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• What is the best way to implement collision detection using Bullet physics engine and a track generated from a curve?

  - by tigrou

  I am developing a small racing game were the track is generated from a curve. As said above, the track is generated, but not infinite. The track of one level could fit with no problem in memory and will contain a reasonably small amount of triangles. For collisions, I would like to use Bullet physics engine and know what is the best way to handle collisions with the track efficiently. NOTE : The track will be stored as a static rigid body (mass = 0). The player will be represented by a sphere shape for collisions. Here is some possibilities i have in mind : Create one rigid body, then, put all triangles of the track (except non collidable stuff) into it. Result : 1 body with many triangles (eg : 30000 triangles) Split the track into several sections (eg: 10 sections). Then, for each section, create a rigid body and put corresponding triangles in it. Result : small amount of bodies with relatively small amount of triangles (eg : 1500 triangles per section). Split the track into many sub-sections (eg : 1200 sections). Here one subsection = very small step when generating the curve. Again for each sub-section, create a body and put triangles in it. Result : many bodies with very small amount of triangles (eg : 20 triangles). Advantage : it could be possible to "extra data" to each of the subsection, that could be used when handling collisions. Same as 2, but only put sections N and N+1 in physics engine (where N = current section where the player is). When player reach section N+1, unload section N and load section N+2 and so on... Issue : harder to implement, problems if the player suddenly "jump" from one section to another (eg : player fly away from section N, and fall on section N + 4 that was underneath : no collision handled, player will fall into void ) Same as 4, but with many sub-sections. Issues : since subsections are very small there will be constantly new bodies added and removed to physics engine at runtime. Possibilities for player to accidently skip some sections and fall into the void are higher than 4.

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• Generate MERGE statements from a table

  - by Bill Graziano

  We have a requirement to build a test environment where certain tables get reset from production every night.  These are mainly lookup tables.  I played around with all kinds of fancy solutions and finally settled on a series of MERGE statements.  And being lazy I didn’t want to write them myself.  The stored procedure below will generate a MERGE statement for the table you pass it.  If you have identity values it populates those properly.  You need to have primary keys on the table for the joins to be generated properly.  The only thing hard coded is the source database.  You’ll need to update that for your environment.  We actually used a linked server in our situation. CREATE PROC dba_GenerateMergeStatement (@table NVARCHAR(128) )ASset nocount on; declare @return int;PRINT '-- ' + @table + ' -------------------------------------------------------------'--PRINT 'SET NOCOUNT ON;--'-- Set the identity insert on for tables with identitiesselect @return = objectproperty(object_id(@table), 'TableHasIdentity')if @return = 1 PRINT 'SET IDENTITY_INSERT [dbo].[' + @table + '] ON; 'declare @sql varchar(max) = ''declare @list varchar(max) = '';SELECT @list = @list + [name] +', 'from sys.columnswhere object_id = object_id(@table)SELECT @list = @list + [name] +', 'from sys.columnswhere object_id = object_id(@table)SELECT @list = @list + 's.' + [name] +', 'from sys.columnswhere object_id = object_id(@table)-- --------------------------------------------------------------------------------PRINT 'MERGE [dbo].[' + @table + '] AS t'PRINT 'USING (SELECT * FROM [source_database].[dbo].[' + @table + ']) as s'-- Get the join columns ----------------------------------------------------------SET @list = ''select @list = @list + 't.[' + c.COLUMN_NAME + '] = s.[' + c.COLUMN_NAME + '] AND 'from INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk , INFORMATION_SCHEMA.KEY_COLUMN_USAGE cwhere pk.TABLE_NAME = @tableand CONSTRAINT_TYPE = 'PRIMARY KEY'and c.TABLE_NAME = pk.TABLE_NAMEand c.CONSTRAINT_NAME = pk.CONSTRAINT_NAMESELECT @list = LEFT(@list, LEN(@list) -3)PRINT 'ON ( ' + @list + ')'-- WHEN MATCHED ------------------------------------------------------------------PRINT 'WHEN MATCHED THEN UPDATE SET'SELECT @list = '';SELECT @list = @list + ' [' + [name] + '] = s.[' + [name] +'],'from sys.columnswhere object_id = object_id(@table)-- don't update primary keysand [name] NOT IN (SELECT [column_name] from INFORMATION_SCHEMA.TABLE_CONSTRAINTS pk , INFORMATION_SCHEMA.KEY_COLUMN_USAGE c where pk.TABLE_NAME = @table and CONSTRAINT_TYPE = 'PRIMARY KEY' and c.TABLE_NAME = pk.TABLE_NAME and c.CONSTRAINT_NAME = pk.CONSTRAINT_NAME)-- and don't update identity columnsand columnproperty(object_id(@table), [name], 'IsIdentity ') = 0 --print @list PRINT left(@list, len(@list) -3 )-- WHEN NOT MATCHED BY TARGET ------------------------------------------------PRINT ' WHEN NOT MATCHED BY TARGET THEN';-- Get the insert listSET @list = ''SELECT @list = @list + '[' + [name] +'], 'from sys.columnswhere object_id = object_id(@table)SELECT @list = LEFT(@list, LEN(@list) - 1)PRINT ' INSERT(' + @list + ')'-- get the values listSET @list = ''SELECT @list = @list + 's.[' +[name] +'], 'from sys.columnswhere object_id = object_id(@table)SELECT @list = LEFT(@list, LEN(@list) - 1)PRINT ' VALUES(' + @list + ')'-- WHEN NOT MATCHED BY SOURCEprint 'WHEN NOT MATCHED BY SOURCE THEN DELETE; 'PRINT ''PRINT 'PRINT ''' + @table + ': '' + CAST(@@ROWCOUNT AS VARCHAR(100));';PRINT ''-- Set the identity insert OFF for tables with identitiesselect @return = objectproperty(object_id(@table), 'TableHasIdentity')if @return = 1 PRINT 'SET IDENTITY_INSERT [dbo].[' + @table + '] OFF; 'PRINT ''PRINT 'GO'PRINT '';

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• AWS EC2 Oracle RDB - Storing and managing my data

  - by llaszews

  When create an Oracle Database on the Amazon cloud you will need to store you database files somewhere on the EC2 cloud. There are basically three places where database files can be stored: 1. Local drive - This is the local drive that is part of the virtual server EC2 instance. 2. Elastic Block Storage (EBS) - Network attached storage that appears as a local drive. 3. Simple Storage Server (S3) - 'Storage for the Internet'. S3 is not high speed and intended for store static document type files. S3 can also be used for storing static web page files. Local drives are ephemeral so not appropriate to be used as a database storage device. The leaves EBS which is the best place to store database files. EBS volumes appear as local disk drives. They are actually network-attached to an Amazon EC2 instance. In addition, EBS persists independently from the running life of a single Amazon EC2 instance. If you use an EBS backed instance for your database data, it will remain available after reboot but not after terminate. In many cases you would not need to terminate your instance but only stop it, which is equivalent of shutdown. In order to save your database data before you terminate an instance, you can snapshot the EBS to S3. Using EBS as a data store you can move your Oracle data files from one instance to another. This allows you to move your database from one region or or zone to another. Unfortunately, to scale out your Oracle RDS on AWS you can not have read only replicas. This is only possible with the other Oracle relational database - MySQL. The free micro instances use EBS as its storage. This is a very good white paper that has more details: AWS Storage Options This white paper also discusses: SQS, SimpleDB, and Amazon RDS in the context of storage devices. However, these are not storage devices you would use to store an Oracle database. This slide deck discusses a lot of information that is in the white paper: AWS Storage Options slideshow

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• Obtaining the correct Client IP address when a Physical Load Balancer and a Web Server Configured With Proxy Plug-in Are Between The Client And Weblogic

  - by adejuanc

  Some Load Balancers like Big-IP have build in interoperability with Weblogic Cluster, this means they know how Weblogic understand a header named 'WL-Proxy-Client-IP' to identify the original client ip.The problem comes when you have a Web Server configured with weblogic plug-in between the Load Balancer and the back-end weblogic servers - WL-Proxy-Client-IP this is not designed to go to Web server proxy plug-in. The plug-in will not use a WL-Proxy-Client-IP header that came in from the previous hop (which is this case is the Physical Load Balancer but could be anything), in order to prevent IP spoofing, therefore the plug-in won't pass on what Load Balancer has set for it.So unfortunately under this Architecture the header will be useless. To get the client IP from Weblogic you need to configure extended log format and create a custom field that gets the appropriate header containing the IP of the client.On WLS versions prior to 10.3.3 use these instructions:You can also create user-defined fields for inclusion in an HTTP access log file that uses the extended log format. To create a custom field you identify the field in the ELF log file using the Fields directive and then you create a matching Java class that generates the desired output. You can create a separate Java class for each field, or the Java class can output multiple fields. For a sample of the Java source for such a class, seeJava Class for Creating a Custom ELF Field to import weblogic.servlet.logging.CustomELFLogger;import weblogic.servlet.logging.FormatStringBuffer;import weblogic.servlet.logging.HttpAccountingInfo;/* This example outputs the X-Forwarded-For field into a custom field called MyOriginalClientIPField */public class MyOriginalClientIPField implements CustomELFLogger{ public void logField(HttpAccountingInfo metrics,  FormatStringBuffer buff) {   buff.appendValueOrDash(metrics.getHeader("X-Forwarded-For");  }}In this case we are using 'X-Forwarded-For' but it could be changed for the header that contains the data you need to use.Compile the class, jar it, and prepend it to the classpath.In order to compile and package the class: 1. Navigate to <WLS_HOME>/user_projects/domains/<SOME_DOMAIN>/bin2. Set up an environment by executing: $ . ./setDomainEnv.sh This will include weblogic.jar into classpath, in order to use any of the libraries included under package weblogic.*3. Compile the class by copying the content of the code above and naming the file as:MyOriginalClientIPField.java4. Run javac to compile the class.$javac MyOriginalClientIPField.java5. Package the compiled class into a jar file by executing:$jar cvf0 MyOriginalClientIPField.jar MyOriginalClientIPField.classExpected output is:added manifestadding: MyOriginalClientIPField.class(in = 711) (out= 711)(stored 0%)6. This will produce a file called:MyOriginalClientIPField.jar This way you will be able to get the real client IP when the request is passing through a Load Balancer and a Web server before reaching WLS. Since 10.3.3 it is possible to configure a specific header that WLS will check when getRemoteAddr is called. That can be set on the WebServer Mbean. In this case, set that to be X-Forwarded-For header coming from Load Balancer as well.

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• PL/SQL to delete invalid data from token Strings

  - by Jie Chen

  Previous article describes how to delete the duplicated values from token string in bulk mode. This one extends it and shows the way to delete invalid data. Scenario Support we have page_two and manufacturers tables in database and the table DDL is: SQL> desc page_two; Name NULL? TYPE ----------------------------------------- -------- ------------------------ MULTILIST04 VARCHAR2(765) SQL> SQL> desc manufacturers; Name NULL? TYPE ----------------------------------------- -------- ------ ID NOT NULL NUMBER NAME VARCHAR In table page_two, column multilist04 stores a token string splitted with common. Each token represent a valid ID in manufacturers table. My expectation is to delete invalid token strings from page_two.multilist04, which have no mapping id in manufacturers.id. For example in below SQL result: ,6295728,33,6295729,6295730,6295731,22, , value 33 and 22 are invalid data because there is no ID equals to 33 or 22 in manufacturers table. So I need to delete 33 and 22. SQL> col rowid format a20; SQL> col multilist04 format a50; SQL> select rowid, multilist04 from page_two; ROWID MULTILIST04 -------------------- -------------------------------------------------- AAB+UrADfAAAAhUAAI ,6295728,6295729,6295730,6295731, AAB+UrADfAAAAhUAAJ ,1111,6295728,6295729,6295730,6295731, AAB+UrADfAAAAhUAAK ,6295728,111,6295729,6295730,6295731, AAB+UrADfAAAAhUAAL ,6295728,6295729,6295730,6295731,22, AAB+UrADfAAAAhUAAM ,6295728,33,6295729,6295730,6295731,22, SQL> select id, encode_name from manufacturers where id in (1111,11,22,33); No rows selected SQL> Solution As there is no existing SPLIT function or related in PL/SQL, I should program it by myself. I code Split intermediate function which is used to get the token value between current splitter and next splitter. Next program is main entry point, it get each column value from page_two.multilist04, process each row based on cursor. When it get each multilist04 value, it uses above Split function to get each token string stored to singValue variant, then check if it exists in manufacturers.id. If not found, set fixFlag to 1, pending to be deleted.

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• Ubuntu Linux won't display netbook's native resolution

  - by Daniel

  FYI: My Netbook model is HP Mini 210-1004sa, which comes with Intel Graphics Media Accelerator 3150, and has a display 10.1" Active Matrix Colour TFT 1024 x 600. I recently removed Windows 7 Starter from my netbook, and replaced it with Ubuntu 12.10. The problem is the OS doesn't seem to recognise the native display resolution of 1024x600 i.e. the bottom bits of Ubuntu is hidden beneath the screen & the only 2 available resolutions are: the default 1024x768 and 800x600. I've also thought about replacing Ubuntu with Lubuntu or Puppy Linux, as the system does run a bit slow, but I can't, as then I won't be able to access the taskbar and application menu which will be hidden beneath the screen. Only Ubuntu with Unity is currently usable, as the Unity Launcher is visible enough. I was able to define a custom resolution 1024x600 using the Q&A: How set my monitor resolution? but when I set that resolution, there appears a black band at the top of the screen and the desktop area is lowered, with bits of it hidden beneath the screen. I tried leaving it at this new resolution and restarting the system to see if the black band would disappear & the display will fit correctly, but it gets reset to 1024x768 at startup and displays following error: Could not apply the stored configuration for monitors none of the selected modes were compatible with the possible modes: Trying modes for CRTC 63 CRTC 63: trying mode 800x600@60Hz with output at 1024x600@60Hz (pass 0) CRTC 63: trying mode 800x600@56Hz with output at 1024x600@60Hz (pass 0) CRTC 63: trying mode 640x480@60Hz with output at 1024x600@60Hz (pass 0) CRTC 63: trying mode 1024x768@60Hz with output at 1024x600@60Hz (pass 1) CRTC 63: trying mode 800x600@60Hz with output at 1024x600@60Hz (pass 1) CRTC 63: trying mode 800x600@56Hz with output at 1024x600@60Hz (pass 1) CRTC 63: trying mode 640x480@60Hz with output at 1024x600@60Hz (pass 1) Trying modes for CRTC 64 CRTC 64: trying mode 1024x768@60Hz with output at 1024x600@60Hz (pass 0) CRTC 64: trying mode 800x600@60Hz with output at 1024x600@60Hz (pass 0) CRTC 64: trying mode 800x600@56Hz with output at 1024x600@60Hz (pass 0) CRTC 64: trying mode 640x480@60Hz with output at 1024x600@60Hz (pass 0) CRTC 64: trying mode 1024x768@60Hz with output at 1024x600@60Hz (pass 1) CRTC 64: trying mode 800x600@60Hz with output at 1024x600@60Hz (pass 1) CRTC 64: trying mode 800x600@56Hz with output at 1024x600@60Hz (pass 1) CRTC 64: trying mode 640x480@60Hz with output at 1024x600@60Hz (pass 1)

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• Does the Ubuntu One sync work?

  - by bisi

  I have been on this for several hours now, trying to get a simple second folder to sync with my (paid) account. I cannot tell you how many times I removed all devices, removed stored passwords, killed all processes of u1, logged out and back in online...and still, the tick in the file browser (Synchronize this folder) is loading and loading and loading. Also, I have logged out, rebooted countless times. And this is after me somehow managing to get the u1 preferences to finally "connect" again. I have also checked the status of your services, and none are close to what I am experiencing. And I have checked the suggested related questions above! So please, just confirm whether it is a problem on my side, or a problem on your side. EDIT: In the mean time, here is what has changed, on top of what is mentioned just above. • My files went from 0MB to 71.9MB, and is still rising. • My first folder of 400.2MB is being filled with the data as I write this. The second folder has the folder sub-structure in place. • Both folders now show in the File Browser that it will be synchronized. I believe that right now, it is all back to normal and working fine, and I guess that's what a good night's sleep can do ;). And we're now only back to the point where synchronizing is slow, but will pick up with the release of Natty (https://wiki.ubuntu.com/UbuntuOne/FAQ/WhyIsItTakingSoLongForMyFilesToSync). But to get to the questions: My about says I use 11.04, Natty Narwhal, but I am quite sure the last distribution I installed was 10.10. Folder A is 400.2MB, and Folder B is 29.5MB I am on a DSL line, behind a regular fritz.box setting. No proxy servers in use, and I did not install any particular firewall features. No physical firewall, just the router (on which I have a TV signal as well), and 2 switches to get to this floor. Status: inactive The ubuntuone-indicator runs the same window as when I click on my name on the top-right corner and select Ubuntu one, or in the Control Center choose Ubuntu one. It wasn't supposed to go further than this was it?

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• Access Control Service v2: Registering Web Identities in your Applications [code]

  - by Your DisplayName here!

  You can download the full solution here. The relevant parts in the sample are: Configuration I use the standard WIF configuration with passive redirect. This kicks automatically in, whenever authorization fails in the application (e.g. when the user tries to get to an area the requires authentication or needs registration). Checking and transforming incoming claims In the claims authentication manager we have to deal with two situations. Users that are authenticated but not registered, and registered (and authenticated) users. Registered users will have claims that come from the application domain, the claims of unregistered users come directly from ACS and get passed through. In both case a claim for the unique user identifier will be generated. The high level logic is as follows: public override IClaimsPrincipal Authenticate( string resourceName, IClaimsPrincipal incomingPrincipal) {     // do nothing if anonymous request     if (!incomingPrincipal.Identity.IsAuthenticated)     {         return base.Authenticate(resourceName, incomingPrincipal);     } string uniqueId = GetUniqueId(incomingPrincipal);     // check if user is registered     RegisterModel data;     if (Repository.TryGetRegisteredUser(uniqueId, out data))     {         return CreateRegisteredUserPrincipal(uniqueId, data);     }     // authenticated by ACS, but not registered     // create unique id claim     incomingPrincipal.Identities[0].Claims.Add( new Claim(Constants.ClaimTypes.Id, uniqueId));     return incomingPrincipal; } User Registration The registration page is handled by a controller with the [Authorize] attribute. That means you need to authenticate before you can register (crazy eh? ;). The controller then fetches some claims from the identity provider (if available) to pre-fill form fields. After successful registration, the user is stored in the local data store and a new session token gets issued. This effectively replaces the ACS claims with application defined claims without requiring the user to re-signin. Authorization All pages that should be only reachable by registered users check for a special application defined claim that only registered users have. You can nicely wrap that in a custom attribute in MVC: [RegisteredUsersOnly] public ActionResult Registered() {     return View(); } HTH

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• Yet another frustum culling question

  - by Christian Frantz

  This one is kinda specific. If I'm to implement frustum culling in my game, that means each one of my cubes would need a bounding sphere. My first question is can I make the sphere so close to the edge of the cube that its still easily clickable for destroying and building? Frustum culling is easily done in XNA as I've recently learned, I just need to figure out where to place the code for the culling. I'm guessing in my method that draws all my cubes but I could be wrong. My camera class currently implements a bounding frustum which is in the update method like so frustum.Matrix = (view * proj); Simple enough, as I can call that when I have a camera object in my class. This works for now, as I only have a camera in my main game class. The problem comes when I decide to move my camera to my player class, but I can worry about that later. ContainmentType CurrentContainmentType = ContainmentType.Disjoint; CurrentContainmentType = CamerasFrustrum.Contains(cubes.CollisionSphere); Can it really be as easy as adding those two lines to my foreach loop in my draw method? Or am I missing something bigger here? UPDATE: I have added the lines to my draw methods and it works great!! So great infact that just moving a little bit removes the whole map. Many factors could of caused this, so I'll try to break it down. cubeBoundingSphere = new BoundingSphere(cubePosition, 0.5f); This is in my cube constructor. cubePosition is stored in an array, The vertices that define my cube are factors of 1 ie: (1,0,1) so the radius should be .5. I least I think it should. The spheres are created every time a cube is created of course. ContainmentType CurrentContainmentType = ContainmentType.Disjoint; foreach (Cube block in cube.cubes) { CurrentContainmentType = cam.frustum.Contains(cube.cubeBoundingSphere); ///more code here if (CurrentContainmentType != ContainmentType.Disjoint) { cube.Draw(effect); } Within my draw method. Now I know this works because the map disappears, its just working wrong. Any idea on what I'm doing wrong?

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• Data Source Use of Oracle Edition Based Redefinition (EBR)

  - by Steve Felts

  Edition-based redefinition is a new feature in the 11gR2 release of the Oracle database. It enables you to upgrade the database component of an application while it is in use, thereby minimizing or eliminating down time. It works by allowing for a pre-upgrade and post-upgrade view of the data to exist at the same time, providing a hot upgrade capability. You can then specify which view you want for a particular session.  See the Oracle Database Advanced Application Developer's Guide for further information. There is also a good white paper at Edition Based Definition. Using this feature of the Oracle database does not require any new WebLogic Server functionality. It is set for each connection in the pool automatically by simply specifying SQL ALTER SESSION SET EDITION = edition_name in the Init SQL parameter in the data source configuration. This can be configured either via the console or via WLST (setInitSQL on the JDBCConnectionPoolParams). This SQL statement is executed for each newly created physical database connection.Note that we are assuming that a data source references only one edition of the database. To make use of this feature, you would have an earlier version of the application with a data source that references the earlier EDITION and a later version of the application with a data source that references the later EDITION.   Once you start talking about multiple versions of a WLS application, you should be using the WLS "side-by-side" or "versioned" deployment feature.  See Developing Applications for Production Redeployment for more information.  By combining Oracle database EBR and WLS versioned deployment, the application can be failed over with no downtime, making the combination of features more powerful than either independently. There is a catch - you need to be running with a versioned database and a versioned application initially so then you can switch versions.  The recommended way to version a WLS application is to simply add the "Weblogic-Application-Version" property in the MANIFEST.MF file(you can also specify it at deployment time). The recommended way to configure the data source is to use a packaged data source descriptor that's stored in the ear or war so that everything is self-contained.  There are some restrictions.  You can't use a packaged data source with Logging Last Resource (LLR) - you need to use a system resource.  You can't use an application-scoped packaged data source with EmulateTwoPhaseCommit for the global-transactions-protocol with a versioned application - use a global scope.  See Configuring JDBC Application Modules for Deployment for more details. There's one known problem - it doesn't work correctly with an XA data source (patch available with bug 14075837).

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• Are closures with side-effects considered "functional style"?

  - by Giorgio

  Many modern programming languages support some concept of closure, i.e. of a piece of code (a block or a function) that Can be treated as a value, and therefore stored in a variable, passed around to different parts of the code, be defined in one part of a program and invoked in a totally different part of the same program. Can capture variables from the context in which it is defined, and access them when it is later invoked (possibly in a totally different context). Here is an example of a closure written in Scala: def filterList(xs: List[Int], lowerBound: Int): List[Int] = xs.filter(x => x >= lowerBound) The function literal x => x >= lowerBound contains the free variable lowerBound, which is closed (bound) by the argument of the function filterList that has the same name. The closure is passed to the library method filter, which can invoke it repeatedly as a normal function. I have been reading a lot of questions and answers on this site and, as far as I understand, the term closure is often automatically associated with functional programming and functional programming style. The definition of function programming on wikipedia reads: In computer science, functional programming is a programming paradigm that treats computation as the evaluation of mathematical functions and avoids state and mutable data. It emphasizes the application of functions, in contrast to the imperative programming style, which emphasizes changes in state. and further on [...] in functional code, the output value of a function depends only on the arguments that are input to the function [...]. Eliminating side effects can make it much easier to understand and predict the behavior of a program, which is one of the key motivations for the development of functional programming. On the other hand, many closure constructs provided by programming languages allow a closure to capture non-local variables and change them when the closure is invoked, thus producing a side effect on the environment in which they were defined. In this case, closures implement the first idea of functional programming (functions are first-class entities that can be moved around like other values) but neglect the second idea (avoiding side-effects). Is this use of closures with side effects considered functional style or are closures considered a more general construct that can be used both for a functional and a non-functional programming style? Is there any literature on this topic? IMPORTANT NOTE I am not questioning the usefulness of side-effects or of having closures with side effects. Also, I am not interested in a discussion about the advantages / disadvantages of closures with or without side effects. I am only interested to know if using such closures is still considered functional style by the proponent of functional programming or if, on the contrary, their use is discouraged when using a functional style.

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• What does path finding in internet routing do and how is it different from A*?

  - by alan2here

  Note: If you don't understand this question then feel free to ask clarification in the comments instead of voting down, it might be that this question needs some more work at the moment. I've been directed here from the Stack Excange chat room Root Access because my question didn't fit on Super User. In many aspects path finding algorithms like A star are very similar to internet routing. For example: A node in an A* path finding system can search for a path though edges between other nodes. A router that's part of the internet can search for a route though cables between other routers. In the case of A*, open and closed lists are kept by the system as a whole, sepratly from any individual node as well as each node being able to temporarily store a state involving several numbers. Routers on the internet seem to have remarkable properties, as I understand it: They are very performant. New nodes can be added at any time that use a free address from a finite (not tree like) address space. It's real routing, like A*, there's never any doubling back for example. Similar IP addresses don't have to be geographically nearby. The network reacts quickly to changes to the networks shape, for example if a line is down. Routers share information and it takes time for new IP's to be registered everywhere, but presumably every router doesn't have to store a list of all the addresses each of it's directions leads most directly to. I'm looking for a basic, general, high level description of the algorithms workings from the point of view of an individual router. Does anyone have one? I presume public internet routers don't use A* as the overheads would be to large, and scale to poorly. I also presume there is a single method worldwide because it seems as if must involve a lot of transferring data to update and communicate a reasonable amount of state between neighboring routers. For example, perhaps the amount of data that needs to be stored in each router scales logarithmically with the number of routers that exist worldwide, the detail and reliability of the routing is reduced over increasing distances, there is increasing backtracking involved in parts of the network that are less geographically uniform or maybe each router really does perform an A* style search, temporarily maintaining open and closed lists when a packet arrives.

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• If most of team can't follow the architecture, what do you do?

  - by Chris

  Hi all, I'm working on a greenfields project with two other developers. We're all contractors, and myself and one other just started working on the project while the orginal one has been doing most of the basic framework coding. In the past month, my fellow programmer and I have been just frustrated by the design descisions done by our co-worker. Here's a little background information: The application at face value appeared to be your standard n-layered web application using C# on the 3.5 framework. We have a data layer, business layer and a web interface. But as we got deeper into the project we found some very interesting things that have caused us some troubles. There is a custom data access sqlHelper type base which only accepts dictionary key/valued entries and returns only data tables. There are no entity objects, but there are some massive objects which do everything and then are tossed into session for persitance. The general idea is that the pages (.aspx) don't do anything, while the controls (.ascx) do everything. The general flow is that a client clicks on a button, which goes to a user control base which passes a process request to the 'BLL' class which goes to the page processor, which then goes to a getControlProcessor, which at last actually processes the request. The request itself is made up of a dictionary which is passing a string valued method name, stored procedure name, a control name and possibly a value. All switching of the processing is done by comparing the string values of the control names and method names. Pages are linked together via a common header control that uses a combination of javascript and tables to create a hyperlink effect. And as I found out yesterday, a simple hyperlink between one page and another does not work because of the need to have quite a bit of information in session to determine which control to display on a page. My fellow programmer and I both believe that this is a strange and uncommon approach to web application development. Both of us have been in this business for over five years and neither of us have seen this approach. My question is this, how would we approach our co-worker and voice our concerns and what should we do if he does not want to accept the criteic? We both do not want to insult the work that has been done, but feel that going forward will create a nightmare for development. Thanks for your comments.

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• Adding JavaScript to your code dependent upon conditions

  - by DavidMadden

  You might be in an environment where you code is source controlled and where you might have build options to different environments.  I recently encountered this where the same code, built on different configurations, would have the website at a different URL.  If you are working with ASP.NET as I am you will have to do something a bit crazy but worth while.  If someone has a more efficient solution please share. Here is what I came up with to make sure the client side script was placed into the HEAD element for the Google Analytics script.  GA wants to be the last in the HEAD element so if you are doing others in the Page_Load then you should do theirs last. The settings object below is an instance of a class that holds information I collection.  You could read from different sources depending on where you stored your unique ID for Google Analytics. *** This has been formatted to fit this screen. *** if (!IsPostBack) { if (settings.GoogleAnalyticsID != null || settings.GoogleAnalyticsID != string.Empty) { string str = @"//<!CDATA[ var _gaq = _gaq || []; _gaq.push(['_setAccount', '"  + settings.GoogleAnalyticsID + "']); _gaq.push(['_trackPageview']);  (function () {  var ga = document.createElement('script');  ga.type = 'text/javascript';  ga.async = true;  ga.src = ('https:' == document.location.protocol  ? 'https://ssl' :  'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0];  s.parentNode.insertBefore(ga, s);})();"; System.Web.UI.HtmlControls.HtmlGenericControl si =  new System.Web.UI.HtmlControls.HtmlGenericControl(); si.TagName = "script"; si.Attributes.Add("type", @"text/javascript"); si.InnerHtml = sb.ToString(); this.Page.Header.Controls.Add(si); } } The code above will prevent the code from executing if it is a PostBack and then if the ID was not able to be read or something caused the settings to be lost by accident. If you have larger function to declare, you can use a StringBuilder to separate the lines. This is the most compact I wished to go and manage readability.

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• Separating logic and data in browser game

  - by Tesserex

  I've been thinking this over for days and I'm still not sure what to do. I'm trying to refactor a combat system in PHP (...sorry.) Here's what exists so far: There are two (so far) types of entities that can participate in combat. Let's just call them players and NPCs. Their data is already written pretty well. When involved in combat, these entities are wrapped with another object in the DB called a Combatant, which gives them information about the particular fight. They can be involved in multiple combats at once. I'm trying to write the logic engine for combat by having combatants injected into it. I want to be able to mock everything for testing. In order to separate logic and data, I want to have two interfaces / base classes, one being ICombatantData and the other ICombatantLogic. The two implementers of data will be one for the real objects stored in the database, and the other for my mock objects. I'm now running into uncertainties with designing the logic side of things. I can have one implementer for each of players and NPCs, but then I have an issue. A combatant needs to be able to return the entity that it wraps. Should this getter method be part of logic or data? I feel strongly that it should be in data, because the logic part is used for executing combat, and won't be available if someone is just looking up information about an upcoming fight. But the data classes only separate mock from DB, not player from NPC. If I try having two child classes of the DB data implementer, one for each entity type, then how do I architect that while keeping my mocks in the loop? Do I need some third interface like IEntityProvider that I inject into the data classes? Also with some of the ideas I've been considering, I feel like I'll have to put checks in place to make sure you don't mismatch things, like making the logic for an NPC accidentally wrap the data for a player. Does that make any sense? Is that a situation that would even be possible if the architecture is correct, or would the right design prohibit that completely so I don't need to check for it? If someone could help me just layout a class diagram or something for this it would help me a lot. Thanks. edit Also useful to note, the mock data class doesn't really need the Entity, since I'll just be specifying all the parameters like combat stats directly instead. So maybe that will affect the correct design.

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• Is this an effective monetization method for an Android game? [on hold]

  - by Matthew Page

  The short version: I plan to make an Android puzzle game where the user tries to get 3-6 numbers to their predetermined goal numbers. The free version of the app will have three predetermined levels (easy, medium, hard). The full version ($0.99, probably) will have a level generator where there will be unlimited easy, medium, or hard levels, as well as a custom difficulty option where users can set specific vales to the number of numbers to equate to their goal, the number of buttons to use, etc. Users will also have the option to get a one-time "hint" for a fee of $0.49, or unlimited hints for a one-time fee of $2.99. The long version: Mechanics of Game and Victory The application is a number puzzle. When the user begins a new game, depending on the input by the user, between 3 and 6 numbers show up on the top of the screen, and between 3 and 6 buttons show up on the bottom of the screen. The buttons all have two options: to increase every number the same way, or decrease every number the same way. The buttons either use addition / subtraction, multiplication / division, or exponents / roots, all depending on the number displayed on the button. Addition buttons are green, multiplication buttons are blue, and exponential buttons are red. The user wins when all of the numbers displayed on the screen equate to their goal number, displayed below each number. Monetization If the user is playing the full (priced) version of the app, upon the start of the game, the user will be confronted with a dialogue asking for the number of buttons and the number of numbers to equate in the game. Then, based on the user input, a random puzzle will be generated. If the user is playing the free version of the app, the user will be asked to either play an “easy”, “hard”, or “expert” puzzle. A pre-determined puzzle from each category will be used in the game. If the user has played that puzzle before, a dialogue will show saying this to the user and advertising the full version of the app. The full version of the app will also be advertised upon the successful or in successful completion of a puzzle. Upon exiting this advertisement, another full screen advertisement will appear from a third party. Also, the solution to the puzzle should be stored by the program, and if the user pays a small fee, he/she can see a hint to the solution to the program. In the free version of the app, the user may use their first hint for free. Also, the user can use unlimited hints for a slightly larger fee. Is this an effective monetization method?

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• What is the most appropriate testing method in this scenario?

  - by Daniel Bruce

  I'm writing some Objective-C apps (for OS X/iOS) and I'm currently implementing a service to be shared across them. The service is intended to be fairly self-contained. For the current functionality I'm envisioning there will be only one method that clients will call to do a fairly complicated series of steps both using private methods on the class, and passing data through a bunch of "data mangling classes" to arrive at an end result. The gist of the code is to fetch a log of changes, stored in a service-internal data store, that has occurred since a particular time, simplify the log to only include the last applicable change for each object, attach the serialized values for the affected objects and return this all to the client. My question then is, how do I unit-test this entry point method? Obviously, each class would have thorough unit tests to ensure that their functionality works as expected, but the entry point seems harder to "disconnect" from the rest of the world. I would rather not send in each of these internal classes IoC-style, because they're small and are only made classes to satisfy the single-responsibility principle. I see a couple possibilities: Create a "private" interface header for the tests with methods that call the internal classes and test each of these methods separately. Then, to test the entry point, make a partial mock of the service class with these private methods mocked out and just test that the methods are called with the right arguments. Write a series of fatter tests for the entry point without mocking out anything, testing the entire functionality in one go. This looks, to me, more like "integration testing" and seems brittle, but it does satisfy the "only test via the public interface" principle. Write a factory that returns these internal services and take that in the initializer, then write a factory that returns mocked versions of them to use in tests. This has the downside of making the construction of the service annoying, and leaks internal details to the client. Write a "private" initializer that take these services as extra parameters, use that to provide mocked services, and have the public initializer back-end to this one. This would ensure that the client code still sees the easy/pretty initializer and no internals are leaked. I'm sure there's more ways to solve this problem that I haven't thought of yet, but my question is: what's the most appropriate approach according to unit testing best practices? Especially considering I would prefer to write this test-first, meaning I should preferably only create these services as the code indicates a need for them.

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• rotating an object on an arc

  - by gardian06

  I am trying to get a turret to rotate on an arc, and have hit a wall. I have 8 possible starting orientations for the turrets, and want them to rotate on a 90 degree arc. I currently take the starting rotation of the turret, and then from that derive the positive, and negative boundary of the arc. because of engine restrictions (Unity) I have to do all of my tests against a value which is between [0,360], and due to numerical precision issues I can not test against specific values. I would like to write a general test without having to go in, and jury rig cases //my current test is: // member variables public float negBound; public float posBound; // found in Start() function (called immediately after construction) // eulerAngles.y is the the degree measure of the starting y rotation negBound = transform.eulerAngles.y-45; posBound = transform.eulerAngles.y+45; // insure that values are within bounds if(negBound<0){ negBound+=360; }else if(posBound>360){ posBound-=360; } // called from Update() when target not in firing line void Rotate(){ // controlls what direction if(transform.eulerAngles.y>posBound){ dir = -1; } else if(transform.eulerAngles.y < negBound){ dir = 1; } // rotate object } follows is a table of values for my different cases (please excuse my force formatting) read as base is the starting rotation of the turret, neg is the negative boundry, pos is the positive boundry, range is the acceptable range of values, and works is if it performs as expected with the current code. |base-|-neg-|-pos--|----------range-----------|-works-| |---0---|-315-|--45--|-315-0,0-45----------|----------| |--45--|---0---|--90--|-0-45,54-90----------|----x----| |-135-|---90--|-180-|-90-135,135-180---|----x----| |-180-|--135-|-225-|-135-180,180-225-|----x----| |-225-|--180-|-270-|-180-225,225-270-|----x----| |-270-|--225-|-315-|-225-270,270-315-|----------| |-315-|--270-|---0---|--270-315,315-0---|----------| I will need to do all tests from derived, or stored values, but can not figure out how to get all of my cases to work simultaneously. //I attempted to concatenate the 2 tests: if((transform.eulerAngles.y>posBound)&&(transform.eulerAngles.y < negBound)){ dir *= -1; } this caused only the first case to be successful // I attempted to store a opposite value, and do a void Rotate(){ // controlls what direction if((transform.eulerAngles.y > posBound)&&(transform.eulerAngles.y<oposite)){ dir = -1; } else if((transform.eulerAngles.y < negBound)&&(transform.eulerAngles.y>oposite)){ dir = 1; } // rotate object } this causes the opposite situation as indicated on the table. What am I missing here?

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• SDL - Getting a single keypress event instead of a keystate?

  - by MrKatSwordfish

  Right now I'm working on a simple SDL project, but I've hit an issue when trying to get a single keypress event to skip past a splash screen. Right now, there are 4 start-up splash screens that I would like to be able to skip with a single keypress (of any key). My issue is that, as of now, if I hold down a key, it skips through each splash screen to the very last one immediately. The splash screens are stored as an array of SDL surfaces which are all loaded at the initialization of the state. I have an variable called currentSplashImage that controls which element of the array is being rendered on the screen. I've set it up so that whenever there's a SDL_KEYDOWN event, it triggers a single incrementation of the currentSplashImage variable. So, I'm really not sure why my code isn't working correctly. For some reason, when I hold down a button, it seems to be treating the held button as a new key press event every time it ticks through the code. Does anyone know how I can go about fixing this issue? [Here's a snippet of code that I've been using...] void SplashScreenState::handleEvents() { SDL_PollEvent( &localEvent ); if ( localEvent.type == SDL_KEYDOWN ) { if ( currentSplashImage < 3 && currentSplashImage >= 0) { currentSplashImage++; } } else if ( localEvent.type == SDL_QUIT ) { smgaEngine.setRunning(false); } } I should also mention that the SDL_Event 'localEvent' is part of the GameState parent class, while this event handling code is part of a SplashScreenState subclass. If anyone knows why this is happening, or if there is any way to improve my code, It'd be helpful to me! :D I'm still a very new programmer, trying to learn. UPDATE: I added a std::cout line to that the code runs multiple times with a single KEYDOWN event. I also tried disabling SDL_EnableKeyRepeat, but it didn't fix the issue. void SplashScreenState::handleEvents() { SDL_PollEvent( &localEvent ); if ( localEvent.type == SDL_KEYDOWN ) { if ( currentSplashImage < 3 && currentSplashImage >= 0) { currentSplashImage++; std::cout << "KEYDOWN.."; //<---- test cout line } } else if ( localEvent.type == SDL_QUIT ) { smgaEngine.setRunning(false); } } This prints out "KEYDOWN..KEYDOWN..KEYDOWN.." in the cout stream when a button is held.

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• Hierachies....from the Top Down

  - by Joe G

  I've been struggling with how to write on the topic of the importance of hierarchy design.  It's not so much that hierarchies haven't always been important, it's more of that with Fusion, the timing of when the hierarchies are designed should take a higher priority.    I will attempt to explain..... When I was implementing applications, back in the day, we had the list of detailed account values to enter with the obvious parent accounts. Then, after the setup was complete and things were functioning, the reporting phase started.  Users explained the elements that they want on the reports, what totals should be included, and how things should be compared.  Frequently, there was at least one calculation that became a nightmare either because it was based on very specific things that didn't relate to anything else or because it was "hardcoded" so that when something changed, someone need to "fix" the report. With Fusion, the process changes slightly.  You still want to enter all of the detailed accounts, but before you start adding parent values, you should investigate the reporting requirements from the top-down.  It's better to build hierarchies based on the reporting requirements than it is to build reports based on random hierarchies. Build reports based on hierarchies that resemble the reports themselves, and maintain the hierarchies without rework of the reports. For example, if you look at an income statement, you may have line items for Material Costs, Employee Costs, Travel & Entertainment, and Total Operating Expenses.  In your hierarchy, you have detail values that roll up to Material Costs, Employee Costs, and Travel & Entertainment which roll up to Total Operating Expenses. Balances are stored automatically in the cube for each of these.  When you define the report, you pick each of these members - no calculations required.  If a new detail value is added, you simply add it to the hierarchy, and there is no need to modify the report. I realize that there are always exceptions that require special handling, but I am confident that you will end up with much fewer exceptions if you make reporting a priority and design your hierarchies from the top-down.

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• How is a switch statement better than a series of if statements? [closed]

  - by user1276078

  Possible Duplicate: Should I use switch statements or long if…else chains? I'm working on a small program that will conduct an Insertion Sort. A number will be inputted through the keyboard and stored in a variable I called "num." I've decided to use a switch statement in order to obtain the number inputted. switch( e.getKeyCode() ) { case KeyEvent.VK_0: num = 0; break; case KeyEvent.VK_1: num = 1; break; case KeyEvent.VK_2: num = 2; break; case KeyEvent.VK_3: num = 3; break; case KeyEvent.VK_4: num = 4; break; case KeyEvent.VK_5: num = 5; break; case KeyEvent.VK_6: num = 6; break; case KeyEvent.VK_7: num = 7; break; case KeyEvent.VK_8: num = 8; break; case KeyEvent.VK_9: num = 9; break; } I realized one other course of action could have been to use a set of if statements. if( e.getKeyCode() == KeyEvent.VK_0 ) num = 0; else if( e.getKeyCode() == KeyEvent.VK_1 ) num = 1; etc. for every number up until 9. I then wondered what the essential difference is between a switch statement and a series of if statements. I know it saves space and time to write, but it's not that much. So, my question is, aside from the space, does a switch statement differ from a series of if statments in any way? Is it faster, less error-prone, etc.? This question really doesn't affect my code that much. I was just wondering. Also, this question pertains to the JAVA language, not any other programming language.

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• How to synchronize the ball in a network pong game?

  - by Thaars

  I’m developing a multiplayer network pong game, my first game ever. The current state is, I’ve running the physic engine with the same configurations on the server and the clients. The own paddle movement is predicted and get just confirmed by the authoritative server. Is a difference detected between them, I correct the position at the client by interpolation. The opponent paddle is also interpolated 200ms to 100ms in the past, because the server is broadcasting snapshots every 100ms to each client. So far it works very well, but now I have to simulate the ball and have a problem to understanding the procedure. I’ve read Valve’s (and many other) articles about fast-paced multiplayer several times and understood their approach. Maybe I can compare my ball with their bullets, but their advantage is, the bullets are not visible. When I have to display the ball, and see my paddle in the present, the opponent in the past and the server is somewhere between it, how can I synchronize the ball over all instances and ensure, that it got ever hit by the paddle even if the paddle is fast moving? Currently my ball’s position is simply set by a server update, so it can happen, that the ball bounces back, even if the paddle is some pixel away (because of a delayed server position). Until now I’ve got no synced clock over all instances. I’m sending a client step index with each update to the server. If the server did his job, he sends the snapshot with the last step index of each client back to the clients. Now I’m looking for the stored position at the returned step index and compare them. Do I need a common clock to sync the ball? EDIT: I've tried to sync a common clock for the server and all clients with a timestamp. But I think it's better to use an own stepping instead of a timestamp (so I don't need to calculate with the ping and so on - and the timestamp will never be exact). The physics are running 60 times per second and now I use this for keeping them synchronized. Is that a good way? When the ball gets calculated by each client, the angle after bouncing can differ because of the different position of the paddles (the opponent is 200ms in the past). When the server is sending his ball position, velocity and angle (because he knows the position of each paddle and is authoritative), the ball could be in a very different position because of the different angles after bouncing (because the clients receive the server data after 100ms). How is it possible to interpolate such a huge difference? I posted this question some days ago at stackoverflow, but got no answer yet. Maybe this is the better place for this question.

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• Ad-hoc reporting similar to Microstrategy/Pentaho - is OLAP really the only choice (is OLAP even sufficient)?

  - by TheBeefMightBeTough

  So I'm getting ready to develop an API in Java that will provide all dimensions, metrics, hierarchies, etc to a user such that they can pick and choose what they want (say, e.g., dimensions of Location (a store) and Weekly, and the metric Product Sales $), provide their choices to the api, and have it spit out an object that contains the answer to their question (the object would probably be a set of cells). I don't even believe there will be much drill up/down. The data warehouse the APIwill interface with is in a standard form (FACT tables, dimensions, star schema format). My question is, is an OLAP framework such as Mondrian the only way to achieve something akin to ad-hoc reporting? I can envisage a really large Cube (or VirtualCube) that contains most of the dimensions and metrics the user could ever want, which would give the illusion of ad-hoc reporting. The problem is that there is a ton of setup to do (so much XML) to get the framework to work with the data. Further it requires specific knowledge, such as MDX, and even moreso learning the framework peculiars (Mondrian API). Finally, I am not positive it will scale much better than simply making queries against a SQL database. OLAP to me feels like very old technology. Is performance really an issue anymore? The alternative I can think of would be dynamic SQL. If the existing tables in the data warehouse conform to a naming scheme (FACT_, DIM_, etc), or if a very simple config file/ database table containing config information existed that stored which tables are fact tables, which are dimensions, and what metrics are available, then couldn't the api read from that and assembly the appropriate sql query? Would this necessarily be harder than learning MDX, Mondrian (or another OLAP framework), and creating all the cubes? In general, I feel that OLAP is at the same time too powerful (supports drill up/down, complex functions) and outdated and am reluctant to base my architecture on it. However, I am unsure if the alternative(s), such as rolling my own ad-hoc reporting framework using dynamic SQL would remove any complexity while still fulfilling requirements, both functional and non-functional (e.g., scalability; some FACT tables have many millions of rows). I also wonder about other techniques (e.g., hive). Has anyone here tried to do ad-hoc reporting? Any advice? I expect this project to take a pretty long time (3 months min, but probably longer), so I just do not want to commit to an architecture without being absolutely sure of its pros and cons. Thanks so much.

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• openGL textures in bitmap mode

  - by evenex_code

  For reasons detailed here I need to texture a quad using a bitmap (as in, 1 bit per pixel, not an 8-bit pixmap). Right now I have a bitmap stored in an on-device buffer, and am mounting it like so: glBindBuffer(GL_PIXEL_UNPACK_BUFFER, BFR.G[(T+1)%2]); glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, W, H, 0, GL_COLOR_INDEX, GL_BITMAP, 0); The OpenGL spec has this to say about glTexImage2D: "If type is GL_BITMAP, the data is considered as a string of unsigned bytes (and format must be GL_COLOR_INDEX). Each data byte is treated as eight 1-bit elements..." Judging by the spec, each bit in my buffer should correspond to a single pixel. However, the following experiments show that, for whatever reason, it doesn't work as advertised: 1) When I build my texture, I write to the buffer in 32-bit chunks. From the wording of the spec, it is reasonable to assume that writing 0x00000001 for each value would result in a texture with 1-px-wide vertical bars with 31-wide spaces between them. However, it appears blank. 2) Next, I write with 0x000000FF. By my apparently flawed understanding of the bitmap mode, I would expect that this should produce 8-wide bars with 24-wide spaces between them. Instead, it produces a white 1-px-wide bar. 3) 0x55555555 = 1010101010101010101010101010101, therefore writing this value ought to create 1-wide vertical stripes with 1 pixel spacing. However, it creates a solid gray color. 4) Using my original 8-bit pixmap in GL_BITMAP mode produces the correct animation. I have reached the conclusion that, even in GL_BITMAP mode, the texturer is still interpreting 8-bits as 1 element, despite what the spec seems to suggest. The fact that I can generate a gray color (while I was expecting that I was working in two-tone), as well as the fact that my original 8-bit pixmap generates the correct picture, support this conclusion. Questions: 1) Am I missing some kind of prerequisite call (perhaps for setting a stride length or pack alignment or something) that will signal to the texturer to treat each byte as 8-elements, as it suggests in the spec? 2) Or does it simply not work because modern hardware does not support it? (I have read that GL_BITMAP mode was deprecated in 3.3, I am however forcing a 3.0 context.) 3) Am I better off unpacking the bitmap into a pixmap using a shader? This is a far more roundabout solution than I was hoping for but I suppose there is no such thing as a free lunch.

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• Integrating with a payment provider; Proper and robust OOP approach

  - by ExternalUse

  History We are currently using a so called redirect model for our online payments (where you send the payer to a payment gateway, where he inputs his payment details - the gateway will then return him to a success/failure callback page). That's easy and straight-forward, but unfortunately quite inconvenient and at times confusing for our customers (leaving the site, changing their credit card details with an additional login on another site etc). Intention & Problem description We are now intending to switch to an integrated approach using an exchange of XML requests and responses. My problem is on how to cater with all (or rather most) of the things that may happen during processing - bearing in mind that normally simplicity is robust whereas complexity is fragile. Examples User abort: The user inputs Credit Card details and hits submit. An XML message to the provider's gateway is sent and waiting for response. The user hits "stop" in his browser or closes the window. ignore_user_abort() in PHP may be an option - but is that reliable? might it be better to redirect the user to a "please wait"-page, that in turn opens an AJAX or other request to the actual processor that does not rely on the connection? Database goes away sounds over-complicated, but with e.g. a webserver in the States and a DB in the UK, it has happened and will happen again: User clicks together his order, payment request has been sent to the provider but the response cannot be stored in the database. What approach could I use, using PHP to sort of start an SQL like "Transaction" that only at the very end gets committed or rolled back, depending on the individual steps? Should then neither commit or roll back have happened, I could sort of "lock" the user to prevent him from paying again or to improperly account for payments - but how? And what else do I need to consider technically? None of the integration examples of e.g. Worldpay, Realex or SagePay offer any insight, and neither Google or my search terms were good enough to find somebody else's thoughts on this. Thank you very much for any insight on how you would approach this!

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