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• Circle physics and collision using vectors

  - by Joe Hearty

  This is a problem I've been having, When making a set number of filled circles at random locations on a JPanel and applying a gravity (a negative change in the y), each of the circles collide. I want them to have collision detection and push in the opposite direction using vectors but I don't know how to apply that to my scenario could someone help? public void drawballs(Graphics g){ g.setColor (Color.white); //displays circles for(int i = 0; i<xlocationofcircles.length-1; i++){ g.fillOval( (int) xlocationofcircles[i], (int) (ylocationofcircles[i]) ,16 ,16 ); ylocationofcircles[i]+=.2; //gravity if(ylocationofcircles[i] > 550) //stops gravity at bottom of screen ylocationofcircles[i]-=.2; //Check distance between circles(i think..) float distance =(xlocationofcircles[i+1]-xlocationofcircles[i]) + (ylocationofcircles[i+1]-xlocationofcircles[i]); if( Math.sqrt(distance) <16) ...

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• Collision representation in game overworlds

  - by Akroy

  I'm implementing a 2D overworld where one can walk through an area that is not tile based. I was wondering the best way to implement collisions. In the past when I've done similar things, I've used one image (or set of images) to show an elaborately drawn world and then a second binary image that does nothing but differentiate "wall" and "not wall". Then, I'd use the first for all drawing to the screen, but the second for collision detection. Having another image of the same size to represent collisions seems like lots of overhead. Is there a better way to handle this? (I'm currently using C++ with SDL, although I'm more interested in general concepts)

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• 3d Collision Handling

  - by TobSpr

  I have trouble while detecting collisions on my 3D-Game. I have set-up Rays, to detect collisions (Screenshot) and my main-rountine already analyzes them. But now there's the question what to do with that. One possibility would be, to move the player back to the last position, but that's dirty, and does not work if the player can walk in multiple directions (e.g. if the player runs along a wall). My question is, what to do with the collision data / or in which direction, by which amount move the player? I'm sure there is an algorithm for that (as for almost all is).

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• Checking collision of bullets and Asteroids

  - by Moaz ELdeen

  I'm trying to detect collision between two list of bullets and asteroids. The code works fine, but when the bullet intersects with an asteroid, and that bullet passes through another asteroid, the code gives an assertion, and it says about it can't increment the iterator. I'm sure there is a small bug in that code, but I can't find it. for (list<Bullet>::iterator itr_bullet = ship.m_Bullets.begin(); itr_bullet!=ship.m_Bullets.end();) { for (list<Asteroid>::iterator itr_astroid = asteroids.begin(); itr_astroid!=asteroids.end(); itr_astroid++) { if(checkCollision(itr_bullet->getCenter(),itr_astroid->getCenter(), itr_bullet->getRadius(), itr_astroid->getRadius())) { itr_astroid = asteroids.erase(itr_astroid); } } itr_bullet++; }

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• Color based collision detection

  - by user1486826

  I am making a game where you fly a ship around some randomly generated planets. Since I am using a for loop to draw over 5000 planets, using the rectangle class or an oval-type class for this is not an option, since creating many objects will severely affect performance. Bitmasking each planet will likely result in performance issues too, so the only candidate is color based collision detection, because I don't need to apply some sort of object to everything I want to check for collisions. Is any way to check the perimeter around the ship for a certain color?

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• Make the player run onto stairs smoothly

  - by misiMe

  I have a 2D Platform game, where the player Always runs to the right, but the terrain isn't Always horizontal. Example: I implemented a bounding-box collision system that just checks for intersections with player box and the other blocks, to stop player from running if you encounter a big block, so that you have to jump, but when I put stairs, I want him to run smoothly just like he is on the horizontal ground. With the collision system you have to jump the stairs in order to pass them! I thought about generating a line between the edges of the stairs, and imposing the player movement on that line... What do you think? Is there something more clever to do?

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• how to keep display tick rate steady when using continuous collision detection?

  - by nas Ns

  (I've just found about this forum). I hope it is ok to repost my question again here. I posted this question at stackoverflow, but it looks like I might get better help here. Here is the question: I've implemented basic particles motion simulation with continuous collision detection. But there is small issue in display. Assume simple case of circles moving inside square. All elastic collisions. no firction. All motion is constant speed. No forces are involved, no gravity. So when a particle is moving, it is always moving at constant speed (in between collisions) What I do now is this: Let the simulation time step be 1 second (for example). This is the time step simulation is advanced before displaying the new state (unless there is a collision sooner than this). At start of each time step, time for the next collision between any particles or a particle with a wall is determined. Call this the TOC time; let’s say TOC was .5 seconds in this case. Since TOC is smaller than the standard time step, then the system is moved by TOC and the new system is displayed so that the new display shows any collisions as just taking place (say 2 circles just touched each other’s, or a circle just touched a wall) Next, the collision(s) are resolved (i.e. speeds updated, changed directions etc..). A new step is started. The same thing happens. Now assume there is no collision detected within the next 1 second (those 2 circles above will not be in collision any more, even though they are still touching, due to their speeds showing they are moving apart now), Hence, simulation time is advanced now by the full one second, the standard time step, and particles are moved on the screen using 1 second simulation time and new display is shown. You see what has just happened: One frame ran for .5 seconds, but the next frame runs for 1 second, may be the 3rd frame is displayed after 2 seconds, may be the 4th frame is displayed after 2.8 seconds (because TOC was .8 seconds then) and so on. What happens is that the motion of a particle on the screen appears to speed up or slow down, even though it is moving at constant speed and was not even involved in a collision. i.e. Looking at one particle on its own, I see it suddenly speeding up or slowing down, becuase another particle had hit a wall. This is because the display tick is not uniform. i.e. the frame rate update is changing, giving the false illusion that a particle is moving at non-constant speed while in fact it is moving at constant speed. The motion on the screen is not smooth, since the screen is not updating at constant rate. I am not able to figure how to fix this. If I want to show 2 particles at the moment of the collision, I must draw the screen at different times. Drawing the screen always at the same tick interval, results in seeing 2 particles before the collision, and then after the collision, and not just when they colliding, which looked bad when I tried it. So, how do real games handle this issue? How to display things in order to show collisions when it happen, yet keep the display tick constant? These 2 requirements seem to contradict each other’s.

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• Per Pixel Collision Detection

  - by CJ Cohorst

  Just a quick question, I have this collision detection code: public bool PerPixelCollision(Player player, Game1 dog) { Matrix atob = player.Transform * Matrix.Invert(dog.Transform); Vector2 stepX = Vector2.TransformNormal(Vector2.UnitX, atob); Vector2 stepY = Vector2.TransformNormal(Vector2.UnitY, atob); Vector2 iBPos = Vector2.Transform(Vector2.Zero, atob); for(int deltax = 0; deltax < player.playerTexture.Width; deltax++) { Vector2 bpos = iBPos; for (int deltay = 0; deltay < player.playerTexture.Height; deltay++) { int bx = (int)bpos.X; int by = (int)bpos.Y; if (bx >= 0 && bx < dog.dogTexture.Width && by >= 0 && by < dog.dogTexture.Height) { if (player.TextureData[deltax + deltay * player.playerTexture.Width].A > 150 && dog.TextureData[bx + by * dog.Texture.Width].A > 150) { return true; } } bpos += stepY; } iBPos += stepX; } return false; } What I want to know is where to put in the code where something happens. For example, I want to put in player.playerPosition.X -= 200 just as a test, but I don't know where to put it. I tried putting it under the return true and above it, but under it, it said unreachable code, and above it nothing happened. I also tried putting it by bpos += stepY; but that didn't work either. Where do I put the code? Any help is appreciated. Thanks in advance!

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• Space-efficient data structures for broad-phase collision detection

  - by Marian Ivanov

  As far as I know, these are three types of data structures that can be used for collision detection broadphase: Unsorted arrays: Check every object againist every object - O(n^2) time; O(log n) space. It's so slow, it's useless if n isn't really small. for (i=1;i<objects;i++){ for(j=0;j<i;j++) narrowPhase(i,j); }; Sorted arrays: Sort the objects, so that you get O(n^(2-1/k)) for k dimensions O(n^1.5) for 2d and O(n^1.67) for 3d and O(n) space. Assuming the space is 2D and sortedArray is sorted so that if the object begins in sortedArray[i] and another object ends at sortedArray[i-1]; they don't collide Heaps of stacks: Divide the objects between a heap of stacks, so that you only have to check the bucket, its children and its parents - O(n log n) time, but O(n^2) space. This is probably the most frequently used approach. Is there a way of having O(n log n) time with less space? When is it more efficient to use sorted arrays over heaps and vice versa?

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• Collision detection code style

  - by Marian Ivanov

  Not only there are two useful broad-phase algorithms and a lot of useful narrowphase algorithms, there are also multiple code styles. Arrays vs. calling Make an array of broadphase checks, then filter them with narrowphase checks, then resolve them. function resolveCollisions(thingyStructure * a,thingyStructure * b,int index){ possibleCollisions = getPossibleCollisions(b,a->get(index)); for(i=0; i<possibleCollitionsNumber; i++){ if(narrowphase(possibleCollisions[i],a[index])) { collisions->push(possibleCollisions[i]); }; }; for(i=0; i<collitionsNumber; i++){ //CODE FOR RESOLUTION }; }; Make the broadphase call the narrowphase, and the narrowphase call the resolution function resolveCollisions(thingyStructure * a,thingyStructure * b,int index){ broadphase(b,a->get(index)); }; function broadphase(thingy * with, thingy * what){ while(blah){ //blahcode narrowphase(what,collidingThing); }; }; Events vs. in-the-loop Fire an event. This abstracts the check away, but it's trickier to make an equal interaction. a[index] -> collisionEvent(eventdata); //much later int collisionEvent(eventdata){ //resolution gets here } Resolve the collision inside the loop. This glues narrowphase and resolution into one layer. if(narrowphase(possibleCollisions[i],a[index])) { //CODE GOES HERE }; The questions are: Which of the first two is better, and how am I supposed to make a zero-sum Newtonian interaction under B1.

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• Breakout ball collision detection, bouncing against the walls

  - 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

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• XNA 4.0 2D sidescroller variable terrain heightmap for walking/collision

  - by JiminyCricket

  I've been fooling around with moving on sloped tiles in XNA and it is semi-working but not completely satisfactory. I also have been thinking that having sets of predetermined slopes might not give me terrain that looks "organic" enough. There is also the problem of having to construct several different types of tile for each slope when they're chained together (only 45 degree tiles will chain perfectly as I understand it). I had thought of somehow scanning for connected chains of sloped tiles and treating it as a new large triangle, as I was having trouble with glitching at the edges where sloped tiles connect. But, this leads back to the problem of limiting the curvature of the terrain. So...what I'd like to do now is create a simple image or texture of the terrain of a level (or section of the level) and generate a simple heightmap (of the Y's for each X) for the terrain. The player's Y position would then just be updated based on their X position. Is there a simple way of doing this (or a better way of solving this problem)? The main problem I can see with this method is the case where there are areas above the ground that can be walked on. Maybe there is a way to just map all walkable ground areas? I've been looking at this helpful bit of code: http://thirdpartyninjas.com/blog/2010/07/28/sloped-platform-collision/ but need a way to generate the actual points/vectors.

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• Circle collision detection and Vector math: HELP?

  - by Griffin

  Hey so i'm currently going through the wildbunny blog to learn about collision detection, but i'm a bit confused on how the vectors he's talking about come into play QUOTED BLOG: p = ||A-B|| – (r1+r2) The two spheres are penetrating by distance p. We would also like the penetration vector so that we can correct the penetration once we discover it. This is the vector that moves both circles to the point where they just touch, correcting the penetration. Importantly it is not only just a vector that does this, it is the only vector which corrects the penetration by moving the minimum amount. This is important because we only want to correct the error, not introduce more by moving too much when we correct, or too little. N = (A-B) / ||A-B|| P = N*p Here we have calculated the normalised vector N between the two centres and the penetration vector P by multiplying our unit direction by the penetration distance. Ok so i understand that p is the distance each circle is penetrating each other, but i don't get what exactly N and P is. it seems to me N is just the coordinates of the 3rd point of the right trianlge formed by point A and B (A-B) then being divided by the hypotenuse of that triangle or distance between A and B (||A-B||) Whats the significance of this? Also, what is the penetration vector used for? It seems to me like a movement that one of the circles would perform to get un-penetrated.

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• Can't detect collision properly using Rectangle.Intersects()

  - by Daniel Ribeiro

  I'm using a single sprite sheet image as the main texture for my breakout game. The image is this: My code is a little confusing, since I'm creating two elements from the same Texture using a Point, to represent the element size and its position on the sheet, a Vector, to represent its position on the viewport and a Rectangle that represents the element itself. Texture2D sheet; Point paddleSize = new Point(112, 24); Point paddleSheetPosition = new Point(0, 240); Vector2 paddleViewportPosition; Rectangle paddleRectangle; Point ballSize = new Point(24, 24); Point ballSheetPosition = new Point(160, 240); Vector2 ballViewportPosition; Rectangle ballRectangle; Vector2 ballVelocity; My initialization is a little confusing as well, but it works as expected: paddleViewportPosition = new Vector2((GraphicsDevice.Viewport.Bounds.Width - paddleSize.X) / 2, GraphicsDevice.Viewport.Bounds.Height - (paddleSize.Y * 2)); paddleRectangle = new Rectangle(paddleSheetPosition.X, paddleSheetPosition.Y, paddleSize.X, paddleSize.Y); Random random = new Random(); ballViewportPosition = new Vector2(random.Next(GraphicsDevice.Viewport.Bounds.Width), random.Next(GraphicsDevice.Viewport.Bounds.Top, GraphicsDevice.Viewport.Bounds.Height / 2)); ballRectangle = new Rectangle(ballSheetPosition.X, ballSheetPosition.Y, ballSize.X, ballSize.Y); ballVelocity = new Vector2(3f, 3f); The problem is I can't detect the collision properly, using this code: if(ballRectangle.Intersects(paddleRectangle)) { ballVelocity.Y = -ballVelocity.Y; } What am I doing wrong?

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• Collision detection with non-rectangular images

  - by Adam Smith

  I'm creating a game and I need to detect collisions between a character and some parts of the environment. Since my character's frames are taken from a sprite sheet with a transparent background, I'm wondering how I should go about detecting collisions between a wall and my character only if the colliding parts are non-transparent in both images. I thought about checking only if part of the rectangle the character is in touches the rectangle a tile is in and comparing the alpha channels, but then I have another choice to make... Either I test every single pixel against every single pixel in the other image and if one is true, I detect a collision. That would be terribly ineficient. The other option would be to keep a x,y position of the leftmost, rightmost, etc. non-transparent pixel of each image and compare those instead. The problem with this one might be that, for instance, the character's hand could be above a tile (so it would be in a transparent zone of the tile) but a pixel that is not the rightmost could touch part of the tile without being detected. Another problem would be that in different frames, the rightmost, leftmost, etc. pixels might not be at the same position. Should I not bother with that and just check the collisions on the rectangles? It would be simpler, but I'm afraid people.will feel that there are collisions sometimes that shouldn't happen.

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• Basic 3D Collision detection in XNA 4.0

  - by NDraskovic

  I have a problem with detecting collision between 2 models using BoundingSpheres in XNA 4.0. The code I'm using i very simple: private bool IsCollision(Model model1, Matrix world1, Model model2, Matrix world2) { for (int meshIndex1 = 0; meshIndex1 < model1.Meshes.Count; meshIndex1++) { BoundingSphere sphere1 = model1.Meshes[meshIndex1].BoundingSphere; sphere1 = sphere1.Transform(world1); for (int meshIndex2 = 0; meshIndex2 < model2.Meshes.Count; meshIndex2++) { BoundingSphere sphere2 = model2.Meshes[meshIndex2].BoundingSphere; sphere2 = sphere2.Transform(world2); if (sphere1.Intersects(sphere2)) return true; } } return false; } The problem I'm getting is that when I call this method from the Update method, the program behaves as if this method always returns true value (which of course is not correct). The code for calling is very simple (although this is only the test code): if (IsCollision(model1, worldModel1, model2, worldModel2)) { Window.Title = "Intersects"; } What is causing this?

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• libgdx collision detection / bounding the object

  - by johnny-b

  i am trying to get collision detection so i am drawing a red rectangle to see if it is working, and when i do the code below in the update method. to check if it is going to work. the position is not in the right place. the red rectangle starts from the middle and not at the x and y point?Huh so it draws it wrong. i also have a getter method so nothing wrong there. bullet.set(getX(), getY(), getOriginX(), getOriginY()); this is for the render shapeRenderer.begin(ShapeType.Filled); shapeRenderer.setColor(Color.RED); shapeRenderer.rect(bullet.getX(), bullet.getY(), bullet.getOriginX(), bullet.getOriginY(), 15, 5, bullet.getRotation()); shapeRenderer.end(); i have tried to do it with a circle but the circle draws in the middle and i want it to be at the tip of the bullet. at the front of the bullet. x, y point. boundingCircle.set(getX() + getOriginX(), getY() + getOriginY(), 4.0f); shapeRenderer.begin(ShapeType.Filled); shapeRenderer.setColor(Color.RED); shapeRenderer.circle(bullet.getBoundingCircle().x, bullet.getBoundingCircle().y, bullet.getBoundingCircle().radius); shapeRenderer.end(); thank you need it to be of the x and y as the bullet is in the middle of the sprite when drawn originally via paint.

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• Collision detection - player gets stuck in platform when jumping

  - by Sun

  So I'm having some problems with my collision detection with my platformer. Take the image below as an example. When I'm running right I am unable to go through the platform, but when I hold my right key and jump, I end up going through the object as shown in the image, below is the code im using: if(shapePlatform.intersects(player.getCollisionShape())){ Vector2f vectorSide = new Vector2f(shapePlatform.getCenter()[0] - player.getCollisionShape().getCenter()[0], shapePlatform.getCenter()[1] - player.getCollisionShape().getCenter()[1]); player.setVerticleSpeed(0f); player.setJumping(false); if(vectorSide.x > 0 && !(vectorSide.y > 0)){ player.getPosition().set(player.getPosition().x-3, player.getPosition().y); }else if(vectorSide.y > 0){ player.getPosition().set(player.getPosition().x, player.getPosition().y); }else if(vectorSide.x < 0 && !(vectorSide.y > 0)){ player.getPosition().set(player.getPosition().x+3, player.getPosition().y); } } I'm basically getting the difference between the centre of the player and the centre of the colliding platform to determine which side the player is colliding with. When my player jumps and walks right on the platform he goes right through. The same can also be observed when I jump on the actual platform, should I be resetting the players y in this situation?

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• 3D physics engine for accurate collision handling on desktop/laptop computers (non-console)

  - by Georges Oates Larsen

  What are your suggestions for a physics engine that satisfies the following criteria? Capable of calculating collisions between multiple concave mesh-based colliders Handles many collisions going on at once (for instance one mesh being wedged between two others, which themselves may be wedged between two meshes) Does not allow for collider passthrough, even at high speeds. For instance, if I am applying force to a programmatically hinged object that makes it spin, I do not want it to pass through another rigidbody that it collides with while spinning. I have this problem using PhysX As implied before, reacts well to hinged objects, preferably has its own implementation of a hinge, but I am willing to program my own. The important part is that it has some sort of interface that guarantees accurate collision tracking even when dealing with these things Platform independent -- runs on mac as well as PC, also not tied down to specific graphics cards I think that's the best way to explain what I am looking for. Basically, I need SUPER reliable collisions. Something that can't be accomplished with a simple ray casting approach that sends a ray from the last position of the object to the current position (as this object may be potentially large and colliding with small objects via rotation) Bonus points for also including an OPEN SOURCE engine.

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• Collision detection between a sprite and rectangle in canvas

  - by Andy

  I'm building a Javascript + canvas game which is essentially a platformer. I have the player all set up and he's running, jumping and falling, but I'm having trouble with the collision detection between the player and blocks (the blocks will essentially be the platforms that the player moves on). The blocks are stored in an array like this: var blockList = [[50, 400, 100, 100]]; And drawn to the canvas using this: this.draw = function() { c.fillRect(blockList[0][0], blockList[0][1], 100, 100); } I'm checking for collisions using something along these lines in the player object: this.update = function() { // Check for collitions with blocks for(var i = 0; i < blockList.length; i++) { if((player.xpos + 34) > blockList[i][0] && player.ypos > blockList[i][1]) { player.xpos = blockList[i][0] - 28; return false; } } // Other code to move the player based on keyboard input etc } The idea is if the player will collide with a block in the next game update (the game uses a main loop running at 60Htz), the function will return false and exit, thus meaning the player won't move. Unfortunately, that only works when the player hits the left side of the block, and I can't work out how to make it so the player stops if it hits any side of the block. I have the properties player.xpos and player.ypos to help here.

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• How does this circle collision detection math work?

  - by Griffin

  I'm going through the wildbunny blog to learn about collision detection. I'm confused about how the vectors he's talking about come into play. Here's the part that confuses me: p = ||A-B|| – (r1+r2) The two spheres are penetrating by distance p. We would also like the penetration vector so that we can correct the penetration once we discover it. This is the vector that moves both circles to the point where they just touch, correcting the penetration. Importantly it is not only just a vector that does this, it is the only vector which corrects the penetration by moving the minimum amount. This is important because we only want to correct the error, not introduce more by moving too much when we correct, or too little. N = (A-B) / ||A-B|| P = N*p Here we have calculated the normalised vector N between the two centres and the penetration vector P by multiplying our unit direction by the penetration distance. I understand that p is the distance by which the circles penetrate, but I don't get what exactly N and P are. It seems to me N is just the coordinates of the 3rd point of the right trianlge formed by point A and B (A-B) then being divided by the hypotenuse of that triangle or distance between A and B (||A-B||). What's the significance of this? Also, what is the penetration vector used for? It seems to me like a movement that one of the circles would perform to get un-penetrated.

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• Wall jumping collision detection anomaly

  - by Nanor

  I'm creating a game where the player ascends a tower by wall jumping his way to the top. When the player has collided with the right wall they can only jump left and vice versa. Here is my current implementation: if(wallCollision() == "left"){ player.setPosX(0); player.setVelX(0); ignoreCollisions = true; player.setCanJump(true); player.setFacingLeft(false); } else if (wallCollision() == "right"){ player.setPosX(screenWidth-playerWidth*2); player.setVelX(0); ignoreCollisions = true; player.setCanJump(true); player.setFacingLeft(true); } else{ player.setVelY(player.getVelY() + gravity); } and private String wallCollision(){ if(player.getPosX() < playerWidth && !ignoreCollisions) return "left"; else if(player.getPosX() > screenWidth - playerWidth*2 && !ignoreCollisions) return "right"; else{ timeToJump += Gdx.graphics.getDeltaTime(); if(timeToJump > 0.50f){ timeToJump = 0; ignoreCollisions = false; } return "jumping"; } } If the player is colliding with the left wall it will switch between the states left and jumping repeatedly due to the varible ignoreCollisions being switched repeatedly in collision checks. This will give a chance to either jump as intended or simply ascend vertically instead of diagonally. I can't figure out an implementation that will reliably make sure the player jumps as intended. Does anyone have any pointers?

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• Determining whether two fast moving objects should be submitted for a collision check

  - by dreta

  I have a basic 2D physics engine running. It's pretty much a particle engine, just uses basic shapes like AABBs and circles, so no rotation is possible. I have CCD implemented that can give accurate TOI for two fast moving objects and everything is working smoothly. My issue now is that i can't figure out how to determine whether two fast moving objects should even be checked against each other in the first place. I'm using a quad tree for spacial partitioning and for each fast moving object, i check it against objects in each cell that it passes. This works fine for determining collision with static geometry, but it means that any other fast moving object that could collide with it, but isn't in any of the cells that are checked, is never considered. The only solution to this i can think of is to either have the cells large enough and cross fingers that this is enough, or to implement some sort of a brute force algorithm. Is there a proper way of dealing with this, maybe somebody solved this issue in an efficient manner. Or maybe there's a better way of partitioning space that accounts for this?

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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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• 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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