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• Collision Detection for a 2D RPG

  - by PHMitrious

  First of all, I have done some research on this topic before asking, and I'm asking this question as a mean to get some opinions on this topic, so I don't make a decision only on my own, but taking into account other people's experience as well. I'm starting a 2D online RPG project. I am using SFML for graphics and input and I'm creating a basic game structure and all for the game, creating modules for each part of the game. Well, let me get to the point I just wanted to give you guys some context. I want to decide on how I'm going to work with collision detection. Well I'm kinda going to work on maps with a tile map divided in layers (as usual) and add an extra 2 layers - not exactly in the map - for objects. So I'll have collisions between objects and agents (players - npcs - monsters - spells etc) and agents and tiles. The seconds one can be easily solved the first one need a little bit of work. I considered both creating a basic collision test engine using polygons and a quadtree to diminish tests since I'm going to be working with big maps with lots of objects - creating both a physical and graphical world representation. And I also considered using a physics engine like Box2D for collision tests. I think the first approach would take more work on my part but the second one would have the overhead of using a whole physics engine for just collision detection and no physics. What do you guys think ?

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• improve Collision detection memory usage (blocks with bullets)

  - by Eddy

  i am making a action platform 2D game, something like Megaman. I am using XNA to make it. already made player phisics,collisions, bullets, enemies and AIs, map editor, scorolling X Y camera (about 75% of game is finished ). as i progressed i noticed that my game would be more interesting to play if bullets would be destroyed on collision with regular(stationary ) map blocks, only problem is that if i use my collision detection (each bullet with each block) sometimes it begins to lag(btw if my bullet exits the screen player can see it is removed from bullet list) So how to improve my collision detection so that memory usage would be so high? :) ( on a map 300x300 blocks for example don't think that bigger map should be made); int block = 0; int bulet= 0; bool destroy_bullet = false; while (bulet < bullets.Count) { while (block < blocks.Count) { if (bullets[bulet].P_Bul_rec.Intersects( blocks[block].rect)) {//bullets and block are Lists that holds objects of bullet and block classes //P_Bul_rec just bullet rectangle destroy_bullet = true; } block++; } if (destroy_bullet) { bullets.RemoveAt(bulet); destroy_bullet = false; } else { bulet++; } block = 0; }

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• Confusion with floats converted into ints during collision detection

  - by TheBroodian

  So in designing a 2D platformer, I decided that I should be using a Vector2 to track the world location of my world objects to retain some sub-pixel precision for slow-moving objects and other such subtle nuances, yet representing their bodies with Rectangles, because as far as collision detection and resolution is concerned, I don't need sub-pixel precision. I thought that the following line of thought would work smoothly... Vector2 wrldLocation; Point WorldLocation; Rectangle collisionRectangle; public void Update(GameTime gameTime) { Vector2 moveAmount = velocity * (float)gameTime.ElapsedGameTime.TotalSeconds wrldLocation += moveAmount; WorldLocation = new Point((int)wrldLocation.X, (int)wrldLocation.Y); collisionRectangle = new Rectangle(WorldLocation.X, WorldLocation.Y, genericWidth, genericHeight); } and I guess in theory it sort of works, until I try to use it in conjunction with my collision detection, which works by using Rectangle.Offset() to project where collisionRectangle would supposedly end up after applying moveAmount to it, and if a collision is found, finding the intersection and subtracting the difference between the two intersecting sides to the given moveAmount, which would theoretically give a corrected moveAmount to apply to the object's world location that would prevent it from passing through walls and such. The issue here is that Rectangle.Offset() only accepts ints, and so I'm not really receiving an accurate adjustment to moveAmount for a Vector2. If I leave out wrldLocation from my previous example, and just use WorldLocation to keep track of my object's location, everything works smoothly, but then obviously if my object is being given velocities less than 1 pixel per update, then the velocity value may as well be 0, which I feel further down the line I may regret. Does anybody have any suggestions about how I might go about resolving this?

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• Java : 2D Collision Detection

  - by neko

  I'm been working on 2D rectangle collision for weeks and still cannot get this problem fixed. The problem I'm having is how to adjust a player to obstacles when it collides. I'm referencing this link. The player sometime does not get adjusted to obstacles. Also, it sometimes stuck in obstacle guy after colliding. Here, the player and the obstacle are inheriting super class Sprite I can detect collision between the two rectangles and the point by ; public Point getSpriteCollision(Sprite sprite, double newX, double newY) { // set each rectangle Rectangle spriteRectA = new Rectangle( (int)getPosX(), (int)getPosY(), getWidth(), getHeight()); Rectangle spriteRectB = new Rectangle( (int)sprite.getPosX(), (int)sprite.getPosY(), sprite.getWidth(), sprite.getHeight()); // if a sprite is colliding with the other sprite if (spriteRectA.intersects(spriteRectB)){ System.out.println("Colliding"); return new Point((int)getPosX(), (int)getPosY()); } return null; } and to adjust sprites after a collision: // Update the sprite's conditions public void update() { // only the player is moving for simplicity // collision detection on x-axis (just x-axis collision detection at this moment) double newX = x + vx; // calculate the x-coordinate of sprite move Point sprite = getSpriteCollision(map.getSprite().get(1), newX, y);// collision coordinates (x,y) if (sprite == null) { // if the player is no colliding with obstacle guy x = newX; // move } else { // if collided if (vx > 0) { // if the player was moving from left to right x = (sprite.x - vx); // this works but a bit strange } else if (vx < 0) { x = (sprite.x + vx); // there's something wrong with this too } } vx=0; y+=vy; vy=0; } I think there is something wrong in update() but cannot fix it. Now I only have a collision with the player and an obstacle guy but in future, I'm planning to have more of them and making them all collide with each other. What would be a good way to do it? Thanks in advance.

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• Pixel Perfect Collision Detection in Cocos2dx

  - by Happybirthday

  I am trying to port the pixel perfect collision detection in Cocos2d-x the original version was made for Cocos2D and can be found here: http://www.cocos2d-iphone.org/forums/topic/pixel-perfect-collision-detection-using-color-blending/ Here is my code for the Cocos2d-x version bool CollisionDetection::areTheSpritesColliding(cocos2d::CCSprite *spr1, cocos2d::CCSprite *spr2, bool pp, CCRenderTexture* _rt) { bool isColliding = false; CCRect intersection; CCRect r1 = spr1-boundingBox(); CCRect r2 = spr2-boundingBox(); intersection = CCRectMake(fmax(r1.getMinX(),r2.getMinX()), fmax( r1.getMinY(), r2.getMinY()) ,0,0); intersection.size.width = fmin(r1.getMaxX(), r2.getMaxX() - intersection.getMinX()); intersection.size.height = fmin(r1.getMaxY(), r2.getMaxY() - intersection.getMinY()); // Look for simple bounding box collision if ( (intersection.size.width0) && (intersection.size.height0) ) { // If we're not checking for pixel perfect collisions, return true if (!pp) { return true; } unsigned int x = intersection.origin.x; unsigned int y = intersection.origin.y; unsigned int w = intersection.size.width; unsigned int h = intersection.size.height; unsigned int numPixels = w * h; //CCLog("Intersection X and Y %d, %d", x, y); //CCLog("Number of pixels %d", numPixels); // Draw into the RenderTexture _rt-beginWithClear( 0, 0, 0, 0); // Render both sprites: first one in RED and second one in GREEN glColorMask(1, 0, 0, 1); spr1-visit(); glColorMask(0, 1, 0, 1); spr2-visit(); glColorMask(1, 1, 1, 1); // Get color values of intersection area ccColor4B *buffer = (ccColor4B *)malloc( sizeof(ccColor4B) * numPixels ); glReadPixels(x, y, w, h, GL_RGBA, GL_UNSIGNED_BYTE, buffer); _rt-end(); // Read buffer unsigned int step = 1; for(unsigned int i=0; i 0 && color.g 0) { isColliding = true; break; } } // Free buffer memory free(buffer); } return isColliding; } My code is working perfectly if I send the "pp" parameter as false. That is if I do only a bounding box collision but I am not able to get it working correctly for the case when I need Pixel Perfect collision. I think the opengl masking code is not working as I intended. Here is the code for "_rt" _rt = CCRenderTexture::create(visibleSize.width, visibleSize.height); _rt-setPosition(ccp(origin.x + visibleSize.width * 0.5f, origin.y + visibleSize.height * 0.5f)); this-addChild(_rt, 1000000); _rt-setVisible(true); //For testing I think I am making a mistake with the implementation of this CCRenderTexture Can anyone guide me with what I am doing wrong ? Thank you for your time :)

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• Android Touch Event Collision Detection

  - by chrissb

  I'm relatively new to both Java and Android, so hopefully the problem I'm having is stemming from something pretty minor that I've overlooked. I've got a (very early stage) game that I've started working on, for Android using Java. At this stage, when the user touches the screen, if they touched a point at which there is an enemy, the enemies health is decreased and they become immobile (for the current implementation at least). The issue that I'm having is that the touch detection doesn't always seem to work. I've got a testing sprite set up that goes to the eventX and eventY coordinates of the touch down event, and it always seems to collide with the enemy object. Yet, the enemy doesn't always register as being hit, and sometimes a hit is registered when the sprite indicates the touch coordinates were outside of the enemies bounding box. I realise that this probably doesn't mean much without any code, so here's what I've got so far. Be gentle, as this is literally my first attempt at something more than basic movement etc. First off, the MainGamePanel class registers the touch event, and informs the levelmanager class (which is what I set up to monitor/handle enemies) public boolean onTouchEvent(MotionEvent event) { if (event.getAction() == MotionEvent.ACTION_DOWN){ levelManager.handleActionDown((int)event.getX(), (int)event.getY()); targetX=event.getX(); targetY=event.getY(); } if (event.getAction() == MotionEvent.ACTION_MOVE) { //the gestures } if (event.getAction() == MotionEvent.ACTION_UP) { //touch was released } return true; } From there, in the levelmanager class the touch event is passed on to all of the enemies within a list array: public static void handleActionDown(int eventX,int eventY){ hit=false; for (enemy1 en : enemy1array){ en.handleActionDown(eventX, eventY); } } The rest of the collision code is handled within the enemies handleActionDown function: public void handleActionDown(int eventX, int eventY) { if(eventX>this.x-enemy1bitmap.getWidth() && eventX<this.x+enemy1bitmap.getWidth() && eventY>this.y-enemy1bitmap.getHeight() && eventY<this.x+enemy1bitmap.getHeight()){ takeDamage(1); levelmanager.setHit(); } } I should probably be using getWidth()/2 and getHeight()/2 for it to be more accurate, but I expanded the area to test this - although I've noticed no improvement. At this stage, the games detection over whether or not the enemy is hit is spotty at best. Generally it takes two or three attempts before a collision is successfully registered, even though the sprite that is being used for testing and set to the eventX and eventY coordinates always indicates that the collision should have worked. Hopefully someone can steer me in the right direction here, and if more information is needed, ask away! Cheers, -Chris

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• Different bounding volumes for culling and collision detection

  - by Serthy

  Should an object in a 3D-engine use different bounding volumes for collision-detection (broad-phase) and culling? Basically class renderBounds and class physBounds versus class boundingVolume? Each of this classes then could either contain the same type of volumes (AABB's, kDOP's, sphere's etc.) or a special fitting one for the particular object. (note: without considering of using an external physics engine)

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• HTML5 platformer collision detection problem

  - by fnx

  I'm working on a 2D platformer game, and I'm having a lot of trouble with collision detection. I've looked trough some tutorials, questions asked here and Stackoverflow, but I guess I'm just too dumb to understand what's wrong with my code. I've wanted to make simple bounding box style collisions and ability to determine on which side of the box the collision happens, but no matter what I do, I always get some weird glitches, like the player gets stuck on the wall or the jumping is jittery. You can test the game here: Platform engine test. Arrow keys move and z = run, x = jump, c = shoot. Try to jump into the first pit and slide on the wall. Here's the collision detection code: function checkCollisions(a, b) { if ((a.x > b.x + b.width) || (a.x + a.width < b.x) || (a.y > b.y + b.height) || (a.y + a.height < b.y)) { return false; } else { handleCollisions(a, b); return true; } } function handleCollisions(a, b) { var a_top = a.y, a_bottom = a.y + a.height, a_left = a.x, a_right = a.x + a.width, b_top = b.y, b_bottom = b.y + b.height, b_left = b.x, b_right = b.x + b.width; if (a_bottom + a.vy > b_top && distanceBetween(a_bottom, b_top) + a.vy < distanceBetween(a_bottom, b_bottom)) { a.topCollision = true; a.y = b.y - a.height + 2; a.vy = 0; a.canJump = true; } else if (a_top + a.vy < b_bottom && distanceBetween(a_top, b_bottom) + a.vy < distanceBetween(a_top, b_top)) { a.bottomCollision = true; a.y = b.y + b.height; a.vy = 0; } else if (a_right + a.vx > b_left && distanceBetween(a_right, b_left) < distanceBetween(a_right, b_right)) { a.rightCollision = true; a.x = b.x - a.width - 3; //a.vx = 0; } else if (a_left + a.vx < b_right && distanceBetween(a_left, b_right) < distanceBetween(a_left, b_left)) { a.leftCollision = true; a.x = b.x + b.width + 3; //a.vx = 0; } } function distanceBetween(a, b) { return Math.abs(b-a); }

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• Isometric Collision Detection

  - by Sleepy Rhino

  I am having some issues with trying to detect collision of two isometric tile. I have tried plotting the lines between each point on the tile and then checking for line intercepts however that didn't work (probably due to incorrect formula) After looking into this for awhile today I believe I am thinking to much into it and there must be a easier way. I am not looking for code just some advise on the best way to achieve detection of overlap

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• 2D Tile Based Collision Detection

  - by MrPlosion1243

  There are a lot of topics about this and it seems each one addresses a different problem, this topic does the same. I was looking into tile collision detection and found this where David Gouveia explains a great way to get around the person's problem by separating the two axis. So I implemented the solution and it all worked perfectly from all the testes I through at it. Then I implemented more advanced platforming physics and the collision detection broke down. Unfortunately I have not been able to get it to work again which is where you guys come in :)! I will present the code first: public void Update(GameTime gameTime) { if(Input.GetKeyDown(Keys.A)) { velocity.X -= moveAcceleration; } else if(Input.GetKeyDown(Keys.D)) { velocity.X += moveAcceleration; } if(Input.GetKeyDown(Keys.Space)) { if((onGround && isPressable) || (!onGround && airTime <= maxAirTime && isPressable)) { onGround = false; airTime += (float)gameTime.ElapsedGameTime.TotalSeconds; velocity.Y = initialJumpVelocity * (1.0f - (float)Math.Pow(airTime / maxAirTime, Math.PI)); } } else if(Input.GetKeyReleased(Keys.Space)) { isPressable = false; } if(onGround) { velocity.X *= groundDrag; velocity.Y = 0.0f; } else { velocity.X *= airDrag; velocity.Y += gravityAcceleration; } velocity.Y = MathHelper.Clamp(velocity.Y, -maxFallSpeed, maxFallSpeed); velocity.X = MathHelper.Clamp(velocity.X, -maxMoveSpeed, maxMoveSpeed); position += velocity * (float)gameTime.ElapsedGameTime.TotalSeconds; position = new Vector2((float)Math.Round(position.X), (float)Math.Round(position.Y)); if(Math.Round(velocity.X) != 0.0f) { HandleCollisions2(Direction.Horizontal); } if(Math.Round(velocity.Y) != 0.0f) { HandleCollisions2(Direction.Vertical); } } private void HandleCollisions2(Direction direction) { int topTile = (int)Math.Floor((float)Bounds.Top / Tile.PixelTileSize); int bottomTile = (int)Math.Ceiling((float)Bounds.Bottom / Tile.PixelTileSize) - 1; int leftTile = (int)Math.Floor((float)Bounds.Left / Tile.PixelTileSize); int rightTile = (int)Math.Ceiling((float)Bounds.Right / Tile.PixelTileSize) - 1; for(int x = leftTile; x <= rightTile; x++) { for(int y = topTile; y <= bottomTile; y++) { Rectangle tileBounds = new Rectangle(x * Tile.PixelTileSize, y * Tile.PixelTileSize, Tile.PixelTileSize, Tile.PixelTileSize); Vector2 depth; if(Tile.IsSolid(x, y) && Intersects(tileBounds, direction, out depth)) { if(direction == Direction.Horizontal) { position.X += depth.X; } else { onGround = true; isPressable = true; airTime = 0.0f; position.Y += depth.Y; } } } } } From the code you can see when velocity.X is not equal to zero the HandleCollisions() Method is called along the horizontal axis and likewise for the vertical axis. When velocity.X is not equal to zero and velocity.Y is equal to zero it works fine. When velocity.Y is not equal to zero and velocity.X is equal to zero everything also works fine. However when both axis are not equal to zero that's when it doesn't work and I don't know why. I basically teleport to the left side of a tile when both axis are not equal to zero and there is a air block next to me. Hopefully someone can see the problem with this because I sure don't as far as I'm aware nothing has even changed from what I'm doing to what the linked post's solution is doing. Thanks.

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• Switching my collision detection to array lists caused it to stop working

  - by Charlton Santana

  I have made a collision detection system which worked when I did not use array list and block generation. It is weird why it's not working but here's the code, and if anyone could help I would be very grateful :) The first code if the block generation. private static final List<Block> BLOCKS = new ArrayList<Block>(); Random rnd = new Random(System.currentTimeMillis()); int randomx = 400; int randomy = 400; int blocknum = 100; String Title = "blocktitle" + blocknum; private Block block; public void generateBlocks(){ if(blocknum > 0){ int offset = rnd.nextInt(250) + 100; //500 is the maximum offset, this is a constant randomx += offset;//ofset will be between 100 and 400 int randomyoff = rnd.nextInt(80); //500 is the maximum offset, this is a constant randomy = platformheighttwo - 6 - randomyoff;//ofset will be between 100 and 400 block = new Block(BitmapFactory.decodeResource(getResources(), R.drawable.block2), randomx, randomy); BLOCKS.add(block); blocknum -= 1; } The second is where the collision detection takes place note: the block.draw(canvas); works perfectly. It's the blocks that don't work. for(Block block : BLOCKS) { block.draw(canvas); if (sprite.bottomrx < block.bottomrx && sprite.bottomrx > block.bottomlx && sprite.bottomry < block.bottommy && sprite.bottomry > block.topry ){ Log.d(TAG, "Collided!!!!!!!!!!!!1"); } // bottom left touching block? if (sprite.bottomlx < block.bottomrx && sprite.bottomlx > block.bottomlx && sprite.bottomly < block.bottommy && sprite.bottomly > block.topry ){ Log.d(TAG, "Collided!!!!!!!!!!!!1"); } // top right touching block? if (sprite.toprx < block.bottomrx && sprite.toprx > block.bottomlx && sprite.topry < block.bottommy && sprite.topry > block.topry ){ Log.d(TAG, "Collided!!!!!!!!!!!!1"); } //top left touching block? if (sprite.toprx < block.bottomrx && sprite.toprx > block.bottomlx && sprite.topry < block.bottommy && sprite.topry > block.topry ){ Log.d(TAG, "Collided!!!!!!!!!!!!1"); } } The values eg bottomrx are in the block.java file..

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• Problems with moving 2D circle/box collision detection

  - by dario3004

  This is my first game ever and I'm a newbie in computer physics. I've got this code for the collision detection and it works fine for BOTTOM and TOP collision.It miss the collision detection with the paddle's edge and angles so I've (roughly) tried to implement it. Main method that is called for bouncing, it checks if it bounce with wall, or with top (+ right/left side) or with bottom (+ right/left side): protected void handleBounces(float px, float py) { handleWallBounce(px, py); if(mBall.y < getHeight()/4){ if (handleRedFastBounce(mRed, px, py)) return; if (handleRightSideBounce(mRed,px,py)) return; if (handleLeftSideBounce(mRed,px,py)) return; } if(mBall.y > getHeight()/4 * 3){ if (handleBlueFastBounce(mBlue, px, py)) return; if (handleRightSideBounce(mBlue,px,py)) return; if (handleLeftSideBounce(mBlue,px,py)) return; } } This is the code for the BOTTOM bounce: protected boolean handleRedFastBounce(Paddle paddle, float px, float py) { if (mBall.goingUp() == false) return false; // next position tx = mBall.x; ty = mBall.y - mBall.getRadius(); // actual position ptx = px; pty = py - mBall.getRadius(); dyp = ty - paddle.getBottom(); xc = tx + (tx - ptx) * dyp / (ty - pty); if ((ty < paddle.getBottom() && pty > paddle.getBottom() && xc > paddle.getLeft() && xc < paddle.getRight())) { mBall.x = xc; mBall.y = paddle.getBottom() + mBall.getRadius(); mBall.bouncePaddle(paddle); playSound(mPaddleSFX); increaseDifficulty(); return true; } else return false; } As long as I understood it should be something like this: So I tried to make the "left side" and "right side" bounce method: protected boolean handleLeftSideBounce(Paddle paddle, float px, float py){ // next position tx = mBall.x + mBall.getRadius(); ty = mBall.y; // actual position ptx = px + mBall.getRadius(); pty = py; dyp = tx - paddle.getLeft(); yc = ty + (pty - ty) * dyp / (ptx - tx); if (ptx < paddle.getLeft() && tx > paddle.getLeft()){ System.out.println("left side bounce1"); System.out.println("yc: " + yc + "top: " + paddle.getTop() + " bottom: " + paddle.getBottom()); if (yc > paddle.getTop() && yc < paddle.getBottom()){ System.out.println("left side bounce2"); mBall.y = yc; mBall.x = paddle.getLeft() - mBall.getRadius(); mBall.bouncePaddle(paddle); playSound(mPaddleSFX); increaseDifficulty(); return true; } } return false; } I think I'm quite near to the solution but I'm having big troubles with the new "yc" formula. I tried so many versions of it but since I don't know the theory behind it I can't adjust for the Y axis. Since the Y axis is inverted I even tried this: yc = ty - (pty - ty) * dyp / (ptx - tx); I tried Googling it but I can't seem to find a solution for it. Also this method fails when ball touches the angle and I don't think is a nice way because it just test "one" point of the ball and probably there will be many cases in which the ball won't bounce.

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• 3D collision detection with meshes using only raycasting?

  - by Nick

  I'm building a game using WebGL and Three.js, and so far I have a terrain with a guy walking on it. I simply cast a ray downwards to know the terrain height. How can I do this for other 3D objects, like the inside of a house? Is this possible by casting many rays in every direction of the player? If not, I would like to know how I can achieve the simplest collision detection possible for other meshes. Do you have to cast a ray to every triangle in every mesh nearby?

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• Collision Detection Game Design and Architecture

  - by Chompas

  I've reading some articles about collision detection. My question here is about ideas on the design for it. Baically I have a C++ game that has a main loop with entities with an update method. Based on keyboard input, these characters updates their positions. My question is not about how to detect collisions, it's about getting ideas in which is the best way to implement this. The game has a main character but also enemies that have to collide between them, so I'm not sure where to make all the iterations for checking collisions and if the right way is to check everything against everything. Thanks in advance.

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• Collision detection of convex shapes on voxel terrain

  - by Dave

  I have some standard convex shapes (cubes, capsules) on a voxel terrain. It is very easy to detect single vertex collisions. However, it becomes computationally expensive when many vertices are involved. To clarify, currently my algorithm represents a cube as multiple vertices covering every face of the cube, not just the corners. This is because the cubes can be much bigger than the voxels, so multiple sample points (vertices) are required (the distance between sample points must be at least the width of a voxel). This very rapidly becomes intractable. It would be great if there were some standard algorithm(s) for collision detection between convex shapes and arbitrary voxel based terrain (like there is with OBB's and seperating axis theorem etc). Any help much appreciated.

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• Collision detection with heightmap based terrain

  - by Truman's world

  I am developing a 2D tank game. The terrain is generated by Midpoint Displacement Algorithm, so the terrain is represented by an array: index ---> height of terrain [0] ---> 5 [1] ---> 8 [2] ---> 4 [3] ---> 6 [4] ---> 8 [5] ---> 9 ... ... The rendered mountain looks like this: * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 0 1 2 3 4 5 ... I want tanks to be able to move smoothly on the terrain (I mean tanks can rotate according to the height when they move), but the surface of the terrain is not flat, it is polygonal. Can anyone give me some help with collision detection in this situation? Thanks in advance.

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• Narrow-phase collision detection algorithms

  - by Marian Ivanov

  There are three phases of collision detection. Broadphase: It loops between all objecs that can interact, false positives are allowed, if it would speed up the loop. Narrowphase: Determines whether they collide, and sometimes, how, no false positives Resolution: Resolves the collision. The question I'm asking is about the narrowphase. There are multiple algorithms, differing in complexity and accuracy. Hitbox intersection: This is an a-posteriori algorithm, that has the lowest complexity, but also isn't too accurate, Color intersection: Hitbox intersection for each pixel, a-posteriori, pixel-perfect, not accuratee in regards to time, higher complexity Separating axis theorem: This is used more often, accurate for triangles, however, a-posteriori, as it can't find the edge, when taking last frame in account, it's more stable Linear raycasting: A-priori algorithm, useful for semi-realistic-looking physics, finds the intersection point, even more accurate than SAT, but with more complexity Spline interpolation: A-priori, even more accurate than linear rays, even more coplexity. There are probably many more that I've forgot about. The question is, in when is it better to use SAT, when rays, when splines, and whether there is anything better.

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• Typical collision detection

  - by marcg11

  I would like to know how is the typical collision detection of most games. For example, you control a character which can move in 2 dimensional directions (except up and down). Now lets asume he walks into a wall, most of the games depending on character angle and the BB normal face will only stop the player in one axis, but will continue moving in the other along the wall axis. How is that done? I've only managed to stop the character from going through the wall by seting the position to the last one in the past frame if the new position colllisions the bounding box. But this just makes the player stop sharply and unrealisticly.

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• Making an efficient collision detection system

  - by Sri Harsha Chilakapati

  I'm very new to game development (just started 3 months ago) and I'm learning through creating a game engine. It's located here. In terms of collision, I know only brute-force detection, in which case, the game slows down if there are a number of objects. So my question is How should I program the collisions? I want them to happen automatically for every object and call the object's collision(GObject other) method on each collision. Are there any new algorithms which can make this fast? If so, can anybody shed some light on this topic?

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• Collision detection with entities/AI

  - by James Williams

  I'm making my first game in Java, a top down 2D RPG. I've handled basic collision detection, rendering and have added an NPC, but I'm stuck on how to handle interaction between the player and the NPC. Currently I'm drawing out my level and then drawing characters, NPCs and animated tiles on top of this. The problem is keeping track of the NPCs so that my Character class can interact with methods in the NPC classes on collision. I'm not sure my method of drawing the level and drawing everything else on top is a good one - can anyone shed any light on this topic?

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• Making a collision detection system

  - by Sri Harsha Chilakapati

  I'm very new to game development (just started 3 months ago) and I've learning through creating a game engine. It's located here. In terms of collision, I know only brutefoce detection, in which case, the game slows down if there are a number of objects. So my question is How should I program the collisions? I want them to happen automatically for every object and call the object's collision(GObject other) method on each collision. Are there any new algorithms which can make this fast? If so, can anybody6 sh6ed some light on this topic? And I think of making it like the game maker Thanks

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• Continuous Collision Detection Techniques

  - by Griffin

  I know there are quite a few continuous collision detection algorithms out there , but I can't find a list or summary of different 2D techniques; only tutorials on specific algorithms. What techniques are out there for calculating when different 2D bodies will collide and what are the advantages / disadvantages of each? I say techniques and not algorithms because I have not yet decided on how I will store different polygons which might be concave or even have holes. I plan to make a decision on this based on what the algorithm requires (for instance if an algorithm breaks down a polygon into triangles or convex shapes I will simply store the polygon data in this form).

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• Circle vs Edge collision detection / resolution

  - by topheman

  I made a javascript class Ball.js that handles physics interactions betweens balls as well as painting. In the v1.0, the ball vs ball collision detection and resolution is well handled. In the next version (v2), I'm trying to add edgeCollision handling. I'm having some problems, maybe you will be able to help me. All the v2 branch source code is on github repository : https://github.com/topheman/Ball.js/tree/v2 The v2 demos (where you can see the bug I will be talking about) : http://labs.topheman.com/Ball-v2/#help As you will see on the demo, I have two major problems that I'm having a really hard time to solve on Ball.js : method resolveEdgeCollision : bounce angle is inconsistent method checkEdgeCollision : if the ball's velocity (the length that it runs each frame) is higher than its diameter, eventually, it will pass through an edge, without triggering any collision Any Ideas ?...

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• Collision detection in multiplayer games

  - by Bane

  This a followup to my previous question: How to implement physics and AoE spells in an MMO game?. There, we concluded that all physics have to be done on the server, and that I should use cylinders for calculations. Now, how can I check for collision detection on a ground-to-player basis on the server? It's fairly easy if the ground is a flat space, I just check if the player's z coordinate is lower than some value and voila, but, what if the map/ground itself is a model? How do I know where hills are on the server-side? How do I know when object collisions happen? I'm using node.js and socket.io.

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• Fixing a collision detection bug in Slick2D

  - by Jesse Prescott

  My game has a bug with collision detection. If you go against the wall and tap forward/back sometimes the game thinks the speed you travelled at is 0 and the game doesn't know how to get you out of the wall. My collision detection works by getting the speed you hit the wall at and if it is positive it moves you back, if it is negative it moves you forward. It might help if you download it: https://rapidshare.com/files/1550046269/game.zip Sorry if I explained badly, it's hard to explain. float maxSpeed = 0.3f; float minSpeed = -0.2f; float acceleration = 0.002f; float deacceleration = 0.001f; float slowdownSpeed = 0.002f; float rotateSpeed = 0.08f; static float currentSpeed = 0; boolean up = false; boolean down = false; boolean noKey = false; static float rotate = 0; //Image effect system static String locationCarNormal; static String locationCarFront; static String locationCarBack; static String locationCarBoth; static boolean carFront = false; static boolean carBack = false; static String imageRef; boolean collision = false; public ComponentPlayerMovement(String id, String ScarNormal, String ScarFront, String ScarBack, String ScarBoth) { this.id = id; playerBody = new Rectangle(900/2-16, 700/2-16, 32, 32); locationCarNormal = ScarNormal; locationCarFront = ScarFront; locationCarBack = ScarBack; locationCarBoth = ScarBoth; imageRef = locationCarNormal; } @Override public void update(GameContainer gc, StateBasedGame sbg, int delta) throws SlickException { Input input = gc.getInput(); playerBody.transform(Transform.createRotateTransform(2)); float hip = currentSpeed * delta; float unstuckspeed = 0.05f * delta; if(carBack && !carFront) { imageRef = locationCarBack; ComponentImageRender.updateImage(); } else if(carFront && !carBack) { imageRef = locationCarFront; ComponentImageRender.updateImage(); } else if(carFront && carBack) { imageRef = locationCarBoth; ComponentImageRender.updateImage(); } if(input.isKeyDown(Input.KEY_RIGHT)) { rotate += rotateSpeed * delta; owner.setRotation(rotate); } if(input.isKeyDown(Input.KEY_LEFT)) { rotate -= rotateSpeed * delta; owner.setRotation(rotate); } if(input.isKeyDown(Input.KEY_UP)) { if(!collision) { up = true; noKey = false; if(currentSpeed < maxSpeed) { currentSpeed += acceleration; } MapCoordStorage.mapX += hip * Math.sin(Math.toRadians(rotate)); MapCoordStorage.mapY -= hip * Math.cos(Math.toRadians(rotate)); } else { currentSpeed = 1; } } else if(input.isKeyDown(Input.KEY_DOWN) && !collision) { down = true; noKey = false; if(currentSpeed > minSpeed) { currentSpeed -= slowdownSpeed; } MapCoordStorage.mapX += hip * Math.sin(Math.toRadians(rotate)); MapCoordStorage.mapY -= hip * Math.cos(Math.toRadians(rotate)); } else { noKey = true; if(currentSpeed > 0) { currentSpeed -= deacceleration; } else if(currentSpeed < 0) { currentSpeed += acceleration; } MapCoordStorage.mapX += hip * Math.sin(Math.toRadians(rotate)); MapCoordStorage.mapY -= hip * Math.cos(Math.toRadians(rotate)); } if(entityCollisionWith()) { collision = true; if(currentSpeed > 0 || up) { up = true; currentSpeed = 0; carFront = true; MapCoordStorage.mapX += unstuckspeed * Math.sin(Math.toRadians(rotate-180)); MapCoordStorage.mapY -= unstuckspeed * Math.cos(Math.toRadians(rotate-180)); } else if(currentSpeed < 0 || down) { down = true; currentSpeed = 0; carBack = true; MapCoordStorage.mapX += unstuckspeed * Math.sin(Math.toRadians(rotate)); MapCoordStorage.mapY -= unstuckspeed * Math.cos(Math.toRadians(rotate)); } else { currentSpeed = 0; } } else { collision = false; up = false; down = false; } if(currentSpeed >= -0.01f && currentSpeed <= 0.01f && noKey && !collision) { currentSpeed = 0; } } public static boolean entityCollisionWith() throws SlickException { for (int i = 0; i < BlockMap.entities.size(); i++) { Block entity1 = (Block) BlockMap.entities.get(i); if (playerBody.intersects(entity1.poly)) { return true; } } return false; } }

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