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• Variable number of GUI Buttons

  - by Wakaka

  I have a generic HTML5 Canvas GUI Button class and a Scene class. The Scene class has a method called createButton(), which will create a new Button with onclick parameter and store it in a list of buttons. I call createButton() for all UI buttons when initializing the Scene. Because buttons can appear and disappear very often during rendering, Scene would first deactivate all buttons (temporarily remove their onclick, onmouseover etc property) before each render frame. During rendering, the renderer would then activate the required buttons for that frame. The problem is that part of the UI requires a variable number of buttons, and their onclick, onmouseover etc properties change frequently. An example is a buffs system. The UI will list all buffs as square sprites for the current unit selected, and mousing over each square will bring up a tooltip with some information on the buff. But the number of buffs is variable thus I won't know how many buttons to create at the start. What's the best way to solve this problem? P.S. My game is in Javascript, and I know I can use HTML buttons, but would like to make my game purely Canvas-based. Create buttons on-the-fly during rendering. Thus I will only have buttons when I require them. After the render frame these buttons would be useless and removed. Create a fixed set of buttons that I'm going to assume the number of buffs per unit won't exceed. During each render frame activate the buttons accordingly and set their onmouseover property. Assign a button to each Buff instance. This sounds wrong as the buff button is a part of the GUI which can only have one unit selected. Assigning a button to every single Buff in the game seems to be overkill. Also, I would need to change the button's position every render frame since its order in the unit's list of buffs matter. Any other solutions? I'm actually quite for idea (1) but am worried about the memory/time issues of creating a new Button() object every render frame. But this is in Javascript where object creation is oh-so-common ({} mainly) due to automatic garbage collection. What is your take on this? Thanks!

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• Unable to create suitable graphics device?

  - by kraze

  I've been following the Eye of the Dragon tutorial, which is basicly a guide to making a 2D RPG game, obviously. I recently finished the tutorial about making pop up screens in the menu and changed the screen to load as a full screen. Whenever I try and load the game it just goes black and my mouse sits there. I cannot change out of it other then with CtrlAltDel. Once i do that it says No suitable graphics card found, unable to create graphics device. I read somewhere about XNA not allowing more then one screen when any one of them is full screen. but it wasnt very informative. Anyone have any ideas whats going on and/or how to fix this? Just incase if this helps this is the code for the graphics device: public Game1() { graphics = new GraphicsDeviceManager(this); graphics.PreferredBackBufferWidth = 900; graphics.PreferredBackBufferHeight = 768; graphics.IsFullScreen = true; this.Window.Title = "Eyes of the Dragon"; Content.RootDirectory = "Content"; }

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• Sprite rotation

  - by Kipras

  I'm using OpenGL and people suggest using glRotate for sprite rotation, but I find that strange. My problem with it is that it rotates the whole matrix, which sort of screws up all my collision detection and so on and so forth. Imagine I had a sprite at position (100, 100) and in position (100, 200) is an obstacle and the sprite's facing it. I rotate the sprite away from the obstacle and when move upwards my y axis, even though the projection shows like it's going away from the obstacle, the sprite will intersect it. So I don't see another way of a rotating a sprite and not screwing up all collision detection other than doing mathematical operations on the image itself. Am I right or am I missing something?

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• Adding multiplayer to an HTML5 game

  - by espais

  I am interested in making a game that I currently have a co-op experience, however I'm curious as to the best method of implementing this in HTML5. I have made games before using straight C sockets, and also with the Net library for SDL. What are some of my best options for doing this in a canvas-based environment? At present, all I can come up with are either AJAX/database solutions (with a high refresh rate), or somehow implementing a PHP server that would funnel the data through sockets. The overall gameplay would be a 2.5D platformer-ish type of game, so both clients would need to be continually updated with player positions, enemy positions, projectiles, environmental data, etc.

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• What is the difference between a View and a View Controller?

  - by Mark F

  from an iphone development perspective

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• Vertex data split into separate buffers or one one structure?

  - by kiba2

  Is it better to have all vertex data in one structure like this: class MyVertex { int x,y,z; int u,v; int normalx, normaly, normalz; } Or to have each component (location, normal, texture coordinates) in separate arrays/buffers? To me it always seemed logical to keep the data grouped together in one structure because they'd always be the same for each instance of a shared vertex and that seems to be true for things like character models (ex: the normal should be an average of adjacent normals for smooth lighting). One instance where this doesn't seem to work is other kinds of meshes like say a cube where the texture coordinates for each may be the same but that causes them to be different where the vertices are shared. Does everybody normally keep them separate? Won't this make them less space efficient if there needs to be an instance of texture coordinates and normals for each triangle vertex (They won't be indexed)? Can OpenGL even handle this mixing of indexed (for location) vs non-indexed buffers in the same VBO?

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• MouseEvent.CLICK not working? (AS3)

  - by Jake

  ok so here's my code in AS3, I'd like to know why when i actually click on the picture, nothing happens. And if any of you have great tutorial of what to learn after classes/functions in AS3, let me know =D : package { import flash.display.Bitmap; import flash.display.Sprite; import flash.display.Shape; import flash.events.MouseEvent; public class Main extends Sprite { [Embed(source="../Pics/Picture.png")] private var HeroClass:Class; private var hero:Bitmap = new HeroClass(); public function Main():void { addChild(hero); hero.addEventListener(MouseEvent.CLICK, onClick); function onClick(e:MouseEvent):void { trace("hey"); hero.visible = false; } } } }

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• rotating an object on an arc

  - by gardian06

  I am trying to get a turret to rotate on an arc, and have hit a wall. I have 8 possible starting orientations for the turrets, and want them to rotate on a 90 degree arc. I currently take the starting rotation of the turret, and then from that derive the positive, and negative boundary of the arc. because of engine restrictions (Unity) I have to do all of my tests against a value which is between [0,360], and due to numerical precision issues I can not test against specific values. I would like to write a general test without having to go in, and jury rig cases //my current test is: // member variables public float negBound; public float posBound; // found in Start() function (called immediately after construction) // eulerAngles.y is the the degree measure of the starting y rotation negBound = transform.eulerAngles.y-45; posBound = transform.eulerAngles.y+45; // insure that values are within bounds if(negBound<0){ negBound+=360; }else if(posBound>360){ posBound-=360; } // called from Update() when target not in firing line void Rotate(){ // controlls what direction if(transform.eulerAngles.y>posBound){ dir = -1; } else if(transform.eulerAngles.y < negBound){ dir = 1; } // rotate object } follows is a table of values for my different cases (please excuse my force formatting) read as base is the starting rotation of the turret, neg is the negative boundry, pos is the positive boundry, range is the acceptable range of values, and works is if it performs as expected with the current code. |base-|-neg-|-pos--|----------range-----------|-works-| |---0---|-315-|--45--|-315-0,0-45----------|----------| |--45--|---0---|--90--|-0-45,54-90----------|----x----| |-135-|---90--|-180-|-90-135,135-180---|----x----| |-180-|--135-|-225-|-135-180,180-225-|----x----| |-225-|--180-|-270-|-180-225,225-270-|----x----| |-270-|--225-|-315-|-225-270,270-315-|----------| |-315-|--270-|---0---|--270-315,315-0---|----------| I will need to do all tests from derived, or stored values, but can not figure out how to get all of my cases to work simultaneously. //I attempted to concatenate the 2 tests: if((transform.eulerAngles.y>posBound)&&(transform.eulerAngles.y < negBound)){ dir *= -1; } this caused only the first case to be successful // I attempted to store a opposite value, and do a void Rotate(){ // controlls what direction if((transform.eulerAngles.y > posBound)&&(transform.eulerAngles.y<oposite)){ dir = -1; } else if((transform.eulerAngles.y < negBound)&&(transform.eulerAngles.y>oposite)){ dir = 1; } // rotate object } this causes the opposite situation as indicated on the table. What am I missing here?

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• Shader compile log depending on hardware

  - by dreta

  I'm done with the core of my graphics engine and I'm testing it on every platform I can get my hands on. Now, what I noticed is that different drivers return different shader and program compile log content. For example, on my friend's laptop if you successfuly compile a shader then the log is simply empty. However on my PC I get some useful information along with it. So if I compile a vertex shader, I'll get: Vertex shader was successfully compiled to run on hardware. Which isn't that impressive, but is what happens when I compile a program. On my friend's computer the log is empty, since the program compiles. However on my own computer I get: Vertex shader(s) linked, fragment shader(s) linked. Which is awesome, because I'm attaching a geometry shader with 0 (I have a geometry shader file with trash, so it doesn't compile and the pointer is set to 0), and the compiler just tells me which shaders linked. Now it got me thinking, if I was going to buy a graphics card, is there a way for me to get the information about whether or not I'll get this "extended" compile information? Maybe it's vendor specific? Now I don't expect an answer TBH, this seems a bit obscure, but maybe somebody has any experience with this and could post it.

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• What's a good way to check that a player has clicked on an object in a 3D game?

  - by imja

  I'm programming a 3D game (using C++ and OpenGL), and I have a few 3D objects in the scene, we can say they are boxes for this example. I want to let the player click on those boxes to select them (ie. they might change color) with the typical restriction like if more than one box is located where the user clicked, only the one closest to the camera would get selected. What would be the best way to do this? The fact that these objects go through several transforms before getting to window coordinates is what makes this a bit tricky. One approach I thought about was that if the player clicks on the screen, I could normalize the x,y coordinates of mouse click and then transform the bounding box coordinates of the objects into clip-space so that I could compare then to the normalized mouse coordinates. I guess I could then do some sort of ray-box collision test to see if any objects lie as the path of the mouse click. I'm afraid I might be over complicating it. Any better methods out there?

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• Detecting pixels in a rotated Texture2D in XNA?

  - by PugWrath

  I know things similar to this have been posted, but I'm still trying to find a good solution... I'm drawing Texture2D objects on the ground in my game, and for Mouse-Over or targeting methods, I'm detecting whether or not the pixel in that Texture at the mouse position is Color.Transparent. This works perfectly when I do not rotate the texture, but I'd like to be able to rotate textures to add realism/variety. However, I either need to create a new Texture2D that is rotated at the correct angle so that I can detect its pixels, or I need to find some other method of detection... Any thoughts?

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• How to debug Android App Eclipse?

  - by user2534694

  Ok. So while this isnt a programming question. I wanted to know how do people debug apps? How do you view log cat, and where these exceptions are thrown etc? And do I need to run the app on the emulator to see all the stuff, or is there a way to view this after running the app on my phone(while not being connected to the computer) Links to plugins and tips would be really helpful, as im gonna start work on my next game, and while the first one works fine, had a lot of problems while debugging.

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• What is the standard way of delivering HTML5 games to portals and such?

  - by Bane

  Let me explain what I mean by "standard way of delivering"... Think about Flash games sites. Flash games can be delivered as a single file, either hosted by the site, or, I guess, provided by someone else. HTML5 games, on the other hand, don't have something so standard. Usually, they have their own page, and portals just link to that page. I think that it greatly hinders the purpose of that portal, because, well, you want people to stay on your site and look for other games. Now, I think that a some kind of iframe way of delivering games would help solve this problem greatly. I saw some games doing that, and they were often included on tutorial sites to show a live example, which is obviously a great thing. So, is there a standard at all? Any suggestions? Can you create a game that just preloads itself in an iframe (I heard something about a "single document" or something)?

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• SDL_DisplayFormat works, but not SDL_DisplayFormatAlpha

  - by Bounderby

  The following code is intended to display a green square on a black background. It executes, but the green square does not show up. However, if I change SDL_DisplayFormatAlpha to SDL_DisplayFormat the square is rendered correctly. So what don't I understand? It seems to me that I am creating *surface with an alpha mask and I am using SDL_MapRGBA to map my green color, so it would be consistent to use SDL_DisplayFormatAlpha as well. (I removed error-checking for clarity, but none of the SDL API calls fail in this example.) #include <SDL.h> int main(int argc, const char *argv[]) { SDL_Init( SDL_INIT_EVERYTHING ); SDL_Surface *screen = SDL_SetVideoMode( 640, 480, 32, SDL_HWSURFACE | SDL_DOUBLEBUF ); SDL_Surface *temp = SDL_CreateRGBSurface( SDL_HWSURFACE, 100, 100, 32, 0, 0, 0, ( SDL_BYTEORDER == SDL_BIG_ENDIAN ? 0x000000ff : 0xff000000 ) ); SDL_Surface *surface = SDL_DisplayFormatAlpha( temp ); SDL_FreeSurface( temp ); SDL_FillRect( surface, &surface->clip_rect, SDL_MapRGBA( screen->format, 0x00, 0xff, 0x00, 0xff ) ); SDL_Rect r; r.x = 50; r.y = 50; SDL_BlitSurface( surface, NULL, screen, &r ); SDL_Flip( screen ); SDL_Delay( 1000 ); SDL_Quit(); return 0; }

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• Can minecraft support an asymmetrical mesh?

  - by Qwaar

  So in a bout of fancy I have decided I want to play as a Zaku II from gundam, and was saddened that player skins must be symmetrical. Then I remembered my friends mod that let him play as a MLP pony, and another one that let you shapeshift into mobs. So I decided I could just butcher a player model mesh and slap on the shoulder spike and shield, slap a Zaku skin I found on it, port the colors over onto more texture for the shoulder portions, and call it a day once I added it to the shiftable list, before butchering a gun mod to turn a gun into a ZMP-78. Before I get started on this though, I need to know if minecraft will support an asymmetrical mesh.

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• How to get the blocks seen by the player?

  - by m4tx

  I'm writing a Minecraft-like game using Ogre engine and I have a problem. I must optimize my game, because when I try draw 10000 blocks, I have 2 FPS... So, I got the idea that blocks display of the plane and to hide the invisible blocks. But I have a problem - how do I know which blocks at a time are visible to the player? And - if you know of other optimization methods for such a game, write what and how to use them in Ogre.

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• Set a 2d camera's position so that a building is under the players feet

  - by Potato

  My issue is this: i am making a scrolling game in XNA, and the camera updates based on the players velocity, but the player never actually moves, he is always in the center of the screen. When he hits the top of the building though i want him to always be on top and sink through the texture in a way like this: what i am doing to make this happen is i am just setting his velocity to 0, so its not moving, but the more velocity he hits a building with the more he sinks through it. I also tried setting the buildings position to the plays Bounding Box's bottom, and this achieved the look i wanted but this also resulted in the other buildings rising in the air, because the velocity was still moving (even if i set it to 0). if it was not a scrolling game, this would be not a problem, because you just set the players position to the top of the building, but because the player never actually moves, i actually need to move the camera to the point where the building is under the players feet without the other buildings rising. (Take note this is note a real camera, it is just a class that moves the objects in the world based on the players velocity). All questions are welcome.

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• android multitouch problem

  - by Max

  Im aware that there a a couple of posts on this matter, but Ive tried all of them and none of them gets rid of my problem. Im starting to get close to the end of my game so I bought a cabel to try it on a real phone, and as I expected my multitouch dosnt work. I use 2 joysticks, one to move my character and one to change his direction so he can shoot while walking backwards etc. my local variable: public void update(MotionEvent event) { if (event == null && lastEvent == null) { return; } else if (event == null && lastEvent != null) { event = lastEvent; } else { lastEvent = event; } int index = event.getActionIndex(); int pointerId = event.getPointerId(index); statement for left Joystick: if (pointerId == 0 && event.getAction() == MotionEvent.ACTION_DOWN && (int) event.getX() > steeringxMesh - 50 && (int) event.getX() < steeringxMesh + 50 && (int) event.getY() > yMesh - 50 && (int) event.getY() < yMesh + 50) { dragging = true; } else if (event.getAction() == MotionEvent.ACTION_UP) { dragging = false; } if (dragging) { //code for moving my character statement for my right joystick: if (pointerId == 1 && event.getAction() == MotionEvent.ACTION_DOWN && (int) event.getX() > shootingxMesh - 50 && (int) event.getX() < shootingxMesh + 50 && (int) event.getY() > yMesh - 50 && (int) event.getY() < yMesh + 50) { shooting = true; } else if (event.getAction() == MotionEvent.ACTION_UP) { shooting = false; } if (shooting) { // code for aiming } This class is my main-Views onTouchListener and is called in a update-method that gets called in my game-loop, so its called every frame. Im really at a loss here, I've done a couple of tutorials and Ive tried all relevant solutions to similar posts. Can post entire Class if necessary but I think this is all the relevant code. Just hope someone can make some sence out of this.

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• Open Source HTML/JS game(s) with license that would allow embedding in my app?

  - by DustMason

  I'm working on an educational app for kids. At the end of the sign-up process, the kids must wait for a confirmation from their parents in order to gain access to the app. While they wait for this to happen, we want to let the kid play a simple game as a way to keep their interest up. Is there a marketplace or repository for games with such a license that we could either purchase (affordably) or use for free in our own app?

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• LibGDX - Textures rendering at wrong position

  - by ACluelessGuy

  Update 2: Let me further explain my problem since I think that i didn't make it clear enough: The Y-coordinates on the bottom of my screen should be 0. Instead it is the height of my screen. That means the "higher" i touch/click the screen the less my y-coordinate gets. Above that the origin is not inside my screen, atleast not the 0 y-coordinate. Original post: I'm currently developing a tower defence game for fun by using LibGDX. There are places on my map where the player is or is not allowed to put towers on. So I created different ArrayLists holding rectangles representing a tile on my map. (towerPositions) for(int i = 0; i < map.getLayers().getCount(); i++) { curLay = (TiledMapTileLayer) map.getLayers().get(i); //For all Cells of current Layer for(int k = 0; k < curLay.getWidth(); k++) { for(int j = 0; j < curLay.getHeight(); j++) { curCell = curLay.getCell(k, j); //If there is a actual cell if(curCell != null) { tileWidth = curLay.getTileWidth(); tileHeight = curLay.getTileHeight(); xTileKoord = tileWidth*k; yTileKoord = tileHeight*j; switch(curLay.getName()) { //If layer named "TowersAllowed" picked case "TowersAllowed": towerPositions.add(new Rectangle(xTileKoord, yTileKoord, tileWidth, tileHeight)); // ... AND SO ON If the player clicks on a "allowed" field later on he has the opportunity to build a tower of his coice via a menu. Now here is the problem: The towers render, but they render at wrong position. (They appear really random on the map, no certain pattern for me) for(Rectangle curRect : towerPositions) { if(curRect.contains(xCoord, yCoord)) { //Using a certain tower in this example (left the menu out if(gameControl.createTower("towerXY")) { //RenderObject is just a class holding the Texture and x/y coordinates renderList.add(new RenderObject(new Texture(Gdx.files.internal("TowerXY.png")), curRect.x, curRect.y)); } } } Later on i render it: game.batch.begin(); for(int i = 0; i < renderList.size() ; i++) { game.batch.draw(renderList.get(i).myTexture, renderList.get(i).x, renderList.get(i).y); } game.batch.end(); regards

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• Basic modelling of radar

  - by Hawk66

  I'm currently researching how to model/simulate radar for my naval simulation. Since the emphasis is on modelling ASW or submarines in general, I need only a basic radar model - at least for the beginning. So, does anybody know a resource for such a simple model? The model should take signal strength of the sensor, the size of the target and the terrain (height/ground clutter) into account. Thanks.

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

  - by ssb

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

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• Instead of the specified Texture, black circles on a green background are getting rendered. Why?

  - by vinzBad

  I'm trying to render a Texture via OpenGL. But instead of the texture black circles on a green background are rendered. (They scale, depending what the rotation of the texture is) Example: The texture I'm trying to render is the following: This is the code I use to render the texture, it's located in my Sprite-class. public void Render() { Matrix4 matrix = Matrix4.CreateTranslation(-OriginX, -OriginY, 0) * Matrix4.CreateRotationZ(Rotation) * Matrix4.CreateTranslation(X, Y, 0); Vector2[] corners = { new Vector2(0,0), //top left new Vector2(Width ,0),//top right new Vector2(Width,Height),//bottom rigth new Vector2(0,Height)//bottom left }; //copy the corners to the uv coordinates Vector2[] uv = corners.ToArray<Vector2>(); //transform the coordinates for (int i = 0; i < 4; i++) corners[i] = new Vector2(Vector3.Transform(new Vector3(corners[i]), matrix)); //GL.Color3(TintColor); GL.BindTexture(TextureTarget.Texture2D, _ID); GL.Begin(BeginMode.Quads); { for (int i = 0; i < 4; i++) { GL.TexCoord2(uv[i]); GL.Vertex3(corners[i].X, corners[i].Y, _layerDepth); } } GL.End(); if (EnableDebugDraw) { GL.Color3(Color.Violet); GL.PointSize(3); GL.Begin(BeginMode.Points); { for (int i = 0; i < 4; i++) GL.Vertex2(corners[i]); } GL.End(); GL.Color3(Color.Green); GL.Begin(BeginMode.Points); GL.Vertex2(X, Y); GL.End(); } } This is how I setup OpenGL. public static void SetupGL() { GL.Enable(EnableCap.AlphaTest); GL.AlphaFunc(AlphaFunction.Greater, 0.1f); GL.Enable(EnableCap.Texture2D); GL.Hint(HintTarget.PerspectiveCorrectionHint, HintMode.Nicest); } With this function I load the texture: public static uint LoadTexture(string path) { uint id; GL.GenTextures(1, out id); GL.BindTexture(TextureTarget.Texture2D, id); Bitmap bitmap = new Bitmap(path); BitmapData data = bitmap.LockBits(new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppArgb); GL.TexImage2D(TextureTarget.Texture2D, 0, PixelInternalFormat.Rgba, data.Width, data.Height, 0, OpenTK.Graphics.OpenGL.PixelFormat.Bgra, PixelType.UnsignedByte, data.Scan0); bitmap.UnlockBits(data); GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (int)TextureMinFilter.Linear); GL.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, (int)TextureMagFilter.Linear); return id; } And here I call Sprite.Render() protected override void OnRenderFrame(FrameEventArgs e) { GL.ClearColor(Color.MidnightBlue); GL.Clear(ClearBufferMask.ColorBufferBit); _sprite.Render(); SwapBuffers(); base.OnRenderFrame(e); } As I stole this code from the Textures-Example from OpenTK, I don't understand why this doesn't work.

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• Informing GUI objects about screen size - Designing

  - by Mosquito

  I have a problem with designing classes for my game which I create. In my app, there is: class CGame which contains all the information about game itself, e.g. screen width, screen height, etc. In the main() function I create a pointer to CGame instance. class CGUIObject which includes fields specifying it's position and draw() method, which should know how to draw an object according to screen size. class CGUIManager which is a singleton and it includes a list of CGUIObject's. For each object in a list it just calls draw() method. For clarity's sake, I'll put some simple code: class CGame { int screenWidth; int screenHeight; }; class CGUIObject { CPoint position; void draw(); // this one needs to know what is a screen's width and height }; class CGUIManager // it's a singleton { vector<CGUIObject*> guiObjects; void drawObjects(); }; And the main.cpp: CGame* g; int main() { g = new CGame(); while(1) { CGUIManager::Instance().drawObjects(); } return 0; } Now the problem is, that each CGUIObject needs to know the screen size which is held by CGame, but I find it very dumb to include pointer to CGame instance in every object. Could anyone, please, tell me what would be the best approach to achieve this?

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• Determining the angle to fire a shot when target and shooter moves, and bullet moves with shooter velocity added in

  - by Azaral

  I saw this question: Predicting enemy position in order to have an object lead its target and followed the link in the answer to stack overflow. In the stack overflow page I used the 2nd answer, the one that is a large mathematical derivation. My situation is a little different though. My first question though is will the answer provided in the stack overflow page even work to begin with, assuming the original circumstances of moving target and stationary shooter. My situation is a little different than that situation. My target moves, the shooter moves, and the bullets from the shooter start off with the velocities in x and y added to the bullets' x and y velocities. If you are sliding to the right, the bullets will remain in front of you as you move so as long as your velocity remains constant. What I'm trying to do is to get the enemy to be able to determine where they need to shoot in order to hit the player. Unless the player and enemy is stationary, the velocity from the ship adding to the velocity of the bullets will cause a miss. I'd rather like to prevent that. I used the formula in the stack overflow answer and did what I thought were the appropriate adjustments. I've been banging at this for the last four hours and I just can't make it click. It is probably something really simple and boneheaded that I am missing (that seems to be a lot of my problems lately). Here is the solution presented from the stack overflow answer: It boils down to solving a quadratic equation of the form: a * sqr(x) + b * x + c == 0 Note that by sqr I mean square, as opposed to square root. Use the following values: a := sqr(target.velocityX) + sqr(target.velocityY) - sqr(projectile_speed) b := 2 * (target.velocityX * (target.startX - cannon.X) + target.velocityY * (target.startY - cannon.Y)) c := sqr(target.startX - cannon.X) + sqr(target.startY - cannon.Y) Now we can look at the discriminant to determine if we have a possible solution. disc := sqr(b) - 4 * a * c If the discriminant is less than 0, forget about hitting your target -- your projectile can never get there in time. Otherwise, look at two candidate solutions: t1 := (-b + sqrt(disc)) / (2 * a) t2 := (-b - sqrt(disc)) / (2 * a) Note that if disc == 0 then t1 and t2 are equal. If there are no other considerations such as intervening obstacles, simply choose the smaller positive value. (Negative t values would require firing backward in time to use!) Substitute the chosen t value back into the target's position equations to get the coordinates of the leading point you should be aiming at: aim.X := t * target.velocityX + target.startX aim.Y := t * target.velocityY + target.startY Here is my code, after being corrected by Sam Hocevar (thank you again for your help!). It still doesn't work. For some reason it never enters the section of code inside the if(disc = 0) (obviously because it is always less than zero but...). However, if I plug the numbers from my game log on the enemy and player positions and velocities it outputs a valid firing solution. I have looked at the code side by side a couple of times now and I can't find any differences. There has got to be something simple I'm missing here. If someone else could look at this code and determine what is going on here I'd appreciate it. I know it's not going through that section because if it were, shouldShoot would become true and the enemy would be blasting away at the player. This section calls the function in question, CalculateShootHeading() if(shouldMove) { UseEngines(); } x += xVelocity; y += yVelocity; CalculateShootHeading(); if(shouldShoot) { ShootWeapons(); } UpdateWeapons(); This is CalculateShootHeading(). This is inside the enemy class so x and y are the enemy's x and y and the same with velocity. One output from my game log gives Player X = 2108, Player Y = -180.956, Player X velocity = 10.9949, Player Y Velocity = -6.26017, Enemy X = 1988.31, Enemy Y = -339.051, Enemy X velocity = 1.81666, Enemy Y velocity = -9.67762, 0 enemy projectiles. The output from the console tester is Bullet position = 2210.49, -239.313 and Player Position = 2210.49, -239.313. This doesn't make any sense. The only thing that could be different is the code or the input into my function in the game and I've checked that and I don't think that it is wrong as it's updated before this and never changed. float const bulletSpeed = 30.f; float const dx = playerX - x; float const dy = playerY - y; float const vx = playerXVelocity - xVelocity; float const vy = playerYVelocity - yVelocity; float const a = vx * vx + vy * vy - bulletSpeed * bulletSpeed; float const b = 2.f * (vx * dx + vy * dy); float const c = dx * dx + dy * dy; float const disc = b * b - 4.f * a * c; shouldShoot = false; if (disc >= 0.f) { float t0 = (-b - std::sqrt(disc)) / (2.f * a); float t1 = (-b + std::sqrt(disc)) / (2.f * a); if (t0 < 0.f || (t1 < t0 && t1 >= 0.f)) { t0 = t1; } if (t0 >= 0.f) { float shootx = vx + dx / t0; float shooty = vy + dy / t0; heading = std::atan2(shooty, shootx) * RAD2DEGREE; } shouldShoot = true; }

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