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  • Database Context and Singleton injection with IoC

    - by zaitsman
    All of the below relates to a ASP.NET c# app. I have a Singleton Settings MemoryCache that reads values from database on first access and caches these, then invalidates them using SQL Service Broker message and re-reads as required. For the purposes of standard controllers, i create my Db Context in a request scope. However, this obviously means that i can't use the same context in the Settings Cache class, since that is a singleton and we have a scope collision. At the moment, i ended up with two db contexts - the Controllers get it via IoC container, whereas a Singleton just creates it's own. However, i am not satisfied with this approach (mostly due to the way i feel about two contexts, the cache doesn't set anything on the db hence concurrency is not an issue as much). What is a better way to do it?

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  • Sound Delay With AVAudio Player

    - by Will Youmans
    I'm using the following code in my viewDidLoad to load a sound: NSURL * url = [NSURL fileURLWithPath: [NSString stringWithFormat:@"%@/Moto - Hit Sound.mp3", [[NSBundle mainBundle] resourcePath]]]; NSError * error; hitSoundPlayer = [[AVAudioPlayer alloc]initWithContentsOfURL:url error:&error]; hitSoundPlayer.numberOfLoops = 0; Then I'm using this in a void method to play the sound: if(CGRectIntersectsRect(main.frame, enemy1.frame)){ [hitSoundPlayer play]; } This does seem to work, however the first time the sound is played there is a lot of lag and the game stops temporarily. I'm using this same method for when in an IBAction and it works fine, it must be the fact that it's also detecting a collision that makes the sound lag. If I want to be able to play sounds quickly and on the spot without any sort of lag am I doing the right thing? Do I want to use another method? I'm not using any frameworks like cocos2d. If you need to see any more code just ask.

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  • XNA tempory pause

    - by Marivs
    I need to do a temporary pause. If I do a collision with an enemy I want to pause the game for 1.5 seconds. Take a look here to my code: bool tPause; float timer; public ovveride Update(GameTime gameTime) { if(!tPause) { //... if(enemy.rectangle.Intersects(player.rectangle)) { timer+=(float)gameTime.ElapsedGameTime.TotalMilliseconds; tPause=true; if(timer>1500) { tPause=false; timer=0; } } //... } } It doesn't function.

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  • Convert URI to GUID

    - by David Rutten
    What is a good way to convert a file path (URI) into a System.Guid? I'd like to minimize the possibility of a collision, but I'm happy with a reasonably unique hashing (probably never more than a few dozen/hundred items in the database)

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  • Graphical sandbox for pathfinding

    - by vrode
    If you needed a clean and consistent sandbox for pathfinding what would you use? I want to experiment with different pathfinding algorithms by sending virtual units (robots) around obstacles on a geometric plane. But I don't need a feature overkill like a game engine or Flash might have, just an animated report and native collision detector. I prefer it to be scripted in python, but if there are java or C++ alternatives I would appreciate them as well.

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  • Are there any ball tracking algorithms/patterns around in game programming

    - by user214626
    Hello, I am a newbie to game programming,I would need the suggestions and help of the wonderful people around here. I have set of players, and a ball, the players can kick the ball around the ground (not yet a football game, neither a foosball game too ).Are there any algorithms/ patterns for addressing the problems with tracking the ball and taking decisions, Is that too much to ask.What I was looking at is something like a collision detection algorithm for the common problem of 2 objects interacting with one another.

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  • Short Python alphanumeric hash with minimal collisions

    - by ensnare
    I'd like to set non-integer primary keys for a table using some kind of hash function. md5() seems to be kind of long (32-characters). What are some alternative hash functions that perhaps use every letter in the alphabet as well as integers that are perhaps shorter in string length and have low collision rates? Thanks!

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  • How to detect if an ellipse intersects(collides with) a circle

    - by php html
    I want to improve a collision system. Right now I detect if 2 irregular objects collide if their bounding rectangles collide. I want to obtain the for rectangle the corresponding ellipse while for the other one to use a circle. I found a method to obtain the ellipse coordinates but I have a problem when I try to detect if it intersects the circle. Do you know a algorithm to test if a circle intersects an ellipse?

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  • Is SPLFileObject atomic?

    - by Jakub Lédl
    I'm wondering whether methods of PHPs SPLFileObject are atomic (e.g. thread-safe) or not? If they aren't, I'll implement my own class, which will use flock(), but is this enough? Is the flock function really thread-safe? What if the collision occurs after I fopen() the file, but before I flock() it?

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  • Setting the origin to center of the screen instead of the top left screen?(iPhone)

    - by thyrgle
    Hi, I am working on an iPhone app and I am trying to make something that has to do with line-circle collision detection. I am using the slope of the line and checking if the coordinates of a circle suffice the equation y = mx + b. But, with the current origin (0,0) at the top left it is a pain to get the slope. Any way I can convert the coordinates so the origin is in the center of the screen?

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  • Removing entry from table

    - by Bnhjhvbq7
    Can't remove an entry from table. here's my code dropItem = dropList[ math.random( #dropList ) ] dropSomething[brick.index] = crackSheet:grabSprite(dropItem, true) dropSomething[brick.index].x = brick.x dropSomething[brick.index].y = brick.y dropSomething[brick.index].name = dropItem dropSomething[brick.index].type = "dropppedItems" collision function bounce(event) local item = event.other if item.type == "dropppedItems" then if item.name == "bomb" then Lives = Lives - 1 LivesNum.text = tostring(Lives) end item:removeSelf(); end end What I've tried: item:removeSelf(); - removes the whole table item = nil - seams to do nothing, the object continue to move and i still see the image

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  • Determining if two lines intersect

    - by Faken
    I have two lines that extend to infinity but both have a starting point. They are both described by a starting point and a vector in the direction of the line extending to infinity. I want to find out if the two lines intersect but i don't need to know where they intersect (its part of a collision detection algorithm). Everything i have looked at so far describes finding the intersection point of two lines or line segments. Anyone know a fast algorithm to solve this?

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  • What's the big deal with brute force on hashes like MD5

    - by Jan Kuboschek
    I just spent some time reading http://stackoverflow.com/questions/2768248/is-md5-really-that-bad (I highly recommend!). In it, it talks about hash collisions. Maybe I'm missing something here, but can't you just encrypt your password using, say, MD5 and then, say, SHA-1 (or any other, doesn't matter.) Wouldn't this increase the processing power required to brute-force the hash and reduce the possibility of collision?

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  • Movement prediction for non-shooters

    - by ShadowChaser
    I'm working on an isometric 2D game with moderate-scale multiplayer, approximately 20-30 players connected at once to a persistent server. I've had some difficulty getting a good movement prediction implementation in place. Physics/Movement The game doesn't have a true physics implementation, but uses the basic principles to implement movement. Rather than continually polling input, state changes (ie/ mouse down/up/move events) are used to change the state of the character entity the player is controlling. The player's direction (ie/ north-east) is combined with a constant speed and turned into a true 3D vector - the entity's velocity. In the main game loop, "Update" is called before "Draw". The update logic triggers a "physics update task" that tracks all entities with a non-zero velocity uses very basic integration to change the entities position. For example: entity.Position += entity.Velocity.Scale(ElapsedTime.Seconds) (where "Seconds" is a floating point value, but the same approach would work for millisecond integer values). The key point is that no interpolation is used for movement - the rudimentary physics engine has no concept of a "previous state" or "current state", only a position and velocity. State Change and Update Packets When the velocity of the character entity the player is controlling changes, a "move avatar" packet is sent to the server containing the entity's action type (stand, walk, run), direction (north-east), and current position. This is different from how 3D first person games work. In a 3D game the velocity (direction) can change frame to frame as the player moves around. Sending every state change would effectively transmit a packet per frame, which would be too expensive. Instead, 3D games seem to ignore state changes and send "state update" packets on a fixed interval - say, every 80-150ms. Since speed and direction updates occur much less frequently in my game, I can get away with sending every state change. Although all of the physics simulations occur at the same speed and are deterministic, latency is still an issue. For that reason, I send out routine position update packets (similar to a 3D game) but much less frequently - right now every 250ms, but I suspect with good prediction I can easily boost it towards 500ms. The biggest problem is that I've now deviated from the norm - all other documentation, guides, and samples online send routine updates and interpolate between the two states. It seems incompatible with my architecture, and I need to come up with a better movement prediction algorithm that is closer to a (very basic) "networked physics" architecture. The server then receives the packet and determines the players speed from it's movement type based on a script (Is the player able to run? Get the player's running speed). Once it has the speed, it combines it with the direction to get a vector - the entity's velocity. Some cheat detection and basic validation occurs, and the entity on the server side is updated with the current velocity, direction, and position. Basic throttling is also performed to prevent players from flooding the server with movement requests. After updating its own entity, the server broadcasts an "avatar position update" packet to all other players within range. The position update packet is used to update the client side physics simulations (world state) of the remote clients and perform prediction and lag compensation. Prediction and Lag Compensation As mentioned above, clients are authoritative for their own position. Except in cases of cheating or anomalies, the client's avatar will never be repositioned by the server. No extrapolation ("move now and correct later") is required for the client's avatar - what the player sees is correct. However, some sort of extrapolation or interpolation is required for all remote entities that are moving. Some sort of prediction and/or lag-compensation is clearly required within the client's local simulation / physics engine. Problems I've been struggling with various algorithms, and have a number of questions and problems: Should I be extrapolating, interpolating, or both? My "gut feeling" is that I should be using pure extrapolation based on velocity. State change is received by the client, client computes a "predicted" velocity that compensates for lag, and the regular physics system does the rest. However, it feels at odds to all other sample code and articles - they all seem to store a number of states and perform interpolation without a physics engine. When a packet arrives, I've tried interpolating the packet's position with the packet's velocity over a fixed time period (say, 200ms). I then take the difference between the interpolated position and the current "error" position to compute a new vector and place that on the entity instead of the velocity that was sent. However, the assumption is that another packet will arrive in that time interval, and it's incredibly difficult to "guess" when the next packet will arrive - especially since they don't all arrive on fixed intervals (ie/ state changes as well). Is the concept fundamentally flawed, or is it correct but needs some fixes / adjustments? What happens when a remote player stops? I can immediately stop the entity, but it will be positioned in the "wrong" spot until it moves again. If I estimate a vector or try to interpolate, I have an issue because I don't store the previous state - the physics engine has no way to say "you need to stop after you reach position X". It simply understands a velocity, nothing more complex. I'm reluctant to add the "packet movement state" information to the entities or physics engine, since it violates basic design principles and bleeds network code across the rest of the game engine. What should happen when entities collide? There are three scenarios - the controlling player collides locally, two entities collide on the server during a position update, or a remote entity update collides on the local client. In all cases I'm uncertain how to handle the collision - aside from cheating, both states are "correct" but at different time periods. In the case of a remote entity it doesn't make sense to draw it walking through a wall, so I perform collision detection on the local client and cause it to "stop". Based on point #2 above, I might compute a "corrected vector" that continually tries to move the entity "through the wall" which will never succeed - the remote avatar is stuck there until the error gets too high and it "snaps" into position. How do games work around this?

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  • b2Body moves without stopping

    - by SentineL
    I got a quite strange bug. It is difficult to explain it in two words, but i'll try to do this in short. My b2Body has restitution, friction, density, mass and collision group. I controlling my b2Body via setting linear velocity to it (called on every iteration): (void)moveToDirection:(CGPoint)direction onlyHorizontal:(BOOL)horizontal { b2Vec2 velocity = [controlledObject getBody]-GetLinearVelocity(); double horizontalSpeed = velocity.x + controlledObject.acceleration * direction.x; velocity.x = (float32) (abs((int) horizontalSpeed) < controlledObject.runSpeed ? horizontalSpeed : controlledObject.maxSpeed * direction.x); if (!horizontal) { velocity.y = velocity.y + controlledObject.runSpeed * direction.y; } [controlledObject getBody]->SetLinearVelocity(velocity); } My floor is static b2Body, it has as restitution, friction, density, mass and same collision group in some reason, I'm setting b2Body's friction of my Hero to zero when it is moving, and returning it to 1 when he stops. When I'm pushing run button, hero runs. when i'm releasing it, he stops. All of this works perfect. On jumping, I'm setting linear velocity to my Hero: (void)jump { b2Vec2 velocity = [controlledObject getBody]->GetLinearVelocity(); velocity.y = velocity.y + [[AppDel cfg] getHeroJumpVlelocity]; [controlledObject getBody]->SetLinearVelocity(velocity); } If I'll run, jump, and release run button, while he is in air, all will work fine. And here is my problem: If I'll run, jump, and continue running on landing (or when he goes from one static body to another: there is small fall, probably), Hero will start move, like he has no friction, but he has! I checked this via beakpoints: he has friction, but I can move left of right, and he will never stop, until i'll jump (or go from one static body to another), with unpressed running button. I allready tried: Set friction to body on every iteration double-check am I setting friction to right fixture. set Linear Damping to Hero: his move slows down on gugged moveing. A little more code: I have a sensor and body fixtures in my hero: (void) addBodyFixture { b2CircleShape dynamicBox; dynamicBox.m_radius = [[AppDel cfg] getHeroRadius]; b2FixtureDef bodyFixtureDef; bodyFixtureDef.shape = &dynamicBox; bodyFixtureDef.density = 1.0f; bodyFixtureDef.friction = [[AppDel cfg] getHeroFriction]; bodyFixtureDef.restitution = [[AppDel cfg] getHeroRestitution]; bodyFixtureDef.filter.categoryBits = 0x0001; bodyFixtureDef.filter.maskBits = 0x0001; bodyFixtureDef.filter.groupIndex = 0; bodyFixtureDef.userData = [NSNumber numberWithInt:FIXTURE_BODY]; [physicalBody addFixture:bodyFixtureDef]; } (void) addSensorFixture { b2CircleShape sensorBox; sensorBox.m_radius = [[AppDel cfg] getHeroRadius] * 0.95; sensorBox.m_p.Set(0, -[[AppDel cfg] getHeroRadius] / 10); b2FixtureDef sensor; sensor.shape = &sensorBox; sensor.filter.categoryBits = 0x0001; sensor.filter.maskBits = 0x0001; sensor.filter.groupIndex = 0; sensor.isSensor = YES; sensor.userData = [NSNumber numberWithInt:FIXTURE_SENSOR]; [physicalBody addFixture:sensor]; } Here I'm tracking is hero in air: void FixtureContactListener::BeginContact(b2Contact* contact) { // We need to copy out the data because the b2Contact passed in // is reused. Squirrel *squirrel = (Squirrel *)contact->GetFixtureB()->GetBody()->GetUserData(); if (squirrel) { [squirrel addContact]; } } void FixtureContactListener::EndContact(b2Contact* contact) { Squirrel *squirrel = (Squirrel *)contact->GetFixtureB()->GetBody()->GetUserData(); if (squirrel) { [squirrel removeContact]; } } here is Hero's logic on contacts: - (void) addContact { if (contactCount == 0) [self landing]; contactCount++; } - (void) removeContact { contactCount--; if (contactCount == 0) [self flying]; if (contactCount <0) contactCount = 0; } - (void)landing { inAir = NO; acceleration = [[AppDel cfg] getHeroRunAcceleration]; [sprite stopAllActions]; (running ? [sprite runAction:[self runAction]] : [sprite runAction:[self standAction]]); } - (void)flying { inAir = YES; acceleration = [[AppDel cfg] getHeroAirAcceleration]; [sprite stopAllActions]; [self flyAction]; } here is Hero's moving logic: - (void)stop { running = NO; if (!inAir) { [sprite stopAllActions]; [sprite runAction:[self standAction]]; } } - (void)left { [physicalBody setFriction:0]; if (!running && !inAir) { [sprite stopAllActions]; [sprite runAction:[self runAction]]; } running = YES; moveingDirection = NO; [bodyControls moveToDirection:CGPointMake(-1, 0) onlyHorizontal:YES]; } - (void)right { [physicalBody setFriction:0]; if (!running && !inAir) { [sprite stopAllActions]; [sprite runAction:[self runAction]]; } running = YES; moveingDirection = YES; [bodyControls moveToDirection:CGPointMake(1, 0) onlyHorizontal:YES]; } - (void)jump { if (!inAir) { [bodyControls jump]; } } and here is my update method (called on every iteration): - (void)update:(NSMutableDictionary *)buttons { if (!isDead) { [self updateWithButtonName:BUTTON_LEFT inButtons:buttons whenPressed:@selector(left) whenUnpressed:@selector(stop)]; [self updateWithButtonName:BUTTON_RIGHT inButtons:buttons whenPressed:@selector(right) whenUnpressed:@selector(stop)]; [self updateWithButtonName:BUTTON_UP inButtons:buttons whenPressed:@selector(jump) whenUnpressed:@selector(nothing)]; [self updateWithButtonName:BUTTON_DOWN inButtons:buttons whenPressed:@selector(nothing) whenUnpressed:@selector(nothing)]; [sprite setFlipX:(moveingDirection)]; } [self checkPosition]; if (!running) [physicalBody setFriction:[[AppDel cfg] getHeroFriction]]; else [physicalBody setFriction:0]; } - (void)updateWithButtonName:(NSString *)buttonName inButtons:(NSDictionary *)buttons whenPressed:(SEL)pressedSelector whenUnpressed:(SEL)unpressedSelector { NSNumber *buttonNumber = [buttons objectForKey:buttonName]; if (buttonNumber == nil) return; if ([buttonNumber boolValue]) [self performSelector:pressedSelector]; else [self performSelector:unpressedSelector]; } - (void)checkPosition { b2Body *body = [self getBody]; b2Vec2 position = body->GetPosition(); CGPoint inWorldPosition = [[AppDel cfg] worldMeterPointFromScreenPixel:CGPointMake(position.x * PTM_RATIO, position.y * PTM_RATIO)]; if (inWorldPosition.x < 0 || inWorldPosition.x > WORLD_WIDGH / PTM_RATIO || inWorldPosition.y <= 0) { [self kill]; } }

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  • Remote I/O costs with a Content Delivery Network

    - by x711Li
    As far as I know, the time complexity of scanning a directory and the amount of files in said directory are correlated due to I/O costs. Would the administrative costs of placing the files in a hashed directory tree for uploading/downloading files through a CDN API be worth it for the added efficiency? For instance, given a filename foo.mp3, the MD5 hash for this is 10ebb1120767e9de166e0f5905077cb1. Thus, storing foo.mp3 in ./10/eb/foo.mp3 would allow for less files per directory (assuming MD5 generates patterns with in Base36, this allows for 36^2 root directories with 36^2 subdirectories each and little chance of hash collision) Considering the directories themselves are not loaded, would the I/O costs of directory scanning still exist with direct uploading/downloading?

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  • Why does Chrome show overlapping text?

    - by dog44wgm
    In Chrome, news articles at: http://www.theprovince.com with a leading photo and caption show the caption text overlapped with the body text. I have an image but as a new user here I'm not allowed to upload it. It happens at that site almost always, here's an example from today: http://www.theprovince.com/sports/Canucks+Blackhawks+collision+Titanic+proportions/5721421/story.html It rarely happens elsewhere. The same link works fine in Internet Explorer so I'm guessing it's a Chrome issue. It's been like this for many months, I read the site almost everyday. I click on "Print this Article" to get a proper look at it, but it's annoying, hope someone has the answer. Thanks in advance.

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  • Is SHA-1 secure for password storage?

    - by Tgr
    Some people throw around remarks like "SHA-1 is broken" a lot, so I'm trying to understand what exactly that means. Let's assume I have a database of SHA-1 password hashes, and an attacker whith a state of the art SHA-1 breaking algorithm and a botnet with 100,000 machines gets access to it. (Having control over 100k home computers would mean they can do about 10^15 operations per second.) How much time would they need to find out the password of any one user? find out the password of a given user? find out the password of all users? find a way to log in as one of the users? find a way to log in as a specific user? How does that change if the passwords are salted? Does the method of salting (prefix, postfix, both, or something more complicated like xor-ing) matter? Here is my current understanding, after some googling. Please correct in the answers if I misunderstood something. If there is no salt, a rainbow attack will immediately find all passwords (except extremely long ones). If there is a sufficiently long random salt, the most effective way to find out the passwords is a brute force or dictionary attack. Neither collision nor preimage attacks are any help in finding out the actual password, so cryptographic attacks against SHA-1 are no help here. It doesn't even matter much what algorithm is used - one could even use MD5 or MD4 and the passwords would be just as safe (there is a slight difference because computing a SHA-1 hash is slower). To evaluate how safe "just as safe" is, let's assume that a single sha1 run takes 1000 operations and passwords contain uppercase, lowercase and digits (that is, 60 characters). That means the attacker can test 1015*60*60*24 / 1000 ~= 1017 potential password a day. For a brute force attack, that would mean testing all passwords up to 9 characters in 3 hours, up to 10 characters in a week, up to 11 characters in a year. (It takes 60 times as much for every additional character.) A dictionary attack is much, much faster (even an attacker with a single computer could pull it off in hours), but only finds weak passwords. To log in as a user, the attacker does not need to find out the exact password; it is enough to find a string that results in the same hash. This is called a first preimage attack. As far as I could find, there are no preimage attacks against SHA-1. (A bruteforce attack would take 2160 operations, which means our theoretical attacker would need 1030 years to pull it off. Limits of theoretical possibility are around 260 operations, at which the attack would take a few years.) There are preimage attacks against reduced versions of SHA-1 with negligible effect (for the reduced SHA-1 which uses 44 steps instead of 80, attack time is down from 2160 operations to 2157). There are collision attacks against SHA-1 which are well within theoretical possibility (the best I found brings the time down from 280 to 252), but those are useless against password hashes, even without salting. In short, storing passwords with SHA-1 seems perfectly safe. Did I miss something?

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  • Simulating the effects of wind

    - by jernej
    I am developing a mobile game for Android. It is a 3D jumping game (like ski jump) where wind plays a important role so i need to simulate it. How could I achieve this? The game uses libgdx for rendering and a port of Bullet physics engine for physics. To simulate the jump I have 2 spheres which are placed at the start and at the end of the player and gravity is applied to them (they role down the hill and jump at the end). I use them to calculate the angle and the position of the player. If a button is pressed some extra y speed is applied to them (to simulate the jump before the end of the jumping ramp). But now I have to add wind to it. How is this usually done? Which collision box/method should I use? The way I understand it I only have to apply some force with direction to the player while in mid air. How can I do this in Bullet?

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