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• Keeping Score in XNA Game

  - by Seven

  Hi. I'm following an XNA tutorial and have the following code for collision detecting (detecting when a bullet collides with a target). Basically I'm looking to increment a score variable to display the score to the screen without re-writing the whole program. No matter where I place it in this method it seems to start incrementing from the number of targets, not from zero. Is there something simple I'm missing here? Any help would be greatly appreciated. Thanks. private CollisionType CheckCollision(BoundingSphere sphere) { if (completeCityBox.Contains(sphere) != ContainmentType.Contains) return CollisionType.Boundary; for (int i = 0; i < targetList.Count; i++) { if (targetList[i].Contains(sphere) != ContainmentType.Disjoint) { targetList.RemoveAt(i); i--; AddTargets(); return CollisionType.Target; } } return CollisionType.None; }

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• How to create your own advert engine for an Android App?

  - by Richard Green

  I have an Android App and I would like to start putting non-intrusive advert into the app. However, I have the benefit of knowing exactly what products I would like to put in these adverts (which will basically be amazon "similar products" type things and a few other suppliers). Is there any ad-engine out there that will allow me to do this? The ones I see already just put what they think are suitable. I have scoured and I can't find an example of this... Any ideas? Should I just bite the bullet and write my own classes to do this ?

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• Corona SDK - Make a character pass through a platform

  - by Andy Res

  I'm building a game that has a character which should jump up on multiple platforms. The jumping functionality is done, but I would like if the character is just below a platform (static body), when I press the "jump" button, the character should pass through that platform and then sit on it. Right now it collides with the platform, and character cannot jump on it. Do you have any idea how this can be achieved? Right now the platforms are represented by rectangles with "static" body type: local platform = display.newRect( 50, 280, 150, 10 ) platform:setFillColor ( 55, 55, 55) physics.addBody ( platform, "static", {density=1.0, friction=1.0, bounce=0 }) And I was thinking if I could change, or remove the body type of platform when the character collids with it, so he can pass trough platform, but I don't know how to do this, or in general if this will work... maybe there are some built in techniques on how to achieve the effect I want?

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• What Math topics & resources to consider as beginner to indulge the book - Introduction to Algorithm

  - by sector7

  I'm a programmer who's beginning to appreciate the knowledge & usability of Algorithms in my work as I move forward with my skill-set. I don't want to take the short path by learning how to apply algorithms "as-is" but would rather like to know the foundation and fundamentals behind them. For that I need Math, at which I'm pretty "basic". I'm considering getting tuition's for that. What I would like is to have a concise syllabus/set of topics/book which I could hand over to my math tutor to get started. HIGHLY DESIRED: one book. the silver bullet. (fingers crossed!) PS: I've got some leads but want to hear you guys/gurus out: Discrete Math, Combinatorics, Graph theory, Calculus, Linear Algebra, and Number Theory. Looking forward to your answers. Thanks!

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• Problems with the Enterframe Event

  - by user434565

  Hey guys, I have been developing a game using Flex, and used the Timer class to keep the main loop going. However, when I tried using the enterFrame event to do the main loop, there were a few problems. First of all, physics simulation seemed way too fast. Is the enterFrame event called more than once per frame? I set the application's global frame rate to 24, so shouldn't the application set off the event every 1/24 of a second? And the second problem is that when the game runs like this, some MXML components that are added are not shown. I have absolutely no idea why this happens. Help me please?!? Thanks.

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• NoSQL is not about object databases

  - by Bertrand Le Roy

  NoSQL as a movement is an interesting beast. I kinda like that it’s negatively defined (I happen to belong myself to at least one other such a-community). It’s not in its roots about proposing one specific new silver bullet to kill an old problem. it’s about challenging the consensus. Actually, blindly and systematically replacing relational databases with object databases would just replace one set of issues with another. No, the point is to recognize that relational databases are not a universal answer -although they have been used as one for so long- and recognize instead that there’s a whole spectrum of data storage solutions out there. Why is it so hard to recognize, by the way? You are already using some of those other data storage solutions every day. Let me cite a few: The file system Active Directory XML / JSON documents The Web e-mail Logs Excel files EXIF blobs in your photos Relational databases And yes, object databases It’s just a fact of modern life. Notice by the way that most of the data that you use every day is unstructured and thus mostly unsuitable for relational storage. It really is more a matter of recognizing it: you are already doing NoSQL. So what happens when for any reason you need to simultaneously query two or more of these heterogeneous data stores? Well, you build an index of sorts combining them, and that’s what you query instead. Of course, there’s not much distance to travel from that to realizing that querying is better done when completely separated from storage. So why am I writing about this today? Well, that’s something I’ve been giving lots of thought, on and off, over the last ten years. When I built my first CMS all that time ago, one of the main problems my customers were facing was to manage and make sense of the mountain of unstructured data that was constituting most of their business. The central entity of that system was the file system because we were dealing with lots of Word documents, PDFs, OCR’d articles, photos and static web pages. We could have stored all that in SQL Server. It would have worked. Ew. I’m so glad we didn’t. Today, I’m working on Orchard (another CMS ;). It’s a pretty young project but already one of the questions we get the most is how to integrate existing data. One of the ideas I’ll be trying hard to sell to the rest of the team in the next few months is to completely split the querying from the storage. Not only does this provide great opportunities for performance optimizations, it gives you homogeneous access to heterogeneous and existing data sources. For free.

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• What will be important in Training in 2011?

  - by anders.northeved

    Now that we have started a new year I would like to give you a list of topics I think we will be discussing in training and learning in 2011. Some of the areas we have discussed earlier will still be just as important in 2011: Time-to-knowledge Still one of the most important issues for the training department. Internal content production Related to time-to-knowledge. How do we convert internal knowledge to a format that can be used for teaching others? LMS integration How do we get our existing LMS fully integrated with our other ERP modules like HCM, Order Management, Finance, Payroll etc. Some areas have been discussed before, but we’ll focus more on these in 2011: Combining internal and external training A majority of training departments use a combination of external and internal training. Having the right mix is vital for the quality and efficiency for most training organizations. Certification More rules and regulations means managing all employee certifications is more important than ever. Evolving trends in 2011: Social Learning We have been talking about this for a long time, but 2011 will be the year where we will start using it for real (OK, I also said so last year – but this year I’m right…). Real-life use of SCORM 2004 Again a topic we have talked about for a long time, but we are now actually starting to use it to give learners a better e-learning experience. How do we engage and delight the learner? e-learning makes economical sense, it can be easy to understand, it is convenient – but how do we make it more engaging and delight our learners? How to include more types of training in LMS One of the main focus area of 2011 will be how to manage and measure mobile learning , on-the-job-training and other forms of training in the LMS. Mobile Learning With the ever growing use of smart phones mobile learning will be THE hot topic of 2011 in the training world. New topics we will begin discussing in 2011: What is beyond web 2.0 and social learning? - could it be content verification and personal accreditation? Why gaming will not be the silver bullet for all types of e-learning Many people believe gaming can be used for any kind of training, but the creation is too expensive and time consuming for most applications. Do you agree with these predictions? What are your own predictions? Let me see your comments! (photo: © Marti, photoxpress.com)

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• Package system broken - E: Sub-process /usr/bin/dpkg returned an error code (1)

  - by delha

  After installing some packages and libraries I have an error on Package Manager, I can't run any update because it says: "The package system is broken If you are using third party repositories then disable them, since they are a common source of problems. Now run the following command in a terminal: apt-get install -f " I've tried to do what it says and it returns me: jara@jara-Aspire-5738:~$ sudo apt-get install -f Reading package lists... Done Building dependency tree Reading state information... Done Correcting dependencies... Done The following packages were automatically installed and are no longer required: libcaca-dev libopencv2.3-bin nite-dev python-bluez ps-engine libslang2-dev python-sphinx ros-electric-geometry-tutorials ros-electric-geometry-visualization python-matplotlib libzzip-dev ros-electric-orocos-kinematics-dynamics ros-electric-physics-ode libbluetooth-dev libaudiofile-dev libassimp2 libnetpbm10-dev ros-electric-laser-pipeline python-epydoc ros-electric-geometry-experimental libasound2-dev evtest python-matplotlib-data libyaml-dev ros-electric-bullet ros-electric-executive-smach ros-electric-documentation libgl2ps0 libncurses5-dev ros-electric-robot-model texlive-fonts-recommended python-lxml libwxgtk2.8-dev daemontools libxxf86vm-dev libqhull-dev libavahi-client-dev ros-electric-geometry libgl2ps-dev libcurl4-openssl-dev assimp-dev libusb-1.0-0-dev libopencv2.3 ros-electric-diagnostics-monitors libsdl1.2-dev libjs-underscore libsdl-image1.2 tipa libusb-dev libtinfo-dev python-tz python-sip libfltk1.1 libesd0 libfreeimage-dev ros-electric-visualization x11proto-xf86vidmode-dev python-docutils libvtk5.6 ros-electric-assimp x11proto-scrnsaver-dev libnetcdf-dev libidn11-dev libeigen3-dev joystick libhdf5-serial-1.8.4 ros-electric-joystick-drivers texlive-fonts-recommended-doc esound-common libesd0-dev tcl8.5-dev ros-electric-multimaster-experimental ros-electric-rx libaudio-dev ros-electric-ros-tutorials libwxbase2.8-dev ros-electric-visualization-common python-sip-dev ros-electric-visualization-tutorials libfltk1.1-dev libpulse-dev libnetpbm10 python-markupsafe openni-dev tk8.5-dev wx2.8-headers freeglut3-dev libavahi-common-dev python-roman python-jinja2 ros-electric-robot-model-visualization libxss-dev libqhull5 libaa1-dev ros-electric-eigen freeglut3 ros-electric-executive-smach-visualization ros-electric-common-tutorials ros-electric-robot-model-tutorials libnetcdf6 libjs-sphinxdoc python-pyparsing libaudiofile0 Use 'apt-get autoremove' to remove them. The following extra packages will be installed: libcv-dev The following NEW packages will be installed libcv-dev 0 upgraded, 1 newly installed, 0 to remove and 4 not upgraded. 2 not fully installed or removed. Need to get 0 B/3,114 kB of archives. After this operation, 11.1 MB of additional disk space will be used. Do you want to continue [Y/n]? y (Reading database ... 261801 files and directories currently installed.) Unpacking libcv-dev (from .../libcv-dev_2.1.0-7build1_amd64.deb) ... dpkg: error processing /var/cache/apt/archives/libcv-dev_2.1.0-7build1_amd64.deb (-- unpack): trying to overwrite '/usr/bin/opencv_haartraining', which is also in package libopencv2.3-bin 2.3.1+svn6514+branch23-12~oneiric dpkg-deb: error: subprocess paste was killed by signal (Broken pipe) Errors were encountered while processing: /var/cache/apt/archives/libcv-dev_2.1.0-7build1_amd64.deb E: Sub-process /usr/bin/dpkg returned an error code (1) I've tried everything people recommend on internet like: sudo apt-get clean sudo apt-get autoremove sudo apt-get update sudo apt-get upgrade sudo apt-get -f install Also I've tried to install the synaptic manager but it doesn't let me install anything.. As you can see nothing works so I'm desperate! I'm using ubuntu 11.10, 64 bits Thanks!!

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• Cocos2d: Changing b2Body x val every frame causes jitter

  - by Joey Green

  So, I have a jumping mechanism similar to what you would see in doodle jump where character jumps and you use the accelerometer to make character change direction left or right. I have a player object with position and a box2d b2Body with position. I'm changing the player X position via the accelerometer and the Y position according to box2d. pseudocode for this is like so -----accelerometer acceleration------ player.position = new X -----world update--------- physicsWorld-step() //this will get me the new Y according to the physics similation //so we keep the bodys Y value but change x to new X according to accelerometer data playerPhysicsBody.position = new pos(player.position.x, keepYval) player.position = playerPhysicsBody.position Now this is simplifying my code, but I'm doing the position conversion back and forth via mult or divide by PTM_. Well, I'm getting a weird jitter effect after I get big jump in acceleration data. So, my questions are: 1) Is this the right approach to have the accelerometer control the x pos and box2d control the y pos and just sync everthing up every frame? 2) Is there some issue with updating a b2body x position every frame? 3) Any idea what might be creating this jitter effect? I've collecting some data while running the game. Pre-body is before I set the x value on the b2Body in my update method after I world-step(). Post of course is afterwards. As you can see there is definitively a pattern. 012-06-19 08:14:13.118 Game[1073:707] pre-body pos 5.518720~24.362963 2012-06-19 08:14:13.120 Game[1073:707] post-body pos 5.060156~24.362963 2012-06-19 08:14:13.131 Game[1073:707] player velocity x: -31.833529 2012-06-19 08:14:13.133 Game[1073:707] delta 0.016669 2012-06-19 08:14:13.135 Game[1073:707] pre-body pos 5.060156~24.689455 2012-06-19 08:14:13.137 Game[1073:707] post-body pos 5.502138~24.689455 2012-06-19 08:14:13.148 Game[1073:707] player velocity x: -31.833529 2012-06-19 08:14:13.150 Game[1073:707] delta 0.016667 2012-06-19 08:14:13.151 Game[1073:707] pre-body pos 5.502138~25.006948 2012-06-19 08:14:13.153 Game[1073:707] post-body pos 5.043575~25.006948 2012-06-19 08:14:13.165 Game[1073:707] player velocity x: -31.833529 2012-06-19 08:14:13.167 Game[1073:707] delta 0.016644 2012-06-19 08:14:13.169 Game[1073:707] pre-body pos 5.043575~25.315441 2012-06-19 08:14:13.170 Game[1073:707] post-body pos 5.485580~25.315441 2012-06-19 08:14:13.180 Game[1073:707] player velocity x: -31.833529 2012-06-19 08:14:13.182 Game[1073:707] delta 0.016895 2012-06-19 08:14:13.185 Game[1073:707] pre-body pos 5.485580~25.614935 2012-06-19 08:14:13.188 Game[1073:707] post-body pos 5.026768~25.614935 2012-06-19 08:14:13.198 Game[1073:707] player velocity x: -31.833529 2012-06-19 08:14:13.199 Game[1073:707] delta 0.016454 2012-06-19 08:14:13.207 Game[1073:707] pre-body pos 5.026768~25.905428 2012-06-19 08:14:13.211 Game[1073:707] post-body pos 5.469213~25.905428 2012-06-19 08:14:13.217 Game[1073:707] acceleration x -0.137421 2012-06-19 08:14:13.223 Game[1073:707] player velocity x: -65.022644 2012-06-19 08:14:13.229 Game[1073:707] delta 0.016603

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• How one decision can turn web services to hell

  - by DigiMortal

  In this posting I will show you how one stupid decision may turn developers life to hell. There is a project where bunch of complex applications exchange data frequently and it is very hard to change something without additional expenses. Well, one analyst thought that string is silver bullet of web services. Read what happened. Bad bad mistake In the early stages of integration project there was analyst who also established architecture and technical design for web services. There was one very bad mistake this analyst made: All data must be converted to strings before exchange! Yes, that’s correct, this was the requirement. All integers, decimals and dates are coming in and going out as strings. There was also explanation for this requirement: This way we can avoid data type conversion errors! Well, this guy works somewhere else already and I hope he works in some burger restaurant – far away from computers. Consequences If you first look at this requirement it may seem like little annoying piece of crap you can easily survive. But let’s see the real consequences one stupid decision can cause: hell load of data conversions are done by receiving applications and SSIS packages, SSIS packages are not error prone and they depend heavily on strings they get from different services, there are more than one format per type that is used in different services, for larger amounts of data all these conversion tasks slow down the work of integration packages, practically all developers have been in hurry with some SSIS import tasks and some fields that are not used in different calculations in SSAS cube are imported without data conversions (by example, some prices are strings in format “1.021 $”). The most painful problem for developers is the part of data conversions because they don’t expect that there is such a stupid requirement stated and therefore they are not able to estimate the time their tasks take on these web services. Also developers must be prepared for cases when suddenly some service sends data that is not in acceptable format and they must solve the problems ASAP. This puts unexpected load on developers and they are not very happy with it because they can’t understand why they have to live with this horror if it is possible to fix. What to do if you see something like this? Well, explain the problem to customer and demand special tasks to project schedule to get this mess solved before going on with new developments. It is cheaper to solve the problems now that later.

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• Space partitioning when everything is moving

  - by Roy T.

  Background Together with a friend I'm working on a 2D game that is set in space. To make it as immersive and interactive as possible we want there to be thousands of objects freely floating around, some clustered together, others adrift in empty space. Challenge To unburden the rendering and physics engine we need to implement some sort of spatial partitioning. There are two challenges we have to overcome. The first challenge is that everything is moving so reconstructing/updating the data structure has to be extremely cheap since it will have to be done every frame. The second challenge is the distribution of objects, as said before there might be clusters of objects together and vast bits of empty space and to make it even worse there is no boundary to space. Existing technologies I've looked at existing techniques like BSP-Trees, QuadTrees, kd-Trees and even R-Trees but as far as I can tell these data structures aren't a perfect fit since updating a lot of objects that have moved to other cells is relatively expensive. What I've tried I made the decision that I need a data structure that is more geared toward rapid insertion/update than on giving back the least amount of possible hits given a query. For that purpose I made the cells implicit so each object, given it's position, can calculate in which cell(s) it should be. Then I use a HashMap that maps cell-coordinates to an ArrayList (the contents of the cell). This works fairly well since there is no memory lost on 'empty' cells and its easy to calculate which cells to inspect. However creating all those ArrayLists (worst case N) is expensive and so is growing the HashMap a lot of times (although that is slightly mitigated by giving it a large initial capacity). Problem OK so this works but still isn't very fast. Now I can try to micro-optimize the JAVA code. However I'm not expecting too much of that since the profiler tells me that most time is spent in creating all those objects that I use to store the cells. I'm hoping that there are some other tricks/algorithms out there that make this a lot faster so here is what my ideal data structure looks like: The number one priority is fast updating/reconstructing of the entire data structure Its less important to finely divide the objects into equally sized bins, we can draw a few extra objects and do a few extra collision checks if that means that updating is a little bit faster Memory is not really important (PC game)

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• Star rating not showing in rich snippets

  - by Danny R

  We've recently been doing a lot of work on our site's SEO (www.betterthanreviews.com). We recently did a push to update the rich snippets breadcrumb, meta description, and star rating. After giving Google some time to index the site, it has updated the breadcrumbs and meta descriptions for our review pages, but the stars are still not showing. This is currently how it appears on a Google search (link to the actual page: http://www.betterthanreviews.com/home-security/livewatch): This is what the Rich Snippets is supposed to look like, and how it appears in Google's testing tool: More context: As seen in our html, we are using schema.org language. We initially were using schema.org/Corporation for the site, but we now have the page labeled as schema.org/HomeAndConstructionBusiness because Google will not show star ratings for the Corporation language. However, in our Webmaster Tools, the Structured Data is still showing the Corporation language, which could be a potential issue. Here is a look at some of the coding that we used. But it can be looked at closer by inspecting the element: <div class="aggregate-rating" itemprop="aggregateRating" itemscope="" itemtype="http://schema.org/AggregateRating"> <div class="review row_fluid" itemprop="review" itemscope="" itemtype="http://schema.org/Review"> <div class="row_fluid rating" itemprop="reviewRating" itemscope="" itemtype="http://schema.org/Rating"> <meta content="4.5" itemprop="ratingValue" title="4.5 out of 5 stars" class="star-rating-readonly"> <meta content="2013-12-05" itemprop="datePublished"> <p class="review-headline" itemprop="headline">Way better than my previous system</p> <div> <p class="reviewer" itemprop="author">Scott H. </p> <span class="bullet">•</span> <p class="created_at">2 months ago</p> <p class="content" itemprop="description">I love it! The experience I have had so far is extremely positive. I had another alarm system before and I didn't like it but this one is really nice. I am telling everybody about it.</p> </div> </div> Any suggestions for how to fix this?

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• Career Advice: finding challenging work in software and web development

  - by dianovich

  Having left my physics degree early, I started out in the realm of web design / front end web development and was able to get work quite quickly. I moved on to spend a chunk of my time on servers and gained experience with frameworks like Wordpress and Drupal, then the likes of Codeigniter and CakePHP and became comfortable in Debian-based and RHEL/CentOS environments. I ventured in to iOS development and published a couple of native apps to the app store too! I have started to spend a good deal of my time writing Python and have invested a little time in Django. The problem is, I still spend a fair chunk of my time doing more front end web development (writing markup and CSS for site themes, design-lead JavaScript, small applications for which application architecture and software engineering are relatively unimportant or too time consuming to invest in) in my job. What I want to do is really exercise the systematic/logical portion of my brain and tackle challenging problems on a daily basis. I want to have to care about big-oh running times, modularity in software, DRY, performance tuning and development methodologies. I want to work for a firm whose clients say: "Yes, these things are important to us and we'll pay you to get them right." But it is difficult: I have no formal training and am potentially becoming a jack of all trades. Not that being a jack of many trades is necessarily a bad thing, but the scope of work I find myself involved in is far too broad. And, there are only so many hours in a day outside of work! My question is: where do I go from here? I am starting to work on a few open source projects and have started to publish content to my blog. But this isn't likely to make it past the recruitment consultants and HR departments of many-a-firm. And I do not, for example, work in a team that practices agile methodologies, so how do I get work in such a team to gain experience? While I have been responsible for implementing version control and some solid working practices into our current environment, there is only so far I can go in this context. What would convince you that i'm worth taking a risk? What would convince you that i'll have caught up the other guys in your employ in next to no time?

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• Is there an appropriate coding style for implementing an algorithm during an interview?

  - by GlenPeterson

  I failed an interview question in C years ago about converting hex to decimal by not exploiting the ASCII table if (inputDigitByte > 9) hex = inputDigitByte - 'a'. The rise of Unicode has made this question pretty silly, but the point was that the interviewer valued raw execution speed above readability and error handling. They tell you to review algorithms textbooks to prepare for these interviews, yet these same textbooks tend to favor the implementation with the fewest lines of code, even if it has to rely on magic numbers (like "infinity") and a slower, more memory-intensive implementation (like a linked list instead of an array) to do that. I don't know what is right. Coding an algorithm within the space of an interview has at least 3 constraints: time to code, elegance/readability, and efficiency of execution. What trade-offs are appropriate for interview code? How much do you follow the textbook definition of an algorithm? Is it better to eliminate recursion, unroll loops, and use arrays for efficiency? Or is it better to use recursion and special values like "infinity" or Integer.MAX_VALUE to reduce the number of lines of code needed to write the algorithm? Interface: Make a very self-contained, bullet-proof interface, or sloppy and fast? On the one extreme, the array to be sorted might be a public static variable. On the other extreme, it might need to be passed to each method, allowing methods to be called individually from different threads for different purposes. Is it appropriate to use a linked-list data structure for items that are traversed in one direction vs. using arrays and doubling the size when the array is full? Implementing a singly-linked list during the interview is often much faster to code and easier remember for recursive algorithms like MergeSort. Thread safety - just document that it's unsafe, or say so verbally? How much should the interviewee be looking for opportunities for parallel processing? Is bit shifting appropriate? x / 2 or x >> 1 Polymorphism, type safety, and generics? Comments? Variable and method names: qs(a, p, q, r) vs: quickSort(theArray, minIdx, partIdx, maxIdx) How much should you use existing APIs? Obviously you can't use a java.util.HashMap to implement a hash-table, but what about using a java.util.List to accumulate your sorted results? Are there any guiding principals that would answer these and other questions, or is the guiding principal to ask the interviewer? Or maybe this should be the basis of a discussion while writing the code? If an interviewer can't or won't answer one of these questions, are there any tips for coaxing the information out of them?

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• My grid based collision detection is slow

  - by Fibericon

  Something about my implementation of a basic 2x4 grid for collision detection is slow - so slow in fact, that it's actually faster to simply check every bullet from every enemy to see if the BoundingSphere intersects with that of my ship. It becomes noticeably slow when I have approximately 1000 bullets on the screen (36 enemies shooting 3 bullets every .5 seconds). By commenting it out bit by bit, I've determined that the code used to add them to the grid is what's slowest. Here's how I add them to the grid: for (int i = 0; i < enemy[x].gun.NumBullets; i++) { if (enemy[x].gun.bulletList[i].isActive) { enemy[x].gun.bulletList[i].Update(timeDelta); int bulletPosition = 0; if (enemy[x].gun.bulletList[i].position.Y < 0) { bulletPosition = (int)Math.Floor((enemy[x].gun.bulletList[i].position.X + 900) / 450); } else { bulletPosition = (int)Math.Floor((enemy[x].gun.bulletList[i].position.X + 900) / 450) + 4; } GridItem bulletItem = new GridItem(); bulletItem.index = i; bulletItem.type = 5; bulletItem.parentIndex = x; if (bulletPosition > -1 && bulletPosition < 8) { if (!grid[bulletPosition].Contains(bulletItem)) { for (int j = 0; j < grid.Length; j++) { grid[j].Remove(bulletItem); } grid[bulletPosition].Add(bulletItem); } } } } And here's how I check if it collides with the ship: if (ship.isActive && !ship.invincible) { BoundingSphere shipSphere = new BoundingSphere( ship.Position, ship.Model.Meshes[0].BoundingSphere.Radius * 9.0f); for (int i = 0; i < grid.Length; i++) { if (grid[i].Contains(shipItem)) { for (int j = 0; j < grid[i].Count; j++) { //Other collision types omitted else if (grid[i][j].type == 5) { if (enemy[grid[i][j].parentIndex].gun.bulletList[grid[i][j].index].isActive) { BoundingSphere bulletSphere = new BoundingSphere(enemy[grid[i][j].parentIndex].gun.bulletList[grid[i][j].index].position, enemy[grid[i][j].parentIndex].gun.bulletModel.Meshes[0].BoundingSphere.Radius); if (shipSphere.Intersects(bulletSphere)) { ship.health -= enemy[grid[i][j].parentIndex].gun.damage; enemy[grid[i][j].parentIndex].gun.bulletList[grid[i][j].index].isActive = false; grid[i].RemoveAt(j); break; //no need to check other bullets } } else { grid[i].RemoveAt(j); } } What am I doing wrong here? I thought a grid implementation would be faster than checking each one.

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• Game Review: God of Light

  Luckily I came across this title at a very early stage. If I remember correctly, I took notice of God of Light on Twitter right on the weekend it has been published on the Play Store. "Sit back and become immersed into the world of God of Light, the game that rethinks the physics puzzle genre with its unique environment exploration gameplay, amazing graphics and exclusive soundtrack created by electronic music icon UNKLE. Join cute game mascot, Shiny, on his way to saving the universe from the impending darkness. Play through a variety of exciting game worlds and dozens of levels with mind-blowing puzzles. Your goal is to explore game levels, seek for game objects that reflect, split, combine, paint, bend and teleport rays of light energy to activate the Sources of Life and bring light back to the universe." Mastering the various reflection items in God of Light is very easy to learn and new elements are introduced during the game. Amazing puzzle game Here's the initial review I posted on the Play Store: "Great change in puzzles Fantastic and refreshing concept of puzzle solving. The effects and the music match very well, putting the player in the right mood to game. Get enlightened and grow your skills until you are a true God of Light." And it remains true, even after completing the first realm completely. Similar to Quell it took me only a couple of hours during the evening to complete all levels in the available three realms, unfortunately. God of Light currently consists of 75 levels, well it's 25 in each realm to be precise, and the challenges are increasing. Compared to the iOS version from the AppStore, God of Light is available for free on Android - at least the first realm (25 levels). Unlocking the other two remaining realms is done through an in-app purchase. The visual appearance, the sound effects and the background music provided by UNKLE makes God of Light a superb package for any puzzle gamer. Whether it is simply reflecting light over multiple mirrors, or later on bending the rays of light with black holes, or using prisms to either split, enforce, or colourise your beam, God of Light is great fun and offers a good amount of joy. Check out the following screenshots for some impressions. God of Light: Astonishing graphics and visual appeal throughout the game God of Light - Introduction to the game during the first levels. New light items are introduced at each stage during the game play God of Light: Increasing complexity and puzzle fun Hopefully, Playmous is going to provide more astonishing looking realms and interesting gimmicks in future versions. Play Store: God of Light Also, check out the latest game updates on the official web site of Playmous

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• The Case for Complimentary Software Copies

  - by GGBlogger

  As the Geriatric Geek you can understand that I’ve been writing and studying for over 60 years. That means that I’ve seen insane changes in the computer software industry. I’ve made the joke that I get a new college education every 6 months or so. Of course that’s an exaggeration but it doesn’t make the feeling go away. I have a long standing and strong relationship with Microsoft so I’m armed with virtually every tool they make. It also means that I have access to tons of training material. But here’s the rub… Last year I started a definitive read of Professional Visual Basic 2008. The purpose was to fill in holes in my understanding of various things. I’m currently on page 1119 of some 1400 pages. During this sojourn I’ve decided that the future is web related which is to say that the future of “thick client” applications running as Windows applications is likely to slowly disappear. To that end I’ve taken a side trip or two into the world of ASP (including XML), Silverlight and cloud development. After carefully avoiding (that’s tongue in cheek) XML for years I finally had to bite the bullet, so to speak, and start learning XML in earnest. The most recent result of that was trail downloads of Altova’s MissionKit 2010 for Software Architects and Liquid Technologies Liquid XML Studio Developer Edition. These are both beautiful products and I want to learn them and write about them. Now comes the rub… While 30 day evaluations are generous in allowing casual users to assess these technologies for purchase they are NOT long enough to allow an author to evaluate, learn and ultimately write about them. Even if I devoted the full 30 days to learning, using and writing about say Altova’s suite I wouldn’t have enough time. Liquid XML may be a little easier to learn (one product as opposed to 8).  Add to that the fact that I frequently get sidetracked to add to my kit and it really blows out. It can be extremely frustrating when I’ve devoted hours to a project and suddenly discover that to complete it I will either need to purchase a license or abandon the project. Since my life blood does not depend on the product I end up abandoning the project and moving on. So to the folks from whom I request complimentary copies… I guarantee that if I convert your product to doing paid development work I will purchase a license to do that but as long as I am using your product to study for the purpose of writing samples, teaching use or otherwise promoting your product to other paying customers I will ask that you give me a license so that I can do that without facing the dread expiration of a 30 day trial.

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• How do I import my first sprites?

  - by steven_desu

  Continuing from this question (new question - now unrelated) So I have a thorough background in programming already (algorithms, math, logic, graphing problems, etc.) however I've never attempted to code a game before. In fact, I've never had anything more than minimal input from a user during the execution of a program. Generally input was given from a file or passed through console, all necessary functions were performed, then the program terminated with an output. I decided to try and get in on the world of game development. From several posts I've seen around gamedev.stackexchange.com XNA seems to be a favorite, and it was recommended to me when I asked where to start. I've downloaded and installed Visual Studio 2010 along with the XNA Framework and now I can't seem to get moving in the right direction. I started out looking on Google for "xna game studio tutorial", "xna game development beginners", "my first xna game", etc. I found lots of crap. The official "Introduction to Game Studio 4.0" gave me this (plus my own train of thought happily pasted on top thanks to MSPaint): http://tinypic.com/r/2w1sgvq/7 The "Get Additional Help" link (my best guess, since there was no "Continue" or "Next" link) lead me to this page: http://tinypic.com/r/2qa0dgx/7 I tried every page. The forum was the only thing that seemed helpful, however searching for "beginner", "newbie", "getting started", "first project", and similar on the forums turned up many threads with specific questions that are a bit above my level ("beginner to collision detection", for instance) Disappointed I returned to the XNA Game Studio home page. Surely their own website would have some introduction, tutorial, or at least a useful link to a community. EVERYTHING on their website was about coding Windows Phone 7.... Everything. http://tinypic.com/r/10eit8i/7 http://tinypic.com/r/120m9gl/7 Giving up on any official documentation after a while, I went back to Google. I managed to locate www.xnadevelopment.com. The website is built around XNA Game Studio 3.0, but how different can 3.0 be from 4.0?.... Apparently different enough. http://tinypic.com/r/5d8mk9/7 http://tinypic.com/r/25hflli/7 Figuring that this was the correct folder, I right-clicked.... http://tinypic.com/r/24o94yu/7 Hmm... maybe by "Add Content Reference" they mean "Add a reference to an existing file (content)"? Let's try it (after all- it's my only option) http://tinypic.com/r/2417eqt/7 At this point I gave up. I'm back. My original goal in my last question was to create a keyboard-navigable 3D world (no physics necessary, no logic or real game necessary). After my recent failures my goal has been revised. I want to display an image on the screen. Hopefully in time I'll be able to move it with the keyboard.

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• Smooth animation when using fixed time step

  - by sythical

  I'm trying to implement the game loop where the physics is independent from rendering but my animation isn't as smooth as I would like it to be and it seems to periodically jump. Here is my code: // alpha is used for interpolation double alpha = 0, counter_old_time = 0; double accumulator = 0, delta_time = 0, current_time = 0, previous_time = 0; unsigned frame_counter = 0, current_fps = 0; const unsigned physics_rate = 40, max_step_count = 5; const double step_duration = 1.0 / 40.0, accumulator_max = step_duration * 5; // information about the circ;e (position and velocity) int old_pos_x = 100, new_pos_x = 100, render_pos_x = 100, velocity_x = 60; previous_time = al_get_time(); while(true) { current_time = al_get_time(); delta_time = current_time - previous_time; previous_time = current_time; accumulator += delta_time; if(accumulator > accumulator_max) { accumulator = accumulator_max; } while(accumulator >= step_duration) { if(new_pos_x > 1330) velocity_x = -15; else if(new_pos_x < 70) velocity_x = 15; old_pos_x = new_pos_x; new_pos_x += velocity_x; accumulator -= step_duration; } alpha = accumulator / static_cast<double>(step_duration); render_pos_x = old_pos_x + (new_pos_x - old_pos_x) * alpha; al_clear_to_color(al_map_rgb(20, 20, 40)); // clears the screen al_draw_textf(font, al_map_rgb(255, 255, 255), 20, 20, 0, "current_fps: %i", current_fps); // print fps al_draw_filled_circle(render_pos_x, 400, 15, al_map_rgb(255, 255, 255)); // draw circle // I've added this to test how the program will behave when rendering takes // considerably longer than updating the game. al_rest(0.008); al_flip_display(); // swaps the buffers frame_counter++; if(al_get_time() - counter_old_time >= 1) { current_fps = frame_counter; frame_counter = 0; counter_old_time = al_get_time(); } } I have added a pause during the rendering part because I wanted to see how the code would behave when a lot of rendering is involved. Removing it makes the animation smooth but then I'll have to make sure that I don't let the frame rate drop too much and that doesn't seem like a good solution. I've been trying to fix this for a week and have had no luck so I'd be very grateful if someone can read through my code. Thank you! Edit: I added the following code to work out the actual velocity (pixels per second) of the ball each time the ball is rendered and surprisingly it's not constant so I'm guessing that's the issue. I'm not sure why it's not constant. alpha = accumulator / static_cast<double>(step_duration); render_pos_x = old_pos_x + (new_pos_x - old_pos_x) * alpha; cout << (render_pos_x - old_render_pos) / delta_time << endl; old_render_pos = render_pos_x;

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• Suggestions for getting an open source electron beam tracking code going

  - by Boaz

  I work in the field of accelerator physics and synchrotron radiation. High energy electrons circulating in large rings of magnets produce x-rays that are used for a variety of different kinds of science. Running and improving these facilities requires controlling and modelling the electron beam as it circulates in the ring. A code to model this basically requires trackers to follow the electrons through the elements (something called a symplectic integrator), and then the computation of different parameters associated with this motion. The problem with these codes is that every facility has there own. In principle the code is not so complex. And as a modelling project, one might think it has some general interest. Who doesn't want to be able to create a track in space out of magnets and watch the electrons circulate? There is a Matlab based code to do this called Accelerator Toolbox, but the creator of the code is no longer in the field. I put the code in Sourceforge under the name atcollab. The basic resource is in C- it is the set of symplectic integrators. These are available in the atcollab code here. It has been useful to put the code on Sourceforge in order to exchange code, but the community of users is quite small and most are too busy to put that much time into collaboration. So in terms of really improving the code, I don't think it has been so successful. Any piece of this picture could be recreated without that much difficulty, but overall it is a bit complex, and because each lab has their own installation with lots of add-on Matlab code, people find it hard to really work together and share code. Somehow I think we need to involve a wider community in our development, or just use some standard tools. But for that, I suppose it needs to be of some general interest. I think symplectic integrators may have some general interest. And the part about a plug-in architecture to build up the ring ought to fit other patterns. Or the other option is to just accept that this is not a problem of general interest, and work harder within our small community. Suggestions, or anecdotes of analogous experience would be appreciated.

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• Register Game Object Components in Game Subsystems? (Component-based Game Object design)

  - by topright

  I'm creating a component-based game object system. Some tips: GameObject is simply a list of Components. There are GameSubsystems. For example, rendering, physics etc. Each GameSubsystem contains pointers to some of Components. GameSubsystem is a very powerful and flexible abstraction: it represents any slice (or aspect) of the game world. There is a need in a mechanism of registering Components in GameSubsystems (when GameObject is created and composed). There are 4 approaches: 1: Chain of responsibility pattern. Every Component is offered to every GameSubsystem. GameSubsystem makes a decision which Components to register (and how to organize them). For example, GameSubsystemRender can register Renderable Components. pro. Components know nothing about how they are used. Low coupling. A. We can add new GameSubsystem. For example, let's add GameSubsystemTitles that registers all ComponentTitle and guarantees that every title is unique and provides interface to quering objects by title. Of course, ComponentTitle should not be rewrited or inherited in this case. B. We can reorganize existing GameSubsystems. For example, GameSubsystemAudio, GameSubsystemRender, GameSubsystemParticleEmmiter can be merged into GameSubsystemSpatial (to place all audio, emmiter, render Components in the same hierarchy and use parent-relative transforms). con. Every-to-every check. Very innefficient. con. Subsystems know about Components. 2: Each Subsystem searches for Components of specific types. pro. Better performance than in Approach 1. con. Subsystems still know about Components. 3: Component registers itself in GameSubsystem(s). We know at compile-time that there is a GameSubsystemRenderer, so let's ComponentImageRender will call something like GameSubsystemRenderer::register(ComponentRenderBase*). pro. Performance. No unnecessary checks as in Approach 1. con. Components are badly coupled with GameSubsystems. 4: Mediator pattern. GameState (that contains GameSubsystems) can implement registerComponent(Component*). pro. Components and GameSubystems know nothing about each other. con. In C++ it would look like ugly and slow typeid-switch. Questions: Which approach is better and mostly used in component-based design? What Practice says? Any suggestions about implementation of Approach 4? Thank you.

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• What are some good realistic programming related movies (docu-dramas, documentaries, accurate fiction, etc)?

  - by EpsilonVector

  A while ago I asked this question and the result was this. Following the response I got in the meta question I'm re-asking the question with new guidelines to focus it on the direction I wanted it to have originally. ================================================================== The guidelines are as follows: by "programming related" I mean movies from which we can learn about stuff like the development process, or history of software/computers, or programming culture. In other words, they must be grounded in the industry. No tangential stuff. Good entries answer as many of the following criteria as possible: Teach you about the history of the industry, or the development process, or teach you about important industry related topics (software patents for example) Are based on real life events, companies, people, practices, and they are the main focus of the movie After watching them, you feel like you understand or know something about the programmers' world that you didn't before (or you can see how someone could have such a response). You can point to it and say "this faithfully represents the industry/programmer culture at some point in time". This might be something you would show laymen to explain to them what "your people" are like and what is it that you do. Examples for good entries include: Pirates of Silicon Valley- the story of how Microsoft and Apple started the industry. Revolution OS- The story of Linux's rise to fame, and a pretty good cover of the Free Software/Open Source world. Aardvark'd: 12 Weeks with Geeks- development process. Examples for bad entries: Movies who's sole relevance is that they can be appreciated by programmers. The point of this question is not to be "what are some good movies" with "for a programmer" appended to it. Just because the writers got a few computer jokes right in itself doesn't make it about the industry. Movies where there's a computer related element, but are not about the industry. For example, 24 (the TV series). It's a product of the information age but it isn't actually about it. Another example is movies where there's a really cool programmer character, but are overall about something completely different. Likewise, The Big Bang Theory is not about physics, even though they have a cool physicist as a character. Science fiction, even if it draws ideas from computers. For example, the Matrix trilogy. Movies that you can't point to them and say: this is a faithful representation of our world (at some point in time). If you can't do that then it doesn't mirror the industry. Keep it one entry per answer so that the voting could sort the entries out.

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• What does the Spring framework do? Should I use it? Why or why not?

  - by sangfroid

  So, I'm starting a brand-new project in Java, and am considering using Spring. Why am I considering Spring? Because lots of people tell me I should use Spring! Seriously, any time I've tried to get people to explain what exactly Spring is or what it does, they can never give me a straight answer. I've checked the intros on the SpringSource site, and they're either really complicated or really tutorial-focused, and none of them give me a good idea of why I should be using it, or how it will make my life easier. Sometimes people throw around the term "dependency injection", which just confuses me even more, because I think I have a different understanding of what that term means. Anyway, here's a little about my background and my app : Been developing in Java for a while, doing back-end web development. Yes, I do a ton of unit testing. To facilitate this, I typically make (at least) two versions of a method : one that uses instance variables, and one that only uses variables that are passed in to the method. The one that uses instance variables calls the other one, supplying the instance variables. When it comes time to unit test, I use Mockito to mock up the objects and then make calls to the method that doesn't use instance variables. This is what I've always understood "dependency injection" to be. My app is pretty simple, from a CS perspective. Small project, 1-2 developers to start with. Mostly CRUD-type operations with a a bunch of search thrown in. Basically a bunch of RESTful web services, plus a web front-end and then eventually some mobile clients. I'm thinking of doing the front-end in straight HTML/CSS/JS/JQuery, so no real plans to use JSP. Using Hibernate as an ORM, and Jersey to implement the webservices. I've already started coding, and am really eager to get a demo out there that I can shop around and see if anyone wants to invest. So obviously time is of the essence. I understand Spring has quite the learning curve, plus it looks like it necessitates a whole bunch of XML configuration, which I typically try to avoid like the plague. But if it can make my life easier and (especially) if make it can make development and testing faster, I'm willing to bite the bullet and learn Spring. So please. Educate me. Should I use Spring? Why or why not?

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• design a model for a system of dependent variables

  - by dbaseman

  I'm dealing with a modeling system (financial) that has dozens of variables. Some of the variables are independent, and function as inputs to the system; most of them are calculated from other variables (independent and calculated) in the system. What I'm looking for is a clean, elegant way to: define the function of each dependent variable in the system trigger a re-calculation, whenever a variable changes, of the variables that depend on it A naive way to do this would be to write a single class that implements INotifyPropertyChanged, and uses a massive case statement that lists out all the variable names x1, x2, ... xn on which others depend, and, whenever a variable xi changes, triggers a recalculation of each of that variable's dependencies. I feel that this naive approach is flawed, and that there must be a cleaner way. I started down the path of defining a CalculationManager<TModel> class, which would be used (in a simple example) something like as follows: public class Model : INotifyPropertyChanged { private CalculationManager<Model> _calculationManager = new CalculationManager<Model>(); // each setter triggers a "PropertyChanged" event public double? Height { get; set; } public double? Weight { get; set; } public double? BMI { get; set; } public Model() { _calculationManager.DefineDependency<double?>( forProperty: model => model.BMI, usingCalculation: (height, weight) => weight / Math.Pow(height, 2), withInputs: model => model.Height, model.Weight); } // INotifyPropertyChanged implementation here } I won't reproduce CalculationManager<TModel> here, but the basic idea is that it sets up a dependency map, listens for PropertyChanged events, and updates dependent properties as needed. I still feel that I'm missing something major here, and that this isn't the right approach: the (mis)use of INotifyPropertyChanged seems to me like a code smell the withInputs parameter is defined as params Expression<Func<TModel, T>>[] args, which means that the argument list of usingCalculation is not checked at compile time the argument list (weight, height) is redundantly defined in both usingCalculation and withInputs I am sure that this kind of system of dependent variables must be common in computational mathematics, physics, finance, and other fields. Does someone know of an established set of ideas that deal with what I'm grasping at here? Would this be a suitable application for a functional language like F#? Edit More context: The model currently exists in an Excel spreadsheet, and is being migrated to a C# application. It is run on-demand, and the variables can be modified by the user from the application's UI. Its purpose is to retrieve variables that the business is interested in, given current inputs from the markets, and model parameters set by the business.

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• 2D Animation Smoothness - Delta time vs. Kinematics

  - by viperld002

  I'm animating a sprite in 2D with key frames of rotation and xy-positions. I've recently had a discussion with someone saying that when the device (happens to be an iPad using cocos2D) hits a performance bump due to whatever else the user may be doing, lag will arise and that the best way to fight it is to not use actual positions, but velocities, accelerations and torques with kinematics. His message is to evaluate the positions and rotations from these speeds at the current point in time. I've never experienced a situation where I've heard of using kinematics to stem lag in 2D animations and am not sure of how effective it could be. Also, it seems to be overkill. The application is not networked so it's all running on a local device. The desired effect is that the animation always plays as closely as it can to the target frame rate. Wouldn't the technique suffer the same problems as just using the time since the last frame or a fixed time step since the kinematics would also require some time value to perform the calculation? What techniques could you suggest to best achieve the desired effect? EDIT 1 Thank you for your responses, they are very illuminating. I want to clarify my question before choosing an answer however, to make sure that this post really serves it's purpose. I have a sprite of a ball, and a text file with 3 arrays worth of information (rotation,translations x, translations y) with each unit of information existing as a key frame to be stepped through (0 to 49 and back to 0 to replay it again). I have this playing by interpolating from the current key frame to the next, every n-units of time. The animation is visibly correct when compared to a video I was given of it, and it is smooth because of the interpolations between the key frames. This is the existing state of the project. There are no physics simulated, only a static animation of a ball moving in a way an artist specifically designed. Should I, instead of rotation in degrees and translations by positions in space, derive velocities, accelerations and torques to express this static animation as a function of time? As in, position now = foo(time now), where foo uses kinematics.

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