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  • How to write reusable code in node.js

    - by lortabac
    I am trying to understand how to design node.js applications, but it seems there is something I can't grasp about asynchronous programming. Let's say my application needs to access a database. In a synchronous environment I would implement a data access class with a read() method, returning an associative array. In node.js, because code is executed asynchronously, this method can't return a value, so, after execution, it will have to "do" something as a side effect. It will then contain some code which does something else than just reading data. Let's suppose I want to call this method multiple times, each time with a different success callback. Since the callback is included in the method itself, I can't find a clean way to do this without either duplicating the method or specifying all possible callbacks in a long switch statement. What is the proper way to handle this problem? Am I approaching it the wrong way?

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  • Extreme Optimization – Numerical Algorithm Support

    - by JoshReuben
    Function Delegates Many calculations involve the repeated evaluation of one or more user-supplied functions eg Numerical integration. The EO MathLib provides delegate types for common function signatures and the FunctionFactory class can generate new delegates from existing ones. RealFunction delegate - takes one Double parameter – can encapsulate most of the static methods of the System.Math class, as well as the classes in the Extreme.Mathematics.SpecialFunctions namespace: var sin = new RealFunction(Math.Sin); var result = sin(1); BivariateRealFunction delegate - takes two Double parameters: var atan2 = new BivariateRealFunction (Math.Atan2); var result = atan2(1, 2); TrivariateRealFunction delegate – represents a function takes three Double arguments ParameterizedRealFunction delegate - represents a function taking one Integer and one Double argument that returns a real number. The Pow method implements such a function, but the arguments need order re-arrangement: static double Power(int exponent, double x) { return ElementaryFunctions.Pow(x, exponent); } ... var power = new ParameterizedRealFunction(Power); var result = power(6, 3.2); A ComplexFunction delegate - represents a function that takes an Extreme.Mathematics.DoubleComplex argument and also returns a complex number. MultivariateRealFunction delegate - represents a function that takes an Extreme.Mathematics.LinearAlgebra.Vector argument and returns a real number. MultivariateVectorFunction delegate - represents a function that takes a Vector argument and returns a Vector. FastMultivariateVectorFunction delegate - represents a function that takes an input Vector argument and an output Matrix argument – avoiding object construction  The FunctionFactory class RealFromBivariateRealFunction and RealFromParameterizedRealFunction helper methods - transform BivariateRealFunction or a ParameterizedRealFunction into a RealFunction delegate by fixing one of the arguments, and treating this as a new function of a single argument. var tenthPower = FunctionFactory.RealFromParameterizedRealFunction(power, 10); var result = tenthPower(x); Note: There is no direct way to do this programmatically in C# - in F# you have partial value functions where you supply a subset of the arguments (as a travelling closure) that the function expects. When you omit arguments, F# generates a new function that holds onto/remembers the arguments you passed in and "waits" for the other parameters to be supplied. let sumVals x y = x + y     let sumX = sumVals 10     // Note: no 2nd param supplied.     // sumX is a new function generated from partially applied sumVals.     // ie "sumX is a partial application of sumVals." let sum = sumX 20     // Invokes sumX, passing in expected int (parameter y from original)  val sumVals : int -> int -> int val sumX : (int -> int) val sum : int = 30 RealFunctionsToVectorFunction and RealFunctionsToFastVectorFunction helper methods - combines an array of delegates returning a real number or a vector into vector or matrix functions. The resulting vector function returns a vector whose components are the function values of the delegates in the array. var funcVector = FunctionFactory.RealFunctionsToVectorFunction(     new MultivariateRealFunction(myFunc1),     new MultivariateRealFunction(myFunc2));  The IterativeAlgorithm<T> abstract base class Iterative algorithms are common in numerical computing - a method is executed repeatedly until a certain condition is reached, approximating the result of a calculation with increasing accuracy until a certain threshold is reached. If the desired accuracy is achieved, the algorithm is said to converge. This base class is derived by many classes in the Extreme.Mathematics.EquationSolvers and Extreme.Mathematics.Optimization namespaces, as well as the ManagedIterativeAlgorithm class which contains a driver method that manages the iteration process.  The ConvergenceTest abstract base class This class is used to specify algorithm Termination , convergence and results - calculates an estimate for the error, and signals termination of the algorithm when the error is below a specified tolerance. Termination Criteria - specify the success condition as the difference between some quantity and its actual value is within a certain tolerance – 2 ways: absolute error - difference between the result and the actual value. relative error is the difference between the result and the actual value relative to the size of the result. Tolerance property - specify trade-off between accuracy and execution time. The lower the tolerance, the longer it will take for the algorithm to obtain a result within that tolerance. Most algorithms in the EO NumLib have a default value of MachineConstants.SqrtEpsilon - gives slightly less than 8 digits of accuracy. ConvergenceCriterion property - specify under what condition the algorithm is assumed to converge. Using the ConvergenceCriterion enum: WithinAbsoluteTolerance / WithinRelativeTolerance / WithinAnyTolerance / NumberOfIterations Active property - selectively ignore certain convergence tests Error property - returns the estimated error after a run MaxIterations / MaxEvaluations properties - Other Termination Criteria - If the algorithm cannot achieve the desired accuracy, the algorithm still has to end – according to an absolute boundary. Status property - indicates how the algorithm terminated - the AlgorithmStatus enum values:NoResult / Busy / Converged (ended normally - The desired accuracy has been achieved) / IterationLimitExceeded / EvaluationLimitExceeded / RoundOffError / BadFunction / Divergent / ConvergedToFalseSolution. After the iteration terminates, the Status should be inspected to verify that the algorithm terminated normally. Alternatively, you can set the ThrowExceptionOnFailure to true. Result property - returns the result of the algorithm. This property contains the best available estimate, even if the desired accuracy was not obtained. IterationsNeeded / EvaluationsNeeded properties - returns the number of iterations required to obtain the result, number of function evaluations.  Concrete Types of Convergence Test classes SimpleConvergenceTest class - test if a value is close to zero or very small compared to another value. VectorConvergenceTest class - test convergence of vectors. This class has two additional properties. The Norm property specifies which norm is to be used when calculating the size of the vector - the VectorConvergenceNorm enum values: EuclidianNorm / Maximum / SumOfAbsoluteValues. The ErrorMeasure property specifies how the error is to be measured – VectorConvergenceErrorMeasure enum values: Norm / Componentwise ConvergenceTestCollection class - represent a combination of tests. The Quantifier property is a ConvergenceTestQuantifier enum that specifies how the tests in the collection are to be combined: Any / All  The AlgorithmHelper Class inherits from IterativeAlgorithm<T> and exposes two methods for convergence testing. IsValueWithinTolerance<T> method - determines whether a value is close to another value to within an algorithm's requested tolerance. IsIntervalWithinTolerance<T> method - determines whether an interval is within an algorithm's requested tolerance.

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  • Ajax does not send the data to my php file [migrated]

    - by Mert METIN
    I try to send my data to php file but does not work. This my ajax file var artistIds = new Array(); $(".p16 input:checked").each(function(){ artistIds.push($(this).attr('id')); }); $.post('/json/crewonly/deleteDataAjax2', { artistIds: artistIds },function(response){ if(response == 'ok') alert('dolu'); elseif (response == 'error') alert('bos'); }); and this is my php public function deleteDataAjax2() { extract($_POST); if (isset($artistIds)) $this->sendJSONResponse('ok'); else $this->sendJSONResponse('error'); } However, my artistIds in php side is null. Why ?

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  • DeskLights Turns Desk Surface Into Giant Multi-Purpose Notifier

    - by Jason Fitzpatrick
    We’ve seen desks with LEDs under frosted glass before, but this is the first desk we’ve seen where the LEDs serve as a sophisticated notification system. Check out the video above to see desk, designed by Michael LaGrasta, in action. The secret sauce is an array of LED modules, linked to an Arduino board, which is in turn running a tiny web server. Hit up the link below for the full build guide. DeskLights 2.0 [via IKEAHackers] Hack Your Kindle for Easy Font Customization HTG Explains: What Is RSS and How Can I Benefit From Using It? HTG Explains: Why You Only Have to Wipe a Disk Once to Erase It

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  • Powder games: how do they work?

    - by Marc Müller
    Hey guys, I recently found these two gems: http://powdertoy.co.uk/ http://dan-ball.jp/en/javagame/dust/ My question is: How are the physics with so many elements efficiently handled? Am I just severely underestimating modern computing power or is it possible to 'just' have a two-dimensional array, each cell of which describes what is placed at the according position and simulate each cell in every step. Or are there more complex things being done like summarising large areas of the same kind into a single data set and separating said set as needed? Are there any open-source games like this I could look at?

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  • Will having many timers affect my game performance?

    - by iQue
    I'm making a game for android, and earlier today I was trying to add some cool stuff to my game. The problem is this thing needs like 5 timers. I build my timers like this: timer += deltaTime; if(timer >= 2.0f){ doStuff; timer -= 2.0f; } // this timers gets stuff done every 2 secs Will having to many timers like this, getting checked every frame, screw up my games performance? The effect I wanted to add was a crosshair every 2 sec, then remove it after 2 sec and do a timed animation. So an array of crosshairs dependent on a bunch of timers to be exact. This caused my game to shut down when used, so thats why Im wondering if using that many timers causes my game to flip out.

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  • Why doesn't the Visual Studio C compiler like this? [migrated]

    - by justin
    The following code compiles fine on Linux using gcc -std=c99 but gets the following errors on the Visual Studio 2010 C compiler: Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 16.00.40219.01 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. fib.c fib.c(42) : error C2057: expected constant expression fib.c(42) : error C2466: cannot allocate an array of constant size 0 fib.c(42) : error C2133: 'num' : unknown size The user inputs the amount of Fibonacci numbers to generate. I'm curious as to why the Microsoft compiler doesn't like this code. http://pastebin.com/z0uEa2zw

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  • What is the best way to construct a "remove multiple items" area (ASP.NET VB) [on hold]

    - by Darkcat Studios
    Lets say for example I have a (variable length) 2 dimensional array of product names and their unique product codes. I can display this list in a datagrid, table etc. (Imagine this as a standard shopping basket type scenario) What I need to do is be able to tick multiple items (?) , then on clicking a submit button, fire an action. The bit im struggling with is how do i: A: programatically display asp:checkboxes for each item (and give them a unique ID) B: know which are ticked on firing the final action (not sure if this question is best suited to the main stack but theres so much activity on there that questions just get lost now!)

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  • The best tile based level design [on hold]

    - by ReallyGoodPie
    My current method for tile based levels is to put everything in an array like the following: grass = g sky = s house = h ... """ ["SSSSSSSSSSSSSSSSSSSSSSSSSSSSSS"], ["SSSSSSSSSSSSSSSSSSSSSSSSSSSSSS"], ["HHHHHHHHHHHHHHSSSSSSSSSSSSSSSS"], ["GGGGGGGGGGGGGGGGGGGGGGGGGGGGGG"], """ I would then run a for loop to pass these on to a sprite class, bliting the images to the screen. This is what I'd generally do in pygame when I am creating levels for a tile based RPG's. However, as I've gone on, I have added allot more sprites and image and it is seriously becoming more and more confusing to work with this and allot of mistakes are being made. What is the best alternative or other methods for doing this?

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  • Networking Client Server Packet logic (How they communicate)

    - by Trixmix
    I want to know what is the logic behind server client communication through packets for a real time game. for example the server sends x packets then the client receives x packets and processes them.. Basically what is the process to keep the client and server in sync and able to receive and send packets. more in depth example of what I want to know: client step 1 wait for a packet step 2 read x packets step 3 process x packets step 4 send x packets and so on... I need to know the very basic outline of the communication. Big questions are: 1) do I send and read packets all at one time? i.e for loop though the incoming packets array list and read them all or one every server loop or what... 2) what order should I do things i.e first receive then read then process then send etc.. 3) what I asked above a step by step of what the server / client should do.. Thanks!

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  • Tools for assembling textures into DDS files

    - by Nicol Bolas
    There are plenty of tools for making images. I'm not looking for one of those; I have many tools for creating an image. I've got tools for compressing images, generating mipmaps, and even for poking at their basic data format. My issue is with texture assembly. DDS files support cubemaps, array textures, and even cubemap arrays. But I don't know of a tool that can pack a series of images into a cubemap or the like. What tools are available for doing this kind of thing?

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  • How can I best study a problem to determine whether recursion can/should be used?

    - by user10326
    In some cases, I fail to see that a problem could be solved by the divide and conquer method. To give a specific example, when studying the find max sub-array problem, my first approach is to brute force it by using a double loop to find the max subarray. When I saw the solution using the divide and conquer approach which is recursion-based, I understood it but ok. From my side, though, when I first read the problem statement, I did not think that recursion is applicable. When studying a problem, is there any technique or trick to see that a recursion based (i.e. divide and conquer) approach can be used or not?

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  • Multiple Object Instantiation

    - by Ricky Baby
    I am trying to get my head around object oriented programming as it pertains to web development (more specifically PHP). I understand inheritance and abstraction etc, and know all the "buzz-words" like encapsulation and single purpose and why I should be doing all this. But my knowledge is falling short with actually creating objects that relate to the data I have in my database, creating a single object that a representative of a single entity makes sense, but what are the best practises when creating 100, 1,000 or 10,000 objects of the same type. for instance, when trying to display a list of the items, ideally I would like to be consistent with the objects I use, but where exactly should I run the query/get the data to populate the object(s) as running 10,000 queries seems wasteful. As an example, say I have a database of cats, and I want a list of all black cats, do I need to set up a FactoryObject which grabs the data needed for each cat from my database, then passes that data into each individual CatObject and returns the results in a array/object - or should I pass each CatObject it's identifier and let it populate itself in a separate query.

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  • PHP Riak in place update

    - by WojonsTech
    From what I can see, when using Riak to update an object, I first need to load the object into PHP, then edit the object, then store the object back to the Riak database. I was wondering if there is a way to update a bucket without pulling it into PHP first. That way, it would save on the network I/O and latency of pulling it into the PHP script. Can objects be edited directly on the Riak side of things? Edit: Is there away to push data to the end of a raik object, so if i have an object that is numeric array can i make a push to add subject that i know its not there or no in place updates what so ever

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  • Passing additional parameters to JQuery bind event function

    - by kazim sardar mehdi
    To pass the additional parameter to the event function pass an array of key value, as the second parameter to the bind event bind('click', { message: time }, onClick); e.g { message: time } and access it in the function using event(function parameter).data.message(key)   <div id="div1" style="border: 1px solid black; width: 100px; height: 100px">click me</div> <script type="text/javascript"> function onClick(event) { alert(event.data.message); } var time = "loaded at:" + new Date().toString(); $("div.#div1").bind('click', { message: time }, onClick); </script>

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  • Loading Wavefront Data into VAO and Render It

    - by Jordan LaPrise
    I have successfully loaded a triangulated wavefront(.obj) into 6 vectors, the first 3 vectors contain the locations for vertices, uv coords, and normals. The last three have the indices stored for each of the faces. I have been looking into using VAO's and VBO's to render, and I'm not quite sure how to load and render the data. One of my biggest concerns is the fact that indexed rendering only allows you to have one array of indices, meaning I somehow have to make all of the first three vectors the same size, the only way I thought of doing this, is to make 3 new vertex's of equal size, and load in the data for each face, but that would completely defeat the purpose of indexing. Any help would be appreciated. Thanks in advance, Jordan

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  • Lvalue required error [migrated]

    - by ankur.trapasiya
    While working with pointers i wrote the following code, int main() { int a[]={10,20,30,40,50}; int i; for(i=0;i<5;i++) { printf("\n%d",*a); a++; } return 0; } Now as per my understanding array name itself is an address in c and the pointer arithmetic done is here is correct as per my knowledge. But when i try to run the code it is giving me "Lvalue Required" error. So what is the exact reason for occuring Lvalue required error because before this also i have come across situations where this error is there. Secondly why the arithmetic on the pointer is not legal here in this case?

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  • Is it possible to construct a cube with fewer than 24 vertices

    - by Telanor
    I have a cube-based world like Minecraft and I'm wondering if there's a way to construct a cube with fewer than 24 vertices so I can reduce memory usage. It doesn't seem possible to me for 2 reasons: the normals wouldn't come out right and per-face textures wouldn't work. Is this the case or am I wrong? Maybe there's some fancy new DX11 tech that can help? Edit: Just to clarify, I have 2 requirements: I need surface normals for each cube face in order to do proper lighting and I need a way to address a different indexes in a texture array for each cube face

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  • game performance

    - by iQue
    I'm making a game for android, and earlier today I was trying to add some cool stuff to my game. The problem is this thing needs like 5 timers. I build my timers like this: timer += deltaTime; if(timer >= 2.0f){ doStuff; timer -= 2.0f; } // this timers gets stuff done every 2 secs Will having to many timers like this, getting checked every frame, screw up my games performance? The effect I wanted to add was a crosshair every 2 sec, then remove it after 2 sec and do a timed animation. So an array of crosshairs dependent on a bunch of timers to be exact. This caused my game to shut down when used, so thats why Im wondering if using that many timers causes my game to flip out.

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  • How to explain OOP to a matlab programmer?

    - by Oak
    I have a lot of friends who come from electrical / physical / mechanical engineering background, and are curious about what is "OOP" all about. They all know Matlab quite well, so they do have basic programming background; but they have a very hard time grasping a complex type system which can benefit from the concepts OOP introduces. Can anyone propose a way I can try to explain it to them? I'm just not familiar with Matlab myself, so I'm having troubles finding parallels. I think using simple examples like shapes or animals is a bit too abstract for those engineers. So far I've tried using a Matrix interface vs array-based / sparse / whatever implementations, but that didn't work so well, probably because different matrix types are already well-supported in Matlab.

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  • Drawing simple geometric figures with DrawUserPrimitives?

    - by Navy Seal
    I'm trying to draw a simple triangle based on an array of vertex. I've been searching for a tutorial and I found a simple example on riemers but I couldn't get it to work. I think it was made for XNA 3 and it seems there were some changes to XNA 4? Using this example: http://www.riemers.net/eng/Tutorials/XNA/Csharp/Series1/The_first_triangle.php I get this error: Additional information: The current vertex declaration does not include all the elements required by the current vertex shader. TextureCoordinate0 is missing. I'm not english so I'm having some trouble to understand everything. For what I understand error is confusing because I'm trying to draw a triangle color based and not texture based and it shouldn't need a texture. Also I saw some articles about dynamic shadows and lights and I would like to know if this is the kind of code used to do it with some tweaks like culling because I'm wondering if its heavy code for performance in real time.

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  • Unable to access A class variables in B Class - Unity-Monodevelop

    - by Syed
    I have made a class including variables in Monodevelop which is: public class GridInfo : MonoBehaviour { public float initPosX; public float initPosY; public bool inUse; public int f; public int g; public int h; public GridInfo parent; public int y,x; } Now I am using its class variable in another class, Map.cs which is: public class Map : MonoBehaviour { public static GridInfo[,] Tile = new GridInfo[17, 23]; void Start() { Tile[0,0].initPosX = initPosX; //Line 49 } } Iam not getting any error on runtime, but when I play in unity it is giving me error NullReferenceException: Object reference not set to an instance of an object Map.Start () (at Assets/Scripts/Map.cs:49) I am not inserting this script in any gameobject, as Map.cs will make a GridInfo type array, I have also tried using variables using GetComponent, where is the problem ?

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  • How does btrfs RAID work in degraded mode?

    - by turbo
    My idea was that (using loopback devices) it works like this Create the raid array sudo mkfs.btrfs -m raid1 -d raid1 /dev/loop1 /dev/loop2 You mount them sudo mount /dev/loop1 /mnt and mark them touch goodcondition You unmount and simulate disk failure (remove disk or delete loopback device loop2 in my case) You mount degraded -o degraded and mark again touch degraded You add the bad disk again sudo btrfs dev add /dev/loop2 You rebalance sudo btrfs fi ba /mnt And Raid 1 should work again. But that's not the case. sudo btrfs fi show: Total devices 3 FS bytes used 28.00KB devid 3 size 4.00GB used 264.00MB path /dev/loop1 devid 2 size 4.00GB used 272.00MB path /dev/loop2 *** Some devices missing The file degraded lives on loop1 but not on loop2 when loop2 is mounted in degraded mode. Why is that?

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  • Collision detection with heightmap based terrain

    - by Truman's world
    I am developing a 2D tank game. The terrain is generated by Midpoint Displacement Algorithm, so the terrain is represented by an array: index ---> height of terrain [0] ---> 5 [1] ---> 8 [2] ---> 4 [3] ---> 6 [4] ---> 8 [5] ---> 9 ... ... The rendered mountain looks like this: * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 0 1 2 3 4 5 ... I want tanks to be able to move smoothly on the terrain (I mean tanks can rotate according to the height when they move), but the surface of the terrain is not flat, it is polygonal. Can anyone give me some help with collision detection in this situation? Thanks in advance.

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  • How to create a 3D world with 2D sprites similar to Ragnorak online?

    - by Romoku
    As far as I know Ragnorak Online is a 3D game world with 2D sprites overlayed. I would like to use this style in a game I am making in Unity, so I would like the player to be able to select little square tiles on the terrain. There are a couple routes I could take such as using a bunch of cubic polygons and linking them together or using one big map. The former approach doesn't seem to make any sense if the world is not flat as polygons wouldn't be reused often. The goal is to break down a 3D polygon into tiles which is heard to wrap my head around. I believe using something like an interval tree or array would be appropriate to store the rectangle grid, but how would I display a rectangle around the selection the player has his mouse over on the polygon terrain itself? Here is a screenshot. Here is a gameplay video. Here is the camera usage.

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