Re: [Plib-users] Matrices and sgCoord

[Dimitris M. <dm...@ya...>]

>Dimitris,=0A=0A>    Hello and welcome to the PLIB community.  I didn't rep=
ly to your=0A>first request because SSG is not my strong point.=0A=0AThank =
you for the invitation in the PLIB community, and please tell me if by repl=
ying to plib-users list I am ok with proper responding in the list.=0A=0A=
=0A>  If I may ask, are you writing a trireme simulation?  If so, I=0A>invi=
te you to look (if you haven't already) at the "Triereis" project.=0A>It us=
es PLIB as well.=0A=0AEhm...In deed I am writing a game for trireme warfare=
, but it is not a simulation exactly, and I haven't started now. It's going=
 to be something like Pirates.=0AI did saw the project days ago(triereis), =
but i didn't see any code.=0ALast I can't abandon Methos, it's an old proje=
ct of me and it is a dream I wish to finish it up.=0A=0A=0A=0A>    The ques=
tion about the transformation matrix with "getSpeed" in=0A>the bottom row i=
nstead of the last column is a tricky question for me.=0A>Just by doing the=
 mathematics, it seems to me that you are changing only=0A>the "w" coordina=
te of the point (have you read the OpenGL "red book" on=0A=0AWhat exactly s=
hould I read ? I have the red book borrowed from my uni, about 1.4 opengl.=
=0ACan you give me a hint ? If i must look sth specifically...?=0A=0A>the s=
ubject?), which would make the object move either directly towards=0A>or di=
rectly away from the origin.  Whether this is right or wrong I do=0A>not kn=
ow without further study.=0A=0AWell neither do I feel strong in math :-) an=
d I don't really know if it's right as algorithm...But it should as matrix =
multiplication be workable enough.=0AIf you compile the code, you may see t=
he results...Funny ones...=0A=0A>John F. Fay=0A>Technical Fellow=0A>Jacobs =
Technology TEAS Group=0A>850-883-1294 =0A=0A-----Original Message-----=0AFr=
om: pli...@li...=0A[mailto:plib-users-bounces@l=
ists.sourceforge.net] On Behalf Of Dimitris=0AMexis=0ASent: Tuesday, July 2=
4, 2007 9:26 AM=0ATo: pli...@li...=0ASubject: [Plib-use=
rs] Matrices and sgCoord=0A=0AThe following code has been a success in orde=
r to make the object move=0Aat a constant speed.=0A=0AsgCoord stigma;=0A=0A=
void GLObject::setStigma( sgMat4 & objDst){=0A    sgSetCoord( & stigma, obj=
Dst);=0A}=0A=0AGLObject::move(){=0A    //The rotation matrix for moving aro=
und trireme.=0A    sgMat4 RotateMatrix =3D   {=0A        1, 0, 0, 0,=0A    =
    0, 1, 0, 0,=0A        0, 0, 1, 0,=0A        0,( getSpeed()), 0, 1=0A   =
 };=0A    =0AsgMakeCoordMat4( SHIPSRC, &trireme->getStigma());=0AsgMultMat4=
( SHIPDST, SHIPSRC, RotateMatrix);=0AsetStigma( SHIPDST);=0A=0AWhat I don;t=
 understand is that I took the usual matrix and instead=0Atweaking the last=
 column element by the second row,=0AI inversed it and put the getSpeed() w=
hich is <>0 in the bottom row!=0AWhy? this?=0AI made then the matrix multip=
lications, and took the result to sgCoord.=0AIs this right approach? Ok it =
works, but it worths?=0A=0A=0A=0A=0A=0A       =0A__________________________=
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