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  • What is wrong with my Dot Product?

    - by Clay Ellis Murray
    I am trying to make a pong game but I wanted to use dot products to do the collisions with the paddles, however whenever I make a dot product objects it never changes much from .9 this is my code to make vectors vector = { make:function(object){ return [object.x + object.width/2,object.y + object.height/2] }, normalize:function(v){ var length = Math.sqrt(v[0] * v[0] + v[1] * v[1]) v[0] = v[0]/length v[1] = v[1]/length return v }, dot:function(v1,v2){ return v1[0] * v2[0] + v1[1] * v2[1] } } and this is where I am calculating the dot in my code vector1 = vector.normalize(vector.make(ball)) vector2 = vector.normalize(vector.make(object)) dot = vector.dot(vector1,vector2) Here is a JsFiddle of my code currently the paddles don't move. Any help would be greatly appreciated

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  • Interpolate air drag for my game?

    - by Valentin Krummenacher
    So I have a little game which works with small steps, however those steps vary in time, so for example I sometimes have 10 Steps/second and then I have 20 Steps/second. This changes automatically depending on how many steps the user's computer can take. To avoid inaccurate positioning of the game's player object I use y=v0*dt+g*dt^2/2 to determine my objects y-position, where dt is the time since the last step, v0 is the velocity of my object in the beginning of my step and g is the gravity. To calculate the velocity in the end of a step I use v=v0+g*dt what also gives me correct results, independent of whether I use 2 steps with a dt of for example 20ms or one step with a dt of 40ms. Now I would like to introduce air drag. For simplicity's sake I use a=k*v^2 where a is the air drag's acceleration (I am aware that it would usually result in a force, but since I assume 1kg for my object's mass the force is the same as the resulting acceleration), k is a constant (in this case I'm using 0.001) and v is the speed. Now in an infinitely small time interval a is k multiplied by the velocity in this small time interval powered by 2. The problem is that v in the next time interval would depend on the drag of the last which again depends on the v of the last interval and so on... In other words: If I use a=k*v^2 I get different results for my position/velocity when I use 2 steps of 20ms than when I use one step of 40ms. I used to have this problem for my position too, but adding +g*dt^2/2 to the formula for my position fixed the problem since it takes into account that the position depends on the velocity which changes slightly in every infinitely small time interval. Does something like that exist for air drag too? And no, I dont mean anything like Adding air drag to a golf ball trajectory equation or similar, for that kind of method only gives correct results when all my steps are the same. (I hope you can understand my intermediate english, it's not my main language so I would like to say sorry for all the silly mistakes I might have made in my question)

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  • What is wrong with my Dot Product? [Javascript]

    - by Clay Ellis Murray
    I am trying to make a pong game but I wanted to use dot products to do the collisions with the paddles, however whenever I make a dot product objects it never changes much from .9 this is my code to make vectors vector = { make:function(object){ return [object.x + object.width/2,object.y + object.height/2] }, normalize:function(v){ var length = Math.sqrt(v[0] * v[0] + v[1] * v[1]) v[0] = v[0]/length v[1] = v[1]/length return v }, dot:function(v1,v2){ return v1[0] * v2[0] + v1[1] * v2[1] } } and this is where I am calculating the dot in my code vector1 = vector.normalize(vector.make(ball)) vector2 = vector.normalize(vector.make(object)) dot = vector.dot(vector1,vector2) Here is a JsFiddle of my code currently the paddles don't move. Any help would be greatly appreciated

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  • cocos2d: syncing CCAnimation frames with Box2d Shape manipulations

    - by Hezi Cohen
    hi everybody! my cocos2d game currently has a ccsprite attached to a box2d body. during the game i apply different CCAnimations on my sprite, i would like to perform certain manipulations to the box2d body according to the frame currently displayed by the sprite (change rotation of the body, etc.) my current idea on implementing this is to subclass ccsprite and change the setDisplayFrame implementation but i thought somebody here probably did the same and already has a solution, so any suggestions on how to implement this? thanks!

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  • Swinging a sword in Xcode with Sprite Kit

    - by jking14
    I'm working on making an RPG in Xcode, and I'm having a major gameplay issue when it comes to having my character swing his sword in a way that is realistic and gameplay compatible. Right now, when the player taps the screen and the sword is in one of the player's hand, it rotates the upright sword 90 degrees. The sword which is a parent of the player floats in front of the player because of a collision issue I'm looking for any advice anyone can give on how to add a sword to the game and have it swing in a way that looks somewhat realistic and can damage enemies that are more than a single pixel away from the player

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  • How to impale and stack targets correctly according to the collider and its coordinate?

    - by David Dimalanta
    I'm making another simple game, a catch game, where a spawning target game object must be captured using a skewer to impale it. Here how: At the start, the falling object (in red) will fall in a vertical direction (in blue) When aimed properly, the target will fall down along the line of the skewer. (in blue) Then, another target is spawned and will fall vertically. (in red) When aimed successfully again in a streak, the second target will fall along the skewer and stacked. Same process over and over when another target is spawned. However, when I test run it on the scene tab in Unity, when impaled several targets, instead of a smooth flow and stacking it ended up overlaying it instead of stacking it up like a pancake. Here's what it look like: As I noticed when reaching the half-way of my progress, I tried to figure out how to deal with collider bodies without sticking each other so that it will actually stack like in the example of the image at no. 3. Here's the script code I added in the target game object: using UnityEngine; using System.Collections; public class ImpaleStateTest : MonoBehaviour { public GameObject target; public GameObject skewer; public bool drag = false; private float stack; private float impaleCount; void Start () { stack = 0; impaleCount = 0; } void Update () { if(drag) { target.transform.position = new Vector3 (DragTest.dir.transform.position.x, DragTest.dir.transform.position.y - 0.35f, 0); target.transform.rotation = DragTest.degrees; target.rigidbody2D.fixedAngle = true; target.rigidbody2D.isKinematic = true; target.rigidbody2D.gravityScale = 0; if(Input.GetMouseButton(0)) { Debug.Log ("Skewer: " + DragTest.dir.transform.position.x); Debug.Log ("Target: " + target.transform.position.x); } } } void OnTriggerEnter2D(Collider2D collider) { impaleCount++; Debug.Log ("Impaled " + impaleCount + " time(s)!"); drag = true; audio.Play (); } } Aside from that, I'm not sure if it's right but, the only way to stick the impaled targets while dragging the skewer left or right is to get the X coordinates from the skewer only. Is there something else to recommend it in order to improve this behavior as realistic as possible? Please help.

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  • Finding the contact point with SAT

    - by Kai
    The Separating Axis Theorem (SAT) makes it simple to determine the Minimum Translation Vector, i.e., the shortest vector that can separate two colliding objects. However, what I need is the vector that separates the objects along the vector that the penetrating object is moving (i.e. the contact point). I drew a picture to help clarify. There is one box, moving from the before to the after position. In its after position, it intersects the grey polygon. SAT can easily return the MTV, which is the red vector. I am looking to calculate the blue vector. My current solution performs a binary search between the before and after positions until the length of the blue vector is known to a certain threshold. It works but it's a very expensive calculation since the collision between shapes needs to be recalculated every loop. Is there a simpler and/or more efficient way to find the contact point vector?

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  • How to create water like in new super mario bros?

    - by user1103457
    I assume the water in New super mario bros works the same as in the first part of this tutorial: http://gamedev.tutsplus.com/tutorials/implementation/make-a-splash-with-2d-water-effects/ But in new super mario bros the water also has constant waves on the surface, and the splashes look very different. What's also a difference is that in the tutorial, if you create a splash, it first creates a deep "hole" in the water at the origin of the splash. In new super mario bros this hole is absent or much smaller. When I refer to the splashes in new super mario bros I am referring to the splashes that the player creates when jumping in and out of the water. For reference you could use this video: http://www.ign.com/videos/2012/11/17/new-super-mario-bros-u-3-star-coin-walkthrough-sparkling-waters-1-waterspout-beach just after 00:50, when the camera isn't moving you can get a good look at the water and the constant waves. there are also some good examples of the splashes during that time. How do they create the constant waves and the splashes? I am programming in XNA. (I have tried this myself but couldn't really get it all to work well together) (and as bonus questions: how do they create the light spots just under the surface of the waves, and how do they texture the deeper parts of the water? This is the first time I try to create water like this.)

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  • Titan – The Mystery of the Missing Waves

    - by Akemi Iwaya
    The moon Titan holds a unique distinction…it is the only other known ‘object’ in our solar system with a dense atmosphere and stable bodies of surface liquid. Unlike Earth though, there are no waves on Titan. This mystery has planetary scientists baffled and on a quest to understand this incredible phenomenon. Titan: The Mystery of the Missing Waves [YouTube]     

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  • Box2D Platform body not moving player body along with it

    - by onedayitwillmake
    I am creating a game using Box2D (Javascript implementation) - and I added the ability to have a static platform, that is moved along an axis as a function of a sine. My problem is when the player lands on the platform, as the platform moves along the X axis - the player is not moved along with it, as you visually would expect. The player can land on the object, and if it hits the side of the object, it does colide with it and is pushed. This image might explain better than I did: After jumping on to the red platform the player character will fall off as the platform moves to the right UPDATE: Here is a live demo showing the problem: http://onedayitwillmake.com/ChuClone/slideexample.php

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  • How to make a ball fall faster on a ramp? Unity3D/C#

    - by Timothy Williams
    So, I'm making a ball game. Where you pick up the ball, drop it on a ramp, and it flies off in to blocks. The only problem right now is it falls at a normal speed, then lightly falls off, not nearly fast enough to get over the wall and hit the blocks. Is there any way to make the ball go faster down the ramp? Maybe even make it go faster depending on what height you dropped it from (e.g. if you hold it way above the ramp, and drop it, it will drop faster than if you dropped it right above the ramp.) Thanks.

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  • Is there an algorithm for a pool game?

    - by Dmitri
    Hello! I am looking for algorithm to calculate direction and speed of balls in a pool game. I am sure there has to be some type of open source code for this since pool games are some of the oldest computer games I can remember. I mean, when one ball hits another, I need a algorithm to calculate direction of both of them. It will depend of exact angle of where they hit each other and on speed. I want to practice Java coding, so I am looking for java code or package that has this type of code.

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  • 2D Planet Gravity

    - by baked
    I'm trying to make a simple game where a spaceship is launched and then its path is effected by the gravity of planets. Similar to this game: http://sciencenetlinks.com/interactives/gravity.html I wish to know how to replicate the effect the planets have on the spaceship in this game so a spaceship can 'loop' around a planet to change direction. I have managed to achieve some bogus results where the spaceship loops in a huge ellipse around the planet or is only slightly affected by the gravity of a planet using Vectors. Thanks in advance. p.s I have plenty of coding experience just none to do with game dev.

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  • How to make a ball fall faster on a ramp?

    - by Timothy Williams
    So, I'm making a ball game. Where you pick up the ball, drop it on a ramp, and it flies off in to blocks. The only problem right now is it falls at a normal speed, then lightly falls off, not nearly fast enough to get over the wall and hit the blocks. Is there any way to make the ball go faster down the ramp? Maybe even make it go faster depending on what height you dropped it from (e.g. if you hold it way above the ramp, and drop it, it will drop faster than if you dropped it right above the ramp.)

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  • How to change speed without changing path travelled?

    - by Ben Williams
    I have a ball which is being thrown from one side of a 2D space to the other. The formula I am using for calculating the ball's position at any one point in time is: x = x0 + vx0*t y = y0 + vy0*t - 0.5*g*t*t where g is gravity, t is time, x0 is the initial x position, vx0 is the initial x velocity. What I would like to do is change the speed of this ball, without changing how far it travels. Let's say the ball starts in the lower left corner, moves upwards and rightwards in an arc, and finishes in the lower right corner, and this takes 5s. What I would like to be able to do is change this so it takes 10s or 20s, but the ball still follows the same curve and finishes in the same position. How can I achieve this? All I can think of is manipulating t but I don't think that's a good idea. I'm sure it's something simple, but my maths is pretty shaky.

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  • Bullet Physic: Transform body after adding

    - by Mathias Hölzl
    I would like to transform a rigidbody after adding it to the btDiscreteDynamicsWorld. When I use the CF_KINEMATIC_OBJECT flag I am able to transform it but it's static (no collision response/gravity). When I don't use the CF_KINEMATIC_OBJECT flag the transform doesn't gets applied. So how to I transform non-static objects in bullet? DemoCode: btBoxShape* colShape = new btBoxShape(btVector3(SCALING*1,SCALING*1,SCALING*1)); /// Create Dynamic Objects btTransform startTransform; startTransform.setIdentity(); btScalar mass(1.f); //rigidbody is dynamic if and only if mass is non zero, otherwise static bool isDynamic = (mass != 0.f); btVector3 localInertia(0,0,0); if (isDynamic) colShape->calculateLocalInertia(mass,localInertia); btDefaultMotionState* myMotionState = new btDefaultMotionState(); btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,colShape,localInertia); btRigidBody* body = new btRigidBody(rbInfo); body->setCollisionFlags(body->getCollisionFlags()|btCollisionObject::CF_KINEMATIC_OBJECT); body->setActivationState(DISABLE_DEACTIVATION); m_dynamicsWorld->addRigidBody(body); startTransform.setOrigin(SCALING*btVector3( btScalar(0), btScalar(20), btScalar(0) )); body->getMotionState()->setWorldTransform(startTransform);

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  • Farseer: How can I crush Mario? [on hold]

    - by Homer_Simpson
    I want that Mario dies if the box is crushing him. My game has a similar level like this level from New Super Mario Bros. Wii: http://www.youtube.com/watch?v=tYyu6tFAa2M At the beginning of the level, you see some boxes falling to the ground. If a box crushes Mario, he dies. I want to do exactly the same in my game, but I don't know how to do that in Farseer. How can I do that in Farseer 3.3.1? Do you have any suggestions? I don't know how to do the collision detection. I use rectangles for the boxes and ground in Farseer. Mario is a polygon.

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  • How to fetch only the sprites in the player's range of motion for collision testing? (2D, axis aligned sprites)

    - by Twodordan
    I am working on a 2D sprite game for educational purposes. (In case you want to know, it uses WebGl and Javascript) I've implemented movement using the Euler method (and delta time) to keep things simple. Now I'm trying to tackle collisions. The way I wrote things, my game only has rectangular sprites (axis aligned, never rotated) of various/variable sizes. So I need to figure out what I hit and which side of the target sprite I hit (and I'm probably going to use these intersection tests). The old fashioned method seems to be to use tile based grids, to target only a few tiles at a time, but that sounds silly and impractical for my game. (Splitting the whole level into blocks, having each sprite's bounding box fit multiple blocks I might abide. But if the sprites change size and move around, you have to keep changing which tiles they belong to, every frame, it doesn't sound right.) In Flash you can test collision under one point, but it's not efficient to iterate through all the elements on stage each frame. (hence why people use the tile method). Bottom line is, I'm trying to figure out how to test only the elements within the player's range of motion. (I know how to get the range of motion, I have a good idea of how to write a collisionCheck(playerSprite, targetSprite) function. But how do I know which sprites are currently in the player's vicinity to fetch only them?) Please discuss. Cheers!

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  • Kepler orbit : get position on the orbit over time

    - by Artefact2
    I'm developing a space-simulation related game, and I am having some trouble implementing the movement of binary stars, like this: The two stars orbit their centroid, and their trajectories are ellipses. I basically know how to determine the angular velocity at any position, but not the angular velocity over time. So, for a given angle, I can very easily compute the stars position (cf. http://en.wikipedia.org/wiki/Orbit_equation). I'd want to get the stars position over time. The parametric equations of the ellipse works but doesn't give the correct speed : { X(t) = a×cos(t) ; Y(t) = b×sin(t) }. Is it possible, and how can it be done?

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  • How to fo fluid dynamics like Where's My Water?

    - by Edgar Miranda
    There is a game on the app store called "Where's My Water" that is really fun and uses fluid dynamics in it's gameplay. You can check out a video of the game play here... http://www.youtube.com/watch?v=UnFFWnwOohk. You use your finger to remove dirt from the screen, and then the water just flows to the new area. Anyone know what engine this was made in and how they where able to get the fluid dynamics in there? I'm using the Corona SDK for mobile development and want to do something similar like this (a game with fluid dynamics).

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  • Platformer Starter Kit - Collision Issues

    - by Cyral
    I'm having trouble with my game that is based off the XNA Platformer starter kit. My game uses smaller tiles (16x16) then the original (32x40) which I'm thinking may be having an effect on collision (Being it needs to be more precise). Standing on the edge of a tile and jumping causes the player to move off the the tile when he lands. And 80% of the time, when the player lands, he goes flying though SOLID tiles in a diagonal fashion. This is very annoying as it is almost impossible to test other features, when spawning and jumping will result in the player landing in another part of the level or falling off the edge completely. The code is as follows: /// <summary> /// Updates the player's velocity and position based on input, gravity, etc. /// </summary> public void ApplyPhysics(GameTime gameTime) { float elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds; Vector2 previousPosition = Position; // Base velocity is a combination of horizontal movement control and // acceleration downward due to gravity. velocity.X += movement * MoveAcceleration * elapsed; velocity.Y = MathHelper.Clamp(velocity.Y + GravityAcceleration * elapsed, -MaxFallSpeed, MaxFallSpeed); velocity.Y = DoJump(velocity.Y, gameTime); // Apply pseudo-drag horizontally. if (IsOnGround) velocity.X *= GroundDragFactor; else velocity.X *= AirDragFactor; // Prevent the player from running faster than his top speed. velocity.X = MathHelper.Clamp(velocity.X, -MaxMoveSpeed, MaxMoveSpeed); // Apply velocity. Position += velocity * elapsed; Position = new Vector2((float)Math.Round(Position.X), (float)Math.Round(Position.Y)); // If the player is now colliding with the level, separate them. HandleCollisions(); // If the collision stopped us from moving, reset the velocity to zero. if (Position.X == previousPosition.X) velocity.X = 0; if (Position.Y == previousPosition.Y) velocity.Y = 0; } /// <summary> /// Detects and resolves all collisions between the player and his neighboring /// tiles. When a collision is detected, the player is pushed away along one /// axis to prevent overlapping. There is some special logic for the Y axis to /// handle platforms which behave differently depending on direction of movement. /// </summary> private void HandleCollisions() { // Get the player's bounding rectangle and find neighboring tiles. Rectangle bounds = BoundingRectangle; int leftTile = (int)Math.Floor((float)bounds.Left / Tile.Width); int rightTile = (int)Math.Ceiling(((float)bounds.Right / Tile.Width)) - 1; int topTile = (int)Math.Floor((float)bounds.Top / Tile.Height); int bottomTile = (int)Math.Ceiling(((float)bounds.Bottom / Tile.Height)) - 1; // Reset flag to search for ground collision. isOnGround = false; // For each potentially colliding tile, for (int y = topTile; y <= bottomTile; ++y) { for (int x = leftTile; x <= rightTile; ++x) { // If this tile is collidable, ItemCollision collision = Level.GetCollision(x, y); if (collision != ItemCollision.Passable) { // Determine collision depth (with direction) and magnitude. Rectangle tileBounds = Level.GetBounds(x, y); Vector2 depth = RectangleExtensions.GetIntersectionDepth(bounds, tileBounds); if (depth != Vector2.Zero) { float absDepthX = Math.Abs(depth.X); float absDepthY = Math.Abs(depth.Y); // Resolve the collision along the shallow axis. if (absDepthY < absDepthX || collision == ItemCollision.Platform) { // If we crossed the top of a tile, we are on the ground. if (previousBottom <= tileBounds.Top) isOnGround = true; // Ignore platforms, unless we are on the ground. if (collision == ItemCollision.Impassable || IsOnGround) { // Resolve the collision along the Y axis. Position = new Vector2(Position.X, Position.Y + depth.Y); // Perform further collisions with the new bounds. bounds = BoundingRectangle; } } else if (collision == ItemCollision.Impassable) // Ignore platforms. { // Resolve the collision along the X axis. Position = new Vector2(Position.X + depth.X, Position.Y); // Perform further collisions with the new bounds. bounds = BoundingRectangle; } } } } } // Save the new bounds bottom. previousBottom = bounds.Bottom; } It also tends to jitter a little bit sometimes, I'm solved some of this with some fixes I found here on stackexchange, But Ive only seen one other case of the flying though blocks problem. This question seems to have a similar problem in the video, but mine is more crazy. Again this is a very annoying bug! Any help would be greatly appreciated! EDIT: Speed stuff // Constants for controling horizontal movement private const float MoveAcceleration = 13000.0f; private const float MaxMoveSpeed = 1750.0f; private const float GroundDragFactor = 0.48f; private const float AirDragFactor = 0.58f; // Constants for controlling vertical movement private const float MaxJumpTime = 0.35f; private const float JumpLaunchVelocity = -3500.0f; private const float GravityAcceleration = 3400.0f; private const float MaxFallSpeed = 550.0f; private const float JumpControlPower = 0.14f;

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  • How are bullets simulated in video games?

    - by mahen23
    I have been playing games like MW2 recently and, as a programmer, I tend to ask myself how do they make the game so immersive. For example, how to they simulate bullet speed. When an NPC fires a bullet from his gun, does the bullet really travel from his gun to the given target or do they they completely ignore this part and just put a bullet hole on the target? If the bullet is really travelling from the gun to the target, at what speed is it actually travelling?

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  • Grams to Pounds: A Domino Chain Reaction [Video]

    - by Jason Fitzpatrick
    Most of us have seen a domino knock down or two in our day, but this demonstration video shows how a series of increasingly larger dominoes allow a tiny domino to knock over a 100 pound domino. A domino can knock over another domino about 50% larger than itself. A chain of dominos of increasing size makes a kind of mechanical chain reaction that starts with a tiny push and knocks down an impressively large domino. The only question we have after watching the video is: where can we find 29 appropriately sized dominoes? [via Neatorama] HTG Explains: What Is Windows RT and What Does It Mean To Me? HTG Explains: How Windows 8′s Secure Boot Feature Works & What It Means for Linux Hack Your Kindle for Easy Font Customization

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  • How to control a spaceship near a planet in Unity3D?

    - by tyjkenn
    Right now I have spaceship orbiting a small planet. I'm trying to make an effective control system for that spaceship, but it always end up spinning out of control. After spinning the ship to change direction, the thrusters thrust the wrong way. Normal airplane controls don't work, since the ship is able to leave the atmosphere and go to other planets, in the journey going "upside-down". Could someone please enlighten me on how to get thrusters to work the way they are supposed to?

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  • Integration error in high velocity

    - by Elektito
    I've implemented a simple simulation of two planets (simple 2D disks really) in which the only force is gravity and there is also collision detection/response (collisions are completely elastic). I can launch one planet into orbit of the other just fine. The collision detection code though does not work so well. I noticed that when one planet hits the other in a free fall it speeds backward and goes much higher than its original position. Some poking around convinced me that the simplistic Euler integration is causing the error. Consider this case. One object has a mass of 1kg and the other has a mass equal to earth. Say the object is 10 meters above ground. Assume that our dt (delta t) is 1 second. The object goes to the height of 9 meters at the end of the first iteration, 7 at the end of the second, 4 at the end of the third and 0 at the end of the fourth iteration. At this points it hits the ground and bounces back with the speed of 10 meters per second. The problem is with dt=1, on the first iteration it bounces back to a height of 10. It takes several more steps to make the object change its course. So my question is, what integration method can I use which fixes this problem. Should I split dt to smaller pieces when velocity is high? Or should I use another method altogether? What method do you suggest? EDIT: You can see the source code here at github:https://github.com/elektito/diskworld/

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