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• What causes Box2D revolute joints to separate?

  - by nbolton

  I have created a rag doll using dynamic bodies (rectangles) and simple revolute joints (with lower and upper angles). When my rag doll hits the ground (which is a static body) the bodies seem to fidget and the joints separate. It looks like the bodies are sticking to the ground, and the momentum of the rag doll pulls the joint apart (see screenshot below). I'm not sure if it's related, but I'm using the Badlogic GDX Java wrapper for Box2D. Here's some snippets of what I think is the most relevant code: private RevoluteJoint joinBodyParts( Body a, Body b, Vector2 anchor, float lowerAngle, float upperAngle) { RevoluteJointDef jointDef = new RevoluteJointDef(); jointDef.initialize(a, b, a.getWorldPoint(anchor)); jointDef.enableLimit = true; jointDef.lowerAngle = lowerAngle; jointDef.upperAngle = upperAngle; return (RevoluteJoint)world.createJoint(jointDef); } private Body createRectangleBodyPart( float x, float y, float width, float height) { PolygonShape shape = new PolygonShape(); shape.setAsBox(width, height); BodyDef bodyDef = new BodyDef(); bodyDef.type = BodyType.DynamicBody; bodyDef.position.y = y; bodyDef.position.x = x; Body body = world.createBody(bodyDef); FixtureDef fixtureDef = new FixtureDef(); fixtureDef.shape = shape; fixtureDef.density = 10; fixtureDef.filter.groupIndex = -1; fixtureDef.filter.categoryBits = FILTER_BOY; fixtureDef.filter.maskBits = FILTER_STUFF | FILTER_WALL; body.createFixture(fixtureDef); shape.dispose(); return body; } I've skipped the method for creating the head, as it's pretty much the same as the rectangle method (just using a cricle shape). Those methods are used like so: torso = createRectangleBodyPart(x, y + 5, 0.25f, 1.5f); Body head = createRoundBodyPart(x, y + 7.4f, 1); Body leftLegTop = createRectangleBodyPart(x, y + 2.7f, 0.25f, 1); Body rightLegTop = createRectangleBodyPart(x, y + 2.7f, 0.25f, 1); Body leftLegBottom = createRectangleBodyPart(x, y + 1, 0.25f, 1); Body rightLegBottom = createRectangleBodyPart(x, y + 1, 0.25f, 1); Body leftArm = createRectangleBodyPart(x, y + 5, 0.25f, 1.2f); Body rightArm = createRectangleBodyPart(x, y + 5, 0.25f, 1.2f); joinBodyParts(torso, head, new Vector2(0, 1.6f), headAngle); leftLegTopJoint = joinBodyParts(torso, leftLegTop, new Vector2(0, -1.2f), 0.1f, legAngle); rightLegTopJoint = joinBodyParts(torso, rightLegTop, new Vector2(0, -1.2f), 0.1f, legAngle); leftLegBottomJoint = joinBodyParts(leftLegTop, leftLegBottom, new Vector2(0, -1), -legAngle * 1.5f, 0); rightLegBottomJoint = joinBodyParts(rightLegTop, rightLegBottom, new Vector2(0, -1), -legAngle * 1.5f, 0); leftArmJoint = joinBodyParts(torso, leftArm, new Vector2(0, 1), -armAngle * 0.7f, armAngle); rightArmJoint = joinBodyParts(torso, rightArm, new Vector2(0, 1), -armAngle * 0.7f, armAngle);

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• 3D/perspective Top down shooter bullet issues

  - by Tseng

  I'm developing a top-down shooter with multiple levels (ground for ground units, middle level for buildings, top level for air unity). The problem is the collision. Though I can make the collider box of a bullet be long enough to reach the ground (and collide with it), the real issue is optical. When the bullet is fired from a aircraft and collides with some object on the ground (building, ground unit) it will be optically offset due to the perspective camera, because it looks like the shot "by-passed" the target as seen below Is there any way to make the bullets collide perspectively correct? I'm using Unity3d Engine and it offers only simple colliders (box, sphere, cylinder, mesh and wheel), though I don't think a cone-formed collider would solve this issue. I'd need a (cheap) way to check if it's overlapping a destructible object? I thought of casting a ray from the camera through the bullet and if it hits something destructible, trigger an action, but that's quite punctual and maybe to performance heavy on certain number of bullets

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• Jumping with Mecanim synchronization

  - by Abhishek Deb

  I am using Unity3D 4.1 for one of my projects. I have a robot character which is always running. I am using mecanim animation system. What I really want:When I press Space bar, the character should jump up in the air, triggering an animation clip and then by the time it reaches the ground, the animation clip should also end. What actually is happening:When I press Space bar, the character jumps in the air. Animation clip plays as it should, but ends way before it reaches the ground. So, it looks like he is running in the mid air. What have I done: I have this humanoid robot setup with a jump animation bounded with the space bar key. Also, instead of using root motion, I am directly moving the robot from code. //Jumping if(Input.GetKeyDown(KeyCode.Space)){ rigidbody.AddForce(Vector3.up*jumpVelocty); anim.SetBool("Jump",true); } else anim.SetBool("Jump",false); Character's Details: Rigidbody = Mass:30, Freeze rotaion:x,y,z Capsule Collider = Material: metal, center(0,4.5,0), radius:1, height:11 Script = jumpVelocity:20000 Jump Animation Clip: ~ 2 seconds. I am really out of ideas how to synchronize everything. Should I make the character jump in some other way so that it quickly comes down and touches the ground to match the animation clip? If yes, please provide a direction.

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• How do I prevent other dynamic bodies from affecting the player's velocity with Box2D?

  - by Milo

  I'm working on my player object for my game. PhysicsBodyDef def; def.fixedRotation = true; def.density = 1.0f; def.position = Vec2(200.0f, 200.0f); def.isDynamic = true; def.size = Vec2(50.0f,200.0f); m_player.init(def,&m_physicsEngine.getWorld()); This is how he moves: b2Vec2 vel = getBody()->GetLinearVelocity(); float desiredVel = 0; if (m_keys[ALLEGRO_KEY_A] || m_keys[ALLEGRO_KEY_LEFT]) { desiredVel = -5; } else if (m_keys[ALLEGRO_KEY_D] || m_keys[ALLEGRO_KEY_RIGHT]) { desiredVel = 5; } else { desiredVel = 0; } float velChange = desiredVel - vel.x; float impulse = getBody()->GetMass() * velChange; //disregard time factor getBody()->ApplyLinearImpulse( b2Vec2(impulse,0), getBody()->GetWorldCenter(),true); This creates a few problems. First, to move the player at a constant speed he must be given a high velocity. The problem with this is if he just comes in contact with a small box, he makes it move a lot. Now, I can fix this by lowering his density, but then comes my main issue: I need other objects to be able to run into him, but when they do, he should be like a static wall and not move. I'm not sure how to do that without high density. I cannot use collision groups since I still need him to be solid toward other dynamic things. How can this be done? Essentially, how do I prevent other dynamic bodies from affecting the player's velocity?

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• How to calculate turn heading to a missile?

  - by Tony

  I have a missile that is shot from a ship at an angle, the missile then turns towards the target in an arc with a given turn radius. How do I determine the point on the arc when I need to start turning so the missile is heading straight for the target? EDIT What I need to do before I launch the missiles is calculate and draw the flight paths. So in the attached example the launch vehicle has a heading of 90 deg and the targets are behind it. Both missiles are launched at a relative heading of -45deg or + 45 deg to the launch vehicle's heading. The missiles initially turn towards the target with a known turn radius. I have to calculate the point at which the turn takes the missile to heading at which it will turn to directly attack the target. Obviously if the target is at or near 45 degrees then there is no initial turn the missile just goes straight for the target. After the missile is launched the map will also show the missile tracking on this line as indication of its flight path. What I am doing is working on a simulator which mimics operational software. So I need to draw the calculated flight path before I allow the missile to be launched. In this example the targets are behind the launch vehicle but the precalculated paths are drawn.

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• Simple project - make a 3D box tumble and fall to the ground [closed]

  - by Dominic Bou-Samra

  Possible Duplicate: Resources to learn programming rigid body simulation Hi guys, I want to try learning rigid-body dynamic simulation. I have done a fluid and cloth simulation before, but never anything rigid. My maths knowledge is limited in that I don't know the notation that well. Are there any good cliff-notes, tutorials, guides on how I would accomplish a simple task like this? I don't want a super complex pdf that's only a little relevant. Thanks.

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• Collision detection via adjacent tiles - sprite too big

  - by BlackMamba

  I have managed to create a collision detection system for my tile-based jump'n'run game (written in C++/SFML), where I check on each update what values the surrounding tiles of the player contain and then I let the player move accordingly (i. e. move left when there is an obstacle on the right side). This works fine when the player sprite is not too big: Given a tile size of 5x5 pixels, my solution worked quite fine with a spritesize of 3x4 and 5x5 pixels. My problem is that I actually need the player to be quite gigantic (34x70 pixels given the same tilesize). When I try this, there seems to be an invisible, notably smaller boundingbox where the player collides with obstacles, the player also seems to shake strongly. Here some images to explain what I mean: Works: http://tinypic.com/r/207lvfr/8 Doesn't work: http://tinypic.com/r/2yuk02q/8 Another example of non-functioning: http://tinypic.com/r/kexbwl/8 (the player isn't falling, he stays there in the corner) My code for getting the surrounding tiles looks like this (I removed some parts to make it better readable): std::vector<std::map<std::string, int> > Game::getSurroundingTiles(sf::Vector2f position) { // converting the pixel coordinates to tilemap coordinates sf::Vector2u pPos(static_cast<int>(position.x/tileSize.x), static_cast<int>(position.y/tileSize.y)); std::vector<std::map<std::string, int> > surroundingTiles; for(int i = 0; i < 9; ++i) { // calculating the relative position of the surrounding tile(s) int c = i % 3; int r = static_cast<int>(i/3); // we subtract 1 to place the player in the middle of the 3x3 grid sf::Vector2u tilePos(pPos.x + (c - 1), pPos.y + (r - 1)); // this tells us what kind of block this tile is int tGid = levelMap[tilePos.y][tilePos.x]; // converts the coords from tile to world coords sf::Vector2u tileRect(tilePos.x*5, tilePos.y*5); // storing all the information std::map<std::string, int> tileDict; tileDict.insert(std::make_pair("gid", tGid)); tileDict.insert(std::make_pair("x", tileRect.x)); tileDict.insert(std::make_pair("y", tileRect.y)); // adding the stored information to our vector surroundingTiles.push_back(tileDict); } // I organise the map so that it is arranged like the following: /* * 4 | 1 | 5 * -- -- -- * 2 | / | 3 * -- -- -- * 6 | 0 | 7 * */ return surroundingTiles; } I then check in a loop through the surrounding tiles, if there is a 1 as gid (indicates obstacle) and then check for intersections with that adjacent tile. The problem I just can't overcome is that I think that I need to store the values of all the adjacent tiles and then check for them. How? And may there be a better solution? Any help is appreciated. P.S.: My implementation derives from this blog entry, I mostly just translated it from Objective-C/Cocos2d.

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• What is a technique for 2D ray-box intersection that is suitable for old console hardware?

  - by DJCouchyCouch

  I'm working on a Sega Genesis homebrew game (it has a 7mhz 68000 CPU). I'm looking for a way to find the intersection between a particle sprite and a background tile. Particles are represented as a point with a movement vector. Background tiles are 8 x 8 pixels, with an (X,Y) position that is always located at a multiple of 8. So, really, I need to find the intersection point for a ray-box collision; I need to find out where along the edge of the tile the ray/particle hits. I have these two hard constraints: I'm working with pixel locations (integers). Floating point is too expensive. It doesn't have to be super exact, just close enough. Multiplications, divisions, dot products, et cetera, are incredibly expensive and are to be avoided. So I'm looking for an efficient algorithm that would fit those constraints. Any ideas? I'm writing it in C, so that would work, but assembly should be good as well.

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• Move projectile in direction the gun is facing

  - by Manderin87

  I am attempting to have a projectile follow the direction a gun is facing. When using the following code I am unable to make the projectile go in the right direction. float speed = .5f; float dX = (float) -Math.cos(Math.toRadians(degree)) * speed; float dY = (float) Math.sin(Math.toRadians(degree)) * speed; Can anyone tell me what I am doing wrong? The degree is the direction the gun is facing in degree's.

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• Need help with a complex 3d scene (using Ogre and bullet)

  - by Matthias

  In my setup there is a box with a hole on one side, and a freely movable "stick" (or bar, tube). This stick can be inserted/moved through the hole into the box. This hole is exactly as wide as the diameter of the stick. In reality, when you would now hold the end of the stick in your hand and move the hand left/right or up/down, the other end of the stick, which is inside the box, would move into the opposite direction of your hand movement (because the stick is affixed at the pivot point where it is entering the box through the hole). (I hope you understand what I mean so far.) Now I need to simulate such a setup in a 3d program. I have already successfully developed an Ogre3d framework for this application, including bullet. But what I don't know is how I can implement in my program what I have described above. This application must include two more features: The scene camera is attached to the end of the stick that is inserted into the box. So when the user would move the mouse (to control "his" end of the stick outside the box), then the camera attached to the stick would move in the opposite direction, as described above. The stick has some length, and the user can push it further into the box, or pull it closer to him again. That means of course that the max. radius on which the end of the stick inside the box can move depends on how far the stick is pushed into the box. Thus, the more the stick is pushed into the box, the larger the max. radius of this end of the stick with the camera will be. I understand this is maybe quite a complex thing, so I don't expect any real source code here. I already have the Ogre and bullet part as said up and running, as well as a camera attached to the stick. This works fine. What I don't know though is how I can simulate the setup described above. Especially the requirement that the stick is affixed at the position of the hole on the box, where it is inserted into the box. Any ideas how I could approach to implement the described setup?

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• Calculate gears rotation for a realtime simulation

  - by nkint

  Hi I'm trying to do a game with real time simulations of gears. There is a big Gear with inside a smaller gear. I managed to draw gears with different diameters but equal size teeth, but if i try to move the smaller one inside the bigger one the movement is odd. see the animated gif. the biggest gear is in center C1 and the small in the center C2. I calculate C2 position in this way: C2.x = C1.x + C1_RADIUS-C2_RADIUS) * cos(t); C2.y = C1.y - C1_RADIUS-C2_RADIUS) * sin(t); for t that goes from 0 to TWO_PI in n steps. I apply as rotation the angle t, but maybe it is wrong and i have to calculate another rotation for get a perfect joint

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• Farseer: Cutting body from texture

  - by Robin Betka

  Is it possible to cut a body from a texture in Farseer 3.0? I have a texture converted to a body with multiple fixtures ( using BayazitDecomposer, CreatePolygon method, ..) and can even do it as a BreakableBody. But when I try to cut it with the cutting tool, the fixture itself gets cutted but it's connections get discarded! So when I have 14 fixtures, and cut fixture 3 for example, fixture 3 gets cutted but 1,2 and 3-14 just go away. Is there a way to do it? It would work already if I could convert the texture into a body with 1 fixture only, but I haven't figured out it that's possible. BayazitDecomposer creates the multiple verticles, but letting it away creates something weird and I get assert messages all the time. I know I couldn't break it that way but I don't need that anyway when I could cut it. The breaking is just the work around I'm using now. Extending the cuttingtool to support multiple fixtures is very hard especially when you consider that in one cut multiple fixtures could be cutted and then connected again.

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• Simulating smooth movement along a line after calculating a collision containing a restitution of zero in 2D

  - by Casey

  [for tl;dr see after listing] //...Code to determine shapes types involved in collision here... //...Rectangle-Line collision detected. if(_rbTest->GetCollisionShape()->Intersects(*_ground->GetCollisionShape())) { //Convert incoming shape to a line. a2de::Line l(*dynamic_cast<a2de::Line*>(_ground->GetCollisionShape())); //Get line's normal. a2de::Vector2D normal_vector(l.GetSlope().GetY(), -l.GetSlope().GetX()); a2de::Vector2D::Normalize(normal_vector); //Accumulate forces involved. a2de::Vector2D intermediate_forces; a2de::Vector2D normal_force = normal_vector * _rbTest->GetMass() * _world->GetGravityHandler()->GetGravityValue(); intermediate_forces += normal_force; //Calculate final velocity: See [1] double Ma = _rbTest->GetMass(); a2de::Vector2D Ua = _rbTest->GetVelocity(); double Mb = _ground->GetMass(); a2de::Vector2D Ub = _ground->GetVelocity(); double mCr = Mb * _ground->GetRestitution(); a2de::Vector2D collision_velocity( ((Ma * Ua) + (Mb * Ub) + ((mCr * Ub) - (mCr * Ua))) / (Ma + Mb)); //Calculate reflection vector: See [2] a2de::Vector2D reflect_velocity( -collision_velocity + 2 * (a2de::Vector2D::DotProduct(collision_velocity, normal_vector)) * normal_vector ); //Affect velocity to account for restitution of colliding bodies. reflect_velocity *= (_ground->GetRestitution() * _rbTest->GetRestitution()); _rbTest->SetVelocity(reflect_velocity); //THE ULTIMATE ISSUE STEMS FROM THE FOLLOWING LINE: //Move object away from collision one pixel to prevent constant collision. _rbTest->SetPosition(_rbTest->GetPosition() + normal_vector); _rbTest->ApplyImpulse(intermediate_forces); } Sources: (1) Wikipedia: Coefficient of Restitution: Speeds after impact (2) Wikipedia: Specular Reflection: Direction of reflection First, I have a system in place to account for friction (that is, a coefficient of friction) but is not used right now (in addition, it is zero, which should not affect the math anyway). I'll deal with that after I get this working. Anyway, when the restitution of either object involved in the collision is zero the object stops as required, but if movement along the same direction (again, irrespective of the friction value that isn't used) as the line is attempted the object moves as if slogging through knee deep snow. If I remove the line of code in question and the object is not push away one pixel the object barely moves at all. All because the object collides, is stopped, is pushed up, collides, is stopped...etc. OR collides, is stopped, collides, is stopped, etc... TL;DR How do I only account for a collision ONCE for restitution purposes (BONUS: but CONTINUALLY for frictional purposes, to be implemented later)

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• 2D water with dynamic waves

  - by user1103457

  New Super Mario Bros has really cool 2D water that I'd like to learn how to create. Here's a video showing it. When something hits the water, it creates a wave. There are also constant "background" waves. You can get a good look at the constant waves just after 00:50 when the camera isn't moving. I assume the splashes in NSMB work as in the first part of this tutorial. But in NSMB the water also has constant waves on the surface, and the splashes look very different. Another 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. I am referring to the splashes that the player creates when jumping in and out of the water. How do they create the constant waves and the splashes? I am especially interested in the splashes, and how they work together with the constant waves. I am programming in XNA. I've tried this myself, but couldn't really get it all to work well together. 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. EDIT: I assume the constant waves are created using a sine function. The splashes are probably created in a way like in the tutorial. (But they are not the same, so I am still interested in how to make this kind of splashes) But I have a lot of trouble combining those things. I know I can use the sine function to set the height of a specific watercolumn but the splashes are using the speed, to determine the new height. I can't figure out how to combine those. Not that I am not asking how the developers of new super mario bros did this exactly. I am just interested in ways to recreate an effect like it. This week I have an examweek so I don't have time to work on the code. After this week I will spend a lot of time on it. But I am constantly thinking about it, so that's why I will be checking comments etc. I just won't be looking at the code since it might be too time-consuming.

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• Collisions between moving ball and polygons

  - by miguelSantirso

  I know this is a very typical problem and that there area a lot of similar questions, but I have been looking for a while and I have not found anything that fits what I want. I am developing a 2D game in which I need to perform collisions between a ball and simple polygons. The polygons are defined as an array of vertices. I have implemented the collisions with the bounding boxes of the polygons (that was easy) and I need to refine that collision in the cases where the ball collides with the bounding box. The ball can move quite fast and the polygons are not too big so I need to perform continuous collisions. I am looking for a method that allows me to detect if the ball collides with a polygon and, at the same time, calculate the new direction for the ball after bouncing in the polygon. (I am using XNA, in case that helps)

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• What causes Box2D revolute joints to separate?

  - by nbolton

  I have created a rag doll using dynamic bodies (rectangles) and simple revolute joints (with lower and upper angles). When my rag doll hits the ground (which is a static body) the bodies seem to fidget and the joints separate. It looks like the bodies are sticking to the ground, and the momentum of the rag doll pulls the joint apart (see screenshot below). I'm not sure if it's related, but I'm using the Badlogic GDX Java wrapper for Box2D. Here's some snippets of what I think is the most relevant code: private RevoluteJoint joinBodyParts( Body a, Body b, Vector2 anchor, float lowerAngle, float upperAngle) { RevoluteJointDef jointDef = new RevoluteJointDef(); jointDef.initialize(a, b, a.getWorldPoint(anchor)); jointDef.enableLimit = true; jointDef.lowerAngle = lowerAngle; jointDef.upperAngle = upperAngle; return (RevoluteJoint)world.createJoint(jointDef); } private Body createRectangleBodyPart( float x, float y, float width, float height) { PolygonShape shape = new PolygonShape(); shape.setAsBox(width, height); BodyDef bodyDef = new BodyDef(); bodyDef.type = BodyType.DynamicBody; bodyDef.position.y = y; bodyDef.position.x = x; Body body = world.createBody(bodyDef); FixtureDef fixtureDef = new FixtureDef(); fixtureDef.shape = shape; fixtureDef.density = 10; fixtureDef.filter.groupIndex = -1; fixtureDef.filter.categoryBits = FILTER_BOY; fixtureDef.filter.maskBits = FILTER_STUFF | FILTER_WALL; body.createFixture(fixtureDef); shape.dispose(); return body; } I've skipped the method for creating the head, as it's pretty much the same as the rectangle method (just using a cricle shape). Those methods are used like so: torso = createRectangleBodyPart(x, y + 5, 0.25f, 1.5f); Body head = createRoundBodyPart(x, y + 7.4f, 1); Body leftLegTop = createRectangleBodyPart(x, y + 2.7f, 0.25f, 1); Body rightLegTop = createRectangleBodyPart(x, y + 2.7f, 0.25f, 1); Body leftLegBottom = createRectangleBodyPart(x, y + 1, 0.25f, 1); Body rightLegBottom = createRectangleBodyPart(x, y + 1, 0.25f, 1); Body leftArm = createRectangleBodyPart(x, y + 5, 0.25f, 1.2f); Body rightArm = createRectangleBodyPart(x, y + 5, 0.25f, 1.2f); joinBodyParts(torso, head, new Vector2(0, 1.6f), headAngle); leftLegTopJoint = joinBodyParts(torso, leftLegTop, new Vector2(0, -1.2f), 0.1f, legAngle); rightLegTopJoint = joinBodyParts(torso, rightLegTop, new Vector2(0, -1.2f), 0.1f, legAngle); leftLegBottomJoint = joinBodyParts(leftLegTop, leftLegBottom, new Vector2(0, -1), -legAngle * 1.5f, 0); rightLegBottomJoint = joinBodyParts(rightLegTop, rightLegBottom, new Vector2(0, -1), -legAngle * 1.5f, 0); leftArmJoint = joinBodyParts(torso, leftArm, new Vector2(0, 1), -armAngle * 0.7f, armAngle); rightArmJoint = joinBodyParts(torso, rightArm, new Vector2(0, 1), -armAngle * 0.7f, armAngle);

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• Game Institute Math Courses

  - by W3Geek

  I'm 21 years old and I suck at math, I mean really bad. I don't have the necessary logic to apply it towards programming. I would like to learn the math and logic of applying it. I found Game Institute (http://www.gameinstitute.com) awhile back and heard a lot of praise about them. Are there Math courses any good? Thank you. Edit: My high school was terrible and did not prepare me for any math. I am fairly decent at programming, I just don't have the logic to apply any mathematics to programming, as an example I don't understand the algorithm of finding the size of a user's screen. Yes I have heard of KhanAcademy (http://www.khanacademy.org/) and I have completed a lot of maths on his website but I still don't have the logic to apply any of it to programming.

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• How to make the Angry Birds "shot arch" dotted line? [duplicate]

  - by unexpected62

  This question already has an answer here: Show path of a body of where it should go after linear impulse is applied 2 answers I am making a game that includes 2D projectile flight paths like that of Angry Birds. Angry Birds employs the notion that a previous shot is shown with a dotted line "arch" showing the player where that last shot went. I think recording that data is simple enough once a shot is fired, but in my game, I want to show it preemptively, ie: before the shot. How would I go about calculating this dotted line? The other caveat is I have wind in my game. How can you determine a projectile preemptively when wind will affect it too? This seems like a pretty tough problem. My wind right now just applies a constant force every step of animation in the direction of the wind flow. I'm using Box2D and AndEngine if it matters.

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• Simple collision detection in Unity 2D

  - by N1ghtshade3

  I realise other posts exist with this topic yet none have gone into enough detail for me. I am attempting to create a 2D game in Unity using C# as my scripting language. Basically I have two objects, player and bomb. Both were created simply by dragging the respective PNG to the stage. I have set up touch controls to move player left and right; gravity of any kind is not needed as I only require it to move x units when I tap either the left or right side of the screen. This movement is stored in a script called playerController.cs and works just fine. I also have a variable health = 3 for player, which is stored in healthScript.cs. I am now at a point where I am stuck. I would like it so that when player collides with bomb, health decreases by one and the bomb object is destroyed. So what I tried doing is using a new script called playerPhysics.cs, I added the following: void OnCollisionEnter2D(Collision2D coll){ if(coll.gameObject.name=="bomb") GameObject.Destroy("bomb"); healthScript.health -= 1; } While I'm fairly sure I don't know the proper way to reference a variable in another script and that's why the health didn't decrease when I collided, bomb never disappeared from the stage so I'm thinking there's also a problem with my collision. Initially, I had simply attached playerPhysics.cs to player. After searching around though, it appeared as though player also needed a rigidBody attached to it, so I did that. Still no luck. I tried using a circleCollider (player is a circle), using a rigidBody2D, and using all manner of colliders on one and/or both of the objects. If you could please explain what colliders (if any) should be attached to which objects and whether I need to change my script(s), that would be much more helpful than pointing me to one of the generic documentation examples I've already read. Also, if it would be simple to fix the health thing not working that would be an added bonus but not exactly the focus of this question. Bear in mind that this game is 2D; I'm not sure if that changes anything. Thanks!

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• Bouncing ball slowing down over time

  - by user46610

  I use the unreal engine 4 to bounce a ball off of walls in a 2D space, but over time the ball gets slower and slower. Movement happens in the tick function of the ball FVector location = GetActorLocation(); location.X += this->Velocity.X * DeltaSeconds; location.Y += this->Velocity.Y * DeltaSeconds; SetActorLocation(location, true); When a wall gets hit I get a Hit Event with the normal of the collision. This is how I calculate the new velocity of the ball: FVector2D V = this->Velocity; FVector2D N = FVector2D(HitNormal.X, HitNormal.Y); FVector2D newVelocity = -2 * (V.X * N.X + V.Y * N.Y) * N + V; this->Velocity = newVelocity; Over time, the more the ball bounced around, the velocity gets smaller and smaller. How do I prevent speed loss when bouncing off walls like that? It's supposed to be a perfect bounce without friction or anything.

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• Bounding volume hierarchy - linked nodes (linear model)

  - by teodron

  The scenario A chain of points: (Pi)i=0,N where Pi is linked to its direct neighbours (Pi-1 and Pi+1). The goal: perform efficient collision detection between any two, non-adjacent links: (PiPi+1) vs. (PjPj+1). The question: it's highly recommended in all works treating this subject of collision detection to use a broad phase and to implement it via a bounding volume hierarchy. For a chain made out of Pi nodes, it can look like this: I imagine the big blue sphere to contain all links, the green half of them, the reds a quarter and so on (the picture is not accurate, but it's there to help understand the question). What I do not understand is: How can such a hierarchy speed up computations between segments collision pairs if one has to update it for a deformable linear object such as a chain/wire/etc. each frame? More clearly, what is the actual principle of collision detection broad phases in this particular case/ how can it work when the actual computation of bounding spheres is in itself a time consuming task and has to be done (since the geometry changes) in each frame update? I think I am missing a key point - if we look at the picture where the chain is in a spiral pose, we see that most spheres are already contained within half of others or do intersect them.. it's odd if this is the way it should work.

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• Understanding Box2d Restitution & Bouncing

  - by layzrr

  I'm currently trying to implement basketball bouncing into my game using Box2d (jBox2d technically), but I'm a bit confused about restitution. While trying to create the ball in the testbed first, I've run into infinite bouncing, as described in this question, however obviously not using my own implementation. The Box2d manual describes restitution as follows: Restitution is used to make objects bounce. The restitution value is usually set to be between 0 and 1. Consider dropping a ball on a table. A value of zero means the ball won't bounce. This is called an inelastic collision. A value of one means the ball's velocity will be exactly reflected. This is called a perfectly elastic collision. My confusion lies in that I am still getting infinite bouncing with restitution values at 0.75/0.8. The same behavior can be seen in the testbed under Collision Watching - Varying Restitution, on the 6th and 7th balls. I believe the last one has restitution of 1, which makes sense, but I don't understand why the second to last ball bounces infinitely (as is happening with my working basketball I've created). I am looking to understand the restitution concept more fully, as well as look for a solution to infinite bouncing with the Box2d framework. My instinct was to sleep objects that appeared to be moving in very small increments, but this seems like a misuse of the engine. Should I just work with lower restitution values altogether?

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• following a moving sprite

  - by iQue

  Im trying to get my enemies to follow my main-character of the game (2D), but for some reason the game starts lagging like crazy when I do it the way I want to do it, and the following-part dosnt work 100% either, its just 1/24 enemies that comes to my sprite, the other 23 move towards it but stay at a certain point. Might be a poor explenation but dont know how else to put it. Code for moving my enemies: private int enemyX(){ int x = 0; for (int i = 0; i < enemies.size(); i++){ if (controls.pointerPosition.x > enemies.get(i).getX()){//pointerPosition is the position of my main-sprite. x = 5; } else{ x=-5; } Log.d(TAG, "happyX HERE: " + controls.pointerPosition.x); Log.d(TAG, "enemyX HERE: " + enemies.get(i).getX()); } return x; } private int enemyY(){ int y = 0; for (int i = 0; i < enemies.size(); i++){ if (controls.pointerPosition.y > enemies.get(i).getY()){ y = 5; } else{ y=-5; } } return y; } I send it to the update-method in my Enemy-class: private void drawEnemy(Canvas canvas){ addEnemies(); // a method where I add enemies to my arrayList, no parameters except bitmap. for(int i = 0; i < enemies.size(); i++){ enemies.get(i).update(enemyX(), enemyY()); } for(int i = 0; i < enemies.size(); i++){ enemies.get(i).draw(canvas); } } and finally, the update-method itself, located in my Enemy-class: public void update(int velX, int velY) { x += velX; //sets x before I draw y += velY; //sets y before I draw currentFrame = ++currentFrame % BMP_COLUMNS; } So can any1 figure out why it starts lagging so much and how I can fix it? Thanks for your time!

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• What would be a good filter to create 'magnetic deformers' from a depth map?

  - by sebf

  In my project, I am creating a system for deforming a highly detailed mesh (clothing) so that it 'fits' a convex mesh. To do this I use depth maps of the item and the 'hull' to determine at what point in world space the deviation occurs and the extent. Simply transforming all occluded vertices to the depths as defined by the 'hull' is fairly effective, and has good performance, but it suffers the problem of not preserving the features of the mesh and requires extensive culling to avoid false-positives. I would like instead to generate from the depth deviation map a set of simple 'deformers' which will 'push'* all vertices of the deformed mesh outwards (in world space). This way, all features of the mesh are preserved and there is no need to have complex heuristics to cull inappropriate vertices. I am not sure how to go about generating this deformer set however. I am imagining something like an algorithm that attempts to match a spherical surface to each patch of contiguous deviations within a certain range, but do not know where to start doing this. Can anyone suggest a suitable filter or algorithm for generating deformers? Or to put it another way 'compressing' a depth map? (*Push because its fitting to a convex 'bulgy' humanoid so transforms are likely to be 'spherical' from the POV of the surface.)

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• Breakout... Getting the ball reflection X angle when htitting paddle / bricks

  - by Steven Wilson

  Im currently creating a breakout clone for my first ever C# / XNA game. Currently Ive had little trouble creating the paddle object, ball object, and all the bricks. The issue im currently having is getting the ball to bounce off of the paddle and bricks correctly based off of where the ball touches the object. This is my forumala thus far: if (paddleLocation.Intersects(ballLocation)) { position.Y = paddleLocation.Y - texture.Height; motion.Y *= -1; // determine X motion.X = 1 - 2 * (ballLocation.X - paddleLocation.X) / (paddleLocation.Width / 2); } The problem is, the ball goes the opposite direction then its supposed to. When the ball hits the left side of the paddle, instead of bouncing back to the left, it bounces right, and vise versa. Does anyone know what the math equation is to fix this?

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