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• 3D Box Collision Data Import

  - by cboe

  I'm trying to implement a collision system using oriented bounding boxes, using a center for the box, it's extents as a 3D Vector and a rotation matrix, which is all stuff I picked up online and seem to be somewhat the standard. Detecting the center is no problem so I'm gonna leave these out here. My problem however is importing the data from a 3D file. Say I've placed a box with 2 units length on each side aligned to the world axis. The logic results here are extents of 1,1,1 and I use an identity matrix for rotation - easy. However I'm stuck when I rotate the box in the 3D program, say 30 degrees each axis. How would I parse the box? I only have these 8 vertices as information, and I guess what I would need to do is to find out the rotation of said box, apply it to the vertices so they are aligned to world axes and then calculate the extents out of that. How do I get the rotation of the box when I only have the vertex information of the box available?

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• ray collision with rectangle and floating point accuracy

  - by phq

  I'm trying to solve a problem with a ray bouncing on a box. Actually it is a sphere but for simplicity the box dimensions are expanded by the sphere radius when doing the collision test making the sphere a single ray. It is done by projecting the ray onto all faces of the box and pick the one that is closest. However because I'm using floating point variables I fear that the projected point onto the surface might be interpreted as being below in the next iteration, also I will later allow the sphere to move which might make that scenario more likely. Also the bounce coefficient might be as low as zero, making the sphere continue along the surface. So my naive solution is to project not only forwards but backwards to catch those cases. That is where I got into problems shown in the figure: In the first iteration the first black arrow is calculated and we end up at a point on the surface of the box. In the second iteration the "back projection" hits the other surface making the second black arrow bounce on the wrong surface. If there are several boxes close to each other this has further consequences making the sphere fall through them all. So my main question is how to handle possible floating point accuracy when placing the sphere on the box surface so it does not fall through. In writing this question I got the idea to have a threshold to only accept back projections a certain amount much smaller than the box but larger than the possible accuracy limitation, this would only cause the "false" back projection when the sphere hit the box on an edge which would appear naturally. To clarify my original approach, the arrows shown in the image is not only the path the sphere travels but is also representing a single time step in the simulation. In reality the time step is much smaller about 0.05 of the box size. The path traveled is projected onto possible sides to avoid traveling past a thinner object at higher speeds. In normal situations the floating point accuracy is not an issue but there are two situations where I have the concern. When the new position at the end of the time step is located very close to the surface, very unlikely though. When using a bounce factor of 0, here it happens every time the sphere hit a box. To add some loss of accuracy, the motivation for my concern, is that the sphere and box are in different coordinate systems and thus the sphere location is transformed for every test. This last one is why I'm not willing to stand on luck that one floating point value lying on top of the box always will be interpreted the same. I did not know voronoi regions by name, but looking at it I'm not sure how it would be used in a projection scenario that I'm using here.

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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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• Breakout ball collision detection, bouncing against the walls [solved]

  - by Sri Harsha Chilakapati

  I'm currently trying to program a breakout game to distribute it as an example game for my own game engine. http://game-engine-for-java.googlecode.com/ But the problem here is that I can't get the bouncing condition working properly. Here's what I'm using. public void collision(GObject other){ if (other instanceof Bat || other instanceof Block){ bounce(); } else if (other instanceof Stone){ other.destroy(); bounce(); } //Breakout.HIT.play(); } And here's by bounce() method public void bounce(){ boolean left = false; boolean right = false; boolean up = false; boolean down = false; if (dx < 0) { left = true; } else if (dx > 0) { right = true; } if (dy < 0) { up = true; } else if (dy > 0) { down = true; } if (left && up) { dx = -dx; } if (left && down) { dy = -dy; } if (right && up) { dx = -dx; } if (right && down) { dy = -dy; } } The ball bounces the bat and blocks but when the block is on top of the ball, it won't bounce and moves upwards out of the game. What I'm missing? Is there anything to implement? Please help me.. Thanks EDIT: Have changed the bounce method. public void bounce(GObject other){ //System.out.println("y : " + getY() + " other.y + other.height - 2 : " + (other.getY() + other.getHeight() - 2)); if (getX()+getWidth()>other.getX()+2){ setHorizontalDirection(Direction.DIRECTION_RIGHT); } else if (getX()<(other.getX()+other.getWidth()-2)){ setHorizontalDirection(Direction.DIRECTION_LEFT); } if (getY()+getHeight()>other.getY()+2){ setVerticalDirection(Direction.DIRECTION_UP); } else if (getY()<(other.getY()+other.getHeight()-2)){ setVerticalDirection(Direction.DIRECTION_DOWN); } } EDIT: Solved now. See the changed method in my answer.

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• Tile map collision is not working properly

  - by Sigh-AniDe

  I am having problems setting collision between my sprite and the tiles. I have only done the code for colision for moving upwards but some places on the map it moves up and some places it doesn't. Here is what I have so far: Vector2 position; private static float scalingFactor = 32; static int tileWidth = 32; static int tileHeight = 32; int[ , ] map = { {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, }; // This is in turtle.update if ( keyboardState.IsKeyDown( Keys.Up ) ) { if ( position.Y > screenHeight / 4 ) { //// current position of the turtle on the tiles int mapX = ( int )( position.X / scalingFactor ); int mapY = ( int )( position.Y / scalingFactor ) - 1; if ( isMovable( mapX , mapY , map ) ) { position.Y = position.Y - scalingFactor; } } else { MoveUp(); } } private void MoveUp() { motion.Y = -1; } public bool isMovable( int mapX , int mapY , int[ , ] map ) { if ( mapX < 0 || mapX > 19 || mapY < 0 || mapY > 20 ) { return false; } int tile = map[ mapX , mapY ]; if ( tile == 0 ) { return false; } return true; } protected override void Update( GameTime gameTime ) { turtle.Update( screenHeight , scalingFactor , map ); base.Update( gameTime ); }

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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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• Velocity collision detection (2D)

  - by ultifinitus

  Alright, so I have made a simple game engine (see youtube) And my current implementation of collision resolution has a slight problem, involving the velocity of a platform. Basically I run through all of the objects necessary to detect collisions on and resolve those collisions as I find them. Part of that resolution is setting the player's velocity = the platform's velocity. Which works great! Unless I have a row of platforms moving at different velocities or a platform between a stack of tiles.... (current system) bool player::handle_collisions() { collisions tcol; bool did_handle = false; bool thisObjectHandle = false; for (int temp = 0; temp < collideQueue.size(); temp++) { thisObjectHandle = false; tcol = get_collision(prevPos.x,y,get_img()->get_width(),get_img()->get_height(), collideQueue[temp]->get_position().x,collideQueue[temp]->get_position().y, collideQueue[temp]->get_img()->get_width(),collideQueue[temp]->get_img()->get_height()); if (prevPos.y >= collideQueue[temp]->get_prev_pos().y + collideQueue[temp]->get_img()->get_height()) if (tcol.top > 0) { add_pos(0,tcol.top); set_vel(get_vel().x,collideQueue[temp]->get_vel().y); thisObjectHandle = did_handle = true; } if (prevPos.y + get_img()->get_height() <= collideQueue[temp]->get_prev_pos().y) if (tcol.bottom > 0) { add_pos(collideQueue[temp]->get_vel().x,-tcol.bottom); set_vel(get_vel().x/*collideQueue[temp]->get_vel().x*/,collideQueue[temp]->get_vel().y); ableToJump = true; jumpTimes = maxjumpable; thisObjectHandle = did_handle = true; } /// /// ADD CODE FROM NEXT CODE BLOCK HERE (on forum, not in code) /// } for (int temp = 0; temp < collideQueue.size(); temp++) { thisObjectHandle = false; tcol = get_collision(x,y,get_img()->get_width(),get_img()->get_height(), collideQueue[temp]->get_position().x,collideQueue[temp]->get_position().y, collideQueue[temp]->get_img()->get_width(),collideQueue[temp]->get_img()->get_height()); if (prevPos.x + get_img()->get_width() <= collideQueue[temp]->get_prev_pos().x) if (tcol.left > 0) { add_pos(-tcol.left,0); set_vel(collideQueue[temp]->get_vel().x,get_vel().y); thisObjectHandle = did_handle = true; } if (prevPos.x >= collideQueue[temp]->get_prev_pos().x + collideQueue[temp]->get_img()->get_width()) if (tcol.right > 0) { add_pos(tcol.right,0); set_vel(collideQueue[temp]->get_vel().x,get_vel().y); thisObjectHandle = did_handle = true; } } return did_handle; } (if I add the following code {where the comment to do so is}, which is glitchy, the above problem doesn't happen, though it brings others) if (!thisObjectHandle) { if (tcol.bottom > tcol.top) { add_pos(collideQueue[temp]->get_vel().x,-tcol.bottom); set_vel(get_vel().x,collideQueue[temp]->get_vel().y); } else if (tcol.top > tcol.bottom) { add_pos(0,tcol.top); set_vel(get_vel().x,collideQueue[temp]->get_vel().y); } } How would you change my system to prevent this?

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• Why it is called "hash table", or "hash function"? Hash doesn't make any sense to me here

  - by Saeed Neamati

  It's now about 4 years of development that I'm using, hearing, talking about, and implementing hash tables and hash functions. But I really never understand why it's called hash? I remember the first days I started programming, this term was kind'of cumbersome terminology to me. I never figured out what is it, based on its name. I just experimentally understood what it does and why and when should we use it. However, I still sometimes try to figure out why it's called hash. I have no problem with table or function and to be honest, they are pretty deductive, rational terms. However, I think better words could be used instead of hash, like key, or uniqueness. Don't key table or uniqueness table. According to my dictionary, hash means: Fried dish of potato and meats (highly irrelevant) # symbol (AKA number sign, pound sign, etc.) (still irrelevant, maybe just a mis-nomenclature) Apply algorithm to character string (still has nothing to do with uniqueness, which is the most important feature of a hash table) Cut food Another term for hashish Does anyone know why it's called hash?

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• Basic collision direction detection on 2d objects

  - by Osso Buko

  I am trying to develop a platform game for Android by using ANdroid GL Engine (ANGLE). And I am having trouble with collision detection. I have two objects which is shaped as rectangular. And no change in rotation. Here is a scheme of attributes of objects. What i am trying to do is when objects collide they block each other's movement on that direction. Every object has 4 boolean (bTop, bBottom, bRight, bLeft). For example when bBottom is true object can't advance on that direction. I came up with a solution but it seems it only works on one dimensional. Bottom and top or right and left. public void collisionPlatform (MyObject a, MyObject b) { // first obj is player and second is a wall or a platform Vector p1 = a.mPosition; // p1 = middle point of first object Vector d1 = a.mPosition2; // width(mX) and height of first object Vector mSpeed1 = a.mSpeed; // speed vector of first object Vector p2 = b.mPosition; // p1 = middle point of second object Vector d2 = b.mPosition2; // width(mX) and height of second object Vector mSpeed2 = b.mSpeed; // speed vector of second object float xDist, yDist; // distant between middle of two object float width , height; // this is average of two objects measurements width=(width1+width2)/2 xDist=(p1.mX - p2.mX); // calculate distance // if positive first object is at the right yDist=(p1.mY - p2.mY); // if positive first object is below width = d1.mX + d2.mX; // average measurements calculate height = d1.mY + d2.mY; width/=2; height/=2; if (Math.abs(xDist) < width && Math.abs(yDist) < height) { // Two object is collided if(p1.mY>p2.mY) { // first object is below second one a.bTop = true; if(a.mSpeed.mY<0) a.mSpeed.mY=0; b.bBottom = true; if(b.mSpeed.mY>0) b.mSpeed.mY=0; } else { a.bBottom = true; if(a.mSpeed.mY>0) a.mSpeed.mY=0; b.bTop = true; if(b.mSpeed.mY<0) b.mSpeed.mY=0; } } As seen in my code it simply will not work. when object comes from right or left it doesn't work. I tried couple of ways other than this one but none worked. I am guessing right method will include mSpeed vector. But I have no idea how to do it. I really appreciate if you could help. Sorry for my bad english.

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• Oval collision detection not working properly

  - by William

  So I'm trying to implement a test where a oval can connect with a circle, but it's not working. edist = (float) Math.sqrt(Math.pow((px + ((pwidth/2) )) - (bx + (bsize/2)), 2) + Math.pow(-((py + ((pwidth/2)) ) - (bx + (bsize/2))), 2)); and here is the full code (requires Slick2D): import org.newdawn.slick.AppGameContainer; import org.newdawn.slick.BasicGame; import org.newdawn.slick.Color; import org.newdawn.slick.GameContainer; import org.newdawn.slick.Graphics; import org.newdawn.slick.Input; import org.newdawn.slick.SlickException; public class ColTest extends BasicGame{ float px = 50; float py = 50; float pheight = 50; float pwidth = 50; float bx = 200; float by = 200; float bsize = 200; float edist; float pspeed = 3; Input input; public ColTest() { super("ColTest"); } @Override public void init(GameContainer gc) throws SlickException { } @Override public void update(GameContainer gc, int delta) throws SlickException { input = gc.getInput(); try{ if(input.isKeyDown(Input.KEY_UP)) py-=pspeed; if(input.isKeyDown(Input.KEY_DOWN)) py+=pspeed; if(input.isKeyDown(Input.KEY_LEFT)) px-=pspeed; if(input.isKeyDown(Input.KEY_RIGHT)) px+=pspeed; } catch(Exception e){} } public void render(GameContainer gc, Graphics g) throws SlickException { g.setColor(new Color(255,255,255)); g.drawString("col: " + col(), 10, 10); g.drawString("edist: " + edist + " dist: " + dist, 10, 100); g.fillRect(px, py, pwidth, pheight); g.setColor(new Color(255,0,255)); g.fillOval(px, py, pwidth, pheight); g.setColor(new Color(255,255,255)); g.fillOval(200, 200, 200, 200); } public boolean col(){ edist = (float) Math.sqrt(Math.pow((px + ((pwidth/2) )) - (bx + (bsize/2)), 2) + Math.pow(-((py + ((pwidth/2)) ) - (bx + (bsize/2))), 2)); if(edist <= (bsize/2) + (px + (pwidth/2))) return true; else return false; } public float rotate(float x, float y, float ox, float oy, float a, boolean b) { float dst = (float) Math.sqrt(Math.pow(x-ox,2.0)+ Math.pow(y-oy,2.0)); float oa = (float) Math.atan2(y-oy,x-ox); if(b) return (float) Math.cos(oa + Math.toRadians(a))*dst+ox; else return (float) Math.sin(oa + Math.toRadians(a))*dst+oy; } public static void main(String[] args) throws SlickException { AppGameContainer app = new AppGameContainer( new ColTest() ); app.setShowFPS(false); app.setAlwaysRender(true); app.setTargetFrameRate(60); app.setDisplayMode(800, 600, false); app.start(); } }

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• Accelerating 2d object collision with other objects [on hold]

  - by Silent Cave

  Making my very first attempt at game programming with SDL/OpenGL. So I made an object Actor witch can move in all four sides with acceleration. And there are bunch of other rectangles to collide to. the image Movement and collision detection alghorythms work just fine by itself, but when combined to prevent the green rectangle from crossing black rectangles, it gives me a kind of funny resault. Let me show you the code first: from Actor.h class Actor{ public: SDL_Rect * dim; alphaColor * col; float speed; float xlGrav, xrGrav, yuGrav, ydGrav; float acceleration; bool left,right,up,down; Actor(SDL_Rect * dim,alphaColor * col, float speed, float acceleration); bool colides(const SDL_Rect & rect); bool check_for_collisions(const std::vector<SDL_Rect*> & gameObjects ); }; from actor.cpp bool Actor::colides(const SDL_Rect & rect){ if (dim->x + dim->w < rect.x) return false; if (dim->x > rect.x + rect.w) return false; if (dim->y + dim->h < rect.y) return false; if (dim->y > rect.y + rect.h) return false; return true; } movement logic from main.cpp if (actor->left){ if(actor->xlGrav < actor->speed){ actor->xlGrav += actor->speed*actor->acceleration; }else actor->xlGrav = actor->speed; actor->dim->x -= actor->xlGrav; if(actor->check_for_collisions(gameObjects)){ actor->dim->x += actor->xlGrav; actor->xlGrav = 0; } } if (!actor->left){ if(actor->xlGrav - actor->speed*actor->acceleration > 0){ actor->xlGrav -= actor->speed*actor->acceleration; }else actor->xlGrav = 0; actor->dim->x -= actor->xlGrav; if(actor->check_for_collisions(gameObjects)){ actor->dim->x += actor->xlGrav; actor->xlGrav = 0; } } if (actor->right){ if(actor->xrGrav < actor->speed){ actor->xrGrav += actor->speed*actor->acceleration; }else actor->xrGrav = actor->speed; actor->dim->x += actor->xrGrav; if(actor->check_for_collisions(gameObjects)){ actor->dim->x -= actor->xrGrav; actor->xrGrav = 0; } } if (!actor->right){ if(actor->xrGrav - actor->speed*actor->acceleration > 0){ actor->xrGrav -= actor->speed*actor->acceleration; }else actor->xrGrav = 0; actor->dim->x += actor->xrGrav; if(actor->check_for_collisions(gameObjects)){ actor->dim->x -= actor->xrGrav; actor->xrGrav = 0; } } if (actor->up){ if(actor->yuGrav < actor->speed){ actor->yuGrav += actor->speed*actor->acceleration; }else actor->yuGrav = actor->speed; actor->dim->y -= actor->yuGrav; if(actor->check_for_collisions(gameObjects)){ actor->dim->y += actor->yuGrav; actor->yuGrav = 0; } } if (!actor->up){ if(actor->yuGrav - actor->speed*actor->acceleration > 0){ actor->yuGrav -= actor->speed*actor->acceleration; }else actor->yuGrav = 0; actor->dim->y -= actor->yuGrav; if(actor->check_for_collisions(gameObjects)){ actor->dim->y += actor->yuGrav; actor->yuGrav = 0; } } if (actor->down){ if(actor->ydGrav < actor->speed){ actor->ydGrav += actor->speed*actor->acceleration; }else actor->ydGrav = actor->speed; actor->dim->y += actor->ydGrav; if(actor->check_for_collisions(gameObjects)){ actor->dim->y -= actor->ydGrav; actor->ydGrav = 0; } } if (!actor->down){ if(actor->ydGrav - actor->speed*actor->acceleration > 0){ actor->ydGrav -= actor->speed*actor->acceleration; }else actor->ydGrav = 0; actor->dim->y += actor->ydGrav; if(actor->check_for_collisions(gameObjects)){ actor->dim->y -= actor->ydGrav; actor->ydGrav = 0; } } So, if the green box approaches an obstacle from up or left, everything goes as planned - object stops, and it's acceleration drops to zero. But if it comes from bottom or right, it enters into obstacles inner space and starts strangely dance, I'd rather say move in inverted controls. What do I fail to see?

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• XNA 2D vehicle wall collisions

  - by mike

  I am attempting to implement collisions for my truck game, where the truck can drive around the world and hit walls surrounding the level and various randomly placed walls within the level. I am able to get direct collisions working correctly. However, it is getting very complicated and tricky very quickly. I am trying to accommodate various other collisions such as when a truck is against the wall then turns an adjacent direction or when they reverse into a wall. Both of these result in a slight collision as the image of the truck flips around to the direction the player wants to move. All of this has resulted in a whole lot of if statements to check how I should be fixing the collision. This in turn makes the player jump to random locations and "teleport" around corners, etc. The rest of my game is fine, I am not completely new to game development or C# for that matter. It's just the logic of collisions. Any ideas on how I can approach this? Image of the collisions I am trying to resolve: http://tinypic.com/r/2qtflvq/6

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• Simple (and fast) dices physics

  - by Markus von Broady

  I'm programming a throw of 5 dices in Actionscript 3 + AwayPhysics (BulletPhysics port). I had a lot of fun tweaking frictions, masses etc. and in the end I found best results with more physics ticks per frame. Currently I use 10 ticks per frame (1/60 s) and it's OK, though I see a difference in plus for 20 ticks. Even though it's only 5 cubes (dices) in a box (or a floor with 3 walls really) I can't simulate 20 ticks in a frame and keep FPS at 60 on a medium-aged PC. That's why I decided to precompute frames for animation, finishing it in around 1700 ticks in 2 seconds. The flash player is freezed for these 2 seconds, and I'm afraid that this result will be more of a 5 seconds or even more, if I'll simulate multi-threading and compute frames in background of some other heavy processes and CPU drawing (dices is only a part of this game). Because I want both players to see dices roll in same way, I can't compute physics when having free resources, and build a buffer for at least one throw of each type (where type is number of dices thrown). I'm afraid players will see a "preparing dices........." message too often and for too long. I think the only solution to this problem is replacing PhysicsEngine with something simpler, or creating own physicsEngine. Do You have any formulas for cube-cube and cube-wall collision detection, and for calculating how their angular and linear velocities should change after a collision occurs?

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• How to implement a 2d collision detection for Android

  - by Michael Seun Araromi

  I am making a 2d space shooter using opengl ES. Can someone please show me how to implement a collision detection between the enemy ship and player ship. The code for the two classes are below: Player Ship Class: package com.proandroidgames; import java.nio.ByteBuffer; import java.nio.ByteOrder; import java.nio.FloatBuffer; import javax.microedition.khronos.opengles.GL10; public class SSGoodGuy { public boolean isDestroyed = false; private int damage = 0; private FloatBuffer vertexBuffer; private FloatBuffer textureBuffer; private ByteBuffer indexBuffer; private float vertices[] = { 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, }; private float texture[] = { 0.0f, 0.0f, 0.25f, 0.0f, 0.25f, 0.25f, 0.0f, 0.25f, }; private byte indices[] = { 0, 1, 2, 0, 2, 3, }; public void applyDamage(){ damage++; if (damage == SSEngine.PLAYER_SHIELDS){ isDestroyed = true; } } public SSGoodGuy() { ByteBuffer byteBuf = ByteBuffer.allocateDirect(vertices.length * 4); byteBuf.order(ByteOrder.nativeOrder()); vertexBuffer = byteBuf.asFloatBuffer(); vertexBuffer.put(vertices); vertexBuffer.position(0); byteBuf = ByteBuffer.allocateDirect(texture.length * 4); byteBuf.order(ByteOrder.nativeOrder()); textureBuffer = byteBuf.asFloatBuffer(); textureBuffer.put(texture); textureBuffer.position(0); indexBuffer = ByteBuffer.allocateDirect(indices.length); indexBuffer.put(indices); indexBuffer.position(0); } public void draw(GL10 gl, int[] spriteSheet) { gl.glBindTexture(GL10.GL_TEXTURE_2D, spriteSheet[0]); gl.glFrontFace(GL10.GL_CCW); gl.glEnable(GL10.GL_CULL_FACE); gl.glCullFace(GL10.GL_BACK); gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY); gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer); gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer); gl.glDrawElements(GL10.GL_TRIANGLES, indices.length, GL10.GL_UNSIGNED_BYTE, indexBuffer); gl.glDisableClientState(GL10.GL_VERTEX_ARRAY); gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY); gl.glDisable(GL10.GL_CULL_FACE); } } Enemy Ship Class: package com.proandroidgames; import java.nio.ByteBuffer; import java.nio.ByteOrder; import java.nio.FloatBuffer; import java.util.Random; import javax.microedition.khronos.opengles.GL10; public class SSEnemy { public float posY = 0f; public float posX = 0f; public float posT = 0f; public float incrementXToTarget = 0f; public float incrementYToTarget = 0f; public int attackDirection = 0; public boolean isDestroyed = false; private int damage = 0; public int enemyType = 0; public boolean isLockedOn = false; public float lockOnPosX = 0f; public float lockOnPosY = 0f; private Random randomPos = new Random(); private FloatBuffer vertexBuffer; private FloatBuffer textureBuffer; private ByteBuffer indexBuffer; private float vertices[] = { 0.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 1.0f, 1.0f, 0.0f, 0.0f, 1.0f, 0.0f, }; private float texture[] = { 0.0f, 0.0f, 0.25f, 0.0f, 0.25f, 0.25f, 0.0f, 0.25f, }; private byte indices[] = { 0, 1, 2, 0, 2, 3, }; public void applyDamage() { damage++; switch (enemyType) { case SSEngine.TYPE_INTERCEPTOR: if (damage == SSEngine.INTERCEPTOR_SHIELDS) { isDestroyed = true; } break; case SSEngine.TYPE_SCOUT: if (damage == SSEngine.SCOUT_SHIELDS) { isDestroyed = true; } break; case SSEngine.TYPE_WARSHIP: if (damage == SSEngine.WARSHIP_SHIELDS) { isDestroyed = true; } break; } } public SSEnemy(int type, int direction) { enemyType = type; attackDirection = direction; posY = (randomPos.nextFloat() * 4) + 4; switch (attackDirection) { case SSEngine.ATTACK_LEFT: posX = 0; break; case SSEngine.ATTACK_RANDOM: posX = randomPos.nextFloat() * 3; break; case SSEngine.ATTACK_RIGHT: posX = 3; break; } posT = SSEngine.SCOUT_SPEED; ByteBuffer byteBuf = ByteBuffer.allocateDirect(vertices.length * 4); byteBuf.order(ByteOrder.nativeOrder()); vertexBuffer = byteBuf.asFloatBuffer(); vertexBuffer.put(vertices); vertexBuffer.position(0); byteBuf = ByteBuffer.allocateDirect(texture.length * 4); byteBuf.order(ByteOrder.nativeOrder()); textureBuffer = byteBuf.asFloatBuffer(); textureBuffer.put(texture); textureBuffer.position(0); indexBuffer = ByteBuffer.allocateDirect(indices.length); indexBuffer.put(indices); indexBuffer.position(0); } public float getNextScoutX() { if (attackDirection == SSEngine.ATTACK_LEFT) { return (float) ((SSEngine.BEZIER_X_4 * (posT * posT * posT)) + (SSEngine.BEZIER_X_3 * 3 * (posT * posT) * (1 - posT)) + (SSEngine.BEZIER_X_2 * 3 * posT * ((1 - posT) * (1 - posT))) + (SSEngine.BEZIER_X_1 * ((1 - posT) * (1 - posT) * (1 - posT)))); } else { return (float) ((SSEngine.BEZIER_X_1 * (posT * posT * posT)) + (SSEngine.BEZIER_X_2 * 3 * (posT * posT) * (1 - posT)) + (SSEngine.BEZIER_X_3 * 3 * posT * ((1 - posT) * (1 - posT))) + (SSEngine.BEZIER_X_4 * ((1 - posT) * (1 - posT) * (1 - posT)))); } } public float getNextScoutY() { return (float) ((SSEngine.BEZIER_Y_1 * (posT * posT * posT)) + (SSEngine.BEZIER_Y_2 * 3 * (posT * posT) * (1 - posT)) + (SSEngine.BEZIER_Y_3 * 3 * posT * ((1 - posT) * (1 - posT))) + (SSEngine.BEZIER_Y_4 * ((1 - posT) * (1 - posT) * (1 - posT)))); } public void draw(GL10 gl, int[] spriteSheet) { gl.glBindTexture(GL10.GL_TEXTURE_2D, spriteSheet[0]); gl.glFrontFace(GL10.GL_CCW); gl.glEnable(GL10.GL_CULL_FACE); gl.glCullFace(GL10.GL_BACK); gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); gl.glEnableClientState(GL10.GL_TEXTURE_COORD_ARRAY); gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer); gl.glTexCoordPointer(2, GL10.GL_FLOAT, 0, textureBuffer); gl.glDrawElements(GL10.GL_TRIANGLES, indices.length, GL10.GL_UNSIGNED_BYTE, indexBuffer); gl.glDisableClientState(GL10.GL_VERTEX_ARRAY); gl.glDisableClientState(GL10.GL_TEXTURE_COORD_ARRAY); gl.glDisable(GL10.GL_CULL_FACE); } }

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• Move penetrating OBB out of another OBB to resolve collision

  - by Milo

  I'm working on collision resolution for my game. I just need a good way to get an object out of another object if it gets stuck. In this case a car. Here is a typical scenario. The red car is in the green object. How do I correctly get it out so the car can slide along the edge of the object as it should. I tried: if(buildings.size() > 0) { Entity e = buildings.get(0); Vector2D vel = new Vector2D(); vel.x = vehicle.getVelocity().x; vel.y = vehicle.getVelocity().y; vel.normalize(); while(vehicle.getRect().overlaps(e.getRect())) { vehicle.setCenter(vehicle.getCenterX() - vel.x * 0.1f, vehicle.getCenterY() - vel.y * 0.1f); } colided = true; } But that does not work too well. Is there some sort of vector I could calculate to use as the vector to move the car away from the object? Thanks Here is my OBB2D class: public class OBB2D { // Corners of the box, where 0 is the lower left. private Vector2D corner[] = new Vector2D[4]; private Vector2D center = new Vector2D(); private Vector2D extents = new Vector2D(); private RectF boundingRect = new RectF(); private float angle; //Two edges of the box extended away from corner[0]. private Vector2D axis[] = new Vector2D[2]; private double origin[] = new double[2]; public OBB2D(Vector2D center, float w, float h, float angle) { set(center,w,h,angle); } public OBB2D(float left, float top, float width, float height) { set(new Vector2D(left + (width / 2), top + (height / 2)),width,height,0.0f); } public void set(Vector2D center,float w, float h,float angle) { Vector2D X = new Vector2D( (float)Math.cos(angle), (float)Math.sin(angle)); Vector2D Y = new Vector2D((float)-Math.sin(angle), (float)Math.cos(angle)); X = X.multiply( w / 2); Y = Y.multiply( h / 2); corner[0] = center.subtract(X).subtract(Y); corner[1] = center.add(X).subtract(Y); corner[2] = center.add(X).add(Y); corner[3] = center.subtract(X).add(Y); computeAxes(); extents.x = w / 2; extents.y = h / 2; computeDimensions(center,angle); } private void computeDimensions(Vector2D center,float angle) { this.center.x = center.x; this.center.y = center.y; this.angle = angle; boundingRect.left = Math.min(Math.min(corner[0].x, corner[3].x), Math.min(corner[1].x, corner[2].x)); boundingRect.top = Math.min(Math.min(corner[0].y, corner[1].y),Math.min(corner[2].y, corner[3].y)); boundingRect.right = Math.max(Math.max(corner[1].x, corner[2].x), Math.max(corner[0].x, corner[3].x)); boundingRect.bottom = Math.max(Math.max(corner[2].y, corner[3].y),Math.max(corner[0].y, corner[1].y)); } public void set(RectF rect) { set(new Vector2D(rect.centerX(),rect.centerY()),rect.width(),rect.height(),0.0f); } // Returns true if other overlaps one dimension of this. private boolean overlaps1Way(OBB2D other) { for (int a = 0; a < axis.length; ++a) { double t = other.corner[0].dot(axis[a]); // Find the extent of box 2 on axis a double tMin = t; double tMax = t; for (int c = 1; c < corner.length; ++c) { t = other.corner[c].dot(axis[a]); if (t < tMin) { tMin = t; } else if (t > tMax) { tMax = t; } } // We have to subtract off the origin // See if [tMin, tMax] intersects [0, 1] if ((tMin > 1 + origin[a]) || (tMax < origin[a])) { // There was no intersection along this dimension; // the boxes cannot possibly overlap. return false; } } // There was no dimension along which there is no intersection. // Therefore the boxes overlap. return true; } //Updates the axes after the corners move. Assumes the //corners actually form a rectangle. private void computeAxes() { axis[0] = corner[1].subtract(corner[0]); axis[1] = corner[3].subtract(corner[0]); // Make the length of each axis 1/edge length so we know any // dot product must be less than 1 to fall within the edge. for (int a = 0; a < axis.length; ++a) { axis[a] = axis[a].divide((axis[a].length() * axis[a].length())); origin[a] = corner[0].dot(axis[a]); } } public void moveTo(Vector2D center) { Vector2D centroid = (corner[0].add(corner[1]).add(corner[2]).add(corner[3])).divide(4.0f); Vector2D translation = center.subtract(centroid); for (int c = 0; c < 4; ++c) { corner[c] = corner[c].add(translation); } computeAxes(); computeDimensions(center,angle); } // Returns true if the intersection of the boxes is non-empty. public boolean overlaps(OBB2D other) { if(right() < other.left()) { return false; } if(bottom() < other.top()) { return false; } if(left() > other.right()) { return false; } if(top() > other.bottom()) { return false; } if(other.getAngle() == 0.0f && getAngle() == 0.0f) { return true; } return overlaps1Way(other) && other.overlaps1Way(this); } public Vector2D getCenter() { return center; } public float getWidth() { return extents.x * 2; } public float getHeight() { return extents.y * 2; } public void setAngle(float angle) { set(center,getWidth(),getHeight(),angle); } public float getAngle() { return angle; } public void setSize(float w,float h) { set(center,w,h,angle); } public float left() { return boundingRect.left; } public float right() { return boundingRect.right; } public float bottom() { return boundingRect.bottom; } public float top() { return boundingRect.top; } public RectF getBoundingRect() { return boundingRect; } public boolean overlaps(float left, float top, float right, float bottom) { if(right() < left) { return false; } if(bottom() < top) { return false; } if(left() > right) { return false; } if(top() > bottom) { return false; } return true; } };

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• XNA 3D model collision is inaccurate

  - by Daniel Lopez

  I am creating a classic game in 3d that deals with asteriods and you have to shoot them and avoid being hit from them. I can generate the asteroids just fine and the ship can shoot bullets just fine. But the asteroids always hit the ship even it doesn't look they are even close. I know 2D collision very well but not 3D so can someone please shed some light to my problem. Thanks in advance. Code For ModelRenderer: using System; using System.Collections.Generic; using System.Linq; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.GamerServices; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; using Microsoft.Xna.Framework.Media; namespace _3D_Asteroids { class ModelRenderer { private float aspectratio; private Model model; private Vector3 camerapos; private Vector3 modelpos; private Matrix rotationy; float radiansy = 0; private bool isalive; public ModelRenderer(Model m, float AspectRatio, Vector3 initial_pos, Vector3 initialcamerapos) { isalive = true; model = m; if (model.Meshes.Count == 0) { throw new Exception("Invalid model because it contains zero meshes!"); } modelpos = initial_pos; camerapos = initialcamerapos; aspectratio = AspectRatio; return; } public float RadiusOfSphere { get { return model.Meshes[0].BoundingSphere.Radius; } } public BoundingBox BoxBounds { get { return BoundingBox.CreateFromSphere(model.Meshes[0].BoundingSphere); } } public BoundingSphere SphereBounds { get { return model.Meshes[0].BoundingSphere; } } public Vector3 CameraPosition { set { camerapos = value; } get { return camerapos; } } public bool IsAlive { get { return isalive; } } public Vector3 ModelPosition { set { modelpos = value; } get { return modelpos; } } public void RotateY(float radians) { radiansy += radians; rotationy = Matrix.CreateRotationY(radiansy); } public Matrix RotationY { set { rotationy = value; } get { return rotationy; } } public float AspectRatio { set { aspectratio = value; } get { return aspectratio; } } public void Kill() { isalive = false; } public void Draw(float scale) { Matrix world; if (rotationy == new Matrix(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)) { world = Matrix.CreateScale(scale) * Matrix.CreateTranslation(modelpos); } else { world = rotationy * Matrix.CreateScale(scale) * Matrix.CreateTranslation(modelpos); } Matrix view = Matrix.CreateLookAt(camerapos, Vector3.Zero, Vector3.Up); Matrix projection = Matrix.CreatePerspectiveFieldOfView(MathHelper.ToRadians(45.0f), this.AspectRatio, 1f, 100000f); foreach (ModelMesh mesh in model.Meshes) { foreach (BasicEffect effect in mesh.Effects) { effect.World = world; effect.View = view; effect.Projection = projection; } mesh.Draw(); } } public void Draw() { Matrix world; if (rotationy == new Matrix(0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0)) { world = Matrix.CreateTranslation(modelpos); } else { world = rotationy * Matrix.CreateTranslation(modelpos); } Matrix view = Matrix.CreateLookAt(camerapos, Vector3.Zero, Vector3.Up); Matrix projection = Matrix.CreatePerspectiveFieldOfView(MathHelper.ToRadians(45.0f), this.AspectRatio, 1f, 100000f); foreach (ModelMesh mesh in model.Meshes) { foreach (BasicEffect effect in mesh.Effects) { effect.World = world; effect.View = view; effect.Projection = projection; } mesh.Draw(); } } } Code For Game1: using System; using System.Collections.Generic; using System.Linq; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.GamerServices; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; using Microsoft.Xna.Framework.Media; namespace _3D_Asteroids { /// <summary> /// This is the main type for your game /// </summary> public class Game1 : Microsoft.Xna.Framework.Game { GraphicsDeviceManager graphics; int score = 0, lives = 5; SpriteBatch spriteBatch; GameState gstate = GameState.OnMenuScreen; Menu menu = new Menu(Color.Yellow, Color.White); SpriteFont font; Texture2D background; ModelRenderer ship; Model b, a; List<ModelRenderer> bullets = new List<ModelRenderer>(); List<ModelRenderer> asteriods = new List<ModelRenderer>(); float time = 0.0f; int framecount = 0; SoundEffect effect; public Game1() { graphics = new GraphicsDeviceManager(this); graphics.PreferredBackBufferWidth = 1280; graphics.PreferredBackBufferHeight = 796; graphics.ApplyChanges(); Content.RootDirectory = "Content"; } /// <summary> /// Allows the game to perform any initialization it needs to before starting to run. /// This is where it can query for any required services and load any non-graphic /// related content. Calling base.Initialize will enumerate through any components /// and initialize them as well. /// </summary> protected override void Initialize() { // TODO: Add your initialization logic here base.Initialize(); } /// <summary> /// LoadContent will be called once per game and is the place to load /// all of your content. /// </summary> protected override void LoadContent() { // Create a new SpriteBatch, which can be used to draw textures. spriteBatch = new SpriteBatch(GraphicsDevice); font = Content.Load<SpriteFont>("Fonts\\Lucida Console"); background = Content.Load<Texture2D>("Textures\\B1_stars"); Model p1 = Content.Load<Model>("Models\\p1_wedge"); b = Content.Load<Model>("Models\\pea_proj"); a = Content.Load<Model>("Models\\asteroid1"); effect = Content.Load<SoundEffect>("Audio\\tx0_fire1"); ship = new ModelRenderer(p1, GraphicsDevice.Viewport.AspectRatio, new Vector3(0, 0, 0), new Vector3(0, 0, 9000)); } /// <summary> /// UnloadContent will be called once per game and is the place to unload /// all content. /// </summary> protected override void UnloadContent() { } /// <summary> /// Allows the game to run logic such as updating the world, /// checking for collisions, gathering input, and playing audio. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Update(GameTime gameTime) { KeyboardState state = Keyboard.GetState(PlayerIndex.One); switch (gstate) { case GameState.OnMenuScreen: { if (state.IsKeyDown(Keys.Enter)) { switch (menu.SelectedChoice) { case MenuChoices.Play: { gstate = GameState.GameStarted; break; } case MenuChoices.Exit: { this.Exit(); break; } } } if (state.IsKeyDown(Keys.Down)) { menu.MoveSelectedMenuChoiceDown(gameTime); } else if(state.IsKeyDown(Keys.Up)) { menu.MoveSelectedMenuChoiceUp(gameTime); } else { menu.KeysReleased(); } break; } case GameState.GameStarted: { foreach (ModelRenderer bullet in bullets) { if (bullet.ModelPosition.X < (ship.ModelPosition.X + 4000) && bullet.ModelPosition.Z < (ship.ModelPosition.X + 4000) && bullet.ModelPosition.X > (ship.ModelPosition.Z - 4000) && bullet.ModelPosition.Z > (ship.ModelPosition.Z - 4000)) { bullet.ModelPosition += (bullet.RotationY.Forward * 120); } else if (collidedwithasteriod(bullet)) { bullet.Kill(); } else { bullet.Kill(); } } foreach (ModelRenderer asteroid in asteriods) { if (ship.SphereBounds.Intersects(asteroid.BoxBounds)) { lives -= 1; asteroid.Kill(); // This always hits no matter where the ship goes. } else { asteroid.ModelPosition -= (asteroid.RotationY.Forward * 50); } } for (int index = 0; index < asteriods.Count; index++) { if (asteriods[index].IsAlive == false) { asteriods.RemoveAt(index); } } for (int index = 0; index < bullets.Count; index++) { if (bullets[index].IsAlive == false) { bullets.RemoveAt(index); } } if (state.IsKeyDown(Keys.Left)) { ship.RotateY(0.1f); if (state.IsKeyDown(Keys.Space)) { if (time < 17) { firebullet(); //effect.Play(); } } else { time = 0; } } else if (state.IsKeyDown(Keys.Right)) { ship.RotateY(-0.1f); if (state.IsKeyDown(Keys.Space)) { if (time < 17) { firebullet(); //effect.Play(); } } else { time = 0; } } else if (state.IsKeyDown(Keys.Up)) { ship.ModelPosition += (ship.RotationY.Forward * 50); if (state.IsKeyDown(Keys.Space)) { if (time < 17) { firebullet(); //effect.Play(); } } else { time = 0; } } else if (state.IsKeyDown(Keys.Space)) { time += gameTime.ElapsedGameTime.Milliseconds; if (time < 17) { firebullet(); //effect.Play(); } } else { time = 0.0f; } if ((framecount % 60) == 0) { createasteroid(); framecount = 0; } framecount++; break; } } base.Update(gameTime); } void firebullet() { if (bullets.Count < 3) { ModelRenderer bullet = new ModelRenderer(b, GraphicsDevice.Viewport.AspectRatio, ship.ModelPosition, new Vector3(0, 0, 9000)); bullet.RotationY = ship.RotationY; bullets.Add(bullet); } } void createasteroid() { if (asteriods.Count < 2) { Random random = new Random(); float z = random.Next(-13000, -11000); float x = random.Next(-9000, -8000); Random random2 = new Random(); int degrees = random.Next(0, 45); float radians = MathHelper.ToRadians(degrees); ModelRenderer asteroid = new ModelRenderer(a, GraphicsDevice.Viewport.AspectRatio, new Vector3(x, 0, z), new Vector3(0,0, 9000)); asteroid.RotateY(radians); asteriods.Add(asteroid); } } /// <summary> /// This is called when the game should draw itself. /// </summary> /// <param name="gameTime">Provides a snapshot of timing values.</param> protected override void Draw(GameTime gameTime) { GraphicsDevice.Clear(Color.CornflowerBlue); switch (gstate) { case GameState.OnMenuScreen: { spriteBatch.Begin(); spriteBatch.Draw(background, Vector2.Zero, Color.White); menu.DrawMenu(ref spriteBatch, font, new Vector2(GraphicsDevice.Viewport.Width / 2, GraphicsDevice.Viewport.Height / 2) - new Vector2(50f), 100f); spriteBatch.End(); break; } case GameState.GameStarted: { spriteBatch.Begin(); spriteBatch.Draw(background, Vector2.Zero, Color.White); spriteBatch.DrawString(font, "Score: " + score.ToString() + "\nLives: " + lives.ToString(), Vector2.Zero, Color.White); spriteBatch.End(); ship.Draw(); foreach (ModelRenderer bullet in bullets) { bullet.Draw(); } foreach (ModelRenderer asteroid in asteriods) { asteroid.Draw(0.1f); } break; } } base.Draw(gameTime); } bool collidedwithasteriod(ModelRenderer bullet) { foreach (ModelRenderer asteroid in asteriods) { if (bullet.SphereBounds.Intersects(asteroid.BoxBounds)) { score += 10; asteroid.Kill(); return true; } } return false; } } } }

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• How to quickly generate a new string hash after concatenating 2 strings

  - by philcolbourn

  If my math is right, I can quickly generate a new hash value for the concatenation of two strings if I already have the individual hash values for each string. But only if the hash function is of the form: hash(n) = k * hash(n-1) + c(n), and h(0) = 0. In this case, hash( concat(s1,s2) ) = k**length(s2) * hash(s1) + hash(s2) eg. h1 = makeHash32_SDBM( "abcdef", 6 ); h2 = makeHash32_SDBM( "ghijklmn", 8 ); h12 = makeHash32_SDBM( "abcdefghijklmn", 14 ); hx = mod32_powI( 65599, 8 ) * h1 + h2; h1 = 2534611139 h2 = 2107082500 h12 = 1695963591 hx = 1695963591 Note that h12 = hx so this demonstrates the idea. Now, for the SDBM hash k=65599. Whereas the DJB hash has k=33 (or perhaps 31?) and h(0) = 5381 so to make it work you can set h(0) = 0 instead. But a modification on the DJB hash uses xor instead of + to add each character. http://www.cse.yorku.ca/~oz/hash.html Is there another technique to quickly calculate the hash value of concatenated strings if the hash function uses xor instead of +?

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• How to resolve concurrent ramp collisions in 2d platformer?

  - by Shaun Inman

  A bit about the physics engine: Bodies are all rectangles. Bodies are sorted at the beginning of every update loop based on the body-in-motion's horizontal and vertical velocity (to avoid sticky walls/floors). Solid bodies are resolved by testing the body-in-motion's new X with the old Y and adjusting if necessary before testing the new X with the new Y, again adjusting if necessary. Works great. Ramps (rectangles with a flag set indicating bottom-left, bottom-right, etc) are resolved by calculating the ratio of penetration along the x-axis and setting a new Y accordingly (with some checks to make sure the body-in-motion isn't attacking from the tall or flat side, in which case the ramp is treated as a normal rectangle). This also works great. Side-by-side ramps, eg. \/ and /\, work fine but things get jittery and unpredictable when a top-down ramp is directly above a bottom-up ramp, eg. < or > or when a bottom-up ramp runs right up to the ceiling/top-down ramp runs right down to the floor. I've been able to lock it down somewhat by detecting whether the body-in-motion hadFloor when also colliding with a top-down ramp or hadCeiling when also colliding with a bottom-up ramp then resolving by calculating the ratio of penetration along the y-axis and setting the new X accordingly (the opposite of the normal behavior). But as soon as the body-in-motion jumps the hasFloor flag becomes false, the first ramp resolution pushes the body into collision with the second ramp and collision resolution becomes jittery again for a few frames. I'm sure I'm making this more complicated than it needs to be. Can anyone recommend a good resource that outlines the best way to address this problem? (Please don't recommend I use something like Box2d or Chipmunk. Also, "redesign your levels" isn't an answer; the body-in-motion may at times be riding another body-in-motion, eg. a platform, that pushes it into a ramp so I'd like to be able to resolve this properly.) Thanks!

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• 2D game collision response: SAT & minimum displacement along a given axis?

  - by Archagon

  I'm trying to implement a collision system in a 2D game I'm making. The separating axis theorem (as described by metanet's collision tutorial) seems like an efficient and robust way of handling collision detection, but I don't quite like the collision response method they use. By blindly displacing along the axis of least overlap, the algorithm simply ignores the previous position of the moving object, which means that it doesn't collide with the stationary object so much as it enters it and then bounces out. Here's an example of a situation where this would matter: According to the SAT method described above, the rectangle would simply pop out of the triangle perpendicular to its hypotenuse: However, realistically, the rectangle should stop at the lower right corner of the triangle, as that would be the point of first collision if it were moving continuously along its displacement vector: Now, this might not actually matter during gameplay, but I'd love to know if there's a way of efficiently and generally attaining accurate displacements in this manner. I've been racking my brains over it for the past few days, and I don't want to give up yet! (Cross-posted from StackOverflow, hope that's not against the rules!)

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• Is an extra collision-mesh for level-data worth the hassle?

  - by Serthy

  What is the optimal approach for collision-detection with the environment in an 3D engine (with triangle mesh based geometry, no bsp)? A) Use the render mesh [+] no need for additional work for artists to fiddle with collision detection [-] high detail is harder for physics calculation [+/-] maybe use collidable flags for materials [+/-] compute the collision-mesh from the render-mesh B) Use an additional collision mesh [+] faster/more optimal collision-detection [-] additional work (either by the artist or by the programmer who has to develop an algorithm to compute it from the render-mesh) [-] more memory useage How do AAA title handle this? And what are the indie dev's approaches?

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• Gravity stops when side-collision detected

  - by Adrian Marszalek

  Please, look at this GIF: The label on the animation says "Move button is pressed, then released". And you can see when it's pressed (and player's getCenterY() is above wall getCenterY()), gravity doesn't work. I'm trying to fix it since yesterday, but I can't. All methods are called from game loop. public void move() { if (left) { switch (game.currentLevel()) { case 1: for (int i = 0; i < game.lvl1.getX().length; i++) game.lvl1.getX()[i] += game.physic.xVel; break; } } else if (right) { switch (game.currentLevel()) { case 1: for (int i = 0; i < game.lvl1.getX().length; i++) game.lvl1.getX()[i] -= game.physic.xVel; break; } } } int manCenterX, manCenterY, boxCenterX, boxCenterY; //gravity stop public void checkCollision() { for (int i = 0; i < game.lvl1.getX().length; i++) { manCenterX = (int) game.man.getBounds().getCenterX(); manCenterY = (int) game.man.getBounds().getCenterY(); if (game.man.getBounds().intersects(game.lvl1.getBounds(i))) { boxCenterX = (int) game.lvl1.getBounds(i).getCenterX(); boxCenterY = (int) game.lvl1.getBounds(i).getCenterY(); if (manCenterY - boxCenterY > 0 || manCenterY - boxCenterY < 0) { game.man.setyPos(-2f); game.man.isFalling = false; } } } } //left side of walls public void colliLeft() { for (int i = 0; i < game.lvl1.getX().length; i++) { if (game.man.getBounds().intersects(game.lvl1.getBounds(i))) { if (manCenterX - boxCenterX < 0) { for (int i1 = 0; i1 < game.lvl1.getX().length; i1++) { game.lvl1.getX()[i1] += game.physic.xVel; game.man.isFalling = true; } } } } } //right side of walls public void colliRight() { for (int i = 0; i < game.lvl1.getX().length; i++) { if (game.man.getBounds().intersects(game.lvl1.getBounds(i))) { if (manCenterX - boxCenterX > 0) { for (int i1 = 0; i1 < game.lvl1.getX().length; i1++) { game.lvl1.getX()[i1] += -game.physic.xVel; game.man.isFalling = true; } } } } } public void gravity() { game.man.setyPos(yVel); } //not called from gameloop: public void setyPos(float yPos) { this.yPos += yPos; }

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• Minecraft-style player-gound collision detection

  - by khyperia

  The title pretty much says it all... (Minecraft is a game consisting of evenly-spaced cubes for terrain, like voxels) Note: I am using C# XNA. I am pretty sure AABB is the way to go, yet I don't know how to implement it. I admit, I'm almost looking for code, but theories/ideas are very welcome. Important capabilities of my code: I have a function that can get a block anywhere in the world, and get a BoundingBox for that cube. Hence, I have created a BoundingBox for the player to collide with those cubes. My idea was to get the blocks around the player (maybe 4x6x4) and test against those. The problems I have been having: Say the world is a flat plane. If I use the method of go the shortest distance out, then if the player is slightly clipped into the ground (from gravity), but even slighter into the next block over, then the player will be pushed sideways (and so cannot walk along ground). Of course, this is assuming I react to every block intersected. Another problem is knowing which direction to go (aka negative x or positive). That takes me to my final problem- Getting the amount of intersection, in the correct direction (+ or -) has been tough for me. I hope I haven't been too hard to understand, I'm not too good at explaining things... And if this question has already been asked, I'm sorry, I looked for it... for 3 days straight. One last thing, if someone knows exactly how minecraft does it, or has source (I know MC modders have the source, how else would they mod), please point me to it.

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• Tile-based 2D collision detection problems

  - by Vee

  I'm trying to follow this tutorial http://www.tonypa.pri.ee/tbw/tut05.html to implement real-time collisions in a tile-based world. I find the center coordinates of my entities thanks to these properties: public float CenterX { get { return X + Width / 2f; } set { X = value - Width / 2f; } } public float CenterY { get { return Y + Height / 2f; } set { Y = value - Height / 2f; } } Then in my update method, in the player class, which is called every frame, I have this code: public override void Update() { base.Update(); int downY = (int)Math.Floor((CenterY + Height / 2f - 1) / 16f); int upY = (int)Math.Floor((CenterY - Height / 2f) / 16f); int leftX = (int)Math.Floor((CenterX + Speed * NextX - Width / 2f) / 16f); int rightX = (int)Math.Floor((CenterX + Speed * NextX + Width / 2f - 1) / 16f); bool upleft = Game.CurrentMap[leftX, upY] != 1; bool downleft = Game.CurrentMap[leftX, downY] != 1; bool upright = Game.CurrentMap[rightX, upY] != 1; bool downright = Game.CurrentMap[rightX, downY] != 1; if(NextX == 1) { if (upright && downright) CenterX += Speed; else CenterX = (Game.GetCellX(CenterX) + 1)*16 - Width / 2f; } } downY, upY, leftX and rightX should respectively find the lowest Y position, the highest Y position, the leftmost X position and the rightmost X position. I add + Speed * NextX because in the tutorial the getMyCorners function is called with these parameters: getMyCorners (ob.x+ob.speed*dirx, ob.y, ob); The GetCellX and GetCellY methods: public int GetCellX(float mX) { return (int)Math.Floor(mX / SGame.Camera.TileSize); } public int GetCellY(float mY) { return (int)Math.Floor(mY / SGame.Camera.TileSize); } The problem is that the player "flickers" while hitting a wall, and the corner detection doesn't even work correctly since it can overlap walls that only hit one of the corners. I do not understand what is wrong. In the tutorial the ob.x and ob.y fields should be the same as my CenterX and CenterY properties, and the ob.width and ob.height should be the same as Width / 2f and Height / 2f. However it still doesn't work. Thanks for your help.

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• Java - 2d Array Tile Map Collision

  - by Corey

  How would I go about making certain tiles in my array collide with my player? Like say I want every number 2 in the array to collide. I am reading my array from a txt file if that matters and I am using the slick2d library. Here is my code if needed. public class Tiles { Image[] tiles = new Image[3]; int[][] map = new int[500][500]; Image grass, dirt, mound; SpriteSheet tileSheet; int tileWidth = 32; int tileHeight = 32; public void init() throws IOException, SlickException { tileSheet = new SpriteSheet("assets/tiles.png", tileWidth, tileHeight); grass = tileSheet.getSprite(0, 0); dirt = tileSheet.getSprite(7, 7); mound = tileSheet.getSprite(2, 6); tiles[0] = grass; tiles[1] = dirt; tiles[2] = mound; int x=0, y=0; BufferedReader in = new BufferedReader(new FileReader("assets/map.txt")); String line; while ((line = in.readLine()) != null) { String[] values = line.split(","); for (String str : values) { int str_int = Integer.parseInt(str); map[x][y]=str_int; //System.out.print(map[x][y] + " "); y=y+1; } //System.out.println(""); x=x+1; y = 0; } in.close(); } public void update() { } public void render(GameContainer gc) { for(int x = 0; x < 50; x++) { for(int y = 0; y < 50; y ++) { int textureIndex = map[y][x]; Image texture = tiles[textureIndex]; texture.draw(x*tileWidth,y*tileHeight); } } } } I tried something like this, but I it doesn't ever "collide". X and y are my player position. if (tiles.map[(int)x/32][(int)y/32] == 2) { System.out.println("Collided"); }

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• Collision Detection on floor tiles Isometric game

  - by Anivrom

  I am having a very hard to time figuring out a bug in my code. It should have taken me 20 minutes but instead I've been working on it for over 12 hours. I am writing a isometric tile based game where the characters can walk freely amongst the tiles, but not be able to cross over to certain tiles that have a collides flag. Sounds easy enough, just check ahead of where the player is going to move using a Screen Coordinates to Tile method and check the tiles array using our returned xy indexes to see if its collidable or not. if its not, then don't move the character. The problem I'm having is my Screen to Tile method isn't spitting out the proper X,Y tile indexes. This method works flawlessly for selecting tiles with the mouse. NOTE: My X tiles go from left to right, and my Y tiles go from up to down. Reversed from some examples on the net. Here's the relevant code: public Vector2 ScreentoTile(Vector2 screenPoint) { //Vector2 is just a object with x and y float properties //camOffsetX,Y are my camera values that I use to shift everything but the //current camera target when the target moves //tilescale = 128, screenheight = 480, the -46 offset is to center // vertically + 16 px for some extra gfx in my tile png Vector2 tileIndex = new Vector2(-1,-1); screenPoint.x -= camOffsetX; screenPoint.y = screenHeight - screenPoint.y - camOffsetY - 46; tileIndex.x = (screenPoint.x / tileScale) + (screenPoint.y / (tileScale / 2)); tileIndex.y = (screenPoint.x / tileScale) - (screenPoint.y / (tileScale / 2)); return tileIndex; } The method that calls this code is: private void checkTileTouched () { if (Gdx.input.justTouched()) { if (last.x >= 0 && last.x < levelWidth && last.y >= 0 && last.y < levelHeight) { if (lastSelectedTile != null) lastSelectedTile.setColor(1, 1, 1, 1); Sprite sprite = levelTiles[(int) last.x][(int) last.y].sprite; sprite.setColor(0, 0.3f, 0, 1); lastSelectedTile = sprite; } } if (touchDown) { float moveX=0,moveY=0; Vector2 pos = new Vector2(); if (player.direction == direction_left) { moveX = -(player.moveSpeed); moveY = -(player.moveSpeed / 2); Gdx.app.log("Movement", String.valueOf("left")); } else if (player.direction == direction_upleft) { moveX = -(player.moveSpeed); moveY = 0; Gdx.app.log("Movement", String.valueOf("upleft")); } else if (player.direction == direction_up) { moveX = -(player.moveSpeed); moveY = player.moveSpeed / 2; Gdx.app.log("Movement", String.valueOf("up")); } else if (player.direction == direction_upright) { moveX = 0; moveY = player.moveSpeed; Gdx.app.log("Movement", String.valueOf("upright")); } else if (player.direction == direction_right) { moveX = player.moveSpeed; moveY = player.moveSpeed / 2; Gdx.app.log("Movement", String.valueOf("right")); } else if (player.direction == direction_downright) { moveX = player.moveSpeed; moveY = 0; Gdx.app.log("Movement", String.valueOf("downright")); } else if (player.direction == direction_down) { moveX = player.moveSpeed; moveY = -(player.moveSpeed / 2); Gdx.app.log("Movement", String.valueOf("down")); } else if (player.direction == direction_downleft) { moveX = 0; moveY = -(player.moveSpeed); Gdx.app.log("Movement", String.valueOf("downleft")); } //Player.moveSpeed is 1 //tileObjects.x is drawn in the center of the screen (400px,240px) // the sprite width is 64, height is 128 testX = moveX * 10; testY = moveY * 10; testX += tileObjects.get(player.zIndex).x + tileObjects.get(player.zIndex).sprite.getWidth() / 2; testY += tileObjects.get(player.zIndex).y + tileObjects.get(player.zIndex).sprite.getHeight() / 2; moveX += tileObjects.get(player.zIndex).x + tileObjects.get(player.zIndex).sprite.getWidth() / 2; moveY += tileObjects.get(player.zIndex).y + tileObjects.get(player.zIndex).sprite.getHeight() / 2; pos = ScreentoTile(new Vector2(moveX,moveY)); Vector2 pos2 = ScreentoTile(new Vector2(testX,testY)); if (!levelTiles[(int) pos2.x][(int) pos2.y].collides) { Vector2 newPlayerPos = ScreentoTile(new Vector2(moveX,moveY)); CenterOnCoord(moveX,moveY); player.tileX = (int)newPlayerPos.x; player.tileY = (int)newPlayerPos.y; } } } When the player is moving to the left (downleft-ish from the viewers point of view), my Pos2 X values decrease as expected but pos2 isnt checking ahead on the x tiles, it is checking ahead on the Y tiles(as if we were moving DOWN, not left), and vice versa, if the player moves down, it will check ahead on the X values (as if we are moving LEFT, instead of DOWN). instead of the Y values. I understand this is probably the most confusing and horribly written post ever, but I'm confused myself so I'm having a hard time explaining it to others lol. if you need more information please ask!! I'm so frustrated after over 12 hours of working on it I'm about to give up.

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