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• OpenCV 2.4.2 on Matlab 2012b (Windows 7)

  - by Maik Xhani

  Hello i am trying to use OpenCV 2.4.2 in Matlab 2012b. I have tried those actions: downloaded OpenCV 2.4.2 used CMake on opencv folder using Visual Studio 10 and Visual Studio 10 Win64 compiler built Debug and Release version with Visual Studio first without any other option and then with D_SCL_SECURE=1 specified for every project changed Matlab's mexopts.bat and adding new lines refering to library and include (see bottom for mexopts.bat content) with Visual Studio 10 compiler tried to compile a simple file with a OpenCV library inclusion and all goes well. try to compile something that actually uses OpenCV commands and get errors. I used openmexopencv library and when tried to compile something i get this error cv.make mex -largeArrayDims -D_SECURE_SCL=1 -Iinclude -I"C:\OpenCV\build\include" -L"C:\OpenCV\build\x64\vc10\lib" -lopencv_calib3d242 -lopencv_contrib242 -lopencv_core242 -lopencv_features2d242 -lopencv_flann242 -lopencv_gpu242 -lopencv_haartraining_engine -lopencv_highgui242 -lopencv_imgproc242 -lopencv_legacy242 -lopencv_ml242 -lopencv_nonfree242 -lopencv_objdetect242 -lopencv_photo242 -lopencv_stitching242 -lopencv_ts242 -lopencv_video242 -lopencv_videostab242 src+cv\CamShift.cpp lib\MxArray.obj -output +cv\CamShift CamShift.cpp C:\Program Files\MATLAB\R2012b\extern\include\tmwtypes.h(821) : warning C4091: 'typedef ': ignorato a sinistra di 'wchar_t' quando non si dichiara alcuna variabile c:\program files\matlab\r2012b\extern\include\matrix.h(319) : error C4430: identificatore di tipo mancante, verr… utilizzato int. Nota: default-int non Š pi— supportato in C++ the content of my mexopts.bat is @echo off rem MSVC100OPTS.BAT rem rem Compile and link options used for building MEX-files rem using the Microsoft Visual C++ compiler version 10.0 rem rem $Revision: 1.1.6.4.2.1 $ $Date: 2012/07/12 13:53:59 $ rem Copyright 2007-2009 The MathWorks, Inc. rem rem StorageVersion: 1.0 rem C++keyFileName: MSVC100OPTS.BAT rem C++keyName: Microsoft Visual C++ 2010 rem C++keyManufacturer: Microsoft rem C++keyVersion: 10.0 rem C++keyLanguage: C++ rem C++keyLinkerName: Microsoft Visual C++ 2010 rem C++keyLinkerVersion: 10.0 rem rem ******************************************************************** rem General parameters rem ******************************************************************** set MATLAB=%MATLAB% set VSINSTALLDIR=c:\Program Files (x86)\Microsoft Visual Studio 10.0 set VCINSTALLDIR=%VSINSTALLDIR%\VC set OPENCVDIR=C:\OpenCV rem In this case, LINKERDIR is being used to specify the location of the SDK set LINKERDIR=c:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\ set PATH=%VCINSTALLDIR%\bin\amd64;%VCINSTALLDIR%\bin;%VCINSTALLDIR%\VCPackages;%VSINSTALLDIR%\Common7\IDE;%VSINSTALLDIR%\Common7\Tools;%LINKERDIR%\bin\x64;%LINKERDIR%\bin;%MATLAB_BIN%;%PATH% set INCLUDE=%OPENCVDIR%\build\include;%VCINSTALLDIR%\INCLUDE;%VCINSTALLDIR%\ATLMFC\INCLUDE;%LINKERDIR%\include;%INCLUDE% set LIB=%OPENCVDIR%\build\x64\vc10\lib;%VCINSTALLDIR%\LIB\amd64;%VCINSTALLDIR%\ATLMFC\LIB\amd64;%LINKERDIR%\lib\x64;%MATLAB%\extern\lib\win64;%LIB% set MW_TARGET_ARCH=win64 rem ******************************************************************** rem Compiler parameters rem ******************************************************************** set COMPILER=cl set COMPFLAGS=/c /GR /W3 /EHs /D_CRT_SECURE_NO_DEPRECATE /D_SCL_SECURE_NO_DEPRECATE /D_SECURE_SCL=0 /DMATLAB_MEX_FILE /nologo /MD set OPTIMFLAGS=/O2 /Oy- /DNDEBUG set DEBUGFLAGS=/Z7 set NAME_OBJECT=/Fo rem ******************************************************************** rem Linker parameters rem ******************************************************************** set LIBLOC=%MATLAB%\extern\lib\win64\microsoft set LINKER=link set LINKFLAGS=/dll /export:%ENTRYPOINT% /LIBPATH:"%LIBLOC%" libmx.lib libmex.lib libmat.lib /MACHINE:X64 kernel32.lib user32.lib gdi32.lib winspool.lib comdlg32.lib advapi32.lib shell32.lib ole32.lib oleaut32.lib uuid.lib odbc32.lib odbccp32.lib opencv_calib3d242.lib opencv_contrib242.lib opencv_core242.lib opencv_features2d242.lib opencv_flann242.lib opencv_gpu242.lib opencv_haartraining_engine.lib opencv_imgproc242.lib opencv_highgui242.lib opencv_legacy242.lib opencv_ml242.lib opencv_nonfree242.lib opencv_objdetect242.lib opencv_photo242.lib opencv_stitching242.lib opencv_ts242.lib opencv_video242.lib opencv_videostab242.lib /nologo /manifest /incremental:NO /implib:"%LIB_NAME%.x" /MAP:"%OUTDIR%%MEX_NAME%%MEX_EXT%.map" set LINKOPTIMFLAGS= set LINKDEBUGFLAGS=/debug /PDB:"%OUTDIR%%MEX_NAME%%MEX_EXT%.pdb" set LINK_FILE= set LINK_LIB= set NAME_OUTPUT=/out:"%OUTDIR%%MEX_NAME%%MEX_EXT%" set RSP_FILE_INDICATOR=@ rem ******************************************************************** rem Resource compiler parameters rem ******************************************************************** set RC_COMPILER=rc /fo "%OUTDIR%mexversion.res" set RC_LINKER= set POSTLINK_CMDS=del "%LIB_NAME%.x" "%LIB_NAME%.exp" set POSTLINK_CMDS1=mt -outputresource:"%OUTDIR%%MEX_NAME%%MEX_EXT%;2" -manifest "%OUTDIR%%MEX_NAME%%MEX_EXT%.manifest" set POSTLINK_CMDS2=del "%OUTDIR%%MEX_NAME%%MEX_EXT%.manifest" set POSTLINK_CMDS3=del "%OUTDIR%%MEX_NAME%%MEX_EXT%.map"

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• C++ vs Matlab vs Python as a main language for Computer Vision Research

  - by Hough

  Hi all, Firstly, sorry for a somewhat long question but I think that many people are in the same situation as me and hopefully they can also gain some benefit from this. I'll be starting my PhD very soon which involves the fields of computer vision, pattern recognition and machine learning. Currently, I'm using opencv (2.1) C++ interface and I especially like its powerful Mat class and the overloaded operations available for matrix and image operations and seamless transformations. I've also tried (and implemented many small vision projects) using opencv python interface (new bindings; opencv 2.1) and I really enjoy python's ability to integrate opencv, numpy, scipy and matplotlib. But recently, I went back to opencv C++ interface because I felt that the official python new bindings were not stable enough and no overloaded operations are available for matrices and images, not to mention the lack of machine learning modules and slow speeds in certain operations. I've also used Matlab extensively in the past and although I've used mex files and other means to speed up the program, I just felt that Matlab's performance was inadequate for real-time vision tasks, be it for fast prototyping or not. When the project becomes larger and larger, many tasks have to be re-written in C and compiled into Mex files increasingly and Matlab becomes nothing more than a glue language. Here comes the sub-questions: For carrying out research in these fields (machine learning, vision, pattern recognition), what is your main or ideal programming language for rapid prototyping of ideas and testing algorithms contained in papers? For computer vision research work, can you list down the pros and cons of using the following languages? C++ (with opencv + gsl + svmlib + other libraries) vs Matlab (with all its toolboxes) vs python (with the imcomplete opencv bindings + numpy + scipy + matplotlib). Are there computer vision PhD/postgrad students here who are using only C++ (with all its availabe libraries including opencv) without even needing to resort to Matlab or python? In other words, given the current existing computer vision or machine learning libraries, is C++ alone sufficient for fast prototyping of ideas? If you're currently using Java or C# for your research, can you list down the reasons why they should be used and how they compare to other languages in terms of available libraries? What is the de facto vision/machine learning programming language and its associated libraries used in your research group? Thanks in advance. Edit: As suggested, I've opened the question to both academic and non-academic computer vision/machine learning/pattern recognition researchers and groups.

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• Most efficient method to query a Young Tableau

  - by Matthieu M.

  A Young Tableau is a 2D matrix A of dimensions M*N such that: i,j in [0,M)x[0,N): for each p in (i,M), A[i,j] <= A[p,j] for each q in (j,N), A[i,j] <= A[i,q] That is, it's sorted row-wise and column-wise. Since it may contain less than M*N numbers, the bottom-right values might be represented either as missing or using (in algorithm theory) infinity to denote their absence. Now the (elementary) question: how to check if a given number is contained in the Young Tableau ? Well, it's trivial to produce an algorithm in O(M*N) time of course, but what's interesting is that it is very easy to provide an algorithm in O(M+N) time: Bottom-Left search: Let x be the number we look for, initialize i,j as M-1, 0 (bottom left corner) If x == A[i,j], return true If x < A[i,j], then if i is 0, return false else decrement i and go to 2. Else, if j is N-1, return false else increment j This algorithm does not make more than M+N moves. The correctness is left as an exercise. It is possible though to obtain a better asymptotic runtime. Pivot Search: Let x be the number we look for, initialize i,j as floor(M/2), floor(N/2) If x == A[i,j], return true If x < A[i,j], search (recursively) in A[0:i-1, 0:j-1], A[i:M-1, 0:j-1] and A[0:i-1, j:N-1] Else search (recursively) in A[i+1:M-1, 0:j], A[i+1:M-1, j+1:N-1] and A[0:i, j+1:N-1] This algorithm proceed by discarding one of the 4 quadrants at each iteration and running recursively on the 3 left (divide and conquer), the master theorem yields a complexity of O((N+M)**(log 3 / log 4)) which is better asymptotically. However, this is only a big-O estimation... So, here are the questions: Do you know (or can think of) an algorithm with a better asymptotical runtime ? Like introsort prove, sometimes it's worth switching algorithms depending on the input size or input topology... do you think it would be possible here ? For 2., I am notably thinking that for small size inputs, the bottom-left search should be faster because of its O(1) space requirement / lower constant term.

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• Corner Cases, Unexpected and Unusual Matlab

  - by Mikhail

  Over the years, reading others code, I encountered and collected some examples of Matlab syntax which can be at first unusual and counterintuitive. Please, feel free to comment or complement this list. I verified it r2006a. set([], 'Background:Color','red') Matlab is very forgiving sometimes. In this case, setting properties to an array of objects works also with nonsense properties, at least when the array is empty. myArray([1,round(end/2)]) This use of end keyword may seem unclean but is sometimes very handy instead of using length(myArray). any([]) ~= all([]) Surprisigly any([]) returns false and all([]) returns true. And I always thought that all is stronger then any. EDIT: with not empty argument all() returns true for a subset of values for which any() returns true (e.g. truth table). This means that any() false implies all() false. This simple rule is being violated by Matlab with [] as argument. Loren also blogged about it. Select(Range(ExcelComObj)) Procedural style COM object method dispatch. Do not wonder that exist('Select') returns zero! [myString, myCell] Matlab makes in this case an implicit cast of string variable myString to cell type {myString}. It works, also if I would not expect it to do so. [double(1.8), uint8(123)] => 2 123 Another cast example. Everybody would probably expect uint8 value being cast to double but Mathworks have another opinion. a = 5; b = a(); It looks silly but you can call a variable with round brackets. Actually it makes sense because this way you can execute a function given its handle. a = {'aa', 'bb' 'cc', 'dd'}; Surprsisingly this code neither returns a vector nor rises an error but defins matrix, using just code layout. It is probably a relict from ancient times. set(hobj, {'BackgroundColor','ForegroundColor'},{'red','blue'}) This code does what you probably expect it to do. That function set accepts a struct as its second argument is a known fact and makes sense, and this sintax is just a cell2struct away. Equvalence rules are sometimes unexpected at first. For example 'A'==65 returns true (although for C-experts it is self-evident). About which further unexpected/unusual Matlab features are you aware?

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• Why differs floating-point precision in C# when separated by parantheses and when separated by state

  - by Andreas Larsen

  I am aware of how floating point precision works in the regular cases, but I stumbled on an odd situation in my C# code. Why aren't result1 and result2 the exact same floating point value here? const float A; // Arbitrary value const float B; // Arbitrary value float result1 = (A*B)*dt; float result2 = (A*B); result2 *= dt; From this page I figured float arithmetic was left-associative and that this means values are evaluated and calculated in a left-to-right manner. The full source code involves XNA's Quaternions. I don't think it's relevant what my constants are and what the VectorHelper.AddPitchRollYaw() does. The test passes just fine if I calculate the delta pitch/roll/yaw angles in the same manner, but as the code is below it does not pass: X Expected: 0.275153548f But was: 0.275153786f [TestFixture] internal class QuaternionPrecisionTest { [Test] public void Test() { JoystickInput input; input.Pitch = 0.312312432f; input.Roll = 0.512312432f; input.Yaw = 0.912312432f; const float dt = 0.017001f; float pitchRate = input.Pitch * PhysicsConstants.MaxPitchRate; float rollRate = input.Roll * PhysicsConstants.MaxRollRate; float yawRate = input.Yaw * PhysicsConstants.MaxYawRate; Quaternion orient1 = Quaternion.Identity; Quaternion orient2 = Quaternion.Identity; for (int i = 0; i < 10000; i++) { float deltaPitch = (input.Pitch * PhysicsConstants.MaxPitchRate) * dt; float deltaRoll = (input.Roll * PhysicsConstants.MaxRollRate) * dt; float deltaYaw = (input.Yaw * PhysicsConstants.MaxYawRate) * dt; // Add deltas of pitch, roll and yaw to the rotation matrix orient1 = VectorHelper.AddPitchRollYaw( orient1, deltaPitch, deltaRoll, deltaYaw); deltaPitch = pitchRate * dt; deltaRoll = rollRate * dt; deltaYaw = yawRate * dt; orient2 = VectorHelper.AddPitchRollYaw( orient2, deltaPitch, deltaRoll, deltaYaw); } Assert.AreEqual(orient1.X, orient2.X, "X"); Assert.AreEqual(orient1.Y, orient2.Y, "Y"); Assert.AreEqual(orient1.Z, orient2.Z, "Z"); Assert.AreEqual(orient1.W, orient2.W, "W"); } } Granted, the error is small and only presents itself after a large number of iterations, but it has caused me some great headackes.

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• OpenGL 2D Texture Mapping problem.

  - by gutsblow

  Hi there, I am relatively new to OpenGL and I am having some issues when I am rendering an image as a texture for a QUAD which is as the same size of the image. Here is my code. I would be very grateful if someone helps me to solve this problem. The image appears way smaller and is squished. (BTW, the image dimensions are 500x375). glGenTextures( 1, &S_GLator_InputFrameTextureIDSu ); glBindTexture(GL_TEXTURE_2D, S_GLator_InputFrameTextureIDSu); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP); glTexParameteri (GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP); glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); glTexImage2D( GL_TEXTURE_2D, 0, 4, S_GLator_EffectCommonData.mRenderBufferWidthSu, S_GLator_EffectCommonData.mRenderBufferHeightSu, 0, GL_RGBA, GL_UNSIGNED_BYTE, dataP); glBindTexture(GL_TEXTURE_2D, S_GLator_InputFrameTextureIDSu); glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, S_GLator_EffectCommonData.mRenderBufferWidthSu, S_GLator_EffectCommonData.mRenderBufferHeightSu, GL_RGBA, GL_UNSIGNED_BYTE, bufferP); //set the matrix modes glMatrixMode( GL_PROJECTION ); glLoadIdentity(); //gluPerspective( 45.0, (GLdouble)widthL / heightL, 0.1, 100.0 ); glOrtho (0, 1, 0, 1, -1, 1); // Set up the frame-buffer object just like a window. glViewport( 0, 0, widthL, heightL ); glDisable(GL_DEPTH_TEST); glClearColor( 0.0f, 0.0f, 0.0f, 0.0f ); glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ); glMatrixMode( GL_MODELVIEW ); glLoadIdentity(); glBindTexture( GL_TEXTURE_2D, S_GLator_InputFrameTextureIDSu ); //Render the geometry to the frame-buffer object glBegin(GL_QUADS); //input frame glColor4f(1.f,1.f,1.f,1.f); glTexCoord2f(0.0f,0.0f); glVertex3f(0.f ,0.f ,0.0f); glTexCoord2f(1.0f,0.0f); glVertex3f(1.f ,0.f,0.0f); glTexCoord2f(1.0f,1.f); glVertex3f(1.f ,1.f,0.0f); glTexCoord2f(0.0f,1.f); glVertex3f(0.f ,1.f,0.0f); glEnd();

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• How to convert a 32bpp image to an indexed format?

  - by Ed Swangren

  So here are the details (I am using C# BTW): I receive a 32bpp image (JPEG compressed) from a server. At some point, I would like to use the Palette property of a bitmap to color over-saturated pixels (brightness 240) red. To do so, I need to get the image into an indexed format. I have tried converting the image to a GIF, but I get quality loss. I have tried creating a new bitmap in an index format by these methods: // causes a "Parameter not valid" error Bitmap indexed = new Bitmap(orig.Width, orig.Height, PixelFormat.Indexed) // no error, but the resulting image is black due to information loss I assume Bitmap indexed = new Bitmap(orig.Width, orig.Height, PixelFormat.Format8bppIndexed) I am at a loss now. The data in this image is changed constantly by the user, so I don't want to manually set pixels that have a brightness 240 if I can avoid it. If I can set the palette once when the image is created, my work is done. If I am going about this the wrong way to begin with please let me know. EDIT: Thanks guys, here is some more detail on what I am attempting to accomplish. We are scanning a tissue slide at high resolution (pathology application). I write the interface to the actual scanner. We use a line-scan camera. To test the line rate of the camera, the user scans a very small portion and looks at the image. The image is displayed next to a track bar. When the user moves the track bar (adjusting line rate), I change the overall intensity of the image in an attempt to model what it would look like at the new line rate. I do this using an ImageAttributes and ColorMatrix object currently. When the user adjusts the track bar, I adjust the matrix. This does not give me per pixel information, but the performance is very nice. I could use LockBits and some unsafe code here, but I would rather not rewrite it if possible. When the new image is created, I would like for all pixels with a brightness value of 240 to be colored red. I was thinking that defining a palette for the bitmap up front would be a clean way of doing this.

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• Model Fit of Binary GLM with more than 1 or 2 predictors

  - by Salmo salar

  I am trying to predict a binary GLM with multiple predictors. I can do it fine with one predictor variable however struggle when I use multiple Sample data: structure(list(attempt = structure(c(1L, 2L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 2L, 1L, 2L, 1L, 1L, 1L, 1L, 2L, 1L, 2L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 1L, 2L, 1L, 1L, 2L, 1L, 2L, 1L, 1L, 2L, 1L, 2L), .Label = c("1", "2"), class = "factor"), searchtime = c(137, 90, 164, 32, 39, 30, 197, 308, 172, 48, 867, 117, 63, 1345, 38, 122, 226, 397, 0, 106, 259, 220, 170, 102, 46, 327, 8, 10, 23, 108, 315, 318, 70, 646, 69, 97, 117, 45, 31, 64, 125, 17, 240, 63, 549, 1651, 233, 406, 334, 168, 127, 47, 881), mean.search.flow = c(15.97766667, 14.226, 17.15724762, 14.7465, 39.579, 23.355, 110.2926923, 71.95709524, 72.73666667, 32.37466667, 50.34905172, 27.98471429, 49.244, 109.1759778, 77.71733333, 37.446875, 101.23875, 67.78534615, 21.359, 36.54257143, 34.13961111, 64.35253333, 80.98554545, 61.50857143, 48.983, 63.81072727, 26.105, 46.783, 23.0605, 33.61557143, 46.31042857, 62.37061905, 12.565, 42.31983721, 15.3982, 14.49625, 23.77425, 25.626, 74.62485714, 170.1547778, 50.67125, 48.098, 66.83644444, 76.564875, 80.63189189, 136.0573243, 136.3484, 86.68688889, 34.82169565, 70.00415385, 64.67233333, 81.72766667, 57.74522034), Pass = structure(c(1L, 2L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 2L, 2L, 2L, 1L, 2L, 1L, 2L, 1L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 2L, 2L, 1L, 2L, 2L, 2L, 2L, 2L, 1L, 2L, 1L, 1L, 2L, 1L, 1L, 1L, 2L, 1L, 2L, 2L, 1L, 2L, 1L, 2L, 2L, 1L, 2L, 1L, 2L), .Label = c("0", "1"), class = "factor")), .Names = c("attempt", "searchtime", "mean.search.flow", "Pass"), class = "data.frame", row.names = c(1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 12L, 13L, 14L, 15L, 16L, 17L, 18L, 19L, 20L, 21L, 22L, 23L, 24L, 25L, 26L, 28L, 29L, 30L, 31L, 32L, 33L, 34L, 35L, 36L, 37L, 38L, 39L, 40L, 50L, 51L, 53L, 54L, 60L, 61L, 62L, 63L, 64L, 65L, 66L, 67L, 68L, 69L, 70L, 71L, 72L)) First model with single predictor M2 <- glm(Pass ~ searchtime, data = DF3, family = binomial) summary(M2) drop1(M2, test = "Chi") Plot works fine P1 <- predict(M2, newdata = MyData, type = "link", se = TRUE) plot(x=MyData$searchtime, exp(P1$fit) / (1+exp(P1$fit)), type = "l", ylim = c(0,1), xlab = "search time", ylab = "pobability of passage") lines(MyData$searchtime, exp(P1$fit+1.96*P1$se.fit)/ (1 + exp(P1$fit + 1.96 * P1$se.fit)), lty = 2) lines(MyData$searchtime, exp(P1$fit-1.96*P1$se.fit)/ (1 + exp(P1$fit - 1.96 * P1$se.fit)), lty = 2) points(DF3$searchtime, DF3$Search.and.pass) Second model M2a <- glm(Pass ~ searchtime + mean.search.flow+ attempt, data = DF3, family = binomial) summary(M2a) drop1(M2a, test = "Chi") How do I plot this with "dummy" data? I have tried along the lines of Model.matrix and expand.grid, as you would do with glmer, but fail straight away due to the two categorical variables along with factor(attempt)

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• Android - OPENGL cube is NOT in the display

  - by Marc Ortiz

  I'm trying to display a square on my display and i can't. Whats my problem? How can I display it on the screen (center of the screen)? I let my code below! Here's my render class: public class GLRenderEx implements Renderer { private GLCube cube; Context c; GLCube quad; // ( NEW ) // Constructor public GLRenderEx(Context context) { // Set up the data-array buffers for these shapes ( NEW ) quad = new GLCube(); // ( NEW ) } // Call back when the surface is first created or re-created. @Override public void onSurfaceCreated(GL10 gl, EGLConfig config) { // NO CHANGE - SKIP } // Call back after onSurfaceCreated() or whenever the window's size changes. @Override public void onSurfaceChanged(GL10 gl, int width, int height) { // NO CHANGE - SKIP } // Call back to draw the current frame. @Override public void onDrawFrame(GL10 gl) { // Clear color and depth buffers using clear-values set earlier gl.glClear(GL10.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT); gl.glLoadIdentity(); // Reset model-view matrix ( NEW ) gl.glTranslatef(-1.5f, 0.0f, -6.0f); // Translate left and into the // screen ( NEW ) // Translate right, relative to the previous translation ( NEW ) gl.glTranslatef(3.0f, 0.0f, 0.0f); quad.draw(gl); // Draw quad ( NEW ) } } And here is my square class: public class GLCube { private FloatBuffer vertexBuffer; // Buffer for vertex-array private float[] vertices = { // Vertices for the square -1.0f, -1.0f, 0.0f, // 0. left-bottom 1.0f, -1.0f, 0.0f, // 1. right-bottom -1.0f, 1.0f, 0.0f, // 2. left-top 1.0f, 1.0f, 0.0f // 3. right-top }; // Constructor - Setup the vertex buffer public GLCube() { // Setup vertex array buffer. Vertices in float. A float has 4 bytes ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length * 4); vbb.order(ByteOrder.nativeOrder()); // Use native byte order vertexBuffer = vbb.asFloatBuffer(); // Convert from byte to float vertexBuffer.put(vertices); // Copy data into buffer vertexBuffer.position(0); // Rewind } // Render the shape public void draw(GL10 gl) { // Enable vertex-array and define its buffer gl.glEnableClientState(GL10.GL_VERTEX_ARRAY); gl.glVertexPointer(3, GL10.GL_FLOAT, 0, vertexBuffer); // Draw the primitives from the vertex-array directly gl.glDrawArrays(GL10.GL_TRIANGLE_STRIP, 0, vertices.length / 3); gl.glDisableClientState(GL10.GL_VERTEX_ARRAY); } } Thanks!!

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• Android - Transforming widgets within transformed widgets and the resulting usability issues.

  - by Ben Rose

  Hello. I'm new to Android application development and I'm currently experimenting with various UI ideas. In the image below, you can see a vertically scrolling list of horizontally scrolling galleries (and also textviews as you can see). I'm also doing some matrix and camera transformations which I will come to in a minute. For the background of the list elements, I use green. Blue is the background of the galleries, and red is the background for the images. These are just for my benefit of learning. The galleries being used are extended classes where I overrode the drawChild method to perform a canvas scale operation in order for the image closest to the center (width) to be larger than the others. The list view going vertically, I overrode the drawChild method and used the camera rotations from lack of depth dimension in the canvas functionality. The items in the list are scaled down and rotated relative to their position's proximity to the center (height). I understood that scrolling and clicking would not necessarily follow along with the image transforms, but it appears as though the parent Gallery class's drawing is constrained to the original coordinates as well (see photo below). I would love to hear any insight any of you have regarding how I can change the coordinates of the galleries in what is rendered via gallery scroll and the touch responsiveness of said gallery. Images in the gallery are not same dimensions, so don't let that throw you in looking at the image below Thanks in advance! Ben link to image (could not embed) -- Update: I was using my test application UI and noticed that when I got the UI to the point of the linked image and then I touched the top portion of the next row in the list, the gallery updated to display the proper representation. So, I added a call to clearFocus() in the drawChild method and that resulted in more accurate drawing. It does seem a tad slower, and since I'm on the Incredible, I'm worried it is a bloated solution. In any event, I would still appreciate any thoughts you have regarding the best way to have the views display properly and how to translate the touch events in the gallery's new displayed area to its touchable coordinates so that scrolling on the actual images works when the gallery has moved. Thanks!

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• java quaternion 3D rotation implementation

  - by MRM

  I made a method to rotate a list of points using quaternions, but all i get back as output is the same list i gave to rotate on. Maybe i did not understood corectly the math for 3d rotations or my code is not implemented the right way, could you give me a hand? This is the method i use: public static ArrayList<Float> rotation3D(ArrayList<Float> points, double angle, int x, int y, int z) { ArrayList<Float> newpoints = points; for (int i=0;i<points.size();i+=3) { float x_old = points.get(i).floatValue(); float y_old = points.get(i+1).floatValue(); float z_old = points.get(i+2).floatValue(); double[] initial = {1,0,0,0}; double[] total = new double[4]; double[] local = new double[4]; //components for local quaternion //w local[0] = Math.cos(0.5 * angle); //x local[1] = x * Math.sin(0.5 * angle); //y local[2] = y * Math.sin(0.5 * angle); //z local[3] = z * Math.sin(0.5 * angle); //components for final quaternion Q1*Q2 //w = w1w2 - x1x2 - y1y2 - z1z2 total[0] = local[0] * initial[0] - local[1] * initial[1] - local[2] * initial[2] - local[3] * initial[3]; //x = w1x2 + x1w2 + y1z2 - z1y2 total[1] = local[0] * initial[1] + local[1] * initial[0] + local[2] * initial[3] - local[3] * initial[2]; //y = w1y2 - x1z2 + y1w2 + z1x2 total[2] = local[0] * initial[2] - local[1] * initial[3] + local[2] * initial[0] + local[3] * initial[1]; //z = w1z2 + x1y2 - y1x2 + z1w2 total[3] = local[0] * initial[3] + local[1] * initial[2] - local[2] * initial[1] + local[3] * initial[0]; //new x,y,z of the 3d point using rotation matrix made from the final quaternion float x_new = (float)((1 - 2 * total[2] * total[2] - 2 * total[3] * total[3]) * x_old + (2 * total[1] * total[2] - 2 * total[0] * total[3]) * y_old + (2 * total[1] * total[3] + 2 * total[0] * total[2]) * z_old); float y_new = (float) ((2 * total[1] * total[2] + 2 * total[0] * total[3]) * x_old + (1 - 2 * total[1] * total[1] - 2 * total[3] * total[3]) * y_old + (2 * total[2] * total[3] + 2 * total[0] * total[1]) * z_old); float z_new = (float) ((2 * total[1] * total[3] - 2 * total[0] * total[2]) * x_old + (2 * total[2] * total[3] - 2 * total[0] * total[1]) * y_old + (1 - 2 * total[1] * total[1] - 2 * total[2] * total[2]) * z_old); newpoints.set(i, x_new); newpoints.set(i+1, y_new); newpoints.set(i+2, z_new); } return newpoints; } For rotation3D(points, 50, 0, 1, 0) where points is: 0.0, 0.0, -9.0; 0.0, 0.0, -11.0; 20.0, 0.0, -11.0; 20.0, 0.0, -9.0; i get back the same list.

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• Open Cl.I just need to convert the code to using two work items in the for loop .Currentlly it uses one

  - by user1660282

  spmv_csr_scalar_kernel(const int num_rows , const int * ptr , const int * indices , const float * data , const float * x, float * y) { int row = get_global_id(0); if(row < num_rows) { float dot = 0; int row_start = ptr[row]; int row_end = ptr[row+1]; for (int jj = row_start; jj < row_end; jj++) { dot += data[jj] * x[indices[jj]]; } y[row] += dot; } } Above is the Open Cl code for multiplying a sparse matrix in CSR format with a Column vector.It uses one global work item per for loop.Can anybody help me in using two work items in each for loop.I am new to open cl and get a lot of issues if I modify even the smallest thing.Please help me.This a part of my project.I made it this parallel but I wanna make it more parallel.Please help me if you can.plzzzz A single work item executes the for loop from row_start to row_end.I want that this row or for loop is further divided into two parts each executed by a single work item.How do I go on accomplishing that? This is what I could come up with but its returning the wrong output.plzz help __kernel void mykernel(__global int* colvector,__global int* val,__global int* result,__global int* index,__global int* rowptr,__global int* sync) { __global int vals[8]={0,0,0,0,0,0,0,0}; for(int i=0;i<4;i++) { result[i]=0; } barrier(CLK_GLOBAL_MEM_FENCE); int thread_id=get_global_id(0); int warp_id=thread_id/2; int lane=(thread_id)&1; int row=warp_id; if(row<4) { int row_start = rowptr[row]; int row_end = rowptr[row+1]; vals[thread_id]=0; for (int i = row_start+lane; i<row_end; i+=2) { vals[thread_id]+=val[i]*colvector[index[i]]; } vals[thread_id]+=vals[thread_id+1]; if(lane==0){ result[row] += vals[thread_id]; } } }

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• c++ class member functions selected by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched stackoverflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instatiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state info was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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• Problem on a Floyd-Warshall implementation using c++

  - by Henrique

  I've got a assignment for my college, already implemented Dijkstra and Bellman-Ford sucessfully, but i'm on trouble on this one. Everything looks fine, but it's not giving me the correct answer. Here's the code: void FloydWarshall() { //Also assume that n is the number of vertices and edgeCost(i,i) = 0 int path[500][500]; /* A 2-dimensional matrix. At each step in the algorithm, path[i][j] is the shortest path from i to j using intermediate vertices (1..k-1). Each path[i][j] is initialized to edgeCost(i,j) or infinity if there is no edge between i and j. */ for(int i = 0 ; i <= nvertices ; i++) for(int j = 0 ; j <= nvertices ; j++) path[i][j] = INFINITY; for(int j = 0 ; j < narestas ; j++) //narestas = number of edges { path[arestas[j]->v1][arestas[j]->v2] = arestas[j]->peso; //peso = weight of the edge (aresta = edge) path[arestas[j]->v2][arestas[j]->v1] = arestas[j]->peso; } for(int i = 0 ; i <= nvertices ; i++) //path(i, i) = 0 path[i][i] = 0; //test print, it's working fine //printf("\n\n\nResultado FloydWarshall:\n"); //for(int i = 1 ; i <= nvertices ; i++) // printf("distancia ao vertice %d: %d\n", i, path[1][i]); //heres the problem, it messes up, and even a edge who costs 4, and the minimum is 4, it prints 2. //for k = 1 to n for(int k = 1 ; k <= nvertices ; k++) //for i = 1 to n for(int i = 1 ; i <= nvertices ; i++) //for j := 1 to n for(int j = 1 ; j <= nvertices ; j++) if(path[i][j] > path[i][k] + path[k][j]) path[i][j] = path[i][k] + path[k][j]; printf("\n\n\nResultado FloydWarshall:\n"); for(int i = 1 ; i <= nvertices ; i++) printf("distancia ao vertice %d: %d\n", i, path[1][i]); } im using this graph example i've made: 6 7 1 2 4 1 5 1 2 3 1 2 5 2 5 6 3 6 4 6 3 4 2 means we have 6 vertices (1 to 6), and 7 edges (1,2) with weight 4... etc.. If anyone need more info, i'm up to giving it, just tired of looking at this code and not finding an error.

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• segmented reduction with scattered segments

  - by Christian Rau

  I got to solve a pretty standard problem on the GPU, but I'm quite new to practical GPGPU, so I'm looking for ideas to approach this problem. I have many points in 3-space which are assigned to a very small number of groups (each point belongs to one group), specifically 15 in this case (doesn't ever change). Now I want to compute the mean and covariance matrix of all the groups. So on the CPU it's roughly the same as: for each point p { mean[p.group] += p.pos; covariance[p.group] += p.pos * p.pos; ++count[p.group]; } for each group g { mean[g] /= count[g]; covariance[g] = covariance[g]/count[g] - mean[g]*mean[g]; } Since the number of groups is extremely small, the last step can be done on the CPU (I need those values on the CPU, anyway). The first step is actually just a segmented reduction, but with the segments scattered around. So the first idea I came up with, was to first sort the points by their groups. I thought about a simple bucket sort using atomic_inc to compute bucket sizes and per-point relocation indices (got a better idea for sorting?, atomics may not be the best idea). After that they're sorted by groups and I could possibly come up with an adaption of the segmented scan algorithms presented here. But in this special case, I got a very large amount of data per point (9-10 floats, maybe even doubles if the need arises), so the standard algorithms using a shared memory element per thread and a thread per point might make problems regarding per-multiprocessor resources as shared memory or registers (Ok, much more on compute capability 1.x than 2.x, but still). Due to the very small and constant number of groups I thought there might be better approaches. Maybe there are already existing ideas suited for these specific properties of such a standard problem. Or maybe my general approach isn't that bad and you got ideas for improving the individual steps, like a good sorting algorithm suited for a very small number of keys or some segmented reduction algorithm minimizing shared memory/register usage. I'm looking for general approaches and don't want to use external libraries. FWIW I'm using OpenCL, but it shouldn't really matter as the general concepts of GPU computing don't really differ over the major frameworks.

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• How do I stack images to simulate depth using Core Animation?

  - by Jeffrey Berthiaume

  I have a series of UIImages with which I need to simulate depth. I can't use scaling because I need to be able to rotate the parent view, and the images should look like they're stacked visibly in front of each other, not on the same plane. I made a new ViewController-based project and put this in the viewDidLoad (as well as attached three 120x120 pixel images named 1.png, 2.png, and 3.png): - (void)viewDidLoad { // display image 3 UIImageView *three = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"3.png"]]; three.center = CGPointMake(160 + 60, 240 - 60); [self.view addSubview:three]; // rotate image 3 around the z axis // THIS IS INCORRECT CATransform3D theTransform = three.layer.transform; theTransform.m34 = 1.0 / -1000; three.layer.transform = theTransform; // display image 2 UIImageView *two = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"2.png"]]; two.center = CGPointMake(160, 240); [self.view addSubview:two]; // display image 1 UIImageView *one = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"1.png"]]; one.center = CGPointMake(160 - 60, 240 + 60); [self.view addSubview:one]; // rotate image 3 around the z axis // THIS IS INCORRECT theTransform = one.layer.transform; theTransform.m34 = 1.0 / 1000; one.layer.transform = theTransform; // release the images [one release]; [two release]; [three release]; // rotate the parent view around the y axis theTransform = self.view.layer.transform; theTransform.m14 = 1.0 / -500; self.view.layer.transform = theTransform; [super viewDidLoad]; } I have very specific reasons why I'm not using an EAGLView and why I'm not loading the images as CALayers (i.e. why I'm using UIImageViews for each one). This is just a quick demo that I can use to work out exactly what I need in my parent application. Is there some matrix way to translate these 2d images along the z-axis so they will look like what I'm trying to represent? I've gone through the other StackOverflow articles as well as the Wikipedia references, and have not found what I'm looking for -- although I might not necessarily be using the right terms for what I'm trying to do.

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• Mult-line Svg tooltip

  - by John Vaughan

  I have created numerous polygon shapes in SVG format. and grouped them together. When the user hovers over the group a tooltip box appear. I have used ecmascript. What i am looking to do is make the tooltip box a multiline box. Any ideas how to do this? <script type="text/ecmascript"> <![CDATA[ function init(evt) { if ( window.svgDocument == null ) { svgDocument = evt.target.ownerDocument; } tooltip = svgDocument.getElementById('tooltip'); tooltip_bg = svgDocument.getElementById('tooltip_bg'); } function ShowTooltip(evt, mouseovertext) { tooltip.setAttributeNS(null,"x",evt.clientX+17); tooltip.setAttributeNS(null,"y",evt.clientY+14); tooltip.firstChild.data = mouseovertext; tooltip.setAttributeNS(null,"visibility","visible"); length = tooltip.getComputedTextLength(); tooltip_bg.setAttributeNS(null,"width",length+8); tooltip_bg.setAttributeNS(null,"x",evt.clientX+14); tooltip_bg.setAttributeNS(null,"y",evt.clientY+1); tooltip_bg.setAttributeNS(null,"visibility","visibile"); } function HideTooltip(evt) { tooltip.setAttributeNS(null,"visibility","hidden"); tooltip_bg.setAttributeNS(null,"visibility","hidden"); } ]]> </script> <SVG> <g onmousemove="ShowTooltip(evt, 'GHANA 2000')" onmouseout="HideTooltip(evt)"> <path fill="#EEEEEE" d="M250,0c47,0,85.183,10.506,125,33.494L250,250V0z"/> <path id="score" d="M250,57c36.284,0,65.761,8.11,96.5,25.857L250,250V57z"/> <path fill="none" stroke="#FFFFFF" stroke-width="2" stroke-miterlimit="10" d="M250,0c47,0,85.183,10.506,125,33.494L250,250V0z"/> <text transform="matrix(1 0 0 1 283.9883 92.0024)" fill="#FFFFFF" font-family="'WalkwayBlack'" font-size="16">62</text> </g> <rect class="tooltip_bg" id="tooltip_bg" x="0" y="0" width="55" height="17" visibility="hidden"/> <text class="tooltip" id="tooltip" x="0" y="0" visibility="hidden">Tooltip</text> <SVG>

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• c++ class member functions instatiated by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched stackoverflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state info was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (vc++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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• How to set background in OpenGL captured image from OpenCV

  - by user325487

  Hey All, i'm relatively new to Artoolkitplus and openGL i'm having a tough time getting the image i capture through openCV to be set as the background image in OpenGL ... I also cannot convert the image i take through the camera using opencv to be scaled to 320x280 from 640x480 .. i also have to save my image and load if for things to work... here's my code //////////// int findMarker() { IplImage* image = cvQueryFrame( capture ); if( !capture ) { fprintf( stderr, "ERROR: capture is NULL \n" ); getchar(); return -1; } if( !image ) { fprintf( stderr, "ERROR: frame is null...\n" ); getchar(); } //cvShowImage( "Capture", frame ); //image = cvCloneImage( frame ); try{ if(!cvSaveImage("immagineTmp.jpg",image)) printf("Could not save\n"); } catch(void*) {} image = cvLoadImage("immagineTmp.jpg", 1); cvShowImage( "Image", image ); glLoadIdentity(); ////////////// glDisable(GL_DEPTH_TEST); glOrtho(0,640,0,480,-1,1); glGenTextures(1, &bgid); glBindTexture(GL_TEXTURE_2D, bgid); // Create Linear Filtered Texture glBindTexture(GL_TEXTURE_2D, bgid); glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR); glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR); glTexImage2D(GL_TEXTURE_2D, 0, 3, image-width, image-height, 0, GL_RGB, GL_UNSIGNED_BYTE, image-imageData); glBindTexture(GL_TEXTURE_2D, bgid); glBegin(GL_QUADS); glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.2f, -1.0f, -2.0f); glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.2f, -1.0f, -2.0f); glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.2f, 1.0f, -2.0f); glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.2f, 1.0f, -2.0f); glEnd(); glEnable(GL_DEPTH_TEST); glLoadIdentity(); //////////// // do the OpenGL camera setup glMatrixMode(GL_PROJECTION); glLoadMatrixf(tracker-getProjectionMatrix()); int markerId = tracker-calc((unsigned char *)(image-imageData)); float conf = tracker-getConfidence(); // use the result of calc() to setup the OpenGL transformation glMatrixMode(GL_MODELVIEW); glLoadMatrixf(tracker-getModelViewMatrix()); if(markerId!=-1) { printf("\n\nFound marker %d (confidence %d%%)\n\nPose-Matrix:\n ", markerId, (int(conf*100.0f))); for(int i=0; i<16; i++) printf("%.2f %s", tracker-getModelViewMatrix()[i], (i%4==3)?"\n " : ""); } cvReleaseImage(&image); return 0; }

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• Drawing with element array in OpenGL ES

  - by FatalMojo

  Hello! I am trying to use OpenGLES to draw a x by y matrix of squares about an arbitrary point. I have an array sideVertice[] that holds a series of vertex structs defined as such typedef struct { GLfloat x; GLfloat y; GLfloat z; } Vertex3D; and an element array defined as such GLubyte elementArray[]; my draw loop is as such glLoadIdentity(); glVertexPointer(3, GL_FLOAT, 0, cube.sideVertice); for (int i=0; i<((cube.cubeSize + 1)*(cube.cubeSize + 1)); i++) { for (int j=0; j<=3; j++) { elementArray[j] = j + i*4; glDrawElements(GL_TRIANGLE_STRIP, 4, GL_UNSIGNED_BYTE, elementArray); } } for (int i=0; i<=3; i++) elementArray[i] = i; However, the visual output is corrupted and I cannot figure out what the problem is. here is an output of the vertice held in the array: 2010-04-15 23:44:48.816 RubixGL[4203:20b] vertex[0][0] x:-26.000000 y:1.000000 2010-04-15 23:44:48.817 RubixGL[4203:20b] vertex[1][1] x:-26.000000 y:26.000000 2010-04-15 23:44:48.826 RubixGL[4203:20b] vertex[2][2] x:-1.000000 y:1.000000 2010-04-15 23:44:48.829 RubixGL[4203:20b] vertex[3][3] x:-1.000000 y:26.000000 2010-04-15 23:44:48.830 RubixGL[4203:20b] Next Face 2010-04-15 23:44:48.830 RubixGL[4203:20b] vertex[0][4] x:1.000000 y:1.000000 2010-04-15 23:44:48.832 RubixGL[4203:20b] vertex[1][5] x:1.000000 y:26.000000 2010-04-15 23:44:48.837 RubixGL[4203:20b] vertex[2][6] x:26.000000 y:1.000000 2010-04-15 23:44:48.838 RubixGL[4203:20b] vertex[3][7] x:26.000000 y:26.000000 2010-04-15 23:44:48.848 RubixGL[4203:20b] Next Face 2010-04-15 23:44:48.849 RubixGL[4203:20b] vertex[0][8] x:-26.000000 y:-26.000000 2010-04-15 23:44:48.850 RubixGL[4203:20b] vertex[1][9] x:-26.000000 y:-1.000000 2010-04-15 23:44:48.851 RubixGL[4203:20b] vertex[2][10] x:-1.000000 y:-26.000000 2010-04-15 23:44:48.852 RubixGL[4203:20b] vertex[3][11] x:-1.000000 y:-1.000000 2010-04-15 23:44:48.853 RubixGL[4203:20b] Next Face 2010-04-15 23:44:48.853 RubixGL[4203:20b] vertex[0][12] x:1.000000 y:-26.000000 2010-04-15 23:44:48.854 RubixGL[4203:20b] vertex[1][13] x:1.000000 y:-1.000000 2010-04-15 23:44:48.854 RubixGL[4203:20b] vertex[2][14] x:26.000000 y:-26.000000 2010-04-15 23:44:48.855 RubixGL[4203:20b] vertex[3][15] x:26.000000 y:-1.000000 any ideas?

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• Create a Color Picker, similar to Photoshop's, using Javascript and HTML Canvas

  - by André Alçada Padez

  I am not at all versed in Computer Graphics and am in need of creating a color picker as a javascript tool to embed in an HTML page. First, and looking at Photoshop's one, i thought of the RGB palette as a three-dimensional matrix. My first attempt envolved: <script type="text/javascript"> var rgCanvas = document.createElement('canvas'); rgCanvas.width = 256; rgCanvas.height = 256; rgCanvas.style.border = '3px solid black'; for (g = 0; g < 256; g++){ for (r = 0; r < 256; r++){ var context = rgCanvas.getContext('2d'); context.beginPath(); context.moveTo(r,g); context.strokeStyle = 'rgb(' + r + ', ' + g + ', 0)'; context.lineTo(r+1,g+1); context.stroke(); context.closePath(); } } var bCanvas = document.createElement('canvas'); bCanvas.width = 20; bCanvas.height = 256; bCanvas.style.border = '3px solid black'; for (b = 0; b < 256; b++){ var context = bCanvas.getContext('2d'); context.beginPath(); context.moveTo(0,b); context.strokeStyle = 'rgb(' + 0 + ', ' + 0 + ', ' + b + ')'; context.lineTo(20, b); context.stroke(); context.closePath(); } document.body.appendChild(rgCanvas); document.body.appendChild(bCanvas); </script> this results in something like My thought is this is too linear, comparing to the ones i see in Photoshop and on the web. I would like to know the logic behind the color mapping in a picker like this: I don't really need the algorythms itself, i'm mainly trying to understand the logic. Thanks

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• C++ class member functions instantiated by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched Stack Overflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instantiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits that are tested at runtime. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state information was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. The compiler (VC++ 2008) always complained that things didn't match. I would yell, "SFINAE, you moron!" but the moron is probably me. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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• DFS Backtracking with java

  - by Cláudio Ribeiro

  I'm having problems with DFS backtracking in an adjacency matrix. Here's my code: (i added the test to the main in case someone wants to test it) public class Graph { private int numVertex; private int numEdges; private boolean[][] adj; public Graph(int numVertex, int numEdges) { this.numVertex = numVertex; this.numEdges = numEdges; this.adj = new boolean[numVertex][numVertex]; } public void addEdge(int start, int end){ adj[start-1][end-1] = true; adj[end-1][start-1] = true; } List<Integer> visited = new ArrayList<Integer>(); public Integer DFS(Graph G, int startVertex){ int i=0; if(pilha.isEmpty()) pilha.push(startVertex); for(i=1; i<G.numVertex; i++){ pilha.push(i); if(G.adj[i-1][startVertex-1] != false){ G.adj[i-1][startVertex-1] = false; G.adj[startVertex-1][i-1] = false; DFS(G,i); break; }else{ visited.add(pilha.pop()); } System.out.println("Stack: " + pilha); } return -1; } Stack<Integer> pilha = new Stack(); public static void main(String[] args) { Graph g = new Graph(6, 9); g.addEdge(1, 2); g.addEdge(1, 5); g.addEdge(2, 4); g.addEdge(2, 5); g.addEdge(2, 6); g.addEdge(3, 4); g.addEdge(3, 5); g.addEdge(4, 5); g.addEdge(6, 4); g.DFS(g, 1); } } I'm trying to solve the euler path problem. the program solves basic graphs but when it needs to backtrack, it just does not do it. I think the problem might be in the stack manipulations or in the recursive dfs call. I've tried a lot of things, but still can't seem to figure out why it does not backtrack. Can somebody help me ?

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• Are comonads a good fit for modeling the Wumpus world?

  - by Tim Stewart

  I'm trying to find some practical applications of a comonad and I thought I'd try to see if I could represent the classical Wumpus world as a comonad. I'd like to use this code to allow the Wumpus to move left and right through the world and clean up dirty tiles and avoid pits. It seems that the only comonad function that's useful is extract (to get the current tile) and that moving around and cleaning tiles would not use be able to make use of extend or duplicate. I'm not sure comonads are a good fit but I've seen a talk (Dominic Orchard: A Notation for Comonads) where comonads were used to model a cursor in a two-dimensional matrix. If a comonad is a good way of representing the Wumpus world, could you please show where my code is wrong? If it's wrong, could you please suggest a simple application of comonads? module Wumpus where -- Incomplete model of a world inhabited by a Wumpus who likes a nice -- tidy world but does not like falling in pits. import Control.Comonad -- The Wumpus world is made up of tiles that can be in one of three -- states. data Tile = Clean | Dirty | Pit deriving (Show, Eq) -- The Wumpus world is a one dimensional array partitioned into three -- values: the tiles to the left of the Wumpus, the tile occupied by -- the Wumpus, and the tiles to the right of the Wumpus. data World a = World [a] a [a] deriving (Show, Eq) -- Applies a function to every tile in the world instance Functor World where fmap f (World as b cs) = World (fmap f as) (f b) (fmap f cs) -- The Wumpus world is a Comonad instance Comonad World where -- get the part of the world the Wumpus currently occupies extract (World _ b _) = b -- not sure what this means in the Wumpus world. This type checks -- but does not make sense to me. extend f w@(World as b cs) = World (map world as) (f w) (map world cs) where world v = f (World [] v []) -- returns a world in which the Wumpus has either 1) moved one tile to -- the left or 2) stayed in the same place if the Wumpus could not move -- to the left. moveLeft :: World a -> World a moveLeft w@(World [] _ _) = w moveLeft (World as b cs) = World (init as) (last as) (b:cs) -- returns a world in which the Wumpus has either 1) moved one tile to -- the right or 2) stayed in the same place if the Wumpus could not move -- to the right. moveRight :: World a -> World a moveRight w@(World _ _ []) = w moveRight (World as b cs) = World (as ++ [b]) (head cs) (tail cs) initWorld = World [Dirty, Clean, Dirty] Dirty [Clean, Dirty, Pit] -- cleans the current tile cleanTile :: Tile -> Tile cleanTile Dirty = Clean cleanTile t = t Thanks!

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• Finding good heuristic for A* search

  - by Martin

  I'm trying to find the optimal solution for a little puzzle game called Twiddle (an applet with the game can be found here). The game has a 3x3 matrix with the number from 1 to 9. The goal is to bring the numbers in the correct order using the minimum amount of moves. In each move you can rotate a 2x2 square either clockwise or counterclockwise. I.e. if you have this state 6 3 9 8 7 5 1 2 4 and you rotate the upper left 2x2 square clockwise you get 8 6 9 7 3 5 1 2 4 I'm using a A* search to find the optimal solution. My f() is simply the number of rotations need. My heuristic function already leads to the optimal solution but I don't think it's the best one you can find. My current heuristic takes each corner, looks at the number at the corner and calculates the manhatten distance to the position this number will have in the solved state (which gives me the number of rotation needed to bring the number to this postion) and sums all these values. I.e. You take the above example: 6 3 9 8 7 5 1 2 4 and this end state 1 2 3 4 5 6 7 8 9 then the heuristic does the following 6 is currently at index 0 and should by at index 5: 3 rotations needed 9 is currently at index 2 and should by at index 8: 2 rotations needed 1 is currently at index 6 and should by at index 0: 2 rotations needed 4 is currently at index 8 and should by at index 3: 3 rotations needed h = 3 + 2 + 2 + 3 = 10 But there is the problem, that you rotate 4 elements at once. So there a rare cases where you can do two (ore more) of theses estimated rotations in one move. This means theses heuristic overestimates the distance to the solution. My current workaround is, to simply excluded one of the corners from the calculation which solves this problem at least for my test-cases. I've done no research if really solves the problem or if this heuristic still overestimates in same edge-cases. So my question is: What is the best heuristic you can come up with? (Disclaimer: This is for a university project, so this is a bit of homework. But I'm free to use any resource if can come up with, so it's okay to ask you guys. Also I will credit Stackoverflow for helping me ;) )

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