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• What OpenGL functions are not GPU accelerated?

  - by Xavier Ho

  I was shocked when I read this (from the OpenGL wiki): glTranslate, glRotate, glScale Are these hardware accelerated? No, there are no known GPUs that execute this. The driver computes the matrix on the CPU and uploads it to the GPU. All the other matrix operations are done on the CPU as well : glPushMatrix, glPopMatrix, glLoadIdentity, glFrustum, glOrtho. This is the reason why these functions are considered deprecated in GL 3.0. You should have your own math library, build your own matrix, upload your matrix to the shader. For a very, very long time I thought most of the OpenGL functions use the GPU to do computation. I'm not sure if this is a common misconception, but after a while of thinking, this makes sense. Old OpenGL functions (2.x and older) are really not suitable for real-world applications, due to too many state switches. This makes me realise that, possibly, many OpenGL functions do not use the GPU at all. So, the question is: Which OpenGL function calls don't use the GPU? I believe knowing the answer to the above question would help me become a better programmer with OpenGL. Please do share some of your insights.

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• How to display buttons after enterframe event is over in Corona?

  - by user1463542

  I am trying to display two buttons called countd_again and main_menu after my enterframe event is over. I can't see those buttons after enterframe event is over,though. Can you check my code,please? And also i want to add new addListener for the buttons using director and scene. module(..., package.seeall) function new() local localGroup = display.newGroup(); display.setStatusBar(display.HiddenStatusBar) local background = display.newImage("background.png") start=os.time() cnt=1 local countd_again = display.newImage("yeniden.png") countd_again.x=100 countd_again.y=100 countd_again.isVisible= false; countd_again.alpha=0; countd_again.scene="helloWorld"; local main_menu= display.newImage("anamenu.png") main_menu.x=100 main_menu.y=300 main_menu.isVisible=false; main_menu.alpha=0; main_menu.scene="helloWorld" -- listener function local function onEveryFrame( event ) if (cnt~=0) then cnt= 3-(os.time()-start) minute = math.floor(cnt/60) second=cnt%60 --print(minute,second) minTxt=display.newText(minute,50,50,nil,100) secTxt=display.newText(second,250,50,nil,100) transition.to(minTxt, {time=100, alpha=0}) transition.to(secTxt,{time=100, alpha=0}) else Runtime: removeEventListener("enterFrame",onEveryFrame) countd_again.isVisible=true; main_menu.isVisible=true; transition.to(countd_again,{time=500,alpha=1}); transition.to(main_menu,{time=500,alpha=1}); countd_again: addEventListener("touch", changeScene) main_menu: addEventListener("touch", changeScene) end end -- assign the above function as an "enterFrame" listener Runtime:addEventListener( "enterFrame", onEveryFrame ) function changeScene(e) if(e.phase=="ended") then director:changeScene(e.target.scene); end end countd_again: addEventListener("touch", changeScene) main_menu: addEventListener("touch", changeScene) localGroup: insert(countd_again) localGroup:insert(main_menu) localGroup:insert(background) return localGroup; end

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• Instrumenting a string

  - by George Polevoy

  Somewhere in C++ era i have crafted a library, which enabled string representation of the computation history. Having a math expression like: TScalar Compute(TScalar a, TScalar b, TScalar c) { return ( a + b ) * c; } I could render it's string representation: r = Compute(VerbalScalar("a", 1), VerbalScalar("b", 2), VerbalScalar("c", 3)); Assert.AreEqual(9, r.Value); Assert.AreEqual("(a+b)*c==(1+2)*3", r.History ); C++ operator overloading allowed for substitution of a simple type with a complex self-tracking entity with an internal tree representation of everything happening with the objects. Now i would like to have the same possibility for NET strings, only instead of variable names i would like to see a stack traces of all the places in code which affected a string. And i want it to work with existing code, and existing compiled assemblies. Also i want all this to hook into visual studio debugger, so i could set a breakpoint, and see everything that happened with a string. Which technology would allow this kind of things? I know it sound like an utopia, but I think visual studio code coverage tools actually do the same kind of job while instrumenting the assemblies.

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• Compilation problem in the standard x86_64 libraries

  - by user350282

  Hi everyone, I am having trouble compiling a program I have written. I have two different files with the same includes but only one generates the following error when compiled with g++ /usr/lib/gcc/x86_64-linux-gnu/4.4.1/../../../../lib/crt1.o: In function `_start': /build/buildd/eglibc-2.10.1/csu/../sysdeps/x86_64/elf/start.S:109: undefined reference to `main' collect2: ld returned 1 exit status The files I am including in my header are as follows: #include <google/sparse_hash_map> using google::sparse_hash_map; #include <ext/hash_map> #include <math.h> #include <iostream> #include <queue> #include <vector> #include <stack> using std::priority_queue; using std::stack; using std::vector; using __gnu_cxx::hash_map; using __gnu_cxx::hash; using namespace std; Searching the internet for those two lines hasn't resulted in anything to help me. I would be very grateful for any advice. Thank you

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• Which OpenGL functions are not GPU-accelerated?

  - by Xavier Ho

  I was shocked when I read this (from the OpenGL wiki): glTranslate, glRotate, glScale Are these hardware accelerated? No, there are no known GPUs that execute this. The driver computes the matrix on the CPU and uploads it to the GPU. All the other matrix operations are done on the CPU as well : glPushMatrix, glPopMatrix, glLoadIdentity, glFrustum, glOrtho. This is the reason why these functions are considered deprecated in GL 3.0. You should have your own math library, build your own matrix, upload your matrix to the shader. For a very, very long time I thought most of the OpenGL functions use the GPU to do computation. I'm not sure if this is a common misconception, but after a while of thinking, this makes sense. Old OpenGL functions (2.x and older) are really not suitable for real-world applications, due to too many state switches. This makes me realise that, possibly, many OpenGL functions do not use the GPU at all. So, the question is: Which OpenGL function calls don't use the GPU? I believe knowing the answer to the above question would help me become a better programmer with OpenGL. Please do share some of your insights.

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• C++ Matrix class hierachy

  - by bpw1621

  Should a matrix software library have a root class (e.g., MatrixBase) from which more specialized (or more constrained) matrix classes (e.g., SparseMatrix, UpperTriangluarMatrix, etc.) derive? If so, should the derived classes be derived publicly/protectively/privately? If not, should they be composed with a implementation class encapsulating common functionality and be otherwise unrelated? Something else? I was having a conversation about this with a software developer colleague (I am not per se) who mentioned that it is a common programming design mistake to derive a more restricted class from a more general one (e.g., he used the example of how it was not a good idea to derive a Circle class from an Ellipse class as similar to the matrix design issue) even when it is true that a SparseMatrix "IS A" MatrixBase. The interface presented by both the base and derived classes should be the same for basic operations; for specialized operations, a derived class would have additional functionality that might not be possible to implement for an arbitrary MatrixBase object. For example, we can compute the cholesky decomposition only for a PositiveDefiniteMatrix class object; however, multiplication by a scalar should work the same way for both the base and derived classes. Also, even if the underlying data storage implementation differs the operator()(int,int) should work as expected for any type of matrix class. I have started looking at a few open-source matrix libraries and it appears like this is kind of a mixed bag (or maybe I'm looking at a mixed bag of libraries). I am planning on helping out with a refactoring of a math library where this has been a point of contention and I'd like to have opinions (that is unless there really is an objective right answer to this question) as to what design philosophy would be best and what are the pros and cons to any reasonable approach.

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• Three most critical programming concepts

  - by Todd

  I know this has probably been asked in one form or fashion but I wanted to pose it once again within the context of my situation (and probably others here @ SO). I made a career change to Software Engineering some time ago without having an undergrad or grad degree in CS. I've supplemented my undergrad and grad studies in business with programming courses (VB, Java,C, C#) but never performed academic coursework in the other related disciplines (algorithms, design patterns, discrete math, etc.)...just mostly self-study. I know there are several of you who have either performed interviews and/or made hiring decisions. Given recent trends in demand, what would you say are the three most essential Comp Sci concepts that a developer should have a solid grasp of outside of language syntax? For example, I've seen blog posts of the "Absolute minimum X that every programmer must know" variety...that's what I'm looking for. Again if it's truly a redundancy please feel free to close; my feelings won't be hurt. (Closest ones I could find were http://stackoverflow.com/questions/164048/basic-programming-algorithmic-concepts- which was geared towards a true beginner, and http://stackoverflow.com/questions/648595/essential-areas-of-knowledge-which I didn't feel was concrete enough). Thanks in advance all! T.

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• Average over a timeframe with missing data

  - by BHare

  Assuming a table such as: UID Name Datetime Users 4 Room 4 2012-08-03 14:00:00 3 2 Room 2 2012-08-03 14:00:00 3 3 Room 3 2012-08-03 14:00:00 1 1 Room 1 2012-08-03 14:00:00 2 3 Room 3 2012-08-03 14:15:00 1 2 Room 2 2012-08-03 14:15:00 4 1 Room 1 2012-08-03 14:15:00 3 1 Room 1 2012-08-03 14:30:00 6 1 Room 1 2012-08-03 14:45:00 3 2 Room 2 2012-08-03 14:45:00 7 3 Room 3 2012-08-03 14:45:00 8 4 Room 4 2012-08-03 14:45:00 4 I wanted to get the average user count of each room (1,2,3,4) from the time 2PM to 3PM. The problem is that sometimes the room may not "check in" at the 15 minute interval time, so the assumption has to be made that the previous last known user count is still valid. For example the check-in's for 2012-08-03 14:15:00 room 4 never checked in, so it must be assumed that room 4 had 3 users at 2012-08-03 14:15:00 because that is what it had at 2012-08-03 14:00:00 This follows on through so that the average user count I am looking for is as follows: Room 1: (2 + 3 + 6 + 3) / 4 = 3.5 Room 2: (3 + 4 + 4 + 7) / 4 = 4.5 Room 3: (1 + 1 + 1 + 8) / 4 = 2.75 Room 4: (3 + 3 + 3 + 4) / 4 = 3.25 where # is the assumed number based on the previous known check-in. I am wondering if it's possible to so this with SQL alone? if not I am curious of a ingenious PHP solution that isn't just bruteforce math, as such as my quick inaccurate pseudo code: foreach ($rooms_id_array as $room_id) { $SQL = "SELECT * FROM `table` WHERE (`UID` == $room_id && `Datetime` >= 2012-08-03 14:00:00 && `Datetime` <= 2012-08-03 15:00:00)"; $result = query($SQL); if ( count($result) < 4 ) { // go through each date and find what is missing, and then go to previous date and use that instead } else { foreach ($result) $sum += $result; $avg = $sum / 4; } }

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• Cannot make a static reference to the non-static type MyRunnable

  - by kaiwii ho

  Here is the whole code : import java.util.ArrayList; public class Test{ ThreadLocal<ArrayList<E>>arraylist=new ThreadLocal<ArrayList<E>>(){ @Override protected ArrayList<E> initialValue() { // TODO Auto-generated method stub //return super.initialValue(); ArrayList<E>arraylist=new ArrayList<E>(); for(int i=0;i<=20;i++) arraylist.add((E) new Integer(i)); return arraylist; } }; class MyRunnable implements Runnable{ private Test mytest; public MyRunnable(Test test){ mytest=test; // TODO Auto-generated constructor stub } @Override public void run() { System.out.println("before"+mytest.arraylist.toString()); ArrayList<E>myarraylist=(ArrayList<E>) mytest.arraylist.get(); myarraylist.add((E) new Double(Math.random())); mytest.arraylist.set(myarraylist); System.out.println("after"+mytest.arraylist.toString()); } // TODO Auto-generated method stub } public static void main(String[] args){ Test test=new Test<Double>(); System.out.println(test.arraylist.toString()); new Thread(new MyRunnable(test)).start(); new Thread(new MyRunnable(test)).start(); System.out.println(arraylist.toString()); } } my questions are: 1\ why the new Thread(new MyRunnable(test)).start(); cause the error: Cannot make a static reference to the non-static type MyRunnable ? 2\ what is the static reference refer to right here? thx in advanced

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• C++ program crashes at runtime

  - by qwerty

  Hello, I have this simple c++ program #include <cstdlib> #include <iostream> #include <math.h> #include <stdlib.h> #include <time.h> #include <vector> using namespace std; int aleator(int n) { return (rand()%n)+1; } int main() { int r; int indexes[100]={0}; // const int size=100; //int a[size]; std::vector<int>v; srand(time(0)); for (int i=0;i<25;i++) { int index = aleator(100); if (indexes[index] != 0) { // try again i--; continue; } indexes[index] = 1; cout << v[index] ; } cout<<" "<<endl; system("pause"); return 0; } But at runtime it crashes, so i got that error with 'Send error report' and 'Don't send'. What i'm doing wrong? Thanks!

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• What to call factory-like (java) methods used with immutable objects

  - by StaxMan

  When creating classes for "immutable objects" immutable meaning that state of instances can not be changed; all fields assigned in constructor) in Java (and similar languages), it is sometimes useful to still allow creation of modified instances. That is, using an instance as base, and creating a new instance that differs by just one property value; other values coming from the base instance. To give a simple example, one could have class like: public class Circle { final double x, y; // location final double radius; public Circle(double x, double y, double r) { this.x = x; this.y = y; this.r = r; } // method for creating a new instance, moved in x-axis by specified amount public Circle withOffset(double deltaX) { return new Circle(x+deltaX, y, radius); } } So: what should method "withOffset" be called? (note: NOT what its name ought to be -- but what is this class of methods called). Technically it is kind of a factory method, but somehow that does not seem quite right to me, since often factories are just given basic properties (and are either static methods, or are not members of the result type but factory type). So I am guessing there should be a better term for such methods. Since these methods can be used to implement "fluent interface", maybe they could be "fluent factory methods"? Better suggestions? EDIT: as suggested by one of answers, java.math.BigDecimal is a good example with its 'add', 'subtract' (etc) methods. Also: I noticed that there's this question (by Jon Skeet no less) that is sort of related (although it asks about specific name for method)

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• C++ Suppress Automatic Initialization and Destruction

  - by Travis G

  How does one suppress the automatic initialization and destruction of a type? While it is wonderful that T buffer[100] automatically initializes all the elements of buffer, and destroys them when they fall out of scope, this is not the behavior I want. #include <iostream> static int created = 0, destroyed = 0; struct S { S() { ++created; } ~S() { ++destroyed; } }; template <typename T, size_t KCount> class Array { private: T m_buffer[KCount]; public: Array() { // some way to suppress the automatic initialization of m_buffer } ~Array() { // some way to suppress the automatic destruction of m_buffer } }; int main() { { Array<S, 100> arr; } std::cout << "Created:\t" << created << std::endl; std::cout << "Destroyed:\t" << destroyed << std::endl; return 0; } The output of this program is: Created: 100 Destroyed: 100 I would like it to be: Created: 0 Destroyed: 0 My only idea is to make m_buffer some trivially constructed and destructed type like char and then rely on operator[] to wrap the pointer math for me, although this seems like a horribly hacked solution. Another solution would be to use malloc and free, but that gives a level of indirection that I do not want.

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• jquery ajax result with a wrong format

  - by ???

  I am facing a problem which is the result processed by AJAX, this situation is I would like to pass the result (from AJAX) 'f f f f \'' into get_option(''), I don't know why it become like this:- <li \'');="" f="" onclick="get_option('f" class="option normal_size"> <a href="javascript:void(0);">f f f f \'</a> </li> What I want is :- <li onclick="get_option('f f f f\'')" class="option normal_size"> <a href="javascript:void(0);">f f f f \'</a> </li> I guess the problem might be the space, but I don't know how to solve it, can anyone do me a favour? my AJAX coding is:- .ajax({ url:'inc_board_saving.php?board_title_input='+board_title_input_encode+'&cate_selected='+cate_selected_input_encode+'&cate_setting_selected='+cate_setting_selected, type:'GET', data:"nums="+Math.random()*1235, success: function(data){ try{ var content=""; var obj = eval('('+data+')'); for (var i=0;i<obj.length;i++){ content += "<li class='option normal_size' onclick=get_option('"+obj[i].board_name_encode+"');><a href='javascript:void(0);'>"+obj[i].board_name+"</a></li>"; } }catch(e){ return; } } }); Result:- [{"board_id":"66","board_name":"f f f f '","board_name_encode":"f f f f \'"},{"board_id":"65","board_name":"t t t t t","board_name_encode":"t t t t t"},{"board_id":"64","board_name":"yy yyy yy","board_name_encode":"yy yyy yy"}] Thanks all

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• Python parsing error message functions

  - by user1716168

  The code below was created by me with the help of many SO veterans: The code takes an entered math expression and splits it into operators and operands for later use. I have created two functions, the parsing function that splits, and the error function. I am having problems with the error function because it won't display my error messages and I feel the function is being ignored when the code runs. An error should print if an expression such as this is entered: 3//3+4,etc. where there are two operators together, or there are more than two operators in the expression overall, but the error messages dont print. My code is below: def errors(): numExtrapolation,opExtrapolation=parse(expression) if (len(numExtrapolation) == 3) and (len(opExtrapolation) !=2): print("Bad1") if (len(numExtrapolation) ==2) and (len(opExtrapolation) !=1): print("Bad2") def parse(expression): operators= set("*/+-") opExtrapolate= [] numExtrapolate= [] buff=[] for i in expression: if i in operators: numExtrapolate.append(''.join(buff)) buff= [] opExtrapolate.append(i) opExtrapolation=opExtrapolate else: buff.append(i) numExtrapolate.append(''.join(buff)) numExtrapolation=numExtrapolate #just some debugging print statements print(numExtrapolation) print("z:", len(opExtrapolation)) return numExtrapolation, opExtrapolation errors() Any help would be appreciated. Please don't introduce new code that is any more advanced than the code already here. I am looking for a solution to my problem... not large new code segments. Thanks.

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• Problem finding the difference in days between two dates

  - by James

  I have been using a tidy little routine that I found here to calculate the difference in days between two dates in AS3. I am getting some strange results and I am wondering if any of you inter-codal-mega-lords can shed some light? Why is Q1 of 2010 coming up one day short, when in all other cases the routine is performing fine? Many thanks in advance to anyone who can help! function countDays( startDate:Date, endDate:Date ):int { var oneDay:int = 24*60*60*1000; // hours*minutes*seconds*milliseconds var diffDays:int = Math.abs((startDate.getTime() - endDate.getTime())/(oneDay)); return diffDays; } countDays( new Date( 2010, 00, 01 ), new Date( 2011, 00, 01 ) ); // returns 365, which is correct countDays( new Date( 2010, 00, 01 ), new Date( 2010, 03, 01 ) ); // returns 89, which is 1 day short countDays( new Date( 2010, 03, 01 ), new Date( 2010, 06, 01 ) ); // returns 91, which is correct countDays( new Date( 2010, 06, 01 ), new Date( 2010, 09, 01 ) ); // returns 92, which is correct countDays( new Date( 2010, 09, 01 ), new Date( 2011, 00, 01 ) ); // returns 92, which is correct

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• Algorithm to pick values from set to match target value?

  - by CSharperWithJava

  I have a fixed array of constant integer values about 300 items long (Set A). The goal of the algorithm is to pick two numbers (X and Y) from this array that fit several criteria based on input R. Formal requirement: Pick values X and Y from set A such that the expression X*Y/(X+Y) is as close as possible to R. That's all there is to it. I need a simple algorithm that will do that. Additional info: The Set A can be ordered or stored in any way, it will be hard coded eventually. Also, with a little bit of math, it can be shown that the best Y for a given X is the closest value in Set A to the expression X*R/(X-R). Also, X and Y will always be greater than R From this, I get a simple iterative algorithm that works ok: int minX = 100000000; int minY = 100000000; foreach X in A if(X<=R) continue; else Y=X*R/(X-R) Y=FindNearestIn(A, Y);//do search to find closest useable Y value in A if( X*Y/(X+Y) < minX*minY/(minX+minY) ) then minX = X; minY = Y; end end end I'm looking for a slightly more elegant approach than this brute force method. Suggestions?

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• F# How to tokenise user input: separating numbers, units, words?

  - by David White

  I am fairly new to F#, but have spent the last few weeks reading reference materials. I wish to process a user-supplied input string, identifying and separating the constituent elements. For example, for this input: XYZ Hotel: 6 nights at 220EUR / night plus 17.5% tax the output should resemble something like a list of tuples: [ ("XYZ", Word); ("Hotel:", Word); ("6", Number); ("nights", Word); ("at", Operator); ("220", Number); ("EUR", CurrencyCode); ("/", Operator); ("night", Word); ("plus", Operator); ("17.5", Number); ("%", PerCent); ("tax", Word) ] Since I'm dealing with user input, it could be anything. Thus, expecting users to comply with a grammar is out of the question. I want to identify the numbers (could be integers, floats, negative...), the units of measure (optional, but could include SI or Imperial physical units, currency codes, counts such as "night/s" in my example), mathematical operators (as math symbols or as words including "at" "per", "of", "discount", etc), and all other words. I have the impression that I should use active pattern matching -- is that correct? -- but I'm not exactly sure how to start. Any pointers to appropriate reference material or similar examples would be great.

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• Using "from __future__ import division" in my program, but it isn't loaded with my program

  - by Sara Fauzia

  I wrote the following program in Python 2 to do Newton's method computations for my math problem set, and while it works perfectly, for reasons unbeknownst to me, when I initially load it in ipython with %run -i NewtonsMethodMultivariate.py, the Python 3 division is not imported. I know this because after I load my Python program, entering x**(3/4) gives "1". After manually importing the new division, then x**(3/4) remains x**(3/4), as expected. Why is this? # coding: utf-8 from __future__ import division from sympy import symbols, Matrix, zeros x, y = symbols('x y') X = Matrix([[x],[y]]) tol = 1e-3 def roots(h,a): def F(s): return h.subs({x: s[0,0], y: s[1,0]}) def D(s): return h.jacobian(X).subs({x: s[0,0], y: s[1,0]}) if F(a) == zeros(2)[:,0]: return a else: while (F(a)).norm() > tol: a = a - ((D(a))**(-1))*F(a) print a.evalf(10) I would use Python 3 to avoid this issue, but my Linux distribution only ships SymPy for Python 2. Thanks to the help anyone can provide. Also, in case anyone was wondering, I haven't yet generalized this script for nxn Jacobians, and only had to deal with 2x2 in my problem set. Additionally, I'm slicing the 2x2 zero matrix instead of using the command zeros(2,1) because SymPy 0.7.1, installed on my machine, complains that "zeros() takes exactly one argument", though the wiki suggests otherwise. Maybe this command is only for the git version.

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• [Ruby] Modifying object inside a loop doesn't change object outside of the loop?

  - by Jergason

  I am having problems with modifying objects inside blocks and not getting the expected values outside the blocks. This chunk of code is supposed to transform a bunch of points in 3d space, calculate a score (the rmsd or root mean squared deviation), and store both the score and the set of points that produced that score if it is lower than the current lowest score. At the end, I want to print out the best bunch of points. first = get_transformed_points(ARGV[0]) second = get_transformed_points(ARGV[1]) best_rmsd = first.rmsd(second) best_points = second #transform the points around x, y, and z and get the rmsd. If the new points # have a smaller rmsd, store them. ROTATION = 30 #rotate by ROTATION degrees num_rotations = 360/ROTATION radians = ROTATION * (Math::PI/180) num_rotations.times do |i| second = second * x_rotate num_rotations.times do |j| second = second * y_rotate num_rotations.times do |k| second = second * z_rotate rmsd = first.rmsd(second) if rmsd < best_rmsd then best_points = second best_rmsd = rmsd end end end end File.open("#{ARGV[1]}.out", "w") {|f| f.write(best_points.to_s)} I can print out the points that are getting stored inside the block, and they are getting transformed and stored correctly. However, when I write out the points to a file at the end, they are the same as the initial set of points. Somehow the best_points = second chunk doesn't seem to be doing anything outside of the block. It seems like there are some scoping rules that I don't understand here. I had thought that since I declared and defined best_points above, outside of the blocks, that it would be updated inside the blocks. However, it seems that when the blocks end, it somehow reverts back to the original value. Any ideas how to fix this? Is this a problem with blocks specifically?

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• Deterministic floating point and .NET

  - by code2code

  How can I guarantee that floating point calculations in a .NET application (say in C#) always produce the same bit-exact result? Especially when using different versions of .NET and running on different platforms (x86 vs x86_64). Inaccuracies of floating point operations do not matter. In Java I'd use strictfp. In C/C++ and other low level languages this problem is essentially solved by accessing the FPU / SSE control registers but that's probably not possible in .NET. Even with control of the FPU control register the JIT of .NET will generate different code on different platforms. Something like HotSpot would be even worse in this case... Why do I need it? I'm thinking about writing a real-time strategy (RTS) game which heavily depends on fast floating point math together with a lock stepped simulation. Essentially I will only transmit user input across the network. This also applies to other games which implement replays by storing the user input. Not an option are: decimals (too slow) fixed point values (too slow and cumbersome when using sqrt, sin, cos, tan, atan...) update state across the network like an FPS: Sending position information for hundreds or a few thousand units is not an option Any ideas?

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• Flash AS3: How to Make scroll bar react to dynamic textfield movement?

  - by HeroicNate

  I've been looking for a tutorial and answer to this for a while but can't find what I'm looking for. I am loading html text into a dynamic textfield, and I have a scrollbar controlling the scroll using the code below. What I want to do is also add scroll up/down buttons and have the scroll bar move in relation to the text scroll. I was just going to use "tracklistingtext.scrollV -- " for the scroll buttons, but right now the scroll bar doesn't recognize the text movement. What do I need to do to get the scroll bar to listen to the text scroll position? var listTextreq:URLRequest=new URLRequest("tracklist.txt"); var listTextLoader:URLLoader = new URLLoader(); var bounds:Rectangle=new Rectangle(scrollMC.x,scrollMC.y,0,300); var scrolling:Boolean=false; function fileLoaded(event:Event):void { tracklistingtext.htmlText=listTextLoader.data; tracklistingtext.multiline=true; tracklistingtext.wordWrap=true; scrollMC.addEventListener(MouseEvent.MOUSE_DOWN, startScroll); stage.addEventListener(MouseEvent.MOUSE_UP, stopScroll); addEventListener (Event.ENTER_FRAME, enterHandler); } listTextLoader.addEventListener(Event.COMPLETE, fileLoaded); listTextLoader.load(listTextreq); function startScroll(e:Event):void { scrolling=true; scrollMC.startDrag(false,bounds); } function stopScroll(e:Event):void { scrolling=false; scrollMC.stopDrag(); } function enterHandler (e:Event):void { if (scrolling == true) { tracklistingtext.scrollV = Math.round(((scrollMC.y - bounds.y)/300)*tracklistingtext.maxScrollV); } } Any help is greatly appreciated.

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• JavaScript: why `null == 0` is false?

  - by lemonedo

  I had to write a routine that increments the value of a variable by 1 if it is a number, or assigns 0 to the variable if it is not a number. The variable can be incremented by the expression, or be assigned null. No other write access to the variable is allowed. So, the variable can be in three states: it is 0, a positive integer, or null. My first implementation was: v >= 0 ? v += 1 : v = 0 (Yes, I admit that v === null ? v = 0 : v += 1 is the exact solution, but I wanted to be concise then.) It failed since null >= 0 is true. I was confused, since if a value is not a number, an numeric expression involving it must be false always. Then I found that null is like 0, since null + 1 == 1, 1 / null == Infinity, Math.pow(2.718281828, null) == 1, ... Strangely enough, however, null == 0 is evaluated to false. I guess null is the only value that makes the following expression false: (v == 0) === (v >= 0 && v <= 0) So why null is so special in JavaScript?

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• Time complexity of a powerset generating function

  - by Lirik

  I'm trying to figure out the time complexity of a function that I wrote (it generates a power set for a given string): public static HashSet<string> GeneratePowerSet(string input) { HashSet<string> powerSet = new HashSet<string>(); if (string.IsNullOrEmpty(input)) return powerSet; int powSetSize = (int)Math.Pow(2.0, (double)input.Length); // Start at 1 to skip the empty string case for (int i = 1; i < powSetSize; i++) { string str = Convert.ToString(i, 2); string pset = str; for (int k = str.Length; k < input.Length; k++) { pset = "0" + pset; } string set = string.Empty; for (int j = 0; j < pset.Length; j++) { if (pset[j] == '1') { set = string.Concat(set, input[j].ToString()); } } powerSet.Add(set); } return powerSet; } So my attempt is this: let the size of the input string be n in the outer for loop, must iterate 2^n times (because the set size is 2^n). in the inner for loop, we must iterate 2*n times (at worst). 1. So Big-O would be O((2^n)*n) (since we drop the constant 2)... is that correct? And n*(2^n) is worse than n^2. if n = 4 then (4*(2^4)) = 64 (4^2) = 16 if n = 100 then (10*(2^10)) = 10240 (10^2) = 100 2. Is there a faster way to generate a power set, or is this about optimal?

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• Attempt to use a while loop for the 'next' arg of a for loop generates #arg error

  - by JerryK

  Am attempting to teach myself to program using Tcl. The task i've set myself to motivate my learning of Tcl is to solve the 8 queens problem. My approach to creating a program is to successively 'prototype' a solution. I have asked an earlier question related to the correctly laying out the nested for loops and received a helpful answer. To my dismay I find that the next development of my code creates the same interpreter error : "wrong # args" I have been careful to have an open brace at the end of the line preceding the while loop command. I've also tried to put the arguments of the whileloop in braces. This generates a different error. I have sincerely tried to understand the Tcl syntax man page - not too successfully - suggested by the answerer of my earlier question. Here is the code set allowd 1 set notallowd 0 for {set r1p 1} {$r1p <= 8} {incr r1p } { puts "1st row q placed at $r1p" ;# re-initialize r2 'free for q placemnt' array after every change of r1 q pos: for {set i 1 } {$i <= 8} {incr i} { set r2($i) $allowd } for { set r2($r1p) $notallowd ; set r2([expr $r1p-1]) $notallowd ; set r2([expr $r1p+1]) $notallowd ; set r2p 1} {$r2p <= 8} { ;# 'next' arg of r2 forloop will be a whileloop : while r2($r2p)== $notallowd incr r2p } { puts "2nd row q placed at $r2p" ;# end of 'commnd' arg of r2 forloop } } Where am I going wrong? EDIT : to provide clear reply @slebetman As stated in my text, I did brace the arguments of the whileloop (indeed that was how i first wrote the code) below is exactly the layout of the r2 forloop tried: for { set r2($r1p) $notallowd ; set r2([expr $r1p-1]) $notallowd ; set r2([expr $r1p+1]) $notallowd ; set r2p 1} {$r2p <= 8} { ;# 'next' arg of r2 forloop will be a whileloop : while { r2($r2p)== $notallowd } { incr r2p } } { puts "2nd row q placed at $r2p" ;# end of 'commnd' arg of r2 forloop } but this generates the fatal interpreter error : "unknown math function 'r2' while compiling while { r2($r2p .... "

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• Computation overhead in C# - Using getters/setters vs. modifying arrays directly and casting speeds

  - by Jeffrey Kern

  I was going to write a long-winded post, but I'll boil it down here: I'm trying to emulate the graphical old-school style of the NES via XNA. However, my FPS is SLOW, trying to modify 65K pixels per frame. If I just loop through all 65K pixels and set them to some arbitrary color, I get 64FPS. The code I made to look-up what colors should be placed where, I get 1FPS. I think it is because of my object-orented code. Right now, I have things divided into about six classes, with getters/setters. I'm guessing that I'm at least calling 360K getters per frame, which I think is a lot of overhead. Each class contains either/and-or 1D or 2D arrays containing custom enumerations, int, Color, or Vector2D, bytes. What if I combined all of the classes into just one, and accessed the contents of each array directly? The code would look a mess, and ditch the concepts of object-oriented coding, but the speed might be much faster. I'm also not concerned about access violations, as any attempts to get/set the data in the arrays will done in blocks. E.g., all writing to arrays will take place before any data is accessed from them. As for casting, I stated that I'm using custom enumerations, int, Color, and Vector2D, bytes. Which data types are fastest to use and access in the .net Framework, XNA, XBox, C#? I think that constant casting might be a cause of slowdown here. Also, instead of using math to figure out which indexes data should be placed in, I've used precomputed lookup tables so I don't have to use constant multiplication, addition, subtraction, division per frame. :)

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