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• Alternatives to Pessimistic Locking in Cluster Applications

  - by amphibient

  I am researching alternatives to database-level pessimistic locking to achieve transaction isolation in a cluster of Java applications going against the same database. Synchronizing concurrent access in the application tier is clearly not a solution in the present configuration because the same database transaction can be invoked from multiple JVMs concurrently. Currently, we are subject to occasional race conditions which, due to the optimistic locking we have in place via Hibernate, cause a StaleObjectStateException exception and data loss. I have a moderately large transaction within the scope of my refactoring project. Let's describe it as updating one top-level table row and then making various related inserts and/or updates to several of its child entities. I would like to insure exclusive access to the top-level table row and all of the children to be affected but I would like to stay away from pessimistic locking at the database level for performance reasons mostly. We use Hibernate for ORM. Does it make sense to start a single (perhaps synchronous) message queue application into which this method could be moved to insure synchronized access as opposed to each cluster node using its own, which is a clear race condition hazard? I am mentioning this approach even though I am not confident in it because both the top-level table row and its children could also be updated from other system calls, not just the mentioned transaction. So I am seeking to design a solution where the top-level table row and its children will all somehow be pseudo-locked (exclusive transaction isolation) but at the application and not the database level. I am open to ideas and suggestions, I understand this is not a very cut and dried challenge.

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• Batching dynamic sprites in OpenGL

  - by Aaron

  I'm trying to wrap my head around how batching is done in a 2D sprite-based game. My understanding is I'd get the vertices that represent each sprite I want to draw and stuff them all into a single mesh. That way I'd only need a single draw call to render everything. Does this apply when the sprites I render are different between frames, or when some sprites are moving? Because it sounds like I'd then have to recreate my batch mesh each frame, using either glDrawArrays/glDrawElements or a streaming VBO I assume. Does this sound correct?

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• Creating a 2D Line Branch

  - by Danran

  I'm looking into creating a 2D line branch, something for a "lightning effect". I did ask this question before on creating a "lightning effect" (mainly though referring to the process of the glow & after effects the lightning has & to whether it was a good method to use or not); Methods of Creating a "Lightning" effect in 2D However i never did get around to getting it working. So i've been trying today to get a seconded attempt going but i'm getting now-were :/. So to be clear on what i'm trying to-do, in this article posted; http://drilian.com/2009/02/25/lightning-bolts/ I'm trying to create the line segments seen in the images on the site. I'm confused mainly by this line in the pseudo code; // Offset the midpoint by a random amount along the normal. midPoint += Perpendicular(Normalize(endPoint-startPoint))*RandomFloat(-offsetAmount,offsetAmount); If someone could explain this to me it would be really grateful :).

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• Trouble with SAT style vector projection in C#/XNA

  - by ssb

  Simply put I'm having a hard time working out how to work with XNA's Vector2 types while maintaining spatial considerations. I'm working with separating axis theorem and trying to project vectors onto an arbitrary axis to check if those projections overlap, but the severe lack of XNA-specific help online combined with pseudo code everywhere that omits key parts of the algorithm, googling has left me little help. I'm aware of HOW to project a vector, but the way that I know of doing it involves the two vectors starting from the same point. Particularly here: http://www.metanetsoftware.com/technique/tutorialA.html So let's say I have a simple rectangle, and I store each of its corners in a list of Vector2s. How would I go about projecting that onto an arbitrary axis? The crux of my problem is that taking the dot product of say, a vector2 of (1, 0) and a vector2 of (50, 50) won't get me the dot product I'm looking for.. or will it? Because that (50, 50) won't be the vector of the polygon's vertex but from whatever XNA calculates. It's getting the calculation from the right starting point that's throwing me off. I'm sorry if this is unclear, but my brain is fried from trying to think about this. I need a better understanding of how XNA calculates Vector2s as actual vectors and not just as random points.

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• how to modify shadow mapping in "3D Graphics with XNA Game Studio 4.0"?

  - by naprox

  So I've been following the tutorials from the book Sean James's "3D Graphics with XNA Game Studio 4.0", and have been doing fine until i reached the shadow mapping part. in this book it creates point lights with a Sphere model. my first Q is how to draw a directional Light with this frame work? secondly it can do shadow mapping just for one light, how can i do shadow mapping for all or parts of the lights in the game? i just want to know how to modify this codes to do the above tasks. I've followed tutorials on MSDN and some other sites and didn't got the answer. please help me, its so urgent. and if any one wants, the complete code is here: http://www.mediafire.com/?6ct11mc1g8f891h

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• Tracking first visit date in Google Analytics

  - by dusan

  I want track a site's visitor retention using Google Analytics, to see if unregistered users are returning to it, within a time frame of 2+ months from now. This blog post seems to be on the right track, but I want to track unregistered users, so I don't have a "join date" or similar variable at my disposal. This other blog post suggests using all 5 GA custom variables, using the first variable slot on the first week, variable 2 on week 2, etc. This method will allow me to track 5 weeks of visitors. I want to track more than 5 weeks of visitors, so I was thinking on using two custom variables in GA: visitor's first visit date, and visitor's last visit date. How I can save the first visit date? Because if I save another value in the same slot the old value will be overwritten, and I don't know how reliable is to save that variable conditionally (reading the __utmv cookie to check whether the "first visit date" is set, if it isn't set I save the current date)

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• AS3 Calculating Delta Time In Seconds

  - by user1133079

  Here is how I've been trying to implement delta time based on different internet resources. var startTime:Number = getTimer(); game.Update(deltaTime); deltaTime = Number(getTimer() - startTime) * 0.001; My issue with this is it doesn't seem to be giving me accurate timing. The main update shows the frame time at 0.001 and when reinitializing the level it goes to 0.002. I'm using dt else where for a timer and later on time based physics so I would like it to work as expected. I must be missing something silly.

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• How do you keep SOA DRY?

  - by TaylorOtwell

  In our organization, we've shifted to a more "service oriented architecture". To give an example, let's assume we need to retrieve a "Quote" object. This quote has a shipper, a consignee, phone numbers, contacts, email addresses, and other location information. In other words, a Quote object is made up of many other objects. So, it seems like it would make sense to make a "Quote Retrieval Service". In our situation, we've accomplished this by creating a .NET solution and writing the service. The service API looks something like this (in pseudo-code): Function GetQuote(String ID) Returns Quote So, so far so good. Now, when this service is consumed, to keep things "de-coupled", we are creating essentially a duplicate of the Quote object and mapping from the QuoteService version of the Quote into the consumer's version of the Quote. In many cases, these classes will have the exact same properties. So, if the Quote service is consumed by 5 other applications, we would have 6 definitions of what a "Quote" is. One for each consumer, and one for the service. This feels wrong. I thought code was supposed to be DRY, but it seems like our method of SOA is forcing us to create tons of duplicated class definitions. What are we doing wrong, or is the code duplication just a "necessary evil" of SOA?

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• Help parsing long (3.5mil lines) text file, line by line and storing data, need a strategy

  - by Jarrod

  This is a question about solving a particular problem I am struggling with, I am parsing a long list of text data, line by line for a business app in PHP (cron script on the CLI). The file follows the format: HD: Some text here {text here too} DC: A description here DC: the description continues here DC: and it ends here. DT: 2012-08-01 HD: Next header here {supplemental text} ... this repeats over and over for a few hundred megs I have to read each line, parse out the HD: line and grab the text on this line. I then compare this text against data stored in a database. When a match is found, I want to then record the following DC: lines that succeed the matched HD:. Pseudo code: while ( the_file_pointer_isnt_end_of_file) { line = getCurrentLineFromFile title = parseTitleFrom(line) matched = searchForMatchInDB(line) if ( matched ) { recordTheDCLines // <- Best way to do this? } } My problem is that because I am reading line by line, what is the best way to trigger the script to start saving DC lines, and then when they are finished save them to the database? I have a vague idea, but have yet to properly implement it. I would love to hear the communities ideas\suggestions! Thank you.

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• The underlying mechanism in 'yield return www' of Unity3D Game Engine

  - by thyandrecardoso

  In the Unity3D game engine, a common code sequence for getting remote data is this: WWW www = new WWW("http://remote.com/data/location/with/texture.png"); yield return www; What is the underlying mechanism here? I know we use the yield mechanism in order to allow the next frame to be processed, while the download is being completed. But what is going on under the hood when we do the yield return www ? What method is being called (if any, on the WWW class)? Is Unity using threads? Is the "upper" Unity layer getting hold of www instance and doing something?

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• What is an acceptable GC frequency for a SlimDX/Windows/.NET game?

  - by Rei Miyasaka

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

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• Simple algorithm for a sudoku solver java

  - by user142050

  just a quick note first, I originally asked this question on stack overflow but was refered here instead. I've been stuck on this thing for a while, I just can't wrap my head around it. For a homework, I have to produce an algorithm for a sudoku solver that can check what number goes in a blank square in a row, in a column and in a block. It's a regular 9x9 sudoku and I'm assuming that the grid is already printed so I have to produce the part where it solves it. I've read a ton of stuff on the subject I just get stuck expressing it. I want the solver to do the following: If the value is smaller than 9, increase it by 1 If the value is 9, set it to zero and go back 1 If the value is invalid, increase by 1 I've already read about backtracking and such but I'm in the early stage of the class so I'd like to keep it as simple as possible. I'm more capable of writing in pseudo code but not so much with the algorithm itself and it's the algorithm that is needed for this exercise. Thanks in advance for your help guys.

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• "Super meatboy"-ish replay

  - by Ron

  I'm making a platformer built from mini-levels - and I want to create a sort of a replay of all the player tries that the player did for the level. My question is - what is the best way to record the player's actions in-game, so that I could replay them later when he finishes the level. I thought about recording only the player's input and replay them later on, each on a clone of the player. The problem I have with this is with dynamic obstacles (that could be moved around) - if one clone moves them, it throws the simulation off for the rest of the clones. So then I thought about recording every frame the X/Y of the player, and then just replay it - but that seems it could cause a major memory leak and very ineffective. So - does anyone have any ideas? :)

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• Implementing invisible bones

  - by DeadMG

  I suddenly have the feeling that I have absolutely no idea how to implement invisible objects/bones. Right now, I use hardware instancing to store the world matrix of every bone in a vertex buffer, and then send them all to the pipeline. But when dealing with frustrum culling, or having them set to invisible by my simulation for other reasons, means that some of them will be randomly invisible. Does this mean I effectively need to re-fill the buffer from scratch every frame with only the visible unit's matrices? This seems to me like it would involve a lot of wasted bandwidth.

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• How to deal with animated doors in isometric tiles

  - by George Profenza

  I've got a tricky issue I'm not sure how to tackle best: I have an animated tile of a door. When it's closed it should be sorted one way, but when it's openend it will need to be sorted a different way, as it belonging to a different(neighbouring tile). Here's the door closed: and the door opened: I imagine it would be possible to override the sorting system for such tiles and adjust the sorting based on the frame, but it feels a bit hacky. Has anyone encountered a similar scenario ? Any elegant solutions ?

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• 14.04 PlayonLinux and Steam equals jittery choppy freezing video

  - by user2715390

  I trying to get some windows gaming software (warframe) up ad running and it is running but the video is very choppy/freezes even though the reported frame rate is 60fps. I'm using: Ubuntu 14.04 Nvidia 340 driver Play on Linux 4.2.4-2 Wine 1.7.24 & 1.7.22 (switchable) Steam 13 Aug 2014 14:19:47 I used the following link to get it going Warframe Linux/Ubuntu Does anyone have any tips for diagnosing this? Anyway I think it has something to do with syncing. I would like to disable audio in steam or play on linux so I can eliminate any sound issues. How do I do this? Regards WallyZ

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• How do I fix Flash player in Chrome 20?

  - by r0ckarong

  I just updated to Chrome 20.0.1132.43 which includes Flash 11.3.31.109. Since that update most of the flash videos I watch online will randomly display erratic behavior (skipping like a broken CD, "fast forwarding" at twice the frame rate with the audio being scrambled due to too fast playback, restarting every video after two seconds, fullscreen overlay being displayed but no image, fullscreen taking several seconds to actually show a picture, youtube player to go fullscreen but then hang in the controls fadeout animation with no picture -sound keeps playing). Is there anything I can do to resolve or work around this? I'm using Ubuntu 12.10 64Bit and the latest nvidia-current drivers 295.40 on a Geforce GT 440. It used to work in previous versions of Google Chrome.

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• Circle vs Edge collision detection / resolution

  - by topheman

  I made a javascript class Ball.js that handles physics interactions betweens balls as well as painting. In the v1.0, the ball vs ball collision detection and resolution is well handled. In the next version (v2), I'm trying to add edgeCollision handling. I'm having some problems, maybe you will be able to help me. All the v2 branch source code is on github repository : https://github.com/topheman/Ball.js/tree/v2 The v2 demos (where you can see the bug I will be talking about) : http://labs.topheman.com/Ball-v2/#help As you will see on the demo, I have two major problems that I'm having a really hard time to solve on Ball.js : method resolveEdgeCollision : bounce angle is inconsistent method checkEdgeCollision : if the ball's velocity (the length that it runs each frame) is higher than its diameter, eventually, it will pass through an edge, without triggering any collision Any Ideas ?...

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• What are the pros and cons of a non-fixed-interval update loop?

  - by akonsu

  I am studying various approaches to implementing a game loop and I have found this article. In the article the author implements a loop which, if the processing falls behind in time, skips frame renderings and just updates the game in a loop (the last variant called "Constant Game Speed independent of Variable FPS"). I do not understand why it is acceptable to call update_game() in a loop without making sure the update function is called at a particular interval. I do not see any value in doing this. I would think that in my game I want to be sure the game is updated periodically with a known period. So maybe it is worthwhile to have two threads, one would call update periodically, and the other one would redraw the game, also periodically? Would this be a good and practical approach? Of course I would need to synchronise the threads.

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• Why won't videos on a particular website play under Ubuntu 13.04?

  - by Sadi

  Very oddly, I cannot watch any videos a TV channel website, for example this one: http://www.kanald.com.tr/GalipDervis/Videolar/ I can see from the frame source that it contains an embedded Adobe Flash video and some Java scripts (all of which don't pose any problems elsewhere). I've tried different web browsers (Chrome/Chromium/Firefox), but it seems I have some sort of video codec problem in my system. I have installed all sorts of gstreamer plugins, codecs, etc. (maybe too many?) to avoid such problems, but strangely I can watch these videos using Linux Mint 15 Live Session on the same machine. I wonder how I can find out why a particular video (like this one) won't work on my system?

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• Very slow direct3D texture sampling

  - by __dominic

  Hi, So I'm writing a small game using Direct3D 9 and I'm using multitexturing for the terrain. All I'm doing is sampling 3 textures and a blend map and getting the overall color from the three textures based on the color channels from the blend map. Anyway, I am getting a massive frame rate drop when I sample more than 1 texture, I'm going from 120+ fps to just under 50. This is the HLSL code responsible for the slow down: float3 ground = tex2D(GroundTex, multiTex).rgb; float3 stone = tex2D(StoneTex, multiTex).rgb; float3 grass = tex2D(GrassTex, multiTex).rgb; float3 blend = tex2D(BlendMapTex, blendMap).rgb; Am I doing it wrong ? If anyone has any info or tips about texture sampling or anything, that would be nice. Thanks.

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• Relation between developers and clients

  - by guiman

  Hi everyone, i've been facing a situation at work and i would like to share it with you and tell me: Did you had to do it to? Should a developer be in direct contact wit the client? Or there should be an "adapter" guy that translates client needs in pseudo formal requirements understandable to us? I'm currently working in a small company that its taking care of implementing lots of systems, most of them for goverment institutions, in witch it generally means taking software developted 20 years ago and refurbish them so fit up-to-date needs. The clients generally are very used to them and tend to discourage change (they are in their 50s 60s give or take, so not technologie-friendly in general). As you can imagine, dev-team in most cases starts taking care of relation with clients, generating the documentation needed in this cases (CU usually), assisting to weekly meets to see improvements with clients. As for experience, this is a gold mine for me, because gives a nice perspective on all the aspects of software development, but also some problems rise because, if developers come from mars then client are from venus. So there is a fine gap on the vocabulary/experience/capability-to-interpret-needs that generates an noice in the communication, and some times affecting the final product.

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• Locomotion-system with irregular IK

  - by htaunay

  Im having some trouble with locomtions (Unity3D asset) IK feet placement. I wouldn't call it "very bad", but it definitely isn't as smooth as the Locomotion System Examples. The strangest behavior (that is probably linked to the problem) are the rendered foot markers that "guess" where the characters next step will be. In the demo, they are smooth and stable. However, in my project, they keep flickering, as if Locomotion changed its "guess" every frame, and sometimes, the automatic defined step is too close to the previous step, or sometimes, too distant, creating a very irregular pattern. The configuration is (apparently)Identical to the human example in the demo, so I guessing the problem is my model and/or animation. Problem is, I can't figure out was it is =S Has anyone experienced the same problem? I uploaded a video of the bug to help interpreting the issue (excuse the HORRIBLE quality, I was in a hurry).

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• Languages with a clear distinction between subroutines that are purely functional, mutating, state-changing, etc?

  - by CPX

  Lately I've become more and more frustrated that in most modern programming languages I've worked with (C/C++, C#, F#, Ruby, Python, JS and more) there is very little, if any, language support for determining what a subroutine will actually do. Consider the following simple pseudo-code: var x = DoSomethingWith(y); How do I determine what the call to DoSomethingWith(y) will actually do? Will it mutate y, or will it return a copy of y? Does it depend on global or local state, or is it only dependent on y? Will it change the global or local state? How does closure affect the outcome of the call? In all languages I've encountered, almost none of these questions can be answered by merely looking at the signature of the subroutine, and there is almost never any compile-time or run-time support either. Usually, the only way is to put your trust in the author of the API, and hope that the documentation and/or naming conventions reveal what the subroutine will actually do. My question is this: Does there exist any languages today that make symbolic distinctions between these types of scenarios, and places compile-time constraints on what code you can actually write? (There is of course some support for this in most modern languages, such as different levels of scope and closure, the separation between static and instance code, lambda functions, et cetera. But too often these seem to come into conflict with each other. For instance, a lambda function will usually either be purely functional, and simply return a value based on input parameters, or mutate the input parameters in some way. But it is usually possible to access static variables from a lambda function, which in turn can give you access to instance variables, and then it all breaks apart.)

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• What causes the iOS OpenGLES driver to allocate extra memory?

  - by Martin Linklater

  I'm trying to optimize the memory usage of our iOS game and I'm puzzled about when/why the iOS GLES driver allocates extra memory at runtime... When I run our game through Instruments with the OpenGL ES Driver instrument the gartUsedBytes value can fluctuate quite wildly. We preload all our textures and build the buffer objects up front, so it's not the game engine requesting extra memory from GL. Currently we are manually requesting around 50MB of GL memory, yet the gartUsedBytes value sits at around 90MB most of the time, peaking at 125MB from time to time. It seems to be linked to what you are rendering that frame - our PVS only submits VBO's for visible meshes. Can anyone shed some light on what the driver is doing in the background ? Like I said earlier, all our game engine allocations are done on level load, so in theory there shouldn't be any fluctuation on GL memory usage while the level is running. Thanks.

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