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• simple collision detection with box2dweb

  - by skywalker

  im beginner in box2dweb that version of box2d for javascript i wrote simple gravity system and i want to detect the collision between the box and the ground , when the falling box hit the ground execute simple function like function sucs(){alert("the box on the floor !")}; this is my code var CANVAS_WIDTH = 1024, CANVAS_HEIGHT = 700, SCALE = 30; var b2Vec2 = Box2D.Common.Math.b2Vec2 , b2BodyDef = Box2D.Dynamics.b2BodyDef , b2Body = Box2D.Dynamics.b2Body , b2FixtureDef = Box2D.Dynamics.b2FixtureDef , b2Fixture = Box2D.Dynamics.b2Fixture , b2World = Box2D.Dynamics.b2World , b2MassData = Box2D.Collision.Shapes.b2MassData , b2PolygonShape = Box2D.Collision.Shapes.b2PolygonShape , b2CircleShape = Box2D.Collision.Shapes.b2CircleShape , b2DebugDraw = Box2D.Dynamics.b2DebugDraw; var canvas = document.getElementById("canvas"); var context = canvas.getContext("2d"); var world = new b2World(new b2Vec2(0, 8), true); var fixDef = new b2FixtureDef(); var bodyDef = new b2BodyDef(); fixDef.density = 1.0; fixDef.friction = 0.5; bodyDef.type = b2Body.b2_staticBody; fixDef.shape = new b2PolygonShape; fixDef.shape.SetAsBox(20, 2); bodyDef.position.Set(10, 400 / 30 + 1.8); world.CreateBody(bodyDef).CreateFixture(fixDef); fixDef.density = 1.0; fixDef.friction = 0.5; fixDef.restitution = 0.3; bodyDef.type = b2Body.b2_dynamicBody; bodyDef.position.Set(50 / SCALE, 0 / SCALE); //bodyDef.linearVelocity.Set((Math.random() * 12) + 2, (Math.random() * 12) + 2); fixDef.shape = new b2PolygonShape(); fixDef.shape.SetAsBox(25 / SCALE, 25 / SCALE); world.CreateBody(bodyDef).CreateFixture(fixDef); var debugDraw = new b2DebugDraw(); debugDraw.SetSprite(document.getElementById("canvas").getContext("2d")); debugDraw.SetDrawScale(30.0); debugDraw.SetFillAlpha(0.5); debugDraw.SetLineThickness(1.0); debugDraw.SetFlags(b2DebugDraw.e_shapeBit | b2DebugDraw.e_jointBit); world.SetDebugDraw(debugDraw); var image = new Image(); image.src = "image.png"; window.setInterval(gameLoop, 1000 / 60); function gameLoop() { world.Step(1 / 60, 8, 3); world.ClearForces(); context.clearRect(0, 0, CANVAS_WIDTH, CANVAS_HEIGHT); b = world.GetBodyList() var pos = b.GetPosition(); context.save(); context.translate(pos.x * SCALE, pos.y * SCALE); context.rotate(b.GetAngle()); context.drawImage(image, -25, -25); context.restore(); b = b.GetNext(); pos = b.GetPosition(); context.save(); context.translate(pos.x * SCALE, pos.y * SCALE); //b.GetAngle()++; context.rotate(b.GetAngle()); context.drawImage(image, -25, -25); context.restore(); world.DrawDebugData(); };

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• 2D Side Scrolling game and "walk over ground" collision detection

  - by Fire-Dragon-DoL

  The question is not hard, I'm writing a game engine for 2D side scrolling games, however I'm thinking to my 2D side scrolling game and I always come up with the problem of "how should I do collision with the ground". I think I couldn't handle the collision with ground (ground for me is "where the player walk", so something heavily used) in a per-pixel way, and I can't even do it with simple shape comparison (because the ground can be tilted), so what's the correct way? I'know what tiles are and i've read about it, but how much should be big each tile to not appear like a stairs?Are there any other approach? I watched this game and is very nice how he walks on ground: http://www.youtube.com/watch?v=DmSAQwbbig8&feature=player_embedded If there are "platforms" in mid air, how should I handle them?I can walk over them but I can't pass "inside". Imagine a platform in mid air, it allows you to walk over it but limit you because you can't jump in the area she fits Sorry for my english, it's not my native language and this topic has a lot of keywords I don't know so I have to use workarounds Thanks for any answer Additional informations and suggestions: I'm doing a game course in this period and I asked them how to do this, they suggested me this approach (a QuadTree): -All map is divided into "big nodes" -Each bigger node has sub nodes, to find where the player is -You can find player's node with a ray on player position -When you find the node where the player is, you can do collision check through all pixels (which can be 100-200px nothing more) Here is an example, however i didn't show very well the bigger nodes because i'm not very good with photoshop :P How is this approach?

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• Collision Detection and Resolution in Three.js

  - by androidmaster

  So at the moment am making a simple game using three.js and three.firstpersonControls.js but with the current Three.js r66, they apparently removed checkWallCollision and then in the r67 firstpersonControls removed support for that collision. SO my question is how would i go about checking collision in 3D using three.js and then resolution to that collision. (Pushing player out of the block) Note I used a 2D array to generate the world so it's only cubes that I have to check collision with.... if this is a bad question or am lacking something please tell me before you -rep me, am just not sure how to do this and google doesn't want to help

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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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• how to create 2D collision detection

  - by Aidan Mueller

  I would like to know the best or most effective way to test for 2D collision. I also can do AABBs but when you have a line, for example, that is rotated 45º, and it is really long. it will be hitting things when it shouldn't. I might be able to go through the pixels to see if they are touching others, but that might be slow if I had a big picture. and it might add some complications if I had a movie clip made of several images. How do I check collision between two Images? How would I do circle to box? Please help : ) PS: I do know java so you can write with java syntax and then use a made up GL

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• Project collision shapes to plane for 2.5D collision detection

  - by Jkh2

  I am working on a top down 2.5D game. In the game anything that overlaps on the screen should be 'colliding' with each other regardless of whether they are on the same plane in the 3D world. This is illustrated below from a side-ways view: The orange and green circles are spheres floating in the 3D world. They are projected onto a plane parallel to the viewport plane (y = 0 in the image) and if they overlap there is a collision event between them. These spheres are attached to other meshes to represent the sphere bounding boxes for collisions. The way I plan to implement this at the moment is the following: Get the 3D world position at the center of the sphere. Use Camera.WorldToViewportPoint to project the point to the viewport plane. Move a Sphere Collider with the radius of the sphere to that point. Test for collisions using unity colliders. My question is how to extend this to work for rotated cuboids. For instance if I have two rotated cuboids, if I follow the logic above it would not work as intended as the cuboids may not collide but they could still be intersected on the view plane. An example is below: Is there a way to project a cuboid that would be aligned with the plane? Would it be a valid cuboid for all rotations if I did this?

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• Game physics / 2D Collision detection AS3

  - by Jery

  I know there are some methods you can use like hittestPoint and so on, but I want to see where my movieclip colliedes with another another movieclip. Any other methods I can use? by any chance does somebody know some a good introduction to game physics? Im asking because I coded a small engine and pretty much the whole code is spagetti code thats why I would like to know how you can setup something like this properly

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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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• How to optimize collision detection

  - by Niklas

  I am developing a 2D Java Game with LibGDX. This is what it kinda looks like (simplified): The big black circle is the player, which you can move by tilting the smartphone. The red circles and blue rectangles are enemies, which will move from the right of the screen to the left. The player has to avoid crashing into them. Right now I am checking in the Game Loop every enemy against the player, whether they collide or not. This seems kinda inefficient to me, but I don't know how to improve it. I have tried the Quadtree approach, but it did not really work. The player could easily glitch through enemies and the collision was not detected. Unfortunately, I have destroyed the Quadtree implementation. I used this [tutorial/blog] as my Quadtree implementation(http://gamedevelopment.tutsplus.com/tutorials/quick-tip-use-quadtrees-to-detect-likely-collisions-in-2d-space--gamedev-374).

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• checking for collision detection

  - by bill

  I am trying to create a game where you have a player and you can move right,left, and jump. kind of like mario but its not a side scroller. also i want to use 2d array to make a tile map. my big problem is that i dont understand how to check for collision. i spend about 2 week thinking about this and i came up with 2 solution but they both have problems. let say my map is: 0 = sky 1 = player 2 = ground 00000 10002 22022 Solution 1: move the '1'(player) and update the map less say player wants to move right, then x+=grid[x+1][y] this make the collision easy bc you can just check if if(grid[x][y+1] == 2){ //player is standing on top of ground } problem with this when u hit right key player will move (x*Titlewidth) to right. and as you can see the animation wont look smooth. Solution 2: move player and dont update map player_x += 2 this will make the animation more smoother bc i am just moving 2 pixels. problem1: i cant update map bc if player some times will be middle of int(2d array). but thats ok sinces its not a side scroller so updating the map is not a big deal. problem2: only way to check for collision is to use java intersection method. but then player have to be atleast 1 or 2 pixel in ground in order to check for collision. and as you can see that wont look good too. plz note this is my first collision game in java. so plz try to explain alot otherwise i wont understand it.

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• Unity Particle System collision detection problem

  - by Krav

  I'm using Unity 3.5.5f3 wich has the Shuriken particle system. I've made a blood particle system based on Unity's demos. (Exploding paint [Blood]) The blood is flowing and when it collides with a Plane Transform wich I've created a small pool of blood spawns as a Collision Sub Emitter. My main problem is that when I want to add another object to collide it just doesn't want to work. When I create a cube, and set it as a collision plane the collision will only occur at the half of the cube. I want this to happen: When it reaches the cube's surface the sub emmiter activates, and when the surface is horizontal it appears horizontally, and if it's vertical then vertically. Now it just appears horizontally everytime like in the picture. How could I solve it?

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• 2D SAT Collision Detection not working when using certain polygons

  - by sFuller

  My SAT algorithm falsely reports that collision is occurring when using certain polygons. I believe this happens when using a polygon that does not contain a right angle. Here is a simple diagram of what is going wrong: Here is the problematic code: std::vector<vec2> axesB = polygonB->GetAxes(); //loop over axes B for(int i = 0; i < axesB.size(); i++) { float minA,minB,maxA,maxB; polygonA->Project(axesB[i],&minA,&maxA); polygonB->Project(axesB[i],&minB,&maxB); float intervalDistance = polygonA->GetIntervalDistance(minA, maxA, minB, maxB); if(intervalDistance >= 0) return false; //Collision not occurring } This function retrieves axes from the polygon: std::vector<vec2> Polygon::GetAxes() { std::vector<vec2> axes; for(int i = 0; i < verts.size(); i++) { vec2 a = verts[i]; vec2 b = verts[(i+1)%verts.size()]; vec2 edge = b-a; axes.push_back(vec2(-edge.y,edge.x).GetNormailzed()); } return axes; } This function returns the normalized vector: vec2 vec2::GetNormailzed() { float mag = sqrt( x*x + y*y ); return *this/mag; } This function projects a polygon onto an axis: void Polygon::Project(vec2* axis, float* min, float* max) { float d = axis->DotProduct(&verts[0]); float _min = d; float _max = d; for(int i = 1; i < verts.size(); i++) { d = axis->DotProduct(&verts[i]); _min = std::min(_min,d); _max = std::max(_max,d); } *min = _min; *max = _max; } This function returns the dot product of the vector with another vector. float vec2::DotProduct(vec2* other) { return (x*other->x + y*other->y); } Could anyone give me a pointer in the right direction to what could be causing this bug?

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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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• 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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• 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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• efficient collision detection - tile based html5/javascript game

  - by Tom Burman

  Im building a basic rpg game and onto collisions/pickups etc now. Its tile based and im using html5 and javascript. i use a 2d array to create my tilemap. Im currently using a switch statement for whatever key has been pressed to move the player, inside the switch statement. I have if statements to stop the player going off the edge of the map and viewport and also if they player is about to land on a tile with tileID 3 then the player stops. Here is the statement: canvas.addEventListener('keydown', function(e) { console.log(e); var key = null; switch (e.which) { case 37: // Left if (playerX > 0) { playerX--; } if(board[playerX][playerY] == 3){ playerX++; } break; case 38: // Up if (playerY > 0) playerY--; if(board[playerX][playerY] == 3){ playerY++; } break; case 39: // Right if (playerX < worldWidth) { playerX++; } if(board[playerX][playerY] == 3){ playerX--; } break; case 40: // Down if (playerY < worldHeight) playerY++; if(board[playerX][playerY] == 3){ playerY--; } break; } viewX = playerX - Math.floor(0.5 * viewWidth); if (viewX < 0) viewX = 0; if (viewX+viewWidth > worldWidth) viewX = worldWidth - viewWidth; viewY = playerY - Math.floor(0.5 * viewHeight); if (viewY < 0) viewY = 0; if (viewY+viewHeight > worldHeight) viewY = worldHeight - viewHeight; }, false); My question is, is there a more efficient way of handling collisions, then loads of if statements for each key? The reason i ask is because i plan on having many items that the player will need to be able to pickup or not walk through like walls cliffs etc. Thanks for your time and help Tom

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• simple collision detection

  - by Rob

  Imagine 2 squares sitting side by side, both level with the ground: http://img19.imageshack.us/img19/8085/sqaures2.jpg A simple way to detect if one is hitting the other is to compare the location of each side. They are touching if ALL of the following are NOT true: The right square's left side is to the right of the left square's right side. The right square's right side is to the left of the left square's left side. The right square's bottom side is above the left square's top side. The right square's top side is below the left square's bottom side. If any of those are true, the squares are not touching. If all of those are false, the squares are touching. But consider a case like this, where one square is at a 45 degree angle: http://img189.imageshack.us/img189/4236/squaresb.jpg Is there an equally simple way to determine if those squares are touching?

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• Extrapolation breaks collision detection

  - by user22241

  Before applying extrapolation to my sprite's movement, my collision worked perfectly. However, after applying extrapolation to my sprite's movement (to smooth things out), the collision no longer works. This is how things worked before extrapolation: However, after I implement my extrapolation, the collision routine breaks. I am assuming this is because it is acting upon the new coordinate that has been produced by the extrapolation routine (which is situated in my render call ). After I apply my extrapolation How to correct this behaviour? I've tried puting an extra collision check just after extrapolation - this does seem to clear up a lot of the problems but I've ruled this out because putting logic into my rendering is out of the question. I've also tried making a copy of the spritesX position, extrapolating that and drawing using that rather than the original, thus leaving the original intact for the logic to pick up on - this seems a better option, but it still produces some weird effects when colliding with walls. I'm pretty sure this also isn't the correct way to deal with this. I've found a couple of similar questions on here but the answers haven't helped me. This is my extrapolation code: public void onDrawFrame(GL10 gl) { //Set/Re-set loop back to 0 to start counting again loops=0; while(System.currentTimeMillis() > nextGameTick && loops < maxFrameskip){ SceneManager.getInstance().getCurrentScene().updateLogic(); nextGameTick+=skipTicks; timeCorrection += (1000d/ticksPerSecond) % 1; nextGameTick+=timeCorrection; timeCorrection %=1; loops++; tics++; } extrapolation = (float)(System.currentTimeMillis() + skipTicks - nextGameTick) / (float)skipTicks; render(extrapolation); } Applying extrapolation render(float extrapolation){ //This example shows extrapolation for X axis only. Y position (spriteScreenY is assumed to be valid) extrapolatedPosX = spriteGridX+(SpriteXVelocity*dt)*extrapolation; spriteScreenPosX = extrapolationPosX * screenWidth; drawSprite(spriteScreenX, spriteScreenY); } Edit As I mentioned above, I have tried making a copy of the sprite's coordinates specifically to draw with.... this has it's own problems. Firstly, regardless of the copying, when the sprite is moving, it's super-smooth, when it stops, it's wobbling slightly left/right - as it's still extrapolating it's position based on the time. Is this normal behavior and can we 'turn it off' when the sprite stops? I've tried having flags for left / right and only extrapolating if either of these is enabled. I've also tried copying the last and current positions to see if there is any difference. However, as far as collision goes, these don't help. If the user is pressing say, the right button and the sprite is moving right, when it hits a wall, if the user continues to hold the right button down, the sprite will keep animating to the right, while being stopped by the wall (therefore not actually moving), however because the right flag is still set and also because the collision routine is constantly moving the sprite out of the wall, it still appear to the code (not the player) that the sprite is still moving, and therefore extrapolation continues. So what the player would see, is the sprite 'static' (yes, it's animating, but it's not actually moving across the screen), and every now and then it shakes violently as the extrapolation attempts to do it's thing....... Hope this help

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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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• How to perform simple collision detection?

  - by Rob

  Imagine two squares sitting side by side, both level with the ground like so: A simple way to detect if one is hitting the other is to compare the location of each side. They are touching if all of the following are false: The right square's left side is to the right of the left square's right side. The right square's right side is to the left of the left square's left side. The right square's bottom side is above the left square's top side. The right square's top side is below the left square's bottom side. If any of those are true, the squares are not touching. But consider a case like this, where one square is at a 45 degree angle: Is there an equally simple way to determine if those squares are touching?

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• 2D SAT Collision Detection not working when using certain polygons (With example)

  - by sFuller

  My SAT algorithm falsely reports that collision is occurring when using certain polygons. I believe this happens when using a polygon that does not contain a right angle. Here is a simple diagram of what is going wrong: Here is the problematic code: std::vector<vec2> axesB = polygonB->GetAxes(); //loop over axes B for(int i = 0; i < axesB.size(); i++) { float minA,minB,maxA,maxB; polygonA->Project(axesB[i],&minA,&maxA); polygonB->Project(axesB[i],&minB,&maxB); float intervalDistance = polygonA->GetIntervalDistance(minA, maxA, minB, maxB); if(intervalDistance >= 0) return false; //Collision not occurring } This function retrieves axes from the polygon: std::vector<vec2> Polygon::GetAxes() { std::vector<vec2> axes; for(int i = 0; i < verts.size(); i++) { vec2 a = verts[i]; vec2 b = verts[(i+1)%verts.size()]; vec2 edge = b-a; axes.push_back(vec2(-edge.y,edge.x).GetNormailzed()); } return axes; } This function returns the normalized vector: vec2 vec2::GetNormailzed() { float mag = sqrt( x*x + y*y ); return *this/mag; } This function projects a polygon onto an axis: void Polygon::Project(vec2* axis, float* min, float* max) { float d = axis->DotProduct(&verts[0]); float _min = d; float _max = d; for(int i = 1; i < verts.size(); i++) { d = axis->DotProduct(&verts[i]); _min = std::min(_min,d); _max = std::max(_max,d); } *min = _min; *max = _max; } This function returns the dot product of the vector with another vector. float vec2::DotProduct(vec2* other) { return (x*other->x + y*other->y); } Could anyone give me a pointer in the right direction to what could be causing this bug? Edit: I forgot this function, which gives me the interval distance: float Polygon::GetIntervalDistance(float minA, float maxA, float minB, float maxB) { float intervalDistance; if (minA < minB) { intervalDistance = minB - maxA; } else { intervalDistance = minA - maxB; } return intervalDistance; //A positive value indicates this axis can be separated. } Edit 2: I have recreated the problem in HTML5/Javascript: Demo

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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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• Collision Detection problems in Voxel Engine (XNA)

  - by Darestium

  I am creating a minecraft like terrain engine in XNA and have had some collision problems for quite some time. I have checked and changed my code based on other peoples collision code and I still have the same problem. It always seems to be off by about a block. for instance, if I walk across a bridge which is one block high I fall through it. Also, if you walk towards a "row" of blocks like this: You are able to stand "inside" the left most one, and you collide with nothing in the right most side (where there is no block and is not visible on this image). Here is all my collision code: private void Move(GameTime gameTime, Vector3 direction) { float speed = playermovespeed * (float)gameTime.ElapsedGameTime.TotalSeconds; Matrix rotationMatrix = Matrix.CreateRotationY(player.Camera.LeftRightRotation); Vector3 rotatedVector = Vector3.Transform(direction, rotationMatrix); rotatedVector.Normalize(); Vector3 testVector = rotatedVector; testVector.Normalize(); Vector3 movePosition = player.position + testVector * speed; Vector3 midBodyPoint = movePosition + new Vector3(0, -0.7f, 0); Vector3 headPosition = movePosition + new Vector3(0, 0.1f, 0); if (!world.GetBlock(movePosition).IsSolid && !world.GetBlock(midBodyPoint).IsSolid && !world.GetBlock(headPosition).IsSolid) { player.position += rotatedVector * speed; } //player.position += rotatedVector * speed; } ... public void UpdatePosition(GameTime gameTime) { player.velocity.Y += playergravity * (float)gameTime.ElapsedGameTime.TotalSeconds; Vector3 footPosition = player.Position + new Vector3(0f, -1.5f, 0f); Vector3 headPosition = player.Position + new Vector3(0f, 0.1f, 0f); // If the block below the player is solid the Y velocity should be zero if (world.GetBlock(footPosition).IsSolid || world.GetBlock(headPosition).IsSolid) { player.velocity.Y = 0; } UpdateJump(gameTime); UpdateCounter(gameTime); ProcessInput(gameTime); player.Position = player.Position + player.velocity * (float)gameTime.ElapsedGameTime.TotalSeconds; velocity = Vector3.Zero; } and the one and only function in the camera class: protected void CalculateView() { Matrix rotationMatrix = Matrix.CreateRotationX(upDownRotation) * Matrix.CreateRotationY(leftRightRotation); lookVector = Vector3.Transform(Vector3.Forward, rotationMatrix); cameraFinalTarget = Position + lookVector; Vector3 cameraRotatedUpVector = Vector3.Transform(Vector3.Up, rotationMatrix); viewMatrix = Matrix.CreateLookAt(Position, cameraFinalTarget, cameraRotatedUpVector); } which is called when the rotation variables are changed: public float LeftRightRotation { get { return leftRightRotation; } set { leftRightRotation = value; CalculateView(); } } public float UpDownRotation { get { return upDownRotation; } set { upDownRotation = value; CalculateView(); } } World class: public Block GetBlock(int x, int y, int z) { if (InBounds(x, y, z)) { Vector3i regionalPosition = GetRegionalPosition(x, y, z); Vector3i region = GetRegionPosition(x, y, z); return regions[region.X, region.Y, region.Z].Blocks[regionalPosition.X, regionalPosition.Y, regionalPosition.Z]; } return new Block(BlockType.none); } public Vector3i GetRegionPosition(int x, int y, int z) { int regionx = x == 0 ? 0 : x / Variables.REGION_SIZE_X; int regiony = y == 0 ? 0 : y / Variables.REGION_SIZE_Y; int regionz = z == 0 ? 0 : z / Variables.REGION_SIZE_Z; return new Vector3i(regionx, regiony, regionz); } public Vector3i GetRegionalPosition(int x, int y, int z) { int regionx = x == 0 ? 0 : x / Variables.REGION_SIZE_X; int X = x % Variables.REGION_SIZE_X; int regiony = y == 0 ? 0 : y / Variables.REGION_SIZE_Y; int Y = y % Variables.REGION_SIZE_Y; int regionz = z == 0 ? 0 : z / Variables.REGION_SIZE_Z; int Z = z % Variables.REGION_SIZE_Z; return new Vector3i(X, Y, Z); } Any ideas how to fix this problem? EDIT 1: Graphic of the problem: EDIT 2 GetBlock, Vector3 version: public Block GetBlock(Vector3 position) { int x = (int)Math.Floor(position.X); int y = (int)Math.Floor(position.Y); int z = (int)Math.Ceiling(position.Z); Block block = GetBlock(x, y, z); return block; } Now, the thing is I tested the theroy that the Z is always "off by one" and by ceiling the value it actually works as intended. Altough it still could be greatly more accurate (when you go down holes you can see through the sides, and I doubt it will work with negitive positions). I also does not feel clean Flooring the X and Y values and just Ceiling the Z. I am surely not doing something correctly still.

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