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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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• I need help with 2D collision response (of stacking rotating polygons, with friction and gravity, for a game)

  - by Register Sole

  Hi I am looking for suggestions on how to write a collision response for game programming purpose (so not a scientific simulation). I am dealing with 2D polygons that are rotating, and I want them to be able to stack. I also want friction and gravity. I have a detection mechanism that returns the separating axis, how long the polygons are overlapping, and up to 2 points of contact. For the response, I am currently using an impulse-based response, which main idea is: find the separating axis, length of overlap, and the point of contact (if there are two, pick a random point between to simulate averaged force. i believe there are better ways than this) separate the object (modifying their positions, taking into account of their masses. i do not separate them completely though, to keep track that they are colliding to reduce jitter) calculate normal force based on the coefficient of restitution as if there is no friction. calculate friction, as if there is no normal force. I also assume that the direction of the friction is the same throughout the collision. apply the two forces (which result in a rather inaccurate result, since each force is calculated as if the other is not present. for non-rotating bodies though, this method is exact) I am aware that this method requires the coefficient of friction to be sufficiently small due to the assumption that the direction of friction stays the same in a collision. Also, the result is visually satisfying if gravity is not present. However, when there is gravity, objects on ground jitter and drift (even with zero coefficient of restitution)! It also happens for stacking objects. Larger coefficient of restitution and gravity increase the jittering. I hope you can help me with this. Some things i would like to know more about is how to handle collision with two point of contacts (how to end up having an object sitting still on the ground?), how to reduce, and prevent if possible, jitter and drift (do people use the most accurate method possible, or is there a trick to overcome this?), and how to handle multiple objects collision (for example, in the case of stacking objects, how do I check collisions between all of them and keep them all stable at every frame so they don't jitter?). A total reformulation of my algorithm is also welcomed, as long as it works. Another thing to note is that I am not making a Physics game, so I only need a visually satisfying response (though a realistic response is preferable, if it is not performance-heavy). But surely jittering and drifting objects on flat ground are not at all acceptable. In addition, I am a Physics student, so feel free to talk about impulse and whatever needed. Finally, I'm sorry for the long post. I tried to be as concise as I can. Thank you for reading it! EDIT It seems what I didn't manage to come up all this time is to separate resting contact as a class of its own and how to solve them. Currently reading the paper suggested by Jedediah. More suggestions on the topic are welcome :) CASE CLOSED After reading various papers referenced in the paper, successfully implemented simultaneous impulse method (referring to the original paper by Erin Catto, [Catt05]). Thanks maaaan!! The paper is wonderful. The current system is visibly much better than the previous. Still haven't separated resting contact as a class of its own though, which brings me to my next question. Love you all! Haha (sorry, I'm just so happy thanks to you).

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• C++ Parallel Asynchonous task

  - by Doodlemeat

  I am currently building a randomly generated terrain game where terrain is created automatically around the player. I am experiencing lag when the generated process is active, as I am running quite heavy tasks with post-processing and creating physics bodies. Then I came to mind using a parallel asynchronous task to do the post-processing for me. But I have no idea how I am going to do that. I have searched for C++ std::async but I believe that is not what I want. In the examples I found, a task returned something. I want the task to change objects in the main program. This is what I want: // Main program // Chunks that needs to be processed. // NOTE! These chunks are already generated, but need post-processing only! std::vector<Chunk*> unprocessedChunks; And then my task could look something like this, running like a loop constantly checking if there is chunks to process. // Asynced task if(unprocessedChunks.size() > 0) { processChunk(unprocessedChunks.pop()); } I know it's not far from easy as I wrote it, but it would be a huge help for me if you could push me at the right direction. In Java, I could type something like this: asynced_task = startAsyncTask(new PostProcessTask()); And that task would run until I do this: asynced_task.cancel();

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• Libgdx change color of Texture at runtime [on hold]

  - by Springrbua

  i allready asked this on Stackoverflow, but i think this question may belong here. In a Libgdx game i have some Animations for my Player. All the Frames for this Animation are inside a TextureAtlas. The Player Textures show a human, with a white T-Shirt. The T-Shirt is the only white part of the Player. Now i want to be able to replace the white color with red for Player1, with green for Player2 and so on. How can i do that, without loosing the advantage of the TextureAtlas (Texture switching)? Ofc 1 way would be to store 4 versions of every Frame, for 4 different Players (colors). But there are games out there, where you can fully customize the Player, give him a blue hat, red pants and pink shirts and so on. How can this be done? Thanks a lot! EDIT: The question on Stackoverflow

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• Rectangular Raycasting?

  - by igrad

  If you've ever played The Swapper, you'll have a good idea of what I'm asking about. I need to check for, and isolate, areas of a rectangle that may intersect with either a circle or another rectangle. These selected areas will receive special properties, and the areas will be non-static, since the intersecting shapes themselves will also be dynamic. My first thought was to use raycasting detection, though I've only seen that in use with circles, or even ellipses. I'm curious if there's a method of using raycasting with a more rectangular approach, or if there's a totally different method already in use to accomplish this task. I would like something more exact than checking in large chunks, and since I'm using SDL2 with a logical renderer size of 1920x1080, checking if each pixel is intersecting is out of the question, as it would slow things down past a playable speed. I already have a multi-shape collision function-template in place, and I could use that, though it only checks if sides or corners are intersecting; it does not compute the overlapping area, or even find the circle's secant line, though I can't imagine it would be overly complex to implement. TL;DR: I need to find and isolate areas of a rectangle that may intersect with a circle or another rectangle without checking every single pixel on-screen.

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• Whats the right program for me?

  - by andyphillips20

  I would like to learn C++ so I can get a job in the game industry, but there are so many options it a little confusing. I know most of you will say I should read up on C++ before attempting to program it but I learn best by doing things rather then reading. That being said I don't understand some of the thing suggested on other questions, because I've read a few trying to find whats right for me, so putting things in the simplest terms would be helpful. I've been making a couple of games 2d using gamemaker and if theres a C++ equivalent that would be perfect, but if not possible I would like an IDE that allows me to easily continue making 2d games, and is fairly simple to learn. Having a 2d sprite editor would be a nice plus but I can understand if its not every thing I want in one program

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• How do I apply an arcball (using quaternions) along with mouse events, to allow the user to look around the screen using the o3d webgl framework?

  - by Chris

  How do I apply an arcball (using quaternions) along with mouse events, to allow the user to look around the screen using the o3d webgl framework? This sample (http://code.google.com/p/o3d/source/browse/trunk/samples_webgl/o3d-webgl-samples/simpleviewer/simpleviewer.html?r=215) uses the arcball for rotating the transform of an "object", but rather than apply this to a transform, I would like to apply the rotation to the camera's target, to create a first person style ability to look around the scene, as if the camera is inside the centre of the arcball instead of rotating from the outside. The code that is used in this sample is var rotationQuat = g_aball.drag([e.x, e.y]); var rot_mat = g_quaternions.quaternionToRotation(rotationQuat); g_thisRot = g_math.matrix4.mul(g_lastRot, rot_mat); The code that I am using which doesn't work var rotationQuat = g_aball.drag([e.x, e.y]); var rot_mat = g_quaternions.quaternionToRotation(rotationQuat); g_thisRot = g_math.matrix4.mul(g_lastRot, rot_mat); var cameraRotationMatrix4 = g_math.matrix4.lookAt(g_eye, g_target, [g_up[0], g_up[1] * -1, g_up[2]]); var cameraRotation = g_math.matrix4.setUpper3x3(cameraRotationMatrix4,g_thisRot); g_target = g_math.addVector(cameraRotation, g_target); where am I going wrong? Thanks

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• Free movement in a tile-based isometric game

  - by xtr486

  Is there a reasonable easy way to implement free movement in a tile-based isometric game? Meaning that the player wouldn't just instantly jump from one tile to another or not be "snapped" to the grid (for example, if the movement between tiles were animated but you'd be locked from doing anything before the animation finishes). I'm a really beginner with anything related to game programming, but with the help of this site and some other resources it was quite easy to do the basic stuff, but I haven't been able to find any useful resources for this particular problem. Currently I've improvised something close to this: http://jsfiddle.net/KwW5b/4/ (WASD movement). The idea for the movement was to use the mouse map to detect when the player has moved to a different tile and then flip the offsets, and for the most part it works correctly (each corner makes the player move to wrong location: see http://www.youtube.com/watch?v=0xr15IaOhrI, which is probably because I couldn't get the full mouse map work properly), but I have no illusions that it is even close to a good/sane solution. And anyway, it's mostly just to demonstrate what kind of a thing I'd like to implement.

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• sprite animation in openGL

  - by Sid

  I am facing problems on implementing sprite animation in opneGL ES. i've googled it and the only thing i am getting is the Tutorial implementing via Canvas. i know the way but i am having problems in implementing it. What i need : A sprite animation on collision detection. What i did : Collision Detection function working properly. PS : everything is working fine but i want to implement the animation in OPENGL ONLY. Canvas won't work in my case.

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• 3D Location Handling

  - by tgrosinger

  I am thinking about making a simulator type game that will involve having lots of small objects in a 3D space. What is the typical solution for handling these objects? The first thing that comes to mind is a 3D Array, but I can't help but think there is a more efficient solution. Another idea that comes to mind is objects having possession of smaller items. For example a House possesses a Table which possesses a Cup and Bowl. The final way I can think of handling this is just having an array of "objects" that each have an x, y, z value. While this would make storing them easy I do not understand how you would detect collisions without just looking at every possible object and checking to see if it is in the way. Are there other ways of holding onto these objects that is more efficient?

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• What are milestones for a game developer to gauge their progress?

  - by user16710

  I know actually completing a game is a massive milestone, a complete polished, holistic experience. Something that I've not yet been able to commit to. There are of course classes and degrees to earn in several fields that will help gain experience, but how would one judge their own progress and strive to progress further? The yellow brick road to "Rock Star Game Programmer" is very cloudy. At this point I think it may be closer to an ocean, drifting along until you wake up one day at your destination.

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• C# 2d array value check [duplicate]

  - by TLFTN

  This question already has an answer here: 3-in-a-row or more logic 4 answers I've managed to create a 2d array, then made it fill up with random numbers, like this: int[,] grid = new int[5, 5] ; Random randomNumber = new Random(); var rowLength = grid.GetLength(0); var colLength = grid.GetLength(1); for (int row = 0; row < rowLength; row++) { for (int col = 0; col < colLength; col++){ grid[row, col] = randomNumber.Next(5); Console.Write(String.Format("{0}\t", grid[row, col]));} Console.WriteLine(); } This results in an array with random values. Example: 3 0 0 3 3 1 3 3 3 2 0 0 2 0 4 3 3 2 0 3 4 0 3 3 0 Notice those three 3s which are connected to each other(in the second row), now how would I check if there's a match like this?

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• which one is the safe site to buy cheap wildstar gold?

  - by user50866

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• Touch Event Not Work With PinchZoom

  - by Siddharth

  I was implemented pinch zoom functionality for my tower of defense game. I manage different entity to display all the towers. From that entity game player select the tower and drag to the actual position where he want to plot the tower. I set the entity in HUD also, so user scroll and zoom the region, the tower become visible all the time. Basically I have created the different entity to show and hide towers only so I can manage it easily. My problem is when I have not perform the scroll and zoom the tower touch and the dragging easily done but when I zoom and scroll the scene at that time the tower touch event does not call so the player can not able to drag and drop it to actual position. So anybody please help me to come out of it.

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• (Phaser) Preload Future States in Create?

  - by Brian

  I'm a first time user of Phaser, been trying to make a simple point and click type game. I'm trying to keep things very modular, so I'm defining a list of levels (states) in a JSON, and then every level has its own JSON containing the objects within that level. However, I'm encountering an issue in that, when changing states, I get a black flash while the assets for the next state load (this happens whether I iterate through the JSON list or define everything manually). From what I've read, all sprites should be loaded in the preload stage, however, by doing this I'm causing that tiny but noticeable black pause. I know one way would be to simply load every asset at the start of the game, but that seems incredibly inefficient (wouldn't that fill up the memory immensely?). I would rather load a state's assets from the "parent" state. However, in my quick test (which maybe I did wrong) it seems that game.load doesn't work properly if done within the create stage? What is the best approach to doing this?

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• Java - Finding distance between player and tile in array

  - by Corey

  What is the best way performance wise to do this? When I click a tile I want it to get the distance and if I am close enough I can interact with the tile. One way would be to find the tile by doing mouse / tile width when I click correct? But then how would I get that tiles position? I know how to find the distance I just don't know how to get a certain tiles position from the array when I click it

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• Collider2D and Rigidbody2D, how do they work?

  - by user42646

  I have been learning JavaScript and Unity for a week now. I learned how to make Cube as a Ground and another Cube as a player and I used this code to make the Player Cube move forward and backward and jumping var walkspeed: float = 5.0; var jumpheight: float = 250.0; var grounded = false; function Update() { rigidbody.freezeRotation = true; if (Input.GetKey("a")) transform.Translate(Vector3(-1, 0, 0) * Time.deltaTime * walkspeed); if (Input.GetKey("d")) transform.Translate(Vector3(1, 0, 0) * Time.deltaTime * walkspeed); if (Input.GetButton("Jump")) { Jump(); } } function OnCollisionEnter(hit: Collision) { grounded = true; } function Jump() { if (grounded == true) { rigidbody.AddForce(Vector3.up * jumpheight); grounded = false; } } I also learned how to make a character hit box. how to make a sprite and animation. pretty much the basic stuff. Couple of days ago I created simple ground in Photoshop and a simple character and imported them to Unity3D. Whenever I use my code above the character keeps falling from the scene. Like the character has nothing to stand on. After thinking about it it make sense because I really didn't make anything to make the player character understand that he should stand on something so I started reading about this issue and I realized that there is something called Collider2D and Rigidbody2D. Now I'm really stuck here I just don't know what to do. I applied the rigibody2d to my character picture and the Collider2D to the ground picture but whenever I play the project the gravity makes my character falls down. This is my question: How can I make the rigibody2d object realize that it shouldn't fall if there is a Collider2D object under it? So when I jump it's going to jump and the gravity going to bring it back to the ground.

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• How can I derive force vectors from velocity vectors?

  - by PixelRouter

  I'm making a 2d shooter ala Geometry Wars. I've got my own simple physics at work driving the background grid and all my entities. To move anything in the world I apply a Vector2d force to it. The 'engine' calculates the resulting acceleration and therefore the velocity. I am trying to port some code I found which implements the classic 'Boids' flocking algorithm, but the code I have works by calculating the Boids' velocities directly, so If i use it as is, it bypasses my physics engine. How I can translate the velocity vectors into force vectors that I can apply to the Boids and which will result in the proper velocities via my physics engine.

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• Translating multiple objects in GUI based on average position?

  - by user1423893

  I use this method to move a single object in 3D space, it accounts for a local offset based on where the cursor ray hits the widget and the center of the widget. var cursorRay = cursor.Ray; Vector3 goalPosition = translationWidget.GoalPosition; Vector3 position = cursorRay.Origin + cursorRay.Direction * grabDistance; // Constrain object movement based on selected axis switch (translationWidget.AxisSelected) { case AxisSelected.All: goalPosition = position; break; case AxisSelected.None: break; case AxisSelected.X: goalPosition.X = position.X; break; case AxisSelected.Y: goalPosition.Y = position.Y; break; case AxisSelected.Z: goalPosition.Z = position.Z; break; } translationWidget.GoalPosition = goalPosition; Vector3 p = goalPosition - translationWidget.LocalOffset; objectSelected.Position = p; I would like to move multiple objects based on the same principle and using a widget which is located at the average position of all the objects currently selected. I thought that I would have to translate each object based on their offset from the average point and then include the local offset. var cursorRay = cursor.Ray; Vector3 goalPosition = translationWidget.GoalPosition; Vector3 position = cursorRay.Origin + cursorRay.Direction * grabDistance; // Constrain object movement based on selected axis switch (translationWidget.AxisSelected) { case AxisSelected.All: goalPosition = position; break; case AxisSelected.None: break; case AxisSelected.X: goalPosition.X = position.X; break; case AxisSelected.Y: goalPosition.Y = position.Y; break; case AxisSelected.Z: goalPosition.Z = position.Z; break; } translationWidget.GoalPosition = goalPosition; Vector3 p = goalPosition - translationWidget.LocalOffset; int numSelectedObjects = objectSelectedList.Count; for (int i = 0; i < numSelectedObjects; ++i) { objectSelectedList[i].Position = (objectSelectedList[i].Position - translationWidget.Position) + p; } This doesn't work as the object starts shaking, which I think is because I haven't accounted for the new offset correctly. Where have I gone wrong?

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• What is the primary use of Vertex Buffer Objects?

  - by sensae

  From what I've read, it seems VBOs are purely for performance. I'm working on a very rudimentary learning project in lwjgl and I'm just trying to figure out what more advanced features of the library I should be delving into, and what their use is. My understanding is that VBOs allow a person to keep vertexes in VRAM while they aren't currently being drawn in a scene. In my case, I'm just drawing quads and performance probably isn't a concern at all, but I'm trying to piece together what's happening under the hood. If I'm drawing quads directly, I'm drawing from the CPU memory, correct? Also, if I'm not doing any checks for visibility, does that mean I'm rendering absolutely everything in the "scene", regardless of whether its in view? Are VBOs a way to store objects and only render what's needed?

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• Can XNA Content Pipeline split one content file into several .xnb?

  - by Zeta Two

  Let's say I have an xml file which looks like this <Weapons> <Weapon> <Name>Pistol</Name> ... </Weapon> <Weapon> <Name>MachineGun</Name> ... </Weapon> </Weapons> Would it be possible to use a custom importer/writer/reader to create two files, Pistol.xnb and MachineGun.xnb which I can load individually with Content.Load()? While writing this I realized I could just import a Weapon[] list and split them up with a helper, but I'm still wondering if this is possible?

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• GPU optimization question: pre-computed or procedural?

  - by Jay

  Good morning, I'm learning shader program and need some general direction. I want to add noise to my laser beam (like this). Which is the best way to handle it? I could pre-compute an image and pass it to the shader. I could then use the image to change the opacity and easily animate the smoke by changing the offset of the texture lookup. I could also generate noise in the shader and do the same thing the texture was used for. Is it generally better to avoid I/O to the graphics card or the opposite? Thanks!

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• How do I convert screen coordinates to between -1 and 1?

  - by bbdude95

  I'm writing a function that allows me to click on my tiles. The origin for my tiles is the center, however, the mouse's origin is the top left. I need a way to transform my mouse coordinates into my tile coordinates. Here is what I already have (but is not working): void mouseClick(int button, int state, int x, int y) { x -= 400; y -= 300; float xx = x / 100; // This gets me close but the number is still high. float yy = y / 100; // It needs to be between -1 and 1 }

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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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• Basic Android game loop having issues

  - by WillDaBeast509

  I've set up a very basic game loop that should draw a circle, run 100 times, then draw another. I also have a text field that should display how many times the loop has ran. However, the screen seems to not update. It displays a different value for the tick count (different each time the app is ran) and simply stays there. After exiting the app, I get an error saying "Unfortunately, MyApp has stopped." Here is the relevant code: DrawView public class DrawView extends SurfaceView implements SurfaceHolder.Callback { Paint p = new Paint(); MainThread thread; private int y=0; public DrawView(Context c) { super(c); thread = new MainThread(this, getHolder()); thread.running = true; getHolder().addCallback(this); setFocusable(true); } public void draw(Canvas c) { if(c==null) return; //super.onDraw(c); c.drawColor(Color.WHITE); p.setColor(Color.RED); p.setTextSize(32); p.setTypeface(Typeface.SANS_SERIF); c.drawCircle(getWidth()/2-100,getHeight()/2, 50, p); c.drawText("y = " + y, 50, 50, p); if(y>=100) { Log.i("DRAW", "drawing circle"); c.drawCircle(getWidth()/2+100,getHeight()/2, 50, p); } else y++; Log.i("INFO", "y = " + y); } @Override public boolean onTouchEvent(MotionEvent event) { return true; } public void onDraw(Canvas c){} public void surfaceCreated(SurfaceHolder p1) { thread.start(); } public void surfaceChanged(SurfaceHolder p1, int p2, int p3, int p4) { // TODO: Implement this method } public void surfaceDestroyed(SurfaceHolder p1) { thread.running = false; boolean retry = true; while (retry) { try { thread.join(); retry = false; } catch (InterruptedException e) { Log.i("EX", "cathing exception"); } } } } MainThread public class MainThread extends Thread { private DrawView page; private SurfaceHolder holder; public boolean running; public MainThread(DrawView p, SurfaceHolder h) { super(); page = p; holder = h; } @Override public void run() { while(running) { Canvas c = holder.lockCanvas(); page.draw(c); holder.unlockCanvasAndPost(c); } } } Here is an example log outupt: http://pastebin.com/tM9dUPuk It counts the number of ticks correctly and should draw the second circle, but the screen looks like its not updating. After closing the app, the log continues to run and keep outputting "y = 100 drawing circle" until it crashes and shows the error report. What is going on and how can I fix these two problems?

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