direction of the shortest path" before it reaches the target angle (like a car braking before stopping). Intuitively, I think the turret should "start applying torques on the opposite direction of the shortest path when it is about half-way to the target objective". My intuition tells me that it has something to do with the angular velocity. And then there's the fact that the target is mobile - I don't know if I should take that into account somehow or just ignore it. How do I calculate when the turret must "start braking"?

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  • Python/Biomolecular Physics- Trying to code a simple stochastic simulation of a system exhibiting co

    - by user359597
    *edited 6/17/10 I'm trying to understand how to improve my code (make it more pythonic). Also, I'm interested in writing more intuitive 'conditionals' that would describe scenarios that are commonplace in biochemistry. The conditional criteria in the below program is explained in Answer #2, but I am not satisfied with it- it is correct, but isn't obvious and isn't easy to implement for more complicated conditional scenarios. Ideas welcome. Comments/criticisms welcome. First posting experience @ stackoverflow- please comment on etiquette if needed. The code generates a list of values that are the solution to the following exercise: "In a programming language of your choice, implement Gillespie’s First Reaction Algorithm to study the temporal behaviour of the reaction A---B in which the transition from A to B can only take place if another compound, C, is present, and where C dynamically interconverts with D, as modelled in the Petri-net below. Assume that there are 100 molecules of A, 1 of C, and no B or D present at the start of the reaction. Set kAB to 0.1 s-1 and both kCD and kDC to 1.0 s-1. Simulate the behaviour of the system over 100 s." def sim(): # Set the rate constants for all transitions kAB = 0.1 kCD = 1.0 kDC = 1.0 # Set up the initial state A = 100 B = 0 C = 1 D = 0 # Set the start and end times t = 0.0 tEnd = 100.0 print "Time\t", "Transition\t", "A\t", "B\t", "C\t", "D" # Compute the first interval transition, interval = transitionData(A, B, C, D, kAB, kCD, kDC) # Loop until the end time is exceded or no transition can fire any more while t <= tEnd and transition >= 0: print t, '\t', transition, '\t', A, '\t', B, '\t', C, '\t', D t += interval if transition == 0: A -= 1 B += 1 if transition == 1: C -= 1 D += 1 if transition == 2: C += 1 D -= 1 transition, interval = transitionData(A, B, C, D, kAB, kCD, kDC) def transitionData(A, B, C, D, kAB, kCD, kDC): """ Returns nTransition, the number of the firing transition (0: A->B, 1: C->D, 2: D->C), and interval, the interval between the time of the previous transition and that of the current one. """ RAB = kAB * A * C RCD = kCD * C RDC = kDC * D dt = [-1.0, -1.0, -1.0] if RAB > 0.0: dt[0] = -math.log(1.0 - random.random())/RAB if RCD > 0.0: dt[1] = -math.log(1.0 - random.random())/RCD if RDC > 0.0: dt[2] = -math.log(1.0 - random.random())/RDC interval = 1e36 transition = -1 for n in range(len(dt)): if dt[n] > 0.0 and dt[n] < interval: interval = dt[n] transition = n return transition, interval if __name__ == '__main__': sim()

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  • Physics in my game confused after restructuring the Game loop

    - by Julian Assange
    Hello! I'm on my way with making a game in Java. Now I have some trouble with an interpolation based game loop in my calculations. Before I used that system the calculation of a falling object was like this: Delta based system private static final float SPEED_OF_GRAVITY = 500.0f; @Override public void update(float timeDeltaSeconds, Object parentObject) { parentObject.y = parentObject.y + (parentObject.yVelocity * timeDeltaSeconds); parentObject.yVelocity -= SPEED_OF_GRAVITY * timeDeltaSeconds; ...... What you see here is that I used that delta value from previous frame to the current frame to calculate the physics. Now I switched and implement a interpolation based system and I actually left the current system where I used delta to calculate my physics. However, with the interpolation system the delta time is removed - but now are my calculations screwed up and I've tried the whole day to solve this: Interpolation based system private static final float SPEED_OF_GRAVITY = 500.0f; @Override public void update(Object parentObject) { parentObject.y = parentObject.y + (parentObject.yVelocity); parentObject.yVelocity -= SPEED_OF_GRAVITY; ...... I'm totally clueless - how should this be solved? The rendering part is solved with a simple prediction method. With the delta system I could see my object be smoothly rendered to the screen, but with this interpolation/prediction method the object just appear sticky for one second and then it's gone. The core of this game loop is actually from here deWiTTERS Game Loop, where I trying to implement the last solution he describes. Shortly - my physics are in a mess and this need to be solved. Any ideas? Thanks in advance!

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  • Engine for 2D Top-Down Physics-Based Skeletal Animation

    - by RylandAlmanza
    I just watched at the Sui Generis video, and was completely amazed. Specifically, the part where the big troll thing is beating up the player with his flail. This got me really excited, and I would like to try implementing something like this in a 2D Top-Down format. Something like this. That atloria example seems simple enough, but it's not exactly what I'm looking to make. I think atloria is using predefined animations, where as I would like to make something more physics-based like the Sui Generis engine does. So, I'm wondering what physics engines might work for something like this, and if I'd need to implement my own skeletal system, or if I could just use "joints" and such from the engine. The only experience I have in terms of physics engines is Box2D, which I've heard shouldn't be used for top-down settings, and I can think of a few reasons it wouldn't work out well. One of those reasons being gravity. In box 2D, gravity pulls towards a side of the screen (usually the bottom.) I wouldn't want my player's forearms constantly being pulled to one side. :) Also should mention that the programming language doesn't matter all that much to me. I'm currently playing with HTML5 stuff, though. :) Thanks in advance!

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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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  • Multiplayer / Networking options for a 2D game with physics

    - by lahmas
    Summary: My 50% finished 2D sidescroller with Box2D as physics engine should have multiplayer support in the final version. However, the current code is just a singleplayer game. What should I do now? And more important, how should I implement multiplayer and combine it with singleplayer? Is it a bad idea to code the singleplayer mode separated from multiplayer mode (like Notch did it with Minecraft)? The performance in singleplayer should be as good as possible (Simulating physics with using a loopback server to implement singleplayer mode would be a problem there) Full background / questions: I'm working on a relatively large 2D game project in C++, with physics as a core element of it. (I use Box2D for that) The finished game should have full multiplayer support, however I made the mistake that I didn't plan the networking part properly and basically worked on a singleplayer game until now. I thought that multiplayer support could be added to the almost finished singleplayer game in a relatively easy and clear way, but apparently, from what I have read this is wrong. I even read that a multiplayer game should be programmed as one from the beginning, with the singleplayer mode actually just consisting of hosting an invisible local server and connecting to it via loopback. (I found out that most FPS game engines do it that way, an example would be Source) So here I am, with my half finished 2D sidescroller game, and I don't really know how to go on. Simply continueing to work on the singleplayer / client seems useless to me now, as I'd have to recode and refactor even more later. First, a general question to anybody who possibly found himself in a situation like this: How should I proceed? Then, the more specific one - I have been trying to find out how I can approach the networking part for my game: (Possible solutions:) Invisible / loopback server for singleplayer This would have the advantage that there basically is no difference between singleplayer and multiplayer mode. Not much additional code would be needed. A big disadvantage: Performance and other limitations in singleplayer. There would be two physics simulations running. One for the client and one for the loopback server. Even if you work around by providing a direct path for the data from the loopback server, through direct communcation by the threads for example, the singleplayer would be limited. This is a problem because people should be allowed to play around with masses of objects at once. Separated singleplayer / Multiplayer mode There would be no server involved in singleplayer mode. I'm not really sure how this would work. But at least I think that there would be a lot of additional work, because all of the singleplayer features would have to be re-implemented or glued to multiplayer mode. Multiplayer mode as a module for singleplayer This is merely a quick thought I had. Multiplayer could consist of a singleplayer game, with an additional networking module loaded and connected to a server, which sends and receives data and updates the singleplayer world. In the retrospective, I regret not having planned the multiplayer mode earlier. I'm really stuck at this point and I hope that somebody here is able to help me!

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  • Best depth sorting method for a Top Down 2D game using a 3D physics engine

    - by Alic44
    I've spent many days googling this and still have issues with my game engine I'd like to ask about, which I haven't seen addressed before. I think the problem is that my game is an unusual combination of a completely 2D graphical approach using XNA's SpriteBatch, and a completely 3D engine (the amazing BEPU physics engine) with rotation mostly disabled. In essence, my question is similar to this one (the part about "faux 3D"), but the difference is that in my game, the player as well as every other creature is represented by 3D objects, and they can all jump, pick up other objects, and throw them around. What this means is that sorting by one value, such as a Z position (how far north/south a character is on the screen) won't work, because as soon as a smaller creature jumps on top of a larger creature, or a box, and walks backwards, the moment its z value is less than that other creature, it will appear to be behind the object it is actually standing on. I actually originally solved this problem by splitting every object in the game into physics boxes which MUST have a Y height equal to their Z depth. I then based the depth sorting value on the object's y position (how high it is off the ground) PLUS its z position (how far north or south it is on the screen). The problem with this approach is that it requires all moving objects in the game to be split graphically into chunks which match up with a physical box which has its y dimension equal to its z dimension. Which is stupid. So, I got inspired last night to rewrite with a fresh approach. My new method is a little more complex, but I think a little more sane: every object which needs to be sorted by depth in the game exposes the interface IDepthDrawable and is added to a list owned by the DepthDrawer object. IDepthDrawable contains: public interface IDepthDrawable { Rectangle Bounds { get; } //possibly change this to a class if struct copying of the xna Rectangle type becomes an issue DepthDrawShape DepthShape { get; } void Draw(SpriteBatch spriteBatch); } The Bounds Rectangle of each IDepthDrawable object represents the 2D Axis-Aligned Bounding Box it will take up when drawn to the screen. Anything that doesn't intersect the screen will be culled at this stage and the remaining on-screen IDepthDrawables will be Bounds tested for intersections with each other. This is where I get a little less sure of what I'm doing. Each group of collisions will be added to a list or other collection, and each list will sort itself based on its DepthShape property, which will have access to the object-to-be-drawn's physics information. For starting out, lets assume everything in the game is an axis aligned 3D Box shape. Boxes are pretty easy to sort. Something like: if (depthShape1.Back > depthShape2.Front) //if depthShape1 is in front of depthShape2. //depthShape1 goes on top. else if (depthShape1.Bottom > depthShape2.Top) //if depthShape1 is above depthShape2. //depthShape1 goes on top. //if neither of these are true, depthShape2 must be in front or above. So, by sorting draw order by several different factors from the physics engine, I believe I can get a really correct draw order. My question is, is this a good way of going about this, or is there some tried and true, tested way which is completely different and has somehow completely eluded me on the internets? And, if this does seem like a good way to remake my draw order sorting, what's the right sorting algorithm for reordering the Bounds Rectangle collision lists, and how do you deal with a Bounds Rectangle colliding with two different object which don't collide with eachother. I know these are solved problems, but I've only been programming for a year so any specific input here will be greatly appreciated. Thanks for reading this far, ye who made it -- sorry it was so long!

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  • multithreading problem with Nvidia PhysX

    - by xcrypt
    I'm having a multithreading problem with Nvidia PhysX. the SDK requires that you call Simulate() (starts computing new physics positions within a new thread) and FetchResults(waits 'till the physics computations are done). Inbetween Simulate() and FetchResults() you may not 'compute new physics' It is proposed (in a sample) that we create a game loop as such: Logic (you may calculate physics here and other stuff) Render + Simulate() at start of Render call and FetchResults at end of Render() call However, this has given me various little errors that stack up: since you actually render the scene that was computed in the previous iteration in the game loop. I wonder if there's a way around this? I've been trying and trying, but I can't think of a solution...

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  • How do I properly use multithreading with Nvidia PhysX?

    - by xcrypt
    I'm having a multithreading problem with Nvidia PhysX. the SDK requires that you call Simulate() (starts computing new physics positions within a new thread) and FetchResults() (waits 'till the physics computations are done). Inbetween Simulate() and FetchResults() you may not "compute new physics". It is proposed (in a sample) that we create a game loop as such: Logic (you may calculate physics here and other stuff) Render + Simulate() at start of Render call and FetchResults at end of Render() call However, this has given me various little errors that stack up: since you actually render the scene that was computed in the previous iteration in the game loop. Does anyone have a solution to this?

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  • SFX Played Once per Collision or Hit

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

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