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• Calculating the position of an object with regards to current position using OpenGL like matrices

  - by spartan2417

  i have a 1st person camera that collides with walls, i also have a small sphere in front of my camera denoted by the camera position plus the distance ahead. I cannot get the postion of the sphere but i have the position of my camera. e.g. i need to find the position of the point or at the very least find away of calculating the position using the camera positions. code: static Float P_z = 0; P_z = -15; PushMatrix(); LoadMatrix(&Inv); Material(SCEGU_AMBIENT, 0x00000066); TranslateXYZ(0,0,P_z); ScaleXYZ(0.1f,0.1f,0.1f); pointer.Render(); PopMatrix(); where Inv is the camera positions (Inv.w.x,Inv.w.z), pointer is the sphere.

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• How do I create a camera?

  - by Morphex

  I am trying to create a generic camera class for a game engine, which works for different types of cameras (Orbital, GDoF, FPS), but I have no idea how to go about it. I have read about quaternions and matrices, but I do not understand how to implement it. Particularly, it seems you need "Up", "Forward" and "Right" vectors, a Quaternion for rotations, and View and Projection matrices. For example, an FPS camera only rotates around the World Y and the Right Axis of the camera; the 6DoF rotates always around its own axis, and the orbital is just translating for a set distance and making it look always at a fixed target point. The concepts are there; implementing this is not trivial for me. SharpDX seems to have has already Matrices and Quaternions implemented, but I don't know how to use them to create a camera. Can anyone point me on what am I missing, what I got wrong? I would really enjoy if you could give a tutorial, some piece of code, or just plain explanation of the concepts.

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• How to do directional per fragment lighting in world space?

  - by user

  I am attempting to create a GLSL shader for simple, per-fragment directional light. So far, after following many tutorials, I have continually ran into the issue: my light is specified in world coordinates, however, the shader treats the light's position as being in eye space, thus, the light direction changes when I move the camera. My question is, how to I transform a directional light position such as (50, 50, 50, 0) into eye space, or, would doing things this way be the incorrect approach to the problem?

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• How do I create a bounding frustrum from a view & projection matrix?

  - by Narf the Mouse

  Given a left-handed Projection matrix, a left-handed View matrix, a ViewProj matrix of View * Projection - How do I create a bounding Frustum comprised of near, far, left, right and top, bottom planes? The only example I could find on Google (Tutorial 16: Frustum Culling) seems to not work; for example, if the math is used as given, the near-plane's distance is a negative. This places the near-plane behind the camera...

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• Rotating a child shape relative to its parent's orientation

  - by user1423893

  When rotating a shape using a quaternion value I also wish rotate its child shape. The parent and child shapes both start with different orientations but their relative orientations should always be the same. How can I use the difference between the previous and current quaternions of the parent shape in order to transform the child segment and rotate it relative to its parent shape? public Quaternion Orientation { get { return entity.Orientation; } set { Quaternion previousValue = entity.Orientation; entity.Orientation = value; // Use the difference between the quaternion values to update child orientation } }

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• HLSL What you get when you subtract world position from InvertViewProjection.Transform?

  - by cubrman

  In one of NVIDIA's Vertex shaders (the metal one) I found the following code: // transform object normals, tangents, & binormals to world-space: float4x4 WorldITXf : WorldInverseTranspose < string UIWidget="None"; >; // provide tranform from "view" or "eye" coords back to world-space: float4x4 ViewIXf : ViewInverse < string UIWidget="None"; >; ... float4 Po = float4(IN.Position.xyz,1); // homogeneous location coordinates float4 Pw = mul(Po,WorldXf); // convert to "world" space OUT.WorldView = normalize(ViewIXf[3].xyz - Pw.xyz); The term OUT.WorldView is subsequently used in a Pixel Shader to compute lighting: float3 Ln = normalize(IN.LightVec.xyz); float3 Nn = normalize(IN.WorldNormal); float3 Vn = normalize(IN.WorldView); float3 Hn = normalize(Vn + Ln); float4 litV = lit(dot(Ln,Nn),dot(Hn,Nn),SpecExpon); DiffuseContrib = litV.y * Kd * LightColor + AmbiColor; SpecularContrib = litV.z * LightColor; Can anyone tell me what exactly is WorldView here? And why do they add it to the normal?

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• Premultiplying matrices with Perspective destroys them

  - by Shadows In Rain

  If I apply world_to_camera, perspective and camera_to_screen to my mesh, everything is okay. But if I premultiply given matrices (i.e. transform = world_to_camera * perpective * camera_to_screen) before applying, then it seems like only perspective has effect. If it is important... My 3d framework was written from scratch (test project for job interview). But it works flawlessly, or at least I think so. So, question. This is expected behaviour, or my implementation is wrong?

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• Why do we move the world instead of the camera

  - by sharethis

  I heard that in an OpenGL game what we do to let the player move is not to move the camera but to move the whole world around. For example here is an extract of this tutorial: http://open.gl/transformations In real life you're used to moving the camera to alter the view of a certain scene, in OpenGL it's the other way around. The camera in OpenGL cannot move and is defined to be located at (0,0,0) facing the negative Z direction. That means that instead of moving and rotating the camera, the world is moved and rotated around the camera to construct the appropriate view. Why do we do that?

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• Problems with 3D transformation - (SharpDX)

  - by Morphex

  First of all , I have been trying to get this right for a couple of day already, I have read so much info and still fail miserably to understand this. So I am going to tell you that even though I have done fairly amount of research myself, I failed to implement it. I must say miserably I am trying to create a generic camera class for a game engine of sorts - for research purposes only - the thing is I have no idea how to go about it. I have read about quaternions and matrices, but when it comes to the actual implementation I suck at it. Sharpdx has already Matrices and QUaternions implemented. SO no big deal on the map behind it. How in the world would I go about creating a camera? I have seen so many camera examples and still can't make one that works as expected. I would like to implement diferent types too (Orbital, 6DoF, FPS). So what is need for a camera? UP, Forward and Right vectors I read they are needed, also a quaternion for rotations, and View and Projection matrices. I understand that a FPS camera for instance only rotates around the World Y and the Right Axis of the camera. the 6DoF rotates always around their own axis, and the orbital is just translating for set distance and making it look always at a fixed target point. The concepts are there, now implementing this is not trivial for me. Can anyone point me on what am I missing, what I got wrong? I would really enjoy if you could give a tutorial, some piece of code, or just plain explanation of the concepts. Thank you for readin, a frustrated coder.

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• How can I implement smooth rotation from one direction to another?

  - by user1759052

  I'm having a problem with animating rotations with 1Matrix.CreateRotationY() with my basic 3D game. Based on where you click the mouse, I want the 3D object to rotate to that direction and then move. I am using this to determine the target direction: float rot = (float)(Math.Atan2(X, Z)); It gives me the correct value, but I am not sure how to handle the rotation animation from current direction to new direction. I've tried a few things, but to no avail. Do you guys know of any good ways of solving this issue?

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• Ray-Box Intersection during Scene traversal with matrix transforms

  - by Myx

  Hello: There are a few ways that I'm testing my ray-box intersections: Using the ComputeIntersectionBox(...) method, that takes a ray and a box as arguments and computes the closest intersection of the ray and the box. This method works by forming a plane with each of the faces of the box and finding an intersection with each of the planes. Once an intersection is found, a check is made whether or not the point is on the surface of the box by checking that the intersection point is between the corner points. When I look at rays after running this algorithm on two different boxes, I obtain the correct intersections. Using ComputeIntersectionScene(...) method without using the matrix transformations on a scene that has two spheres, a dodecahedron (a triangular mesh), and two boxes. ComputeIntersectionScene(...) recursively traverses all of the nodes of the scene graph and computes the closest intersection with the given ray. This test in particular does not apply any transformations that parent nodes may have that also need to be applied to their children. With this test, I also obtain the correct intersections. Using ComputeIntersectionScene(...) method WITH the matrix transformations. This test works like the one above except that before finding an intersection between the ray and a node in the scene, the ray is transformed into the node's coordinate frame using the inverse of the node's transformation matrix and after the intersection has been computed, this intersection is transformed back into the world coordinates by applying the transformation matrix to the intersection point. When testing with the third method on the same scene file as described in 2, testing with 4 rays (thus one ray intersects the one sphere, one ray the the other sphere, one ray one box, and one ray the other box), only the two spheres get intersected and the two boxes do not get intersections. When I debug looking into my ComputeIntersectionBox(...) method, it actually tells me that the ray intersects every plane on the box but each intersection point does not lie on the box. This seems to be strange behavior, since when using test 2 without transformations, I obtain the correct box intersections (thus, I believe my ray-box intersection to be correct) and when using test 3 WITH transformations, I obtain the correct sphere intersections (thus, I believe my transformed ray should be OK). Any suggestions where I could be going wrong? Thank you in advance.

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• submatrix from a matrix

  - by Grv

  A matrix is of size n*n and it consists only 0 and 1 find the largest submatrix that consists of 1's only eg 10010 11100 11001 11110 largest sub matrix will be of 3*2 from row 2 to row 4 please answer with best space and time complexity

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• I want to create adjacency matrix using python

  - by A A

  I have very large data set it is almost 450000 lines and two rows, i want to compute adjacency matrix using python, because previously i have tried to do it in matlab, and it shows memory error because of large data values. my data values also start from 100 and goes upto 450000, Anyone can help me in this issue, as i am new to python. I have to first import the file into python using excel sheet or notepad and then compute the adjacency matrix

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• OpenGL Projection matrix won't allow displaying anything

  - by user272973

  I'm trying to get some basic OpenGL-ES with Shaders to run on the iPhone, based on some examples. For some reason my projection matrix refuses to result in something on the screen. It feels like a clipping plane is set very near but that contradicts with the values I supply. If I render the same scene with an Orthogonal projection matrix I see my object just no perspective obviously. Here's the code that generates the projection matrix: esPerspective(&proj, 45.f, 768.0/1024.0, 1.f, 10000.f); void esPerspective(ESMatrix *result, float fovy, float aspect, float nearZ, float farZ) { float frustumW, frustumH; frustumH = tanf( fovy / 360.0f * PI ) * nearZ; frustumW = frustumH * aspect; esFrustum( result, -frustumW, frustumW, -frustumH, frustumH, nearZ, farZ ); } void esFrustum(ESMatrix *result, float left, float right, float bottom, float top, float nearZ, float farZ) { float deltaX = right - left; float deltaY = top - bottom; float deltaZ = farZ - nearZ; ESMatrix frust; if ( (nearZ <= 0.0f) || (farZ <= 0.0f) || (deltaX <= 0.0f) || (deltaY <= 0.0f) || (deltaZ <= 0.0f) ) return; frust.m[0][0] = 2.0f * nearZ / deltaX; frust.m[0][1] = frust.m[0][2] = frust.m[0][3] = 0.0f; frust.m[1][1] = 2.0f * nearZ / deltaY; frust.m[1][0] = frust.m[1][2] = frust.m[1][3] = 0.0f; frust.m[2][0] = (right + left) / deltaX; frust.m[2][1] = (top + bottom) / deltaY; frust.m[2][2] = -(nearZ + farZ) / deltaZ; frust.m[2][3] = -1.0f; frust.m[3][2] = -2.0f * nearZ * farZ / deltaZ; frust.m[3][0] = frust.m[3][1] = frust.m[3][3] = 0.0f; esMatrixMultiply(result, &frust, result); } My projection matrix comes out as: [3.21, 0, 0, 0] [0, 2.41, 0, 0] [0, 0, -1, -1] [0, 0, -2, 0] Even if I manually set the [3][3] cell to 1 I still don't see anything. Any ideas?

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• Gnuplot - splot matrix csv data

  - by Jakub Czaplicki

  How can I plot (a 3D plot) a matrix in Gnuplot having such data structure. I cannot find a way to use the first row and column as a x and y ticks (or to ignore them) ,5,6,7,8 1,-6.20,-6.35,-6.59,-6.02 2,-6.39,-6.52,-6.31,-6.00 3,-6.36,-6.48,-6.15,-5.90 4,-5.79,-5.91,-5.87,-5.46 Is the splot 'data.csv' matrix the correct parameter to use ?

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• Matrix multiplication in java

  - by Chapax

  Hi, I wanted to do matrix multiplication in Java, and the speed needs to be very good. I was thinking of calling R through java to achieve this. I had a couple of Qs though: Is calling R using Java a good idea? If yes, are there any code samples that can be shared? What are the other ways that can be considered to do matrix multiplication in Java? Many thanks. --Chapax

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• Adding Names to columns in a matrix

  - by Jeff

  I have my matrix I have created, a pic found here. http://s816.photobucket.com/albums/zz83/gavakie/?action=view&current=matrix.jpg The first three column what whats being grouped by but I can had the names of those columns, how can I do that in Reporting Services?

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• C++ matrix need quick

  - by tobby

  It's given a number n.I have to build a matrix like this. For example if n=3 the matrix is 111 112 123 please help

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• Traspose matrix-style table to 3 columns in Excel

  - by polarbear2k

  I have a matrix-style table in excel where B1:Z1 are column headings and A2:A99 are row headings. I would like to convert this table to a 3 column table (column heading, row heading, cell value). It does not matter in what order the new table is. A B C D A B C A B C 1 H1 H2 H3 1 H1 R1 V1 1 H1 R1 V1 2 R1 V1 V2 V3 => 2 H1 R2 V4 or 2 H2 R1 V2 3 R2 V4 V5 V6 3 H1 R3 V7 3 H3 R1 V3 4 R3 V7 V8 V9 4 H2 R1 V2 4 H1 R2 V4 5 H2 R2 V5 5 H2 R2 V5 6 H2 R3 V8 6 H3 R2 V6 7 H3 R1 V3 7 H1 R3 V7 8 H3 R2 V6 8 H2 R3 V8 9 H3 R3 V9 9 H3 R3 V8 I've been playing around with the OFFSET function to create the whole table but I feel like a combination of TRANSPOSE and V/HLOOKUP is required. Thanks

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• Create a term-document matrix from files

  - by Joe

  I have a set of files from example001.txt to example100.txt. Each file contains a list of keywords from a superset (the superset is available if we want it). So example001.txt might contain apple banana ... otherfruit I'd like to be able to process these files and produce something akin to a matrix so there is the list of examples* on the top row, the fruit down the side, and a '1' in a column if the fruit is in the file. An example might be... x example1 example2 example3 Apple 1 1 0 Babana 0 1 0 Coconut 0 1 1 Any idea how I might build some sort of command-line magic to put this together? I'm on OSX and happy with perl or python...

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• Coordinate spaces and transformation matrices

  - by Belgin

  I'm trying to get an object from object space, into projected space using these intermediate matrices: The first matrix (I) is the one that transforms from object space into inertial space, but since my object is not rotated or translated in any way inside the object space, this matrix is the 4x4 identity matrix. The second matrix (W) is the one that transforms from inertial space into world space, which is just a scale transform matrix of factor a = 14.1 on all coordinates, since the inertial space origin coincides with the world space origin. /a 0 0 0\ W = |0 a 0 0| |0 0 a 0| \0 0 0 1/ The third matrix (C) is the one that transforms from world space, into camera space. This matrix is a translation matrix with a translation of (0, 0, 10), because I want the camera to be located behind the object, so the object must be positioned 10 units into the z axis. /1 0 0 0\ C = |0 1 0 0| |0 0 1 10| \0 0 0 1/ And finally, the fourth matrix is the projection matrix (P). Bearing in mind that the eye is at the origin of the world space and the projection plane is defined by z = 1, the projection matrix is: /1 0 0 0\ P = |0 1 0 0| |0 0 1 0| \0 0 1/d 0/ where d is the distance from the eye to the projection plane, so d = 1. I'm multiplying them like this: (((P x C) x W) x I) x V, where V is the vertex' coordinates in column vector form: /x\ V = |y| |z| \1/ After I get the result, I divide x and y coordinates by w to get the actual screen coordinates. Apparenly, I'm doing something wrong or missing something completely here, because it's not rendering properly. Here's a picture of what is supposed to be the bottom side of the Stanford Dragon: Also, I should add that this is a software renderer so no DirectX or OpenGL stuff here.

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• Using pthread to perform matrix multiplication

  - by shadyabhi

  I have both matrices containing only ones and each array has 500 rows and columns. So, the resulting matrix should be a matrix of all elements having value 500. But, I am getting res_mat[0][0]=5000. Even other elements are also 5000. Why? #include<stdio.h> #include<pthread.h> #include<unistd.h> #include<stdlib.h> #define ROWS 500 #define COLUMNS 500 #define N_THREADS 10 int mat1[ROWS][COLUMNS],mat2[ROWS][COLUMNS],res_mat[ROWS][COLUMNS]; void *mult_thread(void *t) { /*This function calculates 50 ROWS of the matrix*/ int starting_row; starting_row = *((int *)t); starting_row = 50 * starting_row; int i,j,k; for (i = starting_row;i<starting_row+50;i++) for (j=0;j<COLUMNS;j++) for (k=0;k<ROWS;k++) res_mat[i][j] += (mat1[i][k] * mat2[k][j]); return; } void fill_matrix(int mat[ROWS][COLUMNS]) { int i,j; for(i=0;i<ROWS;i++) for(j=0;j<COLUMNS;j++) mat[i][j] = 1; } int main() { int n_threads = 10; //10 threads created bcos we have 500 rows and one thread calculates 50 rows int j=0; pthread_t p[n_threads]; fill_matrix(mat1); fill_matrix(mat2); for (j=0;j<10;j++) pthread_create(&p[j],NULL,mult_thread,&j); for (j=0;j<10;j++) pthread_join(p[j],NULL); printf("%d\n",res_mat[0][0]); return 0; }

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• finding ALL cycles in a huge sparse matrix

  - by Andy

  Hi there, First of all I'm quite a Java beginner, so I'm not sure if this is even possible! Basically I have a huge (3+million) data source of relational data (i.e. A is friends with B+C+D, B is friends with D+G+Z (but not A - i.e. unmutual) etc.) and I want to find every cycle within this (not necessarily connected) directed graph. I've found this thread (http://stackoverflow.com/questions/546655/finding-all-cycles-in-graph/549402#549402) which has pointed me to Donald Johnson's (elementary) cycle-finding algorithm which, superficially at least, looks like it'll do what I'm after (I'm going to try when I'm back at work on Tuesday - thought it wouldn't hurt to ask in the meanwhile!). I had a quick scan through the code of the Java implementation of Johnson's algorithm (in that thread) and it looks like a matrix of relations is the first step, so I guess my questions are: a) Is Java capable of handling a 3+million*3+million matrix? (was planning on representing A-friends-with-B by a binary sparse matrix) b) Do I need to find every connected subgraph as my first problem, or will cycle-finding algorithms handle disjoint data? c) Is this actually an appropriate solution for the problem? My understanding of "elementary" cycles is that in the graph below, rather than picking out A-B-C-D-E-F it'll pick out A-B-F, B-C-D etc. but that's not the end of the world given the task. E / \ D---F / \ / \ C---B---A d) If necessary, I can simplify the problem by enforcing mutuality in relations - i.e. A-friends-with-B <== B-friends-with-A, and if really necessary I can maybe cut down the data size, but realistically it is always going to be around the 1mil mark. z) Is this a P or NP task?! Am I biting off more than I can chew? Thanks all, any help appreciated! Andy

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• OpenCL Matrix Multiplication - Getting wrong answer

  - by Yash

  here's a simple OpenCL Matrix Multiplication kernel which is driving me crazy: __kernel void matrixMul( __global int* C, __global int* A, __global int* B, int wA, int wB){ int row = get_global_id(1); //2D Threas ID x int col = get_global_id(0); //2D Threas ID y //Perform dot-product accumulated into value int value; for ( int k = 0; k < wA; k++ ){ value += A[row*wA + k] * B[k*wB+col]; } C[row*wA+col] = value; //Write to the device memory } Where (inputs) A = [72 45 75 61] B = [26 53 46 76] Output I am getting: C = [3942 7236 3312 5472] But the output should be: C = [3943 7236 4756 8611] The problem I am facing here is that for any dimension array the elements of the first row of the resulting matrix is correct. The elements of all the other rows of the resulting matrix is wrong. By the way I am using pyopencl. I don't know what I mistake I am doing here. I have spent the entire day with no luck. Please help me with this

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• Optimizing a "set in a string list" to a "set as a matrix" operation

  - by Eric Fournier

  I have a set of strings which contain space-separated elements. I want to build a matrix which will tell me which elements were part of which strings. For example: "" "A B C" "D" "B D" Should give something like: A B C D 1 2 1 1 1 3 1 4 1 1 Now I've got a solution, but it runs slow as molasse, and I've run out of ideas on how to make it faster: reverseIn <- function(vector, value) { return(value %in% vector) } buildCategoryMatrix <- function(valueVector) { allClasses <- c() for(classVec in unique(valueVector)) { allClasses <- unique(c(allClasses, strsplit(classVec, " ", fixed=TRUE)[[1]])) } resMatrix <- matrix(ncol=0, nrow=length(valueVector)) splitValues <- strsplit(valueVector, " ", fixed=TRUE) for(cat in allClasses) { if(cat=="") { catIsPart <- (valueVector == "") } else { catIsPart <- sapply(splitValues, reverseIn, cat) } resMatrix <- cbind(resMatrix, catIsPart) } colnames(resMatrix) <- allClasses return(resMatrix) } Profiling the function gives me this: $by.self self.time self.pct total.time total.pct "match" 31.20 34.74 31.24 34.79 "FUN" 30.26 33.70 74.30 82.74 "lapply" 13.56 15.10 87.86 97.84 "%in%" 12.92 14.39 44.10 49.11 So my actual questions would be: - Where are the 33% spent in "FUN" coming from? - Would there be any way to speed up the %in% call? I tried turning the strings into factors prior to going into the loop so that I'd be matching numbers instead of strings, but that actually makes R crash. I've also tried going for partial matrix assignment (IE, resMatrix[i,x] <- 1) where i is the number of the string and x is the vector of factors. No dice there either, as it seems to keep on running infinitely.

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