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• strange behavior in Box2D+LibGDX when applying impulse

  - by Z0lenDer

  I have been playing around with Box2D and LibGDX and have been using a sample code from DecisionTreeGames as the testing ground. Now I have a screen with four walls and a rectangle shape, lets call it a brick. When I use applyLinearImpulse to the brick, it starts bouncing right and left without any pattern and won't stop! I tried adding friction and increasing the density, but the behavior still remains the same. Here are some of the code that might be useful: method for applying the impulse: center = brick.getWorldCenter(); brick.applyLinearImpulse(20, 0, center.x, center.y); Defining the brick: brick_bodyDef.type = BodyType.DynamicBody; brick_bodyDef.position.set(pos); // brick is initially on the ground brick_bodyDef.angle = 0; brick_body = world.createBody(brick_bodyDef); brick_body.setBullet(true); brick_bodyShape.setAsBox(w,h); brick_fixtureDef.density = 0.9f; brick_fixtureDef.restitution = 1; brick_fixtureDef.shape = brick_bodyShape; brick_fixtureDef.friction=1; brick_body.createFixture(fixtureDef); Walls are defined the same only their bullet value is set to false I would really appreciate it if you could help me have a change this code to have a realistic behavior (i.e. when I apply impulse to the brick it should trip a few times and then stop completely).

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• Question about component based design: handling objects interaction

  - by Milo

  I'm not sure how exactly objects do things to other objects in a component based design. Say I have an Obj class. I do: Obj obj; obj.add(new Position()); obj.add(new Physics()); How could I then have another object not only move the ball but have those physics applied. I'm not looking for implementation details but rather abstractly how objects communicate. In an entity based design, you might just have: obj1.emitForceOn(obj2,5.0,0.0,0.0); Any article or explanation to get a better grasp on a component driven design and how to do basic things would be really helpful.

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• Best way to implement mouse-based movement in MMOG

  - by fiftyeight

  I want to design an MMO where players click the destination they want to walk to with their mouse and the character moves there, similar to Runescape in this manner. I think it should be easier than keyboard movement since the client can simply send the server the destination each time the player clicks on a destination. The main thing I'm trying to decide is what to do when there are obstacles in the way. It's no problem to implement a simple path-finding solution on the client, the question is if the server will do path-finding as well, since it'll probably take too much Computation power from the server. What I though is that when there is an obstacle the client will send only the first coordinate it plans to go to and then when he gets there he'll send the next coordinate automatically. For example if there is a rock in the way the character will decide on a route that is made of two destinations so it goes around the rock and when it arrives at the first destination it sends the next coordinate. That way if the player changes destination is the middle he won't send unnecessary information. Is this a good way to implement it and is there a standard way MMOGs usually do it? EDIT: I should also mention that the server will make sure all movements are legal and there aren't any walls in the way etc. In the way I wrote it should be quite easy since all movements will be sent in straight lines so the server will just check there aren't any obstacles along that line.

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• How does a BSP tree work for Z sorting?

  - by Jenko

  I'm developing a 3D engine in software, and so I must compute Z sorting manually. I'm currently using the painters algorithm to sort triangles and then drawing them back-to-front. This causes artifacts that I'm trying to correct. Would using a dynamic BSP-tree ensure "correct Z sorting" of triangles? Why? Because the bounding volumes of triangles would be similar? Since I would have a single "world" BSP tree, would I have to remove and re-add any moved/scaled/rotated object into the tree? Is it possible to add triangles into a BSP tree without the expensive cutting process? Why do you need to cut triangles on the axis planes anyway? Is it faster to traverse a BSP tree from any angle, than to sort all tris each draw like the painters algorithm?

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• What are the reasons for MMOs to have level caps [on hold]

  - by SamStephens

  In many MMOs players character progression is artificially capped, e.g. by level 60 or 90 or 100 or whatever. Why do MMOs have these level caps in the first place? Why not just allow characters to continue to arbitrary levels with a mathematically designed leveling system that keeps the leveling experience interesting and endless? Answers to this question may help us to see the reason behind the feature and decide if and how this should be implemented in our MMOs.

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• Basic AI FSM - Handling state transition

  - by Galvanize

  I'm starting to study on how to implement game AI, and it seems to me that a very simple FSM for my Pong demo would be a nice way to start. My vision on implementing this would be to have a basic state interface and a class for each state, then the NPC would have an instance of the current state. The class should have an update method and directions on wich state to go next, depending on the event received. The question is: How do I handle this event? Should I have a regular addEventListener and a costum event system? Or should I check on update for the things that could change the current state? I'm feeling a bit lost, I feel I have a good grasp on the FSM concept but a good implementation seems tricky, thanks in advance.

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• Is there a simple way to stop enemies standing in the same spot?

  - by Iain

  So: top-down game, my enemies chase the player, when they get within a certain distance they stand still and fire. If they're all coming from the same direction they all end up standing in the same spot (i.e. standing "within" each other), as I'm not currently doing collision detection between enemies - they are free to pass over each other. What's a simple way around this? Either some form of collision detection or some ai?

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• Skip the first RenderTarget when writing to MRT with Opaque blending

  - by cubrman

  I am writing to three rendertargets and whant to know how to tell a GPU not to write to the first RT. When you write a shader you can simply output less data than you have RTs (like output a single float4 when writing to three RTs) and only the first RTs will be affected, but you cannot specify to output this data anywhere else but to COLOR0, then 1, etc. Is there a way to write to several RTs but skip the first target? If I output zeroes, the data in the target will become zeroes, but I need it to remain untuched in the first target and only change in the specified ones. The reason I need this is to prevent data loss when calling SetRendertarget() with DiscardContents RTs. I write to all the RTs at one point and I need to write to only the specified ones afterwards. It must be the first texture as I have a depth buffer linked to it (XNA 4.0). Thanks.

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• Correct order of tasks in each frame for a Physics simulation

  - by Johny

  I'm playing a bit around with 2D physics. I created now some physic blocks which should collide with each other. This works fine "mostly" but sometimes one of the blocks does not react to a collision and i think that's because of my order of tasks done in each frame. At the moment it looks something like this: function GameFrame(){ foreach physicObject do AddVelocityToPosition(); DoCollisionStuff(); // Only for this object not to forget! AddGravitationToVelocity(); end RedrawScene(); } Is this the correct order of tasks in each frame?

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• Moving in a diamond - enemy gets stuck

  - by Fibericon

  I have an enemy that I would like to move as follows: Start at (0, 200, 0) Move to (200, 0, 0) Move to (0, -200, 0) Move to (-200, 0, 0) Move to start point, repeat as long as it remains active. This is what I've done to achieve that: if (position.X < 200 && position.Y > 0) { Velocity = new Vector3(1, -1, 0) * speed; } else if (position.X >= 200 && position.Y <= 0 && position.Y > -200) { Velocity = new Vector3(-1, -1, 0) * speed; } else if (position.X <= 0 && position.Y <= -200) { Velocity = new Vector3(-1, 1, 0) * speed; } else { Velocity = new Vector3(1, 1, 0) * speed; } It moves to the second point, but then gets stuck and appears to vibrate in place. How should I be doing this?

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• how to generate random bubbles from array of sprites in cocos2d?

  - by prakash s

  I am devoloping the bubble shooter game in cocos2d how to generate random bubbles from array of sprites here is my code (void)addTarget { CGSize winSize = [[CCDirector sharedDirector] winSize]; //CCSprite *target = [CCSprite spriteWithFile:@"3.png" rect:CGRectMake(0, 0, 256, 256)]; NSMutableArray * movableSprites = [[NSMutableArray alloc] init]; NSArray *images = [NSArray arrayWithObjects:@"1.png", @"2.png", @"3.png", @"4.png",@"5.png",@"1.png",@"5.png", @"3.png", nil]; for(int i = 0; i < images.count; ++i) { NSString *image = [images objectAtIndex:i]; // generate random number based on size of array (array size is larger than 10) CCSprite*target = [CCSprite spriteWithFile:image]; float offsetFraction = ((float)(i+1))/(images.count+1); target.position = ccp(winSize.width*offsetFraction, winSize.height/2); target.position = ccp(350*offsetFraction, 460); [self addChild:target]; [movableSprites addObject:target]; //[target runAction:]; id actionMove = [CCMoveTo actionWithDuration:10 position:ccp(winSize.width/2,winSize. height/2)]; This code generating bubbles with *.png colour bubbles but i want to generate randomly because for shooting the bubbles by shooter class help me please id actionMoveDone = [CCCallFuncN actionWithTarget:self selector:@selector(spriteMoveFinished:)]; [target runAction:[CCSequence actions:actionMove, actionMoveDone, nil]]; } }

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• Efficiency concerning thread granularity

  - by MaelmDev

  Lately, I've been thinking of ways to use multithreading to improve the speed of different parts of a game engine. What confuses me is the appropriate granularity of threads, especially when dealing with single-instruction-multiple-data (SIMD) tasks. Let's use line-of-sight detection as an example. Each AI actor must be able to detect objects of interest around them and mark them. There are three basic ways to go about this with multithreading: Don't use threading at all. Create a thread for each actor. Create a thread for each actor-object combination. Option 1 is obviously going to be the least efficient method. However, choosing between the next two options is more difficult. Only using one thread per actor is still running through every object in series instead of in parallel. However, are CPU's able to create and join threads in the granularity posed in Option 3 efficiently? It seems like that many calls to the OS could be really slow, and varying enormously between different hardware.

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• Problems with my slotgame

  - by Raiden2k

  I'm coding a slot game for learning. Here's the source code. My questions are below. unit Unit1; {$mode objfpc}{$H+} interface uses Classes, SysUtils, Windows, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls, ExtCtrls, ComCtrls, Menus, ActnList, Spin, FileCtrl; type { TForm1 } TForm1 = class(TForm) FloatSpinEdit1: TFloatSpinEdit; Guthabenlb: TLabel; s4: TLabel; s5: TLabel; s6: TLabel; s7: TLabel; s8: TLabel; s9: TLabel; Timer3: TTimer; Winlb: TLabel; Loselb: TLabel; slotbn: TButton; s1: TLabel; s2: TLabel; s3: TLabel; Timer1: TTimer; Timer2: TTimer; procedure FormCreate(Sender: TObject); procedure slotbnClick(Sender: TObject); procedure Timer1Timer(Sender: TObject); procedure Timer2Timer(Sender: TObject); procedure Timer3Timer(Sender: TObject); private { private declarations } FRollen : array [0..2, 0..9] of String; public { public declarations } end; var Form1: TForm1; wins,loses : Integer; guthaben : Double = 10; implementation {$R *.lfm} { TForm1 } procedure TForm1.slotbnClick(Sender: TObject); begin Guthaben := Guthaben - 1.00; Guthabenlb.Caption := FloatToStr(guthaben) + (' €'); Timer1.Enabled := True; Timer2.Enabled := True; slotbn.Enabled := false; end; procedure TForm1.FormCreate(Sender: TObject); var i: integer; j: integer; n: integer; digits: TStringlist; begin Digits := TStringList.Create; try for i := low(FRollen) to high(FRollen) do begin for j := low(FRollen[i]) to high(FRollen[i]) do Digits.Add(IntToStr(j)); for j := low(FRollen[i]) to high(FRollen[i]) do begin n := Random(Digits.Count); FRollen[i, j] := Digits[n]; Digits.Delete(n); end; end finally Digits.Free; end; for i:=low(FRollen) to high(FRollen) do begin end; end; //==================================================================================================\\ // Drehen der Slots im Zufallsmodus //==================================================================================================// procedure TForm1.Timer1Timer(Sender: TObject); begin s1.Caption := IntToStr(Random(9)); s2.Caption := IntToStr(Random(9)); s3.Caption := IntToStr(Random(9)); s4.Caption := IntToStr(Random(9)); s5.Caption := IntToStr(Random(9)); s6.Caption := IntToStr(Random(9)); s7.Caption := IntToStr(Random(9)); s8.Caption := IntToStr(Random(9)); s9.Caption := IntToStr(Random(9)); end; //==================================================================================================// //===================================================================================================\\ // Gewonnen / Verloren abfrage //===================================================================================================// procedure TForm1.Timer2Timer(Sender: TObject); begin Timer1.Enabled := False; Timer2.Enabled := false; if (s1.Caption = s5.Caption) and (s1.Caption = s9.Caption) then begin Guthaben := Guthaben + 5.00; Inc(wins); end else if (s1.Caption = s4.Caption) and (s1.Caption = s7.Caption) then begin Guthaben := Guthaben + 5.00; Inc(wins); end else if (s2.Caption = s5.Caption) and (s2.Caption = s8.Caption) then begin Guthaben := Guthaben + 5.00; Inc(wins); end else if (s3.Caption = s6.Caption) and (s3.Caption = s9.Caption) then begin Guthaben := Guthaben + 5.00; Inc(wins); end else if (s3.Caption = s5.Caption) and (s3.Caption = s7.Caption) then begin Guthaben := Guthaben + 5.00; Inc(wins); end else Inc(loses); slotbn.Enabled := True; Loselb.Caption := 'Loses: ' + IntToStr(loses); Winlb.Caption := 'Wins: ' + IntTostr(Wins); end; procedure TForm1.Timer3Timer(Sender: TObject); begin if (guthaben = 0) or (guthaben < 0) then begin Timer3.Enabled := False; MessageBox(handle,'Du hast verloren!','Verlierer!',MB_OK); close(); end; end; //======================================================================================================\\ end. How can I replace the labels through icons 16 x 16 pixels? How can I adjust the winning sum according to the icons? (for example 3 crowns give you 40 € and 3 apples only 10 €) How can I adjust the winning sum with a sum for every round?

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• Playing part of a sfx audio file in HTML5 using WebAudio

  - by Matthew James Davis

  I have compiled all of my sound effects into one sequenced .ogg file. I have the start and stop times for each sound effect. How do I play the individual effects? That is, how do I play part of an audio file. More specificially, I've created a dictionary { 'sword_hit': { src: 'sfx.ogg', start: 265, // ms length: 212 // ms } } that my play_sound() function can use to look up 'sword_hit' and play the correct audio file at the correct start time for the correct duration. I simply need to know how to tell the WebAudio API to start playing at start ms and only play for length ms.

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• Having troubles with LibNoise.XNA and generating tileable maps

  - by Jon

  Following up on my previous post, I found a wonderful port of LibNoise for XNA. I've been working with it for about 8 hours straight and I'm tearing my hair out - I just can not get maps to tile, I can't figure out how to do this. Here's my attempt: Perlin perlin = new Perlin(1.2, 1.95, 0.56, 12, 2353, QualityMode.Medium); RiggedMultifractal rigged = new RiggedMultifractal(); Add add = new Add(perlin, rigged); // Initialize the noise map int mapSize = 64; this.m_noiseMap = new Noise2D(mapSize, perlin); //this.m_noiseMap.GeneratePlanar(0, 1, -1, 1); // Generate the textures this.m_noiseMap.GeneratePlanar(-1,1,-1,1); this.m_textures[0] = this.m_noiseMap.GetTexture(this.graphics.GraphicsDevice, Gradient.Grayscale); this.m_noiseMap.GeneratePlanar(mapSize, mapSize * 2, mapSize, mapSize * 2); this.m_textures[1] = this.m_noiseMap.GetTexture(this.graphics.GraphicsDevice, Gradient.Grayscale); this.m_noiseMap.GeneratePlanar(-1, 1, -1, 1); this.m_textures[2] = this.m_noiseMap.GetTexture(this.graphics.GraphicsDevice, Gradient.Grayscale); The first and third ones generate fine, they create a perlin noise map - however the middle one, which I wanted to be a continuation of the first (As per my original post), is just a bunch of static. How exactly do I get this to generate maps that connect to each other, by entering in the mapsize * tile, using the same seed, settings, etc.?

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• How do I create a third Person View using DXUTCamera in DX10?

  - by David

  I am creating a 3d flying game and using DXUTCamera for my view. I can get the camera to take on the characters position, But I would like to view my character in the 3rd person. Here is my code for first person view: //Put the camera on the object. D3DXVECTOR3 viewerPos; D3DXVECTOR3 lookAtThis; D3DXVECTOR3 up ( 5.0f, 1.0f, 0.0f ); D3DXVECTOR3 newUp; D3DXMATRIX matView; //Set the viewer's position to the position of the thing. viewerPos.x = character->x; viewerPos.y = character->y; viewerPos.z = character->z; // Create a new vector for the direction for the viewer to look character->setUpWorldMatrix(); D3DXVECTOR3 newDir, lookAtPoint; D3DXVec3TransformCoord(&newDir, &character->initVecDir, &character->matAllRotations); // set lookatpoint D3DXVec3Normalize(&lookAtPoint, &newDir); lookAtPoint.x += viewerPos.x; lookAtPoint.y += viewerPos.y; lookAtPoint.z += viewerPos.z; g_Camera.SetViewParams(&viewerPos, &lookAtPoint); So does anyone have an ideas how I can move the camera to the third person view? preferably timed so there is a smooth action in the camera movement. (I'm hoping I can just edit this code instead of bringing in another camera class)

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• Explicit resource loading in Ogre (Mogre)

  - by sebf

  I am just starting to learn Mogre and what I would like to do is to be able to load resources 'explicitly' (i.e. I just provide an absolute path instead of using a resource group tied to a directory). This is very different to manually loading resources, which I believe in Ogre has a very specific meaning, to build up the object using Ogres methods. I want to use Ogres resource management system/resource loading code, but to have finer control over which files are loaded and in what groups they are. I remember reading how to do this but cannot find the page again; I think its possible to do something like: Declare a resource group Declare the resource(s) (this is when the actual resource file name is provided) Initialise the resource group to actually load the resource(s) Is this the correct procedure? If so, is there any example code showing how to do this?

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• Moving AI in a multiplayer game

  - by Smallbro

  I've been programming a multiplayer game and its coming together very nicely. It uses both TCP and UDP (UDP for movement and TCP for just about everything else). What I was wondering was how I would go about sending multiple moving AI without much lag. At first I used TCP for everything and it was very slow when people moved. I'm currently using a butchered version of this http://corvstudios.com/tutorials/udpMultiplayer.php for my movement system and I'm wondering what the best method of sending AI movements is. By movements I mean the AI chooses left/right/up/down and the player can see this happening. Thanks.

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• error trying to display semi transparent rectangle

  - by scott lafoy

  I am trying to draw a semi transparent rectangle and I keep getting an error when setting the textures data. The size of the data passed in is too large or too small for this resource. dummyRectangle = new Rectangle(0, 0, 8, 8); Byte transparency_amount = 100; //0 transparent; 255 opaque dummyTexture = new Texture2D(ScreenManager.GraphicsDevice, 8, 8); Color[] c = new Color[1]; c[0] = Color.FromNonPremultiplied(255, 255, 255, transparency_amount); dummyTexture.SetData<Color>(0, dummyRectangle, c, 0, 1); the error is on the SetData line: "The size of the data passed in is too large or too small for this resource." Any help would be appreciated. Thank you.

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• Understanding math used to determine if vector is clockwise / counterclockwise from your vector

  - by MTLPhil

  I'm reading Programming Game AI by Example by Mat Buckland. In the Math & Physics primer chapter there's a listing of the declaration of a class used to represent 2D vectors. This class contains a method called Sign. It's implementation is as follows //------------------------ Sign ------------------------------------------ // // returns positive if v2 is clockwise of this vector, // minus if anticlockwise (Y axis pointing down, X axis to right) //------------------------------------------------------------------------ enum {clockwise = 1, anticlockwise = -1}; inline int Vector2D::Sign(const Vector2D& v2)const { if (y*v2.x > x*v2.y) { return anticlockwise; } else { return clockwise; } } Can someone explain the vector rules that make this hold true? What do the values of y*v2.x and x*v2.y that are being compared actually represent? I'd like to have a solid understanding of why this works rather than just accepting that it does without figuring it out. I feel like it's something really obvious that I'm just not catching on to. Thanks for your help.

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• How should I plan the inheritance structure for my game?

  - by Eric Thoma

  I am trying to write a platform shooter in C++ with a really good class structure for robustness. The game itself is secondary; it is the learning process of writing it that is primary. I am implementing an inheritance tree for all of the objects in my game, but I find myself unsure on some decisions. One specific issue that it bugging me is this: I have an Actor that is simply defined as anything in the game world. Under Actor is Character. Both of these classes are abstract. Under Character is the Philosopher, who is the main character that the user commands. Also under Character is NPC, which uses an AI module with stock routines for friendly, enemy and (maybe) neutral alignments. So under NPC I want to have three subclasses: FriendlyNPC, EnemyNPC and NeutralNPC. These classes are not abstract, and will often be subclassed in order to make different types of NPC's, like Engineer, Scientist and the most evil Programmer. Still, if I want to implement a generic NPC named Kevin, it would nice to be able to put him in without making a new class for him. I could just instantiate a FriendlyNPC and pass some values for the AI machine and for the dialogue; that would be ideal. But what if Kevin is the one benevolent Programmer in the whole world? Now we must make a class for him (but what should it be called?). Now we have a character that should inherit from Programmer (as Kevin has all the same abilities but just uses the friendly AI functions) but also should inherit from FriendlyNPC. Programmer and FriendlyNPC branched away from each other on the inheritance tree, so inheriting from both of them would have conflicts, because some of the same functions have been implemented in different ways on the two of them. 1) Is there a better way to order these classes to avoid these conflicts? Having three subclasses; Friendly, Enemy and Neutral; from each type of NPC; Engineer, Scientist, and Programmer; would amount to a huge number of classes. I would share specific implementation details, but I am writing the game slowly, piece by piece, and so I haven't implemented past Character yet. 2) Is there a place where I can learn these programming paradigms? I am already trying to take advantage of some good design patterns, like MVC architecture and Mediator objects. The whole point of this project is to write something in good style. It is difficult to tell what should become a subclass and what should become a state (i.e. Friendly boolean v. Friendly class). Having many states slows down code with if statements and makes classes long and unwieldy. On the other hand, having a class for everything isn't practical. 3) Are there good rules of thumb or resources to learn more about this? 4) Finally, where does templating come in to this? How should I coordinate templates into my class structure? I have never actually taken advantage of templating honestly, but I hear that it increases modularity, which means good code.

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• OUYA and Unity set up problems

  - by Atkobeau

  I'm having trouble with the Unity / OUYA plugin. I'm using Unity 4 with the latest update on a Windows 7 machine. When I open the starter kit and try to compile the plugin I get the following error: Picked up _JAVA_OPTIONS: -Xmx512M And if I try to Build and Run I get this error: Error building Player: ArgumentException: Illegal characters in path. I'm stumped, I've gone through lots of forum posts here and on stackoverflow and I can't seem to resolve it. My environment variables look like this: PATH - C:\Users\dave\Documents\adt-bundle-windows-x86_64-20130219\sdk\tools; C:\Users\dave\Documents\adt-bundle-windows-x86_64-20130219\sdk\platform-tools\ JAVA_HOME - C:\Program Files (x86)\Java\jdk1.6.0_45\ Everything in the OUYA Panel is white Any ideas?

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• OpenGLES GLSL Shader attributes always bound to 0

  - by codemonkey

  So I have a very simple vertex shader as follows #version 120 attribute vec3 position; attribute vec3 inColor; uniform mat4 mvp; varying vec3 fragColor; void main(void){ fragColor = inColor; gl_Position = mvp * vec4(position, 1.0); } Which I load, as well as the fragment shader: #version 120 varying vec3 fragColor; void main(void) { gl_FragColor = vec4(fragColor,1.0); } Which I then load, compile, and link to my shader program. I check for link status using glGetProgramiv(shaderProgram, GL_LINK_STATUS, &shaderSuccess); which returns GL_TRUE so I think its ok. However, when I query the active attributes and uniforms using #ifdef DEBUG int totalAttributes = -1; glGetProgramiv(shaderProgram, GL_ACTIVE_ATTRIBUTES, &totalAttributes); for(int i=0; i<totalAttributes; ++i) { int name_len=-1, num=-1; GLenum type = GL_ZERO; char name[100]; glGetActiveAttrib(shaderProgram, GLuint(i), sizeof(name)-1, &name_len, &num, &type, name ); name[name_len] = 0; GLuint location = glGetAttribLocation(shaderProgram, name); fprintf(stderr, "Attribute %s is bound at %d\n", name, location); } int totalUniforms = -1; glGetProgramiv(shaderProgram, GL_ACTIVE_UNIFORMS, &totalUniforms); for(int i=0; i<totalUniforms; ++i) { int name_len=-1, num=-1; GLenum type = GL_ZERO; char name[100]; glGetActiveUniform(shaderProgram, GLuint(i), sizeof(name)-1, &name_len, &num, &type, name ); name[name_len] = 0; GLuint location = glGetUniformLocation(shaderProgram, name); fprintf(stderr, "Uniform %s is bound at %d\n", name, location); } #endif I get: Attribute inColor is bound at 0 Attribute position is bound at 1 Uniform mvp is bound at 0 Which leads to failure when trying to use the shader to render the objects. I have tried switching the order of declaration of position & inColor, but still, only position is bound with the other two giving 0 Can someone please explain why this is happening? Thanks

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• Bouncing ball slowing down over time

  - by user46610

  I use the unreal engine 4 to bounce a ball off of walls in a 2D space, but over time the ball gets slower and slower. Movement happens in the tick function of the ball FVector location = GetActorLocation(); location.X += this->Velocity.X * DeltaSeconds; location.Y += this->Velocity.Y * DeltaSeconds; SetActorLocation(location, true); When a wall gets hit I get a Hit Event with the normal of the collision. This is how I calculate the new velocity of the ball: FVector2D V = this->Velocity; FVector2D N = FVector2D(HitNormal.X, HitNormal.Y); FVector2D newVelocity = -2 * (V.X * N.X + V.Y * N.Y) * N + V; this->Velocity = newVelocity; Over time, the more the ball bounced around, the velocity gets smaller and smaller. How do I prevent speed loss when bouncing off walls like that? It's supposed to be a perfect bounce without friction or anything.

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• Why do we use Pythagoras in game physics?

  - by Starkers

  I've recently learned that we use Pythagoras a lot in our physics calculations and I'm afraid I don't really get the point. Here's an example from a book to make sure an object doesn't travel faster than a MAXIMUM_VELOCITY constant in the horizontal plane: MAXIMUM_VELOCITY = <any number>; SQUARED_MAXIMUM_VELOCITY = MAXIMUM_VELOCITY * MAXIMUM_VELOCITY; function animate(){ var squared_horizontal_velocity = (x_velocity * x_velocity) + (z_velocity * z_velocity); if( squared_horizontal_velocity <= SQUARED_MAXIMUM_VELOCITY ){ scalar = squared_horizontal_velocity / SQUARED_MAXIMUM_VELOCITY; x_velocity = x_velocity / scalar; z_velocity = x_velocity / scalar; } } Let's try this with some numbers: An object is attempting to move 5 units in x and 5 units in z. It should only be able to move 5 units horizontally in total! MAXIMUM_VELOCITY = 5; SQUARED_MAXIMUM_VELOCITY = 5 * 5; SQUARED_MAXIMUM_VELOCITY = 25; function animate(){ var x_velocity = 5; var z_velocity = 5; var squared_horizontal_velocity = (x_velocity * x_velocity) + (z_velocity * z_velocity); var squared_horizontal_velocity = 5 * 5 + 5 * 5; var squared_horizontal_velocity = 25 + 25; var squared_horizontal_velocity = 50; // if( squared_horizontal_velocity <= SQUARED_MAXIMUM_VELOCITY ){ if( 50 <= 25 ){ scalar = squared_horizontal_velocity / SQUARED_MAXIMUM_VELOCITY; scalar = 50 / 25; scalar = 2.0; x_velocity = x_velocity / scalar; x_velocity = 5 / 2.0; x_velocity = 2.5; z_velocity = z_velocity / scalar; z_velocity = 5 / 2.0; z_velocity = 2.5; // new_horizontal_velocity = x_velocity + z_velocity // new_horizontal_velocity = 2.5 + 2.5 // new_horizontal_velocity = 5 } } Now this works well, but we can do the same thing without Pythagoras: MAXIMUM_VELOCITY = 5; function animate(){ var x_velocity = 5; var z_velocity = 5; var horizontal_velocity = x_velocity + z_velocity; var horizontal_velocity = 5 + 5; var horizontal_velocity = 10; // if( horizontal_velocity >= MAXIMUM_VELOCITY ){ if( 10 >= 5 ){ scalar = horizontal_velocity / MAXIMUM_VELOCITY; scalar = 10 / 5; scalar = 2.0; x_velocity = x_velocity / scalar; x_velocity = 5 / 2.0; x_velocity = 2.5; z_velocity = z_velocity / scalar; z_velocity = 5 / 2.0; z_velocity = 2.5; // new_horizontal_velocity = x_velocity + z_velocity // new_horizontal_velocity = 2.5 + 2.5 // new_horizontal_velocity = 5 } } Benefits of doing it without Pythagoras: Less lines Within those lines, it's easier to read what's going on ...and it takes less time to compute, as there are less multiplications Seems to me like computers and humans get a better deal without Pythagoras! However, I'm sure I'm wrong as I've seen Pythagoras' theorem in a number of reputable places, so I'd like someone to explain me the benefit of using Pythagoras to a maths newbie. Does this have anything to do with unit vectors? To me a unit vector is when we normalize a vector and turn it into a fraction. We do this by dividing the vector by a larger constant. I'm not sure what constant it is. The total size of the graph? Anyway, because it's a fraction, I take it, a unit vector is basically a graph that can fit inside a 3D grid with the x-axis running from -1 to 1, z-axis running from -1 to 1, and the y-axis running from -1 to 1. That's literally everything I know about unit vectors... not much :P And I fail to see their usefulness. Also, we're not really creating a unit vector in the above examples. Should I be determining the scalar like this: // a mathematical work-around of my own invention. There may be a cleverer way to do this! I've also made up my own terms such as 'divisive_scalar' so don't bother googling var divisive_scalar = (squared_horizontal_velocity / SQUARED_MAXIMUM_VELOCITY); var divisive_scalar = ( 50 / 25 ); var divisive_scalar = 2; var multiplicative_scalar = (divisive_scalar / (2*divisive_scalar)); var multiplicative_scalar = (2 / (2*2)); var multiplicative_scalar = (2 / 4); var multiplicative_scalar = 0.5; x_velocity = x_velocity * multiplicative_scalar x_velocity = 5 * 0.5 x_velocity = 2.5 Again, I can't see why this is better, but it's more "unit-vector-y" because the multiplicative_scalar is a unit_vector? As you can see, I use words such as "unit-vector-y" so I'm really not a maths whiz! Also aware that unit vectors might have nothing to do with Pythagoras so ignore all of this if I'm barking up the wrong tree. I'm a very visual person (3D modeller and concept artist by trade!) and I find diagrams and graphs really, really helpful so as many as humanely possible please!

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