Re: [Plib-users] Matrices and sgCoord
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Re: [Plib-users] Matrices and sgCoord
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From: Dimitris M. <dm...@ya...> - 2007-07-24 19:52:21
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Thank you! For your so immediate answer :-)=0AApparently we have some diver=
sification of versions regarding the book, I do have found the 475 page the=
me on another page...around 698...But no problem, I see what you are tellin=
g me....=0AFirst,to tell you, that I know about multiplying matrices, I hav=
e done many of those in school and university ( about economics really ) :-=
)=0AOn page110 for me, it says m[i][j] is in C the i column and j row whil=
e in OpenGL it is i row and j column. The last one is the "mathematic way" =
right? So T for me in the previous code, should be on the last column, no?=
Or because I am programming C++ I am definetely ok?=0AIt;s bizzare...On the=
page I see the 4 column with x,y,z,1 and in my code I see the last row....=
But it works! What do I do if I want to make a firing flying weapon?=0A=0AW=
ell as I found some voice to reply my concerns...could I continue with my q=
uestions??=0AI am trying to work on picking and sellecting? Have you ever d=
one it ?=0AI can't really pass glLoadName in my models...so if I could I wo=
uld use the so many routines I see on google....but no luck!!!=0AI checked =
out PrettyPollyEngine, and the code is undocumented and has many ins-and-ou=
ts from various classes...so I get lost and lost...and more lost....=0A=0AI=
s there an easy way to handle this? Can I pass LoadNames in the models?=0A=
=0AI had the idea to make 3D coordinates of my models converted to 2D,but i=
t fails... too...=0AI saw many theoretical links on net, but only microsoft=
had some code to show how to deal with this...=0A:-(=0A=0A=0A----- Origina=
l Message ----=0AFrom: Fay John F Dr CTR USAF 46 SK <joh...@eg....=
mil>=0ATo: PLIB Users <pli...@li...>=0ASent: Tuesday, J=
uly 24, 2007 9:43:24 PM=0ASubject: Re: [Plib-users] Matrices and sgCoord=0A=
=0ADimitris,=0A=0A First, the PLIB-users e-mail reflector is exactly the=
right=0Aplace to bring up questions as you have done. You are doing just =
fine=0Ahere.=0A=0A The red book has quite a bit about transformations in=
Chapter 3=0A("Viewing"). One relevant bit is a side note at the top of pa=
ge 76=0Aabout the difference between a two-dimensional matrix and a=0Aone-d=
imensional array in C, about how the rows and columns can be=0Aswitched bet=
ween the two formulations, but I don't think this is your=0Aproblem.=0A=0A =
More relevant to you, I think, is Appendix G ("Homogeneous=0ACoordinates=
and Transformation Matrices"), starting on page 475. It=0Adescribes an ex=
pression of coordinates in the form (x,y,z,w) (transposed=0Ato make a colum=
n vector). It also gives, on pages 478 and 479, the=0Atransformation matri=
ces for each type of transformation.=0A=0A Are you familiar with the mec=
hanics of multiplying matrices=0Atogether, or of multiplying a matrix by a =
vector to get another vector?=0ABased on the matrix multiplication I figure=
you should get the object=0Amoving directly towards or away from your orig=
in if you have the=0A"getSpeed ()" call in the bottom row; if you have it i=
n the right-hand=0Acolumn the object should move in the y-direction.=0A=0AJ=
ohn F. Fay=0ATechnical Fellow=0AJacobs Technology TEAS Group=0A850-883-1294=
=0A=0A-----Original Message-----=0AFrom: pli...@li...urcefo=
rge.net=0A[mailto:pli...@li...] On Behalf Of Di=
mitris=0AMexis=0ASent: Tuesday, July 24, 2007 1:27 PM=0ATo: PLIB Users=0ASu=
bject: Re: [Plib-users] Matrices and sgCoord=0A=0A>Dimitris,=0A=0A> Hell=
o and welcome to the PLIB community. I didn't reply to your=0A>first reque=
st because SSG is not my strong point.=0A=0AThank you for the invitation in=
the PLIB community, and please tell me=0Aif by replying to plib-users list=
I am ok with proper responding in the=0Alist.=0A=0A=0A> If I may ask, are=
you writing a trireme simulation? If so, I=0A>invite you to look (if you =
haven't already) at the "Triereis" project.=0A>It uses PLIB as well.=0A=0AE=
hm...In deed I am writing a game for trireme warfare, but it is not a=0Asim=
ulation exactly, and I haven't started now. It's going to be=0Asomething li=
ke Pirates.=0AI did saw the project days ago(triereis), but i didn't see an=
y code.=0ALast I can't abandon Methos, it's an old project of me and it is =
a dream=0AI wish to finish it up.=0A=0A=0A=0A> The question about the tr=
ansformation matrix with "getSpeed" in=0A>the bottom row instead of the las=
t column is a tricky question for me.=0A>Just by doing the mathematics, it =
seems to me that you are changing=0Aonly=0A>the "w" coordinate of the point=
(have you read the OpenGL "red book" on=0A=0AWhat exactly should I read ? =
I have the red book borrowed from my uni,=0Aabout 1.4 opengl.=0ACan you giv=
e me a hint ? If i must look sth specifically...?=0A=0A>the subject?), whic=
h would make the object move either directly towards=0A>or directly away fr=
om the origin. Whether this is right or wrong I do=0A>not know without fur=
ther study.=0A=0AWell neither do I feel strong in math :-) and I don't real=
ly know if=0Ait's right as algorithm...But it should as matrix multiplicati=
on be=0Aworkable enough.=0AIf you compile the code, you may see the results=
...Funny ones...=0A=0A>John F. Fay=0A>Technical Fellow=0A>Jacobs Technology=
TEAS Group=0A>850-883-1294 =0A=0A-----Original Message-----=0AFrom: plib-u=
ser...@li...=0A[mailto:pli...@li...urc=
eforge.net] On Behalf Of Dimitris=0AMexis=0ASent: Tuesday, July 24, 2007 9:=
26 AM=0ATo: pli...@li...=0ASubject: [Plib-users] Matric=
es and sgCoord=0A=0AThe following code has been a success in order to make =
the object move=0Aat a constant speed.=0A=0AsgCoord stigma;=0A=0Avoid GLObj=
ect::setStigma( sgMat4 & objDst){=0A sgSetCoord( & stigma, objDst);=0A}=
=0A=0AGLObject::move(){=0A //The rotation matrix for moving around trire=
me.=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 understa=
nd is that I took the usual matrix and instead=0Atweaking the last column e=
lement by the second row,=0AI inversed it and put the getSpeed() which is <=
>0 in the bottom row!=0AWhy? this?=0AI made then the matrix multiplications=
, and took the result to sgCoord.=0AIs this right approach? Ok it works, bu=
t it worths?=0A=0A=0A=0A=0A=0A =0A___________________________________=
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