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  • How can I move a polygon edge 1 unit away from the center?

    - by Stephen
    Let's say I have a polygon class that is represented by a list of vector classes as vertices, like so: var Vector = function(x, y) { this.x = x; this.y = y; }, Polygon = function(vectors) { this.vertices = vectors; }; Now I make a polygon (in this case, a square) like so: var poly = new Polygon([ new Vector(2, 2), new Vector(5, 2), new Vector(5, 5), new Vector(2, 5) ]); So, the top edge would be [poly.vertices[0], poly.vertices[1]]. I need to stretch this polygon by moving each edge away from the center of the polygon by one unit, along that edge's normal. The following example shows the first edge, the top, moved one unit up: The final polygon should look like this new one: var finalPoly = new Polygon([ new Vector(1, 1), new Vector(6, 1), new Vector(6, 6), new Vector(1, 6) ]); It is important that I iterate, moving one edge at a time, because I will be doing some collision tests after moving each edge. Here is what I tried so far (simplified for clarity), which fails triumphantly: for(var i = 0; i < vertices.length; i++) { var a = vertices[i], b = vertices[i + 1] || vertices[0]; // in case of final vertex var ax = a.x, ay = a.y, bx = b.x, by = b.y; // get some new perpendicular vectors var a2 = new Vector(-ay, ax), b2 = new Vector(-by, bx); // make into unit vectors a2.convertToUnitVector(); b2.convertToUnitVector(); // add the new vectors to the original ones a.add(a2); b.add(b2); // the rest of the code, collision tests, etc. } This makes my polygon start slowly rotating and sliding to the left, instead of what I need. Finally, the example shows a square, but the polygons in question could be anything. They will always be convex, and always with vertices in clockwise order.

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  • XNA C# Platformer - physics engine or tile based?

    - by Hugh
    I would like to get some opinions on whether i should develop my game using a physics engine (farseer physics seems to be the best option) or follow the traditional tile-based method. Quick background: - its a college project, my first game, but have 4 years academic programming experience - Just want a basic platformer with a few levels, nothing fancy - want a shooting mechanic, run and gun, just like contra or metal slug for example - possibly some simple puzzles I have made a basic prototype with farseer, the level is hardcoded with collisions and not really tiled, more like big full-screen sized tiles, with collision bodies drawn manually along the ground and walls etc. My main problem is i want a simple retro feel to the jumping and physics but because its a physics simulation engine its going to be realistic, whereas typical in air controllable physics for platformers arent realistic. I have to make a box with wheel body fixture under it to have this effect and its glitchy and doesnt feel right. I chose to use a physics engine because i tried the tile method initially and found it very hard to understand, the engine took care of alot things to save me time, mainly being able to do slopes easily was nice and the freedom to draw collision bounds wherever i liked, rather then restricted to a grid, which gave me more freedom for art design also. In conclusion i don't know which method to pick, i want to use a method which will be the most straight forward way to implement and wont give me a headache later on, preferably a method which has an abundance of tutorials and resources so i dont get "stuck" doing something which has been done a million times before! Let me know i haven't provided enough information for you to help me! Thanks in advance, Hugh.

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  • libgdx intersection problem between rectangle and circle

    - by Chris
    My collision detection in libgdx is somehow buggy. player.png is 20*80px and ball.png 25*25px. Code: @Override public void create() { // ... batch = new SpriteBatch(); playerTex = new Texture(Gdx.files.internal("data/player.png")); ballTex = new Texture(Gdx.files.internal("data/ball.png")); player = new Rectangle(); player.width = 20; player.height = 80; player.x = Gdx.graphics.getWidth() - player.width - 10; player.y = 300; ball = new Circle(); ball.x = Gdx.graphics.getWidth() / 2; ball.y = Gdx.graphics.getHeight() / 2; ball.radius = ballTex.getWidth() / 2; } @Override public void render() { Gdx.gl.glClearColor(1, 1, 1, 1); Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT); camera.update(); // draw player, ball batch.setProjectionMatrix(camera.combined); batch.begin(); batch.draw(ballTex, ball.x, ball.y); batch.draw(playerTex, player.x, player.y); batch.end(); // update player position if(Gdx.input.isKeyPressed(Keys.DOWN)) player.y -= 250 * Gdx.graphics.getDeltaTime(); if(Gdx.input.isKeyPressed(Keys.UP)) player.y += 250 * Gdx.graphics.getDeltaTime(); if(Gdx.input.isKeyPressed(Keys.LEFT)) player.x -= 250 * Gdx.graphics.getDeltaTime(); if(Gdx.input.isKeyPressed(Keys.RIGHT)) player.x += 250 * Gdx.graphics.getDeltaTime(); // don't let the player leave the field if(player.y < 0) player.y = 0; if(player.y > 600 - 80) player.y = 600 - 80; // check collision if (Intersector.overlaps(ball, player)) Gdx.app.log("overlaps", "yes"); }

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  • Bomberman clone, how to do bombs?

    - by hustlerinc
    I'm playing around with a bomberman clone to learn game-developement. So far I've done tiles, movement, collision detection, and item pickup. I also have pseudo bombplacing (just graphics and collision, no real functionality). I've made a jsFiddle of the game with the functionality I currently have. The code in the fiddle is very ugly though. Scroll past the map and you find how I place bombs. Anyway, what I would like to do is an object, that has the general information about bombs like: function Bomb(){ this.radius = player.bombRadius; this.placeBomb = function (){ if(player.bombs != 0){ // place bomb } } this.explosion = function (){ // Explosion } } I don't really know how to fit it into the code though. Everytime I place a bomb, do I do var bomb = new Bomb(); or do i need to constantly have that in the script to be able to access it. How does the bomb do damage? Is it as simple as doing X,Y in all directions until radius runs out or object stops it? Can I use something like setTimeout(bomb.explosion, 3000) as timer? Any help is appreciated, be it a simple explanation of the theory or code examples based on the fiddle. When I tried the object way it breaks the code.

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  • Data structure for bubble shooter game

    - by SundayMonday
    I'm starting to make a bubble shooter game for a mobile OS. Assume this is just the basic "three or more same-color bubbles that touch pop" and all bubbles that are separated from their group fall/pop. What data structures are common for storing the bubbles? I've considered using an undirected, connected graph where each node is a bubble. This seems like it could help answer the question "which bubbles (if any) should fall now?" after some arbitrary bubbles are popped and corresponding nodes are removed from the graph. I think the answer is all bubbles that were just disconnected from the graph should fall. However the graph approach might be overkill so I'm not sure. Another consideration for the data structure is collision detection. Perhaps being able to grab a list of neighboring bubbles in constant time for a particular "bubble slot" is useful. So the collision detection would be something like "moving bubble is closest to slot ij, neighbors of slot ij are bubbles a,b,c, moving bubble is sufficiently close to bubble b hence moving bubble should come to rest in slot ij". A game like this could be probably be made with a relatively crude grid structure as the primary data structure. However it seems like answering "which bubbles (if any) should fall now?" would be trickier with this data structure.

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  • Scene graphs and spatial partitioning structures: What do you really need?

    - by tapirath
    I've been fiddling with 2D games for awhile and I'm trying to go into 3D game development. I thought I should get my basics right first. From what I read scene graphs hold your game objects/entities and their relation to each other like 'a tire' would be the child of 'a vehicle'. It's mainly used for frustum/occlusion culling and minimizing the collision checks between the objects. Spatial partitioning structures on the other hand are used to divide a big game object (like the map) to smaller parts so that you can gain performance by only drawing the relevant polygons and again minimizing the collision checks to those polygons only. Also a spatial partitioning data structure can be used as a node in a scene graph. But... I've been reading about both subjects and I've seen a lot of "scene graphs are useless" and "BSP performance gain is irrelevant with modern hardware" kind of articles. Also some of the game engines I've checked like gameplay3d and jmonkeyengine are only using a scene graph (That also may be because they don't want to limit the developers). Whereas games like Quake and Half-Life only use spatial partitioning. I'm aware that the usage of these structures very much depend on the type of the game you're developing so for the sake of clarity let's assume the game is a FPS like Counter-Strike with some better outdoor environment capabilities (like a terrain). The obvious question is which one is needed and why (considering the modern hardware capabilities). Thank you.

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  • Working with lots of cubes. Improving performance?

    - by Randomman159
    Edit: To sum the question up, I have a voxel based world (Minecraft style (Thanks Communist Duck)) which is suffering from poor performance. I am not positive on the source but would like any possible advice on how to get rid of it. I am working on a project where a world consists of a large quantity of cubes (I would give you a number, but it is user defined worlds). My test one is around (48 x 32 x 48) blocks. Basically these blocks don't do anything in themselves. They just sit there. They start being used when it comes to player interaction. I need to check what cubes the users mouse interacts with (mouse over, clicking, etc.), and for collision detecting as the player moves. Now I had a massive amount of lag at first, looping through every block. I have managed to decrease that lag, by looping through all the blocks, and finding which blocks are within a particular range of the character, and then only looping through those blocks for the collision detection, etc. However, I am still going at a depressing 2fps. Does anyone have any other ideas on how I could decrease this lag? Btw, I am using XNA (C#) and yes, it is 3d.

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  • Tile sizes in 2D games

    - by Ephismen
    While developing a small game using tile-mapping method a question came to my mind: I would develop the game on Windows but wouldn't exclude adapting it to another platform. What size(in pixels) would you recommend using for creating the tiles of a tile-mapped game(ie: RPG) with the following requirements? Have an acceptable level of detail without having too many tiles. Having a decent map size. Allow adaptation of the game on a handheld(ie: PSP), smartphone or a computer without too much loss of detail or slowdowns. Allow more or less important zoom-in / zoom-out. Have a resolution of tile that permits either pixel-perfect collision or block-collision. Anything from a good explanation to a game example is useful as long as it can fit the requirements. This question may seem a bit simplistic, but I noticed that many Indies game developer were using inappropriate scales scenery. Also sorry for the poor syntax and the lack of vocabulary of my question, being a non-native English speaker doesn't help when talking about computers programming.

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  • colliding btRigidBody objects behave strangely when moving slowly

    - by Piku
    I'm trying to use Bullet Physics in my iOS game. The engine appears to be correctly compiled in that the demos work fine. In my game I have the player's ship and some enemy ships. They're defined as btRigidBody objects and btCollisionObjects and I'm using btSphereShapes for collision. At 'fast' speeds, collisions appear to happen sensibly - things collide and nothing goes 'weird'. If the speeds are very slow though and the player's ship touches a non-moving object the collision happens, but then the player's ship moves at incredible speed over the next few frames and appears a long distance from where it collided - completely out of proportion to the speed it was moving before impact. To move the things around I'm using setLinearVelocity() each frame, ticking the physics engine, then using getMotionState() to update the rendering code I have. Part of the issue might be I don't quite understand how to set the correct mass or what the best speeds are to use for anything. I'm mostly sticking numbers in and seeing what happens. Should I be using Bullet in this way, and are there any guidelines for deciding on the mass of objects? (am I right in assuming that in collisions heavier objects will force lighter objects to move more)

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  • What's the safest online password system?

    - by Darian Miller
    It's so difficult to track dozens of passwords in different locations. Syncing fails from time to time and you end up with collision correction avoidance syndrome. Is there a single source of safe, online, commercial password storage anywhere? One that will be around for years to come and one that is truly safe enough to ensure protection?

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  • Best way to store a large amount of game objects and update the ones onscreen

    - by user3002473
    Good afternoon guys! I'm a young beginner game developer working on my first large scale game project and I've run into a situation where I'm not quite sure what the best solution may be (if there is a lone solution). The question may be vague (if anyone can think of a better title after having read the question, please edit it) or broad but I'm not quite sure what to do and I thought it would help just to discuss the problem with people more educated in the field. Before we get started, here are some of the questions I've looked at for help in the past: Best way to keep track of game objects Elegant way to simulate large amounts of entities within a game world What is the most efficient container to store dynamic game objects in? I've also read articles about different data structures commonly used in games to store game objects such as this one about slot maps, but none of them are really what I'm looking for. Also, if it helps at all I'm using Python 3 to design the game. It has to be Python 3, if I could I would use C++ or Unityscript or something else, but I'm restricted to having to use Python 3. My game will be a form of side scroller shooter game. In said game the player will traverse large rooms with large amounts of enemies and other game objects to update (think some of the larger areas in Cave Story or Iji). The player obviously can't see the entire room all at once, so there is a viewport that follows the player around and renders only a selection of the room and the game objects that it contains. This is not a foreign concept. The part that's getting me confused has to do with how certain game objects are updated. Some of them are to be updated constantly, regardless of whether or not they can be seen. Other objects however are only to be updated when they are onscreen (for example, an enemy would only be updated to react to the player when it is onscreen or when it is in a certain range of the screen). Another problem is that game objects have to be easily referable by other game objects; something that happens in the player's update() method may affect another object in the world. Collision detection in games is always a serious problem. I need a way of containing the game objects such that it minimizes the number of cases when testing for collisions against one another. The final problem is that of creating and destroying game objects. I think this problem is pretty self explanatory. To store the game objects then I've considered a number of different methods. The original method I had was to simply store all the objects in a hash table by an id. This method was simple, and decently fast as it allows all the objects to be looked up in O(1) complexity, and also allows them to be deleted fairly easily. Hash collisions would not be a major problem; I wasn't originally planning on using computer generated ids to store the game objects I was going to rely on them all using ids given to them by the game designer (such names would be strings like 'Player' or 'EnemyWeapon4'), and even if I did use computer generated ids, if I used a decent hashing algorithm then the chances of collisions would be around 1 in 4 billion. The problem with using a hash table however is that it is inefficient in checking to see what objects are in range of the viewport. Considering the fact that certain game objects move (as well as the viewport itself), the only solution I could think of in order to only update objects that are in the viewport would be to iterate through every object in the hash table and check if it is in the viewport or not, updating only the ones that are in the valid area. This would be incredibly slow in scenarios where the amount of game objects exceeds 500, or even 200. The second solution was to store everything in a 2-d list. The world is partitioned up into cells (a tilemap essentially), where each cell or tile is the same size and is square. Each cell would contain a list of the game objects that are currently occupying it (each game object would be inserted into a cell depending on the center of the object's collision mask). A 2-d list would allow me to take the top-left and bottom-right corners of the viewport and easily grab a rectangular area of the grid containing only the cells containing entities that are in valid range to be updated. This method also solves the problem of collision detection; when I take an entity I can find the cell that it is currently in, then check only against entities in it's cell and the 8 cells around it. One problem with this system however is that it prohibits easy lookup of game objects. One solution I had would be to simultaneously keep a hash table that would contain all the positions of the objects in the 2-d list indexed by the id of said object. The major problem with a 2-d list is that it would need to be rebuilt every single game frame (along with the hash table of object positions), which may be a serious detriment to game speed. Both systems have ups and downs and seem to solve some of each other's problems, however using them both together doesn't seem like the best solution either. If anyone has any thoughts, ideas, suggestions, comments, opinions or solutions on new data structures or better implementations of the existing data structures I have in mind, please post, any and all criticism and help is welcome. Thanks in advance! EDIT: Please don't close the question because it has a bad title, I'm just bad with names!

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  • Storage and BackUp Strategies

    - by Chandra Vennapoosa
    Many of us are familiar with backing up our data.  While it sounds pretty simple, the fact is that most of the computer users do not backup their data. Some of the excuses which they often make involve how long it takes, how slow it is, or how many DVDs or disks they need. However, once disaster strikes, the loss that you will suffer by not having your data backed up can be very severe. Topics Introduction What is an Online Back Up? Online Back Up Strategies Implementing Disaster Avoidance Implementation and Storage Security Issues to Consider Reader complete article : Storage and BackUp Strategies

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  • Creating a new instance, C#

    - by Dave Voyles
    This sounds like a very n00b question, but bear with me here: I'm trying to access the position of my bat (paddle) in my pong game and use it in my ball class. I'm doing this because I want a particle effect to go off at the point of contact where the ball hits the bat. Each time the ball hits the bat, I receive an error stating that I haven't created an instance of the bat. I understand that I have to (or can use a static class), but I'm not sure of how to do so in this example. I've included both my Bat and Ball classes. namespace Pong { #region Using Statements using System; using System.Collections.Generic; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Audio; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.Graphics; using Microsoft.Xna.Framework.Input; #endregion public class Ball { #region Fields private readonly Random rand; private readonly Texture2D texture; private readonly SoundEffect warp; private double direction; private bool isVisible; private float moveSpeed; private Vector2 position; private Vector2 resetPos; private Rectangle size; private float speed; private bool isResetting; private bool collided; private Vector2 oldPos; private ParticleEngine particleEngine; private ContentManager contentManager; private SpriteBatch spriteBatch; private bool hasHitBat; private AIBat aiBat; private Bat bat; #endregion #region Constructors and Destructors /// <summary> /// Constructor for the ball /// </summary> public Ball(ContentManager contentManager, Vector2 ScreenSize) { moveSpeed = 15f; speed = 0; texture = contentManager.Load<Texture2D>(@"gfx/balls/redBall"); direction = 0; size = new Rectangle(0, 0, texture.Width, texture.Height); resetPos = new Vector2(ScreenSize.X / 2, ScreenSize.Y / 2); position = resetPos; rand = new Random(); isVisible = true; hasHitBat = false; // Everything to do with particles List<Texture2D> textures = new List<Texture2D>(); textures.Add(contentManager.Load<Texture2D>(@"gfx/particle/circle")); textures.Add(contentManager.Load<Texture2D>(@"gfx/particle/star")); textures.Add(contentManager.Load<Texture2D>(@"gfx/particle/diamond")); particleEngine = new ParticleEngine(textures, new Vector2()); } #endregion #region Public Methods and Operators /// <summary> /// Checks for the collision between the bat and the ball. Sends ball in the appropriate /// direction /// </summary> public void BatHit(int block) { if (direction > Math.PI * 1.5f || direction < Math.PI * 0.5f) { hasHitBat = true; particleEngine.EmitterLocation = new Vector2(aiBat.Position.X, aiBat.Position.Y); switch (block) { case 1: direction = MathHelper.ToRadians(200); break; case 2: direction = MathHelper.ToRadians(195); break; case 3: direction = MathHelper.ToRadians(180); break; case 4: direction = MathHelper.ToRadians(180); break; case 5: direction = MathHelper.ToRadians(165); break; } } else { hasHitBat = true; particleEngine.EmitterLocation = new Vector2(bat.Position.X, bat.Position.Y); switch (block) { case 1: direction = MathHelper.ToRadians(310); break; case 2: direction = MathHelper.ToRadians(345); break; case 3: direction = MathHelper.ToRadians(0); break; case 4: direction = MathHelper.ToRadians(15); break; case 5: direction = MathHelper.ToRadians(50); break; } } if (rand.Next(2) == 0) { direction += MathHelper.ToRadians(rand.Next(3)); } else { direction -= MathHelper.ToRadians(rand.Next(3)); } AudioManager.Instance.PlaySoundEffect("hit"); } /// <summary> /// JEP - added method to slow down ball after powerup deactivates /// </summary> public void DecreaseSpeed() { moveSpeed -= 0.6f; } /// <summary> /// Draws the ball on the screen /// </summary> public void Draw(SpriteBatch spriteBatch) { if (isVisible) { spriteBatch.Begin(); spriteBatch.Draw(texture, size, Color.White); spriteBatch.End(); // Draws sprites for particles when contact is made particleEngine.Draw(spriteBatch); } } /// <summary> /// Checks for the current direction of the ball /// </summary> public double GetDirection() { return direction; } /// <summary> /// Checks for the current position of the ball /// </summary> public Vector2 GetPosition() { return position; } /// <summary> /// Checks for the current size of the ball (for the powerups) /// </summary> public Rectangle GetSize() { return size; } /// <summary> /// Grows the size of the ball when the GrowBall powerup is used. /// </summary> public void GrowBall() { size = new Rectangle(0, 0, texture.Width * 2, texture.Height * 2); } /// <summary> /// Was used to increased the speed of the ball after each point is scored. /// No longer used, but am considering implementing again. /// </summary> public void IncreaseSpeed() { moveSpeed += 0.6f; } /// <summary> /// Check for the ball to return normal size after the Powerup has expired /// </summary> public void NormalBallSize() { size = new Rectangle(0, 0, texture.Width, texture.Height); } /// <summary> /// Check for the ball to return normal speed after the Powerup has expired /// </summary> public void NormalSpeed() { moveSpeed += 15f; } /// <summary> /// Checks to see if ball went out of bounds, and triggers warp sfx /// </summary> public void OutOfBounds() { // Checks if the player is still alive or not if (isResetting) { AudioManager.Instance.PlaySoundEffect("warp"); { // Used to stop the the issue where the ball hit sfx kept going off when detecting collison isResetting = false; AudioManager.Instance.Dispose(); } } } /// <summary> /// Speed for the ball when Speedball powerup is activated /// </summary> public void PowerupSpeed() { moveSpeed += 20.0f; } /// <summary> /// Check for where to reset the ball after each point is scored /// </summary> public void Reset(bool left) { if (left) { direction = 0; } else { direction = Math.PI; } // Used to stop the the issue where the ball hit sfx kept going off when detecting collison isResetting = true; position = resetPos; // Resets the ball to the center of the screen isVisible = true; speed = 15f; // Returns the ball back to the default speed, in case the speedBall was active if (rand.Next(2) == 0) { direction += MathHelper.ToRadians(rand.Next(30)); } else { direction -= MathHelper.ToRadians(rand.Next(30)); } } /// <summary> /// Shrinks the ball when the ShrinkBall powerup is activated /// </summary> public void ShrinkBall() { size = new Rectangle(0, 0, texture.Width / 2, texture.Height / 2); } /// <summary> /// Stops the ball each time it is reset. Ex: Between points / rounds /// </summary> public void Stop() { isVisible = true; speed = 0; } /// <summary> /// Updates position of the ball /// </summary> public void UpdatePosition() { size.X = (int)position.X; size.Y = (int)position.Y; oldPos.X = position.X; oldPos.Y = position.Y; position.X += speed * (float)Math.Cos(direction); position.Y += speed * (float)Math.Sin(direction); bool collided = CheckWallHit(); particleEngine.Update(); // Stops the issue where ball was oscillating on the ceiling or floor if (collided) { position.X = oldPos.X + speed * (float)Math.Cos(direction); position.Y = oldPos.Y + speed * (float)Math.Sin(direction); } } #endregion #region Methods /// <summary> /// Checks for collision with the ceiling or floor. 2*Math.pi = 360 degrees /// </summary> private bool CheckWallHit() { while (direction > 2 * Math.PI) { direction -= 2 * Math.PI; return true; } while (direction < 0) { direction += 2 * Math.PI; return true; } if (position.Y <= 0 || (position.Y > resetPos.Y * 2 - size.Height)) { direction = 2 * Math.PI - direction; return true; } return true; } #endregion } } namespace Pong { using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.Graphics; using System; public class Bat { public Vector2 Position; public float moveSpeed; public Rectangle size; private int points; private int yHeight; private Texture2D leftBat; public float turbo; public float recharge; public float interval; public bool isTurbo; /// <summary> /// Constructor for the bat /// </summary> public Bat(ContentManager contentManager, Vector2 screenSize, bool side) { moveSpeed = 7f; turbo = 15f; recharge = 100f; points = 0; interval = 5f; leftBat = contentManager.Load<Texture2D>(@"gfx/bats/batGrey"); size = new Rectangle(0, 0, leftBat.Width, leftBat.Height); // True means left bat, false means right bat. if (side) Position = new Vector2(30, screenSize.Y / 2 - size.Height / 2); else Position = new Vector2(screenSize.X - 30, screenSize.Y / 2 - size.Height / 2); yHeight = (int)screenSize.Y; } public void IncreaseSpeed() { moveSpeed += .5f; } /// <summary> /// The speed of the bat when Turbo is activated /// </summary> public void Turbo() { moveSpeed += 8.0f; } /// <summary> /// Returns the speed of the bat back to normal after Turbo is deactivated /// </summary> public void DisableTurbo() { moveSpeed = 7.0f; isTurbo = false; } /// <summary> /// Returns the bat to the nrmal size after the Grow/Shrink powerup has expired /// </summary> public void NormalSize() { size = new Rectangle(0, 0, leftBat.Width, leftBat.Height); } /// <summary> /// Checks for the size of the bat /// </summary> public Rectangle GetSize() { return size; } /// <summary> /// Adds point to the player or the AI after scoring. Currently Disabled. /// </summary> public void IncrementPoints() { points++; } /// <summary> /// Checks for the number of points at the moment /// </summary> public int GetPoints() { return points; } /// <summary> /// Sets thedefault starting position for the bats /// </summary> /// <param name="position"></param> public void SetPosition(Vector2 position) { if (position.Y < 0) { position.Y = 0; } if (position.Y > yHeight - size.Height) { position.Y = yHeight - size.Height; } this.Position = position; } /// <summary> /// Checks for the current position of the bat /// </summary> public Vector2 GetPosition() { return Position; } /// <summary> /// Controls the bat moving up the screen /// </summary> public void MoveUp() { SetPosition(Position + new Vector2(0, -moveSpeed)); } /// <summary> /// Controls the bat moving down the screen /// </summary> public void MoveDown() { SetPosition(Position + new Vector2(0, moveSpeed)); } /// <summary> /// Updates the position of the AI bat, in order to track the ball /// </summary> /// <param name="ball"></param> public virtual void UpdatePosition(Ball ball) { size.X = (int)Position.X; size.Y = (int)Position.Y; } /// <summary> /// Resets the bat to the center location after a new game starts /// </summary> public void ResetPosition() { SetPosition(new Vector2(GetPosition().X, yHeight / 2 - size.Height)); } /// <summary> /// Used for the Growbat powerup /// </summary> public void GrowBat() { // Doubles the size of the bat collision size = new Rectangle(0, 0, leftBat.Width * 2, leftBat.Height * 2); } /// <summary> /// Used for the Shrinkbat powerup /// </summary> public void ShrinkBat() { // 1/2 the size of the bat collision size = new Rectangle(0, 0, leftBat.Width / 2, leftBat.Height / 2); } /// <summary> /// Draws the bats /// </summary> public virtual void Draw(SpriteBatch batch) { batch.Draw(leftBat, size, Color.White); } } }

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  • Do Not Track Plus Stops Web Sites from Tracking You

    - by Jason Fitzpatrick
    Do Not Track Plus is a Firefox extension that combines the do-non’t-track header with protection lists for comprehensive tracking avoidance while surfing the web. Unlike all-or-nothing no tracking flags, the Do Not Track Plus extension for Firefox allows you to set white and black lists for websites you would prefer to be tracked or not tracked by. You may, for example, want a shopping site you get benefits from or a news site that gives you customized articles to be allowed to track you. The tool also preserves anti-tracking cookies even when you wipe the rest of the cookies in your browser’s cache; effectively stopping you from accidentally rescinding your opt out cookies from anti-tracking sites. Do Not Track Plus [Abine via Wired] How to Enable Google Chrome’s Secret Gold IconHTG Explains: What’s the Difference Between the Windows 7 HomeGroups and XP-style Networking?Internet Explorer 9 Released: Here’s What You Need To Know

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  • List of eCommerce sites that use end-to-end SSL?

    - by Jon Schneider
    My development team is considering implementing an eCommerce site using end-to-end SSL -- that is, every page on the site is accessed via an https:// URL -- rather than the more traditional "mixed mode" where most pages are accessed via http:// and only "secure" pages such as login and credit card entry are redirected to https://. Pros of doing such a "pure SSL" approach include avoidance of some session-hijacking attacks such as Firesheep; cons include performance considerations. My question is: Is anyone aware of a list of eCommerce websites (especially USA-based sites), or even specific websites, that use this end-to-end SSL approach? I'm especially interested in "regular" eCommerce sites rather than banks or other "financial" sites.

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  • Rules of Holes #5: Seek Help to Get Out of the Hole

    - by ArnieRowland
    You are moving along, doing good work, maintaining a steady pace. All seems to be going well for you. Then BAM!, a Hole just grabbed you. How the heck did that happen? What went wrong? How did you fall into a Hole? Definitely, you will want to do a post-mortem and try to tease out what misteps led you into the Hole. Certainly you will want to use this opportunity to enhance your Hole avoidance skills. But your first priority is to get out of this Hole right NOW.. Consider the Fifth Rule of Holes...(read more)

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  • Rules of Holes #5: Seek Help to Get Out of the Hole

    - by ArnieRowland
    You are moving along, doing good work, maintaining a steady pace. All seems to be going well for you. Then BAM!, a Hole just grabbed you. How the heck did that happen? What went wrong? How did you fall into a Hole? Definitely, you will want to do a post-mortem and try to tease out what misteps led you into the Hole. Certainly you will want to use this opportunity to enhance your Hole avoidance skills. But your first priority is to get out of this Hole right NOW.. Consider the Fifth Rule of Holes...(read more)

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  • Rules of Holes #2: You Are Still in a Hole

    - by ArnieRowland
    OK. So you followed the First Rule of Holes -you stopped digging yourself in deeper. But now what? You are still in a Hole. Your situation has not changed much, but at least you are no longer making it worse. You need to redirect the digging effort into escape and avoidance efforts. The Hole has a singular purpose -consuming all of your time and effort. AND it has succeeded! But now you are going to redirect your efforts for your own survival. You have encountered the Second Rule of Holes: When you...(read more)

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  • Is there a language offering LISP-like macros with a more complex syntax?

    - by blubb
    LISP's macros are extremely powerful constructs, and the inability to introspect and modify the program itself beyond the method signature level has always struck me as a limitation. Yet I favour "complex" syntax because it tends to be closer to natural language. So far I have failed to find a language which combines a powerful macro mechanism such as LISP's with a naturally looking syntax (1). Is anyone aware of such a language? Footnote: I would consider python to have a naturally looking syntax as it allows constructs like this: if 0 < a < 5 and b in list. The avoidance of braces to structure blocks is irrelevant in this case, though.

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  • Rules of Holes -#2: You Are Still in a Hole

    - by ArnieRowland
    OK. So you followed the First Rule of Holes -you stopped digging yourself in deeper. But now what? You are still in a Hole. Your situation has not changed much, but at least you are no longer making it worse. You need to redirect the digging effort into escape and avoidance efforts. The Hole has a singular purpose -consuming all of your time and effort. AND it has succeeded! But now you are going to redirect your efforts for your own survival. You need to look around, take stock of the situation....(read more)

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  • Exploring TCP throughput with DTrace (2)

    - by user12820842
    Last time, I described how we can use the overlap in distributions of unacknowledged byte counts and send window to determine whether the peer's receive window may be too small, limiting throughput. Let's combine that comparison with a comparison of congestion window and slow start threshold, all on a per-port/per-client basis. This will help us Identify whether the congestion window or the receive window are limiting factors on throughput by comparing the distributions of congestion window and send window values to the distribution of outstanding (unacked) bytes. This will allow us to get a visual sense for how often we are thwarted in our attempts to fill the pipe due to congestion control versus the peer not being able to receive any more data. Identify whether slow start or congestion avoidance predominate by comparing the overlap in the congestion window and slow start distributions. If the slow start threshold distribution overlaps with the congestion window, we know that we have switched between slow start and congestion avoidance, possibly multiple times. Identify whether the peer's receive window is too small by comparing the distribution of outstanding unacked bytes with the send window distribution (i.e. the peer's receive window). I discussed this here. # dtrace -s tcp_window.d dtrace: script 'tcp_window.d' matched 10 probes ^C cwnd 80 10.175.96.92 value ------------- Distribution ------------- count 1024 | 0 2048 | 4 4096 | 6 8192 | 18 16384 | 36 32768 |@ 79 65536 |@ 155 131072 |@ 199 262144 |@@@ 400 524288 |@@@@@@ 798 1048576 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 3848 2097152 | 0 ssthresh 80 10.175.96.92 value ------------- Distribution ------------- count 268435456 | 0 536870912 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 5543 1073741824 | 0 unacked 80 10.175.96.92 value ------------- Distribution ------------- count -1 | 0 0 | 1 1 | 0 2 | 0 4 | 0 8 | 0 16 | 0 32 | 0 64 | 0 128 | 0 256 | 3 512 | 0 1024 | 0 2048 | 4 4096 | 9 8192 | 21 16384 | 36 32768 |@ 78 65536 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 5391 131072 | 0 swnd 80 10.175.96.92 value ------------- Distribution ------------- count 32768 | 0 65536 |@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 5543 131072 | 0 Here we are observing a large file transfer via http on the webserver. Comparing these distributions, we can observe: That slow start congestion control is in operation. The distribution of congestion window values lies below the range of slow start threshold values (which are in the 536870912+ range), so the connection is in slow start mode. Both the unacked byte count and the send window values peak in the 65536-131071 range, but the send window value distribution is narrower. This tells us that the peer TCP's receive window is not closing. The congestion window distribution peaks in the 1048576 - 2097152 range while the receive window distribution is confined to the 65536-131071 range. Since the cwnd distribution ranges as low as 2048-4095, we can see that for some of the time we have been observing the connection, congestion control has been a limiting factor on transfer, but for the majority of the time the receive window of the peer would more likely have been the limiting factor. However, we know the window has never closed as the distribution of swnd values stays within the 65536-131071 range. So all in all we have a connection that has been mildly constrained by congestion control, but for the bulk of the time we have been observing it neither congestion or peer receive window have limited throughput. Here's the script: #!/usr/sbin/dtrace -s tcp:::send / (args[4]-tcp_flags & (TH_SYN|TH_RST|TH_FIN)) == 0 / { @cwnd["cwnd", args[4]-tcp_sport, args[2]-ip_daddr] = quantize(args[3]-tcps_cwnd); @ssthresh["ssthresh", args[4]-tcp_sport, args[2]-ip_daddr] = quantize(args[3]-tcps_cwnd_ssthresh); @unacked["unacked", args[4]-tcp_sport, args[2]-ip_daddr] = quantize(args[3]-tcps_snxt - args[3]-tcps_suna); @swnd["swnd", args[4]-tcp_sport, args[2]-ip_daddr] = quantize((args[4]-tcp_window)*(1 tcps_snd_ws)); } One surprise here is that slow start is still in operation - one would assume that for a large file transfer, acknowledgements would push the congestion window up past the slow start threshold over time. The slow start threshold is in fact still close to it's initial (very high) value, so that would suggest we have not experienced any congestion (the slow start threshold is adjusted when congestion occurs). Also, the above measurements were taken early in the connection lifetime, so the congestion window did not get a changes to get bumped up to the level of the slow start threshold. A good strategy when examining these sorts of measurements for a given service (such as a webserver) would be start by examining the distributions above aggregated by port number only to get an overall feel for service performance, i.e. is congestion control or peer receive window size an issue, or are we unconstrained to fill the pipe? From there, the overlap of distributions will tell us whether to drill down into specific clients. For example if the send window distribution has multiple peaks, we may want to examine if particular clients show issues with their receive window.

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  • Limit scope of #define

    - by Ujjwal Singh
    What is the correct strategy to limit the scope of #define and avoid unwarrented token collisions. In the following configuration: Main.c # include "Utility_1.h" # include "Utility_2.h" VOID Utility() // Was written without knowing of: Utility_1 & Utility_2 { const UINT ZERO = 0; } VOID Main() { ... } // Collision; for Line:5 Compiler does not indicate what replaced Utility_1.h # define ZERO "Zero" # define ONE "One" BOOL Utility_1(); Utility_2.h # define ZERO '0' # define ONE '1' BOOL Utility_2(); Utility_2.c # include "Utility_2.h" BOOL Utility_2() { // Using: ZERO & ONE } //Collision: Character Literal replaced with String {Edit} Note: This is supposed to be a generic quesition so do not limit yourself to enum or other defined types. i.e. What to do when: I MUST USE #define Please comment on my proposed solution below.. _

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  • Teacher confused about MVC?

    - by Gideon
    I have an assignment to create a game in java using MVC as a pattern. The thing is that stuff I read about MVC aren't really what the teacher is telling me. What I read is that the Model are the information objects, they are manipulated by the controllers. So in a game the controller mutates the placement of the objects and check if there is any collision etc. What my teacher told me is that I should put everything that is universal to the platform in the models and the controllers should only tell the model which input is given. That means the game loop will be in a model class, but also collision checks etc. So what I get from his story is that the View is the screen, the Controller is the unput handeler, and the Model is the rest. Can someone point me in the right direction?

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  • Writing a Python extension in Go (golang)

    - by tehwalrus
    I currently use Cython to link C and Python, and get speedup in slow bits of python code. However, I'd like to use go routines to implement a really slow (and very parallelizable) bit of code, but it must be callable from python. (I've already seen this question) I'm (sort of) happy to go via C (or Cython) to set up data structures etc if necessary, but avoiding this extra layer would be good from a bug fix/avoidance point of view. What is the simplest way to do this without having to reinvent any wheels?

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