Urgent:Matrices....I need help!

OpenGL OpenGL: Advanced Coding
1

Yes I have only the weekend to code so I don´t want to waste all my time with this one.
I want to rotate a vertex by the OpenGl-Rotation-Matrix-myself.I do it this way:

//Types:
typedef vertex float[3];//[0]=x,[1]=y,[2]=z
typedef matrix4x4 float[16];

//Code:
vertex V,vrot;
matrix4x4 M;
glMatrix(GL_MODELVIEW);//is it called glLoadMatrix??,doesn´t´matter…

glRotatef(xrot,…);
glRotatef(yrot,…);

glGetFloatV(GL_MODELVIEW,matrix4x4);

vrot[0]=M[0]*V[0] + M[1]*V[1] + M[2] *V[2];
vrot[1]=M[4]*V[0] + M[5]*V[1] + M[6] *V[2];
vrot[2]=M[8]*V[0] + M[9]*V[1] + M[10]*V[2];

Is this correct?
This seems to give me wrong results,but it is part of another (alot more complex)caculation so I just want to know if this is wrong or not.(It seems that this code is the prob,but I don´t know what is wrong in here)

Please help me fast and thanx in advance,XBTC!

[This message has been edited by XBCT (edited 06-24-2000).]

2

Here it is:

vrot[0]=M[0]*V[0] + M[4]*V[1] + M[8] *V[2];
vrot[1]=M[1]*V[0] + M[5]*V[1] + M[9] *V[2];
vrot[2]=M[2]*V[0] + M[6]*V[1] + M[10]*V[2];

I’m assuming you just want to rotate it? Otherwise you will have to use the w-component of the vertex and more than the upper 3x3 of the model view matrix.

3

Thanx alot for your answer!
I think what I did is the notation in the mathematical way.Yours seems to be the correct OpenGl-way(columns-rows swapped).
Thanx again!

P.s.:You´re right,I only want to rotate.
XBTC

[This message has been edited by XBCT (edited 06-24-2000).]

4

Kinda cool that I helped a “frequent contributor” in the “advanced opengl coding” forum since I’ve only been coding opengl for less than three days =)

5

Yes it’s interesting…

Well I opened up a tutorial page (unrelated to OpenGL, but about 3D nonetheless) at Planetquake after messing around with an editor for about a week…
( http://www.planetquake.com/gothic )

it’s funny sometimes

[This message has been edited by drakaza (edited 06-24-2000).]

6

Ceasar:Yeah thanx again(even I don´t know everything,my know of matrices is very weak)!
Drakaza: Don´t seem any connection between your site and my post,but I edit q3-levels myself and your page is really cool!!!

Greets,XBTC!

[This message has been edited by XBCT (edited 06-25-2000).]

7

XBCT, I was just saying that it’s funny how sometimes, people with the less experience than others know more than others…

I’ve been OpenGL coding for a few months and I STILL don’t get the hang of matrices completely…all of my functions in my code use matrices differently, i mean like flipped around, so i don’t know which ones are right!

But on the other hand, an editor like Q3Rad seems like a simple toy…while others would
argue the opposite to the death.

That’s the connection

8

It should be noted that OpenGL matrices are not “swapped”. Base vectors are laid out consecutively in memory just as you would expect. The OpenGL Specification uses the mathematically correct column-order notation, not traditionaly used in 3D graphics, along with post-multiplication. Postmultiplying with column-major matrices is equivalent to premultiplying with row-major matrices.

Really, the only thing that is swapped is the notational convention used in the spec.