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• OpenGL ES 2.0 equivalent of glOrtho()?

  - by Zippo

  In my iphone app, I need to project 3d scene into the 2D coordinates of the screen for some calculations. My objects go through various rotations, translations and scaling. So I figured I need to multiply the vertices with ModelView matrix first, then I need to multiply it with the Orthogonal projection matrix. First of all am on the right track? I have the Model View Matrix, but need the projection matrix. Is there a glOrtho() equivalent in ES 2.0?

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• Best way to represent a 2-D array in C++ with size determined at run time

  - by Tristan Havelick

  In C++ I'd like to do something like: int n = get_int_from_user(); char* matrix = new char[n][n]; matrix[0][0] = 'c'; //... matrix[n][n] = 'a'; delete [][] matrix; but of course this doesn't work. What is the best way to do something similar? I've seen some solutions to this but they seem pretty messy.

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• Does XNA 4 support 3D affine transformations for 2D images?

  - by Paul Baker Salt Shaker

  Looooong story short I'm essentially trying to code Mode 7 in XNA. Before I continue bashing my brains out in research and various failed matrix math equations; I just want to make sure that XNA supports this just out-of-the-box (so to speak). I'd prefer not to have to import other libraries, because I want to learn how it works myself that way I understand the whole thing better. However that's all for naught if it won't work at all. So no opengl, directx, etc if possible (will eventually do it just to optimize everything, but not for now). tl;dr: Can I has Mode 7 in XNA?

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• Correct way to handle path-finding collision matrix

  - by Xander Lamkins

  Here is an example of me utilizing path finding. The red grid represents the grid utilized by my A* library to locate a distance. This picture is only an example, currently it is all calculated on the 1x1 pixel level (pretty darn laggy). I want to make it so that the farther I click, the less accurate it will be (split the map into larger grid pieces). Edit: as mentioned by Eric, this is not a required game mechanic. I am perfectly fine with any method that allows me to make this accurate while still fast. This isn't the really the topic of this question though. The problem I have is, my current library uses a two dimensional grid of integers. The higher the number in a cell, the more resistance for that grid tile. Currently I'm setting all unwalkable spots to Integer Max. Here is an example of what I want: I'm just not sure how I should set up the arrays of integers of the grid. Every time an element is added/removed to/from the game, it's collision details are updated in the table. Here is a picture of what the map looks like on my collision layer: I probably shouldn't be creating new arrays every time I have to do a path find because my game needs to support tons of PF at the same time. Should I have multiple arrays that are all updated when the dynamic elements are updated (a building is built/a building is destroyed). The problem I see with this is that it will probably make the creation and destruction of buildings a little more laggy than I would want because it would be setting the collision grid for each built in accuracy level. I would also have to add more/remove some arrays if I ever in the future changed the map size. Should I generate the new array based on an accuracy value every time I need to PF? The problem I see with this is that it will probably make any form of PF just as laggy because it will have to search through a MapWidth x MapHeight number of cells to shrink it all down. Or is there a better way? I'm certainly not the best at optimizing really anything. I've just started dealing with XNA so I'm not used to having optimization code really doing much of an affect until now... :( If you need code examples, please ask. I'll add it as an edit. EDIT: While this doesn't directly relate to the question, I figure the more information I provide, the better. To keep your units from moving as accurately to the players desired position, I've decided that once the unit PFs over to the less accurate grid piece, it will then PF on a more accurate level to the exact position requested.

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• Deformation of Sphere using Transformations

  - by Mert Toka

  I have a graphic related question. I need to have a transformation matrix that I have no idea about what it is. The problem is to create right image from the right sphere. I created those images in Maya, but I need some matrices for the graphics course. Here is the image: Our professor told us to use some sine and cosine in our transformations, but I have no idea what he meant. I thought of intersecting a plane from the grid(that is xz plane) and sphere, and then scaling down the resulting circle. Would that work? I also checked this paper, however it looks like a bit advanced for me. Another thing is I guess that paper is not about the same type of information I was looking for. It would be great if you could help me.

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• Passing an objects rotation down through its children

  - by MintyAnt

  In my topdown 2d game you have a player with a sword, like an old Zelda game. The sword is a seperate entity, and its collision box "rotates" around the player like an orbit, but always follows the player wherever he goes. The player and sword both have a vector2 heading. The sword is a weapon object that is attached to the character. In order to allow swinging in a direction, I have the following property inside sword (RotateCopy returns a copy of the mHeading after rotation) public Vector2 Heading { get { return mHeading.RotateCopy(mOwner.Rotation); } } This seems a bit messy to me, and slower than it could be. Is there a better way to "translate" the base/owner component rotations through to whatever component I am using, like this sword? Would using a rotation MATRIX be better? (Curretnly rotates by sin/cos) If so, how can I "add" up the matrices? Thank you.

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• Orthographic Projection with variable FOV

  - by cubrman

  We are building agame with orthographic view. The problem we face is the fact that with different resolution you can see different area of the game world. E.g. if you have higher resolution you can see more around you. To solve this we currently use a common scale factor that every model is scaled by, depending on resolution. But this has drawbacks when drawing shadows - I cannot set a higher view angle for the orthographic shadow camera, while when using the perspective shadow camera I get significantly worse shadow quality. So the question is is there any way to controll FOV when using orthographic projection, or, more specifically, what is the easiest way to scale the world uniformly up or down with orthographic projection matrix? I saw that in 3ds MAX you can control FOV for an orthographic camera I wonder how they implemented it.

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• Projecting onto different size screens by cropping

  - by Jason

  Hi, I am building a phone application which will display a shape on screen. The shape should look the same on different screen sizes. I. Decided the best way to do this is to show more of the background on larger screen keeping the shapes proportion the same on all screens. My problem is I am not sure how to achieve this, I can query the screen size at runtime and calculate how different it is from the six is designed for but I am not sure what to do with this value. What kind of projection should I use for my orthographic matrix an hour will I display more on larger screens and not loose information on smaller screens? Thanks, Jason.

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• Color Matrix Image Drawing Effects

  Program demonstrates the graphics effects of drawing an image with a ColorMatrix.

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• Y Axis inverted on vertex output

  - by Yonathan Klijnsma

  I've got my project running and somehow it seems my vertex y components are inverted. 10 in the positive on Y goes down and 10 negative on the Y axis goes up. I can't find anything with the initialization and I am not doing any negative scaling in the view matrix. I've never had something like this happen before, does anyone have some tips or things to look for ? How I am sending verteces to the GPU ( Currently intermediate mode ) glVertex3f( x_pos_n, 10, z_pos ); I am using CG in the project but even without shaders the Y axis seems to be inverted.

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• Find largest rectangle containing all zero's in an N X N binary matrix

  - by Rajendra

  Given an N X N binary matrix (containing only 0's or 1's). How can we go about finding largest rectangle containing all 0's? Example: I 0 0 0 0 1 0 0 0 1 0 0 1 II->0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 <--IV 0 0 1 0 0 0 IV is a 6 X 6 binary matrix, return value in this case will be Cell 1: (2, 1) and Cell 2: (4, 4). Resulting sub-matrix can be square or rectangle. Return value can be size of the largest sub-matrix of all 0's also, for example, here 3 X 4.

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• obtain OpenGL camera(view) matrix from openCV findhomography

  - by user1828449

  I want to build an AR application on Android by opencv and opengl. I found GL_MODELVIEW can place camera and model in world coordinates like the following link I tried to load a simple model-view matrix by gl.glLoadMatrixf(newMat, 0); and it works so I want to draw 3d model on the top of my target image if i got the four corner points of the target image because model-view matrix is needed I want to know if I can obtain the camera view matrix by opencv's findhomography

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• calculate nxn matrix determinant C#

  - by vj4u

  please Can any one tell how to calculate nxn matrix determinant in c#

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• Is there a library for Linear algebra matrix handling in Java?

  - by Mario Ortegón

  Is there any libraries in java that allow using mathematical matrices? I am looking for a library that allows me to perform operations in matrices such as invert, scalar multiplication, linear transformations, etc. etc. etc. In a nutshell, the operations required for lineal algebra.

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• maple 13 tridiagonal matrix help

  - by user292569

  i am trying to make a 100 x 100 tridiagonal matrix with 2's going down the diagonal and -1's surrounding the 2's. i can make a tridiagonal matrix with only 1's in the three diagonals and preform matrix addition to get what i want, but i want to know if there is a way to customize the three diagonals to what ever you want. maplehelp doesn't list anything useful.

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• Can anyone recommend some Transformation Matrix tutorials for dummies?

  - by gargantaun

  Can anyone recommend some good starting points for understanding Transformation Matrices for dummies like me with poor math skills. I'm willing to learn the math, and I'm not a complete idiot (I hope) but the examples I'm finding seem to require a huge leap from what I know, to what I need to know.

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• How to represent double values as circles in a 2d matrix in java

  - by marco

  Hello, so I want to write a matrix explorer which enables me to reorder rows and columns of a matrix. For this porpouse I used the Jtable class. Now the problem that I have is that it is very difficult to reorder a matrix by looking at double values, so I would like to print the matrix not with the double values but with circles in which the radius of the circle represents the value. So that I can tell the difference between big values and small values quicker. Anybody has any idea how I can turn this double values into filled circles with JTable or any table class for that matter?

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• High speed matrix manipulation in c#?

  - by Donnie

  I'm working on some image manipulation code in c# and need to do some matrix operations (specifically 2D convolution). I have the code written in matlab which uses the conv2 function ... is there a library for C# / .NET that does good high-speed matrix manipulations? I'd be fine if it requires some specific GPU and does the matrix math on-GPU if that's what it takes.

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• Numpy Matrix keeps giving me an Error,

  - by uberjumper

  Okay this is werid, i keep getting the error, randomly. ValueError: matrix must be 2-dimensional So i tracked it down, and cornered it to basically something like this: a_list = [[(1,100) for _ in range(32)] for _ in range(32)] numpy.matrix(a_list) Whats wrong with this? If i print a_list it is clearly a 2d matrix of tuples, however numpy does not believe so.

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• How can I save and read to XML the new C++ style matrix objects in OpenCV?

  - by neuviemeporte

  The old, C style cvMat matrices could be passed to the cvSave() function for easy writing to an XML file. The new C++ style cv::Mat and cv::Mat_ matrices are not accepted by this function. The OpenCV reference has a section on XML persistence, but the three classes (FileStorage, FileNode and FileNodeIterator) lack any description or example and I can't figure out how to use them from the interface. Thanks.

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• C++ Matrix class hierachy

  - by bpw1621

  Should a matrix software library have a root class (e.g., MatrixBase) from which more specialized (or more constrained) matrix classes (e.g., SparseMatrix, UpperTriangluarMatrix, etc.) derive? If so, should the derived classes be derived publicly/protectively/privately? If not, should they be composed with a implementation class encapsulating common functionality and be otherwise unrelated? Something else? I was having a conversation about this with a software developer colleague (I am not per se) who mentioned that it is a common programming design mistake to derive a more restricted class from a more general one (e.g., he used the example of how it was not a good idea to derive a Circle class from an Ellipse class as similar to the matrix design issue) even when it is true that a SparseMatrix "IS A" MatrixBase. The interface presented by both the base and derived classes should be the same for basic operations; for specialized operations, a derived class would have additional functionality that might not be possible to implement for an arbitrary MatrixBase object. For example, we can compute the cholesky decomposition only for a PositiveDefiniteMatrix class object; however, multiplication by a scalar should work the same way for both the base and derived classes. Also, even if the underlying data storage implementation differs the operator()(int,int) should work as expected for any type of matrix class. I have started looking at a few open-source matrix libraries and it appears like this is kind of a mixed bag (or maybe I'm looking at a mixed bag of libraries). I am planning on helping out with a refactoring of a math library where this has been a point of contention and I'd like to have opinions (that is unless there really is an objective right answer to this question) as to what design philosophy would be best and what are the pros and cons to any reasonable approach.

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• Implementation of a distance matrix of a binary tree that is given in the adjacency-list representation

  - by Denise Giubilei

  Given this problem I need an O(n²) implementation of this algorithm: "Let v be an arbitrary leaf in a binary tree T, and w be the only vertex connected to v. If we remove v, we are left with a smaller tree T'. The distance between v and any vertex u in T' is 1 plus the distance between w and u." This is a problem and solution of a Manber's exercise (Exercise 5.12 from U. Manber, Algorithms: A Creative Approach, Addison-Wesley (1989).). The thing is that I can't deal properly with the adjacency-list representation so that the implementation of this algorithm results in a real O(n²) complexity. Any ideas of how the implementation should be? Thanks.

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• building a pairwise matrix in scipy/numpy in Python from dictionaries

  - by user248237

  I have a dictionary whose keys are strings and values are numpy arrays, e.g.: data = {'a': array([1,2,3]), 'b': array([4,5,6]), 'c': array([7,8,9])} I want to compute a statistic between all pairs of values in 'data' and build an n by x matrix that stores the result. Assume that I know the order of the keys, i.e. I have a list of "labels": labels = ['a', 'b', 'c'] What's the most efficient way to compute this matrix? I can compute the statistic for all pairs like this: result = [] for elt1, elt2 in itertools.product(labels, labels): result.append(compute_statistic(data[elt1], data[elt2])) But I want result to be a n by n matrix, corresponding to "labels" by "labels". How can I record the results as this matrix? thanks.

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• i want to find determinant of 4x4 matrix in c#

  - by vj4u

  i want to find determinant of 4x4 matrix in c# please help urgent int ss = 4; int count = 0; int[,] matrix=new int[ss,ss]; ArrayList al = new ArrayList() {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16 }; for (int i = 0; i < ss; i++) { for (int j = 0; j < ss; j++) { matrix[i, j] =Convert.ToInt32( al[count]); ++count; Response.Write(matrix[i, j] + " "); } Response.Write("<br/>"); }

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• Is the use of union in this matrix class completely safe?

  - by identitycrisisuk

  Unions aren't something I've used that often and after looking at a few other questions on them here it seems like there is almost always some kind of caveat where they might not work. Eg. structs possibly having unexpected padding or endian differences. Came across this in a math library I'm using though and I wondered if it is a totally safe usage. I assume that multidimensional arrays don't have any extra padding and since the type is the same for both definitions they are guaranteed to take up exactly the same amount of memory? template<typename T> class Matrix44T { ... union { T M[16]; T m[4][4]; } m; }; Are there any downsides to this setup? Would the order of definition make any difference to how this works?

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