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• XNA 2D vehicle wall collisions

  - by mike

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

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• Fast, accurate 2d collision

  - by Neophyte

  I'm working on a 2d topdown shooter, and now need to go beyond my basic rectangle bounding box collision system. I have large levels with many different sprites, all of which are different shapes and sizes. The textures for the sprites are all square png files with transparent backgrounds, so I also need a way to only have a collision when the player walks into the coloured part of the texture, and not the transparent background. I plan to handle collision as follows: Check if any sprites are in range of the player Do a rect bounding box collision test Do an accurate collision (Where I need help) I don't mind advanced techniques, as I want to get this right with all my requirements in mind, but I'm not sure how to approach this. What techniques or even libraries to try. I know that I will probably need to create and store some kind of shape that accurately represents each sprite minus the transparent background. I've read that per pixel is slow, so given my large levels and number of objects I don't think that would be suitable. I've also looked at Box2d, but haven't been able to find much documentation, or any examples of how to get it up and running with SFML.

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• Matrix loading problems with jbullet and lwjgl

  - by Quintin

  The following code does not load the matrix correctly from jbullet. //box is a RigidBody Transform trans = new Transform(); trans = box.getMotionState().getWorldTransform(trans); float[] matrix = new float[16]; trans.getOpenGLMatrix(matrix); // pass that matrix to OpenGL and render the cube FloatBuffer buffer = ByteBuffer.allocateDirect(4*16).asFloatBuffer().put(matrix); buffer.rewind(); glPushMatrix(); glMultMatrix(buffer); glBegin(GL_POINTS); glVertex3f(0,0,0); glEnd(); glPopMatrix(); the jbullet is configured as so: CollisionConfiguration = new DefaultCollisionConfiguration(); dispatcher = new CollisionDispatcher(collisionConfiguration); Vector3f worldAabbMin = new Vector3f(-10000,-10000,-10000); Vector3f worldAabbMax = new Vector3f(10000,10000,10000); AxisSweep3 overlappingPairCache = new AxisSweep3(worldAabbMin, worldAabbMax); SequentialImpulseConstraintSolver solver = new SequentialImpulseConstraintSolver(); dynamicWorld = new DiscreteDynamicsWorld(dispatcher, overlappingPairCache, solver, collisionConfiguration); dynamicWorld.setGravity(new Vector3f(0,-10,0)); dynamicWorld.getDispatchInfo().allowedCcdPenetration = 0f; CollisionShape groundShape = new BoxShape(new Vector3f(1000.f, 50.f, 1000.f)); Transform groundTransform = new Transform(); groundTransform.setIdentity(); groundTransform.origin.set(new Vector3f(0.f, -60.f, 0.f)); float mass = 0f; Vector3f localInertia = new Vector3f(0, 0, 0); DefaultMotionState myMotionState = new DefaultMotionState(groundTransform); RigidBodyConstructionInfo rbInfo = new RigidBodyConstructionInfo(mass, myMotionState, groundShape, localInertia); RigidBody body = new RigidBody(rbInfo); dynamicWorld.addRigidBody(body); dynamicWorld.clearForces(); Nothing is rendered on the screen. What am I doing wrong?

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• Damageable ground similar to pocket tanks or archanists [closed]

  - by XenElement

  Possible Duplicate: Implementing a 2D destructible landscape (like Worms) A really cool feature in both the iPhone game pocket tanks and the online jagex game archanists is ground which can be blown up. When a projectile collides with the ground, an area equal to the blast radius which overlaps the ground is removed. It's strictly two dimensional, but it makes the experience that much more dynamic since you can dig a hole under your opponents or yourself. How is this implemented?

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• Why does the player fall down when in between platforms? Tile based platformer

  - by inzombiak

  I've been working on a 2D platformer and have gotten the collision working, except for one tiny problem. My games a tile based platformer and whenever the player is in between two tiles, he falls down. Here is my code, it's fire off using an ENTER_FRAME event. It's only for collision from the bottom for now. var i:int; var j:int; var platform:Platform; var playerX:int = player.x/20; var playerY:int = player.y/20; var xLoopStart:int = (player.x - player.width)/20; var yLoopStart:int = (player.y - player.height)/20; var xLoopEnd:int = (player.x + player.width)/20; var yLoopEnd:int = (player.y + player.height)/20; var vy:Number = player.vy/20; var hitDirection:String; for(i = yLoopStart; i <= yLoopEnd; i++) { for(j = xLoopStart; j <= xLoopStart; j++) { if(platforms[i*36 + j] != null && platforms[i*36 + j] != 0) { platform = platforms[i*36 + j]; if(player.hitTestObject(platform) && i >= playerY) { hitDirection = "bottom"; } } } } This isn't the final version, going to replace hitTest with something more reliable , but this is an interesting problem and I'd like to know whats happening. Is my code just slow? Would firing off the code with a TIMER event fix it? Any information would be great.

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• How do I find actors in an area on a poly-precise basis?

  - by Almo

  Ok, I've been asking various questions and getting some good answers, but I think I need to rethink my method, so I'll describe the problem. I have a player who has a big blue box in front of him. This box shows which KActors will be pushed when he pulls the trigger: Currently, the blue box spawns a descendant of Actor which checks collision to see which KActors are touching it: foreach Owner.TouchingActors(class'DynamicSMActor', DynamicActorItt) { // do stuff } The problem is, if you check for touching between Actors and KActors, it looks like it does a plain axis-aligned bounding-box collision. The power will push the box on the lower right, when it's clear it's not touching the blue box. How should I do this properly? I just need a way to find out which KActors are touching that area, on a poly-by-poly level. These collisions are only done with rectangular boxes and simple sphere collision; we are aware of the potential for performance issues with complex objects and poly-collision. I've tried making the collision checker a KActor, but it doesn't report any TouchingActors. This issue is causing us trouble in a lot of other places as well. So solving this problem is a core issue in our game.

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• How to detect and collide two elastic line segments?

  - by Tautrimas

  There are 4 moving physical nodes in 3D space. They are paired with two elastic line segments / strings (1 <- 2; 3 <- 4). Part I: How to detect the collision of two segments? Part II: On the moment of collision, fifth node is created at the intersection point and here you have the force-based graph. 5-th node (bend point) can slide among the strings as in a real world. Given the new coordinates of 4 nodes, how to calculate the position of the 5-th node on the next frame? I assume string force on the nodes to be F = -k * x where x is the string length. All I came up to is that the force between 5 and 1 equals 5 and 2 (the same with 3 and 4). What are the other properties?.

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• How do 2D physics engines solve the problem of resolving collisions along tiled walls/floors in non-grid-based worlds?

  - by ssb

  I've been working on implementing my SAT algorithm which has been coming along well, but I've found that I'm at a wall when it comes to its actual use. There are plenty of questions regarding this issue on this site, but most of them either have no clear, good answer or have a solution based on checking grid positions. To restate the problem that I and many others are having, if you have a tiled surface, like a wall or a floor, consisting of several smaller component rectangles, and you traverse along them with another rectangle with force being applied into that structure, there are cases where the object gets caught on a false collision on an edge that faces the inside of the shape. I have spent a lot of time thinking about how I could possibly solve this without having to resort to a grid-based system, and I realized that physics engines do this properly. What I want to know is how they do this. What do physics engines do beyond basic SAT that allows this kind of proper collision resolution in complex environments? I've been looking through the source code to Box2D trying to find out how they do it but it's not quite as easy as looking at a Collision() method. I think I'm not good enough at physics to know what they're doing mathematically and not good enough at programming to know what they're doing programmatically. This is what I aim to fix.

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• Using Bullet physics engine to find the moment of object contact before penetration

  - by MooMoo

  I would like to use Bullet Physics engine to simulate the objects in 3D world. One of the objects in the world will move using the position from 3D mouse control. I will call it "Mouse Object" and any object in the world as "Object A" I define the time before "mouse object" and "Object A" collide as t-1 The time "mouse object" penetrate "Object A" as t Now there is a problem about rendering the scene because when I move the mouse very fast, "Mouse object" will reside in "Object A" before "Object A" start to move. I would like the "Mouse Object" to stop right away attach to the "Object A". Also If the "Object A" move, the "Mouse object" should move following (attach) the "Object A" without stop at the first collision take place. This is what i did I find the position of the "Mouse Object" at time t-1 and time t. I will name it as pos(t-1) and pos(t) The contact time will be sometime between t-1 to t, which the time of contact I name it as t_contact, therefore the contact position (without penetration) between "Mouse object" and "Object A" will be pos(t_contact) then I create multiple "Mouse object"s using this equation pos[n] = pos(t-1) * C * ( pos(t) - pos(t-1) ) where 0 <= C <= 1 if I choose C = 0.1, 0.2, 0.3,0.4..... 1.0, I will get pos[n] for 10 values Then I test collision for all of these 10 "Mouse Objects" and choose the one that seperate between "no collision" and "collision". I feel this method is super non-efficient. I am not sure the way other people find the time-of-contact or the position-of-contact when "Object A" can move.

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• How to find 2D grid cells swept by a moving circle?

  - by Nevermind

  I'm making a game based on a 2D grid, with some cells passable and some not. Dynamic objects can move continuously, independent of the grid, but need to collide with impassable cells. I wrote an algorithm to trace a ray against the grid, that gives me all cells that ray intersects. However, actual object are not point-sized; I'm currently representing them as circles. But I can't figure out an effective algorithm to trace a moving circle. Here's a picture of what I need: The numbers show in what order the circle collides with grid cells. Does anybody know the algorithm to find these collisions? Preferably in C#. Update The circle can be bigger than a single grid cell.

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• How to handle circle penetration

  - by Kaertserif

  I've been working on cirlce to circle collision and have gotten the intersection method working correctly, but I'm having problems using the returned values to actually seperate the circles from one another. This is the method which calculates the depth of the circle collision public static Vector2 GetIntersectionDepth(Circle a, Circle b) { float xValue = a.Center.X - b.Center.X; float yValue = a.Center.Y - b.Center.Y; Vector2 depth = Vector2.Zero; float distance = Vector2.Distance(a.Center, b.Center); if (a.Radius + b.Radius > distance) { float result = (a.Radius + b.Radius) - distance; depth.X = (float)Math.Cos(result); depth.Y = (float)Math.Sin(result); } return depth; } This is where I'm trying to apply the values to actually seperate the circles. Vector2 depth = Vector2.Zero; for (int i = 0; i < circlePositions.Count; i++) { for (int j = 0; j < circlePositions.Count; j++) { Circle bounds1 = new Circle(circlePositions[i], circle.Width / 2); Circle bounds2 = new Circle(circlePositions[j], circle.Width / 2); if(i != j) depth = CircleToCircleIntersection.GetIntersectionDepth(bounds1, bounds2); if (depth != Vector2.Zero) { circlePositions[i] = new Vector2(circlePositions[i].X + depth.X, circlePositions[i].Y + depth.Y); } } } If you can offer any help in this I would really appreciate it.

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• How to design 2D collision callback methods?

  - by Ahmed Fakhry

  In a 2D game where you have a lot of possible combination of collision between objects, such as: object A vs object B = object B vs A; object A vs object C = object C vs A; object A vs object D = object D vs A; and so on ... Do we need to create callback methods for all single type of collision? and do we need to create the same method twice? Like, say a bullet hits a wall, now I need a method to penetrate the wall for the wall, and a method to destroy the bullet for the bullet!! At the same time, a bullet can hit many objects in the game, and hence, more different callback methods!!! Is there a design pattern for that?

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• Cocos2D - Detecting collision

  - by Grace

  I am a beginner in cocos2d and im facing a problem with detecting collision for my coins. Sometimes it works sometimes it doesn't. So basically, im creating a game which the user (ship) have to avoid the obstacles and collect coins on the way. The collision of the obstacle works well but not for the coins. I was thinking maybe the loops for creating many coins is the problem but im not sure. Can anyone help? My codes: - (void)update:(ccTime)dt{ double curTime = CACurrentMediaTime(); if (curTime > _nextBridgeSpawn) { float randSecs = [self randomValueBetween:3.0 andValue:5.0]; _nextBridgeSpawn = randSecs + curTime; float randX = [self randomValueBetween:50 andValue:500]; float randDuration = [self randomValueBetween:8.0 andValue:10.0]; CCSprite *bridge = [_bridge objectAtIndex:_nextBridge]; _nextBridge++; if (_nextBridge >= _bridge.count) _nextBridge = 0; [bridge stopAllActions]; bridge.position = ccp(winSize.width/2, winSize.height); bridge.visible = YES; [bridge runAction:[CCSequence actions: [CCMoveBy actionWithDuration:randDuration position:ccp(0, -winSize.height)], [CCCallFuncN actionWithTarget:self selector:@selector(setInvisible:)], nil]]; this is where i declare my coins (continued from the update method) int randCoin = [self randomValueBetween:0 andValue:5]; _coin = [[CCArray alloc] initWithCapacity:randCoin]; for(int i = 0; i < randCoin; ++i) { coin = [CCSprite spriteWithFile:@"coin.png"]; coin.visible = NO; [self addChild:coin]; [_coin addObject:coin]; } float randCoinX = [self randomValueBetween:winSize.width/5 andValue:winSize.width - (border.contentSize.width *2)]; float randCoinY = [self randomValueBetween:100 andValue:700]; float randCoinPlace = [self randomValueBetween:30 andValue:60]; for (int i = 0; i < _coin.count; ++i) { CCSprite *coin2 = [_coin objectAtIndex:i]; coin2.position = ccp(randCoinX, (bridge.position.y + randCoinY) + (randCoinPlace *i)); coin2.visible = YES; [coin2 runAction:[CCSequence actions: [CCMoveBy actionWithDuration:randDuration position:ccp(0, -winSize.height-2000)], [CCCallFuncN actionWithTarget:self selector:@selector(setInvisible:)], nil]]; } } this is to check for collision (also in the update method) for (CCSprite *bridge in _bridge) { if (!bridge.visible) continue; if (CGRectIntersectsRect(ship.boundingBox, bridge.boundingBox)){ bridge.visible = NO; [ship runAction:[CCBlink actionWithDuration:1.0 blinks:5]]; } } } //this is the collision for coins which only work at times for (CCSprite *coin2 in _coin) { if (!coin2.visible) continue; if (CGRectIntersectsRect(ship.boundingBox, coin2.boundingBox)) { NSLog(@"Coin collected"); coin2.visible = NO; } } } Thank you.

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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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• Pygame - CollideRect - But How Do They Collide?

  - by Chakotay

  I'm having some trouble figuring out how I can handle collisions that are specifically colliding on the top or bottom a rect. How can specify those collisions? Here's a little code snippet to give you an idea of my approach. As it is now it doesn't matter where it collides. # the ball has hit one of the paddles. send it back in another direction. if paddleRect.colliderect(ballRect) or paddle2Rect.colliderect(ballRect): ballHitPaddle.play() if directionOfBall == 'upleft': directionOfBall = 'upright' elif directionOfBall == 'upright': directionOfBall = 'upleft' elif directionOfBall == 'downleft': directionOfBall = 'downright' elif directionOfBall == 'downright': directionOfBall = 'downleft' Thanks in advance. **EDIT** Paddle rect: top ____ | | | | | | Sides | | ---- bottom I need to know if the ball has hit either the top or the bottom.

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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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• Bitmap & Object Collision Help

  - by MarkEz

  Is it possible to detect when an object and a bitmap collide. I have an arraylist of sprites that I am shooting with an image. I tried using this method here but as soon as the bitmap appears the sprite disappears, this is in the Sprite class: public boolean isCollision(Bitmap other) { // TODO Auto-generated method stub if(other.getWidth() > x && other.getWidth() < x + width && >other.getHeight() > y && other.getHeight() < y + height); return true; }

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• Android Bitmap: Collision Detecting

  - by Aekasitt Guruvanich

  I am writing an Android game right now and I would need some help in the collision of the Pawns on screen. I figured I could run a for loop on the Player class with all Pawn objects on the screen checking whether or not Width*Height intersects with each other, but is there a more efficient way to do this? And if you do it this way, many of the transparent pixel inside the rectangular area will also be considered as collision as well. Is there a way to check for collision between Bitmap on a Canvas that disregard transparent pixels? The class for player is below and the Pawn class uses the same method of display. Class Player { private Resources res; // Used for referencing Bitmap from predefined location private Bounds bounds; // Class that holds the boundary of the screen private Bitmap image; private float x, y; private Matrix position; private int width, height; private float velocity_x, velocity_y; public Player (Resources resources, Bounds boundary) { res = resources; bounds = boundary; image = BitmapFactory.decodeResource(res, R.drawable.player); width = image.getWidth(); height = image.getHeight(); position = new Matrix(); x = bounds.xMax / 2; // Initially puts the Player in the middle of screen y = bounds.yMax / 2; position.preTranslate(x,y); } public void draw(Canvas canvas) { canvas.drawBitmap(image, position, null); } }

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• Using PhysX, how can I predict where I will need to generate procedural terrain collision shapes?

  - by Sion Sheevok

  In this situation, I have terrain height values I generate procedurally. For rendering, I use the camera's position to generate an appropriate sized height map. For collision, however, I need to have height fields generated in areas where objects may intersect. My current potential solution, which may be naive, is to iterate over all "awake" physics actors, use their bounds/extents and velocities to generate spheres in which they may reside after a physics update, then generate height values for ranges encompassing clustered groups of actors. Much of that data is likely already calculated by PhysX already, however. Is there some API, maybe a set of queries, even callbacks from the spatial system, that I could use to predict where terrain height values will be needed?

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• How would I detect if two 2D arrays of any shape collided?

  - by user2104648

  Say there's two or more moveable objects of any shape in 2D plane, each object has its own 2D boolean array to act as a bounds box which can range from 10 to 100 pixels, the program then reads each pixel from a image that represents it, and appropriatly changes the array to true(pixel has a alpha more then 1) or false(pixel has a alpha less than one). Each time one of these objects moves, what would be the best accurate way to test if they hit another object in Java using as few APIs/libraries as possible?

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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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• Bitmap & Object Collision Help

  - by MarkEz

  Is it possible to detect when an object and a bitmap collide. I have an arraylist of sprites that I am shooting with an image. I tried using this method here but as soon as the bitmap appears the sprite disappears, this is in the Sprite class: public boolean isCollision(Bitmap other) { if(other.getWidth() > x && other.getWidth() < x + width && >other.getHeight() > y && other.getHeight() < y + height); return true; }

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• Elastic Collision Formula in Java

  - by Shijima

  I'm trying to write a Java formula based on this tutorial: 2-D elastic collisions without Trigonometry. I am in the section "Elastic Collisions in 2 Dimensions". In step 1, it mentions "Next, find the unit vector of n, which we will call un. This is done by dividing by the magnitude of n". My below code represents the normal vector of 2 objects (I'm using a simple array to represent the normal vector), but I am not really sure what the tutorial means by dividing the magnitude of n to get the un. int[] normal = new int[2]; normal[0] = ball2.x - ball1.x; normal[1] = ball2.y - ball1.y; Can anyone please explain what un is, and how I can calculate it with my array in Java?

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• XNA - Detect click on triangle/circle form of a texture

  - by chr1s89

  How can i detect clicks on a texture (will be a button in my game) that has a form of a triangle or circle. I know only the rectangle solution where u can use the positions + the width/height but this dont work for that because clicks will be detected at the transparent pixels. I heard of pixel-perfect collision is it the right way for this? It would be great if someone can give me a example for such a solution or other.

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• 2D Game Development dynamics in c++ [on hold]

  - by novice

  I am new to developing computer graphic applications in c++ using OpenGl. I want to develop games but I really am facing problems when it comes to understanding concepts like trajectory, collisions, gravity and also the use of various physics engines that are available. when i search the internet I kind of get lost because they aren't for beginners like me. There is some hardcore mathematics, physics and coding involved. I need to pick the concepts that are mostly needed in game dev like trajectory, collision etc. Any good tutorials that can help me out in picking these concepts from the start.

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