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  • Need a solution to store images (1 billion, 1000,000,000) which users will upload to a website via php or javascript upload [on hold]

    - by wish_you_all_peace
    I need a solution to store images (1 billion) which users will upload to a website via PHP or Javascript upload (website will have 1 billion page views a month using Linux Debian distros) assuming 20 photos per user maximum (10 thumbnails of size 90px by 90px and 10 large, script resized images of having maximum width 500px or maximum height 500px depending on shape of image, meaning square, rectangle, horizontal, vertical etc). Assume this to be a LEMP-stack (Linux Nginx MySQL PHP) social-media or social-matchmaking type application whose content will be text and images. Since everyone knows storing tons of images (website users uploaded images in this case) are bad inside a single directory or NFS etc, please explain all the details about the architecture and configuration of the entire setup of storage solution, to store 1 billion images on any method you recommend (no third-party cloud storage like S3 etc. It has to be within the private data center using our own hardware and resources.). The solution has to include both the storage solution and organizing the images uploaded by users. How will we organize the users images if a single user will not have more than 20 images (10 thumbs and 10 large of having either width or height 500px)? Please consider that this has to be organized in a structural way so we can fetch a single user's images via PHP/Javascript or API programmatically through some type of user's unique identifier(s).

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  • 3D terrain map with Hexagon Grids

    - by Rob
    I'm working on a hobby project (I'm a web/backend developer by day) and I want to create a 3D Tile (terrain) engine. I'm using XNA, but I can use MonoGame, OpenGL, or straight DirectX, so the answer does not have to be XNA specific. I'm more looking for some high level advice on how to approach this problem. I know about creating height maps and such, there are thousands of references out there on the net for that, this is a bit more specific. I'm more concerned with is the approach to get a 3D hexagon tile grid out of my terrain (since the terrain, and all 3d objects, are basically triangles). The first approach I thought about is to basically draw the triangles on the screen in the following order (blue numbers) to give me the triangles for terrain (black triangles) and then make hexes out of the triangles (red hex). This approach seems complicated to me since i'm basically having to draw 4 different types of triangles. The next approach I thought of was to use the existing triangles like I did for a square grid and get my hexes from 6 triangles as follows This seems like the easier approach to me since there are only 2 types of triangles (i would have to play with the heights and widths to get a "perfect" hexagon, but the idea is the same. So I'm looking for: 1) Any suggestions on which approach I should take, and why. 2) How would I translate mouse position to a hexagon grid position (especially when moving the camera around), for example in the second image if the mouse pointer were the green circle, how would I determine to highlight that hexagon and then translating that into grid coordinates (assuming it is 0,0)? 3) Any references, articles, books, etc - to get me going in the right direction. Note: I've done hex grid's and mouse-grid coordinate conversion before in 2d. looking for some pointers on how to do the same in 3d. The result I would like to achieve is something similar to this video.

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  • Mouse pointer strange problem...

    - by Paska
    Hi all, i have last ubuntu installed (10.10), but from an year and thousand updates, video drivers updates, an hundreds of tricks, the mouse pointer is showed like an UGLY square... These are the screenshots: First Second I have no idea what to do to solve this problem. Anyone of you have an idea to solve it? Edit: this problem was encountered from 8.10+! Edit 2, Video card specifications: paska@ubuntu:~$ hwinfo --gfxcard 35: PCI 100.0: 0300 VGA compatible controller (VGA) [Created at pci.318] UDI: /org/freedesktop/Hal/devices/pci_1106_3230 Unique ID: VCu0.QX54AGQKWeE Parent ID: vSkL.CP+qXDDqow8 SysFS ID: /devices/pci0000:00/0000:00:01.0/0000:01:00.0 SysFS BusID: 0000:01:00.0 Hardware Class: graphics card Model: "VIA K8M890CE/K8N890CE [Chrome 9]" Vendor: pci 0x1106 "VIA Technologies, Inc." Device: pci 0x3230 "K8M890CE/K8N890CE [Chrome 9]" SubVendor: pci 0x1043 "ASUSTeK Computer Inc." SubDevice: pci 0x81b5 Revision: 0x11 Memory Range: 0xd0000000-0xdfffffff (rw,prefetchable) Memory Range: 0xfa000000-0xfaffffff (rw,non-prefetchable) Memory Range: 0xfbcf0000-0xfbcfffff (ro,prefetchable,disabled) IRQ: 16 (10026 events) I/O Ports: 0x3c0-0x3df (rw) Module Alias: "pci:v00001106d00003230sv00001043sd000081B5bc03sc00i00" Driver Info #0: Driver Status: viafb is not active Driver Activation Cmd: "modprobe viafb" Config Status: cfg=new, avail=yes, need=no, active=unknown Attached to: #17 (PCI bridge) Primary display adapter: #35 paska@ubuntu:~$ thanks, A

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  • OpenGL: Where shoud I place shaders?

    - by mivic
    I'm trying to learn OpenGL ES 2.0 and I'm wondering what is the most common practice to "manage" shaders. I'm asking this question because in the examples I've found (like the one included in the API Demo provided with the android sdk), I usually see everything inside the GLRenderer class and I'd rather separate things so I can have, for example, a GLImage object that I can reuse whenever I want to draw a textured quad (I'm focusing on 2D only at the moment), just like I had in my OpenGL ES 1.0 code. In almost every example I've found, shaders are just defined as class attributes. For example: public class Square { public final String vertexShader = "uniform mat4 uMVPMatrix;\n" + "attribute vec4 aPosition;\n" + "attribute vec4 aColor;\n" + "varying vec4 vColor;\n" + "void main() {\n" + " gl_Position = uMVPMatrix * aPosition;\n" + " vColor = aColor;\n" + "}\n"; public final String fragmentShader = "precision mediump float;\n" + "varying vec4 vColor;\n" + "void main() {\n" + " gl_FragColor = vColor;\n" + "}\n"; // ... } I apologize in advance if some of these questions are dumb, but I've never worked with shaders before. 1) Is the above code the common way to define shaders (public final class properties)? 2) Should I have a separate Shader class? 3) If shaders are defined outside the class that uses them, how would I know the names of their attributes (e.g. "aColor" in the following piece of code) so I can bind them? colorHandle = GLES20.glGetAttribLocation(program, "aColor");

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  • Ubuntu 14.04: After login, top- and sidepanel don't load and system settings don't open

    - by Löwe Simon
    I have Ubuntu 14.04 on a Medion Erazer with the Nvidia GTX570M card. At first, while I had not installed the last nvidia driver, each time I would try to suspend my pc it would freeze frame on the login. Once I managed to install the nvidia drivers, everything seemed to work up until I noticed that suddenly the system settings would not open anymore. I then rebooted my pc, but when I logged in I just end up with my cursor but no top panel or side pannel. Thankfully, I had installed the gnome desktops which works, except for the fact the system settings do not open also in the gnome desktop. I have tried following: Problems after upgrading to 14.04 (only background and pointer after login) except for reinstalling nvidia, since then I would be back at square one with suspend not working. When I try to launch system settings through the terminal, I get: simon@simon-X681X:~$ unity-control-center libGL error: No matching fbConfigs or visuals found libGL error: failed to load driver: swrast (unity-control-center:2806): Gdk-ERROR **: The program 'unity-control-center' received an X Window System error. This probably reflects a bug in the program. The error was 'BadLength (poly request too large or internal Xlib length erro'. (Details: serial 229 error_code 16 request_code 155 (GLX) minor_code 1) (Note to programmers: normally, X errors are reported asynchronously; that is, you will receive the error a while after causing it. To debug your program, run it with the GDK_SYNCHRONIZE environment variable to change this behavior. You can then get a meaningful backtrace from your debugger if you break on the gdk_x_error() function.) Trace/breakpoint trap (core dumped) I know the 2 problems seem unrelated, but since they occured together, I am wondering if that is really the case. Your help is much appreciated, Simon

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  • How to implement curved movement while tracking the appropriate angle?

    - by Vexille
    I'm currently coding a 2D top-down car game which will be turn-based. And since it's turn-based, the cars won't be controlled directly (i.e. with a simple velocity vector that adjusts its angle when the player wants to turn), but instead it's movement path has to be planned beforehand, and then the car needs to follow the path when the turn ends (think Steambirds). This question has some interesting information, but its focus is on homing-missile behaviour, which I kinda had figured out, but doesn't really apply to my case, I think, since I need to show a preview of the path when the player is planning his turn, then have the car follow that path. In that same question, there's an excellent answer by Andrew Russel which mentions Equations of Motion and Bézier's Curve. Some of his other suggestions of implementation are specific to XNA though, so they don't help much (I'm using Marmalade SDK). If I assume Bézier's Curve as the solution of choice, I'm left with one specific problem: I'll have the car's position (the first endpoint) and the target/final position (the last endpoint), but what should I use as the control point (assuming a square/quadratic curve)? And whether I use Bézier's Curve or another parametric equation, I'd still be left with another issue: the car can't just follow the curve, it must turn (i.e. adjust its angle) accordingly. So how can I figure out which way the car should be pointing to at any given point in the curve?

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  • Java Deployment Team at JavaOne 2012

    - by _chrisb
    This year the Java Deployment team has some pretty exciting sessions at JavaOne. We will be talking about a lot of new features including Java on the Mac, Java FX deployment, and bundled applications. All presentations and the booth are located at the Hilton San Francisco Union Square, 333 O'Farrell Street. Booth The Java Deployment booth is located in the Hilton San Francisco Grand Ballroom. We will available to discuss Java Deployment and answer your questions at the following days and times: Monday, October 1st 10:30 AM - 5:00 PM Tuesday, October 2nd 10:00 AM - 5:00 PM Wednesday, October 3rd 9:30 AM - 5:00 PM Sessions Java Deployment on Mac OS X - CON7488 This is a great opportunity to learn about what's new in Java for Mac. Oracle now distributes Java for Mac so there are some exciting new changes. Scott Kovatch and Chris Bensen Located in the Hilton San Francisco Imperial Ballroom B Monday, October 1, 1:00 PM - 2:00 PM Deploy Your Application with OpenJDK 7 on Mac OS X - CON8224 Learn about packaging and distributing Java applications to the Mac AppStore with step by step examples and tips. Scott Kovatch Located in the Hilton San Francisco Imperial Ballroom B Monday, October 1, 3:00 PM - 4:00 PM The Java User Experience Team Presents the Latest UI Updates - BOF3615 Discover the eye candy that the user interface experts have been working on. Jeff Hoffman and Terri Yamamoto Located in the Hilton San Francisco Imperial Ballroom B Monday, October 1, 5:30 PM - 6:15 PM Mastering Java Deployment Skills - CON7797 Find out what Java Deployment has been cooking. This is the best place to learn about self-contained application packaging. Igor Nekrestyanov and Mark Howe Located in the Hilton San Francisco Imperial Ballroom B Thursday, October 4th, 12:30 PM to 1:30 PM For those who will not be able to aqttend we will share all slides after the JavaOne. And just to make it easy to find us, here is a map: View Larger Map

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  • Render rivers in a grid.

    - by Gabriel A. Zorrilla
    I have created a random height map and now i want to create rivers. I've made an algorithm based on a* to make rivers flow from peaks to sea and now i'm in the quest of figuring out an elegant algorithm to render them. It's a 2D, square, mapgrid. The cells which the river pases has a simple integer value with this form :rivernumber && pointOrder. Ie: 10, 11, 12, 13, 14, 15, 16...1+N for the first river, 20,21,22,23...2+N for the second, etc. This is created in the map grid generation time and it's executed just once, when the world is generated. I wanted to treat each river as a vector, but there is a problem, if the same river has branches (because i put some noise to generate branches), i can not just connect the points in order. The second alternative is to generate a complex algorithm where analizes each point, checks if the next is not a branch, if so trigger another algorithm that take care of the branch then returns to the main river, etc. Very complex and inelegant. Perhaps there is a solution in the world generation algorithm or in the river rendering algorithm that is commonly used in these cases and i'm not aware of. Any tips? Thanks!!

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  • NRF Big Show 2011 -- Part 3

    - by David Dorf
    I'm back from the NRF show having been one of the lucky people who's flight was not canceled. The show was very crowded with a reported 20% increase in attendance and everyone seemed in high spirits. After two years of sluggish retail sales, things are really picking up and it was reflected in everyone's mood. The pop-up Disney Store in the Oracle booth was great and attracted lots of interest in their mobile POS. I know many attendees visited the Disney Store in Times Square to see the entire operation. It's an impressive two-story store that keeps kids engaged. The POS demonstration station, where most of our innovations were demoed, was always crowded. Unfortunately most of the demos used WiFi and the signals from other booths prevented anything from working reliably. Nevertheless, the demo team did an excellent job walking people through the scenarios and explaining how shopping is being impacted by mobile, analytics, and RFID. Big Show Links Disney uncovers its store magic Top 10 Things You Missed at the NRF Big Show 2011 Oracle Retail Stores Innovation Station at NRF Big Show 2011 (video) The buzz of the show was again around mobile solutions. Several companies are creating mobile POS using the iPod Touch, including integrations to Oracle POS for the following retailers: Disney Stores with InfoGain Victoria's Secret with InfoGain Urban Outfitters with Starmount The Gap with Global Bay Keeping with the mobile theme, the NRF release a revised version of their Mobile Blueprint at NRF. It will be posted to the NRF site very soon. The alternate payments section had a major rewrite that provides a great overview and proximity and remote payment technologies. NRF Mobile Blueprint Links New mobile blueprint provides fresh insights NRF Mobile Blueprint 2011 (slides) I hope to do some posts on some of the interesting companies I spoke with in the coming weeks.

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  • Go Big or Go Home

    - by Justin Kestelyn
    The Oracle Develop conference (#oracledevelop10), being co-located for the first time ever with JavaOne in San Francisco, is guaranteed to be the ultimate rush for developers this year. Where else can you go to learn about, interact with, and meet fellow devotees of the entire Oracle Development stack (welcome, Oracle Solaris)? This will also be the first time that the community space traditionally located at Oracle OpenWorld - and hosted by Oracle Technology Network, as always - will be present at the "developer" conference during this busy week. So, Oracle OpenWorld's loss is Oracle Develop's gain. And what a community space it will be: nearly 4,000 square feet for meeting space, contests and give-aways, consumption of various beverages, special speakers (Oracle ACEs among them, no doubt), and video-casting. The entire Oracle Technology Network crew will be on hand to "facilitate" your experience, of course. Even better, you can rub shoulders and share war stories with attendees from that "other" conference, JavaOne. (You have access to both conferences as a single package, so you may be having a conversation with yourself.) We call the whole enchilada "The Zone". As time goes on, we'll bring you more news about the activities described above, as well as OTN Night (which proves to be more raucous than ever), technical sessions and keynotes not to be missed, the unconference/open sessions, things to do at night, and more. In the meantime, stay in touch with us via Twitter or Oracle Mix.

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  • View Word Definitions in IE 8 with the Define with Bing Accelerator

    - by Asian Angel
    Do you need an easy way to view word definitions while browsing with Internet Explorer? The Define with Bing Accelerator will display definitions in the same (or a new) tab and save you time while browsing. Using Define with Bing The installation consists of two steps. First, click on Add to Internet Explorer to start the process. Next you will be asked to confirm the installation. Once you have clicked Add your new accelerator is ready to use (no browser restart required). Whenever you encounter a word that needs defining highlight it, click on the small blue square, go to All Accelerators, and then Define with Bing. There are two ways to access the definition: Hover your mouse over the Define with Bing text to open a small popup window Click on Define with Bing to open a definition search in a new tab Being able to access a definition or explanation in the same tab will definitely save you time while browsing. In the example shown here you can get an idea of what SCORM means but clicking on the links inside the popup window is not recommended (webpage opens in popup and is not resizable). In the situation shown above it is better to click on Define with Bing and see more information in a new tab. Conclusion The Define with Bing Accelerator can be a very useful time saver while browsing with Internet Explorer. Finding those word definitions will be a much more pleasant experience now. Add the Define with Bing Accelerator to Internet Explorer Similar Articles Productive Geek Tips Add Google Dictionary Power to ChromeChoose Custom New Tab Pages in ChromeSearch Alternative Search Engines from within Bing’s Search PageView Word Definitions in Google Chrome with DictionaryTipThe New Bing Bar Provides Easy Access to Searches and Microsoft Live Services TouchFreeze Alternative in AutoHotkey The Icy Undertow Desktop Windows Home Server – Backup to LAN The Clear & Clean Desktop Use This Bookmarklet to Easily Get Albums Use AutoHotkey to Assign a Hotkey to a Specific Window Latest Software Reviews Tinyhacker Random Tips CloudBerry Online Backup 1.5 for Windows Home Server Snagit 10 VMware Workstation 7 Acronis Online Backup Sculptris 1.0, 3D Drawing app AceStock, a Tiny Desktop Quote Monitor Gmail Button Addon (Firefox) Hyperwords addon (Firefox) Backup Outlook 2010 Daily Motivator (Firefox)

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  • Top Down RPG Movement w/ Correction?

    - by Corey Ogburn
    I would hope that we have all played Zelda: A Link to the Past, please correct me if I'm wrong, but I want to emulate that kind of 2D, top-down character movement with a touch of correction. It has been done in other games, but I feel this reference would be the easiest to relate to. More specifically the kind of movement and correction I'm talking about is: Floating movement not restricted to tile based movement like Pokemon and other games where one tap of the movement pad moves you one square in that cardinal direction. This floating movement should be able to achieve diagonal motion. If you're walking West and you come to a wall that is diagonal in a North East/South West fashion, you are corrected into a South West movement even if you continue holding left (West) on the controller. This should work for both diagonals correcting in both directions. If you're a few pixels off from walking squarely into a door or hallway, you are corrected into walking through the hall or down the hallway, i.e. bumping into the corner causes you to be pushed into the hall/door. I've hunted for efficient ways to achieve this and have had no luck. To be clear I'm talking about the human character's movement, not an NPC's movement. Are their resources available on this kind of movement? Equations or algorithms explained on a wiki or something? I'm using the XNA Framework, is there anything in it to help with this?

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  • Collision Detection Code Structure with Sloped Tiles

    - by ProgrammerGuy123
    Im making a 2D tile based game with slopes, and I need help on the collision detection. This question is not about determining the vertical position of the player given the horizontal position when on a slope, but rather the structure of the code. Here is my pseudocode for the collision detection: void Player::handleTileCollisions() { int left = //find tile that's left of player int right = //find tile that's right of player int top = //find tile that's above player int bottom = //find tile that's below player for(int x = left; x <= right; x++) { for(int y = top; y <= bottom; y++) { switch(getTileType(x, y)) { case 1: //solid tile { //resolve collisions break; } case 2: //sloped tile { //resolve collisions break; } default: //air tile or whatever else break; } } } } When the player is on a sloped tile, he is actually inside the tile itself horizontally, that way the player doesn't look like he is floating. This creates a problem because when there is a sloped tile next to a solid square tile, the player can't move passed it because this algorithm resolves any collisions with the solid tile. Here is a gif showing this problem: So what is a good way to structure my code so that when the player is inside a sloped tile, solid tiles get ignored?

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  • Installation taking a very long time, hangs at "Configuring bcmwl-kernel-source"

    - by user290522
    I am installing Ubuntu 14.04(32-bit) on my laptop (Compaq Presario V2000), and after about 7 hours, it is still in Configuring bcmwl-kernel-source (i386) mode. The messages I read are as follows: ubuntu kernel: [22814.858163] ACPI: \_SB_.PCI0.LPC0.LPC0.ACAD: ACPI_NOTIFY_BUS_CHECK event: unsupported with the numbers in the square brackets increasing. I have had Windows XP professional on this laptop, and I am erasing it. I am not sure if I should turn off the laptop, and start all over again. About 4 years ago I installed Ubuntu on this laptop, and that was very fast. The only problem I encountered was my wireless, and could not make it to work, and switched back to Windows. I appreciate any comments regarding this installation taking such a long time. After 40 hours the installation was still in configuring mode with the following messages: ubuntu CRON[29329]: (root) CMD ( cd/ && run-part .. report /etc/cron-hourly) I did the following to check for errors: pressed ctrl-alt-f2. This time the system froze. I had no other choice but to turn off the laptop, and start all over again. The exact model of the laptop is "Compaq Presario V2069CL Notebook PC" with AMD processor.

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  • CSO Summit @ Executive Edge

    - by Naresh Persaud
    If you are attending the Executive Edge at Open World be sure to check out the sessions at the Chief Security Officer Summit. Former Sr. Counsel for the National Security Agency, Joel Brenner ,  will be speaking about his new book "America the Vulnerable". In addition, PWC will present a panel discussion on "Crisis Management to Business Advantage: Security Leadership". See below for the complete agenda. TUESDAY, October 2, 2012 Chief Security Officer Summit Welcome Dave Profozich, Group Vice President, Oracle 10:00 a.m.–10:15 a.m. America the Vulnerable Joel Brenner, former Senior Counsel, National Security Agency 10:15 a.m.–11:00 a.m. The Threats are Outside, the Risks are Inside Sonny Singh, Senior Vice President, Oracle 11:00 a.m.–11:20 a.m. From Crisis Management to Business Advantage: Security Leadership Moderator: David Burg, Partner, Forensic Technology Solutions, PwC Panelists: Charles Beard, CIO and GM of Cyber Security, SAIC Jim Doggett, Chief Information Technology Risk Officer, Kaiser Permanente Chris Gavin, Vice President, Information Security, Oracle John Woods, Partner, Hunton & Williams 11:20 a.m.–12:20 p.m. Lunch Union Square Tent 12:20 p.m.–1:30 p.m. Securing the New Digital Experience Amit Jasuja, Senior Vice President, Identity Management and Security, Oracle 1:30 p.m.–2:00 p.m. Securing Data at the Source Vipin Samar, Vice President, Database Security, Oracle 2:00 p.m.–2:30 p.m. Security from the Chairman’s Perspective Jeff Henley, Chairman of the Board, Oracle Dave Profozich, Group Vice President, Oracle 2:30 p.m.–3:00 p.m.

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  • Box2d - Attaching a fired arrow to a moving enemy

    - by Satchmo Brown
    I am firing an arrow from the player to moving enemies. When the arrow hits the enemy, I want it to attach exactly where it hit and cause the enemy (a square) to tumble to the ground. Excluding the logistics of the movement and the spin (it already works), I am stuck on the attaching of the two bodies. I tried to weld them together initially but when they fell, they rotated in opposite directions. I have figured that a revolute joint is probably what I am after. The problem is that I can't figure out a way to attach them right where they collide. Using code from iforce2d: b2RevoluteJointDef revoluteJointDef; revoluteJointDef.bodyA = m_body; revoluteJointDef.bodyB = m_e->m_body; revoluteJointDef.collideConnected = true; revoluteJointDef.localAnchorA.Set(0,0);//the top right corner of the box revoluteJointDef.localAnchorB.Set(0,0);//center of the circle b2RevoluteJoint m_joint = *(b2RevoluteJoint*)m_game->m_world->CreateJoint( &revoluteJointDef ); m_body->SetLinearVelocity(m_e->m_body->GetLinearVelocity()); This attaches them but in the center of both of their points. Does anyone know how I would go about getting the exact point of collision so I can link these? Is this even the right method of doing this? Update: I have the exact point of collision. But I still am not sure this is even the method I want to go about this. Really, I just want to attach body A to B and have body B unaffected in any way.

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  • AceCypher is an Addictive Cypher Slide Puzzle Game

    - by Akemi Iwaya
    Are you ready for a game that will test your logical thinking skills while providing hours of fun? Then you may want to have a look at this awesome cypher slide puzzler! AceCypher is great puzzle game for those times when you only have a few minutes to play or want a fun way to pass the time while relaxing. The overall premise and style of game play for AceCypher is simple. You move individual rows (left, right) or columns (up, down) one space at a time in order to shift the positions of numbers on the game board through ’round-a-bout’ trading. The goal is to make the four numbers in the red square match the code shown in the upper right corner (including positions). Sounds simple so far, right? But the challenge comes from the random boards you will be given to work with…some will not be too hard to solve while others will tax your brain (and patience!) quite well.     

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  • C#/.NET Little Wonders: Use Cast() and TypeOf() to Change Sequence Type

    - by James Michael Hare
    Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. We’ve seen how the Select() extension method lets you project a sequence from one type to a new type which is handy for getting just parts of items, or building new items.  But what happens when the items in the sequence are already the type you want, but the sequence itself is typed to an interface or super-type instead of the sub-type you need? For example, you may have a sequence of Rectangle stored in an IEnumerable<Shape> and want to consider it an IEnumerable<Rectangle> sequence instead.  Today we’ll look at two handy extension methods, Cast<TResult>() and OfType<TResult>() which help you with this task. Cast<TResult>() – Attempt to cast all items to type TResult So, the first thing we can do would be to attempt to create a sequence of TResult from every item in the source sequence.  Typically we’d do this if we had an IEnumerable<T> where we knew that every item was actually a TResult where TResult inherits/implements T. For example, assume the typical Shape example classes: 1: // abstract base class 2: public abstract class Shape { } 3:  4: // a basic rectangle 5: public class Rectangle : Shape 6: { 7: public int Widtgh { get; set; } 8: public int Height { get; set; } 9: } And let’s assume we have a sequence of Shape where every Shape is a Rectangle… 1: var shapes = new List<Shape> 2: { 3: new Rectangle { Width = 3, Height = 5 }, 4: new Rectangle { Width = 10, Height = 13 }, 5: // ... 6: }; To get the sequence of Shape as a sequence of Rectangle, of course, we could use a Select() clause, such as: 1: // select each Shape, cast it to Rectangle 2: var rectangles = shapes 3: .Select(s => (Rectangle)s) 4: .ToList(); But that’s a bit verbose, and fortunately there is already a facility built in and ready to use in the form of the Cast<TResult>() extension method: 1: // cast each item to Rectangle and store in a List<Rectangle> 2: var rectangles = shapes 3: .Cast<Rectangle>() 4: .ToList(); However, we should note that if anything in the list cannot be cast to a Rectangle, you will get an InvalidCastException thrown at runtime.  Thus, if our Shape sequence had a Circle in it, the call to Cast<Rectangle>() would have failed.  As such, you should only do this when you are reasonably sure of what the sequence actually contains (or are willing to handle an exception if you’re wrong). Another handy use of Cast<TResult>() is using it to convert an IEnumerable to an IEnumerable<T>.  If you look at the signature, you’ll see that the Cast<TResult>() extension method actually extends the older, object-based IEnumerable interface instead of the newer, generic IEnumerable<T>.  This is your gateway method for being able to use LINQ on older, non-generic sequences.  For example, consider the following: 1: // the older, non-generic collections are sequence of object 2: var shapes = new ArrayList 3: { 4: new Rectangle { Width = 3, Height = 13 }, 5: new Rectangle { Width = 10, Height = 20 }, 6: // ... 7: }; Since this is an older, object based collection, we cannot use the LINQ extension methods on it directly.  For example, if I wanted to query the Shape sequence for only those Rectangles whose Width is > 5, I can’t do this: 1: // compiler error, Where() operates on IEnumerable<T>, not IEnumerable 2: var bigRectangles = shapes.Where(r => r.Width > 5); However, I can use Cast<Rectangle>() to treat my ArrayList as an IEnumerable<Rectangle> and then do the query! 1: // ah, that’s better! 2: var bigRectangles = shapes.Cast<Rectangle>().Where(r => r.Width > 5); Or, if you prefer, in LINQ query expression syntax: 1: var bigRectangles = from s in shapes.Cast<Rectangle>() 2: where s.Width > 5 3: select s; One quick warning: Cast<TResult>() only attempts to cast, it won’t perform a cast conversion.  That is, consider this: 1: var intList = new List<int> { 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 }; 2:  3: // casting ints to longs, this should work, right? 4: var asLong = intList.Cast<long>().ToList(); Will the code above work?  No, you’ll get a InvalidCastException. Remember that Cast<TResult>() is an extension of IEnumerable, thus it is a sequence of object, which means that it will box every int as an object as it enumerates over it, and there is no cast conversion from object to long, and thus the cast fails.  In other words, a cast from int to long will succeed because there is a conversion from int to long.  But a cast from int to object to long will not, because you can only unbox an item by casting it to its exact type. For more information on why cast-converting boxed values doesn’t work, see this post on The Dangers of Casting Boxed Values (here). OfType<TResult>() – Filter sequence to only items of type TResult So, we’ve seen how we can use Cast<TResult>() to change the type of our sequence, when we expect all the items of the sequence to be of a specific type.  But what do we do when a sequence contains many different types, and we are only concerned with a subset of a given type? For example, what if a sequence of Shape contains Rectangle and Circle instances, and we just want to select all of the Rectangle instances?  Well, let’s say we had this sequence of Shape: 1: var shapes = new List<Shape> 2: { 3: new Rectangle { Width = 3, Height = 5 }, 4: new Rectangle { Width = 10, Height = 13 }, 5: new Circle { Radius = 10 }, 6: new Square { Side = 13 }, 7: // ... 8: }; Well, we could get the rectangles using Select(), like: 1: var onlyRectangles = shapes.Where(s => s is Rectangle).ToList(); But fortunately, an easier way has already been written for us in the form of the OfType<T>() extension method: 1: // returns only a sequence of the shapes that are Rectangles 2: var onlyRectangles = shapes.OfType<Rectangle>().ToList(); Now we have a sequence of only the Rectangles in the original sequence, we can also use this to chain other queries that depend on Rectangles, such as: 1: // select only Rectangles, then filter to only those more than 2: // 5 units wide... 3: var onlyBigRectangles = shapes.OfType<Rectangle>() 4: .Where(r => r.Width > 5) 5: .ToList(); The OfType<Rectangle>() will filter the sequence to only the items that are of type Rectangle (or a subclass of it), and that results in an IEnumerable<Rectangle>, we can then apply the other LINQ extension methods to query that list further. Just as Cast<TResult>() is an extension method on IEnumerable (and not IEnumerable<T>), the same is true for OfType<T>().  This means that you can use OfType<TResult>() on object-based collections as well. For example, given an ArrayList containing Shapes, as below: 1: // object-based collections are a sequence of object 2: var shapes = new ArrayList 3: { 4: new Rectangle { Width = 3, Height = 5 }, 5: new Rectangle { Width = 10, Height = 13 }, 6: new Circle { Radius = 10 }, 7: new Square { Side = 13 }, 8: // ... 9: }; We can use OfType<Rectangle> to filter the sequence to only Rectangle items (and subclasses), and then chain other LINQ expressions, since we will then be of type IEnumerable<Rectangle>: 1: // OfType() converts the sequence of object to a new sequence 2: // containing only Rectangle or sub-types of Rectangle. 3: var onlyBigRectangles = shapes.OfType<Rectangle>() 4: .Where(r => r.Width > 5) 5: .ToList(); Summary So now we’ve seen two different ways to get a sequence of a superclass or interface down to a more specific sequence of a subclass or implementation.  The Cast<TResult>() method casts every item in the source sequence to type TResult, and the OfType<TResult>() method selects only those items in the source sequence that are of type TResult. You can use these to downcast sequences, or adapt older types and sequences that only implement IEnumerable (such as DataTable, ArrayList, etc.). Technorati Tags: C#,CSharp,.NET,LINQ,Little Wonders,TypeOf,Cast,IEnumerable<T>

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  • No NFC for the iPhone, and here's why

    - by David Dorf
    I, like many others in the retail industry, was hoping the iPhone 5 would include an NFC chip that enabled a mobile wallet.  In previous postings I've discussed the possible business case and the foreshadowing of Passbook, but it wasn't meant to be.  A few weeks ago I was considering all the rumors, and it suddenly occurred to me that it wasn't in Apple's best interest to support an NFC chip.  Yes they have patents in this area, but perhaps they are more defensive than indicating new development. Steve Jobs wanted to always win, but more importantly he didn't want others to win at his expense.  It drove him nuts that Windows was more successful than MacOS, and clearly he was bothered by Samsung and other handset manufacturers copying the iPhone.  But he was most angry at Google for their stewardship of Android. If the iPhone 5 had an NFC chip, who would benefit most?  Google Wallet is far and away the leader in NFC-based payments via mobile phones in the US.  Even without Steve at the helm, Apple isn't going to do anything to help Google.  Plus Apple doesn't like to do things in an open way -- then they lose control.  For example, you don't see iPhones with expandable memory, replaceable batteries, or USB connectors.  Adding a standards-based NFC chip just isn't in their nature. So I don't think Apple is holding back on the NFC chip for the 5S or 6.  It just isn't going to happen unless they can figure out how to prevent others from benefiting from it. All the other handset manufacturers will use NFC as a differentiator, which may be enough to keep Google and Isis afloat, and of course Square and PayPal aren't betting on NFC anyway.  This isn't the end of alternative payments, its just a major speed bump.

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  • Extreme Optimization –Mathematical Constants and Basic Functions

    - by JoshReuben
    Machine constants The MachineConstants class - contains constants for floating-point arithmetic because the CLS System.Single and Double floating-point types do not follow the standard conventions and are useless. machine constants for the Double type: machine precision: Epsilon , SqrtEpsilon CubeRootEpsilon largest possible value: MaxDouble , SqrtMaxDouble, LogMaxDouble smallest Double-precision floating point number that is greater than zero: MinDouble , SqrtMinDouble , LogMinDouble A similar set of constants is available for the Single Datatype  Mathematical Constants The Constants class contains static fields for many mathematical constants and common expressions involving small integers – if you are doing thousands of iterations, you wouldn't want to calculate OneOverSqrtTwoPi , Sqrt17 or Log17 !!! Fundamental constants E - The base for the natural logarithm, e (2.718...). EulersConstant - (0.577...). GoldenRatio - (1.618...). Pi - the ratio between the circumference and the diameter of a circle (3.1415...). Expressions involving fundamental constants: TwoPi, PiOverTwo, PiOverFour, LogTwoPi, PiSquared, SqrPi, SqrtTwoPi, OneOverSqrtPi, OneOverSqrtTwoPi Square roots of small integers: Sqrt2, Sqrt3, Sqrt5, Sqrt7, Sqrt17 Logarithms of small integers: Log2, Log3, Log10, Log17, InvLog10  Elementary Functions The IterativeAlgorithm<T> class in the Extreme.Mathematics namespace defines many elementary functions that are missing from System.Math. Hyperbolic Trig Functions: Cosh, Coth, Csch, Sinh, Sech, Tanh Inverse Hyperbolic Trig Functions: Acosh, Acoth, Acsch, Asinh, Asech, Atanh Exponential, Logarithmic and Miscellaneous Functions: ExpMinus1 - The exponential function minus one, ex-1. Hypot - The hypotenuse of a right-angled triangle with specified sides. LambertW - Lambert's W function, the (real) solution W of x=WeW. Log1PlusX - The natural logarithm of 1+x. Pow - A number raised to an integer power.

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  • Making a 2D game with responsive resolution

    - by alexandervrs
    I am making a 2D game, however I wish for it to be resolution agnostic. My target resolution i.e. where things look as intended is 1600 x 900. My ideas are: Make the HUD stay fixed to the sides no matter what resolution, use different size for HUD graphics under a certain resolution and another under a certain large one. Use large HD PNG sprites/backgrounds which are a power of 2, so they scale nicely. No vectors. Use the player's native resolution. Scale the game area (not the HUD) to fit (resulting zooming in some and cropping the game area sides if necessary for widescreen, no stretch), but always fill the screen. Have a min and max resolution limit for small and very large displays where you will just change the resolution(?) or scale up/down to fit. What I am a bit confused though is what math formula I would use to scale the game area correctly based on the resolution no matter the aspect ratio, fully fit in a square screen and with some clip to the sides for widescreen. Pseudocode would help as well. :)

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  • Pathfinding and BSP with Box2D

    - by Amplify91
    I'm looking into implementing AI in my 2D side-scrolling platformer, and I'm looking into using algorithms such as A*. For many kinds of pathfinding, we need some sort of grid or systems of nodes or polygon areas. My problem is that I am using Box2d for physics and I am not sure how best to create a structure that my AI can use besides placing individual nodes manually (something I really want to avoid) and using some sort of steering behavior. My level design is tile-based with each tile being about half of the height/width of my main character. The tiles are not all square (some are sloped). I'd like to have a system that can see what the terrain looks like for pathfinding and also keep track of the positions of other actors such as enemies. I'd like to avoid directly placing any nodes into my level design except for possible endpoints or goals. This question is related: How do you do AI path following within a 2d physics engine like farseer/box2d?, but it doesn't specify what kind of structure I could use instead of a list of nodes. I'm looking for some kind of grid or type of BSP that I can query for algorithms like A*.

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  • Inconsistent movement / line-of-sight around obstacles on a hexagonal grid

    - by Darq
    In a roguelike game I've been working on, one of my core design goals has been to allow the player to "Play the game, not the grid." In essence, I want the player's positioning to be tactical because of elements in the game world, not simply because some grid tiles are more advantageous than others, in relation to enemies. I am fine with world geometry not being realistic, but it needs to be consistent. In this process I have ran into most of the common problems (Square tiles? Diagonal movement, LOS, corner cases, etc.) and have moved to a hexagonal tile grid. For the most part this has been great, and I've not had too many inconsistencies. Recently however I have been stumped by the following: Points A and B are both distance 4 from the player (red lines). Line-of-sight to both are blocked by walls (black tiles). However, due to the hexagonal grid, A can be reached in 4 moves, whereas B requires 5 moves (blue lines). On a hex grid, "shortest path" seems divorced from "direct path", there may be multiple shortest paths to any point, but there is only one direct path (or two in some situations). This is fine, geometry need not be realistic. However this also seems inconsistent, similar obstacles are more effective in some positions than in others. A player running away from an enemy should be able to run in any direction, increasing the distance between the two actors. However when placing obstacles or traps between themselves and enemies, the player is best served by running in one of the six directions that don't have multiple shortest paths. Is there a way to rationalise this? Am I missing something that makes this behaviour consistent? Or is there a way to make this behaviour consistent? I am most certainly over-thinking this, but as it is one of my goals, I should do it due diligence.

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  • Meaning of offset in pygame Mask.overlap methods

    - by Alan
    I have a situation in which two rectangles collide, and I have to detect how much did they collide so so I can redraw the objects in a way that they are only touching each others edges. It's a situation in which a moving ball should hit a completely unmovable wall and instantly stop moving. Since the ball sometimes moves multiple pixels per screen refresh, it it possible that it enters the wall with more that half its surface when the collision is detected, in which case i want to shift it position back to the point where it only touches the edges of the wall. Here is the conceptual image it: I decided to implement this with masks, and thought that i could supply the masks of both objects (wall and ball) and get the surface (as a square) of their intersection. However, there is also the offset parameter which i don't understand. Here are the docs for the method: Mask.overlap Returns the point of intersection if the masks overlap with the given offset - or None if it does not overlap. Mask.overlap(othermask, offset) -> x,y The overlap tests uses the following offsets (which may be negative): +----+----------.. |A | yoffset | +-+----------.. +--|B |xoffset | | : :

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  • Why does my system use so much cache?

    - by Dave M G
    Previously, on my desktop computer running Ubuntu 14.04, I had 4GB RAM, which I thought should be plenty. However, after being on for a while, my computer would seem to get slow. I have a system resource monitor app in my Gnome panel, which I assume represents the available RAM (?). It shows a dark green area as being "Memory", and a light green area as "Cache". The "Cache" would slowly grow until it filled the whole graph, and then programs would get slow to load, or it would take a while to switch programs. I could alleviate the problem somewhat with this command, but eventually the computer cache fills up again, so it's only a bandaid: sudo sh -c "sync; echo 3 > /proc/sys/vm/drop_caches" So, I figured I'd get more RAM, so I replaced one 2GB stick with an 8GB stick, and now I have 10 GB ram. And my "cache" still slowly maxes out and my computer slows as a result. Also, sometimes the computer starts out with "cache" maxed when I first boot and log in. Not always though, I don't know if there's a pattern that determines why it happens. Why is Ubuntu using up so much cache? Is 10GB not enough for Ubuntu? Here's what my system monitor looks like in my Gnome panel. The middle square shows RAM usage. The light green area is the "cache": This is my memory and swap history, which doesn't seem to include any information about "cache". I realize at this point I'm not totally clear on the difference between "cache" and "swap":

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