.\" Copyright Equivalent Software HB   1992
.\" This program and documentation may be distributed freely under
.\" the terms of GNU GENERAL PUBLIC LICENSE.
.TH GEOMETRIC 3X "July , 1991" 3X
.SH NAME
geometric - Vector and matrix functions for the sipp(3X) library

.SH SYNOPSIS
\fI#include <geometric.h>\fR
.sp
[g]cc [\fIflags\fR] \fIfiles\fR -lsipp -lm [ \fIlibraries\fR ]

.SH DESCRIPTION
The sipp(3X) 3D rendering library uses a lot of vector calculations
and geometric transformations.  The functions which implement these
features are declared in geometric.h and are described in this manual.

.SH VECTOR OPERATIONS
Sipp uses row vectors, not column vectors and a vector is defined as
follows:

\fItypedef \ struct\ {\fR
.br
\fI	double\ x;\fR
.br
\fI	double\ y;\fR
.br
\fI	double\ z;\fR
.br
\fI}\ Vector;\fR

A vector is used both for directional vectors and points (positional
vectors).  In the description of the sipp vector macros and functions
below, lower case letters denote scalar values and upper case letters
denote vectors.

.IP \fIMakeVector(V,\ xx,\ yy,\ zz)
Put \fIxx\fR, \fIyy\fR and \fIzz\fR in the x, y and z slot of the
Vector \fIV\fR respectively.

.IP \fIVecNegate(A)\fR
Negate all components of the Vector \fIA\fR.

.IP \fIVecDot(A,\ B)\fR
Return the dot product of the two Vectors \fIA\fR and \fIB\fR.

.IP \fIVecLen(A)\fR
Return the length of the Vector \fIA\fR.

.IP \fIVecCopy(B,\ A)\fR
Copy the Vector \fIA\fR to the Vector \fIB\fR (\fIB\fR = \fIA\fR;
using C notation).

.IP \fIVecAdd(C,\ A,\ B)\fR
Add the two Vectors \fIA\fR and \fIB\fR and put the result in \fIC\fR
(Add \fIA\fR to \fIB\fR giving \fIC\fR; using COBOL notation).

.IP \fIVecSub(C,\ A,\ B)\fR
Subtract the Vector \fIB\fR from Vector \fIA\fR and put the result in
\fIC\fR (\fIC\fR = \fIA\fR - \fIB\fR; using C notation).

.IP \fIVecScalMul(B,\ a,\ A)\fR
Multiply the Vector \fIA\fR with the scalar \fIa\fR and put the result
in Vector \fIB\fR (\fIB\fR = \fIa\fR * \fIA\fR; using C notation).

.IP \fIVecAddS(C,\ a,\ A,\ B)\fR
Multiply the Vector \fIA\fR with the scalar \fIa\fR, add it to Vector
\fIB\fR and put the result in Vector \fIC\fR (\fIC\fR = \fIa\fR *
\fIA\fR + \fIB\fR; using C notation). 

.IP \fIVecComb(C,\ a,\ A,\ b,\ B)\fR
Linearly combine the two Vectors \fIA\fR and \fIB\fR and put the
result in Vector \fIC\fR (\fIC\fR = \fIa\fR * \fIA\fR + \fIb\fR *
\fIB\fR; using C notation).  

.IP \fIVecCross(C,\ A,\ B)\fR
Cross multiply Vector \fIA\fR with Vector \fIB\fR and put the result
in \fIC\fR (\fIC\fR = \fIA\fR X \fIB\fR; using C notation).

.IP \fIvoid\ vecnorm(v)\fR
.br
\fIVector\ *v;\fR
.sp
Normalize the vector \fIv\fR, i.e. keep the direction but make it have
length 1.  The length of \fIv\fR should not be equal to 0 to begin with.
.B NOTE:
This is the only function operating on vectors in sipp.

.SH MATRIX OPERATIONS
An ordinary homogenous transformation matrix has 4 X 4 elements.
However, all linear transformations only use 4 X 3 values so to save
space a sipp transformation matrix only store 4 X 3 values.  Thus the
transformation matrix used in sipp is defined as follows:

\fItypedef\ struct\ {\fR
.br
\fI	double\ mat[4][3];\fR
.br
\fI}\ Transf_mat;\fR

We wrap a struct around the two-dimensional array since we want to be
able to say things like \fI&mat\fR without being forced to write
\fI(Transf_mat\ *)\ &mat[0]\fR which we find horribly ugly.

There is a predefined identity matrix declared in geometric.h which
you can use if you want to:

\fIextern\ Transf_mat\ ident_matrix;\fR

The rest of this section describes the macro and functions defined in
the sipp library which work on sipp transformation matrixes.

.IP \fIMatCopy(A,\ B)\fR
This macro copies the matrix \fIB\fR to the matrix \fIA\fR. \fIA\fR
and \fIB\fR should both be pointers.
.B NOTE:
This is the only macro operating on matrices in sipp.


.IP \fITransf_mat\ *transf_mat_create(initmat)\fR
.br
\fITransf_mat\ *initmat;\fR
.sp
Allocate memory for a new transformation matrix and if \fIinitmat\fR
is equal to \fINULL\fR, set the new matrix to the identity matrix.
Otherwise set the new matrix to the contents of \fIinitmat\fR.  Return
a pointer to the new matrix.

.IP \fITransf_mat\ *transf_mat_destruct(mat)\fR
.br
\fITransf_mat\ *initmat;\fR
.sp
Free the memory associated with the matrix \fImat\fR.

.IP \fIvoid\ mat_translate(mat,\ dx,\ dy,\ dz)\fR
.br
\fITransf_mat\ *mat;\fR
.br
\fIdouble\ dx;\fR
.br
\fIdouble\ dy;\fR
.br
\fIdouble\ dz;\fR
.sp
Set \fImat\fR to the transformation matrix that represents the
concatenation of the previous transformation in \fImat\fR and a
translation along the vector (\fIdx\fR,\ \fIdy\fR,\ \fIdz\fR).

.IP \fIvoid\ mat_rotate_x(mat,\ ang)\fR
.br
\fITransf_mat\ *mat;\fR
.br
\fIdouble\ ang;\fR
.sp
Set \fImat\fR to the transformation matrix that represents the
concatenation of the previous transformation in \fImat\fR and a
rotation with the angle \fIang\fR around the X axis. The angle
\fIang\fR is expressed in radians.

.IP \fIvoid\ mat_rotate_y(mat,\ ang)\fR
.br
\fITransf_mat\ *mat;\fR
.br
\fIdouble\ ang;\fR
.sp
Set \fImat\fR to the transformation matrix that represents the
concatenation of the previous transformation in \fImat\fR and a
rotation with the angle \fIang\fR around the Y axis.  The angle
\fIang\fR is expressed in radians.

.IP \fIvoid\ mat_rotate_z(mat,\ ang)\fR
.br
\fITransf_mat\ *mat;\fR
.br
\fIdouble\ ang;\fR
.sp
Set \fImat\fR to the transformation matrix that represents the
concatenation of the previous transformation in \fImat\fR and a
rotation with the angle \fIang\fR around the Z axis.  The angle
\fIang\fR is expressed in radians.

.IP \fIvoid\ mat_rotate(mat,\ point,\ vector,\ ang)\fR
.br
\fITransf_mat\ *mat;\fR
.br
\fIVector\ *point;\fR
.br
\fIVector\ *vector\fR
.br
\fIdouble\ ang;\fR
.sp
Set \fImat\fR to the transformation matrix that represents the
concatenation of the previous transformation in \fImat\fR and a
rotation with the angle \fIang\fR around the line represented by the
point \fIpoint\fR and the vector \fIvector\fR.  The angle
\fIang\fR is expressed in radians.

.IP \fIvoid\ mat_scale(mat,\ xscale,\ yscale,\ zscale)\fR
.br
\fITransf_mat\ *mat;\fR
.br
\fIdouble\ xscale;\fR
.br
\fIdouble\ yscale;\fR
.br
\fIdouble\ zscale;\fR
.sp
Set \fImat\fR to the transformation matrix that represents the
concatenation of the previous transformation in \fImat\fR and a
scaling with the scaling factors (\fIxscale\fR,\ \fIyscale\fR,\ \fIzscale\fR).

.IP \fIvoid\ mat_mirror_plane(mat,\ point,\ normal)\fR
.br
\fITransf_mat\ *mat;\fR
.br
\fIVector\ *point;\fR
.br
\fIVector\ *normal\fR
.sp
Set \fImat\fR to the transformation matrix that represents the
concatenation of the previous transformation in \fImat\fR and a
mirroring in the plane defined by the point \fIpoint\fR and the normal
vector \fInormal\fR. 

.IP \fIvoid\ mat_mul(res,\ a,\ b)\fR
.br
\fITransf_mat\ *res\fR
.br
\fITransf_mat\ *a\fR
.br
\fITransf_mat\ *b\fR
.sp
Multiply the two matrixes \fIa\fR and \fIb\fR and put the result in
the matrix \fIres\fR.  All three parameters are pointers to matrixes.
It is possible for \fIres\fR to point at the same matrix as either
\fIa\fR or \fIb\fR since the result is stored in a temporary matrix
during the computations.

.IP \fIvoid\ point_transform(res,\ vec,\ mat)\fR
.br
\fIVector\ *res\fR
.br
\fIVector\ *vec;\fR
.br
\fITransf_mat\ *mat;\fR
.sp
Transform the point (vector) \fIvec\fR with the transformation matrix
\fImat\fR and put the result into the vector \fIres\fR.  The two
vectors \fIres\fR and \fIvec\fR should not be the same vector since no
temporary is used during the computations.

.SH SEE ALSO
sipp(3X) - simple polygon processor, a 3d-graphics library
.br
shaders(3X) - a collection of shaders for \fIsipp\fR.
.br
primitives(3X) - a collection of object primitives for \fIsipp\fR.
.br
sipp_pixmap(3X) - pixmap handling code for \fIsipp\fR.
.br
sipp_bitmap(3X) - bitmap handling code for \fIsipp\fR.

.SH AUTHORS
Jonas Yngvesson\	\	(jonas-y@isy.liu.se)
.br
Inge Wallin\		(ingwa@isy.liu.se)

.SH BUGS
No known bugs.