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• Rotating an object about a point (2D) using box2d

  - by noob

  i just started developing using box2d on flixel and i realise the pivot point of the rotation of an object in box2d is set to the center of an object. i had read on forums and i found out that SetAsBox can change the pivot point of the object, however, i cannot seem to get it work to rotate about a point. what i would like to achieve is to rotate an object about a point like earth revolving around the sun. any one can help me with it? really thanks a lot and sorry for the bad english

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• Why does my sprite glitch when moving? [closed]

  - by rphello101

  Using Slick 2D/Java, I'm using the mouse to rotate a sprite and WASD to move it (A and D are used to strafe). I finally got the directional keys and rotation to work in sync, but I'm having problems with sporadic movement. It seems that the move speed is not always set to the value I have it at. Sometimes the sprite with just shoot across the screen. Furthermore, it seems that at 0 degrees, when the left key is pressed, the sprite moves backwards, not to the left. There also seems to be quite a bit of glitching when two keys are pressed, like left and up. Anyone see anything obvious? Here is the rotational code: int mX = Mouse.getX(); int mY = HEIGHT - Mouse.getY(); int pX = sprite.x+sprite.image.getWidth()/2; int pY = sprite.y+sprite.image.getHeight()/2; double mAng; if(mX!=pX){ mAng = Math.toDegrees(Math.atan2(mY - pY, mX - pX)); if(mAng==0 && mX<=pX) mAng=180; } else{ if(mY>pY) mAng=90; else mAng=270; } sprite.angle = mAng; sprite.image.setRotation((float) mAng); Movement code: Input input = gc.getInput(); Vector2f direction = new Vector2f(); Vector2f velocity = new Vector2f(); Vector2f left; Vector2f right; direction.x = (float) Math.cos(Math.toRadians(sprite.angle)); direction.y = (float) Math.sin(Math.toRadians(sprite.angle)); if(direction.length()>0) direction = direction.normalise(); left = new Vector2f(-direction.y, direction.x); right = new Vector2f(direction.y, -direction.x); velocity.x = (float) (direction.x * sprite.moveSpeed); velocity.y = (float) (direction.y * sprite.moveSpeed); if(input.isKeyDown(sprite.up)){ sprite.x += velocity.x*delta; sprite.y += velocity.y*delta; }if (input.isKeyDown(sprite.down)){ sprite.x -= velocity.x*delta; sprite.y -= velocity.y*delta; }if (input.isKeyDown(sprite.left)){ sprite.x += left.x * sprite.moveSpeed * delta; sprite.y += left.y * sprite.moveSpeed * delta; }if (input.isKeyDown(sprite.right)){ sprite.x += right.x * sprite.moveSpeed * delta; sprite.y += right.y * sprite.moveSpeed * delta; }

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• Bitmap font rendering, UV generation and vertex placement

  - by jack

  I am generating a bitmap, however, I am not sure on how to render the UV's and placement. I had a thread like this once before, but it was too loosely worded as to what I was looking to do. What I am doing right now is creating a large 1024x1024 image with characters evenly placed every 64 pixels. Here is an example of what I mean. I then save the bitmap X/Y information to a file (which is all multiples of 64). However, I am not sure how to properly use this information and bitmap to render. This falls into two different categories, UV generation and kerning. Now I believe I know how to do both of these, however, when I attempt to couple them together I will get horrendous results. For example, I am trying to render two different text arrays, "123" and "njfb". While ignoring the texture quality (I will be increasing the texture to provide more detail once I fix this issue), here is what it looks like when I try to render them. http://img64.imageshack.us/img64/599/badfontrendering.png Now for the algorithm. I am doing my letter placement with both GetABCWidth and GetKerningPairs. I am using GetABCWidth for the width of the characters, then I am getting the kerning information for adjust the characters. Does anyone have any suggestions on how I can implement my own bitmap font renderer? I am trying to do this without using external libraries such as angel bitmap tool or freetype. I also want to stick to the way the bitmap font sheet is generated so I can do extra effects in the future. Rendering Algorithm for(U32 c = 0, vertexID = 0, i = 0; c < numberOfCharacters; ++c, vertexID += 4, i += 6) { ObtainCharInformation(fontName, m_Text[c]); letterWidth = (charInfo.A + charInfo.B + charInfo.C) * scale; if(c != 0) { DWORD BytesReq = GetGlyphOutlineW(dc, m_Text[c], GGO_GRAY8_BITMAP, &gm, 0, 0, &mat); U8 * glyphImg= new U8[BytesReq]; DWORD r = GetGlyphOutlineW(dc, m_Text[c], GGO_GRAY8_BITMAP, &gm, BytesReq, glyphImg, &mat); for (int k=0; k<nKerningPairs; k++) { if ((kerningpairs[k].wFirst == previousCharIndex) && (kerningpairs[k].wSecond == m_Text[c])) { letterBottomLeftX += (kerningpairs[k].iKernAmount * scale); break; } } letterBottomLeftX -= (gm.gmCellIncX * scale); } SetVertex(letterBottomLeftX, 0.0f, zFight, vertexID); SetVertex(letterBottomLeftX, letterHeight, zFight, vertexID + 1); SetVertex(letterBottomLeftX + letterWidth, letterHeight, zFight, vertexID + 2); SetVertex(letterBottomLeftX + letterWidth, 0.0f, zFight, vertexID + 3); zFight -= 0.001f; float BottomLeftX = (F32)(charInfo.bitmapXOrigin) / (float)m_BitmapWidth; float BottomLeftY = (F32)(charInfo.bitmapYOrigin + charInfo.charBitmapHeight) / (float)m_BitmapWidth; float TopLeftX = BottomLeftX; float TopLeftY = (F32)(charInfo.bitmapYOrigin) / (float)m_BitmapWidth; float TopRightX = (F32)(charInfo.bitmapXOrigin + charInfo.B - charInfo.C) / (float)m_BitmapWidth; float TopRightY = TopLeftY; float BottomRightX = TopRightX; float BottomRightY = BottomLeftY; SetTextureCoordinate(TopLeftX, TopLeftY, vertexID + 1); SetTextureCoordinate(BottomLeftX, BottomLeftY, vertexID + 0); SetTextureCoordinate(BottomRightX, BottomRightY, vertexID + 3); SetTextureCoordinate(TopRightX, TopRightY, vertexID + 2); /// index setting letterBottomLeftX += letterWidth; previousCharIndex = m_Text[c]; }

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• GoogleAppEngine : ClassNotFoundException : javax.jdo.metadata.ComponentMetadata

  - by James.Elsey

  I'm trying to deploy my application to a locally running GoogleAppEngine development server, but I'm getting the following stack trace when I start the server Apr 23, 2010 9:03:33 PM com.google.apphosting.utils.jetty.JettyLogger warn WARNING: Nested in org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'clientDao' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Cannot resolve reference to bean 'entityManagerFactory' while setting bean property 'entityManagerFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is java.lang.NoClassDefFoundError: javax/jdo/metadata/ComponentMetadata: java.lang.ClassNotFoundException: javax.jdo.metadata.ComponentMetadata at java.net.URLClassLoader$1.run(URLClassLoader.java:217) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:205) at java.lang.ClassLoader.loadClass(ClassLoader.java:319) at com.google.appengine.tools.development.IsolatedAppClassLoader.loadClass(IsolatedAppClassLoader.java:151) at java.lang.ClassLoader.loadClass(ClassLoader.java:264) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:332) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:264) at javax.jdo.JDOHelper$18.run(JDOHelper.java:2009) at javax.jdo.JDOHelper$18.run(JDOHelper.java:2007) at java.security.AccessController.doPrivileged(Native Method) at javax.jdo.JDOHelper.forName(JDOHelper.java:2006) at javax.jdo.JDOHelper.invokeGetPersistenceManagerFactoryOnImplementation(JDOHelper.java:1155) at javax.jdo.JDOHelper.getPersistenceManagerFactory(JDOHelper.java:803) at javax.jdo.JDOHelper.getPersistenceManagerFactory(JDOHelper.java:698) at org.datanucleus.jpa.EntityManagerFactoryImpl.initialisePMF(EntityManagerFactoryImpl.java:482) at org.datanucleus.jpa.EntityManagerFactoryImpl.<init>(EntityManagerFactoryImpl.java:255) at org.datanucleus.store.appengine.jpa.DatastoreEntityManagerFactory.<init>(DatastoreEntityManagerFactory.java:68) at org.datanucleus.store.appengine.jpa.DatastorePersistenceProvider.createContainerEntityManagerFactory(DatastorePersistenceProvider.java:45) at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:224) at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:291) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1369) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1335) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:473) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409) at java.security.AccessController.doPrivileged(Native Method) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164) at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:269) at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:104) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1245) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1010) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:472) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409) at java.security.AccessController.doPrivileged(Native Method) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:429) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:380) at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:255) at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:199) at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:45) at org.mortbay.jetty.handler.ContextHandler.startContext(ContextHandler.java:530) at org.mortbay.jetty.servlet.Context.startContext(Context.java:135) at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1218) at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:500) at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:448) at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:40) at org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:117) at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:40) at org.mortbay.jetty.handler.HandlerWrapper.doStart(HandlerWrapper.java:117) at org.mortbay.jetty.Server.doStart(Server.java:217) at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:40) at com.google.appengine.tools.development.JettyContainerService.startContainer(JettyContainerService.java:181) at com.google.appengine.tools.development.AbstractContainerService.startup(AbstractContainerService.java:116) at com.google.appengine.tools.development.DevAppServerImpl.start(DevAppServerImpl.java:217) at com.google.appengine.tools.development.DevAppServerMain$StartAction.apply(DevAppServerMain.java:162) at com.google.appengine.tools.util.Parser$ParseResult.applyArgs(Parser.java:48) at com.google.appengine.tools.development.DevAppServerMain.<init>(DevAppServerMain.java:113) at com.google.appengine.tools.development.DevAppServerMain.main(DevAppServerMain.java:89) The server is running at http://localhost:1234/ I'm a little confused over this, since I have the same application running locally on GlassFish/MySQL. All I have done is to swap in the relevant jar files, and change the persistence.xml. My applicationContext.xml looks as follows : <context:annotation-config/> <bean id="clientDao" class="com.jameselsey.salestracker.dao.jpa.JpaDaoClient"> <property name="entityManagerFactory" ref="entityManagerFactory"/> </bean> <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"/> <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager"> <property name="entityManagerFactory" ref="entityManagerFactory" /> </bean> <bean id="org.springframework.context.annotation.internalPersistenceAnnotationProcessor" class="com.jameselsey.salestracker.util.GaeFixInternalPersistenceAnnotationProcessor" /> <bean class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor"/> <tx:annotation-driven/> <bean id="clientService" class="com.jameselsey.salestracker.service.ClientService"/> </beans> My JPA DAO looks like this public class JpaDao extends JpaDaoSupport { protected <T> List<T> findAll(Class<T> clazz) { return getJpaTemplate().find("select c from " + clazz.getName() + " c"); } protected <T> T findOne(String jpql, Map params) { List<T> results = getJpaTemplate().findByNamedParams(jpql, params); if(results.isEmpty()) { return null; } if(results.size() > 1) { throw new IncorrectResultSizeDataAccessException(1, results.size()); } return results.get(0); } } And an example implemented method looks like this : @Override public Client getClientById(Integer clientId) { String jpql = "SELECT c " + "FROM com.jameselsey.salestracker.domain.Client c " + "WHERE c.id = " + clientId; return (Client) getJpaTemplate().find(jpql).get(0); } Like I say, this works ok on Glassfish/MySQL, is it possible this error could be a red herring to something else?

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• HLSL - Creating Shadows in 2D

  - by richard

  The way that I create shadows is by the following technique: http://www.catalinzima.com/2010/07/my-technique-for-the-shader-based-dynamic-2d-shadows/ But I have questions to HLSL. The way that I currently do it is, I have a black and white image, where Black means 'object', and white means 'nothing'. I then distort the image like in the tutorial. I do this with a pixel shader, but instead of rendering to the screen, I render to a texture, back to my application. I then take this, and create the shadows, and then send it back to the graphics card to undo the distortion, after the shadow has been added - this comes back and I have a stencil of shadow. I can put this ontop of the original image and send them back to the graphics card, which then puts them on the screen. To me this is alot of back and forth. Is there a way i can avoid this? The problem that I am having is that I need to basically go through all positions in the texture 3 times, and use the new new texture every time instead of the orginal one. I tried to read up on Passes, but i don't think that i am heading in the right direction there. Help?

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• OpenGL Shading Program Object Memory Requirement

  - by Hans Wurst

  gDEbugger states that OpenGL's program objects only occupy an insignificant amount of memory. How much is this actually? I don't know if the stuff I looked up in mesa is actually that I was looking for but it requires 16KB [Edit: false, confusing struct names, less than 1KB immediate, some further behind pointers] per program object. Not quite insignificant. So is it recommended to create a unique program object for each object of the scene? Or to share a single program object and set the scene's object's custom variables just before its draw call?

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• Mesh with quads to triangle mesh

  - by scape

  I want to use Blender for making models yet realize some of the polygons are not triangles but contain quads or more (example: cylinder top and bottom). I could export the the mesh as a basic mesh file and import it in to an openGL application and workout rendering the quads as tris, but anything with more than 4 vert indices is beyond me. Is it typical to convert the mesh to a triangle-based mesh inside blender before exporting it? I actually tried this through the quads_convert_to_tris method within a blender py script and the top of the cylinder does not look symmetrical. What is typically done to render a loaded mesh as a tri?

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• Example of DOD design (on a generic Zombie game)

  - by Jeffrey

  I can't seem to find a nice explanation of the Data Oriented Design for a generic zombie game (it's just an example, pretty common example). Could you make an example of the Data Oriented Design on creating a generic zombie class? Is the following good? Zombie list class: class ZombieList { GLuint vbo; // generic zombie vertex model std::vector<color>; // object default color std::vector<texture>; // objects textures std::vector<vector3D>; // objects positions public: unsigned int create(); // return object id void move(unsigned int objId, vector3D offset); void rotate(unsigned int objId, float angle); void setColor(unsigned int objId, color c); void setPosition(unsigned int objId, color c); void setTexture(unsigned int, unsigned int); ... void update(Player*); // move towards player, attack if near } Example: Player p; Zombielist zl; unsigned int first = zl.create(); zl.setPosition(first, vector3D(50, 50)); zl.setTexture(first, texture("zombie1.png")); ... while (running) { // main loop ... zl.update(&p); zl.draw(); // draw every zombie } Or would creating a generic World container that contains every action from bite(zombieId, playerId) to moveTo(playerId, vector) to createPlayer() to shoot(playerId, vector) to face(radians)/face(vector); and contains: std::vector<zombie> std::vector<player> ... std::vector<mapchunk> ... std::vector<vbobufferid> player_run_animation; ... be a good example? Whats the proper way to organize a game with DOD?

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• Understanding how to create/use textures for games when limited by power of two sizes

  - by Matthias Reisner

  I have some questions about the creating graphics for a game. As an example. I want to create a motorbike. (1pixel = 1centimeter) So my motorbike will have 200 width and 150 height. (200x150) But the libgdx only allows to load sizes with the power of 2?! (2,4,8,16,...) First I thought about that way. I will create my bike with the size (200x150) and save it as png. Than I will open it again (e.g. with gimp) resize the image to a size which uses values with power of 2 (128x128). I will load that as texture in the programm and set width as 200 and height as 150. But wouldn't it be a problem? Because I will lose some pixel information when I make the first conversation.?! Isn't it?

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• Objective C - Aggro with Images

  - by Will

  I have three UIImageViews. enemy1, enemy1AggroBox and mainSprite. What I want to do is when mainSprite and enemy1AggroBox interect, I want enemy1 to start moving towards mainSprite. Basically creating aggro for a game. if(CGRectIntersectsRect(mainSprite.frame, enemy1AggroBox.frame)){ //Code here// } My plan would be to call this method in viewDidLoad. I'm not using any sort of framework like cocos2d or OpenGLES. If you need to see any more code just ask.

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• Too sell or give for free

  - by QAH

  Hello everyone! I am currently making a game that I was originally planning to sell. It is a simple 2D arcade style game for the PC. I've seen many indie games become popular and generate revenue from advertisements, but the game itself remains free. I need some advice on whether or not I should sell my game, release it for free with advertisements, or ask for donations and keep the game free. I feel that my game is fun, but of course the graphics aren't tip top because I am a programmer, not an artist. I just take screenshots of 3D models I get from Turbosquid and crop around it to make a sprite. Also, and I could be very wrong about this, it seems that there are more legal issues surrounding selling a game than making it free and generating revenue from advertisement, or asking for donations. If I am wrong, someone please correct me. Also, I am very interested in generating some revenue for my work, but that isn't at the very top of my list. I am in my last year of high school, soon to be going to college, and I am going to major in computer science/software engineering. So I am trying to gain some preliminary experience at home by coding stuff every day. One way of getting this experience is by making this game. So what do you think? What route should I take? What has worked well with other indie games? Thanks in advance.

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• Why does glGetString returns a NULL string

  - by snape

  I am trying my hands at GLFW library. I have written a basic program to get OpenGL renderer and vendor string. Here is the code #include <GL/glew.h> #include <GL/glfw.h> #include <cstdio> #include <cstdlib> #include <string> using namespace std; void shutDown(int returnCode) { printf("There was an error in running the code with error %d\n",returnCode); GLenum res = glGetError(); const GLubyte *errString = gluErrorString(res); printf("Error is %s\n", errString); glfwTerminate(); exit(returnCode); } int main() { // start GL context and O/S window using GLFW helper library if (glfwInit() != GL_TRUE) shutDown(1); if (glfwOpenWindow(0, 0, 0, 0, 0, 0, 0, 0, GLFW_WINDOW) != GL_TRUE) shutDown(2); // start GLEW extension handler glewInit(); // get version info const GLubyte* renderer = glGetString (GL_RENDERER); // get renderer string const GLubyte* version = glGetString (GL_VERSION); // version as a string printf("Renderer: %s\n", renderer); printf("OpenGL version supported %s\n", version); // close GL context and any other GLFW resources glfwTerminate(); return 0; } I googled this error and found out that we have to initialize the OpenGL context before calling glGetString(). Although I have initialized OpenGL context using glfwInit() but still the function returns a NULL string. Any ideas? Edit I have updated the code with error checking mechanisms. This code on running outputs the following There was an error in running the code with error 2 Error is no error

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• Generating geometry when using VBO

  - by onedayitwillmake

  Currently I am working on a project in which I generate geometry based on the players movement. A glorified very long trail, composed of quads. I am doing this by storing a STD::Vector, and removing the oldest verticies once enough exist, and then calling glDrawArrays. I am interested in switching to a shader based model, usually examples I see the VBO is generated at start and then that's basically it. What is the best route to go about creating geometry in real time, using shader / VBO approach

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• How can I test if my rotated rectangle intersects a corner?

  - by Raven Dreamer

  I have a square, tile-based collision map. To check if one of my (square) entities is colliding, I get the vertices of the 4 corners, and test those 4 points against my collision map. If none of those points are intersecting, I know I'm good to move to the new position. I'd like to allow entities to rotate. I can still calculate the 4 corners of the square, but once you factor in rotation, those 4 corners alone don't seem to be enough information to determine if the entity is trying to move to a valid state. For example: In the picture below, black is unwalkable terrain, and red is the player's hitbox. The left scenario is allowed because the 4 corners of the red square are not in the black terrain. The right scenario would also be (incorrectly) allowed, because the player, cleverly turned at a 45* angle, has its corners in valid spaces, even if it is (quite literally) cutting the corner. How can I detect scenarios similar to the situation on the right?

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• How to implement smooth flocking

  - by Craig

  I'm working on a simple survival game, avoid the big guy and chase the the small guys to stay alive for as long as possible. I have taken the chase and evade example from MSDN create and drawn 20 mice on the screen. I want the small guys to flock when they arent evading. They are doing this, but it isnt as smooth as I would like it to be. How do i make the movement smoother? Its very jittery.# Below is what I have going at the moment, flocking code is within the IF statement, when it isnt set to evading. Any help would be greatly appreciated! :) namespace ChaseAndEvade { class MouseSprite { public enum MouseAiState { // evading the cat Evading, // the mouse can't see the "cat", and it's wandering around. Wander } // how fast can the mouse move? public float MaxMouseSpeed = 4.5f; // and how fast can it turn? public float MouseTurnSpeed = 0.20f; // MouseEvadeDistance controls the distance at which the mouse will flee from // cat. If the mouse is further than "MouseEvadeDistance" pixels away, he will // consider himself safe. public float MouseEvadeDistance = 100.0f; // this constant is similar to TankHysteresis. The value is larger than the // tank's hysteresis value because the mouse is faster than the tank: with a // higher velocity, small fluctuations are much more visible. public float MouseHysteresis = 60.0f; public Texture2D mouseTexture; public Vector2 mouseTextureCenter; public Vector2 mousePosition; public MouseAiState mouseState = MouseAiState.Wander; public float mouseOrientation; public Vector2 mouseWanderDirection; int separationImpact = 4; int cohesionImpact = 6; int alignmentImpact = 2; int sensorDistance = 50; public void UpdateMouse(Vector2 position, MouseSprite [] mice, int numberMice, int index) { Vector2 catPosition = position; int enemies = numberMice; // first, calculate how far away the mouse is from the cat, and use that // information to decide how to behave. If they are too close, the mouse // will switch to "active" mode - fleeing. if they are far apart, the mouse // will switch to "idle" mode, where it roams around the screen. // we use a hysteresis constant in the decision making process, as described // in the accompanying doc file. float distanceFromCat = Vector2.Distance(mousePosition, catPosition); // the cat is a safe distance away, so the mouse should idle: if (distanceFromCat > MouseEvadeDistance + MouseHysteresis) { mouseState = MouseAiState.Wander; } // the cat is too close; the mouse should run: else if (distanceFromCat < MouseEvadeDistance - MouseHysteresis) { mouseState = MouseAiState.Evading; } // if neither of those if blocks hit, we are in the "hysteresis" range, // and the mouse will continue doing whatever it is doing now. // the mouse will move at a different speed depending on what state it // is in. when idle it won't move at full speed, but when actively evading // it will move as fast as it can. this variable is used to track which // speed the mouse should be moving. float currentMouseSpeed; // the second step of the Update is to change the mouse's orientation based // on its current state. if (mouseState == MouseAiState.Evading) { // If the mouse is "active," it is trying to evade the cat. The evasion // behavior is accomplished by using the TurnToFace function to turn // towards a point on a straight line facing away from the cat. In other // words, if the cat is point A, and the mouse is point B, the "seek // point" is C. // C // B // A Vector2 seekPosition = 2 * mousePosition - catPosition; // Use the TurnToFace function, which we introduced in the AI Series 1: // Aiming sample, to turn the mouse towards the seekPosition. Now when // the mouse moves forward, it'll be trying to move in a straight line // away from the cat. mouseOrientation = ChaseAndEvadeGame.TurnToFace(mousePosition, seekPosition, mouseOrientation, MouseTurnSpeed); // set currentMouseSpeed to MaxMouseSpeed - the mouse should run as fast // as it can. currentMouseSpeed = MaxMouseSpeed; } else { // if the mouse isn't trying to evade the cat, it should just meander // around the screen. we'll use the Wander function, which the mouse and // tank share, to accomplish this. mouseWanderDirection and // mouseOrientation are passed by ref so that the wander function can // modify them. for more information on ref parameters, see // http://msdn2.microsoft.com/en-us/library/14akc2c7(VS.80).aspx ChaseAndEvadeGame.Wander(mousePosition, ref mouseWanderDirection, ref mouseOrientation, MouseTurnSpeed); // if the mouse is wandering, it should only move at 25% of its maximum // speed. currentMouseSpeed = .25f * MaxMouseSpeed; Vector2 separate = Vector2.Zero; Vector2 moveCloser = Vector2.Zero; Vector2 moveAligned = Vector2.Zero; // What the AI does when it sees other AIs for (int j = 0; j < enemies; j++) { if (index != j) { // Calculate a vector towards another AI Vector2 separation = mice[index].mousePosition - mice[j].mousePosition; // Only react if other AI is within a certain distance if ((separation.Length() < this.sensorDistance) & (separation.Length()> 0) ) { moveAligned += mice[j].mouseWanderDirection; float distance = Math.Abs(separation.Length()); if (distance == 0) distance = 1; moveCloser += mice[j].mousePosition; separation.Normalize(); separate += separation / distance; } } } if (moveAligned.LengthSquared() != 0) { moveAligned.Normalize(); } if (moveCloser.LengthSquared() != 0) { moveCloser.Normalize(); } moveCloser /= enemies; mice[index].mousePosition += (separate * separationImpact) + (moveCloser * cohesionImpact) + (moveAligned * alignmentImpact); } // The final step is to move the mouse forward based on its current // orientation. First, we construct a "heading" vector from the orientation // angle. To do this, we'll use Cosine and Sine to tell us the x and y // components of the heading vector. See the accompanying doc for more // information. Vector2 heading = new Vector2( (float)Math.Cos(mouseOrientation), (float)Math.Sin(mouseOrientation)); // by multiplying the heading and speed, we can get a velocity vector. the // velocity vector is then added to the mouse's current position, moving him // forward. mousePosition += heading * currentMouseSpeed; } } }

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• Is there a global "low resolution" filter for OpenGL?

  - by Ian Henry

  I'm trying to learn a little about OpenGL, so I'm making a simple 2D game (with OpenTK), and so far it's coming along well. I thought it would be fun to give it that, for lack of a better word, retropixelated look of games from the early nineties. I figured it would be an easy thing to do -- simply draw everything at half its normal size and scale up with no anti-aliasing. But I can't find any resources on how to do this. I can set the min/mag filters of my textures to nearest and that works fine for my sprites, but I'm using lots of primitives and I'd like the effect to apply to them as well. The one idea I had was to draw everything at half size, then somehow copy the render buffer to a texture, then render that texture full-size, but I don't know how to do that, and it seems like there must be a better way. Can anyone help me out?

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• Is it possible to construct a cube with fewer than 24 vertices

  - by Telanor

  I have a cube-based world like Minecraft and I'm wondering if there's a way to construct a cube with fewer than 24 vertices so I can reduce memory usage. It doesn't seem possible to me for 2 reasons: the normals wouldn't come out right and per-face textures wouldn't work. Is this the case or am I wrong? Maybe there's some fancy new DX11 tech that can help? Edit: Just to clarify, I have 2 requirements: I need surface normals for each cube face in order to do proper lighting and I need a way to address a different indexes in a texture array for each cube face

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• Low coupling and tight cohesion

  - by hidayat

  Of course it depends on the situation. But when a lower lever object or system communicate with an higher level system, should callbacks or events be preferred to keeping a pointer to higher level object? For example, we have a world class that has a member variable vector<monster> monsters. When the monster class is going to communicate with the world class, should I prefer using a callback function then or should I have a pointer to the world class inside the monster class?

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• 3D Ball Physics Theory: collision response on ground and against walls?

  - by David

  I'm really struggling to get a strong grasp on how I should be handling collision response in a game engine I'm building around a 3D ball physics concept. Think Monkey Ball as an example of the type of gameplay. I am currently using sphere-to-sphere broad phase, then AABB to OBB testing (the final test I am using right now is one that checks if one of the 8 OBB points crosses the planes of the object it is testing against). This seems to work pretty well, and I am getting back: Plane that object is colliding against (with a point on the plane, the plane's normal, and the exact point of intersection. I've tried what feels like dozens of different high-level strategies for handling these collisions, without any real success. I think my biggest problem is understanding how to handle collisions against walls in the x-y axes (left/right, front/back), which I want to have elasticity, and the ground (z-axis) where I want an elastic reaction if the ball drops down, but then for it to eventually normalize and be kept "on the ground" (not go into the ground, but also not continue bouncing). Without kluging something together, I'm positive there is a good way to handle this, my theories just aren't getting me all the way there. For physics modeling and movement, I am trying to use a Euler based setup with each object maintaining a position (and destination position prior to collision detection), a velocity (which is added onto the position to determine the destination position), and an acceleration (which I use to store any player input being put on the ball, as well as gravity in the z coord). Starting from when I detect a collision, what is a good way to approach the response to get the expected behavior in all cases? Thanks in advance to anyone taking the time to assist... I am grateful for any pointers, and happy to post any additional info or code if it is useful. UPDATE Based on Steve H's and eBusiness' responses below, I have adapted my collision response to what makes a lot more sense now. It was close to right before, but I didn't have all the right pieces together at the right time! I have one problem left to solve, and that is what is causing the floor collision to hit every frame. Here's the collision response code I have now for the ball, then I'll describe the last bit I'm still struggling to understand. // if we are moving in the direction of the plane (against the normal)... if (m_velocity.dot(intersection.plane.normal) <= 0.0f) { float dampeningForce = 1.8f; // eventually create this value based on mass and acceleration // Calculate the projection velocity PVRTVec3 actingVelocity = m_velocity.project(intersection.plane.normal); m_velocity -= actingVelocity * dampeningForce; } // Clamp z-velocity to zero if we are within a certain threshold // -- NOTE: this was an experimental idea I had to solve the "jitter" bug I'll describe below float diff = 0.2f - abs(m_velocity.z); if (diff > 0.0f && diff <= 0.2f) { m_velocity.z = 0.0f; } // Take this object to its new destination position based on... // -- our pre-collision position + vector to the collision point + our new velocity after collision * time // -- remaining after the collision to finish the movement m_destPosition = m_position + intersection.diff + (m_velocity * intersection.tRemaining * GAMESTATE->dt); The above snippet is run after a collision is detected on the ball (collider) with a collidee (floor in this case). With a dampening force of 1.8f, the ball's reflected "upward" velocity will eventually be overcome by gravity, so the ball will essentially be stuck on the floor. THIS is the problem I have now... the collision code is running every frame (since the ball's z-velocity is constantly pushing it a collision with the floor below it). The ball is not technically stuck, I can move it around still, but the movement is really goofy because the velocity and position keep getting affected adversely by the above snippet. I was experimenting with an idea to clamp the z-velocity to zero if it was "close to zero", but this didn't do what I think... probably because the very next frame the ball gets a new gravity acceleration applied to its velocity regardless (which I think is good, right?). Collisions with walls are as they used to be and work very well. It's just this last bit of "stickiness" to deal with. The camera is constantly jittering up and down by extremely small fractions too when the ball is "at rest". I'll keep playing with it... I like puzzles like this, especially when I think I'm close. Any final ideas on what I could be doing wrong here? UPDATE 2 Good news - I discovered I should be subtracting the intersection.diff from the m_position (position prior to collision). The intersection.diff is my calculation of the difference in the vector of position to destPosition from the intersection point to the position. In this case, adding it was causing my ball to always go "up" just a little bit, causing the jitter. By subtracting it, and moving that clamper for the velocity.z when close to zero to being above the dot product (and changing the test from <= 0 to < 0), I now have the following: // Clamp z-velocity to zero if we are within a certain threshold float diff = 0.2f - abs(m_velocity.z); if (diff > 0.0f && diff <= 0.2f) { m_velocity.z = 0.0f; } // if we are moving in the direction of the plane (against the normal)... float dotprod = m_velocity.dot(intersection.plane.normal); if (dotprod < 0.0f) { float dampeningForce = 1.8f; // eventually create this value based on mass and acceleration? // Calculate the projection velocity PVRTVec3 actingVelocity = m_velocity.project(intersection.plane.normal); m_velocity -= actingVelocity * dampeningForce; } // Take this object to its new destination position based on... // -- our pre-collision position + vector to the collision point + our new velocity after collision * time // -- remaining after the collision to finish the movement m_destPosition = m_position - intersection.diff + (m_velocity * intersection.tRemaining * GAMESTATE->dt); UpdateWorldMatrix(m_destWorldMatrix, m_destOBB, m_destPosition, false); This is MUCH better. No jitter, and the ball now "rests" at the floor, while still bouncing off the floor and walls. The ONLY thing left is that the ball is now virtually "stuck". He can move but at a much slower rate, likely because the else of my dot product test is only letting the ball move at a rate multiplied against the tRemaining... I think this is a better solution than I had previously, but still somehow not the right idea. BTW, I'm trying to journal my progress through this problem for anyone else with a similar situation - hopefully it will serve as some help, as many similar posts have for me over the years.

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• Aw, Snap! in Google Chrome [on hold]

  - by D. S. Schneider

  Just wondering if anyone else's experiencing the "Aw, Snap!" bug in Google Chrome. I'm developing a brand new engine which occasionaly triggers this bug and as far as I know, there's nothing one can do to find out what actually triggered the issue. I've also tested my engine with Firefox, which runs just fine. Anyway, just wanted to know if someone else is facing this while developing games for Google Chrome and has a clue about what can be done to avoid it. I'm using plain JavaScript and the audio and canvas elements from HTML5. Thanks!

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• Acceptable GC frequency for a SlimDX/Windows/.NET game?

  - by Rei Miyasaka

  I understand that the Windows GC is much better than the Xbox/WP7 GC, being that it's generational and multithreaded -- so I don't need to worry quite as much about avoiding memory allocation. SlimDX even has some unavoidable functions that generate some amount of garbage (specifically, MapSubresource creates DataBoxes), yet people don't seem to be too upset about it. I'd like to use some functional paradigms to write my code too, which also means creating objects like closures and monads. I know premature optimization isn't a good thing, but are there rules of thumb or metrics that I can follow to know whether I need to cut down on allocations? Is, say, one gen 0 GC per frame too much? One thing that has me stumped is object promotions. Gen 0 GCs will supposedly finish within a millisecond or two, but if I'm understanding correctly, it's the gen 1 and 2 promotions that start to hurt. I'm not too sure how I can predict/prevent these.

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• Deserialize inherited classes into the same list in XNA

  - by M0rgenstern

  I am writing a Gui for a game (for what else ...). Therefor I wrote a class GuiElement which has some serializeable fields. From this class I deflect a Class "Button" which has one serializeable field more. Furthermore, I have a Class GuiWindow, which is as well deflected from "GuiElement". An Object of this Class has a Field "HandledElements" of the type "List". To know the layout of the Menues, I use XML-Files, which look like that (for example): <?xml version="1.0" encoding="utf-8" ?> <XnaContent xmlns:Generic="System.Collections.Generic"> <Asset Type="System.Collections.Generic.List[GUI.GuiWindow]"> <Item> <Position>0 0</Position> <AlternativeImagePath></AlternativeImagePath> <IsActive>true</IsActive> <Name>MainMenu</Name> <HandledElements> <Item> <Position>100 100</Position> <AlternativeImagePath></AlternativeImagePath> <IsActive>true</IsActive> <Name>Optionen</Name> <Caption>Optionen</Caption> </Item> </HandledElements> </Item> <Item> <Position>0 0</Position> <AlternativeImagePath></AlternativeImagePath> <IsActive>false</IsActive> <Name>Options</Name> <HandledElements> </HandledElements> </Item> </Asset> </XnaContent> As you can see, the first window has in its "HandledElements" List an Item with the Field . This is a field which only a Button has. The Problem is now: I can't deserialize this XML file, because GuiElement does not have this Field, it only has the few fields above. I thought it would know automatically which Class to use,but it doesn't. Do I really have to give my windows a list for each child class of GuiElement? Or can I do another workaround?

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• Calculating 2D (screen) coordinates from 3D positions in XNA 4.0

  - by NDraskovic

  I have a program that draws some items to the scene by loading their positions from a file. Now I want to place a Ray on the same location where the items are drawn. So my question is how can I calculate the position of the ray (it's 2D components) by using 3D coordinates of each particular item? The items don't move anywhere, so once they are placed they stay until the end of the programs execution. Thanks.

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• Physics timestep questions

  - by SSL

  I've got a projectile working perfectly using the code below: //initialised in loading screen 60 is the FPS - projectilEposition and velocity are Vector3 types gravity = new Vector3(0, -(float)9.81 / 60, 0); //called every frame projectilePosition += projectileVelocity; This seems to work fine but I've noticed in various projectile examples I've seen that the elapsedtime per update is taken into account. What's the difference between the two and how can I convert the above to take into account the elapsedtime? (I'm using XNA - do I use ElapsedTime.TotalSeconds or TotalMilliseconds)? Edit: Forgot to add my attempt at using elapsedtime, which seemed to break the physics: projectileVelocity.Y += -(float)((9.81 * gameTime.ElapsedGameTime.TotalSeconds * gameTime.ElapsedGameTime.TotalSeconds) * 0.5f); Thanks for the help

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• Grid pathfinding with a lot of entities

  - by Vee

  I'd like to explain this problem with a screenshot from a released game, DROD: Gunthro's Epic Blunder, by Caravel Games. The game is turn-based and tile-based. I'm trying to create something very similar (a clone of the game), and I've got most of the fundamentals done, but I'm having trouble implementing pathfinding. Look at the screenshot. The guys in yellow are friendly, and want to kill the roaches. Every turn, every guy in yellow pathfinds to the closest roach, and every roach pathfinds to the closest guy in yellow. By closest I mean the target with the shortest path, not a simple distance calculation. All of this without any kind of slowdown when loading the level or when passing turns. And all of the entities change position every turn. Also (not shown in screenshot), there can be doors that open and close and change the level's layout. Impressive. I've tried implementing pathfinding in my clone. First attempt was making every roach find a path to a yellow guy every turn, using a breadth-first search algorithm. Obviously incredibly slow with more than a single roach, and would get exponentially slower with more than a single yellow guy. Second attempt was mas making every yellow guy generate a pathmap (still breadth-first search) every time he moved. Worked perfectly with multiple roaches and a single yellow guy, but adding more yellow guys made the game slow and unplayable. Last attempt was implementing JPS (jump point search). Every entity would individually calculate a path to its target. Fast, but with a limited number of entities. Having less than half the entities in the screenshot would make the game slow. And also, I had to get the "closest" enemy by calculating distance, not shortest path. I've asked on the DROD forums how they did it, and a user replied that it was breadth-first search. The game is open source, and I took a look at the source code, but it's C++ (I'm using C#) and I found it confusing. I don't know how to do it. Every approach I tried isn't good enough. And I believe that DROD generates global pathmaps, somehow, but I can't understand how every entity find the best individual path to other entities that move every turn. What's the trick? This is a reply I just got on the DROD forums: Without having looked at the code I'd wager it's two (or so) pathmaps for the whole room: One to the nearest enemy, and one to the nearest friendly for every tile. There's no need to make a separate pathmap for every entity when the overall goal is "move towards nearest enemy/friendly"... just mark every tile with the number of moves it takes to the nearest target and have the entity chose the move that takes it to the tile with the lowest number. To be honest, I don't understand it that well.

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