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• Performance issues with visibility detection and object transparency

  - by maul

  I'm working on a 3d game that has a view similar to classic isometric games (diablo, etc.). One of the things I'm trying to implement is the effect of turning walls transparent when the player walks behind them. By itself this is not a huge issue, but I'm having trouble determining which walls should be transparent exactly. I can't use a circle or square mask. There are a lot of cases where the wall piece at the same (relative) position has different visibility depending on the surrounding area. With the help of a friend I came up with this algorithm: Create a grid around the player that contains a lot of "visibility points" (my game is semi tile-based so I create one point for every tile on the grid) - the size of the square's side is close to the radius where I make objects transparent. I found 6x6 to be a good value, so that's 36 visibility points total. For every visibility point on the grid, check if that point is in the player's line of sight. For every visibility point that is in the LOS, cast a ray from the camera to that point and mark all objects the ray hits as transparent. This algorithm works - not perfectly, but only requires some tuning - however this is very slow. As you can see, it requries 36 ray casts minimum, but most of the time 60-70 depending on the position. That's simply too much for the CPU. Is there a better way to do this? I'm using Unity 3D but I'm not looking for an engine-specific solution.

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• Heightmap in Shader not working

  - by CSharkVisibleBasix

  I'm trying to implement GPU based geometry clipmapping and have problems to apply a simple heightmap to my terrain. For the heightmap I use a simple texture with the surface format "single". I've taken the texture from here. To apply it to my terrain, I use the following shader code: texture Heightmap; sampler2D HeightmapSampler = sampler_state { Texture = <Heightmap>; MinFilter = Point; MagFilter = Point; MipFilter = Point; AddressU = Mirror; AddressV = Mirror; }; Vertex Shader: float4 worldPos = mul(float4(pos.x,0.0f,pos.y, 1.0f), worldMatrix); float elevation = tex2Dlod(HeightmapSampler, float4(worldPos.x, worldPos.z,0,0)); worldPos.y = elevation * 128; The complete vertex shader (also containig clipmapping transforms) looks like this: float4x4 View : View; float4x4 Projection : Projection; float3 CameraPos : CameraPosition; float LODscale; //The LOD ring index 0:highest x:lowest float2 Position; //The position of the part in the world texture Heightmap; sampler2D HeightmapSampler = sampler_state { Texture = <Heightmap>; MinFilter = Point; MagFilter = Point; MipFilter = Point; AddressU = Mirror; AddressV = Mirror; }; //Accept only float2 because we extract 3rd dim out of Heightmap float4 wireframe_VS(float2 pos : POSITION) : POSITION{ float4x4 worldMatrix = float4x4( LODscale, 0, 0, 0, 0, LODscale, 0, 0, 0, 0, LODscale, 0, - Position.x * 64 * LODscale + CameraPos.x, 0, Position.y * 64 * LODscale + CameraPos.z, 1); float4 worldPos = mul(float4(pos.x,0.0f,pos.y, 1.0f), worldMatrix); float elevation = tex2Dlod(HeightmapSampler, float4(worldPos.x, worldPos.z,0,0)); worldPos.y = elevation * 128; float4 viewPos = mul(worldPos, View); float4 projPos = mul(viewPos, Projection); return projPos; }

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• Shadow mapping: what is the light looking at?

  - by PgrAm

  I'm all set to set up shadow mapping in my 3d engine but there is one thing I am struggling to understand. The scene needs to be rendered from the light's point of view so I simply first move my camera to the light's position but then I need to find out which direction the light is looking. Since its a point light its not shining in any particular direction. How do I figure out what the orientation for the light point of view is?

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• Why do my gvfs mounts not show up under ~/.gvfs?

  - by kynan

  From what I read, when mounting a network share via nautilus or gvfs-mount the mount point should be in ~/.gvfs. This seems not to be the case for me: I tried mounting both an FTP and SMB share via both nautilus and gvfs-mount under both Ubuntu Maverick and Natty and in none of the cases did I see any mount point under ~/.gvfs. I can access the shares just find in nautilus, but I want to have access via the command line, which is why I need a mount point in the file system. Edit: Debugging following James Henstridge's answer and enzotib's comment revealed that on my laptop gvfs-fuse-daemon is running and consequently gvfs mounts show up in ~/.gvfs, whereas on the 2 workstations where ~/.gvfs remained empty gvfs-fuse-daemon was not running. On all 3 machines there are other gvfs processes running: gvfsd, gvfs-afc-volume-monitor, ... On the laptop, mount | fgrep gvfs yields gvfs-fuse-daemon on /home/xxx/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=xxx) That raises the questions: How are shares mounted without gvfs-fuse-daemon running? Is there no mount point created in that case and is every access to the share a gvfs library call? Which daemon is responsible? gvfsd? What's the role of gvfs-fuse-daemon? Does it only create a fuse mount point in ~/.gvfs?

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• ASMLib

  - by wcoekaer

  Oracle ASMlib on Linux has been a topic of discussion a number of times since it was released way back when in 2004. There is a lot of confusion around it and certainly a lot of misinformation out there for no good reason. Let me try to give a bit of history around Oracle ASMLib. Oracle ASMLib was introduced at the time Oracle released Oracle Database 10g R1. 10gR1 introduced a very cool important new features called Oracle ASM (Automatic Storage Management). A very simplistic description would be that this is a very sophisticated volume manager for Oracle data. Give your devices directly to the ASM instance and we manage the storage for you, clustered, highly available, redundant, performance, etc, etc... We recommend using Oracle ASM for all database deployments, single instance or clustered (RAC). The ASM instance manages the storage and every Oracle server process opens and operates on the storage devices like it would open and operate on regular datafiles or raw devices. So by default since 10gR1 up to today, we do not interact differently with ASM managed block devices than we did before with a datafile being mapped to a raw device. All of this is without ASMLib, so ignore that one for now. Standard Oracle on any platform that we support (Linux, Windows, Solaris, AIX, ...) does it the exact same way. You start an ASM instance, it handles storage management, all the database instances use and open that storage and read/write from/to it. There are no extra pieces of software needed, including on Linux. ASM is fully functional and selfcontained without any other components. In order for the admin to provide a raw device to ASM or to the database, it has to have persistent device naming. If you booted up a server where a raw disk was named /dev/sdf and you give it to ASM (or even just creating a tablespace without asm on that device with datafile '/dev/sdf') and next time you boot up and that device is now /dev/sdg, you end up with an error. Just like you can't just change datafile names, you can't change device filenames without telling the database, or ASM. persistent device naming on Linux, especially back in those days ways to say it bluntly, a nightmare. In fact there were a number of issues (dating back to 2004) : Linux async IO wasn't pretty persistent device naming including permissions (had to be owned by oracle and the dba group) was very, very difficult to manage system resource usage in terms of open file descriptors So given the above, we tried to find a way to make this easier on the admins, in many ways, similar to why we started working on OCFS a few years earlier - how can we make life easier for the admins on Linux. A feature of Oracle ASM is the ability for third parties to write an extension using what's called ASMLib. It is possible for any third party OS or storage vendor to write a library using a specific Oracle defined interface that gets used by the ASM instance and by the database instance when available. This interface offered 2 components : Define an IO interface - allow any IO to the devices to go through ASMLib Define device discovery - implement an external way of discovering, labeling devices to provide to ASM and the Oracle database instance This is similar to a library that a number of companies have implemented over many years called libODM (Oracle Disk Manager). ODM was specified many years before we introduced ASM and allowed third party vendors to implement their own IO routines so that the database would use this library if installed and make use of the library open/read/write/close,.. routines instead of the standard OS interfaces. PolyServe back in the day used this to optimize their storage solution, Veritas used (and I believe still uses) this for their filesystem. It basically allowed, in particular, filesystem vendors to write libraries that could optimize access to their storage or filesystem.. so ASMLib was not something new, it was basically based on the same model. You have libodm for just database access, you have libasm for asm/database access. Since this library interface existed, we decided to do a reference implementation on Linux. We wrote an ASMLib for Linux that could be used on any Linux platform and other vendors could see how this worked and potentially implement their own solution. As I mentioned earlier, ASMLib and ODMLib are libraries for third party extensions. ASMLib for Linux, since it was a reference implementation implemented both interfaces, the storage discovery part and the IO part. There are 2 components : Oracle ASMLib - the userspace library with config tools (a shared object and some scripts) oracleasm.ko - a kernel module that implements the asm device for /dev/oracleasm/* The userspace library is a binary-only module since it links with and contains Oracle header files but is generic, we only have one asm library for the various Linux platforms. This library is opened by Oracle ASM and by Oracle database processes and this library interacts with the OS through the asm device (/dev/asm). It can install on Oracle Linux, on SuSE SLES, on Red Hat RHEL,.. The library itself doesn't actually care much about the OS version, the kernel module and device cares. The support tools are simple scripts that allow the admin to label devices and scan for disks and devices. This way you can say create an ASM disk label foo on, currently /dev/sdf... So if /dev/sdf disappears and next time is /dev/sdg, we just scan for the label foo and we discover it as /dev/sdg and life goes on without any worry. Also, when the database needs access to the device, we don't have to worry about file permissions or anything it will be taken care of. So it's a convenience thing. The kernel module oracleasm.ko is a Linux kernel module/device driver. It implements a device /dev/oracleasm/* and any and all IO goes through ASMLib - /dev/oracleasm. This kernel module is obviously a very specific Oracle related device driver but it was released under the GPL v2 so anyone could easily build it for their Linux distribution kernels. Advantages for using ASMLib : A good async IO interface for the database, the entire IO interface is based on an optimal ASYNC model for performance A single file descriptor per Oracle process, not one per device or datafile per process reducing # of open filehandles overhead Device scanning and labeling built-in so you do not have to worry about messing with udev or devlabel, permissions or the likes which can be very complex and error prone. Just like with OCFS and OCFS2, each kernel version (major or minor) has to get a new version of the device drivers. We started out building the oracleasm kernel module rpms for many distributions, SLES (in fact in the early days still even for this thing called United Linux) and RHEL. The driver didn't make sense to get pushed into upstream Linux because it's unique and specific to the Oracle database. As it takes a huge effort in terms of build infrastructure and QA and release management to build kernel modules for every architecture, every linux distribution and every major and minor version we worked with the vendors to get them to add this tiny kernel module to their infrastructure. (60k source code file). The folks at SuSE understood this was good for them and their customers and us and added it to SLES. So every build coming from SuSE for SLES contains the oracleasm.ko module. We weren't as successful with other vendors so for quite some time we continued to build it for RHEL and of course as we introduced Oracle Linux end of 2006 also for Oracle Linux. With Oracle Linux it became easy for us because we just added the code to our build system and as we churned out Oracle Linux kernels whether it was for a public release or for customers that needed a one off fix where they also used asmlib, we didn't have to do any extra work it was just all nicely integrated. With the introduction of Oracle Linux's Unbreakable Enterprise Kernel and our interest in being able to exploit ASMLib more, we started working on a very exciting project called Data Integrity. Oracle (Martin Petersen in particular) worked for many years with the T10 standards committee and storage vendors and implemented Linux kernel support for DIF/DIX, data protection in the Linux kernel, note to those that wonder, yes it's all in mainline Linux and under the GPL. This basically gave us all the features in the Linux kernel to checksum a data block, send it to the storage adapter, which can then validate that block and checksum in firmware before it sends it over the wire to the storage array, which can then do another checksum and to the actual DISK which does a final validation before writing the block to the physical media. So what was missing was the ability for a userspace application (read: Oracle RDBMS) to write a block which then has a checksum and validation all the way down to the disk. application to disk. Because we have ASMLib we had an entry into the Linux kernel and Martin added support in ASMLib (kernel driver + userspace) for this functionality. Now, this is all based on relatively current Linux kernels, the oracleasm kernel module depends on the main kernel to have support for it so we can make use of it. Thanks to UEK and us having the ability to ship a more modern, current version of the Linux kernel we were able to introduce this feature into ASMLib for Linux from Oracle. This combined with the fact that we build the asm kernel module when we build every single UEK kernel allowed us to continue improving ASMLib and provide it to our customers. So today, we (Oracle) provide Oracle ASMLib for Oracle Linux and in particular on the Unbreakable Enterprise Kernel. We did the build/testing/delivery of ASMLib for RHEL until RHEL5 but since RHEL6 decided that it was too much effort for us to also maintain all the build and test environments for RHEL and we did not have the ability to use the latest kernel features to introduce the Data Integrity features and we didn't want to end up with multiple versions of asmlib as maintained by us. SuSE SLES still builds and comes with the oracleasm module and they do all the work and RHAT it certainly welcome to do the same. They don't have to rebuild the userspace library, it's really about the kernel module. And finally to re-iterate a few important things : Oracle ASM does not in any way require ASMLib to function completely. ASMlib is a small set of extensions, in particular to make device management easier but there are no extra features exposed through Oracle ASM with ASMLib enabled or disabled. Often customers confuse ASMLib with ASM. again, ASM exists on every Oracle supported OS and on every supported Linux OS, SLES, RHEL, OL withoutASMLib Oracle ASMLib userspace is available for OTN and the kernel module is shipped along with OL/UEK for every build and by SuSE for SLES for every of their builds ASMLib kernel module was built by us for RHEL4 and RHEL5 but we do not build it for RHEL6, nor for the OL6 RHCK kernel. Only for UEK ASMLib for Linux is/was a reference implementation for any third party vendor to be able to offer, if they want to, their own version for their own OS or storage ASMLib as provided by Oracle for Linux continues to be enhanced and evolve and for the kernel module we use UEK as the base OS kernel hope this helps.

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• Creating SparseImages for Pivot

  - by John Conwell

  Learning how to programmatically make collections for Microsoft Live Labs Pivot has been a pretty interesting ride. There are very few examples out there, and the folks at MS Live Labs are often slow on any feedback.  But that is what Reflector is for, right? Well, I was creating these InfoCard images (similar to the Car images in the "New Cars" sample collection that that MS created for Pivot), and wanted to put a Tag Cloud into the info card.  The problem was the size of the tag cloud might vary in order for all the tags to fit into the tag cloud (often times being bigger than the info card itself).  This was because the varying word lengths and calculated font sizes. So, to fix this, I made the tag cloud its own separate image from the info card.  Then, I would create a sparse image out of the two images, where the tag cloud fit into a small section of the info card.  This would allow the user to see the info card, but then zoom into the tag cloud and see all the tags at a normal resolution.  Kind'a cool. But...I couldn't find one code example (not one!) of how to create a sparse image.  There is one page on the SeaDragon site (http://www.seadragon.com/developer/creating-content/deep-zoom-tools/) that gives over the API for creating images and collections, and it sparsely goes over how to create a sparse image, but unless you are familiar with the API already, the documentation doesn't help very much. The key is the Image.ViewportWidth and Image.ViewportOrigin properties of the image that is getting super imposed on the main image.  I'll walk through the code below.  I've setup a couple Point structs to represent the parent and sub image sizes, as well as where on the parent I want to position the sub image.  Next, create the parent image.  This is pretty straight forward.  Then I create the sub image.  Then I calculate several ratios; the height to width ratio of the sub image, the width ratio of the sub image to the parent image, the height ratio of the sub image to the parent image, then the X and Y coordinates on the parent image where I want the sub image to be placed represented as a ratio of the position to the parent image size. After all these ratios have been calculated, I use them to calculate the Image.ViewportWidth and Image.ViewportOrigin values, then pass the image objects into the SparseImageCreator and call Create. The key thing that was really missing from the API documentation page is that when setting up your sub images, everything is expressed in a ratio in relation to the main parent image.  If I had known this, it would have saved me a lot of trial and error time.  And how did I figure this out?  Reflector of course!  There is a tool called Deep Zoom Composer that came from MS Live Labs which can create a sparse image.  I just dug around the tool's code until I found the method that create sparse images.  But seriously...look at the API documentation from the SeaDragon size and look at the code below and tell me if the documentation would have helped you at all.  I don't think so!   public static void WriteDeepZoomSparseImage(string mainImagePath, string subImagePath, string destination) {     Point parentImageSize = new Point(720, 420);     Point subImageSize = new Point(490, 310);     Point subImageLocation = new Point(196, 17);     List<Image> images = new List<Image>();     //create main image     Image mainImage = new Image(mainImagePath);     mainImage.Size = parentImageSize;     images.Add(mainImage);     //create sub image     Image subImage = new Image(subImagePath);     double hwRatio = subImageSize.X/subImageSize.Y;            // height width ratio of the tag cloud     double nodeWidth = subImageSize.X/parentImageSize.X;        // sub image width to parent image width ratio     double nodeHeight = subImageSize.Y / parentImageSize.Y;    // sub image height to parent image height ratio     double nodeX = subImageLocation.X/parentImageSize.X;       //x cordinate position on parent / width of parent     double nodeY = subImageLocation.Y / parentImageSize.Y;     //y cordinate position on parent / height of parent     subImage.ViewportWidth = (nodeWidth < double.Epsilon) ? 1.0 : (1.0 / nodeWidth);     subImage.ViewportOrigin = new Point(         (nodeWidth < double.Epsilon) ? -1.0 : (-nodeX / nodeWidth),         (nodeHeight < double.Epsilon) ? -1.0 : ((-nodeY / nodeHeight) / hwRatio));     images.Add(subImage);     //create sparse image     SparseImageCreator creator = new SparseImageCreator();     creator.Create(images, destination); }

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• Computer logout after closing the lid

  - by ejp1087

  I would like my computer to logout every time I close the lid. And by that I mean log out completely. Basically I want the startup applications to run every time I open the lid to my computer. Right now, it just locks the screen and comes right back when I type in my password. It would be really great if I can have it such that the startup applications run every time I open the lid. However, would logging out lose any unsaved files? Alternatively, do you know if there is a way to run a command every time I open the lid? Thanks!

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• Performing client-side OAuth authorized Twitter API calls versus server side, how much of a difference is there in terms of performance?

  - by Terence Ponce

  I'm working on a Twitter application in Ruby on Rails. One of the biggest arguments that I have with other people on the project is the method of calling the Twitter API. Before, everything was done on the server: OAuth login, updating the user's Twitter data, and retrieving tweets. Retrieving tweets was the heaviest thing to do since we don't store the tweets in our database, so viewing the tweets means that we have to call the API every time. One of the people in the project suggested that we call the tweets through Javascript instead to lessen the load on the server. We used GET search, which, correct me if I'm wrong, will be removed when v1.0 becomes completely deprecated, but that really isn't a concern now. When the Twitter API has migrated completely to v1.1 (again, correct me if I'm wrong), every calls to the API must be authenticated, so we have to authenticate our Javascript requests to the API. As said here: We don't support or recommend performing OAuth directly through Javascript -- it's insecure and puts your application at risk. The only acceptable way to perform it is if you kept all keys and secrets server-side, computed the OAuth signatures and parameters server side, then issued the request client-side from the server-generated OAuth values. If we do exactly what Twitter suggests, the only difference between this and doing everything server-side is that our server won't have to contact the Twitter API anymore every time the user wants to view tweets. Here's how I would picture what's happening every time the user makes a request: If we do it through Javascript, it would be harder on my part because I would have to create the signatures manually for every request, but I will gladly do it if the boost in performance is worth all the trouble. Doing it through Ruby on Rails would be very easy since the Twitter gem does most of the grunt work already, so I'm really encouraging the other people in the project to agree with me. Is the difference in performance trivial or is it significant enough to switch to Javascript?

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• I want to host clients' websites, but not their email. What's the easiest way to handle this?

  - by Phil

  My company lets non-technical users build their own niche industry websites on our server, which we host. they can currently point their nameservers at their registrar to us, which ends up with them no longer having access to their email if they've already set it up through said registrar. We don't want to interfere with their existing email, nor do we want to get into the business of setting up email for them through our service. Thus, having them point A records/cname to us would work, but is this too complex for a non-technie user? We thought of having them point nameservers to us but pointing the MX records back to them, but this is also beyond their scope. Is there an easy way to 'point records' at their initial state? Any other ideas/feedback?

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• OpenWorld in Small Bites

  - by Kathryn Perry

  Fifty thousand attendees -- that's bigger than the cities some of us live in. Monday morning it took 20 minutes to get from Hall D in Moscone North to a conference room in Moscone South -- the crowds were crushing! A great start to a great week! Larry is as big a name as ever on the program schedule and on the Moscone stage. People were packed in Hall D and clustered around every big screen TV. He stayed on script as he laid out Oracle's SaaS, PaaS, and IaaS strategies. Every seat in Chris Leone's Fusion Apps Cloud Overview was filled on Monday morning. Oracle employees who wanted to get in were turned away. And the same thing happened in the repeat session on Wednesday. Our newest suite of apps is hot! Speaking of hot, the weather was made to order. Then it turned very San Francisco-like on Wednesday afternoon. Downright cold for those who trusted SF temps to hold in the 80's. Who did you follow on Twitter during the conference? So many voices, opinions, and convos! Great combo of social media and sharp minds. Be sure to follow @larryellison, @stevenrmiranda, and @Oracle for updates and MyPOVs. Keywords for the Apps customers at the conference were cloud, mobile, and social. Every day, every session, every speaker. Wednesday afternoon, 4 pm at the Four Seasons hotel. A large roomful of analysts and influencers firing questions at a panel of eight Fusion customers. Steve Miranda moderating. Good energy and a great exchange of information and confidence. Word on the street is that OpenWorld has outgrown San Francisco -- but moving it seems unthinkable. The city isn't just a backdrop for an industry conference - it's a headliner right up there with Larry Ellison and Pearl Jam. As you can imagine, electrical outlets were in high demand at every venue. The most popular hotels and bars near Moscone designed their interiors around accessible electrical power strips. People are plenty willing to buy a drink while they grab a charge. Wednesday afternoon, 4 pm at the Four Seasons hotel. A large roomful of analysts and influencers firing questions at a panel of eight Fusion customers. Steve Miranda moderating. Good energy and a great exchange of information and confidence. Treasure Island in the dark. Eddy Vedder has an amazing voice! And Kings of Leon over delivered on people's expectations. It was cold. It was windy. It was very fun. One analyst said it's the best customer appreciation party in the industry. 

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• How can I store post rankings that change with time?

  - by Daniel Fein

  I'm trying to learn how to code a website algorithm like Reddit.com where there are thousands of posts that need to be ranked. Their ranking algorithm works like this (you don't have to read it, its more of a general question that I have): http://amix.dk/blog/post/19588 Right now I have posts stored in a database, I record their dates and they each have an upvotes and downvotes field so I'm storing their records. I want to figure out how do you store their rankings? When specific posts have ranking values, but they change with time, how could you store their rankings? If they aren't stored, do you rank every post every time a user loads the page? When would you store the posts? Do you run a cron job to automatically give every post a new value every x minutes? Do you store their value? Which is temporary. Maybe, until that post reaches its minimum score and is forgotten?

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• Should I use an interface when methods are only similar?

  - by Joshua Harris

  I was posed with the idea of creating an object that checks if a point will collide with a line: public class PointAndLineSegmentCollisionDetector { public void Collides(Point p, LineSegment s) { // ... } } This made me think that if I decided to create a Box object, then I would need a PointAndBoxCollisionDetector and a LineSegmentAndBoxCollisionDetector. I might even realize that I should have a BoxAndBoxCollisionDetector and a LineSegmentAndLineSegmentCollisionDetector. And, when I add new objects that can collide I would need to add even more of these. But, they all have a Collides method, so everything I learned about abstraction is telling me, "Make an interface." public interface CollisionDetector { public void Collides(Spatial s1, Spatial s2); } But now I have a function that only detects some abstract class or interface that is used by Point, LineSegment, Box, etc.. So if I did this then each implementation would have to to a type check to make sure that the types are the appropriate type because the collision algorithm is different for each different type match up. Another solution could be this: public class CollisionDetector { public void Collides(Point p, LineSegment s) { ... } public void Collides(LineSegment s, Box b) { ... } public void Collides(Point p, Box b) { ... } // ... } But, this could end up being a huge class that seems unwieldy, although it would have simplicity in that it is only a bunch of Collide methods. This is similar to C#'s Convert class. Which is nice because it is large, but it is simple to understand how it works. This seems to be the better solution, but I thought I should open it for discussion as a wiki to get other opinions.

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• Circle-Rectangle collision in a tile map game

  - by furiousd

  I am making a 2D tile map based putt-putt game. I have collision detection working between the ball and the walls of the map, although when the ball collides at the meeting point between 2 tiles I offset it by 0.5 so that it doesn't get stuck in the wall. This aint a huge issue though. if(y % 20 == 0) { y+=0.5; } if(x % 20 == 0) { x+=0.5; } Collisions work as follows Find the closest point between each tile and the center of the ball If distance(ball_x, ball_y, close_x, close_y) <= ball_radius and the closest point belongs to a solid object, collision has occured Invert X/Y speed according to side of object collided with The next thing I tried to do was implement floating blocks in the middle of the map for the ball to bounce off of. When a ball collides with a corner of the block, it gets stuck in it. So I changed my determineRebound() function to treat corners as if they were circles. Here's that functon: `i and j are indexes of the solid object in the 2d map array. x & y are centre point of ball.` void determineRebound(int _i, int _j) { if(y > _i*tile_w && y < _i*tile_w + tile_w) { //Not a corner xs*=-1; } else if(x > _j*tile_w && x < _j*tile_w + tile_w) { //Not a corner ys*=-1; } else { //Corner float nx = x - close_x; float ny = y - close_y; float len = sqrt(nx * nx + ny * ny); nx /= len; ny /= len; float projection = xs * nx + ys * ny; xs -= 2 * projection * nx; ys -= 2 * projection * ny; } } This is where things have gotten messy. Collisions with 'floating' corners work fine, but now when the ball collides near the meeting point of 2 tiles, it detects a corner collision and does not rebound as expected. I'm a bit in over my head at this point. I guess I'm wondering if I'm going about making this sort of game in the right way. Is a 2d tile map the way to go? If so, is there a problem with my collision logic and where am I going wrong? Any advice/feedback would be great.

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• Applications: The Mathematics of Movement, Part 3

  - by TechTwaddle

  Previously: Part 1, Part 2 As promised in the previous post, this post will cover two variations of the marble move program. The first one, Infinite Move, keeps the marble moving towards the click point, rebounding it off the screen edges and changing its direction when the user clicks again. The second version, Finite Move, is the same as first except that the marble does not move forever. It moves towards the click point, rebounds off the screen edges and slowly comes to rest. The amount of time that it moves depends on the distance between the click point and marble. Infinite Move This case is simple (actually both cases are simple). In this case all we need is the direction information which is exactly what the unit vector stores. So when the user clicks, you calculate the unit vector towards the click point and then keep updating the marbles position like crazy. And, of course, there is no stop condition. There’s a little more additional code in the bounds checking conditions. Whenever the marble goes off the screen boundaries, we need to reverse its direction.  Here is the code for mouse up event and UpdatePosition() method, //stores the unit vector double unitX = 0, unitY = 0; double speed = 6; //speed times the unit vector double incrX = 0, incrY = 0; private void Form1_MouseUp(object sender, MouseEventArgs e) {     double x = e.X - marble1.x;     double y = e.Y - marble1.y;     //calculate distance between click point and current marble position     double lenSqrd = x * x + y * y;     double len = Math.Sqrt(lenSqrd);     //unit vector along the same direction (from marble towards click point)     unitX = x / len;     unitY = y / len;     timer1.Enabled = true; } private void UpdatePosition() {     //amount by which to increment marble position     incrX = speed * unitX;     incrY = speed * unitY;     marble1.x += incrX;     marble1.y += incrY;     //check for bounds     if ((int)marble1.x < MinX + marbleWidth / 2)     {         marble1.x = MinX + marbleWidth / 2;         unitX *= -1;     }     else if ((int)marble1.x > (MaxX - marbleWidth / 2))     {         marble1.x = MaxX - marbleWidth / 2;         unitX *= -1;     }     if ((int)marble1.y < MinY + marbleHeight / 2)     {         marble1.y = MinY + marbleHeight / 2;         unitY *= -1;     }     else if ((int)marble1.y > (MaxY - marbleHeight / 2))     {         marble1.y = MaxY - marbleHeight / 2;         unitY *= -1;     } } So whenever the user clicks we calculate the unit vector along that direction and also the amount by which the marble position needs to be incremented. The speed in this case is fixed at 6. You can experiment with different values. And under bounds checking, whenever the marble position goes out of bounds along the x or y direction we reverse the direction of the unit vector along that direction. Here’s a video of it running;   Finite Move The code for finite move is almost exactly same as that of Infinite Move, except for the difference that the speed is not fixed and there is an end condition, so the marble comes to rest after a while. Code follows, //unit vector along the direction of click point double unitX = 0, unitY = 0; //speed of the marble double speed = 0; private void Form1_MouseUp(object sender, MouseEventArgs e) {     double x = 0, y = 0;     double lengthSqrd = 0, length = 0;     x = e.X - marble1.x;     y = e.Y - marble1.y;     lengthSqrd = x * x + y * y;     //length in pixels (between click point and current marble pos)     length = Math.Sqrt(lengthSqrd);     //unit vector along the same direction as vector(x, y)     unitX = x / length;     unitY = y / length;     speed = length / 12;     timer1.Enabled = true; } private void UpdatePosition() {     marble1.x += speed * unitX;     marble1.y += speed * unitY;     //check for bounds     if ((int)marble1.x < MinX + marbleWidth / 2)     {         marble1.x = MinX + marbleWidth / 2;         unitX *= -1;     }     else if ((int)marble1.x > (MaxX - marbleWidth / 2))     {         marble1.x = MaxX - marbleWidth / 2;         unitX *= -1;     }     if ((int)marble1.y < MinY + marbleHeight / 2)     {         marble1.y = MinY + marbleHeight / 2;         unitY *= -1;     }     else if ((int)marble1.y > (MaxY - marbleHeight / 2))     {         marble1.y = MaxY - marbleHeight / 2;         unitY *= -1;     }     //reduce speed by 3% in every loop     speed = speed * 0.97f;     if ((int)speed <= 0)     {         timer1.Enabled = false;     } } So the only difference is that the speed is calculated as a function of length when the mouse up event occurs. Again, this can be experimented with. Bounds checking is same as before. In the update and draw cycle, we reduce the speed by 3% in every cycle. Since speed is calculated as a function of length, speed = length/12, the amount of time it takes speed to reach zero is directly proportional to length. Note that the speed is in ‘pixels per 40ms’ because the timeout value of the timer is 40ms.  The readability can be improved by representing speed in ‘pixels per second’. This would require you to add some more calculations to the code, which I leave out as an exercise. Here’s a video of this second version,

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• Keeping files that are often changed in sync between desktop and laptop

  - by N.N.

  I'm looking for a way to keep a desktop and a laptop in sync. What I want to keep in sync are some folders, mainly ~/Documents, that are changed often when working on them. If it matters I can connect to my desktop from anywhere via an URL but my laptop is harder to access since it might be behind NAT and such. I have been looking at Ubuntu One but it seems to not go well with working on documents written in LaTeX. If I work on a .tex file in the Ubuntu One directory and compile it (with pdflatex) every now and then (as often as every 10 sec when working) it will create several new files including a pdf which are uploaded to Ubuntu One and this seems stupid since it will create continuous upload when working on .tex files. I also usually keep .tex documents version controlled by git and then every commit (which also can happen frequently) will cause upload (by changes in ./.git) so that it happens continuously when working. Another example is editing images that are saved often. What I think would be best is for sync to happen every tenth minute or at the end of every working session (but there might be some other way to handle this?).

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• The Oracle Platform

  - by Naresh Persaud

  Today’s enterprises typically create identity management infrastructures using ad-hoc, multiple point solutions. Relying on point solutions introduces complexity and high cost of ownership leading many organizations to rethink this approach. In a recent worldwide study of 160 companies conducted by Aberdeen Research, there was a discernible shift in this trend as businesses are now looking to move away from the point solution approach from multiple vendors and adopt an integrated platform approach. By deploying a comprehensive identity and access management strategy using a single platform, companies are saving as much as 48% in IT costs, while reducing audit deficiencies by nearly 35%. According to Aberdeen's research, choosing an integrated suite or “platform” of solutions for Identity Management from a single vendor can have many advantages over choosing “point solutions” from multiple vendors. The Oracle Identity Management Platform is uniquely designed to offer several compelling benefits to our customers.  Shared Services: Instead of separate solutions for - Administration, Authentication, Authorization, Audit and so on–  Oracle Identity Management offers a set of share services that allows these services to be consumed by each component in the stack and by developers of new applications  Actionable Intelligence: The most compelling benefit of the Oracle platform is ” Actionable intelligence” which means if there is a compliance violation, the same platform can fix it. And If a user is logging in from an un-trusted device or we detect an attack and act proactively on that information. Suite Interoperability: With the oracle platform the components all connect and integrated with each other. So if an organization purchase the platform for provisioning and wants to manage access, then the same platform can offer access management which leads to cost savings. Extensible and Configurable: With point solutions – you typically get limited ability to extend the tool to address custom requirements. But with the Oracle platform all of the components have a common way to extend the UI and behavior Find out more about the Oracle Platform approach in this presentation. Platform approach-series-the oracleplatform-final View more PowerPoint from OracleIDM

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• How to interpret this crontab command?

  - by Bakhtiyor

  I know that if I wrote in crontab -e following command 01 04 * * * somecommand then it will run somecommand at 4:01am on every day of every month. What happens if I wrote * * * * * somecommand? Will it run somecommand every single minute? Will this syntax work also? And it is possible to use special strings like @reboot, @daily, etc as it is explained here. At what time of the day somecommand will be executed if I write @daily somecommand command?

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• Behaviour Trees with irregular updates

  - by Robominister

  I'm interested in behaviour trees that aren't iterated every game tick, but every so often. (Edit: the tree could specify how many frames within the main game loop to wait before running its tick function again). Every theoretical implementation I have seen of behaviour trees talks of the tree search being carried out every game update - which seems necessary, because a leaf node (eg a behaviour, like 'return to base') needs to be constantly checked to see if is still running, failed or completed. Can anyone suggest how I might start implementing a tree that isnt run every tick, or point me in the direction of good material specific to this case (I am struggling to find anything)? My thoughts so far: action leaf nodes (when they start) must only push some kind of action object onto a list for an entity, rather than directly calling any code that makes the entity do something. The list of actions for the entity would be run every frame (update any that need to run, pop any that have completed from the list). the return state from a given action must be fed back into the tree, so that when we run the tree iteration again (and reach the same action leaf node - so the tree has so far determined that we ought to still be trying this action) - that the action has completed, or is still running etc. If my actual action code is running from an action list on an entity, then I possibly need to cancel previously running actions in the list - i am thinking that I can just delete the entire stack of queued up actions. I've seen the idea of ActionLists which block lower priority actions when a higher priority one is added, but this seems like very close logic to behaviour trees, and I dont want to be duplicating behaviour. This leaves me with some questions 1) How would I feed the action return state back into the tree? Its obvious I need to store some information relating to 'currently executing actions' on the entity, and check that in the tree tick, but I can't imagine how. 2) Does having a seperate behaviour tree (for deciding behaviour) and action list (for carrying out actual queued up actions) sound like a reasonable approach? 3) Is the approach of updating a behaviour tree irregularly actually used by anyone? It seems like a nice idea for budgeting ai search time when you have a lot of ai entities to process. (Edit) - I am also thinking about storing a single instance of a given behaviour tree in memory, and providing it by reference to any entity that uses it. So any information about what action was last selected for execution on an entity must be stored in a data context relative to the entity (which the tree can check). (I am probably answering my own questions as i go!) I hope I have expressed my questions adequately! Thanks in advance for any help :)

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• Custom Windows Panel

  Every control in this panel can change the size and move on the panel

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• Help identify the pattern for reacting on updates

  - by Mike

  There's an entity that gets updated from external sources. Update events are at random intervals. And the entity has to be processed once updated. Multiple updates may be multiplexed. In other words there's a need for the most current state of entity to be processed. There's a point of no-return during processing where the current state (and the state is consistent i.e. no partial update is made) of entity is saved somewhere else and processing goes on independently of any arriving updates. Every consequent set of updates has to trigger processing i.e. system should not forget about updates. And for each entity there should be no more than one running processing (before the point of no-return) i.e. the entity state should not be processed more than once. So what I'm looking for is a pattern to cancel current processing before the point of no return or abandon processing results if an update arrives. The main challenge is to minimize race conditions and maintain integrity. The entity sits mainly in database with some files on disk. And the system is in .NET with web-services and message queues. What comes to my mind is a database queue-like table. An arriving update inserts row in that table and the processing is launched. The processing gathers necessary data before the point of no-return and once it reaches this barrier it looks into the queue table and checks whether there're more recent updates for the entity. If there are new updates the processing simply shuts down and its data is discarded. Otherwise the processing data is persisted and it goes beyond the point of no-return. Though it looks like a solution to me it is not quite elegant and I believe this scenario may be supported by some sort of middleware. If I would use message queues for this then there's a need to access the queue API in the point of no-return to check for the existence of new messages. And this approach also lacks elegance. Is there a name for this pattern and an existing solution?

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• Facebook App EULA & Restrictions: What can't they do that my web app can?

  - by Adam Tannon

  I have written a nifty little web app (in Java/GWT/JS) and have been experimenting with the idea of making it available through Facebook as a Facebook App as well. After spending some time reading Facebook's developer docs, it seems like I can just create a Facebook App to point at any URL I want and use that as the app/canvas. It accomplishes this via iframes. So, my tentative plan is to just point it towards my (existing) web app so that I don't have to totally re-write it. But then that got me thinking: Facebook must regulate what sorts of things can be done through a Facebook App, vs. what an app can't do. For instance, I can't imagine I can point a Facebook App to point at a URL for a web app that accepts e-commerce payments (that would by-pass Facebook altogether and not allow them to take a cut from the ecom transaction!). Also, I can't imagine that Facebook allows developers to point their Facebook Apps to just any old URL without some sort of a scan, otherwise that would open Facebook up to the horrors of every security threat knownst to humanity. I know for a fact that when you write an iOS native app and put it up on the Apple App Store, that Apple actually scans your source code for violations of their EULA. So my question: does Facebook do the same? If so, what are their terms & conditions for what a Facebook app can/can't do? Suprisingly, I can't find this anywhere!! Thanks in advance!

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• How do I keep a 3D model on the screen in OpenGL?

  - by NoobScratcher

  I'm trying to keep a 3D model on the screen by placing my glDrawElement functions inside the draw function with the declarations at the top of .cpp. When I render the model, the model attaches it self to the current vertex buffer object. This is because my whole graphical user interface is in 2D quads except the window frame. Is there a way to avoid this from happening? or any common causes of this? Creating the file object: int index = IndexAssigner(1, 1); //make a fileobject and store list and the index of that list in a c string ifstream file (list[index].c_str() ); //Make another string //string line; points.push_back(Point()); Point p; int face[4]; Model rendering code: int numfloats = 4; float* point=reinterpret_cast<float*>(&points[0]); int num_bytes=numfloats*sizeof(float); cout << "Size Of Point" << sizeof(Point) << endl; GLuint vertexbuffer; glGenVertexArrays(1, &vao[3]); glGenBuffers(1, &vertexbuffer); glBindBuffer(GL_ARRAY_BUFFER, vertexbuffer); glBufferData(GL_ARRAY_BUFFER, points.size()*sizeof(points), points.data(), GL_STATIC_DRAW); glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, num_bytes, &points[0]); glEnableClientState(GL_VERTEX_ARRAY); glVertexPointer(3, GL_FLOAT, points.size(), &points[0]); glEnableClientState(GL_INDEX_ARRAY); glIndexPointer(GL_FLOAT, faces.size(), faces.data()); glEnableVertexAttribArray(0); glDrawElements(GL_QUADS, points.size(), GL_UNSIGNED_INT, points.data()); glDrawElements(GL_QUADS, faces.size(), GL_UNSIGNED_INT, faces.data());

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• Prevent collisions between mobs/npcs/units piloted by computer AI : How to avoid mobile obstacles?

  - by Arthur Wulf White

  Lets says we have character a starting at point A and character b starting at point B. character a is headed to point B and character b is headed to point A. There are several simple ways to find the path(I will be using Dijkstra). The question is, how do I take preventative action in the code to stop the two from colliding with one another? case2: Characters a and b start from the same point in different times. Character b starts later and is the faster of the two. How do I make character b walk around character a without going through it? case3:Lets say we have m such characters in each side and there is sufficient room to pass through without the characters overlapping with one another. How do I stop the two groups of characters from "walking on top of one another" and allow them pass around one another in a natural organic way. A correct answer would be any algorithm, that given the path to the destination and a list of mobile objects that block the path, finds an alternative path or stops without stopping all units when there is sufficient room to traverse.

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• How can I support scrolling when using batched rendering for my tiles?

  - by dardanel

  I have tiled map 100*75 and tiles are 32*32 pixel.I want to use batching for performance .I don't figure it out , because of my game needs scrolling and every frame i draw 22*16 tiles (my screen is 20*16 tile) .I thought that batching tiles for every frame .Is it good or any suggestion? edit :to more clarify I want to use occlusion culling and batching at the same time.I thought that drawing only visible areas and batching them together .But there is a something i couldn't figure out .When scrolling screen with translate matrix , if one row become invisible , I bind new row and batch them again.Every batched objects needs to buffer again.So I batch tiles and buffer to VBO every time when one row become invisible .I don't know these way is efficient or not .This is my question .And i am open to any suggestions.

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• Algorithm for procedural city generation?

  - by Zove Games

  I am planning on making a (simple) procedural city generator using Java. I need ideas on whan algorithm to use for the layout, and the actual buildings. The city will mostly have skyscrapers, not really much complex stuff. For the layout I already have a simple algorithm implemented: Create a Map with java.awt.Point keys and Integer values. Fill it with all the points in the city's bounds with the value as -1 (unnassigned) Shuffle the map, and assign the 1st 10 of the keys IDs (from 1-10) Loop until all points have IDs: Loop though all points: Assign points next to an assigned point IDs of the point next to them, if 2 or more points border the point, then randomly choose which ID the point will get. You will end up with 10 random regions. Make roads bordering these regions. Fill the inside of each region with a randomly spaced and randomly rotated grid PROBLEM: This is not the fastest way to do it. What algorithm should I use for the layout. And what should I use to make each building's design? I don't even know how I'm going to do that yet (fractals maybe). I just need some ideas, not actual code.

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