Programmers' Manual - IRIT

Introduction

This manual describes the different libraries of the IRIT solid modeling environment. Quite a few libraries can be found to manipulate geometry in general, freeform curves and surfaces, symbolic computation, trimmed surfaces, freeform trivariate functions, Boolean operations, input output data file parsing, and miscelleneous.

All interface to the libraries should be made via the appropriate header files that can be found in the include subdirectory. Most libraries have a single header file that is named the same as the library. Functions and constants that are visible to the users of the libraries are prefixed with a unique prefix, usually derived from the library name itself. External definitions that start with an underscore should not be used, even if found in header files.

The header file include/irit_sm.h must be sourced by every source file in the solid modeller. In most cases, this file is sourced indirectly via local header files.

The following libraries are avaliable in IRIT:

Name of Library Tasks
bool Boolean operations on polygonal models.
cagd Low level freeform curves and surfaces.
geom General geometry functions.
misc memory allocation, configuration files, attributes, etc.
prsr input and output for file/sockets of objects of IRIT.
symb Symbolic manipulation of curves and surfaces.
trim Trimmed surfaces support.
triv Freeform trivariate functions.
xtra Public domain code that is not part of IRIT.
The following chapters reference the different function of different libraries. Chapter~ref{chap-examples} provides several examples of writing C code using the IRIT libraries.

Boolean Library, bool_lib

General Information

On of the crucial operation in any solid modeling environment is the ability to perform Boolean operations among different geometric objects. The interface of the library is defined in include/bool_lib.h. This library supports only Boolean operations of polygonal objects. The Boolean operations of OR, AND, SUBtract, NEGate, CUT, and MERGE are supported via the BoolOperType typedef:
BoolOperType Meaning
BOOL_OPER_OR Union of two geometrical objects
BOOL_OPER_AND Intersection of two geometrical objects
BOOL_OPER_SUB The difference of two geometrical objects
BOOL_OPER_NEG Unary Inside-out of one geometrical object
BOOL_OPER_CUT Boundary of one object outside the other
BOOL_OPER_MERGE Simple merge without any computation
The BoolOperType typedef is used in two dimensional Boolean operations invoked via Boolean2D . Three dimensional Boolean operations are invoked via BooleanXXX where XXX is one of OR, AND, SUB, NEG, CUT or MERGE, denoting the same as in the table above. In addition several state functions are available to control the way the Boolean operations are conducted. Functions to enable the dump of (only) the intersection curves, to handle coplanar polygons, and to set the axis along which the sweep is performed are provided. All globals in this library have a profix of Bool .

Library Functions

Click Here for the list of functions of this library.

CAGD Library, cagd_lib

General Information

This library provides a rich set of function to create, convert, display and process freeform Bezier and NURBs curves and surfaces. The interface of the library is defined in include/cagd_lib.h . This library mainly supports low level freeform curve and surface operations. Supported are curves and surfaces from scalars to five dimensions as E1/P1 to E5/P5 using the CagdPointType . Pi is a rational (projective) version of Ei, with an additional W coefficient. Polynomial in the power basis have some very limited support as well. Different data structures to hold UV parameter values, control points, vectors, planes, bounding boxes, polylines and polygons are defined as well as the data strcutures to hold the curves and surfaces themselves,

typedef struct CagdCrvStruct {
    struct CagdCrvStruct *Pnext;
    struct IPAttributeStruct *Attr;
    CagdGeomType GType;
    CagdPointType PType;
    int Length;            /* Number of control points (== order in Bezier). */
    int Order;	    /* Order of curve (only for Bspline, ignored in Bezier). */
    CagdBType Periodic;			   /* Valid only for Bspline curves. */
    CagdRType *Points[CAGD_MAX_PT_SIZE];     /* Pointer on each axis vector. */
    CagdRType *KnotVector;
} CagdCrvStruct;

typedef struct CagdSrfStruct {
    struct CagdSrfStruct *Pnext;
    struct IPAttributeStruct *Attr;
    CagdGeomType GType;
    CagdPointType PType;
    int ULength, VLength;	 /* Mesh size in the tensor product surface. */
    int UOrder, VOrder;   /* Order in tensor product surface (Bspline only). */
    CagdBType UPeriodic, VPeriodic;      /* Valid only for Bspline surfaces. */
    CagdRType *Points[CAGD_MAX_PT_SIZE];     /* Pointer on each axis vector. */
    CagdRType *UKnotVector, *VKnotVector;
} CagdSrfStruct;
Curves and surfaces have a geometric type GType to prescribe the type of entity (such as CAGD_SBEZIER_TYPE for Bezier surface) and a point type PType to prescribe the point type of the entity (such as CAGD_PT_E3_TYPE for three dimensional Euclidean control points). Length and Order slots are used to hold the number of control points in the mesh and or control polygon and the order(s) of the basis functions. Periodic flag(s) are used to denote periodic end conditions. In addition, KnotVector slot(s) are used if the entity exploits Bspline basis functions, or NULL otherwise. The control polygon and/or mesh itself is organized in the Points slot as a vector of size CAGD_MAX_PT_SIZE of vectors of CagdRType s. For surfaces, the mesh is ordered U first and the macros of CAGD_NEXT_U CAGD_NEXT_V , and CAGD_MESH_UV can be used to determine indices in the mesh. All structures in the cagd library can be allocated using New constrcutures (i.e. CagdUVNew or CagdCrfNew , freed using Free destructores (i.e. CagdSrfFree or {CagdBBoxFree}, linked list free using FreeList destructores (i.e. CagdPolylineFreeList ), and copied using copy constructores {i.e. CagdPtCopy or CagdCtlPtCopyList ). This library has its own error handler, which by default prints an error message and exit the program called CagdFatalError . Most globals in this library have a prefix of Cagd for general cagd routines. Prefix of Bzr is used for Bezier routines, prefix of Bsp for Bspline specific routines, prefix of Cnvrt for conversion routines, and Afd for adaptive forward differencing routines.

Library Functions

Click Here for the list of functions of this library.

Geometry Library, geom_lib

General Information

This library handles general geometric queries such as a distance between two lines, bounding boxes, convexity of polygons etc. Several header files can be found for this library:
Header (include/*.h) Functionality
bbox.h Bounding boxes related functions
convex.h Convexity of polygons and convex polygon decomposition
geomat3d.h General three dimensional geometry queries
geomvals.h Area, Volume, and Size queries on polygonal objects
intrnrml.h Internal normal interpolation for polygonal models
ln_sweep.h A line sweep implemetation
poly_cln.h Clean up degenerated polygons/polylines
primitiv.h Constructors of polygonal BOXes, CYLINDERs, etc.

Library Functions

Click Here for the list of functions of this library.

Miscelleneous Library, misc_lib

General Information

This library holds general miscelleneous functions such as reading configuration files, low level homogeneous matrices computation, low level attributes and general machine specific low level routines. Several header files can be found for this library:
Header (include/*.h) Functionality
config.h Manipulation of configuration files (*.cfg files)
dist_pts.h Enegry based distribution of points.
gen_mat.h Homogeneous matrices manipulation
getarg.h Command line parsing for application tools
imalloc.h Low level dynamic memory functions for IRIT
miscattr.h Low level attribute related functions
priorque.h An implementation of a priority queue
xgeneral.h Low level, machine specific, routines

Library Functions

Click Here for the list of functions of this library.

Prsr Library, prsr_lib

General Information

This library provides the data file interface for IRIT. Functions are provided to read and write data files, both compressed (on unix only, using compress ), and uncompressed, in binary and/or ascii text modes. This library is also used to exchange data between the IRIT server and the display devices' clients. Several header files can be found for this library:
Header (include/*.h) Functionality
allocate.h High level dynamic allocation of objects
attribut.h High level attributes for objects
ip_cnvrt.h Freeform to polygon and polyline high level conversion
iritprsr.h Main interface to reading and writing data
irit_soc.h Socket communication for data exchange

Library Functions

Click Here for the list of functions of this library.

Symbolic Library, symb_lib

General Information

This library provides a rich set of function to symbolically manipulate freeform curves and surfaces. This library heavily depends on the cagd library. Functions are provided to low level add, subtract, and multiply freeform curves and surfaces, to compute fields such as curvature, and to extract singular points such as extremums, zeros, and inflections. High level tools to metamorph curves and surfaces, to compute layout (prisa) of freeform surfaces, to compute offset approximations of curves and surfaces, and to compose curves and surfaces are also provided. The interface of the library is defined in include/symb_lib.h . This library has its own error handler, which by default prints an error message and exit the program called SymbFatalError . Globals in this library have a prefix of Symb for general symbolic routines. Prefix of Bzr is used for Bezier routines, and prefix of Bsp for Bspline specific routines.

Library Functions

Click Here for the list of functions of this library.

Trimmed surfaces Library, trim_lib

General Information

This library provides a set of function to manipulate freeform trimmed Bezier and/or NURBs surfaces. This library heavily depends on the cagd library. Functions are provided to create, copy, and destruct trimmed surfaces to extract isoparametric curves, to evaluate, refine and subdivide, to read and write trimmed surfaces, degree raise, and approximate using polygonal representations. The interface of the library is defined in include/trim_lib.h . This library has its own error handler, which by default prints an error message and exit the program called TrimFatalError . All globals in this library have a prefix of Trim .

Library Functions

Click Here for the list of functions of this library.

Trivariate Library, triv_lib

General Information

This library provides a rich set of function to manipulate freeform Bezier and/or NURBs trivariate. This library heavily depends on the cagd library. Functions are provided to create, copy, and destruct trivariates, to extract isoparametric surfaces, to evaluate, refine and subdivide, to read and write trivariates, to differentiate, degree raise, make compatible and approximate iso-surface at iso values using polygonal representations. The interface of the library is defined in include/triv_lib.h . This library has its own error handler, which by default prints an error message and exit the program called TrivFatalError . All globals in this library have a prefix of Triv .

Library Functions

Click Here for the list of functions of this library.

Extra Library, xtra_lib

General Information

This library is not an official part of IRIT and contains public domain code that is used by routines in IRIT. The interface of the library is defined in include/extra_fn.h .

Library Functions

Click Here for the list of functions of this library.

Programming Examples

This chapter describes several simple examples of C programs that exploits the libraries of IRIT. All external function are defined in the include subdirectory of IRIT and one can 'grep' there for the exact include file that contains a certain function name. All C programs in all C files should include 'irit_sm.h' as their first include file of IRIT, before any other include file of IRIT. Header files are set so C++ code can compile and link to it without any special treatment.

Setting up the Compilation Environment

In order to compile programs that uses the libraries of IRIT, a makefile has to be constructed. Assuming IRIT is installed in /usr/local/irit , here is a simple makefile that can be used (for a unix environment): 
IRIT_DIR = /usr/local/irit

include $(IRIT_DIR)/makeflag.unx

OBJS	= program.o

program: $(OBJS)
	$(CC) $(CFLAGS) -o program $(OBJS) $(LIBS) -lm $(MORELIBS)
The simplicity of this makefile is drawn from the complexity of makeflag.unx. The file makeflag.unx sets the CC, CFLAGS, LIBS, and MORELIBS for the machined using among other things. Furthermore, makeflag.unx also sets the default compilation rules from C sources to object files. The file makeflag.unx had to be modified once, when IRIT was installed on this system. If the used system is not a unix environment, then the file makefile.unx will have to be replaced with the proper makeflag file. In an OS2 environment, using the emx gcc compiler, the makefile is even simpler since the linking rule is also defined in makeflag.os2: 
IRIT_DIR = usrlocalirit

include $(IRIT_DIR)makeflag.os2

OBJS	= program.o

program.exe: $(OBJS)
Finally, here is a proper makefile for Windows NT: 
IRIT_DIR = usrlocalirit

include $(IRIT_DIR)makeflag.wnt

OBJS	= program.obj

program.exe: $(OBJS)
        $(IRITCONLINK) -out:program.exe $(OBJS) $(LIBS) $(W32CONLIBS)