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• Automatically zoom out the camera to show all players

  - by user36159

  I am building a game in XNA that takes place in a rectangular arena. The game is multiplayer and each player may go where they like within the arena. The camera is a perspective camera that looks directly downwards. The camera should be automatically repositioned based on the game state. Currently, the xy position is a weighted sum of the xy positions of important entities. I would like the camera's z position to be calculated from the xy coordinates so that it zooms out to the point where all important entities are visible. My current approach is to: hw = the greatest x distance from the camera to an important entity hh = the greatest y distance from the camera to an important entity Calculate z = max(hw / tan(FoVx), hh / tan(FoVy)) My code seems to almost work as it should, but the resulting z values are always too low by a factor of about 4. Any ideas?

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• Game Institute Math Courses

  - by W3Geek

  I'm 21 years old and I suck at math, I mean really bad. I don't have the necessary logic to apply it towards programming. I would like to learn the math and logic of applying it. I found Game Institute (http://www.gameinstitute.com) awhile back and heard a lot of praise about them. Are there Math courses any good? Thank you. Edit: My high school was terrible and did not prepare me for any math. I am fairly decent at programming, I just don't have the logic to apply any mathematics to programming, as an example I don't understand the algorithm of finding the size of a user's screen. Yes I have heard of KhanAcademy (http://www.khanacademy.org/) and I have completed a lot of maths on his website but I still don't have the logic to apply any of it to programming.

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• Foreach loop with 2d array of objects

  - by Jacob Millward

  I'm using a 2D array of objects to store data about tiles, or "blocks" in my gameworld. I initialise the array, fill it with data and then attempt to invoke the draw method of each object. foreach (Block block in blockList) { block.Draw(spriteBatch); } I end up with an exception being thrown "Object reference is not set to an instance of an object". What have I done wrong? EDIT: This is the code used to define the array Block[,] blockList; Then blockList = new Block[screenRectangle.Width, screenRectangle.Height]; // Fill with dummy data for (int x = 0; x <= screenRectangle.Width / texture.Width; x++) { for (int y = 0; y <= screenRectangle.Height / texture.Width; y++) { if (y >= screenRectangle.Height / (texture.Width*2)) { blockList[x, y] = new Block(1, new Rectangle(x * 16, y * 16, texture.Width, texture.Height), texture); } else { blockList[x, y] = new Block(0, new Rectangle(x * 16, y * 16, texture.Width, texture.Height), texture); } } }

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• How do I prevent other dynamic bodies from affecting the player's velocity with Box2D?

  - by Milo

  I'm working on my player object for my game. PhysicsBodyDef def; def.fixedRotation = true; def.density = 1.0f; def.position = Vec2(200.0f, 200.0f); def.isDynamic = true; def.size = Vec2(50.0f,200.0f); m_player.init(def,&m_physicsEngine.getWorld()); This is how he moves: b2Vec2 vel = getBody()->GetLinearVelocity(); float desiredVel = 0; if (m_keys[ALLEGRO_KEY_A] || m_keys[ALLEGRO_KEY_LEFT]) { desiredVel = -5; } else if (m_keys[ALLEGRO_KEY_D] || m_keys[ALLEGRO_KEY_RIGHT]) { desiredVel = 5; } else { desiredVel = 0; } float velChange = desiredVel - vel.x; float impulse = getBody()->GetMass() * velChange; //disregard time factor getBody()->ApplyLinearImpulse( b2Vec2(impulse,0), getBody()->GetWorldCenter(),true); This creates a few problems. First, to move the player at a constant speed he must be given a high velocity. The problem with this is if he just comes in contact with a small box, he makes it move a lot. Now, I can fix this by lowering his density, but then comes my main issue: I need other objects to be able to run into him, but when they do, he should be like a static wall and not move. I'm not sure how to do that without high density. I cannot use collision groups since I still need him to be solid toward other dynamic things. How can this be done? Essentially, how do I prevent other dynamic bodies from affecting the player's velocity?

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• Customize Colors for Sprites in Web Game

  - by NateDSaint

  So I'm working on an html5/javascript/css3-based game. Without going into too much detail, I'm thinking of having the characters be simple 8 or 16-bit style sprites, but I'd like to allow the user to customize the colors of their character. Here are some examples of what I'm talking about : http://jsfiddle.net/simurai/CGmCe/light/ http://www.splashnology.com/article/sprite-animation-in-css3/1485/ So the problem I'm having is two-fold: 1) Should I use something other than a sprite map for my characters, like actually draw them as shapes and animate them in a canvas element? That way I can fill the sprite with colors of the user's choosing? My fear there is that this would be inefficient as far as resources and also waste a lot of time hand-drawing everything, but could allow other customization (like height/width etc). 2) Are there potentially some web apis that would allow you to alter colors inside of a sprite? I suppose I could do it on the back-end with GD, but I'm trying to make it entirely in-browser (including local storage). It's not a definitive one-answer only question, but I'm hoping someone can suggest something they've seen that approaches the same problem from another angle or gives us a way to customize the sprites or manipulate them in some manner. Or avoid them altogether, and use a different method.

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• How to create an extensible rope in Box2D?

  - by Thomas

  Let's say I'm trying to create a ninja lowering himself down a rope, or pulling himself back up, all whilst he might be swinging from side to side or hit by objects. Basically like http://ninja.frozenfractal.com/ but with Box2D instead of hacky JavaScript. Ideally I would like to use a rope joint in Box2D that allows me to change the length after construction. The standard Box2D RopeJoint doesn't offer that functionality. I've considered a PulleyJoint, connecting the other end of the "pulley" to an invisible kinematic body that I can control to change the length, but PulleyJoint is more like a rod than a rope: it constrains maximum length, but unlike RopeJoint it constrains the minimum as well. Re-creating a RopeJoint every frame using a new length is rather inefficient, and I'm not even sure it would work properly in the simulation. I could create a "chain" of bodies connected by RotationJoints but that is also less efficient, and less robust. I also wouldn't be able to change the length arbitrarily, but only by adding and removing a whole number of links, and it's not obvious how I would connect the remainder without violating existing joints. This sounds like something that should be straightforward to do. Am I overlooking something?

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• How to cull liquids

  - by Cyral

  I use culling on my Tiles in my 2D Tile Based Platformer, so only ones needed are drawn on screen. Thats easy to do. However, My Liquid tiles (Water, lava, etc) require an Update Method aswell as the normal Draw, which does checks against tiles, makes it flow, etc. So how should I cull liquid updates in my game? Not culling is to slow, culling only on screen looks awkward when you move. What do you think would be best for the player? Maybe someway of culling the visible tiles PLUS also adding the width/height of the viewport to start culling tiles at a fast enough rate in front of the player so it dosent look awkward when moving? (Not sure how to do this though, something with MaxSpeed of player and width of screen)

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• Novice prototyping a massive multiplayer webpage based gaming system

  - by Sean Hendlin

  I'm trying to build a website based game in which various pages of the site act as different areas of the game. I am wondering what you would recommended as a design structure. Which languages would be best if building what will hopefully becomes a massive system able to scale to massive amounts of users. I am wondering if and how various elements from differing languages could be meshed to interact with each other. For example could I use html5, javascript, and PHP? What about asp.net how might that factor in? I'm a newbie programmer but I've been working on this idea for years and I want to build it to reality. Your comments and suggestions are appreciated. P.S.: The game is not all graphics and animation (though flash like appearance and some animation would be nice). What I am thinking of is essentially a heavily gamified system of forms. And LOTS of data in many different categories cross referencing each-other. I'm not sure how to go about structuring the collection of data. Also while I know javascript can be used to process some functions, I'm wondering what sort of base system I would need to handle the server side processing of what I am expecting to be some pretty significant algorithm processing. That is to say I expect to have many many many functions and I'm not sure how to mange this using javascript. I feel like they would be forgotten, mixed up, disorganizes as they essentially only exist where they are coded. I guess I need to learn something of libraries? OK, Thank you! Is enough from me for now.

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• Can I become a Game Designer? [on hold]

  - by user32721

  This is my first time posting something on a forum in 4 years. I am posting this because I want to adjust my expectations and goals regarding game design. I am in college in Morocco (Al Akhawayn university). just started my junior year. I am a communications major (school of humanities) and a gender studies minor. I want to become a video game designer. It is the only career that I am interested in. I have been playing ever since I was 5 and haven't stopped yet. Currently I don't have any noteworthy skills to become a designer. I don't know how to program (don't really have the patience for it) and I can't draw to save my life. I haven't tried visual software like MAYA or MAX so I can't comment on graphic design. So I basically want to know whether my current education is capable of helping me reach my goal. If not then should I take a master's in game design (in the U.S?) or switch my minor to computer science? I am sorry that this post is long! I look forward to hearing your advice!

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• How to spawn a character at certain point and walk to a set point

  - by Robert H.

  I am making a game where I have a background image of a neighborhood. Each location has a different number of customers that are generated to walk on sidewalks. They all walk to a specific location (like a stand or cart that sells stuff), after they get to location I want them to interact with the cart. However, if another customer is already in a sale interaction then the others get in line in order of arrival. After the transaction the customers walk off screen. Any information on how I can do this and what game engine would be needed? Any one have any idea where I should go for this. I already have my game done up through Eclipse/Java without any game engine.

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• Wheel rotation, to change velocity of vehicle

  - by Lewis

  I update the velocity of my vehicle like so: [v setVelocity: ((2 * 3.14 * 100 * (wheel.getRotationValue / 360) / 30)) * gameSpeed]; // update on 60 fps this gets velocity on all frames divide by 60 for 1 frame. This is done in my update method in my world class. Now wheel.getRotationValue returns the rotation value which is worked out like this: - (void)ccTouchesMoved:(NSSet *)touches withEvent:(UIEvent *)event { UITouch *touch = [touches anyObject]; CGPoint location = [touch locationInView:[touch view]]; location = [[CCDirector sharedDirector] convertToGL:location]; if (CGRectContainsPoint(wheel.boundingBox, location)) { CGPoint firstLocation = [touch previousLocationInView:[touch view]]; CGPoint location = [touch locationInView:[touch view]]; CGPoint touchingPoint = [[CCDirector sharedDirector] convertToGL:location]; CGPoint firstTouchingPoint = [[CCDirector sharedDirector] convertToGL:firstLocation]; CGPoint firstVector = ccpSub(firstTouchingPoint, wheel.position); CGFloat firstRotateAngle = -ccpToAngle(firstVector); CGFloat previousTouch = CC_RADIANS_TO_DEGREES(firstRotateAngle); CGPoint vector = ccpSub(touchingPoint, wheel.position); CGFloat rotateAngle = -ccpToAngle(vector); CGFloat currentTouch = CC_RADIANS_TO_DEGREES(rotateAngle); float limit = 0.5; rotationValue += (currentTouch - previousTouch) * limit; } touching = YES; } Say I steer the vehicle to the far right of the screen, and want to move it to the far left, It wont start moving to the left of the screen until the rotationValue is past 0 degrees again (the wheel is in its center posistion) and is dragged past this value. Is there anyway to change the code I have above, so that movement on the wheel is recognised instantly and updates the velocity of v instantly too?

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• Handling different screen densities in Android Devices?

  - by DevilWithin

  Well, i know there are plenty of different-sized screens in devices that run Android. The SDK I code with deploys to all major desktop platforms and android. I am aware i must have special cares to handle the different screen sizes and densities, but i just had an idea that would work in theory, and my question is exactly about that method, How could it FAIL ? So, what I do is to have an ortho camera of the same size for all devices, with possible tweaks, but anyway that would grant the proper positioning of all elements in all devices, right? We can assume everything is drawn in OpenGLES and input handling is converted to the proper camera coordinates. If you need me to improve the question, please tell me.

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• Can't remove JPanel from JFrame while adding new class into it

  - by A.K.

  Basically, I have my Frame class, which instantiates all the properties for the JFrame, and draws a JLabel with an image (my title screen). Then I made a separate JPanel with a start button on it, and made a mouse listener that will allow me to remove these objects while adding in a new Board() class (Which paints the main game). *Note: The JLabel is SEPARATE from the JPanel, but it still gets moved to the side by it. Problem: Whenever I click the button though, it only shows a little square of what I presume is my board class trying to run. Code below for the Frame Class: package OurPackage; //Made By A.K. 5/24/12 //Contains Frame. import java.awt.BorderLayout; import java.awt.Color; import java.awt.Container; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.GridBagLayout; import java.awt.GridLayout; import java.awt.Image; import java.awt.Rectangle; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.KeyEvent; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.awt.event.MouseListener; import javax.swing.*; import javax.swing.plaf.basic.BasicOptionPaneUI.ButtonActionListener; public class Frame implements MouseListener { public static boolean StartGame = false; ImageIcon img = new ImageIcon(getClass().getResource("/Images/ActionJackTitle.png")); ImageIcon StartImg = new ImageIcon(getClass().getResource("/Images/JackStart.png")); public Image Title; JLabel TitleL = new JLabel(img); public JPanel panel = new JPanel(); JButton StartB = new JButton(StartImg); JFrame frm = new JFrame("Action-Packed Jack"); public Frame() { TitleL.setPreferredSize(new Dimension(1200, 420)); frm.add(TitleL); frm.setLayout(new GridBagLayout()); frm.add(panel); panel.setSize(new Dimension(220, 45)); panel.setLayout(new GridBagLayout ()); panel.add(StartB); StartB.addMouseListener(this); StartB.setPreferredSize(new Dimension(220, 45)); frm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frm.setSize(1200, 420); frm.setVisible(true); frm.setResizable(false); frm.setLocationRelativeTo(null); } public static void main(String[] args) { new Frame(); } public void mouseClicked(MouseEvent e) { StartB.setContentAreaFilled(false); panel.remove(StartB); frm.remove(panel); frm.remove(TitleL); //frm.setLayout(null); frm.add(new Board()); //Add Game "Tiles" Or Content. x = 1200 frm.validate(); System.out.println("Hit!"); } @Override public void mouseEntered(MouseEvent arg0) { // TODO Auto-generated method stub } @Override public void mouseExited(MouseEvent arg0) { // TODO Auto-generated method stub } @Override public void mousePressed(MouseEvent arg0) { // TODO Auto-generated method stub } @Override public void mouseReleased(MouseEvent arg0) { // TODO Auto-generated method stub } }

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• How to manage my model

  - by Christophe Debove

  I have in my model, a list of Classes : Player, NonPlayerCharacter, Monster, Item, NonMovableItem etc With AndEngine I've a list of sprite for each piece of my model, How can I manage the relashionship between my model's classes and the graphical elements, what is the degree of abstaction recommended for my problem? One sprite for one Model or one Model for one Sprite or n for n for exemple If I do drag&drop have I to make abstraction of the Sprite Class, another exemple a map is a List of sprite or a list of element of my model?

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• How does Starcraft 2 load it's metadata?

  - by chobok

  Lets say you are playing Starcraft 2 melee map. The game loads the map. Melee maps have the following dependencies: Liberty (Mod) Liberty Multi (Mod) I think the game engine will load the data from Liberty (Mod) first, then from Liberty Multi (Mod). For data that exists in both dependencies, the engine will use the one from Liberty Multi (Mod). Is this correct? Liberty Multi (Mod) is updated with each patch of Starcraft 2. Does the game engine load just the latest version of Liberty Multi (Mod)? or Does the game engine load all the versions and overwrite duplicate data with the latest version?

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• Can anyone recommend an AI sandbox?

  - by user19433

  I'm passionate person, who has been around AI from a long time [1] but never going in deep enough. Now it's time! I've been really looking for some way to concentrate on AI coding but couldn't succeeded to find an AI environment I can focus on. I just want to use an AI sandbox environment which would let me have tools like: visibility information character controller able to easily define a level, with obstacles of course physics collider management triggers management don't need to be a shiny, eye candy graphical render : this is about pathfinding, tactical reasoning, etc.. I have tried : Unreal Dev Kit : while the new release announce is about C++ coding, this is about external tools and will be released in 2013 Cry Engine : really interesting as AI is presents here but coding with it appears to be an hell: did I got it wrong ? Half Life source, C4, Torque, Dx Studio : either quite old, not very useful or costly these imply to dig in documentation (when provided) to code everything, graphics included. Unity 3D : the most promising platform. While you also need to create your own environment, there are lot of examples. The disadvantage is, in addition to spend time to have this env. working, is the languages choice : C#, Javascript or Boo. C# is not that hard, but this implies you'll allways have to convert papers (I love those from Lars Linden) books codes, or anything you can have in Aigamedev are most often in C++. This is extra work. I've look at "Simple Path", the very good Arong Greenberg work but no source provided and AngryAnt work. AI Sandbox : this seems to be exactly what as AI coder I want to use. I saw some preview but from 2009 we still don't know what it will be about precisely, will it be opensource or free (I strongly doubt), will I be able to buy it? will it really provide me tools I need to focus on AI ? That being said, what is the best environment to be able to focus on AI coding only, is it even possible?

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• Play audio in javascript with a good performance

  - by João

  I'm developing a browser game where the player can shoot. Everytime he shoots it play a sound. Currently i'm using this code to play sounds in JavaScript: var audio = document.createElement("audio"); audio.src = "my_sound.mp3"; audio.play(); I'm worried about performance here. Will 10 simultaneous sounds impact my game performance too much? Will all audio objects stay in memory even after they are played?

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• box2d resize bodies arround point

  - by philipp

  I have a compound object, consisting of a b2Body, vector-graphics and a list polygons which describe the b2body's shapes. This object has its own transformation matrix to centralize the storage of transformations. So far everything is working quiet fine, even scaling works, but not if i scale around a point. In the initialization phase of the object it is scaled around a point. This happens in this order: transform the main matrix transform the vector graphics and the polygons recreate the b2Body After this function ran, the shapes and all the graphics are exactly where they should be, BUT: after the first steps of the b2World the graphical stuff moves away from the body. When I ran the debugger I found out that the position of the body is 0/0 the red dot shows the center of scaling. the first image shows the basic setup and the second the final position of the graphics. This distance stays constant for the rest of the simulation. If I set the position via myBody.SetPosition( sx, sy ); the whole scenario just plays a bit more distant for the origin. Any Idea how to fix this? EDIT:: I came deeper down to the problem and it lies in the fact that i must not scale the transform matrix for the b2body shapes around the center, but set the b2body's position back to the point after scaling. But how can I calculate that point? EDIT 2 :: I came ever deeper down to it, even solved it, but this is a slow solution and i hope that there is somebody who understands what formula I need. assuming to have a set polygons relative to an origin as basis shapes for a b2body: scaling the whole object around a certain point is done in the following steps: i scale everything around the center except the polygons i create a clone of the polygons matrix i scale this clone around the point i calculate dx, dy as difference of clone.tx - original.tx and clone.ty - original.ty i scale the original polygon matrix NOT around the point i recreate the body i create the fixture i set the position of the body to dx and dy done! So what i an interested in is a formula for dx and dy without cloning matrices, scaling the clone around a point, getting dx and dy and finally scale the vertex matrix.

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• Collision Detection for a 2D RPG

  - by PHMitrious

  First of all, I have done some research on this topic before asking, and I'm asking this question as a mean to get some opinions on this topic, so I don't make a decision only on my own, but taking into account other people's experience as well. I'm starting a 2D online RPG project. I am using SFML for graphics and input and I'm creating a basic game structure and all for the game, creating modules for each part of the game. Well, let me get to the point I just wanted to give you guys some context. I want to decide on how I'm going to work with collision detection. Well I'm kinda going to work on maps with a tile map divided in layers (as usual) and add an extra 2 layers - not exactly in the map - for objects. So I'll have collisions between objects and agents (players - npcs - monsters - spells etc) and agents and tiles. The seconds one can be easily solved the first one need a little bit of work. I considered both creating a basic collision test engine using polygons and a quadtree to diminish tests since I'm going to be working with big maps with lots of objects - creating both a physical and graphical world representation. And I also considered using a physics engine like Box2D for collision tests. I think the first approach would take more work on my part but the second one would have the overhead of using a whole physics engine for just collision detection and no physics. What do you guys think ?

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• Applying Textures to Hexagonal Tiles Seamlessly

  - by PATRY

  I'm doing a tactical game (X-Com / Fallout style) for fun. I've decided to use a hexagonal map, but I'm having a graphic problem. My current map display is HUD-like, with only the border of the map cells displayed, without any texture. it's simple and allow for display of different types of informations by varying the color of the border. For exemple the "danger view mode" displays the borders with a color going from green (no damage possible) to red (prob of damage 90%). Now, It's a bit hard to differentiate the kind of tile the player is on. I could put a plain color (green is grass, pale blue is water...), but this is going to limit the possibilities. Thus, i would like to display a texture on my tiles. Since the map are generated, i can not use a picture for the whole map with the HUD over. So, my question is : does any one knows how i could generate the sealess hexagonal textures (algo or plugin), or if there is a site with some hexagonal tiles ?

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• Typical collision detection

  - by marcg11

  I would like to know how is the typical collision detection of most games. For example, you control a character which can move in 2 dimensional directions (except up and down). Now lets asume he walks into a wall, most of the games depending on character angle and the BB normal face will only stop the player in one axis, but will continue moving in the other along the wall axis. How is that done? I've only managed to stop the character from going through the wall by seting the position to the last one in the past frame if the new position colllisions the bounding box. But this just makes the player stop sharply and unrealisticly.

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• Regulating how much to draw based on how much was drawn last frame.

  - by Mike Howard

  I have a 3D game world on an iPhone (limited graphics speed), and I'm already regulating whether I draw each shape on the screen based on it's size and distance from the camera. Something like... if (how_big_it_looks_from_the_camera > constant) then draw What I want to do now is also take into account how many shapes are being drawn, so that in busier areas of the game world I can draw less than I otherwise would. I tried to do this by dividing how_big_it_looks by the number of shapes that were drawn last frame (well, the square root of this but I'm simplifying - the problem is the same). if (how_big_it_looks / shapes_drawn > constant2) then draw But the check happens at the level of objects which represent many drawn shapes, and if an object containing many shapes is switched on, it increases shapes_drawn lots and switches itself back off the next frame. It flickers on and off. I tried keeping a kind of weighted average of previous values, by each frame doing something like shapes_drawn_recently = 0.9 * shapes_drawn_recently + 0.1 * shapes_just_drawn, but of course it only slows the flickering down because of the nature of the feedback loop. Is there a good way of solving this? My project is in Objective-C, but a general algorithm or pseudo-code is good too. Thanks.

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• Textures of .x model deformed in XNA

  - by marc wellman

  I want to have a 3D model with textures built in SketchUp 8 be imported as a .x model in XNA. So far I have used several .x exporters like http://edecadoudal.googlepages.com/xExporter.rb 3D RAD zbylsxexporter With all of them I have the same problem: The model gets built correctly but the textures are deformed. The sizes of my texture files are multiples of four and inside Sketchup the model looks prefect. That's the texture file which is 256x256: And this is how it looks like in my XNA program: What can I do?

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• Game Code Design for Rendering

  - by kuroutadori

  I first created a game on the iPhone and I'm now porting it to Android. I wrote most of the code in C++, but when it came to porting it wasn't so easy. The Android way is to have two threads, one for rendering and one for updating. This due to some devices blocking when updating the hardware. My problem is that I am coming from the iPhone. When I transition, say from the Menu to the Game, I would stop the Animation (Rendering) and load up the next Manager (the Menu has a Manager and so has the Game). I could implement the same thing on Android, but I have noticed on game ports like Quake, don't do this - as far as I can tell. I have learnt that I cannot just dynamically add another Renderer class the the tree because I will probably get a dequeuing buffer error - which I believe to be a problem with the OpenGL ES side. So how is it done?

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• Error in my Separating Axis Theorem collision code

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; int x; int y; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } public void update(int xPos, int yPos){ x = xPos; y = yPos; } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(new Vect(vertices[0].x+x, vertices[0].y+y)); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(new Vect(vertices[i].x+x, vertices[i].y+y)); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if(y > other.x && other.y > x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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