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• Understanding the levels of computing

  - by RParadox

  Sorry, for my confused question. I'm looking for some pointers. Up to now I have been working mostly with Java and Python on the application layer and I have only a vague understanding of operating systems and hardware. I want to understand much more about the lower levels of computing, but it gets really overwhelming somehow. At university I took a class about microprogramming, i.e. how processors get hard-wired to implement the ASM codes. Up to now I always thought I wouldn't get more done if learned more about the "low level". One question I have is: how is it even possible that hardware gets hidden almost completely from the developer? Is it accurate to say that the operating system is a software layer for the hardware? One small example: in programming I have never come across the need to understand what L2 or L3 Cache is. For the typical business application environment one almost never needs to understand assembler and the lower levels of computing, because nowadays there is a technology stack for almost anything. I guess the whole point of these lower levels is to provide an interface to higher levels. On the other hand I wonder how much influence the lower levels can have, for example this whole graphics computing thing. So, on the other hand, there is this theoretical computer science branch, which works on abstract computing models. However, I also rarely encountered situations, where I found it helpful thinking in the categories of complexity models, proof verification, etc. I sort of know, that there is a complexity class called NP, and that they are kind of impossible to solve for a big number of N. What I'm missing is a reference for a framework to think about these things. It seems to me, that there all kinds of different camps, who rarely interact. The last few weeks I have been reading about security issues. Here somehow, much of the different layers come together. Attacks and exploits almost always occur on the lower level, so in this case it is necessary to learn about the details of the OSI layers, the inner workings of an OS, etc.

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• Accounting for waves when doing planar reflections

  - by CloseReflector

  I've been studying Nvidia's examples from the SDK, in particular the Island11 project and I've found something curious about a piece of HLSL code which corrects the reflections up and down depending on the state of the wave's height. Naturally, after examining the brief paragraph of code: // calculating correction that shifts reflection up/down according to water wave Y position float4 projected_waveheight = mul(float4(input.positionWS.x,input.positionWS.y,input.positionWS.z,1),g_ModelViewProjectionMatrix); float waveheight_correction=-0.5*projected_waveheight.y/projected_waveheight.w; projected_waveheight = mul(float4(input.positionWS.x,-0.8,input.positionWS.z,1),g_ModelViewProjectionMatrix); waveheight_correction+=0.5*projected_waveheight.y/projected_waveheight.w; reflection_disturbance.y=max(-0.15,waveheight_correction+reflection_disturbance.y); My first guess was that it compensates for the planar reflection when it is subjected to vertical perturbation (the waves), shifting the reflected geometry to a point where is nothing and the water is just rendered as if there is nothing there or just the sky: Now, that's the sky reflecting where we should see the terrain's green/grey/yellowish reflection lerped with the water's baseline. My problem is now that I cannot really pinpoint what is the logic behind it. Projecting the actual world space position of a point of the wave/water geometry and then multiplying by -.5f, only to take another projection of the same point, this time with its y coordinate changed to -0.8 (why -0.8?). Clues in the code seem to indicate it was derived with trial and error because there is redundancy. For example, the author takes the negative half of the projected y coordinate (after the w divide): float waveheight_correction=-0.5*projected_waveheight.y/projected_waveheight.w; And then does the same for the second point (only positive, to get a difference of some sort, I presume) and combines them: waveheight_correction+=0.5*projected_waveheight.y/projected_waveheight.w; By removing the divide by 2, I see no difference in quality improvement (if someone cares to correct me, please do). The crux of it seems to be the difference in the projected y, why is that? This redundancy and the seemingly arbitrary selection of -.8f and -0.15f lead me to conclude that this might be a combination of heuristics/guess work. Is there a logical underpinning to this or is it just a desperate hack? Here is an exaggeration of the initial problem which the code fragment fixes, observe on the lowest tessellation level. Hopefully, it might spark an idea I'm missing. The -.8f might be a reference height from which to deduce how much to disturb the texture coordinate sampling the planarly reflected geometry render and -.15f might be the lower bound, a security measure.

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• Using all Ten IO slots on a 7420

  - by user12620172

  So I had the opportunity recently to actually use up all ten slots in a clustered 7420 system. This actually uses 20 slots, or 22 if you count the clusteron card. I thought it was interesting enough to share here. This is at one of my clients here in southern California. You can see the picture below. We have four SAS HBAs instead of the usual two. This is becuase we wanted to split up the back-end taffic for different workloads. We have a set of disk trays coming from two SAS cards for nothing but Exadata backups. Then, we have a different set of disk trays coming off of the other two SAS cards for non-Exadata workloads, such as regular user file storage. We have 2 Infiniband cards which allow us to do a full mesh directly into the back of the nearby, production Exadata, specifically for fast backups and restores over IB. You can see a 3rd IB card here, which is going to be connected to a non-production Exadata for slower backups and restores from it.The 10Gig card is for client connectivity, allowing other, non-Exadata Oracle databases to make use of the many snapshots and clones that can now be created using the RMAN copies from the original production database coming off the Exadata. This allows for a good number of test and development Oracle databases to use these clones without effecting performance of the Exadata at all.We also have a couple FC HBAs, both for NDMP backups to an Oracle/StorageTek tape library and also for FC clients to come in and use some storage on the 7420.  Now, if you are adding more cards to your 7420, be aware of which cards you can place in which slots. See the bottom graphic just below the photo.  Note that the slots are numbered 0-4 for the first 5 cards, then the "C" slots which is the dedicated Cluster card (called the Clustron), and then another 5 slots numbered 5-9. Some rules for the slots: Slots 1 & 8 are automatically populated with the two default SAS cards. The only other slots you can add SAS cards to are 2 & 7. Slots 0 and 9 can only hold FC cards. Nothing else. So if you have four SAS cards, you are now down to only four more slots for your 10Gig and IB cards. Be sure not to waste one of these slots on a FC card, which can go into 0 or 9, instead.  If at all possible, slots should be populated in this order: 9, 0, 7, 2, 6, 3, 5, 4

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• How can I cleanly and elegantly handle data and dependancies between classes

  - by Neophyte

  I'm working on 2d topdown game in SFML 2, and need to find an elegant way in which everything will work and fit together. Allow me to explain. I have a number of classes that inherit from an abstract base that provides a draw method and an update method to all the classes. In the game loop, I call update and then draw on each class, I imagine this is a pretty common approach. I have classes for tiles, collisions, the player and a resource manager that contains all the tiles/images/textures. Due to the way input works in SFML I decided to have each class handle input (if required) in its update call. Up until now I have been passing in dependencies as needed, for example, in the player class when a movement key is pressed, I call a method on the collision class to check if the position the player wants to move to will be a collision, and only move the player if there is no collision. This works fine for the most part, but I believe it can be done better, I'm just not sure how. I now have more complex things I need to implement, eg: a player is able to walk up to an object on the ground, press a key to pick it up/loot it and it will then show up in inventory. This means that a few things need to happen: Check if the player is in range of a lootable item on keypress, else do not proceed. Find the item. Update the sprite texture on the item from its default texture to a "looted" texture. Update the collision for the item: it might have changed shape or been removed completely. Inventory needs to be updated with the added item. How do I make everything communicate? With my current system I will end up with my classes going out of scope, and method calls to each other all over the place. I could tie up all the classes in one big manager and give each one a reference to the parent manager class, but this seems only slightly better. Any help/advice would be greatly appreciated! If anything is unclear, I'm happy to expand on things.

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• Does it make the game more fun when the user is forced to progress through the levels sequentially rather than letting them pick and play?

  - by BeachRunnerJoe

  Hello. For the first time in my game, I'm stuck with a real design dilemma. I guess that's a good thing ;) I'm building a word puzzle game that has five levels, each with 30 puzzles. Currently, the user has to solve one puzzle at a time before moving to the next. However, I'm finding the user occasionally gets stuck on a puzzle, at which point they can no longer play until they solve it. This is obviously bad because many people will probably just quit playing the game and delete the app. The only elegant solution I can find to helping the player get unstuck is changing the design of the game to allow the users to pick any puzzle to play at any time. This way, if they get stuck, they can come back to it later and at least they have other puzzles to play in the meantime. It's my opinion, however, that this new flow design doesn't make the game as fun as the original flow design where the player has to complete a puzzle before moving to the next. To me, it's like anything else, when you only have one of something, it's more enjoyable, but when you have 30 of something, it's far less enjoyable. In fact, when I present the user with 30 puzzles to choose from, I'm concerned I might be making them feel like it's a lot of work they have to do and that's bad. I even had a tester voluntarily tell me that being forced to complete a puzzle before moving to the next is actually motivating. My questions are... Do you agree/disagree? Do you have any suggestions for how I can help the player get unstuck? Thanks so much in advance for your thoughts! EDIT: I should mention that I've already considered a few other solutions to helping the user get unstuck, but none of them seem like good ideas. They are... Add more hints: Currently, the user gets two hints per puzzle. If I increase the hint count, it only makes the game more easy and still leaves the possibility of the user getting stuck. Add a "Show Solution" button: This seems like a bad idea because it's my opinion this takes the fun out of the game for many people who would probably otherwise solve the puzzle if they didn't have the quick option to see the solution.

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• JCP.next.3: time to get to work

  - by Patrick Curran

  As I've previously reported in this blog, we planned three JSRs to improve the JCP’s processes and to meet our members’ expectations for change. The first - JCP.next.1, or more formally JSR 348: Towards a new version of the Java Community Process - was completed in October 2011. This focused on a small number of simple but important changes to make our process more transparent and to enable broader participation. We're already seeing the benefits of these changes as new and existing JSRs adopt the new requirements. However, because we wanted to complete this JSR quickly we deliberately postponed a number of more complex items, including everything that would require modifying the JSPA (the legal agreement that members sign when they join the organization) to a follow-on JSR. The second JSR (JSR 355: JCP Executive Committee Merge) is in progress now and will complete later this year. This JSR is even simpler than the first, and is focused solely on merging the two Executive Committees into one for greater efficiency and to encourage synergies between the Java ME and Java SE platforms. Continuing the momentum to move Java and the JCP forward we have just filed the third JSR (JCP.next.3) as JSR 358: A major revision of the Java Community Process. This JSR will modify the JSPA as well as the Process Document, and will tackle a large number of complex issues, many of them postponed from JSR 348. For these reasons we expect to spend a considerable amount of time working on it - at least a year, and probably more. The current version of the JSPA was created back in 2002, although some minor changes were introduced in 2005. Since then the organization and the environment in which we operate have changed significantly, and it is now time to revise our processes to ensure that they meet our current needs. We have a long list of topics to be considered, including the role of independent implementations (those not derived from the Reference Implementation), licensing and open source, ensuring that our new transparency requirements are implemented correctly, compatibility policy and TCKs, the role of individual members, patent policy, and IP flow. The Expert Group for JSR 358, as with all process-change JSRs, consists of all members of the Executive Committees. Even though the JSR has just been filed we started discussions on the various topics several months ago (see the EC's meeting minutes for details) and our EC members - including the new members who joined within the last year or two - are actively engaged. Now it's your opportunity to get involved. As required by version 2.8 of our Process (introduced with JSR 348) we will conduct all our business in the open. We have a public java.net project where you can follow and participate in our work. All of our deliberations will be copied to a public Observer mailing list, we'll track our issues on a public Issue Tracker, and all our documents (meeting agendas and minutes, task lists, working drafts) will be published in our Document Archive. We're just getting started, but we do want your input. Please visit us on java.net where you can learn how to participate. Let's get to work...

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• Trying to use stencils in 2D while retaining layer depth

  - by Steve

  This is a screen of what's going on just so you can get a frame of reference. http://i935.photobucket.com/albums/ad199/fobwashed/tilefloors.png The problem I'm running into is that my game is slowing down due to the amount of texture swapping I'm doing during my draw call. Since walls, characters, floors, and all objects are on their respective sprite sheet containing those types, per tile draw, the loaded texture is swapping no less than 3 to 5+ times as it cycles and draws the sprites in order to layer properly. Now, I've tried throwing all common objects together into their respective lists, and then using layerDepth drawing them that way which makes things a lot better, but the new problem I'm running into has to do with the way my doors/windows are drawn on walls. Namely, I was using stencils to clear out a block on the walls that are drawn in the shape of the door/window so that when the wall would draw, it would have a door/window sized hole in it. This is the way my draw was set up for walls when I was going tile by tile rather than grouped up common objects. first it would check to see if a door/window was on this wall. If not, it'd skip all the steps and just draw normally. Otherwise end the current spriteBatch Clear the buffers with a transparent color to preserve what was already drawn start a new spritebatch with stencil settings draw the door area end the spriteBatch start a new spritebatch that takes into account the previously set stencil draw the wall which will now be drawn with a hole in it end that spritebatch start a new spritebatch with the normal settings to continue drawing tiles In the tile by tile draw, clearing the depth/stencil buffers didn't matter since I wasn't using any layerDepth to organize what draws on top of what. Now that I'm drawing from lists of common objects rather than tile by tile, it has sped up my draw call considerably but I can't seem to figure out a way to keep the stencil system to mask out the area a door or window will be drawn into a wall. The root of the problem is that when I end a spriteBatch to change the DepthStencilState, it flattens the current RenderTarget and there is no longer any depth sorting for anything drawn further down the line. This means walls always get drawn on top of everything regardless of depth or positioning in the game world and even on top of each other as the stencil has to happen once for every wall that has a door or window. Does anyone know of a way to get around this? To boil it down, I need a way to draw having things sorted by layer depth while also being able to stencil/mask out portions of specific sprites.

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• List of common pages to have in the footer [closed]

  - by user359650

  I would like to post this question as a reference for webmasters wondering what pages they should include in the footer. I will use answers to complete my initial list: About us / About MyCompany / MyCompany About / About us: description about the company, its mission, and its vision. History: summary of milestones achieved by the company. The team / Management / Board of directors: depending on size of the company there may be one of more pages describing the people involved in the company, depending on their position. Awards: list of awards received by the company if any. In the press / They're talking about us: list of links to external websites, usually highly regarded news websites, which mentioned the company in one of their articles. Media Wallpapers: wallpapers with company logo in different colors and formats that fans can set as desktop image for their computer. logos: company logo in different colors and formats that websites/blogs posting about the website can use for illustration purposes. Media kits: documents, usually in PDF format summarizing the key company figures and facts that journalists can download and read to get a quick overview of the company. Misc Contact / Contact us: contact details the company is prepared to disclose if any (address, email, phone) or contact form. Careers / Jobs / Join us: list of open vacancies with contact form to apply. Investors / Partners / Publishers: information and contact forms for companies willing to become Investors/Partners/Publishers or login page to access portal restricted to those who already are. FAQ: list of common questions and answers to guide users and reduce number of support requests. Follow us / Community Facebook / Twitter / Google+: links to the company's pages/accounts on various social networks. Legal Terms / Terms of use / Terms & Conditions: rules users must follow when browsing the website. Privacy / Privacy Statement: explanations as to how the company deals with users' personal data and what users can do about it (request information to be deleted...). cookies: page that starts appearing on more and more websites due to new regulation (notably EU) imposing more transparency and control for users about cookies (e.g. BBC cookie page). Any input is welcome PS: if someone with enough rep could add the footer tag that would be great (min. 300 required).

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• Criteria for a programming language to be considered "mature"

  - by Giorgio

  I was recently reading an answer to this question, and I was struck by the statement "The language is mature". So I was wondering what we actually mean when we say that "A programming language is mature"? Normally, a programming language is initially developed out of a need, e.g. Try out / implement a new programming paradigm or a new combination of features that cannot be found in existing languages. Try to solve a problem or overcome a limitation of an existing language. Create a language for teaching programming. Create a language that solves a particular class of problems (e.g. concurrency). Create a language and an API for a special application field, e.g. the web (in this case the language might reuse a well-known paradigm, but the whole API must be new). Create a language to push your competitor out of the market (in this case the creator might want the new language to be very similar to an existing one, in order to attract developers to the new programming language and platform). Regardless of what the original motivation and scenario in which a language has been created, eventually some languages are considered mature. In my intuition, this means that the language has achieved (at least one of) its goals, e.g. "We can now use language X as a reliable tool for writing web applications." This is however a bit vague, so I wanted to ask what you consider the most important criteria (if any) that are applied when saying that a language is mature. IMPORTANT NOTE This question is (on purpose) language-agnostic because I am only interested in general criteria. Please write only language-agnostic answers and comments! I am not asking whether any specific "language X is mature" or "which programming languages can be considered mature", or whether "language X is more mature than language Y": please avoid posting any opinions or reference about any specific languages because these are out of the scope of this question. EDIT To make the question more precise, by criteria I mean such things as "tool support", "adoption by the industry", "stability", "rich API", "large user community", "successful application record", "standardization", "clean and uniform semantics", and so on.

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• WebLogic Partner Community Newsletter September 2012

  - by JuergenKress

  Dear WebLogic partner community member Happy Birthday to our WebLogic partner Community! We launched the community a year ago, it is growing fast with almost 1,000 members and with a significant impact in our business. The WebLogic partner revenue grew significant last fiscal year. I would like to thank you for your contribution. It is indeed a great opportunity for your WebLogic service revenue, like consulting, implementation or training. There will be thousands of opportunities at our joint customer base, like iAs to WebLogic migration, J2EE platform consolidation or private clouds. We will continue to highlight these opportunities in our newsletter and offer you campaign kits. Please feel free to let us know if you are interested. I would also recommend you to give us your feedback in our WebLogic Partner Community Survey 2012! Your feedback is very important for us. We continue to offer free WebLogic 12c Bootcamps across Europe. Please make sure you register asap for your local training! In addition to this we plan to offer Exalogic 2.01 Bootcamp. If you are interested to attend it then please add your details to our wiki. Our ExaLogic kit is updated with ExaLogic 2.01 ppt & training & Installation check-list & tips & Web tier roadmap. In case you want to learn more about ExaLogic, please visit Qualogy virtual demo center. We have not only released the latest version of Tuxedo 12c but Andrejus also made a Performance Audit Tool - Runtime Diagnosis for ADF Applications which is available now. We uploaded the latest WebLogic 12c and Glassfish ppt presentation for your customer meetings to the WebLogic Community Workspace (WebLogic Community membership required). Are you ready and prepared for Oracle Open World 2012? Make sure you read our tips and enjoy the conference! WebLogic Server 11gR1 Interactive Quick Reference is a wonderful online overview. Make sure you do not miss it! If you want to try WebLogic why not in the Oracle Cloud - Java Cloud Service. Our Java Guru Adam Bien published a new book Real World Java EE Patterns. If you use Java on your machine, Please make sure that you update your Java SE. Jürgen Kress Oracle WebLogic Partner Adoption EMEA To read the newsletter please visit http://tinyurl.com/WebLogicnewsSeptember2012 (OPN Account required) To become a member of the WebLogic Partner Community please register at http://www.oracle.com/partners/goto/wls-emea ( OPN account required). If you need support with your account please contact the Oracle Partner Business Center. Blog Twitter LinkedIn Mix Forum Wiki Technorati Tags: WebLogic Community newsletter,newsletter,WebLogic,WebLogic Community,Oracle,OPN,Jürgen Kress

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• Is it appropriate to try to control the order of finalization?

  - by Strilanc

  I'm writing a class which is roughly analogous to a CancellationToken, except it has a third state for "never going to be cancelled". At the moment I'm trying to decide what to do if the 'source' of the token is garbage collected without ever being set. It seems that, intuitively, the source should transition the associated token to the 'never cancelled' state when it is about to be collected. However, this could trigger callbacks who were only kept alive by their linkage from the token. That means what those callbacks reference might now in the process of finalization. Calling them would be bad. In order to "fix" this, I wrote this class: public sealed class GCRoot { private static readonly GCRoot MainRoot = new GCRoot(); private GCRoot _next; private GCRoot _prev; private object _value; private GCRoot() { this._next = this._prev = this; } private GCRoot(GCRoot prev, object value) { this._value = value; this._prev = prev; this._next = prev._next; _prev._next = this; _next._prev = this; } public static GCRoot Root(object value) { return new GCRoot(MainRoot, value); } public void Unroot() { lock (MainRoot) { _next._prev = _prev; _prev._next = _next; this._next = this._prev = this; } } } intending to use it like this: Source() { ... _root = GCRoot.Root(callbacks); } void TransitionToNeverCancelled() { _root.Unlink(); ... } ~Source() { TransitionToNeverCancelled(); } but now I'm troubled. This seems to open the possibility for memory leaks, without actually fixing all cases of sources in limbo. Like, if a source is closed over in one of its own callbacks, then it is rooted by the callback root and so can never be collected. Presumably I should just let my sources be collected without a peep. Or maybe not? Is it ever appropriate to try to control the order of finalization, or is it a giant warning sign?

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• Applying the Knuth-Plass algorithm (or something better?) to read two books with different length and amount of chapters in parallel

  - by user147133

  I have a Bible reading plan that covers the whole Bible in 180 days. For the most of the time, I read 5 chapters in the Old Testament and 1 or 2 (1.5) chapters in the New Testament each day. The problem is that some chapters are longer than others (for example Psalm 119 which is 7 times longer than a average chapter in the Bible), and the plan I'm following doesn't take that in count. I end up with some days having a lot more to read than others. I thought I could use programming to make myself a better plan. I have a datastructure with a list of all chapters in the bible and their length in number of lines. (I found that the number of lines is the best criteria, but it could have been number of verses or number of words as well) I then started to think about this problem as a line wrap problem. Think of a chapter like a word, a day like a line and the whole plan as a paragraph. The "length" of a word (a chapter) is the number of lines in that chapter. I could then generate the best possible reading plan by applying a simplified Knuth-Plass algorithm to find the best breakpoints. This works well if I want to read the Bible from beginning to end. But I want to read a little from the new testament each day in parallel with the old testament. Of course I can run the Knuth-Plass algorithm on the Old Testament first, then on the New Testament and get two separate plans. But those plans merged is not a optimal plan. Worst-case days (days with extra much reading) in the New Testament plan will randomly occur on the same days as the worst-case days in the Old Testament. Since the New Testament have about 180*1.5 chapters, the plan is generally to read one chapter the first day, two the second, one the third etc... And I would like the plan for the Old Testament to compensate for this alternating length. So I will need a new and better algorithm, or I will have to use the Knuth-Plass algorithm in a way that I've not figured out. I think this could be a interesting and challenging nut for people interested in algorithms, so therefore I wanted to see if any of you have a good solution in mind.

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• Silverlight and WCF caching

  - by subodhnpushpak

  There are scenarios where Silverlight client calls WCF (or REST) service for data. Now, if the data is cached on the WCF layer, the calls can take considerable resources at the server if NOT cached. Keeping that in mind along with the fact that cache is an cross-cutting aspect, and therefore it should be as easy as possible to put Cache wherever required. The good thing about the solution is that it caches based on the inputs. The input can be basic type of any complex type. If input changes the data is fetched and then cached for further used. If same input is provided again, data id fetched from the cache. The cache logic itself is implemented as PostSharp aspect, and it is as easy as putting an attribute over service call to switch on cache. Notice how clean the code is:        [OperationContract]       [CacheOnArgs(typeof(int))] // based on actual value of cache        public string DoWork(int value)        {            return string.Format("You entered: {0} @ cached time {1}", value, System.DateTime.Now);        } The cache is implemented as POST Sharp as below 1: public override void OnInvocation(MethodInvocationEventArgs eventArgs) 2: { 3: try 4: { 5: object value = new object(); 6: object[] args = eventArgs.GetArgumentArray(); 7: if (args != null || args.Count() > 0) 8: { 9:   10: string key = string.Format("{0}_{1}", eventArgs.Method.Name, XMLUtility<object>.GetDataContractXml(args[0], null));// Compute the cache key (details omitted). 11:   12: 13: value = GetFromCache(key); 14: if (value == null) 15: { 16: eventArgs.Proceed(); 17: value = XMLUtility<object>.GetDataContractXml(eventArgs.ReturnValue, null); 18: value = eventArgs.ReturnValue; 19: AddToCache(key, value); 20: return; 21: } 22:   23:   24: Log(string.Format("Data returned from Cache {0}",value)); 25: eventArgs.ReturnValue = value; 26: } 27: } 28: catch (Exception ex) 29: { 30: //ApplicationLogger.LogException(ex.Message, Source.UtilityService); 31: } 32: } 33:   34: private object GetFromCache(string inputKey) { if (ServerConfig.CachingEnabled) { return WCFCache.Current[inputKey]; } return null; }private void AddToCache(string inputKey,object outputValue) 35: { 36: if (ServerConfig.CachingEnabled) 37: { 38: if (WCFCache.Current.CachedItemsNumber < ServerConfig.NumberOfCachedItems) 39: { 40: if (ServerConfig.SlidingExpirationTime <= 0 || ServerConfig.SlidingExpirationTime == int.MaxValue) 41: { 42: WCFCache.Current[inputKey] = outputValue; 43: } 44: else 45: { 46: WCFCache.Current.Insert(inputKey, outputValue, new TimeSpan(0, 0, ServerConfig.SlidingExpirationTime), true); 47:   48: // _bw.DoWork += bw_DoWork; 49: //string arg = string.Format("{0}|{1}", inputKey,outputValue); 50: //_bw.RunWorkerAsync(inputKey ); 51: } 52: } 53: } 54: }     The cache class can be extended to support Velocity / memcahe / Nache. the attribute can be used over REST services as well. Hope the above helps. Here is the code base for the same.   Please do provide your inputs / comments.

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• Calculating a circle or sphere along a vector

  - by Sparky

  Updated this post and the one at Math SE (http://math.stackexchange.com/questions/127866/calculating-a-circle-or-sphere-along-a-vector), hope this makes more sense. I previously posted a question (about half an hour ago) involving computations along line segments, but the question and discussion were really off track and not what I was trying to get at. I am trying to work with an FPS engine I am attempting to build in Java. The problem I am encountering is with hitboxing. I am trying to calculate whether or not a "shot" is valid. I am working with several approaches and any insight would be helpful. I am not a native speaker of English nor skilled in Math so please bear with me. Player position is at P0 = (x0,y0,z0), Enemy is at P1 = (x1,y1,z1). I can of course compute the distance between them easily. The target needs a "hitbox" object, which is basically a square/rectangle/mesh either in front of, in, or behind them. Here are the solutions I am considering: I have ruled this out...doesn't seem practical. [Place a "hitbox" a small distance in front of the target. Then I would be able to find the distance between the player and the hitbox, and the hitbox and the target. It is my understanding that you can compute a circle with this information, and I could simply consider any shot within that circle a "hit". However this seems not to be an optimal solution, because it requires you to perform a lot of calculations and is not fully accurate.] Input, please! Place the hitbox "in" the player. This seems like the better solution. In this case what I need is a way to calculate a circle along the vector, at whatever position I wish (in this case, the distance between the two objects). Then I can pick some radius that encompasses the whole player, and count anything within this area a "hit". I am open to your suggestions. I'm trying to do this on paper and have no familiarity with game engines. If any software folk out there think I'm doing this the hard way, I'm open to help! Also - Anyone with JOGL/LWJGL experience, please chime in. Is this making sense?

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• How to write comments to explain the "why" behind the callback function when the function and parameter names are insufficient for that?

  - by snowmantw

  How should I approach writing comments for callback functions? I want to explain the "why" behind the function when the function and parameter names are insufficient to explain what's going on. I have always wonder why comments like this can be so ordinary in documents of libraries in dynamic languages: /** * cb: callback // where's the arguments & effects? */ func foo( cb ) Maybe the common attitude is "you can look into source code on your own after all" which pushes people into leaving minimalist comments like this. But it seems like there should be a better way to comment callback functions. I've tried to comment callbacks in Haskell way: /** * cb: Int -> Char */ func foo(cb) And to be fair, it's usually neat enough. But it gets into trouble when I need to pass some complex structure. The problem being partly due to the lack of type system: /** * cb: Int -> { err: String -> (), success: () -> Char } // too long... */ func foo(cb) Or I have tried this too: /** * cb: Int -> { err: String -> (), * success: () -> Char } // better ? */ func bar(cb) The problem is that you may put the structure in somewhere else, but you must give it a name to reference it. But then when you name a structure you're about to use immediately looks so redundant: // Somewhere else... // ResultCallback: { err: String -> (), success: () -> Char } /** * cb: Int -> ResultCallback // better ?? */ func foo(cb) And it bothers me if I follow the Java-doc like commenting style since it still seems incomplete. The comments don't tell you anything that you couldn't immediately see from looking at the function. /** * @param cb {Function} yeah, it's a function, but you told me nothing about it... * @param err {Function} where should I put this callback's argument ?? * Not to mention the err's own arguments... */ func foo(cb) These examples are JavaScript like with generic functions and parameter names, but I've encountered similar problems in other dynamic languages which allow complex callbacks.

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• Entity Framework 5, separating business logic from model - Repository?

  - by bnice7

  I am working on my first public-facing web application and I’m using MVC 4 for the presentation layer and EF 5 for the DAL. The database structure is locked, and there are moderate differences between how the user inputs data and how the database itself gets populated. I have done a ton of reading on the repository pattern (which I have never used) but most of my research is pushing me away from using it since it supposedly creates an unnecessary level of abstraction for the latest versions of EF since repositories and unit-of-work are already built-in. My initial approach is to simply create a separate set of classes for my business objects in the BLL that can act as an intermediary between my Controllers and the DAL. Here’s an example class: public class MyBuilding { public int Id { get; private set; } public string Name { get; set; } public string Notes { get; set; } private readonly Entities _context = new Entities(); // Is this thread safe? private static readonly int UserId = WebSecurity.GetCurrentUser().UserId; public IEnumerable<MyBuilding> GetList() { IEnumerable<MyBuilding> buildingList = from p in _context.BuildingInfo where p.Building.UserProfile.UserId == UserId select new MyBuilding {Id = p.BuildingId, Name = p.BuildingName, Notes = p.Building.Notes}; return buildingList; } public void Create() { var b = new Building {UserId = UserId, Notes = this.Notes}; _context.Building.Add(b); _context.SaveChanges(); // Set the building ID this.Id = b.BuildingId; // Seed 1-to-1 tables with reference the new building _context.BuildingInfo.Add(new BuildingInfo {Building = b}); _context.GeneralInfo.Add(new GeneralInfo {Building = b}); _context.LocationInfo.Add(new LocationInfo {Building = b}); _context.SaveChanges(); } public static MyBuilding Find(int id) { using (var context = new Entities()) // Is this OK to do in a static method? { var b = context.Building.FirstOrDefault(p => p.BuildingId == id && p.UserId == UserId); if (b == null) throw new Exception("Error: Building not found or user does not have access."); return new MyBuilding {Id = b.BuildingId, Name = b.BuildingInfo.BuildingName, Notes = b.Notes}; } } } My primary concern: Is the way I am instantiating my DbContext as a private property thread-safe, and is it safe to have a static method that instantiates a separate DbContext? Or am I approaching this all wrong? I am not opposed to learning up on the repository pattern if I am taking the total wrong approach here.

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• Checking timeouts made more readable

  - by Markus

  I have several situations where I need to control timeouts in a technical application. Either in a loop or as a simple check. Of course – handling this is really easy, but none of these is looking cute. To clarify, here is some C# (Pseudo) code: private DateTime girlWentIntoBathroom; girlWentIntoBathroom = DateTime.Now; do { // do something } while (girlWentIntoBathroom.AddSeconds(10) > DateTime.Now); or if (girlWentIntoBathroom.AddSeconds(10) > DateTime.Now) MessageBox.Show("Wait a little longer"); else MessageBox.Show("Knock louder"); Now I was inspired by something a saw in Ruby on StackOverflow: Now I’m wondering if this construct can be made more readable using extension methods. My goal is something that can be read like “If girlWentIntoBathroom is more than 10 seconds ago” 1st attempt if (girlWentIntoBathroom > (10).Seconds().Ago()) MessageBox.Show("Wait a little longer"); else MessageBox.Show("Knock louder"); So I wrote an extension for integer that converts the integer into a TimeSpan public static TimeSpan Seconds(this int amount) { return new TimeSpan(0, 0, amount); } After that, I wrote an extension for TimeSpan like this: public static DateTime Ago(this TimeSpan diff) { return DateTime.Now.Add(-diff); } This works fine so far, but has a great disadvantage. The logic is inverted! Since girlWentIntoBathroom is a timestamp in the past, the right side of the equation needs to count backwards: impossible. Just inverting the equation is no solution, because it will invert the read sentence as well. 2nd attempt So I tried something new: if (girlWentIntoBathroom.IsMoreThan(10).SecondsAgo()) MessageBox.Show("Knock louder"); else MessageBox.Show("Wait a little longer"); IsMoreThan() needs to transport the past timestamp as well as the span for the extension SecondsAgo(). It could be: public static DateWithIntegerSpan IsMoreThan(this DateTime baseTime, int span) { return new DateWithIntegerSpan() { Date = baseTime, Span = span }; } Where DateWithIntegerSpan is simply: public class DateWithIntegerSpan { public DateTime Date {get; set;} public int Span { get; set; } } And SecondsAgo() is public static bool SecondsAgo(this DateWithIntegerSpan dateAndSpan) { return dateAndSpan.Date.Add(new TimeSpan(0, 0, dateAndSpan.Span)) < DateTime.Now; } Using this approach, the English sentence matches the expected behavior. But the disadvantage is, that I need a helping class (DateWithIntegerSpan). Has anyone an idea to make checking timeouts look more cute and closer to a readable sentence? Am I a little too insane thinking about something minor like this?

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• PHP Fingerprinting CMS Versions by their meta tags [migrated]

  - by Mud

  Hey guys I'm having some issues with the speed of my script. I'm a novice I know so getting past that - what suggestions would you have to speed up my script? I was originally just reading in the index.php and then searching the <head> of the page for an array of strings. Then I read about the get_meta_tags and went that way. Then I had issues with some sites having 300 redirects in place so I used curl to check the URL existed and to speed up things but it's still taking 5 minutes or so to execute. <?php function url_exist($url){ $c=curl_init(); curl_setopt($c,CURLOPT_URL,$url); curl_setopt($c,CURLOPT_HEADER,1); curl_setopt($c,CURLOPT_NOBODY,1); curl_setopt($c,CURLOPT_RETURNTRANSFER,1); curl_setopt($c,CURLOPT_FRESH_CONNECT,1); if(!curl_exec($c)){ return false; }else{ return true; } curl_close($c); } function checkVersion($url){ $tags = get_meta_tags($url); if (is_array($tags) && array_key_exists('generator', $tags)) { $v = "<span style='background-color:#7BF55D;color:#A3A0A0'>".$tags['generator']."</span"; }else{ $v="<span style='background-color:#F55D67;color:#A3A0A0'>Metatag not found!</span>"; } return $v; } $row = 1; echo "<table>"; if (($handle = fopen("url.csv", "r")) !== FALSE) { while (($data = fgetcsv($handle, 1000, ",")) !== FALSE) { $num = count($data); $row++; for ($c=0; $c < $num; $c++) { if(url_exist($data[$c])){ echo "<tr><td>".$data[$c]."</td><td>".checkVersion($data[$c])."</td></tr>"; sleep(2); }else{ echo "<tr><td>".$data[$c]."</td><td><td><span style='background-color:#F55D5D;color:#A3A0A0'>URL not valid!<span></td></tr>"; } } } fclose($handle); } echo "</table>"; ?>

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• "You are missing the following 32-bit libraries, and Steam may not run: libc.so.6" The common fixes don't work,

  - by M_Steam_User

  So I know this is a problem that has been asked around a lot, but I've tried a bunch of solutions with no success. I'm running Ubuntu 12.04 (64 bit), and I just installed it yesterday. This is my first time working with linux. The error is: You are missing the following 32-bit libraries, and Steam may not run: libc.so.6 Things I've tried. First, I had downloaded from the steam website. I uninstalled it, and tried again from the ubuntu software centre. sudo apt-get update sudo apt-get install ia32-libs sudo apt-get upgrade This installed a bunch of the 32 bit libraries, but did not fix the issue. This seems like the major fix for most people. The direct approach of sudo apt-get install libc.so.6 returns this: Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package libc.so.6 E: Couldn't find any package by regex 'libc.so.6' I guess libc.so.6 isn't a package, just a single file or something? I also tried gksudo gedit /etc/ld.so.conf.d/steam.conf Added these two lines, those the second one was all ready in the file, but copied over: /usr/lib32 /usr/lib/i386-linux-gnu/mesa Then executed: sudo ldconfig But nothing seemed to happen, steam still doesn't work. So, I feel like it is more likely that I have the library and steam isn't looking in the right place. One thing I've seen is people usually reference /usr/local/lib/ for your library locations. However, I can't find where to cd into /usr/, it isn't in my home folder. If /usr/ is the home folder, there is only a /.local folder which only has /share, no lib anywhere. Sorry for my linux ignorance. I appreciate any help, I honestly have no idea how to confirm I have the library and point steam to it, or if that is even the right thing to do. Edit: Tried this, not entirely sure what it means ~$ ls -l /lib32/libc* -rwxr-xr-x 1 root root 1721832 Sep 30 11:06 /lib32/libc-2.15.so -rw-r--r-- 1 root root 185928 Sep 30 11:06 /lib32/libcidn-2.15.so lrwxrwxrwx 1 root root 15 Sep 30 11:06 /lib32/libcidn.so.1 -> libcidn-2.15.so -rw-r--r-- 1 root root 34316 Sep 30 11:06 /lib32/libcrypt-2.15.so lrwxrwxrwx 1 root root 16 Sep 30 11:06 /lib32/libcrypt.so.1 -> libcrypt-2.15.so lrwxrwxrwx 1 root root 12 Sep 30 11:06 /lib32/libc.so.6 -> libc-2.15.so

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• ExplorerCanvas and JQuery

  - by PhubarBaz

  I am working on a Javascript app (CloudGraph) that uses HTML5 canvas and JQuery. I'm using ExplorerCanvas to support canvas in IE. I recently came across an interesting problem. What I was trying to do is restore the user's settings when the page is loaded. I read some information from a cookie that I set the last time the user accessed the application. One of these settings is the size of the canvas. I decided that the best place to do this would be when the document is ready using JQuery $(document).ready(). This worked fine in browsers that natively support the canvas element. But in IE it kept getting errors the first time I would hit the page. It seemed that the excanvas element wasn't initialized yet because I was getting null reference and unknown properties errors. If I refreshed the page the errors went away but the resized canvas wasn't drawing on the entire area of the canvas. It was like the clipping rectangle was still set to the default canvas size. I found that the canvas element when using excanvas has a div child element which is where the actual drawing takes place. When I changed the width and height of the canvas element in document.ready it didn't change the width and height of the child div. Initially my solution was to also change the div element when changing the canvas element and that worked. But then I realized that having to refresh the page every time I started the app in IE really sucked. That wouldn't be acceptable for users. Since it seemed like the canvas wasn't getting initialized before I was trying to use it I decided to try to initialize my app at a different time. I figured the next best place was in the onload event. Sure enough, moving my initialization to onload fixed all of the problems. So, it looks like the canvas shouldn't be manipulated until the onload event when using ExplorerCanvas. There might be ways to do it when the document is ready. I found some posts on initializing excanvas manually, but for me waiting until onload worked just fine.

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• Silverlight 4 Twitter Client &ndash; Part 5

  - by Max

  In this post, we will look at implementing the following in our twitter client - displaying the profile picture in the home page after logging in. So to accomplish this, we will need to do the following steps. 1) First of all, let us create another field in our Global variable static class to hold the profile image url. So just create a static string field in that. public static string profileImage { get; set; } 2) In the Login.xaml.cs file, before the line where we redirect to the Home page if the login was successful. Create another WebClient request to fetch details from this url - .xml">http://api.twitter.com/1/users/show/<TwitterUsername>.xml I am interested only in the “profile_image_url” node in this xml string returned. You can choose what ever field you need – the reference to the Twitter API Documentation is here. 3) This particular url does not require any authentication so no need of network credentials for this and also the useDefaultCredentials will be true. So this code would look like. WebRequest.RegisterPrefix("http://", System.Net.Browser.WebRequestCreator.ClientHttp); WebClient myService = new WebClient(); myService.AllowReadStreamBuffering = myService.UseDefaultCredentials = true; myService.DownloadStringCompleted += new DownloadStringCompletedEventHandler(TimelineRequestCompleted_User);) myService.DownloadStringAsync(new Uri("http://api.twitter.com/1/users/show/" + TwitterUsername.Text + ".xml")); 4) To parse the xml file returned by this and get the value of the “profile_image_url” node, the LINQ code will look something like XDocument xdoc; xdoc = XDocument.Parse(e.Result); var answer = (from status in xdoc.Descendants("user") select status.Element("profile_image_url").Value); GlobalVariable.profileImage = answer.First().ToString(); 5) After this, we can then redirect to Home page completing our login formalities. 6) In the home page, add a image tag and give it a name, something like <Image Name="image1" Stretch="Fill" Margin="29,29,0,0" Height="73" VerticalAlignment="Top" HorizontalAlignment="Left" Width="73" /> 7) In the OnNavigated to event in home page, we can set the image source url as below image1.Source = new BitmapImage(new Uri(GlobalVariable.profileImage, UriKind.Absolute)); Hope this helps. If you have any queries / suggestions, please feel free to comment below or contact me. Technorati Tags: Silverlight,LINQ,Twitter API,Twitter

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• Is it dangerous for me to give some of my Model classes Control-like methods?

  - by Pureferret

  In my personal project I have tried to stick to MVC, but I've also been made aware that sticking to MVC too tightly can be a bad thing as it makes writing awkward and forces the flow of the program in odd ways (i.e. some simple functions can be performed by something that normally wouldn't, and avoid MVC related overheads). So I'm beginning to feel justified in this compromise: I have some 'manager programs' that 'own' data and have some way to manipulate it, as such I think they'd count as both part of the model, and part of the control, and to me this feels more natural than keepingthem separate. For instance: One of my Managers is the PlayerCharacterManager that has these methods: void buySkill(PlayerCharacter playerCharacter, Skill skill); void changeName(); void changeRole(); void restatCharacter(); void addCharacterToGame(); void createNewCharacter(); PlayerCharacter getPlayerCharacter(); List<PlayerCharacter> getPlayersCharacter(Player player); List<PlayerCharacter> getAllCharacters(); I hope the mothod names are transparent enough that they don't all need explaining. I've called it a manager because it will help manage all of the PlayerCharacter 'model' objects the code creates, and create and keep a map of these. I may also get it to store other information in the future. I plan to have another two similar classes for this sort of control, but I will orchestrate when and how this happens, and what to do with the returned data via a pure controller class. This splitting up control between informed managers and the controller, as opposed to operating just through a controller seems like it will simplify my code and make it flow more. My question is, is this a dangerous choice, in terms of making the code harder to follow/test/fix? Is this somethign established as good or bad or neutral? I oculdn't find anything similar except the idea of Actors but that's not quite why I'm trying to do. Edit: Perhaps an example is needed; I'm using the Controller to update the view and access the data, so when I click the 'Add new character to a player button' it'll call methods in the controller that then go and tell the PlayerCharacterManager class to create a new character instance, it'll call the PlayerManager class to add that new character to the player-character map, and then it'll add this information to the database, and tell the view to update any GUIs effected. That is the sort of 'control sequence' I'm hoping to create with these manager classes.

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• [EF + Oracle] Inserting Data (Sequences) (2/2)

  - by JTorrecilla

  Prologue In the previous chapter we have see how to create DB records with EF, now we are going to Some Questions about Oracle.   ORACLE One characteristic from SQL Server that differs from Oracle is “Identity”. To all that has not worked with SQL Server, this property, that applies to Integer Columns, lets indicate that there is auto increment columns, by that way it will be filled automatically, without writing it on the insert statement. In EF with SQL Server, the properties whose match with Identity columns, will be filled after invoking SaveChanges method. In Oracle DB, there is no Identity Property, but there is something similar. Sequences Sequences are DB objects, that allow to create auto increment, but there are not related directly to a Table. The syntax is as follows: name, min value, max value and begin value. 1: CREATE SEQUENCE nombre_secuencia 2: INCREMENT BY numero_incremento 3: START WITH numero_por_el_que_empezara 4: MAXVALUE valor_maximo | NOMAXVALUE 5: MINVALUE valor_minimo | NOMINVALUE 6: CYCLE | NOCYCLE 7: ORDER | NOORDER 8:    How to get sequence value? To obtain the next val from the sequence: 1: SELECT nb_secuencia.Nextval 2: From Dual Due to there is no direct way to indicate that a column is related to a sequence, there is several ways to imitate the behavior: Use a Trigger (DB), Use Stored Procedures or Functions(…) or my particularly option. EF model, only, imports Table Objects, Stored Procedures or Functions, but not sequences. By that, I decide to create my own extension Method to invoke Next Val from a sequence: 1: public static class EFSequence 2: { 3: public static int GetNextValue(this ObjectContext contexto, string SequenceName) 4: { 5: string Connection = ConfigurationManager.ConnectionStrings["JTorrecillaEntities2"].ConnectionString; 6: Connection=Connection.Substring(Connection.IndexOf(@"connection string=")+19); 7: Connection = Connection.Remove(Connection.Length - 1, 1); 8: using (IDbConnection con = new Oracle.DataAccess.Client.OracleConnection(Connection)) 9: { 10: using (IDbCommand cmd = con.CreateCommand()) 11: { 12: con.Open(); 13: cmd.CommandText = String.Format("Select {0}.nextval from DUAL", SequenceName); 14: return Convert.ToInt32(cmd.ExecuteScalar()); 15: } 16: } 17:  18: } 19: } This Object Context’s extension method are going to invoke a query with the Sequence indicated by parameter. It takes the connection strings from the App settings, removing the meta data, that was created by VS when generated the EF model. And then, returns the next value from the Sequence. The next value of a Sequence is unique, by that, when some concurrent users are going to create records in the DB using the sequence will not get duplicates. This is my own implementation, I know that it could be several ways to do and better ways. If I find any other way, I promise to post it. To use the example is needed to add a reference to the Oracle (ODP.NET) dll.

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• How can I improve the battery life under 12.04 on my Inspiron 14z? [duplicate]

  - by cfogelberg

  This question already has an answer here: Tips to extend battery life for laptops and notebooks 24 answers How do I improve the battery life of my Inspiron 14z under Ubuntu 12.04? This laptop gets 4-5 hours of battery life using Windows (e.g. here). I've removed Windows, installed Ubuntu 12.04 and the initial battery life was only 2 hours. With some tweaks (described below) it's still only ~2.5 hours. For reference, the laptop is the latest model of the 14z: i5-3337U processor 32GB MSATA, 500GB HDD (5400rpm) AMD Radeon HD7570M graphics card I have put ext4 partitions on both the SSD and the HDD, and have mounted / to the SSD and /home to the HDD. I also put a 24gb linux swap partition at the start of the HDD, though I figure this won't be used all that much (the laptop has 8gb of RAM). After googling around and reading Ask Ubuntu and other sites extensively, I have done the following steps, and they have improved the battery life ~30 minutes (exact improvement not clear, but battery life is still nowhere near 4-5 hours). Installed Jupiter (and set Performance to "Power Saving") Installed laptop-mode-tools cat /proc/sys/vm/laptop_mode now outputs 5 (previously it output 0) But it's not clear that this will help: AskUbuntu question Turned down the brightness of my screen from full to 1/3 Other things I have heard about but have not tried for fear of frying the laptop or my linux install: Add "pcie_aspm=force" at the end of the line with "quiet splash" in /boot/grub/grub.cfg Enable ALPM, but it may already be enabled in 12.04? Enable i915 framebuffer compression Use a propietary driver for the graphics card? Turn off the graphics card? (what would happen if I relied on the internal Intel bridge?) Use TLP? Spin down the HDD more aggressively (howto, but I think laptop-mode-tools does this already) The only other thing I've noticed is that plastic just above the F5, F6 and F7 keys gets really hot. According to Jupiter my CPU temperature is only 69 celsius and the System Monitor shows CPU load at 7% so I don't think it's the CPU. Maybe it's the graphics card? Also, I've set up MongoDB and LAMP on the machine as well. When I run powertop MongoDB is high in the list, but I'm not sure if that's relevant to battery life because I'm not actually doing anything with MongoDB most of the time. Edit - Additional info as requested $ lspci -nnk | grep -iEA3 "(graphics|vga)" 00:02.0 VGA compatible controller [0300]: Intel Corporation Ivy Bridge Graphics Controller [8086:0166] (rev 09) Subsystem: Dell Device [1028:057f] Kernel driver in use: i915 Kernel modules: i915 -- 02:00.0 VGA compatible controller [0300]: Advanced Micro Devices [AMD] nee ATI Thames [Radeon 7500M/7600M Series] [1002:6841] Subsystem: Dell Device [1028:057f] Kernel driver in use: radeon Kernel modules: radeon

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• Physics Engine [Collision Response, 2-dimensional] experts, help!! My stack is unstable!

  - by Register Sole

  Previously, I struggle with the sequential impulse-based method I developed. Thanks to jedediah referring me to this paper, I managed to rebuild the codes and implement the simultaneous impulse based method with Projected-Gauss-Seidel (PGS) iterative solver as described by Erin Catto (mentioned in the reference of the paper as [Catt05]). So here's how it currently is: The simulation handles 2-dimensional rotating convex polygons. Detection is using separating-axis test, with a SKIN, meaning closest points between two polygons is detected and determined if their distance is less than SKIN. To resolve collision, simultaneous impulse-based method is used. It is solved using iterative solver (PGS-solver) as in Erin Catto's paper. Error-correction is implemented using Baumgarte's stabilization (you can refer to either paper for this) using J V = beta/dt*overlap, J is the Jacobian for the constraints, V the matrix containing the velocities of the bodies, beta an error-correction parameter that is better be < 1, dt the time-step taken by the engine, and overlap, the overlap between the bodies (true overlap, so SKIN is ignored). However, it is still less stable than I expected :s I tried to stack hexagons (or squares, doesn't really matter), and even with only 4 to 5 of them, they hardly stand still! Also note that I am not looking for a sleeping scheme. But I would settle if you have any explicit scheme to handle resting contacts. That said, I would be more than happy if you have a way of treating it generally (as continuous collision, instead of explicitly as a special state). Ideas I have: I would try adding a damping term (proportional to velocity) to the Baumgarte. Is this a good idea in general? If not I would not want to waste my time trying to tune the parameter hoping it magically works. Ideas I have tried: Using simultaneous position based error correction as described in the paper in section 5.3.2, turned out to be worse than the current scheme. If you want to know the parameters I used: Hexagons, side 50 (pixels) gravity 2400 (pixels/sec^2) time-step 1/60 (sec) beta 0.1 restitution 0 to 0.2 coeff. of friction 0.2 PGS iteration 10 initial separation 10 (pixels) mass 1 (unit is irrelevant for now, i modified velocity directly<-impulse method) inertia 1/1000 Thanks in advance! I really appreciate any help from you guys!! :)

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