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• How does a segment based rendering engine work?

  - by Calmarius

  As far as I know Descent was one of the first games that featured a fully 3D environment, and it used a segment based rendering engine. Its levels are built from cubic segments (these cubes may be deformed as long as it remains convex and sides remain roughly flat). These cubes are connected by their sides. The connected sides are traversable (maybe doors or grids can be placed on these sides), while the unconnected sides are not traversable walls. So the game is played inside of this complex. Descent was software rendered and it had to be very fast, to be playable on those 10-100MHz processors of that age. Some latter levels of the game are huge and contain thousands of segments, but these levels are still rendered reasonably fast. So I think they tried to minimize the amount of cubes rendered somehow. How to choose which cubes to render for a given location? As far as I know they used a kind of portal rendering, but I couldn't find what was the technique used in this particular kind of engine. I think the fact that the levels are built from convex quadrilateral hexahedrons can be exploited.

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• How does a segment-based rendering engine (as in Descent) work?

  - by Calmarius

  As far as I know Descent was one of the first games that featured a fully 3D environment, and it used a segment based rendering engine. Its levels are built from cubic segments (these cubes may be deformed as long as it remains convex and sides remain roughly flat). These cubes are connected by their sides. The connected sides are traversable (maybe doors or grids can be placed on these sides), while the unconnected sides are not traversable walls. So the game is played inside of this complex. Descent was software rendered and it had to be very fast, to be playable on those 10-100MHz processors of that age. Some latter levels of the game are huge and contain thousands of segments, but these levels are still rendered reasonably fast. So I think they tried to minimize the amount of cubes rendered somehow. How to choose which cubes to render for a given location? As far as I know they used a kind of portal rendering, but I couldn't find what was the technique used in this particular kind of engine. I think the fact that the levels are built from convex quadrilateral hexahedrons can be exploited.

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• Why don't we store the syntax tree instead of the source code?

  - by Calmarius

  We have a lot of programming languages. Every language is parsed and syntax checked before translated into code so an abstract syntax tree is built. We have this abstract syntax tree, why don't we store this syntax tree instead of the source code (or next to the source code)? By using an AST instead of the source code. Every programmer in a team can serialize this tree to any language, they want (with the appropriate context free grammar) and parse back to AST when they finished. So this would eliminate the debate about the coding style questions (where to put the { and }, where to put whitespace, indentation, etc.) What are the pros and cons of this approach?

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• Found a better solution to a problem at work - should I deter from posting the code snippet online?

  - by Calmarius

  I think most of us, programmers, used Stack Overflow to solve every day problems: looked for an efficient algorithm to do something. Now imagine a situation: you have a problem to solve. Googled a bit, found a StackOverflow question but you are not really satisfied with the answers so far. So you have to do your own research: you need to do it because you want it in the company's app. Eventually after some hours you have found the better solution. You're happy, you added it to the company's code base, then you want to submit your answer with a code snippet (just several lines) to the question you've found before to help others too. But wait: the company's software is closed source, and you worked on it on the clock. So does this mean I shouldn't post the answer neither at work nor at home to that question in the rest of my life, because I solved it at work, and the company owns that piece of code?

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• Computer does not boot after ram upgrade

  - by Calmarius

  I have a Dell Optiplex GX520 desktop (it's abount 5 yr old) PC with 512 MB DDR2 RAM. Since my computer always swapping I thought I should upgrade my RAM. I bought a Kingmax 2GB DDR2 RAM. But my system does not boot. The status leds are on 2 and 4. The user manual says 'video card failure' wtf? I put back the original module and everything works. I tried many combinations. When I leave the old 512 RAM in and put the 2GB next to it to the other socket my system completes the POST and I'm able to enter the BIOS menu. It says my system has 2.5 GB installed, one 0.5GB and one 2GB in dual asymmetric channel mode. It's seemingly right. Exiting the BIOS setup GRUB loads successfully, but when I try to boot Ubuntu it crashes with kernel panic immediately. Trying to load Windows XP does not get past the loading screen, it crashes with 0x8E stop error. Does this mean the ram I bought is faulty? Or is it just mean that the memory module I bought is too new to be handled my computer? I this case I may exchange the RAM with my friends. No other computer is in my house (my very old box has DDR1 ram, my systers new box has DDR3 ones. I can't plug my memory in neither one.) I'm going to return the RAM to store to replace it with a better one tomorrow. Is there any hope to get this new module work?

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• Is visiting HTTPS websites on a public hotspot secure?

  - by Calmarius

  It's often said that HTTPS SSL/TLS connections are encrypted and said to be secure because the communication between the server and me is encrypted (also provides server authentication) so if someone sniffs my packets, they will need zillions of years to decrypt if using brute force in theory. Let's assume I'm on a public wifi and there is a malicious user on the same wifi who sniffs every packet. Now let's assume I'm trying to access my gmail account using this wifi. My browser does a SSL/TLS handshake with the server and gets the keys to use for encryption and decryption. If that malicious user sniffed all my incoming and outgoing packets. Can he calculate the same keys and read my encrypted traffic too or even send encrypted messages to the server in my name?

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• How to copy VirtualBox VDI contents to a partition and dual boot the OS from it?

  - by Calmarius

  I'm a Linux user but I keep a compressed Windows XP ISO with me on a pen drive for the case I absolutely need Windows to do something. This works in VirtualBox most of the time. But now I want to play some games, so I would like to run the Windows image natively. My computer don't have CD drive so cannot just burn the ISO and make an install normally. What I trying to do is moving the installed Windows image to a physical NTFS partition on my HDD and set up GRUB to let me dual boot it. I found many tutorials that deal with making VDI to physical drive. But they assume I want to overwrite my entire drive. Moving the raw disk image with dd to the partition resulted in a corrupt partition. I also tried the VMDK trick to use that empty partition and install the Windows on it. Although the text mode phase of the installation finishes without problems, the VM won't work, either crashes and keeps rebooting or just immediately or freezes (depending on how I created the VMDK, with -rawdisk /dev/sda3 or -rawdisk /dev/sda -partition 3).

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• Is it possible to boot from internet?

  - by Calmarius

  Let's assume the following situation: you have a computer with empty hard disk, and you don't have a CD, floppy, pen drive nearby to boot the computer from. But you have connection to the Internet. Modern computers support network booting using PXE, but I haven't found anything regarding booting via the internet. So, is it possible to use PXE to load an image from the internet and boot it? By having a running system (even a minimal Linux) in RAM, it should be possible to install it on the hard disk, and build up a working system from here.

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• Getting XText to work

  - by Calmarius

  I know you don't like helping others in their homework but I have to make an XText grammar, write a sample code that matches this grammar and compile it to a html file. The lecturer showed us the steps and everything worked for him... He said "It's so simple it will be a 10 minute work for you". And I believed that. However at home almost nothing works as expected. And of course no more lectures to go only the exam avaits me where I have to show what I done to pass. Moreover the e-mail I sent him bounced back by the mailer-demon... I got Xtext along with Eclipse IDE from the xtext website and I unpacked it and I followed the steps in the official tuturial to get the default project template to work. The tutorial is found here: http://wiki.eclipse.org/Xtext/GettingStarted Now I'm at the step "Model". It says open the "MyModel.mydsl" I do that but the editor does not opened. It said: "Could not open the editor: The editor class could not be instantiated. This usually indicates a missing no-arg constructor or that the editor's class name was mistyped in plugin.xml." Since everything is generated, the error message does not helped me... There was an option to look at the stack trace (it was mile long) and on the top of it there was an exception: java.lang.IllegalStateException: The bundle has not yet been activated. Make sure the Manifest.MF contains 'Bundle-ActivationPolicy: lazy'. I opened Manifast.MF and Bundle-ActivationPolicy: lazy was set... I googled for the solution but no avail. It drove me nuts and I gave up. I have no experience with Eclipse and Java and XText, I just want to do my homework and forget everything until I will need it again... Anyone have experience with XText? Any help appreciated. ps: I will be on it too and I might resolve the problem in several hours. But now I am at a loss.

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• Keeping sync in multiplayer RTS game that uses floating point arithmetic

  - by Calmarius

  I'm writing a 2D space RTS game in C#. Single player works. Now I want to add some multiplayer functionality. I googled for it and it seems there is only one way to have thousands of units continuously moving without a powerful net connection: send only the commands through the network while running the same simulation at every player. And now there is a problem the entire engine uses doubles everywhere. And floating point calculations are depends heavily on compiler optimalizations and cpu architecture so it is very hard to keep things syncronized. And it is not grid based at all, and have a simple phisics engine to move the space-ships (space ships have impulse and angular-momentum...). So recoding the entire stuff to use fixed point would be quite cumbersome (but probably the only solution). So I have 2 options so far: Say bye to the current code and restart from scratch using integers Make the game LAN only where there is enough bandwidth to have 8 players with thousands of units and sending the positions and orientation etc in (almost) every frame... So I looking for better opinions, (or even tips on migrating the code to fixed-point without messing everything up...)

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• How to prevent arbitrary code execution vulnerability in our programs?

  - by Calmarius

  You always read in changelogs when your system or browser or any program updates that they fixed a bug that made possible that an attacker can execute any code in your computer with a forged website, or attacking your computer with carefully forged packets, etc... Because you read it so often that means any program can have similar vulnerabilites... What causes this? how to design our programs to prevent similar issues?

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• Why does multiple sessions started on the same page gets the same session id?

  - by Calmarius

  I tryed the following: <?php session_name('user'); session_start(); // sets an 'user' cookie with session id. // This session stores the user's login data. // Its an ordinary session. $USERSESSION=$_SESSION; // saving this session $userSessId=session_id(); session_write_close(); //closing this session session_name('chatroom'); session_start(); // set a 'chatroom' cookie but contains the same session id and points to the same data :( . // This session would be used to store the chat text. This session would be // shared between all users joined in this chat room by setting the same session id for all members. // by calling session_regenerate_id would make a diffent session id for every user and it won't be a chat room anymore. ?> So I want to do a chat like thing with sessions. On the client side it would be done with ajax that polls this php page in every 5-10 seconds. Sessions may be cached in the server's memory so it can be accessible fast. I can store the chat in the database but my service runs on a free webhost which is limited, only 4 mysql connections allowed at a time which is almost nothing. I try to touch my database as least times as possible.

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• How do i prevent my code from being stolen?

  - by Calmarius

  What happens exactly when I launch a .NET exe? I know that C# is compiled to IL code and I think the generated exe file just a launcher that starts the runtime and passes the IL code to it. But how? And how complex process is it? IL code is embedded in the exe. I think it can be executed from the memory without writing it to the disk while ordinary exe's are not (ok, yes but it is very complicated). My final aim is extracting the IL code and write my own encrypted launcher to prevent scriptkiddies to open my code in Reflector and just steal all my classes easily. Well I can't prevent reverse engineering completely. If they are able to inspect the memory and catch the moment when I'm passing the pure IL to the runtime then it won't matter if it is a .net exe or not, is it? I know there are several obfuscator tools but I don't want to mess up the IL code itself. EDIT: so it seems it isn't worth trying what I wanted. They will crack it anyway... So I will look for an obfuscation tool. And yes my friends said too that it is enough to rename all symbols to a meaningless name. And reverse engineering won't be so easy after all.

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