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• Simulate 'Shock absorbtion' with tire rubber in PhysX (2.8.x)

  - by Mungoid

  This is a kinda tricky question and I fear there is no easy enough solution, but I figured I'd hit SE up before giving up on it and just doing what I can. A machine I am working on has no suspension or shocks or springs of any sort in the real machine, so you would think that when it drives over bumps, it would shake like crazy but because its tires (6 of them) are quite large they seem to absorb a lot of shock from the bumps. Part of this is because the machine is around 30k lbs and it just smashes/compresses any bumps in the ground down (This is another issue im still working on) and the other part is that the tires seem to have a lot of flex to them with a lot of air as well. So my current task is to simulate shock absorption in physx without visibly separating the tires from the spindle/axle.. I have been messing with all kinds of NxMaterial, NxSpring, Joints, etc. and have had no luck getting this to work. The main problem is that the spindle attached to the tire is directly in the center and the axle is basically solidly attached to the chassis, so if i give it any spring or suspension travel, that spindle on the tires will move upwards or downwards, looking very odd because now its not any longer in the center of the tire. I tried giving it a higher restitution but that just makes it bouncy without any shock absorption. Another avenue I am messing with is to actively smooth the terrain in front of the tires so that before it hits a bumpy patch, that patch is smoothed and it doesn't bounce. The only issue with this is that it is pretty expensive to do with 6 tires, high tesselation of the terrain and other complex things going on at the same time in this simulation. I am still working on this but I am hoping to mix and match a few different aspects to get the best possible outcome. This is a bit of a complex issue so I'm not expecting anyone to have a definitive answer, just hoping someone may think of something I haven't =-) -Side note: Yes i know PhysX 2.8.x is quite outdated but we have to stick with it for this implementation. We are in the process of going to another physics engine but it is out of scope to apply that engine to this project.

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• Android Array Lag?

  - by Mike

  I am making a platform game for Android. It is sort of a tile based game. I added bullets and enemies with AI and a bunch of tile types. I created a simple map with no Enemies. Everything was running well and smooth until I shot a bunch of bullets randomly everywhere. A couple of hundreds of bullets later, the FPS lowered. I made a test to find out if the bullets were the problem so I made another simple map with just a tile to stand on and left it for a while. Minutes later, I played around with it a bit to check if the FPS changed and it didnt. I reloaded the same map and shot a lot of bullets. Minutes later, the FPS was visibly lower even after the number of bullets were zero. Points to note: Programmed FPS is 30 Tested on a Samsung Galaxy Y and Samsung Galaxy W Any tile, enemy, bullet that is off screen is not drawn to prevent lag Bullets collide with Tiles (if they dont collide with in 450 frames, they are removed from the array) I used List bullets = new ListArray(); I used bullets.add(new Bullet(x, y, params...)); I used for(...){ if(...){ bullets.remove(i); } } Code for bullet: private void drawBullets(Canvas canvas) { for (int i = 0; i < bullets.size(); i++) { Bullet b = bullets.get(i); b.update(canvas); //updates physics if (b.t > blm) { //if the bullet is past its expiry bullets.remove(i); i--; } else { if (svx((b.x)) > 0 && svx(b.x) < width && svy((b.y)) > 0 && svy(b.y) < height) { // if bullet is not off screen b.draw(canvas); // draw the bullet } } } } I tried searching for solutions and references but I have no luck. I'm guessing that the lag has something to do with the Array and the Bullets or Classes that I've loaded? I'm not sure! Someone please help! Thanks in advance! :)

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• Drawing flaming letters in 3D with OpenGL ES 2.0

  - by Chiquis

  I am a bit confused about how to achieve this. What I want is to "draw with flames". I have achieved this with textures successfully, but now my concern is about doing this with particles to achieve the flaming effect. Am I supposed to create a path along which I should add many particle emitters that will be emitting flame particles? I understand the concept for 2D, but for 3D are the particles always supposed to be facing the user? Something else I'm worried about is the performance hit that will occur by having that many particle emitters, because there can be many letters and drawings at the same time, and each of these elements will have many particle emitters. More detailed explanation: I have a path of points, which is my model. Imagine a dotted letter "S" for example. I want make the "S" be on fire. The "S" is just an example it can be a circle, triangle, a line, pretty much any path described by my set of points. For achieving this fire effect I thought about using particles. So I am using a program called "Particle Designer" to create a fire style particle emitter. This emitter looks perfect on 2D on the iphone screen dimensions. So then I thought that I could probably draw an S or any other figure if i place many particle emitters next to each other following the path described. To move from the 2D version to the 3D version I thought about, scaling the emitter (with a scale matrix multiplication in its model matrix) and then moving it to a point in my 3D world. I did this and it works. So now I have 1 particle emitter in the 3D world. My question is, is this how you would achieve a flaming letter? Is this too inefficient if i expect to have many flaming paths on my world? Am i supposed to rotate the particle's quad so that its always looking at the user? (the last one is because i noticed that if u look at it from the side the particles start to flatten out)

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• Website directory structure regarding subdomains, www, and "global" content

  - by Pawnguy7

  I am trying to make a homemade HTTP server. It occurs to me, though, I never fully understood what you might call "relativity" among web pages. I have come across that www. is a subdomain, and I understand its original purpose. IT sounds like, in general, you would redirect (is that 301 or 302?) it to a... non-subdomain, sort of. As in, redirecting www.example.com to example.com. I am not entirely sure how to make this work when retrieving files for an HTTP server though. I would assume that example.com would be the root, and www manifests as a folder within it. I am unsure. There is also the question of multi-level subdomains, e.g. subdomain2.subdomain1.example.com. It seems to me they are structured "backwards", where you go from the root left in folder structure. In this situation, subdomain2 is a directory within subdomain1, which is a directory in the root. Finally, it occurs to me I might want a sort of global location. For example, maybe all subdomains still use an image as a logo. It makes more sense to me that there is one image, rather than each having a copy. In the same way, albiet more doubtfully, you might have global CSS (though that is a bit contrary to the idea of a subdomain in the first place), or a javascript that is commonly used. (more efficient than each having its copy and better for organization purposes). Finally, mabye you have a global 404 page. I think this might be the case where you have user-created subdomains (say bloggername.example.com), where example.com still has a default 404 when either a subdomain does not exist or page does not exists under a valid blogger. I am confused on what the directory structure for this should be. To summarize: Should and how it have a global files not in a subdirectory, how should www. be handled, (or how a now www or other subdomain should be handled), and the pattern for root/subdomain, as well as subdomain within subdomains (order-wise). Sorry this is multiple questions, but I feel at the root they are all related to the directory.

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• iPhone app development pricing [closed]

  - by AlexMorley-Finch

  I currently manage a website design and development company that integrates itself with print work too. I've been co manager for a couple of months now, however business is slow at the moment. I got an email today from a potential client asking if we do iPhone app development. Obviously we do not. But, seeing as there aren't many other project on the go at the moment, why not give it a go? Searching Google was my first option. I did a bit of background scrubbing. Discovered that I need certain developer tools etc. This can be arranged easily enough. The reason I came to Stack Exchange is for answers to these questions. I am a competant programmer and have had experience in Java, PHP, JavaScript, C++ and C#. So how long would it take me to come to grips with Objective-C? Assuming an 8 hour working day. Not only the language but also the iPhone interface libraries (if any exist) and other native libraries? The potential client said the app will be a catalogue. So I'm assuming either the data will be pulled online or in some kind of local database. I know the requirements are vague but does anyone have any idea of how mug time this would take? To learn the language, design the architecture and code? 40 Hours? 80 Hours? My final question kind of depends on the first two. But obviously the potential client wants a quote. And I have got no idea how much an app costs. I did some research and found a huge range in differences. The majority of the cost would cone from the time to develops the app! So to summarise. How long would it take me to be comfortable coding Objective-C, taking into consideration my past knowledge? I'm assuming a day or two to fully understand but you really don't know. How long would it take me to develop an app? How much should I charge (approx) for the development of this app?

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• Why is Java the lingua franca at so many institutions?

  - by Billy ONeal

  EDIT: This question at first seems to be bashing Java, and I guess at this point it is a bit. However, the bigger point I am trying to make is why any one single language is chosen as the one end all be all solution to all problems. Java happens to be the one that's used so that's the one I had to beat on here, but I'm not intentionality ripping Java a new one :) I don't like Java in most academic settings. I'm not saying the language itself is bad -- it has several extremely desirable aspects, most importantly the ability to run without recompilation on most any platform. Nothing wrong with using the language for Your Next App ^TM. (Not something I would personally do, but that's more because I have less experience with it, rather than it's design being poor) I think it is a waste that high level CS courses are taught using Java as a language. Too many of my co-students cannot program worth a damn, because they don't know how to work in a non-garbage-collected world. They don't fundamentally understand the machines they are programming for. When someone can work outside of a garbage collected world, they can work inside of one, but not vice versa. GC is a tool, not a crutch. But the way it is used to teach computer science students is a as a crutch. Computer science should not teach an entire suite of courses tailored to a single language. Students leave with the idea that all good design is idiomatic Java design, and that Object Oriented Design is the ONE TRUE WAY THAT IS THE ONLY WAY THINGS CAN BE DONE. Other languages, at least one of them not being a garbage collected language, should be used in teaching, in order to give the graduate a better understanding of the machines. It is an embarrassment that somebody with a PHD in CS from a respected institution cannot program their way out of a paper bag. What's worse, is that when I talk to those CS professors who actually do understand how things operate, they share feelings like this, that we're doing a disservice to our students by doing everything in Java. (Note that the above would be the same if I replaced it with any other language, generally using a single language is the problem, not Java itself) In total, I feel I can no longer respect any kind of degree at all -- when I can't see those around me able to program their way out of fizzbuzz problems. Why/how did it get to be this way?

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• password incorrect 3 times + suspected failed update

  - by Cheese

  I have been lurking your site for the past few hours, and have found myself in a bit of a pickle. Visiting my parents, I discover that neither computer, nor laptop work. Long story short, I've got the laptop working, but have completely fudged up the computer. I am a n00b, but I was at least willing to give it a go. The comp originally had ubuntu 11.10 installed, later updated to 12.04. We have cds for both. I do not understand what the initial problem was for my parents, but somehow when I turned on the computer, it worked for me. Soon after, I was nagged to install the latest updates. So, I spent the next half an hour wondering why the updates kept on asking for 11.04 cdroms, until I realised that you could turn off the cdrom necessity. After doing this via console, I installed some of the smaller updates, before being told to do a partial update. This failed a few times, and ended up freezing whilst reinstalling drivers. After a hard restart I continued to type whatever I could find on the forum into the console. At some point, the console started saying that I had 3 incorrect password inputs, and sudo commands stopped altogether. I found another thread discussing this; but people kept on suggesting changing passwords (which I did to no avail) or other things that made use of sudo (which I am locked out of, although I am technically the admin) I found myself somehow on the Ctrl+Alt+F1 console, and after being utterly confused (and Ctrl+AltF5 failing for me), another hard reset occurred. Somewhere along the way I created a USB start up for 14.04, (but this does not seem to work) Now I am left with an admin (and guest) account that log in but have blank screens (with only the desktop background showing) and I can't do anything in the console because I'm locked out. Interestingly, the console now says that I am running 14.04 although all updates said they had failed. Aside from the obvious lessons I have learnt (don't fiddle about in the console when you have no idea what you're doing "Dog wearing safety glasses "I have no idea what I am doing" GIF would be inserted here ) Is there any way I can redeem this almighty muck up? A million thanks for any help!

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• Should i continue my self-taught coding practice or learn how to do coding professionally?

  - by G1i1ch

  Lately I've been getting professional work, hanging out with other programmers, and making friends in the industry. The only thing is I'm 100% self-taught. It's caused my style to extremely deviate from the style of those that are properly trained. It's the techniques and organization of my code that's different. It's a mixture of several things I do. I tend to blend several programming paradigms together. Like Functional and OO. I lean to the Functional side more than OO, but I see the use of OO when something would make more sense as an abstract entity. Like a game object. Next I also go the simple route when doing something. When in contrast, it seems like sometimes the code I see from professional programmers is complicated for the sake of it! I use lots of closures. And lastly, I'm not the best commenter. I find it easier just to read through my code than reading the comment. And most cases I just end up reading the code even if there are comments. Plus I've been told that, because of how simply I write my code, it's very easy to read it. I hear professionally trained programmers go on and on about things like unit tests. Something I've never used before so I haven't even the faintest idea of what they are or how they work. Lots and lots of underscores "_", which aren't really my taste. Most of the techniques I use are straight from me, or a few books I've read. Don't know anything about MVC, I've heard a lot about it though with things like backbone.js. I think it's a way to organize an application. It just confuses me though because by now I've made my own organizational structures. It's a bit of a pain. I can't use template applications at all when learning something new like with Ubuntu's Quickly. I have trouble understanding code that I can tell is from someone trained. Complete OO programming really leaves a bad taste in my mouth, yet that seems to be what EVERYONE else is strictly using. It's left me not that confident in the look of my code, or wondering whether I'll cause sparks when joining a company or maybe contributing to open source projects. In fact I'm rather scared of the fact that people will eventually be checking out my code. Is this just something normal any programmer goes through or should I really look to change up my techniques?

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• How best to look up objects by label?

  - by dsollen

  I am writing the server backed by a pre-written API. I'm going to get a number of strings representing ports, signals, paths, etc etc etc. I need to look up the object associated with a given label, these objects are all in memory (no sql magic to do this for me). My question is, how best do I associate a given unique label with the mutable object it represents? I have enough objects that looking through every signal or every port to find the one that matches is possible, but may be slightly too slow. To be honest the direct 'look at every object' method is probably good enough for so small a body of objects and anything else is premature optimization, but I still am curious what the proper solution would be if I thought my signals were going to grow a bit larger. As I see it there are two options available. First would be to to create a 'store' that is a simple map between object and label. I could have it so that every time I call addObject the object is automatically saved into a hashmap or the like. This works, but relies on my properly adding and deleting each object so the map doesn't grow indefinitely. The biggest issue to me is that this involves having some hidden static map in my ModelObject class that just feels...wrong somehow. The other option is to have some method that can interpret the labels. All of these labels are derived from the underlying objects. So I can look at the signal label, for instance, and say "these 20 characters are the port" to figure out what port I need. This would allow me to quickly figure out what I need. However, if the label method is changed the translateLabelToObject method needs to be updated as well or everything breaks. Which solution is cleaner, or possibly a cleaner solution than either of above? For the record I'm working with sufficient number of variables to make direct comparison a little slow, but not enough to be concerned about memory overhead, written in java. All objects that have labels I need to look up extend the same parent class.

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• Rebuilding a Mac Mini (early 2009)

  - by Kelly Jones

  This weekend I decided to rebuild the family’s Mac Mini.  It’s the early 2009 model and I hadn’t done it since we got it in March of 2009.  Even worse, I had done the import data step (or whatever Apple calls it) which brought over all of the data files and apps from our previous Mac.  AND that install goes back to before 2005, as far as I can remember.  SO, to say that “cruft” had built up in the operating system, is probably a bit of an understatement. The rebuild went pretty smoothly, especially since I had a couple of spare hard drives.  I hooked up a spare USB drive and formatted it for use with the Mac.  I then used Carbon Copy to clone the internal hard drive onto the USB drive.  (Carbon Copy is a great little app that I used several years ago and I was happy to see it was not only still around, but updated as well.) Once I had my backup, I shut down the Mac and replaced the internal hard drive.  I had purchased the hard drive last fall to use with my work laptop, but I got a new work laptop (with awesome dual SSDs) so I wasn’t using it anymore.  The replacement drive (Seagate Momentus 7200.4 ST9500420AS 500GB 7200 RPM 2.5" SATA 3.0Gb/s Internal Notebook Hard Drive) has more than double the original’s capacity and is also faster.  I’ll have to keep an eye on the temperature, since that 7200 drive will run hotter. Opening the Mac Mini is not for the easily intimidated!  That cool little case is quite the pain to open.  Luckily, OWC put a video together here.  After replacing the drive, I then installed a clean copy of OS 10.5 using the DVDs that came with the Mac.  After the OS, it was time to reinstall the apps.  I downloaded some of the freeware, just to make sure I had the latest versions.  For the rest, I just copied from the backup cloned drive to the new drive.  (I love the way most Mac apps are written – with almost everything contained within a “package” that I can just copy from one drive to another.  MUCH better than the Windows way of using shared DLLs and the registry to store critical pieces that the app needs in order to run!) The whole process took longer than I would have preferred, but it was long overdue.  It definitely “feels” faster, especially boot time and application launches.

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• What OpenGL version(s) to learn and/or use?

  - by zuko

  So, I'm new to OpenGL... I have general knowledge of game programming but little practical experience. I've been looking into various articles and books and trying to dive into OpenGL, but I've found the various versions and old vs new way of doing things confusing. I guess my first questions is does anyone know some figures about percentages of gamers that can run each version of OpenGL. What's the market share like? 2.x, 3.x, 4.x... I looked into the requirements for Half Life 2 since I know Valve updated it with OpenGL to run on Mac and I know they usually try to hit a very wide user-base, and they say a minimum of GeForce 8 Series. I looked at the 8800 GT on Nvidia's website and it listed support for OpenGL 2.1. Which, maybe I'm wrong, sounds ancient to me since there's already 4.x. I looked up a driver for 8800GT and it says it supports 4.2! A bit of a discrepancy there, lol. I've also read things like XP only supports up to a certain version, or OS X only supports 3.2, or all kinds of other things. Overall, I'm just confused as to how much support there is for various versions and what version to learn/use. I'm also looking for learning resources. My search results thus far have pointed me to the OpenGL SuperBible. The 4th edition has great reviews on Amazon, but it teaches 2.1. The 5th edition teaches 3.3 and there are a couple things in the reviews that mention the 4th edition is better and that the 5th edition doesn't properly teach the new features or something? Basically, even within learning material I'm seeing discrepancies and I just don't even know where to start. From what I understand, 3.x started a whole new way of doing things and I've read from various articles and reviews that you want to "stay away from deprecated features like glBegin(), glEnd()" yet a lot of books and tutorials I've seen use that method. I've seen people saying that, basically, the new way of doing stuff is more complicated yet the old way is bad . Just a side note, personally, I know I still have a lot to learn beforehand, but I'm interested in tessellation; so I guess that factors into it as well, because, as far as I understand that's only in 4.x? [just btw, my desktop supports 4.2]

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• Advantages to Multiple Methods over Switch

  - by tandu

  I received a code review from a senior developer today asking "By the way, what is your objection to dispatching functions by way of a switch statement?" I have read in many places about how pumping an argument through switch to call methods is bad OOP, not as extensible, etc. However, I can't really come up with a definitive answer for him. I would like to settle this for myself once and for all. Here are our competing code suggestions (php used as an example, but can apply more universally): class Switch { public function go($arg) { switch ($arg) { case "one": echo "one\n"; break; case "two": echo "two\n"; break; case "three": echo "three\n"; break; default: throw new Exception("Unknown call: $arg"); break; } } } class Oop { public function go_one() { echo "one\n"; } public function go_two() { echo "two\n"; } public function go_three() { echo "three\n"; } public function __call($_, $__) { throw new Exception("Unknown call $_ with arguments: " . print_r($__, true)); } } Part of his argument was "It (switch method) has a much cleaner way of handling default cases than what you have in the generic __call() magic method." I disagree about the cleanliness and in fact prefer call, but I would like to hear what others have to say. Arguments I can come up with in support of Oop scheme: A bit cleaner in terms of the code you have to write (less, easier to read, less keywords to consider) Not all actions delegated to a single method. Not much difference in execution here, but at least the text is more compartmentalized. In the same vein, another method can be added anywhere in the class instead of a specific spot. Methods are namespaced, which is nice. Does not apply here, but consider a case where Switch::go() operated on a member rather than a parameter. You would have to change the member first, then call the method. For Oop you can call the methods independently at any time. Arguments I can come up with in support of Switch scheme: For the sake of argument, cleaner method of dealing with a default (unknown) request Seems less magical, which might make unfamiliar developers feel more comfortable Anyone have anything to add for either side? I'd like to have a good answer for him.

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• Boot error aftter clean Ubuntu 13.04 install: [Reboot and select proper boot device]

  - by IcarusNM

  I am having the same problem as this guy where a fresh Ubuntu install completes beautifully but will not boot. I get the ASUS (?) "Reboot and select proper boot device" error, first with Xubuntu 13.10 and after finally giving up there, and Xubuntu 13.4, I am back to regular Ubuntu 13.4. ASUS motherboard Z77, Intel chipset. Standard internal SATA 500GB HD. 64-bit. All-new hardware less than 3 months old. It was running Ubuntu 12.04LTC great until I tried this upgrade. I have re-installed from scratch every which way: with LVM, without LVM; with the default partitions, with my own partitions. With ext3 or ext4. Alongside; replace; upgrade. No difference. On the last two tries, I have booted afterward from the same USB stick, downloaded and run boot-repair, and now I guess I am off to the boot-repair support email with my URLs from that. It did all kinds of cool stuff but ultimately made no difference. I never got anything like this with Ubuntu 12.04. I've now probably re-installed Ubuntu 13.04 ten times slightly different ways. I finally found how to skip the language packs, so at least that sped things up! :) This starts from the ubuntu-13.04-desktop-amd64.iso and UNetbootin as suggested on the official instructions for USB thumb drive creation from OSX. That part all works fine (booting the USB on the PC and trying Ubuntu and/or installing from there on the PC HD.) I have no CD drive on this PC, but I suppose I could get one. I would rather find some Linux install that works from USB like I've always done. After running boot-repair twice, in the ASUS BIOS I now see three different UEFI boot options in the priority list, and they are all labeled exactly the same: ubuntu (P6: WDC WD5000AAKX-00U6AA0) Then there's a non-UEFI option: P6: WDC WD5000AAKX-00U6AA0 (476940MB) And a fifth option appeared after the first boot-repair: Windows Boot Manager (P6: WDC WD5000AAKX-00U6AA0) I have tried all 5 of these, and I get exactly the same error. I have never had Windows installed on this HD. ASUS is calling it Windows Boot Manaer but I presume that's a mistaken label for whatever boot-repair did. I can boot on USB and run GParted and it looks great. The partitions all look normal. I found another case of this online with no solution posted. I can't find much about it online. Needs a Master Boot Record wipe/redo?? I'm not sure how.

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• Building a Store Locator ASP.NET Application Using Google Maps API

  The past couple of projects I've been working on have included the use of the Google Maps API and geocoding service in websites for various reasons. I decided to tie together some of the lessons learned, build an ASP.NETstore locator demo, and write about it on 4Guys. Last week I published the first article in what I think will be a three-part series: Building a Store Locator ASP.NET Application Using Google Maps (Part 1). Part 1 walks through creating a demo where a user can type in an address and any stores within a (roughly) 15 mile area will be displayed in a grid.The article begins with a look at the database used to power the store locator (namely, a single table that contains one row for every location, with each location storing its store number, address, and, most important, latitude and longitude coordinates) and then turns to usingGoogle's geocoding service to translatea user-entered address into latitude and longitude coordinates. The latitude and longitude coordinates are used to find nearby stores, which are then displayed in a grid. Part 2 looks at enhancing the search results to include a map with markers indicating the position of each nearby store location. The Google Maps API, along with a bit of client-side script and server-side logic, make this actually pretty straightforward and easy to implement. Here's a screen shot of the improved store locator results. Part 3, which I plan on publishing next week, looks at how to enhance the map by using information windows to display address information when clicking a marker. Additionally, I'll show how to use custom icons for the markers so that instead of having the same marker for each nearby location the markers will be images numbered 1, 2, 3, and so on, which will correspond to a number assigned to each search result in the grid. The idea here is that by numbering the search results in the grid and the markers on the map visitors will quickly be able to see what marker corresponds to what search result. This article and demo has been a lot of fun to write and create, and I hope you enjoy reading it, too. Building a Store Locator ASP.NET Application Using Google Maps API (Part 1) Building a Store Locator ASP.NET Application Using Google Maps API (Part 2) Happy Programming!Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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• Are there any good Java/JVM libraries for my Expression Tree architecture?

  - by Snuggy

  My team and I are developing an enterprise-level application and I have devised an architecture for it that's best described as an "Expression Tree". The basic idea is that the leaf nodes of the tree are very simple expressions (perhaps simple values or strings). Nodes closer to the trunk will get more and more complex, taking the simpler nodes as their inputs and returning more complex results for their parents. Looking at it the other way, the application performs some task, and for this it creates a root expression. The root expression divides its input into smaller units and creates child expressions, which when evaluated it can use to build it's own result. The subdividing process continues until the simplest leaf nodes. There are two very important aspects of this architecture: It must be possible to manipulate nodes of the tree after it is built. The nodes may be given new input values to work with and any change in result for that node needs to be propagated back up the tree to the root node. The application must make best use of available processors and ultimately be scalable to other computers in a grid or in the cloud. Nodes in the tree will often be updating concurrently and notifying other interested nodes in the tree when they get a new value. Unfortunately, I'm not at liberty to discuss my actual application, but to aid understanding a little bit, you might imagine a kind of spreadsheet application being implemented with a similar architecture, where changes to cells in the table are propagated all over the place to other cells that need the result. The spreadsheet could get so massive that applying multi-core multi-computer distributed system to solve it would be of benefit. I've got my prototype "Expression Engine" working nicely on a single multi-core PC but I've started to run into a few concurrency issues (as expected because I haven't been taking too much care so far) so it's now time to start thinking about migrating the Engine to a more robust library, and that leads to a number of related questions: Is there any precedent for my "Expression Tree" architecture that I could research? What programming concepts should I consider. I realise this approach has many similarities to a functional programming style, and I'm already aware of the concepts of using futures and actors. Are there any others? Are there any languages or libraries that I should study? This question is inspired by my accidental discovery of Scala and the Akka library (which has good support for Actors, Futures, Distributed workloads etc.) and I'm wondering if there is anything else I should be looking at as well?

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• Object Oriented Design of a Small Java Game

  - by user2733436

  This is the problem i am dealing with. I have to make a simple game of NIM. I am learning java using a book so far i have only coded programs that deal with 2 classes. This program would have about 4 classes i guess including the main class. My problem is i am having a difficult time designing classes how they will interact with each other. I really want to think and use a object oriented approach. So the first thing i did was design the Pile CLASS as it seemed the easiest and made the most sense to me in terms of what methods go in it. Here is what i have got down for the Pile Class so far. package Nim; import java.util.Random; public class Pile { private int initialSize; public Pile(){ } Random rand = new Random(); public void setPile(){ initialSize = (rand.nextInt(100-10)+10); } public void reducePile(int x){ initialSize = initialSize - x; } public int getPile(){ return initialSize; } public boolean hasStick(){ if(initialSize>0){ return true; } else { return false; } } } Now i need help in designing the Player Class. By that i mean i am not asking for anyone to write code for me as that defeats the purpose of learning i was just wondering how would i design the player class and what would go on it. My guess is that the player class would contain method for choosing move for computer and also receiving the move human user makes. Lastly i am guessing in the Game class i am guessing the turns would be handeled. I am really lost right now so i was wondering if someone can help me think through this problem it would be great. Starting with the player class would be appreciated. I know there are some solutions for this problem online but i refuse to look at because i want to develop my own approach to such problems and i am confident if i can get through this problem i can solve other problems. I apologize if this question is a bit poor but in specific i need help in designing the Player class.

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• F# and the useful infinite Sequence (I think)

  - by MarkPearl

  So I have seen a few posts done by other F# fans on solving project Euler problems. They looked really interesting and I thought with my limited knowledge of F# I would attempt a few and the first one I had a look at was problem 5. Which said : “2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder. What is the smallest number that is evenly divisible by all of the numbers from 1 to 20?” So I jumped into coding it and straight away got stuck – the C# programmer in me wants to do a loop, starting at one and dividing every number by 1 to 20 to see if they all divide and once a match is found, there is your solution. Obviously not the most elegant way but a good old brute force approach. However I am pretty sure this would not be the F# way…. So after a bit of research I found the Sequences and how useful they were. Sequences seemed like the beginning of an approach to solve my problem. In my head I thought - create a sequence, and then start at the beginning of it and move through it till you find a value that is divisible by 1 to 20. Sounds reasonable? So the question is begged - how would you create a sequence that you are sure will be large enough to hold the solution to the problem? Well… You can’t know! Some more googling and I found what I would call infinite sequences – something that looks like this… let nums = 1 |> Seq.unfold (fun i -> Some (i, i + 1))   My interpretation of this would be as follows… create a sequence, and whenever it is called add 1 to its size (I would appreciate someone helping me on wording this right functionally). Something that I don’t understand fully yet is the forward pipe operator (|>) which I think plays a key role in this code. With this in hand I was able to code a basic optimized solution to this problem. I’m going to go over it some more before I post the full code just in case!

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• Working with Windows and Unix

  - by user554629

  Beware of new line characters One of the most frequent issues we encounter in Tech Support is the corruption of files that are transferred between Windows and Unix.   The transfer can occur at any stage, but ultimately involves a transfer of a file using an ftp client that is running on Windows;  it could be ftp or filezilla. Windows uses two characters to mark the end of a line in a text file (CR/LF),carriage return, linefeed.   Unix uses a single character (CR). In all situations, it is best to use binary mode transfer for all files, including ascii text files. Common problems: upload a core file from unix to windows using ftp in ascii mode.The file is going to be larger on Windows than Unix.ftp doesn't know if this is a text file with real line-ends, it takes every ascii CR and transmits two ascii characters CR/LF.The core file, tar file, library ... will be corrupted when transferred to Oracle. download a shell script to Windows, and transfer it to Unix using ftpIf the file is edited on Windows, the unix script line-end chars will be doubled.Unix doesn't know how to handle that, and will likely tell you the script is not executable.Why?  The first line of a shell script ( called "sh-bang" ), identifies the command interpreter the unix shell should use for this script.   Common examples:#/bin/sh#/bin/ksh#/bin/bash#/bin/perl#/bin/sh^M    # will not be understood.#/bin/env ksh # special syntax.  Find ksh and run it dos2unix is a common utility found on most unix platforms, that repairs the issue of Windows LineEnd characters in unix script files.   I've written my own flavor of this utility for use in Tech Support and build environments, that is a bit easier to use, and has some nice side-effects. accepts a list of files:   dos2unix *.sh repairs the file in-place.  Doesn't generate a new file you have to name retains the same timestamp;  it is the encoding that changed, not the file content. Here are the versions of dos2unix for each of the environments we work in.They are compressed with gzip, to avoid the ftp ascii transfer trap,and because I am quite limited in the number of files I can upload to this blog. AIX Linux Solaris sparc  Windows 

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• what would be a good way to implement/render a 2d tiled map for a browser game?

  - by jj_

  I've made this little rpg ruby game I did while learning and now I'd like to make it into a browser game. I've already set up Sinatra framework to serve it, so what I am looking for, before everything else, is a way to represent the game map in browser (location attributes are stored in db). A new map is randomly generated by code for each new game at each game start. For now forget db, and let's say a map (say 100x100 "squares") is stored as a tridimensional array. (x,y, ...) Last "dimension" of array stores who & what is at that map cell: a player, a building, whatever. So all I have to do is render those "squares" or array cells to a 2d tiled map in the browser. The map does not need to refresh or be dynamically fetched as you scroll it, (at least at this stage of development) but, a technology which would allow me to do so in future would be a good reason for choosing it. Things that I thought of: html tables, html5 canvas, some js framework which is designed exactly with this purpose (which I do not know of = please advice). Yes I know about gamequery-js framework, but I've never used it, and I don't know if it's going to slow down everything down to inusability as I'm adding new features (scrolling, ajax). I really don't know of any other alternatives.. maybe there are lighter approaches? Easier or more minimalistic ways ? More targeted js framework which is the right tool for the job? Maybe just some html canvas code, or even simple image maps, or images with absolute positioning will be enough? The thing is I'd like to start simple, and then gradually make it better, so, as I said before, I'd prefer something that will give me room for improvement or is headed toward new web tendencies but which will also give me a bit of gratification in the beginning :) So.. advices are needed! And appreciated! :) Thanks p.s. Flash is excluded because I don't like it.

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• How to implement a multi-part snake with smooth movement? [closed]

  - by Jamie

  Sorry that i couldnt answer on my previous post but it got closed. I couldnt answer because i had to prepair for my finals. As there were problems with understanding of what im trying to achieve, im going to describe a little bit more in depth. Im creating a game in which you steer a snake. I assume everybody knows how that works. But in my case the snake isnt just propagating in an array element by element. Imagine a 2Dgrid on which the snake moves. Its 10x10 tiles. Lets say one tile is 4x4 meters. The snakes head spawns in the middle of the (3,2) tile (beginning with (0,0)), so its position is (4*3+2,4*2+2)(the 2's are so that the snake is in the middle of the 4x4 tile). And heres where the fun begins. when the snake moves, it doesnt jump to next tile. Instead it moves a fraction of the way there. So lets say the snake is heading to tile (4,2). After it moved once, its position is (4*3+2+0.1,4*2+2), where 0.1 is the fraction of the way it moved. This is done to achieve smooth movement. So now im adding the rest of the body. The rest is supposed to move along the exact same path as the head did. I implemented it so that each part of the body has its own position and direction. Then i apply this algorithm: 1.Move each part in its direction. 2.If a part is in the middle of the tile(which implies all of them are), change each parts direction to the direction of the part proceeding it. As i said before i could make this work, but i cant stop thinking that im overlooking a much easier and cleaner solution. So this is my question. Is there any easier/better/faster way to do this?

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• Should Item Grouping/Filter be in the ViewModel or View layer?

  - by ronag

  I'm in a situation where I have a list of items that need to be displayed depending on their properties. What I'm unsure of is where is the best place to put the filtering/grouping logic of the viewmodel state? Currently I have it in my view using converters, but I'm unsure whether I should have the logic in the viewmodel? e.g. ViewModel Layer: class ItemViewModel { DateTime LastAccessed { get; set; } bool IsActive { get; set; } } class ContainerViewModel { ObservableCollection<Item> Items {get; set;} } View Layer: <TextView Text="Active Items"/> <List ItemsSource={Binding Items, Converter=GroupActiveItemsByDay}/> <TextView Text="Active Items"/> <List ItemsSource={Binding Items, Converter=GroupInActiveItemsByDay}/> or should I build it like this? ViewModel Layer: class ContainerViewModel { ObservableCollection<IGrouping<string, Item>> ActiveItemsByGroup {get; set;} ObservableCollection<IGrouping<string, Item>> InActiveItemsByGroup {get; set;} } View Layer: <TextView Text="Active Items"/> <List ItemsSource={Binding ActiveItemsGroupByDate }/> <TextView Text="Active Items"/> <List ItemsSource={Binding InActiveItemsGroupByDate }/> Or maybe something in between? ViewModel Layer: class ContainerViewModel { ObservableCollection<IGrouping<string, Item>> ActiveItems {get; set;} ObservableCollection<IGrouping<string, Item>> InActiveItems {get; set;} } View Layer: <TextView Text="Active Items"/> <List ItemsSource={Binding ActiveItems, Converter=GroupByDate }/> <TextView Text="Active Items"/> <List ItemsSource={Binding InActiveItems, Converter=GroupByDate }/> I guess my question is what is good practice in terms as to what logic to put into the ViewModel and what logic to put into the Binding in the View, as they seem to overlap a bit?

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• Is there a factory pattern to prevent multiple instances for same object (instance that is Equal) good design?

  - by dsollen

  I have a number of objects storing state. There are essentially two types of fields. The ones that uniquely define what the object is (what node, what edge etc), and the others that store state describing how these things are connected (this node is connected to these edges, this edge is part of these paths) etc. My model is updating the state variables using package methods, so all these objects act as immutable to anyone not in Model scope. All Objects extend one base type. I've toyed with the idea of a Factory approach which accepts a Builder object and constructs the applicable object. However, if an instance of the object already exists (ie would return true if I created the object defined by the builder and passed it to the equal method for the existing instance) the factory returns the current object instead of creating a new instance. Because the Equal method would only compare what uniquely defines the type of object (this is node A to node B) but won't check the dynamic state stuff (node A is currently connected to nodes C and E) this would be a way of ensuring anyone that wants my Node A automatically knows its state connections. More importantly it would prevent aliasing nightmares of someone trying to pass an instance of node A with different state then the node A in my model has. I've never heard of this pattern before, and it's a bit odd. I would have to do some overriding of serialization methods to make it work (ensure that when I read in a serilized object I add it to my facotry list of known instances, and/or return an existing factory in its place), as well as using a weakHashMap as if it was a weakHashSet to know whether an instance exists without worrying about a quasi-memory leak occuring. I don't know if this is too confusing or prone to its own obscure bugs. One thing I know is that plugins interface with lowest level hardware. The plugins have to be able to return state that is different than my memory; to tell my memory when its own state is inconsistent. I believe this is possible despite their fetching objects that exist in my memory; we allow building of objects without checking their consistency with the model until the addToModel is called anyways; and the existing plugins design was written before all this extra state existed and worked fine without ever being aware of it. Should I just be using some other design to avoid this crazyness? (I have another question to that affect that I'm posting).

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• Setting the SlideShowExtender's Index

  - by Bunch

  The AJAX SlideShowExtender is pretty useful. It does what it says and works without much fuss. There was one trick I needed it to perform that I could not find natively within the control. That was to set the slide’s current index. With a little JavaScript however I could make the control do what I wanted. The example below assumes a few things. First you already have a SlideShowExtender setup and working (or see this post). Second this SlideShowExtender is on a page all by itself so the index to set the slide to is passed in the URL. The scenario I had was this SSE was showing full images, the index was passed from another page that had a SSE showing thumbnails. JavaScript in <head> <script type="text/javascript">      function pageLoad() {          var slider = $find("sse");          var photoIndex = GetQuerystring('Index', 0);          slider._currentIndex = photoIndex - 1;          slider._slides = '';          slider.setCurrentImage();      }      function GetQuerystring(key, default_) {          if (default_ == null) default_ = '0';          key = key.replace(/[\[]/, "\\\[").replace(/[\]]/, "\\\]");          var regex = new RegExp("[\\?&]" + key + "=([^&#]*)");          var qs = regex.exec(window.location.href);          if (qs == null)              return default_;          else              return qs[1];      } </script> The GetQuerystring function is what grabs the Index value I pass from the page with the thumbnails. It does not have anything else to do with setting the slide index. The code in the pageLoad function sets the index on the slide_currentIndex line. The slider.setCurrentImage() line does pretty much what it says. I added the slider._slider = ‘’ to avoid an error (not a show stopper just a bit annoying). Control in <body> <cc1:SlideShowExtender ID="ssePhotos" runat="server" TargetControlID="imgFull" AutoPlay="false"          PreviousButtonID="btnPrev" NextButtonID="btnNext" SlideShowServicePath="PlacePhotos.asmx"           SlideShowServiceMethod="GetPlaceFullPhotos" BehaviorID="sse" ImageDescriptionLabelID="lblPictureDescription"> </cc1:SlideShowExtender> The main property to set with the SSE is the BehaviorID. This is what a JavaScript function can use to find the control rather than the control’s ID value. Technorati Tags: AJAX,ASP.Net,JavaScript

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• Help recovering broken OS (permissions issue)

  - by Guandalino

  (At the bottom there is an important update.) I was doing experiments in order to backup a remote account to my local system, Ubuntu 12.04 LTS. I'm not confident with duplicity and probably, due to wrong syntax, some local files have been replaced with remote files. This is just a supposition, I'm not sure this is the real cause of OS corruption. The corruption happened after experimenting with backups, so I think I did something wrong at this regard. I was aware there was a problem when I tried to access a command using sudo: $ sudo ls sudo: unable to open /etc/sudoers: Permission denied sudo: no valid sudoers sources found, quitting sudo: unable to initialize policy plugin This is how /etc/sudoers looks like: $ ls -ald /etc/sudoers -r--r----- 1 root root 788 Oct 2 18:30 /etc/sudoers At this point I tried to reboot and now this is the message I get: The system is running in low graphics mode. Your screen, graphics card and input device settings could not be detected correctly. You will need to configure these yourself. I tried to follow the wizard to configure these settings, but without luck (the system prevents me going on when I press "Next"). The thing that makes me a bit less worried is that all the data on the disk seems readable and I'm able to access them using a live cd. I run memtest and RAM seems to be OK. Do you have any idea about how to recover my system? I'm very glad to provide further information, just let me know what info could be helpful. UPDATE. The issue is about wrong permissions and this is how I discovered: I mounted the root partition of the broken OS on /mnt/broken/ (live CD) and did ls /mnt/broken/. I got a permission denied error, while I expected to have the directory listing. I had to do sudo ls /mnt/broken/ and this worked. Thus without having root permission via sudo it's impossible to access the root of broken os. The current output of ls -ld /mnt/broken/ is: drwxr-x--- 29 1000 812 4096 2012-12-08 21:58 /mnt/broken Any thoughts on how to restore the old (working) set of permissions?

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• is a factory pattern to prevent multuple instances for same object (instance that is Equal) good design?

  - by dsollen

  I have a number of objects storing state. There are essentially two types of fields. The ones that uniquly define what the object is (what node, what edge etc), and the oens that store state describing how these things are connected (this node is connected to these edges, this edge is part of these paths) etc. My model is updating the state variables using package methdos, so these objects all act as immutable to anyone not in Model scope. All Objects extend one base type. I've toyed with the idea of a Factory approch which accepts a Builder object and construct the applicable object. However, if an instance of the object already exists (ie would return true if I created the object defined by the builder and passed it to the equal method for the existing instance) the factory returns the current object instead of creating a new instance. Because the Equal method would only compare what uniquly defines the type of object (this is node A nto node B) but won't check the dynamic state stuff (node A is currently connected to nodes C and E) this would be a way of ensuring anyone that wants my Node A automatically knows it's state connections. More importantly it would prevent aliasing nightmares of someone trying to pass an instance of node A with different state then the node A in my model has. I've never heard of this pattern before, and it's a bit odd. I would have to do some overiding of serlization methods to make it work (ensure when I read in a serilized object I add it to my facotry list of known instances, and/or return an existing factory in it's place), as well as using a weakHashMap as if it was a weakHashSet to know rather an instance exists without worrying about a quasi-memory leak occuring. I don't know if this is too confusing or prone to it's own obscure bugs. One thing I know is that plugins interface with lowest level hardware. The plugins have to be able to return state taht is different then my memory; to tell my memory when it's own state is inconsistent. I believe this is possible despit their fetching objects that exist in my memory; we allow building of objects without checking their consistency with the model until the addToModel is called anyways; and the existing plugins design was written before all this extra state existed and worked fine without ever being aware of it. Should I just be using some other design to avoid this crazyness? (I have another question to that affect I'm posting).

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