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• 2D Gaming - How to reflect a ball off the bat?

  - by sid

  Hi there I am pretty new to XNA & game dev and am stuck at ball reflection. My ball is reflecting once it hits the bat, but only in one angle, no matter which angle the bat is at. Here's the code: if (BallRect.Intersects(BatRect)) { Vector2 NormBallVelocity = Ball.velocity; NormBallVelocity.Normalize(); NormBallVelocity = Vector2.Reflect(Ball.velocity, NormBallVelocity); Ball.velocity = NormBallVelocity; } The ball is retracting its way back. How do I make it look like the ball is reflecting off the bat? I have seen other posts but they are on 3D front I am too new to translate it to 2D terms... Thanks Sid

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• Do I need to check capacity before adding an element to a vector in c++ ?

  - by Cassie

  Hi dear all, I am a newbie to c++ STL vectors so sorry for silly questions in advence. :) In my program, I have a vector which needs to store unknown number of elements. Do I have to check if the vector has achieved its max_size before adding an new element to it ? Will a c++ compiler throw an exception automatically when a program tries to add elements to a full vector ? Thank you very much, Cassie

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• Draw Lines Over a Circle

  - by VOX

  There's a line A-B and C at the center between A and B. It forms a circle as in the figure. If we assume A-B line as a diameter of the circle and then C is it's center. My problem is I have no idea how to draw another three lines (in blue) each 45 degree away from AC or AB. No, this is not a homework, it's part of my complex geometry in a rendering. http://www.freeimagehosting.net/image.php?befcd84d8c.png

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• Interpolation of time series data in R

  - by Pierreten

  I'm not sure what i'm missing here, but i'm basically trying to compute interpolated values for a time series; when I directly plot the series, constraining the interpolation points with "interpolation.date.vector", the plot is correct: plot(date.vector,fact.vector,ylab='Quantity') lines(spline(date.vector,fact.vector,xout=interpolation.date.vector)) When I compute the interpolation, store it in an intermediate variable, and then plot the results; I get a radically incorrect result: intepolated.values <- spline(date.vector,fact.vector,xout=interpolation.date.vector) plot(intepolated.values$x,intepolated.values$y) lines(testinterp$x,testinterp$y) Doesn't the lines() function have to execute the spline() function to retrieve the interpolated points in the same way i'm doing it?

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• AES Cipher not picking up IV

  - by timothyjc

  I am trying to use an IV with AES so that the encrypted text is unpredictable. However, the encrypted hex string is always the same. I have actually tried a few methods of attempting to add some randomness by passing some additional parameters to the cipher init call: 1) Manual IV generation byte[] iv = generateIv(); IvParameterSpec ivspec = new IvParameterSpec(iv); 2) Asking cipher to generate IV AlgorithmParameters params = cipher.getParameters(); params.getParameterSpec(IvParameterSpec.class); 3) Using a PBEParameterSpec byte[] encryptionSalt = generateSalt(); PBEParameterSpec pbeParamSpec = new PBEParameterSpec(encryptionSalt, 1000); All of these seem to have no influence on the encrypted text.... help!!! My code: package com.citc.testencryption; import java.security.NoSuchAlgorithmException; import java.security.SecureRandom; import javax.crypto.Cipher; import javax.crypto.SecretKey; import javax.crypto.SecretKeyFactory; import javax.crypto.spec.IvParameterSpec; import javax.crypto.spec.PBEKeySpec; import android.app.Activity; import android.os.Bundle; import android.util.Log; public class Main extends Activity { public static final int SALT_LENGTH = 20; public static final int PBE_ITERATION_COUNT = 1000; private static final String RANDOM_ALGORITHM = "SHA1PRNG"; private static final String PBE_ALGORITHM = "PBEWithSHA256And256BitAES-CBC-BC"; private static final String CIPHER_ALGORITHM = "PBEWithSHA256And256BitAES-CBC-BC"; private static final String TAG = Main.class.getSimpleName(); @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); try { String password = "password"; String plainText = "plaintext message to be encrypted"; // byte[] salt = generateSalt(); byte[] salt = "dfghjklpoiuytgftgyhj".getBytes(); Log.i(TAG, "Salt: " + salt.length + " " + HexEncoder.toHex(salt)); PBEKeySpec pbeKeySpec = new PBEKeySpec(password.toCharArray(), salt, PBE_ITERATION_COUNT); SecretKeyFactory keyFac = SecretKeyFactory.getInstance(PBE_ALGORITHM); SecretKey secretKey = keyFac.generateSecret(pbeKeySpec); byte[] key = secretKey.getEncoded(); Log.i(TAG, "Key: " + HexEncoder.toHex(key)); // PBEParameterSpec pbeParamSpec = new PBEParameterSpec(salt, ITERATION_COUNT); Cipher encryptionCipher = Cipher.getInstance(CIPHER_ALGORITHM); // byte[] encryptionSalt = generateSalt(); // Log.i(TAG, "Encrypted Salt: " + encryptionSalt.length + " " + HexEncoder.toHex(encryptionSalt)); // PBEParameterSpec pbeParamSpec = new PBEParameterSpec(encryptionSalt, 1000); // byte[] iv = params.getParameterSpec(IvParameterSpec.class).getIV(); // Log.i(TAG, encryptionCipher.getParameters() + " "); byte[] iv = generateIv(); IvParameterSpec ivspec = new IvParameterSpec(iv); encryptionCipher.init(Cipher.ENCRYPT_MODE, secretKey, ivspec); byte[] encryptedText = encryptionCipher.doFinal(plainText.getBytes()); Log.i(TAG, "Encrypted: " + HexEncoder.toHex(encryptedText)); // <== Why is this always the same :( Cipher decryptionCipher = Cipher.getInstance(CIPHER_ALGORITHM); decryptionCipher.init(Cipher.DECRYPT_MODE, secretKey, ivspec); byte[] decryptedText = decryptionCipher.doFinal(encryptedText); Log.i(TAG, "Decrypted: " + new String(decryptedText)); } catch (Exception e) { e.printStackTrace(); } } private byte[] generateSalt() throws NoSuchAlgorithmException { SecureRandom random = SecureRandom.getInstance(RANDOM_ALGORITHM); byte[] salt = new byte[SALT_LENGTH]; random.nextBytes(salt); return salt; } private byte[] generateIv() throws NoSuchAlgorithmException { SecureRandom random = SecureRandom.getInstance(RANDOM_ALGORITHM); byte[] iv = new byte[16]; random.nextBytes(iv); return iv; } }

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• Intersection of line with cube and knowing the point of intersection.

  - by Raj

  Hello everyone, description 1.lines are originating from origin(0,0,0). 2.lines are at some random angle to the Normal of Top face of teh cube. 3.if the lines are intersecting cube , calculate the intersection point. 4.mainly i wan to know how much distance ,line traveled inside the cube. I dont know exactly which approach should i take , i will be pleased and thankful if someone could guied me to the right direction, to use OpenGL, DirectX or some other library, for C# . some example or sample will be appriciated.

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• How do I replace colours in a movieclip?

  - by Oli

  I am trying to take a movieclip of a character and change the colour of their clothes. The character is comprised of vectors. So far I have semi-sucessfully used this method: stop the movieclip take the bitmap data from the current frame use threshold to replace the colour store the resulting bitmap data in an array add an onenterframe function - clear the current frame and add the bitmap data from the processed data in the array So - this works pretty well. Each frame is only processed once at the beginning and then the write to the movieclip is very quick. However! As the replacement is being performed on a bitmap there is an amount of aliasing that takes place to remove jaggies/pixelation. This produces colours that are not matched using threshold. So the main colour is replaced correctly but it is surrounded by a halo of mixed colours :( I am sure there should be a better way to do this. Any ideas or answers would be greatly apreciated - Thanks.

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• solving origin of a vectors

  - by Mike

  I have two endpoints (xa,ya) and (xb,yb) of two vectors, respectively a and b, originating from a same point (xo, yo). Also, I know that |a|=|b|+s, where s is a constant. I tried to compute the origin (xo, yo) but seem to fail at some point. How to solve this?

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• How to modify a given class to use const operators

  - by zsero

  I am trying to solve my question regarding using push_back in more than one level. From the comments/answers it is clear that I have to: Create a copy operator which takes a const argument Modify all my operators to const But because this header file is given to me there is an operator what I cannot make into const. It is a simple: float & operator [] (int i) { return _item[i]; } In the given program, this operator is used to get and set data. My problem is that because I need to have this operator in the header file, I cannot turn all the other operators to const, what means I cannot insert a copy operator. How can I make all my operators into const, while preserving the functionality of the already written program? Here is the full declaration of the class: class Vector3f { float _item[3]; public: float & operator [] (int i) { return _item[i]; } Vector3f(float x, float y, float z) { _item[0] = x ; _item[1] = y ; _item[2] = z; }; Vector3f() {}; Vector3f & operator = ( const Vector3f& obj) { _item[0] = obj[0]; _item[1] = obj[1]; _item[2] = obj[2]; return *this; }; Vector3f & operator += ( const Vector3f & obj) { _item[0] += obj[0]; _item[1] += obj[1]; _item[2] += obj[2]; return *this; }; bool operator ==( const Vector3f & obj) { bool x = (_item[0] == obj[0]) && (_item[1] == obj[1]) && (_item[2] == obj[2]); return x; } // my copy operator Vector3f(const Vector3f& obj) { _item[0] += obj[0]; _item[1] += obj[1]; _item[2] += obj[2]; return this; } };

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• NumPy: how to quickly normalize many vectors?

  - by EOL

  How can a list of vectors be elegantly normalized, in NumPy? Here is an example that does not work: from numpy import * vectors = array([arange(10), arange(10)]) # All x's, then all y's norms = apply_along_axis(linalg.norm, 0, vectors) # Now, what I was expecting would work: print vectors.T / norms # vectors.T has 10 elements, as does norms, but this does not work The last operation yields "shape mismatch: objects cannot be broadcast to a single shape". How can the normalization of the 2D vectors in vectors be elegantly done, with NumPy? Edit: Why does the above not work while adding a dimension to norms does work (as per my answer below)?

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• How to transform a vector<int> into a string?

  - by Legend

  I am trying to pass a value from C++ to TCL. As I cannot pass pointers without the use of some complicated modules, I was thinking of converting a vector to a char array and then passing this as a null terminated string (which is relatively easy). I have a vector as follows: 12, 32, 42, 84 which I want to convert into something like: "12 32 42 48" The approach I am thinking of is to use an iterator to iterate through the vector and then convert each integer into its string representation and then add it into a char array (which is dynamically created initially by passing the size of the vector). Is this the right way or is there a function that already does this?

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• FastVectorHighlighter.Net returning null on GetBestFragment

  - by Midhat

  Hi I have a large index, on which Highlighter.Net works fine, but FastVectorHighlighter returns null as a Best Fragment on Some documents. the searcher works fine. It is just the highlighter. The field has been indexed in the same manner for all documents, so I fail to understand Why it highlights some documents but not all. Using Lucene.Net 2.9.2, built from trunk rev942061

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• Draw a parallel line

  - by VOX

  I have x1,y1 and x2,y2 which forms a line segment. How can I get another line x3,y3 - x4,y4 which is parallel to the first line as in the picture. I can simply add n to x1 and x2 to get a parallel line but it is not what i wanted. I want the lines to be as parallel in the picture.

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• Angles between two n-dimensional vectors in Python

  - by Peter

  In need to determine the angle(s) between two n-dimensional vectors in Python. For example, the input can be two lists like the following: [1,2,3,4] and [6,7,8,9]. Can anybody help me? Thanks in advance!

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• How to JSON serialize math vector type in F#?

  - by The_Ghost

  Hello! I'm trying to serialize "vector" (Microsoft.FSharp.Math) type. And I get that error: Exception Details: System.Runtime.Serialization.SerializationException: Type 'Microsoft.FSharp.Math.Instances+FloatNumerics@115' with data contract name 'Instances.FloatNumerics_x0040_115:http://schemas.datacontract.org/2004/07/Microsoft.FSharp.Math' is not expected. Add any types not known statically to the list of known types - for example, by using the KnownTypeAttribute attribute or by adding them to the list of known types passed to DataContractSerializer. I have tried to put KnownType attribute and some other stuff, but nothing helps! Could someone know the answer? This is the code I use: // [< KnownType( typeof<vector> ) >] type MyType = vector let public writeTest = let aaa = vector [1.1;2.2] let serializer = new DataContractJsonSerializer( typeof<MyType> ) let writer = new StreamWriter( @"c:\test.txt" ) serializer.WriteObject(writer.BaseStream, aaa) writer.Close()

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• Replacing a colour/colours in a movieclip with different colours?

  - by Oli

  I am trying to take a movieclip of a character and change the colour of their clothes. The character is comprised of vectors. So far I have semi-sucessfully used this method: stop the movieclip take the bitmap data from the current frame use threshold to replace the colour store the resulting bitmap data in an array add an onenterframe function - clear the current frame and add the bitmap data from the processed data in the array So - this works pretty well. Each frame is only processed once at the beginning and then the write to the movieclip is very quick. However! As the replacement is being performed on a bitmap there is an amount of aliasing that takes place to remove jaggies/pixelation. This produces colours that are not matched using threshold. So the main colour is replaced correctly but it is surrounded by a halo of mixed colours :( I am sure there should be a better way to do this. Any ideas or answers would be greatly apreciated - Thanks.

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• How to sort TBB concurrent_vector or concurrent_queue?

  - by Jackie

  Now I have a solver in that I need to keep a set of self-defined data type objects in a concurrent_vector or queue. It has to be concurrent because the objects come from different threads.With this concurrent container, I hope to sort these objects, eliminate duplicates and send them back when other threads need them. However, I know TBB offers concurrent_vector and concurrent_queue which can be read and written concurrently from different threads. But how to sort the objects inside a container? Does everyone know how to do that? Thanks.

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• Mapping Vectors

  - by Dan Snyder

  Is there a good way to map vectors? Here's an example of what I mean: vec0 = [0,0,0,0,0,0,0,0,0,0,0] vec1 = [1,4,2,7,3,2] vec2 = [0,0,0,0,0,0,0,0,0] vec2 = [7,2,7,9,9,6,1,0,4] vec4 = [0,0,0,0,0,0] mainvec = [0,0,0,0,0,0,0,0,0,0,0,1,4,2,7,3,2,0,0,0,0,0,0,0,0,0,7,2,7,9,9,6,1,0,4,0,0,0,0,0,0] Lets say mainvec doesn't exist (I'm just showing it to you so you can see the general data structure in mind. Now say I want mainvec(12) which would be 4. Is there a good way to map the call of these vectors without just stitching them together into a mainvec? I realize I could make a bunch of if statements that test the index of mainvec and I can then offset each call depending on where the call is within one of the vectors, so for instance: mainvec(12) = vec1(1) which I could do by: mainvec(index) if (index >=13) vect1(index-11); I wonder if there's a concise way of doing this without if statements. Any Ideas?

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• Who can give me a link for the operator= of vector in MSDN?

  - by 8888q8888

  Who can give me a link for the operator= of vector in MSDN? Why I can only find operator[]? If operator= is just something default, like copy everything in A to B, how this following code works? vector<double> v(100,1); v = vector<double>(200,2); // if operator= is just a trivail version, how to make sure the old v get cleared?

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• how to use vector images from adobe illustrator in flex skinning?

  - by Ankur Sharma

  hi, i have to work on skin in flex, but this time , i have to use vector images from adobe illustrator, this is very easy in case of adobe photoshop, as we have .png files, just import them in flash and make them a movie clip, and u r done with the skinnning but i m facing problem when i m copying images from adobe illustrator in to the flash, actually i have a hslider and i have to put vector skin, but when images copied on adobe flash, they lost their corners, so skinning is not perfect, i hope u got it, plzz tell me the solution of making vector skinning thanx in advance

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• How to systematically generate images from data?

  - by adamvickers

  I work for a performing arts nonprofit. We have seating charts for each of the theaters we work with; each seating chart shows the number of sections, the shape of each section, and the number of rows in each section. We'd like to create dynamic seating charts based on this info. We'd like them to look/feel kinda like this: http://www.fansnap.com/tickets/177754-on. But the tricky part is we'd like to be able to store all the info about each theater (the section names, shape/size of each section, and number of rows in each section) as data and then build a system that reads this data and uses it to create a dynamic map. I'm a life-long web developer, but I don't have have any experience with a difficult graphics problem like this. I realize it's a complex problem and I don't expect anyone to give me a complete answer here, but I would love direction on where I should be looking for more info. Is what I'm describing possible? Does this sort of technique have a name? Where can I learn more about how to accomplish this? What software should I use? Any info would be helpful.

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• Draw 2 parallel lines

  - by Ben Martin

  How can I calculate the points to draw 2 parallel lines. I know the start and end points for the centre of the parallel lines. To makes thing a little bit harder, it needs to support straight and Bezier curved lines.

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• sequential minimal optimization C++

  - by Anton

  Hello. I want to implement the method of SVM. But the problem appeared in his training. It was originally planned to use SMO, but did not find ready-made libraries for C++. If there is a ready, then share it. Thank you in advance. The problem of finding an object in the picture (probably human)

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• RaphaelJS HTML5 Library pathIntersection() bug or alternative optimisation (screenshots)

  - by user1236048

  I have a chart generated using RaphaelJS library. It is just on long path: M 50 122 L 63.230769230769226 130 L 76.46153846153845 130 L 89.6923076923077 128 L 102.92307692307692 56 L 116.15384615384615 106 L 129.3846153846154 88 L 142.6153846153846 114 L 155.84615384615384 52 L 169.07692307692307 30 L 182.3076923076923 62 L 195.53846153846152 130 L 208.76923076923077 74 L 222 130 L 235.23076923076923 66 L 248.46153846153845 102 L 261.6923076923077 32 L 274.9230769230769 130 L 288.15384615384613 130 L 301.38461538461536 32 L 314.6153846153846 86 L 327.8461538461538 130 L 341.07692307692304 70 L 354.30769230769226 130 L 367.53846153846155 102 L 380.7692307692308 120 L 394 112 L 407.2307692307692 68 L 420.46153846153845 48 L 433.6923076923077 92 L 446.9230769230769 128 L 460.15384615384613 110 L 473.38461538461536 78 L 486.6153846153846 130 L 499.8461538461538 56 L 513.0769230769231 116 L 526.3076923076923 80 L 539.5384615384614 58 L 552.7692307692307 40 L 566 130 L 579.2307692307692 94 L 592.4615384615385 64 L 605.6923076923076 122 L 618.9230769230769 98 L 632.1538461538461 120 L 645.3846153846154 70 L 658.6153846153845 82 L 671.8461538461538 76 L 685.0769230769231 124 L 698.3076923076923 110 L 711.5384615384615 94 L 724.7692307692307 130 L 738 130 L 751.2307692307692 66 L 764.4615384615385 118 L 777.6923076923076 70 L 790.9230769230769 130 L 804.1538461538461 44 L 817.3846153846154 130 L 830.6153846153845 36 L 843.8461538461538 92 L 857.076923076923 130 L 870.3076923076923 76 L 883.5384615384614 130 L 896.7692307692307 60 L 910 88 Also below these chart I have a jqueryUI slider of the same width (860px) and centered with the chart. I want when I move the slider to move a dot on the chart accordingly with the slider position. See attached screenshot: As you can see it seems to work fine. I've implemented this behaviour using the pathIntersection() method. On the slide event at each ui.value (x coordinate) I intersect my chartPath (the one from above) with a vertical straight line at the x coordinate. But still there are some problems. One of them is that it runs very hard, and it kinda freezes sometimes.. and very weird sometimes it doesn't seem to intersect at all even it should.. I'll example below 2 cases I identified: M 499.8461538461538 0 L 499.8461538461538 140 M 910 0 L 910 140 Could you please explain why this intersect behaviour happens (it should return a dot).. and the worst part it seems like it happens randomly.. if I use another chartdata. Also if you can identify another (better) solution to syncronise the slider position with the dot on the chart.. would be perfect. I thought about using Element.getPointAtLength(length), but I don't know how. I think I should save the pathSegments and for each to compute the start Length and the finish Length.

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• R: how to make a unique set of names from a vector of strings?

  - by Mike Dewar

  Hi, I have a vector of strings. Check out my vector, it's awesome: > awesome [1] "a" "b" "c" "d" "d" "e" "f" "f" I'd like to make a new vector that is the same length as awesome but where, if necessary, the strings have been uniqueified. For example, a valid output of my desired function would be > awesome.uniqueified [1] "a" "b" "c" "d.1" "d.2" "e" "f.1" "f.2" Is there an easy, R-thonic and beautiful way to do this? I should say my list in real life (it's not called awesome) contains 25000ish mircoarray probeset identifiers. I'm always nervous when I embark on writing little generic functions (which I'm sure I could do) as I'm sure some R guru has come across this problem in the past, nailed it with some incredible algorithm that doesn't even have to store more than half an element in the vector. I'm just not sure what they might have called it. Probably not uniqueify.

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