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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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• "Super meatboy"-ish replay

  - by Ron

  I'm making a platformer built from mini-levels - and I want to create a sort of a replay of all the player tries that the player did for the level. My question is - what is the best way to record the player's actions in-game, so that I could replay them later when he finishes the level. I thought about recording only the player's input and replay them later on, each on a clone of the player. The problem I have with this is with dynamic obstacles (that could be moved around) - if one clone moves them, it throws the simulation off for the rest of the clones. So then I thought about recording every frame the X/Y of the player, and then just replay it - but that seems it could cause a major memory leak and very ineffective. So - does anyone have any ideas? :)

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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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• Creating a frozen bubble clone

  - by Vaughan Hilts

  This photo illustrates the environment: http://i.imgur.com/V4wbp.png I'll shoot the cannon, it'll bounce off the wall and it's SUPPOSED to stick to the bubble. It does at pretty much every other angle. The problem is always reproduced here, when hit off the wall into those bubbles. It also exists in other cases, but I'm not sure what triggers it. What actually happens: The ball will sometimes set to the wrong cell, and my "dropping" code will detect it as a loner and drop it off the stage. *There are many implementations of "Frozen Bubble" on the web, but I can't for the life of me find a good explanation as to how the algorithm for the "Bubble Sticking" works. * I see this: http://www.wikiflashed.com/wiki/BubbleBobble https://frozenbubblexna.svn.codeplex.com/svn/FrozenBubble/ But I can't figure out the algorithims... could anyone explain possibly the general idea behind getting the balls to stick? Code in question: //Counstruct our bounding rectangle for use var nX = currentBall.x + ballvX * gameTime; var nY = currentBall.y - ballvY * gameTime; var movingRect = new BoundingRectangle(nX, nY, 32, 32); var able = false; //Iterate over the cells and draw our bubbles for (var x = 0; x < 8; x++) { for (var y = 0; y < 12; y++) { //Get the bubble at this layout var bubble = bubbleLayout[x][y]; var rowHeight = 27; //If this slot isn't empty, draw if (bubble != null) { var bx = 0, by = 0; if (y % 2 == 0) { bx = x * 32 + 270; by = y * 32 + 45; } else { bx = x * 32 + 270 + 16; by = y * 32 + 45; } //Check var targetBox = new BoundingRectangle(bx, by, 32, 32); if (targetBox.intersects(movingRect)) { able = true; } } } } cellY = Math.round((currentBall.y - 45) / 32); if (cellY % 2 == 0) cellX = Math.round((currentBall.x - 270) / 32); else cellX = Math.round((currentBall.x - 270 - 16) / 32); Any ideas are very much welcome. Things I've tried: Flooring and Ceiling values Changing the wall bounce to a lower value Slowing down the ball None of these seem to affect it. Is there something in my math I'm not getting?

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• Detecting a ledge in Box2D

  - by DormoTheNord

  I'm making a 2D platformer with Box2D. The player needs to be able to grab onto a ledge and pull him/herself up. Right now I have a sensor that extends in every direction from the upper half of the player's body. The logic seems simple enough: if there are tiles inside the sensor and empty space above them, then it's a ledge and the game should act accordingly. The problem is that I can't figure out how to implement that logic with Box2D. Anyone have any ideas?

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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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• 2D Side scroller collision detection

  - by Shanon Simmonds

  I am trying to do some collision detection between objects and tiles, but the tiles do not have there own x and y position, they are just rendered to the x and y position given, there is an array of integers which has the ids of the tiles to use(which are given from an image and all the different colors are assigned different tiles) int x0 = camera.x / 16; int y0 = camera.y / 16; int x1 = (camera.x + screen.width) / 16; int y1 = (camera.y + screen.height) / 16; for(int y = y0; y < y1; y++) { if(y < 0 || y >= height) continue; // height is the height of the level for(int x = x0; x < x1; x++) { if(x < 0 || x >= width) continue; // width is the width of the level getTile(x, y).render(screen, x * 16, y * 16); } } I tried using the levels getTile method to see if the tile that the object was going to advance to, to see if it was a certain tile, but, it seems to only work in some directions. Any ideas on what I'm doing wrong and fixes would be greatly appreciated. What's wrong is that it doesn't collide properly in every direction and also this is how I tested for a collision in the objects class if(!level.getTile((x + xa) / 16, (y + ya) / 16).isSolid()) { x += xa; y += ya; } EDIT: xa and ya represent the direction as well as the movement, if xa is negative it means the object is moving left, if its positive it is moving right, and same with ya except negative for up, positive for down.

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• Intersection points of plane set forming convex hull

  - by Toji

  Mostly looking for a nudge in the right direction here. Given a set of planes (defined as a normal and distance from origin) that form a convex hull, I would like to find the intersection points that form the corners of that hull. More directly, I'm looking for a way to generate a point cloud appropriate to provide to Bullet. Bonus points if someone knows of a way I could give bullet the plane list directly, since I somewhat suspect that's what it's building on the backend anyway.

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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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• 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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• Physic engine for snooker/billard game

  - by Marc Gillé

  I think most billard/snooker games have a lot of problems with their physic engines. They are far away from realistic and you can't really enjoy the game (especially when snooker is your hobby :) ) So I want to try to make an own physic engine (and own snooker game). I think the physic engine is the most important part of such a game. So my question is: Do anybody know an open physic enginge I can start with? Is there any literature about such physic problems?

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• How to implement explosion in OpenGL with a particle effect?

  - by Chan

  I'm relatively new to OpenGL and I'm clueless how to implement explosion. So could anyone give me some ideas how to start? Suppose the explosion occurs at location $(x, y, z)$, then I'm thinking of randomly generate a collection of vectors with $(x, y, z)$ as origin, then draw some particle (glutSolidCube) which move along this vector for some period of time, says after 1000 updates, it disappear. Is this approach feasible? A minimal example would be greatly appreciated.

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• How to implement explosion in OpenGL?

  - by Chan

  I'm relatively new to OpenGL and I'm clueless how to implement explosion. So could anyone give me some ideas how to start? Suppose the explosion occurs at location $(x, y, z)$, then I'm thinking of randomly generate a collection of vectors with $(x, y, z)$ as origin, then draw some particle (glutSolidCube) which move along this vector for some period of time, says after 1000 updates, it disappear. Is this approach feasible? A minimal example would be greatly appreciated.

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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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• What algorithms can I use for bullet movement toward the enemy?

  - by theateist

  I develop 2D strategy game(probably for Android). There are weapons that shooting on enemies. From what I've read in this, this, this and this post I think that I need Linear algebra, but I don't really understand what algorithm I should use so the bullet will go to the target? Do I nee pathfinder, why? Can you please suggest what algorithms and/or books I can use for bullet movement toward the enemy?

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