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• How can I factor momentum into my space sim?

  - by Josh Petite

  I am trying my hand at creating a simple 2d physics engine right now, and I'm running into some problems figuring out how to incorporate momentum into movement of a spaceship. If I am moving in a given direction at a certain velocity, I am able to currently update the position of my ship easily (Position += Direction * Velocity). However, if the ship rotates at all, and I recalculate the direction (based on the new angle the ship is facing), and accelerate in that direction, how can I take momentum into account to alter the "line" that the ship travels? Currently the ship changes direction instantaneously and continues at its current velocity in that new direction when I press the thrust button. I want it to be a more gradual turning motion so as to give the impression that the ship itself has some mass. If there is already a nice post on this topic I apologize, but nothing came up in my searches. Let me know if any more information is needed, but I'm hoping someone can easily tell me how I can throw mass * velocity into my game loop update.

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• Handling Players, enemies and attacks in HTML5

  - by Chris Morris

  I'm building a simple (currently) game with free roaming player and monsters on a map built by a 2D grid. I've been looking at the methods for implementing characters and enemies onto the screen and I've seen two seperate methods for doing this online. Drawing the player onto the screen canvas directly and refreshing the entire screen every FPS tick. Having a separate canvas to handle the player and moving the player canvas on top of the screen canvas via absolute positioning. I can see some pros and cons of both methods but what is generally the best method for doing this? I assume the second due to not having to drain resources by refreshing the map when the user is not moving, but the type of game will generally have constant movement.

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• Starting point for a simple game written in action script [closed]

  - by Hossein

  Possible Duplicate: AS3/Flash Game Dev: Looking for good & current step by step. Hi, I want to develop a simple game like: http://www.albinoblacksheep.com/games/falldown2 And then making it a bit more fancy. But I don't know where to start. I have already started AS3 so I know about the syntax and stuff, but I am kinda lost. Does anyone knows of a nice starting point or a tutorial that can help me with this? Thanks

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• Unable to access jar. Why?

  - by SystemNetworks

  I was making a game in java and exported it as jar file. Then after that, I opeed jar splice. I added the libaries and exported jar. I added the natives then i made a main class. I created a fat jar and put it on my desktop. I'm using Mac OS X 10.8 Mountain Lion. When I put in the terminal, java -jar System Front.jar it says unable to access System Front.jar Even if i double click on the file, it doesen't show up! Help! I'm using slick. I added slick and lwjgl as libraries for the jar splice at the jars.

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• Help with this optimization

  - by Milo

  Here is what I do: I have bitmaps which I draw into another bitmap. The coordinates are from the center of the bitmap, thus on a 256 by 256 bitmap, an object at 0.0,0.0 would be drawn at 128,128 on the bitmap. I also found the furthest extent and made the bitmap size 2 times the extent. So if the furthest extent is 200,200 pixels, then the bitmap's size is 400,400. Unfortunately this is a bit inefficient. If a bitmap needs to be drawn at 500,500 and the other one at 300,300, then the target bitmap only needs to be 200,200 in size. I cannot seem to find a correct way to draw in the components correctly with a reduced size. I figure out the target bitmap size like this: float AvatarComposite::getFloatWidth(float& remainder) const { float widest = 0.0f; float widestNeg = 0.0f; for(size_t i = 0; i < m_components.size(); ++i) { if(m_components[i].getSprite() == NULL) { continue; } float w = m_components[i].getX() + ( ((m_components[i].getSprite()->getWidth() / 2.0f) * m_components[i].getScale()) / getWidthToFloat()); float wn = m_components[i].getX() - ( ((m_components[i].getSprite()->getWidth() / 2.0f) * m_components[i].getScale()) / getWidthToFloat()); if(w > widest) { widest = w; } if(wn > widest) { widest = wn; } if(w < widestNeg) { widestNeg = w; } if(wn < widestNeg) { widestNeg = wn; } } remainder = (2 * widest) - (widest - widestNeg); return widest - widestNeg; } And here is how I position and draw the bitmaps: int dw = m_components[i].getSprite()->getWidth() * m_components[i].getScale(); int dh = m_components[i].getSprite()->getHeight() * m_components[i].getScale(); int cx = (getWidth() + (m_remainderX * getWidthToFloat())) / 2; int cy = (getHeight() + (m_remainderY * getHeightToFloat())) / 2; cx -= m_remainderX * getWidthToFloat(); cy -= m_remainderY * getHeightToFloat(); int dx = cx + (m_components[i].getX() * getWidthToFloat()) - (dw / 2); int dy = cy + (m_components[i].getY() * getHeightToFloat()) - (dh / 2); g->drawScaledSprite(m_components[i].getSprite(),0.0f,0.0f, m_components[i].getSprite()->getWidth(),m_components[i].getSprite()->getHeight(),dx,dy, dw,dh,0); I basically store the difference between the original 2 * longest extent bitmap and the new optimized one, then I translate by that much which I would think would cause me to draw correctly but then some of the components look cut off. Any insight would help. Thanks

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• Libnoise producing completely random noise

  - by Doodlemeat

  I am using libnoise in C++ taken and I have some problems with getting coherent noise. I mean, the noise produced now are completely random and it doesn't look like a noise. Here's a to the image produced by my game. I am diving the map into several chunks, but I can't seem to find any problem doing that since libnoise supports tileable noise. The code can be found below. Every chunk is 8x8 tiles large. Every tile is 64x64 pixels. I am also providing a link to download the entire project. It was made in Visual Studio 2013. Download link This is the code for generating a chunk Chunk *World::loadChunk(sf::Vector2i pPosition) { sf::Vector2i chunkPos = pPosition; pPosition.x *= mChunkTileSize.x; pPosition.y *= mChunkTileSize.y; sf::FloatRect bounds(static_cast<sf::Vector2f>(pPosition), sf::Vector2f(static_cast<float>(mChunkTileSize.x), static_cast<float>(mChunkTileSize.y))); utils::NoiseMap heightMap; utils::NoiseMapBuilderPlane heightMapBuilder; heightMapBuilder.SetSourceModule(mNoiseModule); heightMapBuilder.SetDestNoiseMap(heightMap); heightMapBuilder.SetDestSize(mChunkTileSize.x, mChunkTileSize.y); heightMapBuilder.SetBounds(bounds.left, bounds.left + bounds.width - 1, bounds.top, bounds.top + bounds.height - 1); heightMapBuilder.Build(); Chunk *chunk = new Chunk(this); chunk->setPosition(chunkPos); chunk->buildChunk(&heightMap); chunk->setTexture(&mTileset); mChunks.push_back(chunk); return chunk; } This is the code for building the chunk void Chunk::buildChunk(utils::NoiseMap *pHeightMap) { // Resize the tiles space mTiles.resize(pHeightMap->GetWidth()); for (int x = 0; x < mTiles.size(); x++) { mTiles[x].resize(pHeightMap->GetHeight()); } // Set vertices type and size mVertices.setPrimitiveType(sf::Quads); mVertices.resize(pHeightMap->GetWidth() * pHeightMap->GetWidth() * 4); // Get the offset position of all tiles position sf::Vector2i tileSize = mWorld->getTileSize(); sf::Vector2i chunkSize = mWorld->getChunkSize(); sf::Vector2f offsetPositon = sf::Vector2f(mPosition); offsetPositon.x *= chunkSize.x; offsetPositon.y *= chunkSize.y; // Build tiles for (int x = 0; x < mTiles.size(); x++) { for (int y = 0; y < mTiles[x].size(); y++) { // Sometimes libnoise can return a value over 1.0, better be sure to cap the top and bottom.. float heightValue = pHeightMap->GetValue(x, y); if (heightValue > 1.f) heightValue = 1.f; if (heightValue < -1.f) heightValue = -1.f; // Instantiate a new Tile object with the noise value, this doesn't do anything yet.. mTiles[x][y] = new Tile(this, pHeightMap->GetValue(x, y)); // Get a pointer to the current tile's quad sf::Vertex *quad = &mVertices[(y + x * pHeightMap->GetWidth()) * 4]; quad[0].position = sf::Vector2f(offsetPositon.x + x * tileSize.x, offsetPositon.y + y * tileSize.y); quad[1].position = sf::Vector2f(offsetPositon.x + (x + 1) * tileSize.x, offsetPositon.y + y * tileSize.y); quad[2].position = sf::Vector2f(offsetPositon.x + (x + 1) * tileSize.x, offsetPositon.y + (y + 1) * tileSize.y); quad[3].position = sf::Vector2f(offsetPositon.x + x * tileSize.x, offsetPositon.y + (y + 1) * tileSize.y); // find out which type of tile to render, atm only air or stone TileStop *tilestop = mWorld->getTileStopAt(heightValue); sf::Vector2i texturePos = tilestop->getTexturePosition(); // define its 4 texture coordinates quad[0].texCoords = sf::Vector2f(texturePos.x, texturePos.y); quad[1].texCoords = sf::Vector2f(texturePos.x + 64, texturePos.y); quad[2].texCoords = sf::Vector2f(texturePos.x + 64, texturePos.y + 64); quad[3].texCoords = sf::Vector2f(texturePos.x, texturePos.y + 64); } } } All the code that uses libnoise in some way are World.cpp, World.h and Chunk.cpp, Chunk.h in the project.

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• Stop map from scrolling but let player still move?

  - by ChocoMan

  I have a basic method of scrolling around on a map (moving the map instead of the player), but at when the player gets to a certain proximity to the edge, how do you stop the map from scrolling, but still allow the player to move around until it is away from that proximity? I'm not looking for any code. Just a suggestion so that I can implement it myself. I can see it visually (creating 4 boxed intersecting boundaries for the player to enter), but not sure how to come about stopping and resuming the scrolling of the map.

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• How attach a model with another model on a specific bone?

  - by Mehdi Bugnard

  I meet a difficulty attached to a model to another model on a "bone" accurate. I searched several forums but no result. I saw that many people have asked the same question but no real result see no response. Thread found : How to attach two XNA models together? How can I attach a model to the bone of another model? http://stackoverflow.com/questions/11391852/attach-model-xna But I think it is possible. Here is my code example attached a "cube" of the hand of my player private void draw_itemActionAttached(Model modelInUse) { Matrix[] Model1TransfoMatrix = new Matrix[this.player.Model.Bones.Count]; this.player.Model.CopyAbsoluteBoneTransformsTo(Model1TransfoMatrix); foreach (ModelMesh mesh in modelInUse.Meshes) { foreach (BasicEffect effect in mesh.Effects) { Matrix model2Transform = Matrix.CreateScale(1f) * Matrix.CreateFromYawPitchRoll(0, 0, 0); effect.World = model2Transform * Model1TransfoMatrix[0]; //root bone index effect.View = arcadia.camera.View; effect.Projection = arcadia.camera.Projection; } mesh.Draw(); } }

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• What does SetTextureStage(0, D3DTSS_COLORARG2, 0) in DirectX mean?

  - by Vite Falcon

  I'm trying to convert some DirectX code to Ogre3D and was wondering what the following translates to: pDev->SetTextureStage(0, D3DTSS_TEXCOORDINDEX, 0) pDev->SetTextureStage(0, D3DTSS_COLORARG1, D3DTA_TEXTURE) pDev->SetTextureStage(0, D3DTSS_COLOROP, D3DTOP_MODULATE) pDev->SetTextureStage(0, D3DTSS_COLORARG2, 0) What is the modulation operation happening here? Is the texture getting modulated with the background? Or is it getting zeroed? I've tried searching for what this means and unfortunately I haven't come across anything meaningful. Any help to shed light on this matter will be much appreciated.

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• Align tetrahedrons

  - by thedeadlybutter

  I'm currently generating tetrahedron meshes in Unity When a player clicks the side of a mesh, a new one spawns aligned with it, like this. I'm not sure how nor can I find any information on implementing a tetra hedron grid. I tried playing around with the vertices until I realized I need to adjust position & rotation. Any ideas? EDIT: To be clear, the second image was manually placed objects in the Unity Editor. I'm looking to make an algorithm that places the meshes correctly.

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• Cocos2d copied actions not responding?

  - by Stephen

  I am running an animation on 2 sprites like so: -(void) startFootballAnimation { CCAnimation* footballAnim = [CCAnimation animationWithFrame:@"Football" frameCount:60 delay:0.005f]; spiral = [CCAnimate actionWithAnimation:footballAnim]; CCRepeatForever* repeat = [CCRepeatForever actionWithAction:spiral]; [self runAction:repeat]; [secondFootball runAction:[[repeat copy] autorelease]]; } The problem I am having is I call this method: - (void) slowAnimation { [spiral setDuration:[spiral duration] + 0.01]; } and it only slows down the first sprites animation and not the second one. Do I need to do something different with copied actions to get them to react to the slowing of the animation?

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• Tile map collision is not working properly

  - by Sigh-AniDe

  I am having problems setting collision between my sprite and the tiles. I have only done the code for colision for moving upwards but some places on the map it moves up and some places it doesn't. Here is what I have so far: Vector2 position; private static float scalingFactor = 32; static int tileWidth = 32; static int tileHeight = 32; int[ , ] map = { {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, }; // This is in turtle.update if ( keyboardState.IsKeyDown( Keys.Up ) ) { if ( position.Y > screenHeight / 4 ) { //// current position of the turtle on the tiles int mapX = ( int )( position.X / scalingFactor ); int mapY = ( int )( position.Y / scalingFactor ) - 1; if ( isMovable( mapX , mapY , map ) ) { position.Y = position.Y - scalingFactor; } } else { MoveUp(); } } private void MoveUp() { motion.Y = -1; } public bool isMovable( int mapX , int mapY , int[ , ] map ) { if ( mapX < 0 || mapX > 19 || mapY < 0 || mapY > 20 ) { return false; } int tile = map[ mapX , mapY ]; if ( tile == 0 ) { return false; } return true; } protected override void Update( GameTime gameTime ) { turtle.Update( screenHeight , scalingFactor , map ); base.Update( gameTime ); }

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• Tiled/TMX C++ Library/Parser

  - by Ben

  Where can I find an easy to use and up to date C++ parser/library for the .tmx map format (used by the Tiled Map Editor) ? EDIT: David's comment, 'Unless you want to build your game around the format of the parser..', got me thinking... So I have downloaded pugixml, which is an easy to use xml-parser with very straightforward documentation. Together with the spec for the TMX Map Format, I think I'll give it a try myself. I'll probably compare with Cocos2d-x's CCTMXTiledMap at some point.

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• What's the best game engine to use for my PC game project? [closed]

  - by user19860

  I'm in the planning phase of creating an action-rpg for the PC, and I'd like to create a League of Legends style look for the game (animated/cartoony). Any idea which engine best replicates this look? I ask because when I look at a lot of the UDk/Unreal games, they've all got the more realistic 3-D look that I'd like to avoid, so I was wondering if an alternate look was possible on that type of engine. Source SDK and Unity also look very interesting, I just don't know what types of visual capabilities these engines have. Thanks in advance.

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• Procedural Mesh: UV mapping

  - by Esa

  I made a procedural mesh and now I want to apply a texture to it. The problem is, I cannot get it to stick the way I want it to. The idea is to have the texture painted only once over the whole mesh, so that there is no repeating. How should I map the UV to make that happen? My mesh is a simple plane consisting of 56 triangles. I'd add pictures to clear things up but I cannot since my reputation is below 10 points. Any help is appreciated. EDIT(Kind people gave me up votes, thank you): Meet my mesh: And when textured(tried to repeat the texture): And my texture:

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• How can I apply different actions to different parts of a 2D character?

  - by Praveen Sharath

  I am developing a 2D platform game in Java. The player has a gun in his hand every time. He needs to walk and shoot with the gun(arrow keys for walk and X key to shoot). The walk cycle takes 6 frames and i am able to import the sprite sheet and animate the sequence when I press arrow key. But i need to add the gun motion. The player holds the gun upwards and when X key is pressed he brings it straight and shoots. How to implement the walk + shoot action?

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• What methods should save/load a game state

  - by vedi

  There are a lot of articles about how to save a state of a game and they are pretty good. But I have one conceptual misunderstanding where should I save the state? My game has number of screens and pair of them are MainMenuScreen and MainSceneScreen these are inherited from Screen class. MainMenuScreen is shown at start of the game the MainSceneScreen little later. What is the problem? I navigated to MainSceneScreen, forced Android to stop the application (I change a language settings on the device to achieve it, please let me know if I'm wrong). After that I select the application again and I can see MainMenuScreen is shown. But I want MainSceneScreen to be shown. I suppose I should override resume method. But what class I should override? I have class PsGame that extends Game class of libgdx. I put breakpoints to its resume method and it turned out that method was not called. I investigated the problem and I've found little strange code in onResume method of AndroidApplication class of libgdx: if (!firstResume) graphics.resume(); else firstResume = false; My debugger said firstResume was true and didn't go to *graphics.resume()*line. Sorry for a lot of words but could you answer following question: What did I do wrong? What methods should I override? Thank you in advance.

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• What program should i use for Ludum Dare?

  - by mFontoura

  I want to participate for the first time on Ludum Dare, but i'm not confortable yet with a language to pick one for making a game on a weekend. So i was looking for a program 'gamemaker' style, just to make something for LD. I was going for Construct 2, but i use Linux and they don't have a linux version. So the alternative i use is Stencyl, witch is great and probably is what i'm going to use. However, i wanted to know if there is something similar and better for Linux. Also, if i get a computer with Win8, is it worth the trouble for Construct 2?

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• Sprites, Primitives and logic entity as structs

  - by Jeffrey

  I'm wondering would it be considered acceptable: The window class is responsible for drawing data, so it will have a method: Window::draw(const Sprite&); Window::draw(const Rect&); Window::draw(const Triangle&); Window::draw(const Circle&); and all those primitives + sprites would be just public struct. For example Sprite: struct Sprite { float x, y; // center float origin_x, origin_y; float width, height; float rotation; float scaling; GLuint texture; Sprite(float w, float h); Sprite(float w, float h, float a, float b); void useTexture(std::string file); void setOrigin(float a, float b); void move(float a, float b); // relative move void moveTo(float a, float b); // absolute move void rotate(float a); // relative rotation void rotateTo(float a); // absolute rotation void rotationReset(); void scale(float a); // relative scaling void scaleTo(float a); // absolute scaling void scaleReset(); }; So instead of having each primitive to call their draw() function, which is a little bit off topic for their object, I let the Window class handle all the OpenGL stuff and manipulate them as simple objects that will be drawn later on. Is this pattern used? Does it have any cons against it's primitives-draw-themself pattern? Are there any other related patterns?

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• Draw depth works on WP7 emulator but not device

  - by Luke

  I am making a game on a WP7 device using C# and XNA. I have a system where I always want the object the user is touching to be brought to the top, so every time it is touched I add float.Epsilon to its draw depth (I have it set so that 0 is the back and 1 is the front). On the Emulator that all works fine, but when I run it on my device the draw depths seem to be completely random. I am hoping that anybody knows a way to fix this. I have tried doing a Clean & Rebuild and uninstalling from the device but that is no luck. My call to spritebatch.Begin is: spriteBatch.Begin(SpriteSortMode.FrontToBack, BlendState.AlphaBlend); and to draw I use spriteBatch.Draw(Texture, new Rectangle((int)X, (int)Y, (int)Width, (int)Height), null, Color.White, 0, Vector2.Zero, SpriteEffects.None, mDrawDepth); Where mDrawDepth is a float value of the draw depth (likely to be a very small number; a small multiple of float.Epsilon. Any help much appreciated, thanks!

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• Incorporating XNA into an existing project

  - by Boreal

  My game as-is is using IrrlichtLime, which I'm beginning to dislike because it hides a lot of implementation and makes adding your own implementation incredibly complex. I don't really need the scene manager for anything and the only animation I need is manual (i.e. transforming the bones programmatically). However, I've only ever used XNA in the past as a starting point with the templates. How would I take my current project and add XNA to it?

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• What's a good entity hierarchy for a 2D game?

  - by futlib

  I'm in the process of building a new 2D game out of some code I wrote a while ago. The object hierarchy for entities is like this: Scene (e.g. MainMenu): Contains multiple entities and delegates update()/draw() to each Entity: Base class for all things in a scene (e.g. MenuItem or Alien) Sprite: Base class for all entities that just draw a texture, i.e. don't have their own drawing logic Does it make sense to split up entities and sprites up like that? I think in a 2D game, the terms entity and sprite are somewhat synonymous, right? But I do believe that I need some base class for entities that just draw a texture, as opposed to drawing themselves, to avoid duplication. Most entities are like that. One weird case is my Text class: It derives from Sprite, which accepts either the path of an image or an already loaded texture in its constructor. Text loads a texture in its constructor and passes that to Sprite. Can you outline a design that makes more sense? Or point me to a good object-oriented reference code base for a 2D game? I could only find 3D engine code bases of decent code quality, e.g. Doom 3 and HPL1Engine.

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• Most efficient way to implement delta time

  - by Starkers

  Here's one way to implement delta time: /// init /// var duration = 5000, currentTime = Date.now(); // and create cube, scene, camera ect ////// function animate() { /// determine delta /// var now = Date.now(), deltat = now - currentTime, currentTime = now, scalar = deltat / duration, angle = (Math.PI * 2) * scalar; ////// /// animate /// cube.rotation.y += angle; ////// /// update /// requestAnimationFrame(render); ////// } Could someone confirm I know how it works? Here what I think is going on: Firstly, we set duration at 5000, which how long the loop will take to complete in an ideal world. With a computer that is slow/busy, let's say the animation loop takes twice as long as it should, so 10000: When this happens, the scalar is set to 2.0: scalar = deltat / duration scalar = 10000 / 5000 scalar = 2.0 We now times all animation by twice as much: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 2.0; angle = (Math.PI * 4) // which is 2 rotations When we do this, the cube rotation will appear to 'jump', but this is good because the animation remains real-time. With a computer that is going too quickly, let's say the animation loop takes half as long as it should, so 2500: When this happens, the scalar is set to 0.5: scalar = deltat / duration scalar = 2500 / 5000 scalar = 0.5 We now times all animation by a half: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 0.5; angle = (Math.PI * 1) // which is half a rotation When we do this, the cube won't jump at all, and the animation remains real time, and doesn't speed up. However, would I be right in thinking this doesn't alter how hard the computer is working? I mean it still goes through the loop as fast as it can, and it still has render the whole scene, just with different smaller angles! So this a bad way to implement delta time, right? Now let's pretend the computer is taking exactly as long as it should, so 5000: When this happens, the scalar is set to 1.0: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 1; angle = (Math.PI * 2) // which is 1 rotation When we do this, everything is timsed by 1, so nothing is changed. We'd get the same result if we weren't using delta time at all! My questions are as follows Mostly importantly, have I got the right end of the stick here? How do we know to set the duration to 5000 ? Or can it be any number? I'm a bit vague about the "computer going too quickly". Is there a way loop less often rather than reduce the animation steps? Seems like a better idea. Using this method, do all of our animations need to be timesed by the scalar? Do we have to hunt down every last one and times it? Is this the best way to implement delta time? I think not, due to the fact the computer can go nuts and all we do is divide each animation step and because we need to hunt down every step and times it by the scalar. Not a very nice DSL, as it were. So what is the best way to implement delta time? Below is one way that I do not really get but may be a better way to implement delta time. Could someone explain please? // Globals INV_MAX_FPS = 1 / 60; frameDelta = 0; clock = new THREE.Clock(); // In the animation loop (the requestAnimationFrame callback)… frameDelta += clock.getDelta(); // API: "Get the seconds passed since the last call to this method." while (frameDelta >= INV_MAX_FPS) { update(INV_MAX_FPS); // calculate physics frameDelta -= INV_MAX_FPS; } How I think this works: Firstly we set INV_MAX_FPS to 0.01666666666 How we will use this number number does not jump out at me. We then intialize a frameDelta which stores how long the last loop took to run. Come the first loop frameDelta is not greater than INV_MAX_FPS so the loop is not run (0 = 0.01666666666). So nothing happens. Now I really don't know what would cause this to happen, but let's pretend that the loop we just went through took 2 seconds to complete: We set frameDelta to 2: frameDelta += clock.getDelta(); frameDelta += 2.00 Now we run an animation thanks to update(0.01666666666). Again what is relevance of 0.01666666666?? And then we take away 0.01666666666 from the frameDelta: frameDelta -= INV_MAX_FPS; frameDelta = frameDelta - INV_MAX_FPS; frameDelta = 2 - 0.01666666666 frameDelta = 1.98333333334 So let's go into the second loop. Let's say it took 2(? Why not 2? Or 12? I am a bit confused): frameDelta += clock.getDelta(); frameDelta = frameDelta + clock.getDelta(); frameDelta = 1.98333333334 + 2 frameDelta = 3.98333333334 This time we enter the while loop because 3.98333333334 = 0.01666666666 We run update We take away 0.01666666666 from frameDelta again: frameDelta -= INV_MAX_FPS; frameDelta = frameDelta - INV_MAX_FPS; frameDelta = 3.98333333334 - 0.01666666666 frameDelta = 3.96666666668 Now let's pretend the loop is super quick and runs in just 0.1 seconds and continues to do this. (Because the computer isn't busy any more). Basically, the update function will be run, and every loop we take away 0.01666666666 from the frameDelta untill the frameDelta is less than 0.01666666666. And then nothing happens until the computer runs slowly again? Could someone shed some light please? Does the update() update the scalar or something like that and we still have to times everything by the scalar like in the first example?

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• Beginning android games, 2nd edition engine

  - by Benjamin Stephen

  I recently bought the book from Apress and have worked my way through it, unfortunately, it seems to just be dealing with side scrolling games and not Zelda-like top down games. I was wondering if anyone out there can tell me if it's possible to use their engine to create such a game? It doesn't go into how to build a top down tile map. Using the engine in their book, how can I make a tile map easily that has walls and things like that? Any help would be appreciated. Thanks in advance.

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• Trying to detect collision between two polygons using Separating Axis Theorem

  - 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; 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); } } /* 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(vertices[0]); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(vertices[i]); 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( other.x <= y || 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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