Matrix

ttom · Post by **ttom** » Thu Feb 19, 2004 2:09 am

Hi dear folk:
I read the so book about the opengl or direct3d , they just talk about the
matrix. I found something strange.
Below is the matirx

Transformations

some book write this some book write this
| 1 0 0 0 | | 1 0 0 tx |
| 0 1 0 0 | | 0 1 0 ty |
| 0 0 0 1 | | 0 0 1 tz |
| tx ty tz 1 | | 0 0 0 1 |

My question is what different between they?
ps. sorry for my poor english.

BradB · Post by **BradB** » Thu Feb 19, 2004 3:04 am

One is the transpose of the other. I am not 100% sure, but I believe that OpenGL and directX use opposite conventions for row/column order.
I think the left matrix is OpenGL's style, and the right DX style.

You can move between the two by using rows as columns and columns as rows.

Brad

[dx/x]=HUNT3R · Post by **[dx/x]=HUNT3R** » Thu Feb 19, 2004 2:28 pm

yeah that's right... for some reason a matrix representation in OpenGL is symmetric to the standard representation in DirectX and mathematics. So in DirectX (standard) Mij = OpenGL Mji. If you have the OpenGL Programming Guide (the red book) read page 106.

[dx/x]=HUNT3R · Post by **[dx/x]=HUNT3R** » Thu Feb 19, 2004 2:37 pm

I almost forgot, you are wrong about the order. The left matrix that ttom wrote is the standard matrix form that DirectX also uses. The right matrix is the transpose of the the standard which OpenGL uses.

James · Post by **James** » Tue Feb 24, 2004 10:26 pm

And don't forget that every math textbook that cares about its reputation uses the right matrix format

[dx/x]=HUNT3R · Post by **[dx/x]=HUNT3R** » Tue Feb 24, 2004 11:00 pm

Really? One of my degrees is in mathematics and I've never used the matrix form on the right in school or in any of my textbooks. That's why I was calling the matrix on the left "standard".

Robomaniac · Post by **Robomaniac** » Tue Feb 24, 2004 11:15 pm

He was most likely meaning the "correct" one, but idk