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• Porting WebGL game to iPhone's native OpenGL?

  - by ArtPulse

  We are developing a web game that uses WebGL for the two biggest parts of it. Working with HTML / CSS was too slow and too limited, so it's off the table. Thing is, iOS does not support WebGL publicly just yet, only on iAd. It is my guess Apple will eventually support it once the security issues they and Microsoft claim it has are fixed, and looks stable enough. Problem is, if Apple does not do this by the release of the next mayor iOS version, then we will have in our hands a mobile WebGL game that does not run. 6 months of development and testing to waste. So, questions: If that was the case, how viable (regarding amount of time) is it porting the WebGL part of the game to native iPhone OpenGL? I'm afraid that porting will take longer than the development of the game itself. I saw posts on Stack Overflow (like this) that suggested, on Android, adding the OpenGL interface manually to a WebKit element. It'd be slower than native. But either way... Is this something that could be accepted in the AppStore? Apple is very restrictive with these kind of stuff... Thank you all for your time!

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• Can I perform a search on mail server in Java?

  - by twofivesevenzero

  I am trying to perform a search of my gmail using Java. With JavaMail I can do a message by message search like so: Properties props = System.getProperties(); props.setProperty("mail.store.protocol", "imaps"); Session session = Session.getDefaultInstance(props, null); Store store = session.getStore("imaps"); store.connect("imap.gmail.com", "myUsername", "myPassword"); Folder inbox = store.getFolder("Inbox"); inbox.open(Folder.READ_ONLY); SearchTerm term = new SearchTerm() { @Override public boolean match(Message mess) { try { return mess.getContent().toString().toLowerCase().indexOf("boston") != -1; } catch (IOException ex) { Logger.getLogger(JavaMailTest.class.getName()).log(Level.SEVERE, null, ex); } catch (MessagingException ex) { Logger.getLogger(JavaMailTest.class.getName()).log(Level.SEVERE, null, ex); } return false; } }; Message[] searchResults = inbox.search(term); for(Message m:searchResults) System.out.println("MATCHED: " + m.getFrom()[0]); But this requires downloading each message. Of course I can cache all the results, but this becomes a storage concern with large gmail boxes and also would be very slow (I can only imagine how long it would take to search through gigabytes of text...). So my question is, is there a way of searching through mail on the server, a la gmail's search field? Maybe through Microsoft Exchange? Hours of Googling has turned up nothing.

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• How can I find out if two arguments are instances of the same, but unknown class?

  - by Ingmar

  Let us say we have a method which accepts two arguments o1 and o2 of type Object and returns a boolean value. I want this method to return true only when the arguments are instances of the same class, e.g.: foo(new Integer(4),new Integer(5)); Should return true, however: foo(new SomeClass(), new SubtypeSomeClass()); should return false and also: foo(new Integer(3),"zoo"); should return false. I believe one way is to compare the fully qualified class names: public boolean foo(Object o1, Object o2){ Class<? extends Object> c1 = o1.getClass(); Class<? extends Object> c2 = o2.getClass(); if(c1.getName().equals(c2.getName()){ return true;} return false; } An alternative conditional statement would be : if (c1.isAssignableFrom(c2) && c2.isAssignableFrom(c1)){ return true; } The latter alternative is rather slow. Are there other alternatives to this problem?

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• How can I improve this search usability?

  - by Craig Whitley

  This is the first real programming attempt of mine, and theres some major flaws. It's a learning project, and I'm currently re-writing the entire thing as my php is is really messy. I really want to get an idea on how I can improve the actual usability and accesibility of the site at the same time though - so I know how to implement it correctly. The website is basically a comparison website for gameserver hosting. As I mentioned, its a learning project and I don't actually expect any revenue from it. At the moment theres only test data in it, so in the game input box select either 'Battlefied Bad Company 2' or 'Call of Duty 4: Modern Warfare' and ignore the actual search results. http://www.laglessfrag.com I wasn't really sure how to work the search functionality. Basically when you click a game in the drop down box, it sends an ajax request and finds all the locations available to that specific game in the database. After selecting the country theres another ajax to find all the citys available to the game in that country - which gives me the two unique identifiers I need to create the search results. One major and fundamental flaw is that without javascript enabled, the site ceases to function. I'll overcome that in the next re-write, but without the ajax functionality stopping the user 'going wrong' - how can I implement a search that requires two fields without creating extra steps in new pages after form submissions? I'm also no designer so my whole layout and css is a bit rubbish, but this was mainly a learning project as I'm interested in applications / programming rather than design. It's also slow as its on shared hosting, but if I can get it to work correctly then I'm not impartial to chucking a bit of money at it for faster hosting and maybe a bit of advertising and seeing where it goes (if anywhere!). Any info appreciated.

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• Project Euler problem 214, How can i make it more efficient?

  - by Once

  I am becoming more and more addicted to the Project Euler problems. However since one week I am stuck with the #214. Here is a short version of the problem: PHI() is Euler's totient function, i.e. for any given integer n, PHI(n)=numbers of k<=n for which gcd(k,n)=1. We can iterate PHI() to create a chain. For example starting from 18: PHI(18)=6 = PHI(6)=2 = PHI(2)=1. So starting from 18 we get a chain of length 4 (18,6,2,1) The problem is to calculate the sum of all primes less than 40e6 which generate a chain of length 25. I built a function that calculates the chain length of any number and I tested it for small values: it works well and fast. sum of all primes<=20 which generate a chain of length 4: 12 sum of all primes<=1000 which generate a chain of length 10: 39383 Unfortunately my algorithm doesn't scale well. When I apply it to the problem, it takes several hours to calculate... so I stop it because the Project Euler problems must be solved in less than one minute. I thought that my prime detection function might be slow so I fed the program with a list of primes <40e6 to avoid the primality test... The code runs now a little bit faster, but there is still no way to get a solution in less than a few hours (and I don't want this). So is there any "magic trick" that I am missing here ? I really don't understand how to be more efficient on this one... I am not asking for the solution, because fighting with optimization is all the fun of Project Euler. However, any small hint that could put me on the right track would be welcome. Thanks !

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• Legitimate uses of the Function constructor

  - by Marcel Korpel

  As repeatedly said, it is considered bad practice to use the Function constructor (also see the ECMAScript Language Specification, 5th edition, § 15.3.2.1): new Function ([arg1[, arg2[, … argN]],] functionBody) (where all arguments are strings containing argument names and the last (or only) string contains the function body). To recapitulate, it is said to be slow, as explained by the Opera team: Each time […] the Function constructor is called on a string representing source code, the script engine must start the machinery that converts the source code to executable code. This is usually expensive for performance – easily a hundred times more expensive than a simple function call, for example. (Mark ‘Tarquin’ Wilton-Jones) Though it's not that bad, according to this post on MDC (I didn't test this myself using the current version of Firefox, though). Crockford adds that [t]he quoting conventions of the language make it very difficult to correctly express a function body as a string. In the string form, early error checking cannot be done. […] And it is wasteful of memory because each function requires its own independent implementation. Another difference is that a function defined by a Function constructor does not inherit any scope other than the global scope (which all functions inherit). (MDC) Apart from this, you have to be attentive to avoid injection of malicious code, when you create a new Function using dynamic contents. Lots of disadvantages and it is intelligible that ECMAScript 5 discourages the use of the Function constructor by throwing an exception when using it in strict mode (§ 13.1). That said, T.J. Crowder says in an answer that [t]here's almost never any need for the similar […] new Function(...), either, again except for some advanced edge cases. So, now I am wondering: what are these “advanced edge cases”? Are there legitimate uses of the Function constructor?

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• Any high-level languages that can use c libraries?

  - by Isaiah

  I know this question could be in vain, but it's just out of curiosity, and I'm still much a newb^^ Anyways I've been loving python for some time while learning it. My problem is obviously speed issues. I'd like to get into indie game creation, and for the short future, 2d and pygame will work. But I'd eventually like to branch into the 3d area, and python is really too slow to make anything 3d and professional. So I'm wondering if there has ever been work to create a high-level language able to import and use c libraries? I've looked at Genie and it seems to be able to use certain libraries, but I'm not sure to what extent. Will I be able to use it for openGL programing, or in a c game engine? I do know some lisp and enjoy it a lot, but there aren't a great many libraries out there for it. Which leads to the problem: I can't stand C syntax, but C has libraries galore that I could need! And game engines like irrlicht. Is there any language that can be used in place of C around C? Thanks so much guys

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• Reading numpy arrays outside of Python

  - by Abiel

  In a recent question I asked about the fastest way to convert a large numpy array to a delimited string. My reason for asking was because I wanted to take that plain text string and transmit it (over HTTP for instance) to clients written in other programming languages. A delimited string of numbers is obviously something that any client program can work with easily. However, it was suggested that because string conversion is slow, it would be faster on the Python side to do base64 encoding on the array and send it as binary. This is indeed faster. My question now is, (1) how can I make sure my encoded numpy array will travel well to clients on different operating systems and different hardware, and (2) how do I decode the binary data on the client side. For (1), my inclination is to do something like the following import numpy as np import base64 x = np.arange(100, dtype=np.float64) base64.b64encode(x.tostring()) Is there anything else I need to do? For (2), I would be happy to have an example in any programming language, where the goal is to take the numpy array of floats and turn them into a similar native data structure. Assume we have already done base64 decoding and have a byte array, and that we also know the numpy dtype, dimensions, and any other metadata which will be needed. Thanks.

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• FILE* issue PPU side code

  - by Cristina

  We are working on a homework on CELL programming for college and their feedback response to our questions is kinda slow, thought i can get some faster answers here. I have a PPU side code which tries to open a file passed down through char* argv[], however this doesn't work it cannot make the assignment of the pointer, i get a NULL. Now my first idea was that the file isn't in the correct directory and i copied in every possible and logical place, my second idea is that maybe the PPU wants this pointer in its LS area, but i can't deduce if that's the bug or not. So... My question is what am i doing wrong? I am working with a Fedora 7 SDK Cell, with Eclipse as an IDE. Maybe my argument setup is wrong tho he gets the name of the file correctly. Code on request: images_t *read_bin_data(char *name) { FILE *file; images_t *img; uint32_t *buffer; uint8_t buf; unsigned long fileLen; unsigned long i; //Open file file = (FILE*)malloc(sizeof(FILE)); file = fopen(name, "rb"); printf("[Debug]Opening file %s\n",name); if (!file) { fprintf(stderr, "Unable to open file %s", name); return NULL; } //....... } Main launch: int main(int argc,char* argv[]) { int i,img_width; int modif_this[4] __attribute__ ((aligned(16))) = {1,2,3,4}; images_t *faces, *nonfaces; spe_context_ptr_t ctxs[SPU_THREADS]; pthread_t threads[SPU_THREADS]; thread_arg_t arg[SPU_THREADS]; //intializare img_width img_width = atoi(argv[1]); printf("[Debug]Img size is %i\n",img_width); faces = read_bin_data(argv[3]); //....... } Thanks for the help.

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• Poor DB4O performance - What am I doing wrong?

  - by Jon

  I read Rob Conery's post about Object databases and thought I'd give it a go. I have a class lets say Book with 15 properties mostly string, some int, one Datetime and 2 decimals. I used Rob's code to open the database file etc to test on a Winforms project not a Web project. So I did the following: for(int i = 0; i < 1000000; i++) { var Book = new Book(); //Assign variables s.Save(Book); } s.CommitChanges(); This took at least a couple of minutes. I then tried to retrieve all data to test speed: var spp = s.All<Passports>(); This one line was quick, however, then doing: sppp.Count() as well as a seperate test doing a foreach loop and incrementing a counter took a couple of minutes. This seems quite slow to me. Am I doing something wrong or am I expecting too much?

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• Optimization in Python - do's, don'ts and rules of thumb.

  - by JV

  Well I was reading this post and then I came across a code which was: jokes=range(1000000) domain=[(0,(len(jokes)*2)-i-1) for i in range(0,len(jokes)*2)] I thought wouldn't it be better to calculate the value of len(jokes) once outside the list comprehension? Well I tried it and timed three codes jv@Pioneer:~$ python -m timeit -s 'jokes=range(1000000);domain=[(0,(len(jokes)*2)-i-1) for i in range(0,len(jokes)*2)]' 10000000 loops, best of 3: 0.0352 usec per loop jv@Pioneer:~$ python -m timeit -s 'jokes=range(1000000);l=len(jokes);domain=[(0,(l*2)-i-1) for i in range(0,l*2)]' 10000000 loops, best of 3: 0.0343 usec per loop jv@Pioneer:~$ python -m timeit -s 'jokes=range(1000000);l=len(jokes)*2;domain=[(0,l-i-1) for i in range(0,l)]' 10000000 loops, best of 3: 0.0333 usec per loop Observing the marginal difference 2.55% between the first and the second made me think - is the first list comprehension domain=[(0,(len(jokes)*2)-i-1) for i in range(0,len(jokes)*2)] optimized internally by python? or is 2.55% a big enough optimization (given that the len(jokes)=1000000)? If this is - What are the other implicit/internal optimizations in Python ? What are the developer's rules of thumb for optimization in Python? Edit1: Since most of the answers are "don't optimize, do it later if its slow" and I got some tips and links from Triptych and Ali A for the do's. I will change the question a bit and request for don'ts. Can we have some experiences from people who faced the 'slowness', what was the problem and how it was corrected? Edit2: For those who haven't here is an interesting read Edit3: Incorrect usage of timeit in question please see dF's answer for correct usage and hence timings for the three codes.

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• How do you efficiently bulk index lookups?

  - by Liron Shapira

  I have these entity kinds: Molecule Atom MoleculeAtom Given a list(molecule_ids) whose lengths is in the hundreds, I need to get a dict of the form {molecule_id: list(atom_ids)}. Likewise, given a list(atom_ids) whose length is in the hunreds, I need to get a dict of the form {atom_id: list(molecule_ids)}. Both of these bulk lookups need to happen really fast. Right now I'm doing something like: atom_ids_by_molecule_id = {} for molecule_id in molecule_ids: moleculeatoms = MoleculeAtom.all().filter('molecule =', db.Key.from_path('molecule', molecule_id)).fetch(1000) atom_ids_by_molecule_id[molecule_id] = [ MoleculeAtom.atom.get_value_for_datastore(ma).id() for ma in moleculeatoms ] Like I said, len(molecule_ids) is in the hundreds. I need to do this kind of bulk index lookup on almost every single request, and I need it to be FAST, and right now it's too slow. Ideas: Will using a Molecule.atoms ListProperty do what I need? Consider that I am storing additional data on the MoleculeAtom node, and remember it's equally important for me to do the lookup in the molecule-atom and atom-molecule directions. Caching? I tried memcaching lists of atom IDs keyed by molecule ID, but I have tons of atoms and molecules, and the cache can't fit it. How about denormalizing the data by creating a new entity kind whose key name is a molecule ID and whose value is a list of atom IDs? The idea is, calling db.get on 500 keys is probably faster than looping through 500 fetches with filters, right?

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• Making GUI applications on Linux/Windows. What languages/tools to use?

  - by Javed Ahamed

  My student group and I are trying to continue working on a project we worked on this semester over the summer to become a professional, deployable app. We originally did it in Adobe AIR but it seems now that the computers this program will be running on will be very slow, maybe 600mhz and 128-256mb ram so flash just isn't going to cut it. It is basically a health diagnosis application that we will be shipping out to impoverished countries. Now comes the real question. We are wondering what language to rebuild our application in. It has to have a good gui builder associated with it, like adobe flex/air gui builder or visual studio's gui builder but the application should run on linux primarily, and if it can run on windows thats just a plus. We are all students too without really any outside help so whatever we decide to do this in there must be ample documentation available when we hit problems. Some things we have considered so far are using python and glade or c# and monodevelop, but again we really are not experts on any of this which is why I am asking for help as I would rather spend the time now choosing the right tools instead of wasting time down the line when we hit a roadblock. Thanks in advance!

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• call addsubview again causes slowdown

  - by Tom

  hi guys, i am writing a little music-game for the iphone. I am almost done, this is the only issue which keeps me from rolling it out. any help to solve this is much appreciated. this is what i do: at my appDelegate I add my menu-view-screen to the window. the menu-view-screen acts as a container and controls which view gets presented to the user. means, on the menu-view-screen I got 4 buttons (new game, options, faq, highscore). when the user clicks on a button something as this happens: if (self.gameViewController == nil) { GameViewController *viewController = [[GameViewController alloc] initWithNibName:@"GameViewController" bundle:nil]; self.gameViewController = viewController; [viewController release]; } [self.view addSubview:self.gameViewController.view]; [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleSwitchViewNotificationFromGameView:) name:@"SwitchView" object:gameViewController]; when the user returns to the menu, this piece of code gets executed: [[NSNotificationCenter defaultCenter] removeObserver:self]; [self.gameViewController viewWillDisappear:YES]; [self.gameViewController.view removeFromSuperview]; this works fine for all screens but not for the gamescreen(well this is the only one with heaps of user-interaction) means the responsiveness of the iphone(when playing tones) gets really slow. The performance is fine when I display the gameview for the first time. it starts getting slower as soon as I add it to the menu-views-container-subviews again (addsubview) (basically open up a new game) any ideas what causes(or to get around) this? thanks heaps Best regards Tom

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• Grails or Play! for an ex-RoR developer ?

  - by Kedare

  Hello, I plan to begin learning a Java web framework (I love the Java API), I already used Rails and Django. I want something close to Java, but without all the complexity of J2EE. I've found 2 framework that could be good for me : Grails : Grails looks great, it use Groovy that is better than Java for web application (I think..), but it's slower, that use pure-java components (Hibernate, Strut, Spring), it looks pretty simple to deploy (send .war and it's ok !), the GSP is great ! It's a bit harder to debug (need to restart the server at each modification, and the stacktrace is a mix of Java and Groovy stack that is not always understandable..) Play! : This framework also looks great, it's faster than Grails (It's use directly Java), but I don't really like how it use Java, it modify the source code to transform the properties call as setXXX/getXXX, I'm not kind of that... The framework also have caching function that Grails don't (alreary) has. I don't really like the Template Engine. It's also easer to debug (no need to restart the server, and the stacktrace is clear) What do you recommend for ? I am looking for something easy to learn (I used a lot ruby and java, but a little bit java (But I love the Java API)), that is full featured (That's no a problem with all the Java Library availables, but if it's bundle and integrated I prefer), that scale and that is not too slow (faster than ruby), and if possible I would want something with a decent community to easily find support and answer to my questions ;) PS: No JRuby on Rails Thank you !

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• Flash Without a SWF File?

  - by PeterAllenWebb

  Is there any way to embed Flash completely in HTML, without reference to an external SWF file? I ask because I would like to send an HTML file as an email attachment that the recipient will open in a browser and fill out as a form. The last step is that they will copy the result to their clipboard, paste it into a new message, and email it back. I cannot reliably copy to the clipboard with JavaScript because of the security issues, but there are simple Flash apps to add that capability. I know I could just display the response text (which will be Base64 encoded) to the recipient and have them copy/paste, but it would be nice to provide this small convenience to them. Also, so you are aware, the text is often too large to include in an email using mailto. Yes. This needs to be done via email. The users have slow, occasional satellite email access and no other data connection to the interwebs. To make things worse, I cannot make them install anything. It is a difficult situation.

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• NULL-keys for key/value table

  - by user72185

  (Using Oracle) I have a table with key/value pairs like this: create table MESSAGE_INDEX ( KEY VARCHAR2(256) not null, VALUE VARCHAR2(4000) not null, MESSAGE_ID NUMBER not null ) I now want to find all the messages where key = 'someKey' and value is 'val1', 'val2' or 'val3' - OR value is null in which case there will be no entry in the table at all. This is to save space; there would be a large number of keys with null values if I stored them all. I think this works: SELECT message_id FROM message_index idx WHERE ((key = 'someKey' AND value IN ('val1', 'val2', 'val3')) OR NOT EXISTS (SELECT 1 FROM message_index WHERE key = 'someKey' AND idx.message_id = message_id)) But is is extremely slow. Takes 8 seconds with 700K records in message_index and there will be many more records and more search criteria when moving outside of my test environment. Primary key is key, value, message_id: add constraint PK_KEY_VALUE primary key (KEY, VALUE, MESSAGE_ID) And I added another index for message_id, to speed up searching for missing keys: create index IDX_MESSAGE_ID on MESSAGE_INDEX (MESSAGE_ID) I will be doing several of these key/value lookups in every search, not just one as shown above. So far I am doing them nested, where output id's of one level is the input to the next. E.g.: SELECT message_id from message_index WHERE (key/value compare) AND message_id IN ( SELECT ... and so on ) What can I do to speed this up?

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• How do I merge multiple PDB files ?

  - by blue.tuxedo

  We are currently using a single command line tool to build our product on both Windows and Linux. Si far its works nicely, allowing us to build out of source and with finer dependencies than what any of our previous build system allowed. This buys us great incremental and parallel build capabilities. To describe shortly the build process, we get the usual: .cpp -- cl.exe --> .obj and .pdb multiple .obj and .pdb -- cl.exe --> single .dll .lib .pdb multiple .obj and .pdb -- cl.exe --> single .exe .pdb The msvc C/C++ compiler supports it adequately. Recently the need to build a few static libraries emerged. From what we gathered, the process to build a static library is: multiple .cpp -- cl.exe --> multiple .obj and a single .pdb multiple .obj -- lib.exe --> a single .lib The single .pdb means that cl.exe should only be executed once for all the .cpp sources. This single execution means that we can't parallelize the build for this static library. This is really unfortunate. We investigated a bit further and according to the documentation (and the available command line options): cl.exe does not know how to build static libraries lib.exe does not know how to build .pdb files Does anybody know a way to merge multiple PDB files ? Are we doomed to have slow builds for static libraries ? How do tools like Incredibuild work around this issue ?

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• Fastest way to modify a decimal-keyed table in MySQL?

  - by javanix

  I am dealing with a MySQL table here that is keyed in a somewhat unfortunate way. Instead of using an auto increment table as a key, it uses a column of decimals to preserve order (presumably so its not too difficult to insert new rows while preserving a primary key and order). Before I go through and redo this table to something more sane, I need to figure out how to rekey it without breaking everything. What I would like to do is something that takes a list of doubles (the current keys) and outputs a list of integers (which can be cast down to doubles for rekeying). For example, input {1.00, 2.00, 2.50, 2.60, 3.00} would give output {1, 2, 3, 4, 5). Since this is a database, I also need to be able to update the rows nicely: UPDATE table SET `key`='3.00' WHERE `key`='2.50'; Can anyone think of a speedy algorithm to do this? My current thought is to read all of the doubles into a vector, take the size of the vector, and output a new vector with values from 1 => doubleVector.size. This seems pretty slow, since you wouldn't want to read every value into the vector if, for instance, only the last n/100 elements needed to be modified. I think there is probably something I can do in place, since only values after the first non-integer double need to be modified, but I can't for the life of me figure anything out that would let me update in place as well. For instance, setting 2.60 to 3.00 the first time you see 2.50 in the original key list would result in an error, since the key value 3.00 is already used for the table.

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• Need guidelines for optimizing WebGL performance by minimizing shader changes

  - by brainjam

  I'm trying to get an idea of the practicality of WebGL for rendering large architectural interior scenes, consisting of 100K's of triangles. These triangles are distributed over many objects, and there are many materials in the scene. On the other hand, there are no moving parts. And the materials tend to be fairly simple, mostly based on texture maps. There is a lot of texture map sharing .. for example all the chairs in scene will share a common map. There is also some multitexturing - up to three textures overlaid in a material. I've been doing a little experimentation and reading, and gather that frequently switching materials during a rendering pass will slow things down. For example, a scene with 200K triangles will have significant performance differences, depending on whether there are 10 or 1000 objects, assuming that each time an object is displayed a new material is set up. So it seems that if performance is important the scene should be sorted by materials so as to minimize material switching. What I'm looking for is guidelines on how to think of the overhead of various state changes, and where do I get the biggest bang for the buck. For example, what are the relative performance costs of, say, gl.useProgram(), gl.uniformMatrix4fv(), gl.drawElements() should I try to write ubershaders to minimize shader switching? should I try to aggregate geometry to minimize the number of gl.drawElements() calls I realize that mileage may vary depending on browser, OS, and graphics hardware. And I'm also not looking for heroic measures. Just some guidelines from people who have already had some experience in making scenes fast. I'll add that while I've had some experience with fixed-pipeline OpenGL programming in the past, I'm rather new to the WebGL/OpenGL ES 2.0 way of doing things.

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• Synchronizing screencasting (ffmpeg) and capturing from the webcam (OpenCV)

  - by lyuba

  As from my previous questions, I am trying to build a simple eye tracker. Decided to start from a Linux version (run Ubuntu). To complete this task one should organize screencasting and webcam capturing in such way that frames from both streams exactly match each other and there is the same number of frames in each of them totally. Screencasting fsp fully depends on the camera's fsp, so each time we get the image from the webcam we can potentially grab a screen frame and stay happy. However, all the tools for the fast screencasting, like ffmpeg, for example, return the .avi file as the result and require the fsp already known to be started. From the other side, tools like Java+Robot or ImageMagick seem to require around 20ms to return the .jpg screenshot, which is pretty slow for the task. But they may be requested right after each time the webcam frame is grabbed and provide the needed synchronization. So the sub-questions are: 1. Does the USD camera's frame rate vary during a single session? 2. Are there any tools which provide fast screencasting frame by frame? 3. Is there any way to make ffmpeg push a new frame to the .avi file only when program initiates this request? For my task I may either use C++ or Java. I am, actually, an interface designer, not the driver programmer, and this task seems to be pretty low-level. I would be grateful for any suggestion and tip!

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• Lazy Sequences that "Look Ahead" for Project Euler Problem 14

  - by ivar

  I'm trying to solve Project Euler Problem 14 in a lazy way. Unfortunately, I may be trying to do the impossible: create a lazy sequence that is both lazy, yet also somehow 'looks ahead' for values it hasn't computed yet. The non-lazy version I wrote to test correctness was: (defn chain-length [num] (loop [len 1 n num] (cond (= n 1) len (odd? n) (recur (inc len) (+ 1 (* 3 n))) true (recur (inc len) (/ n 2))))) Which works, but is really slow. Of course I could memoize that: (def memoized-chain (memoize (fn [n] (cond (= n 1) 1 (odd? n) (+ 1 (memoized-chain (+ 1 (* 3 n)))) true (+ 1 (memoized-chain (/ n 2))))))) However, what I really wanted to do was scratch my itch for understanding the limits of lazy sequences, and write a function like this: (def lazy-chain (letfn [(chain [n] (lazy-seq (cons (if (odd? n) (+ 1 (nth lazy-chain (dec (+ 1 (* 3 n))))) (+ 1 (nth lazy-chain (dec (/ n 2))))) (chain (+ n 1)))))] (chain 1))) Pulling elements from this will cause a stack overflow for n2, which is understandable if you think about why it needs to look 'into the future' at n=3 to know the value of the tenth element in the lazy list because (+ 1 (* 3 n)) = 10. Since lazy lists have much less overhead than memoization, I would like to know if this kind of thing is possible somehow via even more delayed evaluation or queuing?

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• 1k of Program Space, 64 bytes of RAM. Is 1 wire communication possible?

  - by Earlz

  (If your lazy see bottom for TL;DR) Hello, I am planning to build a new (prototype) project dealing with physical computing. Basically, I have wires. These wires all need to have their voltage read at the same time. More than a few hundred microseconds difference between the readings of each wire will completely screw it up. The Arduino takes about 114 microseconds. So the most I could read is 2 or 3 wires before the latency would skew the accuracy of the readings. So my plan is to have an Arduino as the "master" of an array of ATTinys. The arduino is pretty cramped for space, but it's a massive playground compared to the tinys. An ATTiny13A has 1k of flash ROM(program space), 64 bytes of RAM, and 64 bytes of (not-durable and slow) EEPROM. (I'm choosing this for price as well as size) The ATTinys in my system will not do much. Basically, all they will do is wait for a signal from the Master, and then read the voltage of 1 or 2 wires and store it in RAM(or possibly EEPROM if it's that cramped). And then send it to the Master using only 1 wire for data.(no room for more than that!). So far then, all I should have to do is implement trivial voltage reading code (using built in ADC). But this communication bit I'm worried about. Do you think a communication protocol(using just 1 wire!) could even be implemented in such constraints? TL;DR: In less than 1k of program space and 64 bytes of RAM(and 64 bytes of EEPROM) do you think it is possible to implement a 1 wire communication protocol? Would I need to drop to assembly to make it fit? I know that currently my Arduino programs linking to the Wiring library are over 8k, so I'm a bit concerned.

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• How to handle dates that repeat indefinitely

  - by Addsy

  I am implementing a fairly simple calendar on a website using PHP and MySQL. I want to be able to handle dates that repeat indefinitely and am not sure of the best way to do it. For a time limited repeating event it seems to make sense to just add each event within the timeframe into my db table and group them with some form of recursion id. But when there is no limit to how often the event repeats, is it better to a) put records in the db for a specific time frame (eg the next 2 years) and then periodically check and add new records as time goes by - The problem with this is that if someone is looking 3 years ahead, the event won't show up b) not actually have records for each event but instead when i check in my php code for events within a specified time period, calculate wether a repeated event will occur within this time period - The problem with this is that it means there isn't a specific record for each event which i can see being a pain when i then want to associate other info (attendance etc) with that event. It also seems like it might be a bit slow Has anyone tried either of these methods? If so how did it work out? Or is there some other ingenious crafty method i'm missing?

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• Save memory in Python. How to iterate over the lines and save them efficiently with a 2million line

  - by skyl

  I have a tab-separated data file with a little over 2 million lines and 19 columns. You can find it, in US.zip: http://download.geonames.org/export/dump/. I started to run the following but with for l in f.readlines(). I understand that just iterating over the file is supposed to be more efficient so I'm posting that below. Still, with this small optimization, I'm using 10% of my memory on the process and have only done about 3% of the records. It looks like, at this pace, it will run out of memory like it did before. Also, the function I have is very slow. Is there anything obvious I can do to speed it up? Would it help to del the objects with each pass of the for loop? def run(): from geonames.models import POI f = file('data/US.txt') for l in f: li = l.split('\t') try: p = POI() p.geonameid = li[0] p.name = li[1] p.asciiname = li[2] p.alternatenames = li[3] p.point = "POINT(%s %s)" % (li[5], li[4]) p.feature_class = li[6] p.feature_code = li[7] p.country_code = li[8] p.ccs2 = li[9] p.admin1_code = li[10] p.admin2_code = li[11] p.admin3_code = li[12] p.admin4_code = li[13] p.population = li[14] p.elevation = li[15] p.gtopo30 = li[16] p.timezone = li[17] p.modification_date = li[18] p.save() except IndexError: pass if __name__ == "__main__": run()

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