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• How can I generate signed distance fields in real time, fast?

  - by heishe

  In a previous question, it was suggested that signed distance fields can be precomputed, loaded at runtime and then used from there. For reasons I will explain at the end of this question (for people interested), I need to create the distance fields in real time. There are some papers out there for different methods which are supposed to be viable in real-time environments, such as methods for Chamfer distance transforms and Voronoi diagram-approximation based transforms (as suggested in this presentation by the Pixeljunk Shooter dev guy), but I (and thus can be assumed a lot of other people) have a very hard time actually putting them to use, since they're usually long, largely bloated with math and not very algorithmic in their explanation. What algorithm would you suggest for creating the distance fields in real-time (favourably on the GPU) especially considering the resulting quality of the distance fields? Since I'm looking for an actual explanation/tutorial as opposed to a link to just another paper or slide, this question will receive a bounty once it's eligible for one :-). Here's why I need to do it in real time:

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• NeoAxis 3D disponible en version 1.3, le moteur de jeu ajoute le SSAO et une meilleure gestion du terrain

  NeoAxis 3D et maintenant disponible en version 1.3 La nouvelle version du moteur de jeu apporte le SSAO, des améliorations sur le terrain et plein d'autres surprises C'est en cette période de Noël que NeoAxis 3D, le moteur de jeu multi-plateforme revient avec une hotte fournit en cadeau pour nous, les développeurs. Tout d'abord, cette version estampillée 1.3 apporte le Screen Space Ambient Occlusion (SSAO). Une technique de rendu temps réel qui est grandement utilisée dans l'industrie pour permettre une approximation efficace de l'ambient occlusion (des ombres sont rajoutés selon le buffer de profondeur).. Celui-ci est implémenté tel un effet après rendu (post processing) afin de garder une bonne synergi...

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• 2-components color model

  - by Cyan

  RGB is the natural color model for OpenGL. But a lot of other color models exist. For example, CMY(K) for printers, YUV for JPEG, the little cousins YCbCr and YCoCg, HSL & HSV from the 70's, and so on. All these models tend to share a common property : they are based on 3 components. Therefore my question is : Does it exist a 2-components color model ? I'm surprised to not find any. I was expecting something along the line of Hue+light could exist. I guess it cannot be as "complete" as a true 3-components color model, but a fine-enough approximation will be good for my usecase. The end objective is to store the 2 components into a single BC5 texture (GL_COMPRESSED_RED_GREEN_RGTC2 in OpenGL). The 3rd component requires a second fetch into a second texture, which hurts performance.

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• Pseudo LRU tree algorithm.

  - by patros

  A lot of descriptions of Pseudo LRU algorithms involve using a binary search tree, and setting flags to "point away" from the node you're searching for every time you access the tree. This leads to a reasonable approximation of LRU. However, it seems from the descriptions that all of the nodes deemed LRU would be leaf nodes. Is there a pseudo-LRU algorithm that deals with a static tree that will still perform reasonably well, while determining that non-leaf nodes are suitable LRU candidates?

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• Psuedo LRU tree algorithm.

  - by patros

  A lot of descriptions of Pseudo LRU algorithms involve using a binary search tree, and setting flags to "point away" from the node you're searching for every time you access the tree. This leads to a reasonable approximation of LRU. However, it seems from the descriptions that all of the nodes deemed LRU would be leaf nodes. Is there a pseudo-LRU algorithm that deals with a static tree that will still perform reasonably well, while determining that non-leaf nodes are suitable LRU candidates?

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• C# regex to validate "realistic" IP values

  - by Joshua

  Regex that somewhat validates if a value has one of the following characteristics: 123-29-123-123.subdomain.zomg.com:8085 123.12.34.56:420 Unfortunately, I'm terrible at Regex, C#, google searches, and the differences between proper nouns and regular ones. It can be a lose approximation, in fact I would go with anything that has a : colon separator with a port after it.

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• Java mouse motion anywhere on screen

  - by Dave

  I'm sure this is possible but all my searching is coming up blank. In Java is it possible to register for a mouse motion event outside of a Java app? So if the mouse pointer moves anywhere on the screen I get a call back. An approximation is possible with polling MouseInfo.getPointerInfo but there must be a better way. Thanks

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• How could I make geometry advanced operations on bezier paths?

  - by yizzreel

  I have a library that draws regular bezier path figures (complex paths formed of a lot of bezier points), using midpoint approximation. I can draw them without problem, but I need to add support for advanced geometry operations: Nearest point of a curve, intersection, figure contains point, and more importantly, path combinations: difference, intersection, exclusive-or, union, ... Is there any good source to get all this? Thanks

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• Edge detection using wavelet

  - by cheoma

  I had done Edge detection using wavelet transform using thus steps changing the image to Gray scale decomposing the image using dwt2(discrete wavelet transform,Haar wavelet filter ) in to horizontal,vertical,diagonal and approximation(detail) further decomposing the horizontal part threshold (global threshold like canny Edge detection ) i got the edge but i got a problem while locating the edge to complete image to mean recovering original image using only the Edges so i need help concerning this either in concept ,mat lab code or references I hope i will get your help soon

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• Java Runtime.freeMemory() returning bizarre results when adding more objects

  - by Sotirios Delimanolis

  For whatever reason, I wanted to see how many objects I could create and populate a LinkedList with. I used Runtime.getRuntime().freeMemory() to get the approximation of free memory in my JVM. I wrote this: public static void main(String[] arg) { Scanner kb = new Scanner(System.in); List<Long> mem = new LinkedList<Long>(); while (true) { System.out.println("Max memory: " + Runtime.getRuntime().maxMemory() + ". Available memory: " + Runtime.getRuntime().freeMemory() + " bytes. Press enter to use more."); String s = kb.nextLine(); if (s.equals("m")) for (int i = 0; i < 1000000; i++) { mem.add(new Long((new Random()).nextLong())); } } } If I write in m, the app adds a million Long objects to the list. You would think the more objects (to which we have references, so can't be gc'ed), the less free memory. Running the code: Max memory: 1897725952. Available memory: 127257696 bytes. m Max memory: 1897725952. Available memory: 108426520 bytes. m Max memory: 1897725952. Available memory: 139873296 bytes. m Max memory: 1897725952. Available memory: 210632232 bytes. m Max memory: 1897725952. Available memory: 137268792 bytes. m Max memory: 1897725952. Available memory: 239504784 bytes. m Max memory: 1897725952. Available memory: 169507792 bytes. m Max memory: 1897725952. Available memory: 259686128 bytes. m Max memory: 1897725952. Available memory: 189293488 bytes. m Max memory: 1897725952. Available memory: 387686544 bytes. The available memory fluctuates. How does this happen? Is the GC cleaning up other things (what other things are there on the heap to really clean up?), is the freeMemory() method returning an approximation that's way off? Am I missing something or am I crazy?

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• Subband decomposition using Daubechies filter

  - by misha

  I have the following two 8-tap filters: h0 ['-0.010597', '0.032883', '0.030841', '-0.187035', '-0.027984', '0.630881', '0.714847', '0.230378'] h1 ['-0.230378', '0.714847', '-0.630881', '-0.027984', '0.187035', '0.030841', '-0.032883', '-0.010597'] Here they are on a graph: I'm using it to obtain the approximation (lower subband of an image). This is a(m,n) in the following diagram: I got the coefficients and diagram from the book Digital Image Processing, 3rd Edition, so I trust that they are correct. The star symbol denotes one dimensional convolution (either over rows or over columns). The down arrow denotes downsampling in one dimension (either over rows, or columns). My problem is that the filter coefficients for h0 and h1 sum to greater than 1 (approximately 1.4 or sqrt(2) to be exact). Naturally, if I convolve any image with the filter, the image will get brighter. Indeed, here's what I get (expected result on right): Can somebody suggest what the problem is here? Why should it work if the convolution filter coefficients sum to greater than 1? I have the source code, but it's quite long so I'm hoping to avoid posting it here. If it's absolutely necessary, I'll put it up later. EDIT What I'm doing is: Decompose into subbands Filter one of the subbands Recompose subbands into original image Note that the point isn't just to have a displayable subband-decomposed image -- I have to be able to perfectly reconstruct the original image from the subbands as well. So if I scale the filtered image in order to compensate for my decomposition filter making the image brighter, this is what I will have to do: Decompose into subbands Apply intensity scaling Filter one of the subbands Apply inverse intensity scaling Recompose subbands into original image Step 2 performs the scaling. This is what @Benjamin is suggesting. The problem is that then step 4 becomes necessary, or the original image will not be properly reconstructed. This longer method will work. However, the textbook explicitly says that no scaling is performed on the approximation subband. Of course, it's possible that the textbook is wrong. However, what's more possible is I'm misunderstanding something about the way this all works -- this is why I'm asking this question.

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• Python: Multi list comprehension, is there such an unwieldy beast of prey ?

  - by bandana

  consider the following python 'code'. it demonstrates the concept of a multi-list comprehension: start = ['a', 'b', 'c'] middle = ['r', 'a', 'a'] finish = ['t', 'r', 't'] l = [s.upper() + m + f for s in start, m in middle, e in finish] >>> print l ['Art', 'Bar', 'Cat'] Alas, the above code does not work in python. What would be a good approximation of multi-list comprehension in python? Please discuss what happens when the lists have different lengths.

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• The ghost of icons past

  - by Kenneth Cochran

  I am fortnightly( or an approximation thereof) visited by the ghosts of icons, long departed. These apparitions only reveal themselves momentarily after I've logged in then vanish. Returning from whence they came. I've investigated their history and found no clues as to why they continue to haunt me. I sought out an exorcist but those I found were only qualified to expel spirits of humans and demons. Not one had any experience with digital poltergeists. Perhaps praying to Saint William of Redmond will improve the Vista before me. Dost thou agree?

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• Approach for monitoring internet backbone traffic volume

  - by Greg Harman

  I'm interested in getting a picture of relative volume across different internet backbones. In particular, I'd like to see how traffic volume over a given route differs over the course of a day or from one day to the next. InternetTrafficReport.com is the closest approximation to this that I've found online, and their approach is to test ping times to a number of key routers from several geographically-dispersed servers. This sounds like one straightforward way to measure, but I don't have several geographically-dispersed servers. Is there a different approach for sampling this type of information from a single server?

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• How do I know if my disks are being hit with too many I/O reads or writes or both?

  - by Mark F

  I know a bit about disk I/O and bottlenecks relating to this especially when relating to databases. How do I really know what the max I/O numbers will be for my disks? What metric might be available to me for working out roughly (but needs to be a good approximation) of how much capacity (if you will) have I got left available in I/O. I've seen it before where things are bubbling along nicely and then all of a sudden, everything screams to a halt, and it ends up being an I/O bound problem. Is there a better way to predict when I/O is reaching its limits? This article was interesting but not giving the answer I desire. So, is my best bet surrounding just looking at 'CPU I/O WAIT'? There must be a more reactive method than this.

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• How do I know if my disks are being hit with too much IO reads or writes or both?

  - by Mark F

  Hi All, So I know a bit about disk I/O and bottlenecks relating to this especially when relating to databases. But how do I really know what the max IO numbers will be for my disks? What metric might be available to me for working out roughly (but needs to be a good approximation) of how much capacity (if you will) have I got left available in I/O. I've seen it before where things are bubbling along nicely and then all of a sudden, everything screams to a halt, and it ends up being an IO bound problem. Is there a better way to predict when IO is reaching its limits? This article was interesting but not giving the answer I desire. "http://serverfault.com/questions/61510/linux-how-can-i-see-whats-waiting-for-disk-io". So is my best bet surrounding just looking at 'CPU IO WAIT'? There must be a more reactive method for this? Best, M

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• Box 2d basic questions

  - by philipp

  I am a bit new to box2d and I am developing an game with type and letters. I am using an svg font and generate the box2d bodies direct from the glyphs path definition, using the convex hull of them. I also have an decomposition routine the decomposes this hull if necessary. All this it is more or less working, except that I got some strange errors which definitely are caused by the scale factors. The problem is caused by two factors: first: the world scale of box2d, second: the the precision of curve-approximation of the glyph vectors. So through scaling down the input vertices for box2d, it happens that they become equal caused by numerical precision, what causes errors in box2d. Through scaling the my glyphs a bit up, this goes away. I also goes away if I chose a different world scale factor, but this slows down the whole animation quite much! So if my view port is about 990px * 600px and i want to animate Glyphs in box2d which should have a size from about 50px * 50px up to 300px * 300px, which scale factor of the b2world should i choose? How small should the smallest distance from on vertex to another be, while approximating the glyph vectors? Thanks for help greetings philipp EDIT:: I continued reading the docs of box2d and after rethinking of the units system, which is designed to handle object from 0.1 up to 10 meters, I calculated a scale factor of 75. So Objects 600px width will are 8 meters wide in box2d and even small objects of about 20px width will become 0.26 meters width in box2d. I will go on trying with this values, but if there is somebody out there who could give me a clever advice i would be happy!

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• Unity3D and Texture2D. GetPixel returns wrong values

  - by Heisenbug

  I'm trying to use Texture2D set and get colors, but I encountered a strange behavior. Here's the code to reproduce it: Texture2D tex = new Texture2D(2,2, TextureFormat.RGBA32 ,false); Color col = new Color(1.0f,0.5f,1.0f,0.5f); //col values: 1.00, 0.500, 1.00, 0.500 tex.setPixel(0,0,col); Color colDebug = tex.getPixel(0,0); //col values: 1.00, 0.502, 1.00, 0.502 The Color retrieved with getPixel is different from the Color set before. I initially thought about float approximation, but when inspectin col the value stored are correct, so can't be that reason. It sounds weird even a sampling error because the getValue returns a value really similar that not seems to be interpolated with anything else. Anyway I tried even to add these lines after building the texture but nothing change: this.tex.filterMode = FilterMode.Point; this.tex.wrapMode = TextureWrapMode.Clamp; this.tex.anisoLevel = 1; What's my mistake? What am I missing? In addition to that. I'm using tex to store Rect coordinates returned from atlas generation, in order to be able of retriving the correct uv coordinate of an atlas inside a shader. Is this a right way to go?

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• How many copies are needed to enlarge an array?

  - by user10326

  I am reading an analysis on dynamic arrays (from the Skiena's algorithm manual). I.e. when we have an array structure and each time we are out of space we allocate a new array of double the size of the original. It describes the waste that occurs when the array has to be resized. It says that (n/2)+1 through n will be moved at most once or not at all. This is clear. Then by describing that half the elements move once, a quarter of the elements twice, and so on, the total number of movements M is given by: This seems to me that it adds more copies than actually happen. E.g. if we have the following: array of 1 element +--+ |a | +--+ double the array (2 elements) +--++--+ |a ||b | +--++--+ double the array (4 elements) +--++--++--++--+ |a ||b ||c ||c | +--++--++--++--+ double the array (8 elements) +--++--++--++--++--++--++--++--+ |a ||b ||c ||c ||x ||x ||x ||x | +--++--++--++--++--++--++--++--+ double the array (16 elements) +--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--+ |a ||b ||c ||c ||x ||x ||x ||x || || || || || || || || | +--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--+ We have the x element copied 4 times, c element copied 4 times, b element copied 4 times and a element copied 5 times so total is 4+4+4+5 = 17 copies/movements. But according to formula we should have 1*(16/2)+2*(16/4)+3*(16/8)+4*(16/16)= 8+8+6+4=26 copies of elements for the enlargement of the array to 16 elements. Is this some mistake or the aim of the formula is to provide a rough upper limit approximation? Or am I missunderstanding something here?

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• Efficient path-finding in free space

  - by DeadMG

  I've got a game situated in space, and I'd like to issue movement orders, which requires pathfinding. Now, it's my understanding that A* and such mostly apply to trees, and not empty space which does not have pathfinding nodes. I have some obstacles, which are currently expressed as fixed AABBs- that is, there is no unbounded "terrain" obstacle. In addition, I expect most obstacles to be reasonably approximable as cubes or spheres. So I've been thinking of applying a much simpler pathfinding algorithm- that is, simply cast a ray from the current position to the target position, and then I can get a list of obstacles using spatial partitioning relatively quickly. What I'm not so sure about is how to determine the part where the ordered unit manoeuvres around the obstacles. What I've been thinking so far is that I will simply use potential fields- that is, all units will feel a strong repulsive force away from each other and a moderate force towards the desired point. This also has the advantage that to issue group orders, I can simply order a mid-level force towards another entity. But this obviously won't achieve the optimal solution. Will potential fields achieve a reasonable approximation given my parameters, or do I need another solution?

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• Advice on reconciling discordant data

  - by Justin

  Let me support my question with a quick scenario. We're writing an app for family meal planning. We'll produce daily plans with a target calorie goal and meals to achieve it for our nuclear family. Our calorie goal will be calculated for each person from their attributes (gender, age, weight, activity level). The weight attribute is the simplest example here. When Dad (the fascist nerd who is inflicting this on his family) first uses the application he throws approximate values into it for Daughter. He thinks she is 5'2" (157 cm) and 125 lbs (56kg). The next day Mom sits down to generate the menu and looks back over what the bumbling Dad did, quietly fumes that he can never recall anything about the family, and says the value is really 118 lbs! This is the first introduction of the discord. It seems, in this scenario, Mom is probably more correct that Dad. Though both are only an approximation of the actual value. The next day the dear Daughter decides to use the program and sees her weight listed. With the vanity only a teenager could muster she changes the weight to 110 lbs. Later that day the Mom returns home from a doctor's visit the Daughter needed and decides that it would be a good idea to update her Daughter's weight in the program. Hooray, another value, this time 117 lbs. Now how do you reconcile these data points? Measurement error, confidence in parties, bias, and more all confound the data. In some idealized world we'd have a weight authority of some nature providing the one and only truth. How about in our world though? And the icing on the cake is that this single data point changes over time. How have you guys solved or managed this conflict?

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• Vote for bugs which impact you!

  - by Sveta Smirnova

  Matt Lord already announced this change, but I am so happy, so want to repeat. MySQL Community Bugs Database Team introduced new button "Affects Me". After you click this button, counter, assigned to each of bug reports, will increase by one. This means we: MySQL Support and Engineering, - will see how many users are affected by the bug. Why is this important? We have always considered community input as we prioritize bug fixes, and this is one more point of reference for us. Before this change we only had a counter for support customers which increased when they opened a support request, complaining they are affected by a bug. But our customers are smart and not always open support request when hit a bug: sometimes they simply implement workaround. Or there could be other circumstances when they don't create a ticket. Or this could be just released version, which big shops frighten to use in production. Therefore, sometimes, when discussing which bug to prioritize and which not we can not rely only on "Affects paying customers" number, rather need to make guess if one or another bug can affect large group of our users. We used number of bug report subscribers, most recent comments, searched forums, but all these methods gave only approximation. Therefore I want to ask you. If you hit a bug which already was reported, but not fixed yet, please click "Affects Me" button! It will take just a few seconds, but your voice will be heard.

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• Algorithm for creating a school timetable.

  - by cand

  Hello all. I've been wondering if there are known solutions for algorithm of creating a school timetable. Basically, it's about optimizing "hour-dispersion" (both in teachers and classes case) for given class-subject-teacher associations. We can assume that we have sets of classes, lesson subjects and teachers associated with each other at the input and that timetable should fit between 8AM and 4PM. I guess that there is probably no accurate algorithm for that, but maybe someone knows a good approximation or hints for developing it. P.S. I know, there was http://stackoverflow.com/questions/1259686/school-timetable-generation-algorithm-closed , but unlike in that case, I'm not looking for actual implementation, rather for thoughts on how to do it or why it's impossible.

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• Space partitioning algorithm

  - by Karol Kolenda

  I have a set of points which are contained within the rectangle. I'd like to split the rectangles into subrectangles based on point density (giving a number of subrectangles or desired density, whichever is easiest). The partitioning doesn't have to be exact (almost any approximation better than regular grid would do), but the algorithm have to cope with the large number of points - approx. 200 millions. The desired number of subrectangles however is substantially lower (around 1000). Does anyone knows any algorithm which may help me with this particular task?

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• Size Mismatch Between Swing Fonts and Printable Fonts in Java

  - by Caleb Rackliffe

  Hi All, I've got a panel displaying a JTextPane backed by a StyledDocument. When I print a string of text in, say Arial 16, the text it prints is of a different size than the Arial 16 Word prints. Is there some sort of flaw in the translation of Swing fonts to Windows system fonts or something of the sort that makes it difficult (or impossible) to print accurately? I can achieve an approximation by scaling down the size of my font before printing, but this never quite gets me the results I would like, as it's not possible in all cases to reproduce things like equivalent numbers of words on a line, etc. Has anybody run into this before?

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