How to convert glRotatef() to multiplication matrice for glMultMatrixd()

Question

I need to perform some operations with different openGL functions.

There for I have a cube initialized as glList. What I'm doing is some transformation with glu standard functions and I like to do exactly the same operations with matrix multiplication. But I got stuck with the rotation function. I want to rotate the cube around the x achsis e.g. 90°:

glRotatef(90.0, 1.0f, 0.0f, 0.0f);

should be replaced by:

GLdouble m[16] ={1.0, 0.0,  0.0,  0.0,
                 0.0, 0.0,  1.0,  0.0,
                 0.0,-1.0,  0.0,  0.0,
                 0.0, 0.0,  0.0,  1.0 };
glMultMatrixd(m);

I found this very usefull site ~~but some how it's not doing exactly the same as the above function~~. Is there a generell principle how to transform the glRotatef() function to a gl transformation matrix?

UPDATE: sorry, I missed the important note a the beginning of the document that the matrices from the document needed to be transposed for use in openGL.

So your question is solved? Then either answer or delete this question. — Nico Schertler, Jul 05 '14 at 13:19
OK, I added my solution and example. If there will be a more generic solution or a better answer i will accept this. — Karl Adler, Jul 05 '14 at 14:27

score 1 · Accepted Answer · edited Jul 05 '14 at 17:24

1

In X-Axis

     |  1  0       0       0 |
 M = |  0  cos(A) -sin(A)  0 |
     |  0  sin(A)  cos(A)  0 |
     |  0  0       0       1 |

In Y-Axsis

     |  cos(A)  0   sin(A)  0 |
 M = |  0       1   0       0 |
     | -sin(A)  0   cos(A)  0 |
     |  0       0   0       1 |

In Z-Axsis

     |  cos(A)  -sin(A)   0   0 |
 M = |  sin(A)   cos(A)   0   0 |
     |  0        0        1   0 |
     |  0        0        0   1 |

NOTE: Matrices in OpenGL use column major memory layout

Example:

#include <math.h>
#define PI 3.14159265

// Rotate -45 Degrees around Y-Achsis
GLdouble cosA = cos(-45.0f*PI/180);
GLdouble sinA = sin(-45.0f*PI/180);

// populate matrix in column major order
GLdouble m[4][4] = {
  { cosA, 0.0, -sinA,  0.0}, // <- X column
  { 0.0,  1.0,   0.0,  0.0}, // <- Y column
  { sinA, 0.0,  cosA,  0.0}, // <- Z column
  { 0.0,  0.0,   0.0,  1.0}  // <- W column
};

//Apply to current matrix
glMultMatrixd(&m[0][0]);
//...

edited Jul 05 '14 at 17:24

datenwolf

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answered Jul 05 '14 at 14:24

Karl Adler

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Matrices don't have to be "transposed" for OpenGL, OpenGL just uses a memory layout (column major) that looks "unintuitive" when used naively with C-style multidimensional arrays. However column major matrices have huge benefits in computer graphics, because most of the time you're interested in the column vectors more than in the row vectors. – datenwolf Jul 05 '14 at 17:21
isn't it somehow the same like transposing it? I just wanted to do it that way, so I could use the same matrices a mentioned in the document above. – Karl Adler Jul 05 '14 at 17:36
If you feed those matrices into a library that uses row major layout, well then yes. However most math packages out there actually use column major order. I just want to emphase on that OpenGL does not intentionally "transposes" the matrices. – datenwolf Jul 05 '14 at 19:05

How to convert glRotatef() to multiplication matrice for glMultMatrixd()

1 Answers1