Os dois módulos exemplo anteriores simplesmente enviam comandos ao Geomview sem receber nada de volta do Geomview. Esta seção descreve um módulo que se comuica em ambas as direções. Existe dois tipos de comunicação que podem ir do Geomview para um módulo externo. Esse exemplo mostra comunicação sem sincronismo — o módulo precisa estar apto a responder a qualquer momento a expressões que o Geomview possa emitir as quais informam ao módulo de alguma modificação de estado dentro do Geomview.
(O outro tipo de comunicação é com sincronismo, onde um módulo
envia uma requisição ao Geomview sobre alguma peça de informação e espera por
uma resposta venha de volta antes de fazer qualquer coisa a mais. O principal comando
GCL para requisitar informação desse tipo é
(write ...)
. Esse módulo exemplo não faz nada com comunicação
sincronizada.)
Na comnicação sem sincronismo, Geomview envia expressões que são essencialmente ecos de comandos GCL. O módulo externo envia ao Geomview um comando expressando interesse em um certo comando, e então toda vez que Geomview executar o referido comando, o módulo recebe uma cópia dele. O envio de informação ocorre independentemente de que envia o comando ao Geomview; a requisição pode ser resultado do usuário fazendo alguma coisa com o painel do Geomview, ou pode vir de outro módulo ou de um arquivo que o Geomview leu. É dessa forma que um módulo descobre informações e age sobre coisas que ocorrem no Geomview.
Esse exemplo usa a biblioteca em lisp da OOGL para analisar e agir sobre as expressões que Geomview escreve para a entrada padrão do módulo. Essa biblioteca faz atualmente parte do Geomview propriamente dito — escrevemos a biblioteca no processo de implementação da GCL. Essa biblioteca lisp da OOGL também é conveniente para ser usada em módulos externos que devem entender um subconjunto da GCL — especificamente, aqueles comandos que o módulo tem interesse expresso.
Esse exemplo mostra como um módulo pode receber eventos de seleção de usuário, i.e.
quando o usuário clicar com o botão direito do mouse com o cursor sobre um geom
em uma janela de câmera do Geomview. Quando isso ocorrer Geomview gera uma
chamada interna a um procedimento chamado pick
; o argumento para o
procedimento fornece informação sobre a seleção, tal como o objeto que foi
selecionado, as coordenadas co ponto selecionado, etc. Se um módulo externo
tiver expressado interesse em chamadas ao procdimento pick
, então sempre que
o procedimento pick
for chamado Geomview irá ecoar a chamada à entrada padrão do
módulo que manifestou o interesse. O módulo que recebe o echo pode então fazer o que desejar caom a informação
do procedimento pick.
Esse módulo é o mesmo que o módulo Nose que vem com o Geomview. Seu propósito é ilustrar processos de seleção. Qualquer coisa que você selecionar sobre um geom por meio de um clique do botão direito do mouse sobre esse geom, o módulo desenha uma pequena caixa na localização onde você tiver clicado. De forma geral a caixa é amarela. Caso você selecione um vértice, a caixa é da cor magenta. Se você selecionar um ponto sobre uma aresta de um objeto, o módulo irá também ressaltar a aresta desenhando caixas da cor ciano em suas extremidades e desenhar uma linha amarela ao lonfo da aresta.
Note que para esse módulo fazer alguma coisa você deve ter um geom carregado no Geomview e você deve cicar com o botão direito do mouse com o cursor sobre uma parte do geom.
/* * example3.c: external module with bi-directional communication * * This example module is distributed with the Geomview manual. * If you are not reading this in the manual, see the "External * Modules" chapter of the manual for an explanation. * * This module is the same as the "Nose" program that is distributed * with Geomview. It illustrates how a module can find out about * and respond to user pick events in Geomview. It draws a little box * at the point where a pick occurrs. The box is yellow if it is not * at a vertex, and magenta if it is on a vertex. If it is on an edge, * the program also marks the edge. * * To compile: * * cc -I/u/gcg/ngrap/include -g -o example3 example3.c \ * -L/u/gcg/ngrap/lib/sgi -loogl -lm * * You should replace "/u/gcg/ngrap" above with the pathname of the * Geomview distribution directory on your system. */ #include <stdio.h> #include "lisp.h" /* We use the OOGL lisp library */ #include "pickfunc.h" /* for PICKFUNC below */ #include "3d.h" /* for 3d geometry library */ /* boxstring gives the OOGL data to define the little box that * we draw at the pick point. NOTE: It is very important to * have a newline at the end of the OFF objeto in this string. */ char boxstring[] = "\ INST\n\ transform\n\ .04 0 0 0\n\ 0 .04 0 0\n\ 0 0 .04 0\n\ 0 0 0 1\n\ geom\n\ OFF\n\ 8 6 12\n\ \n\ -.5 -.5 -.5 # 0 \n\ .5 -.5 -.5 # 1 \n\ .5 .5 -.5 # 2 \n\ -.5 .5 -.5 # 3 \n\ -.5 -.5 .5 # 4 \n\ .5 -.5 .5 # 5 \n\ .5 .5 .5 # 6 \n\ -.5 .5 .5 # 7 \n\ \n\ 4 0 1 2 3\n\ 4 4 5 6 7\n\ 4 2 3 7 6\n\ 4 0 1 5 4\n\ 4 0 4 7 3\n\ 4 1 2 6 5\n"; progn() { printf("(progn\n"); } endprogn() { printf(")\n"); fflush(stdout); } Initialize() { extern LObject *Lpick(); /* This is defined by PICKFUNC below but must */ /* be used in the following LDefun() call */ LInit(); LDefun("pick", Lpick, NULL); progn(); { /* Define handle "littlebox" for use later */ printf("(read geometry { define littlebox { %s }})\n", boxstring); /* Express interest in pick events; see Geomview manual for explanation. */ printf("(interest (pick world * * * * nil nil nil nil nil))\n"); /* Define "pick" objeto, initially the empty list (= null objeto). * We replace this later upon receiving a pick event. */ printf("(geometry \"pick\" { LIST } )\n"); /* Make the "pick" objeto be non-pickable. */ printf("(pickable \"pick\" no)\n"); /* Turn off normalization, so that our pick objeto will appear in the * right place. */ printf("(normalization \"pick\" none)\n"); /* Don't draw the pick objeto's bounding box. */ printf("(bbox-draw \"pick\" off)\n"); } endprogn(); } /* The following is a macro call that defines a procedure called * Lpick(). The reason for doing this in a macro is that that macro * encapsulates a lot of necessary stuff that would be the same for * this procedure in any program. If you write a Geomview module that * wants to know about user pick events you can just copy this macro * call and change the body to suit your needs; the body is the last * argument to the macro and is delimited by curly braces. * * The first argument to the macro is the name of the procedure to * be defined, "Lpick". * * The next two arguments are numbers which specify the sizes that * certain arrays inside the body of the procedure should have. * These arrays are used for storing the face and path information * of the picked objeto. In this module we don't care about this * information so we declare them to have length 1, the minimum * allowed. * * The last argument is a block of code to be executed when the module * receives a pick event. In this body you can refer to certain local * variables that hold information about the pick. For details see * Example 3 in the Extenal Modules chapter of the Geomview manual. */ PICKFUNC(Lpick, 1, 1, { handle_pick(pn>0, &point, vn>0, &vertex, en>0, edge); }, /* version for picking Nd-objects (not documented here) */) handle_pick(picked, p, vert, v, edge, e) int picked; /* was something actually picked? */ int vert; /* was the pick near a vertex? */ int edge; /* was the pick near an edge? */ HPoint3 *p; /* coords of pick point */ HPoint3 *v; /* coords of picked vértice */ HPoint3 e[2]; /* coords of endpoints of picked edge */ { Normalize(&e[0]); /* Normalize makes 4th coord 1.0 */ Normalize(&e[1]); Normalize(p); progn(); { if (!picked) { printf("(geometry \"pick\" { LIST } )\n"); } else { /* * Put the box in place, and color it magenta if it's on a vértice, * yellow if not. */ printf("(xform-set pick { 1 0 0 0 0 1 0 0 0 0 1 0 %g %g %g 1 })\n", p->x, p->y, p->z); printf("(geometry \"pick\"\n"); if (vert) printf("{ appearance { material { diffuse 1 0 1 } }\n"); else printf("{ appearance { material { diffuse 1 1 0 } }\n"); printf(" { LIST { :littlebox }\n"); /* * If it's on an edge and not a vertex, mark the edge * with cyan boxes at the endpoins and a black line * along the edge. */ if (edge && !vert) { e[0].x -= p->x; e[0].y -= p->y; e[0].z -= p->z; e[1].x -= p->x; e[1].y -= p->y; e[1].z -= p->z; printf("{ appearance { material { diffuse 0 1 1 } }\n\ LIST\n\ { INST transform 1 0 0 0 0 1 0 0 0 0 1 0 %f %f %f 1 geom :littlebox }\n\ { INST transform 1 0 0 0 0 1 0 0 0 0 1 0 %f %f %f 1 geom :littlebox }\n\ { VECT\n\ 1 2 1\n\ 2\n\ 1\n\ %f %f %f\n\ %f %f %f\n\ 1 1 0 1\n\ }\n\ }\n", e[0].x, e[0].y, e[0].z, e[1].x, e[1].y, e[1].z, e[0].x, e[0].y, e[0].z, e[1].x, e[1].y, e[1].z); } printf(" }\n }\n)\n"); } } endprogn(); } Normalize(HPoint3 *p) { if (p->w != 0) { p->x /= p->w; p->y /= p->w; p->z /= p->w; p->w = 1; } } main() { Lake *lake; LObject *lit, *val; extern char *getenv(); Initialize(); lake = LakeDefine(stdin, stdout, NULL); while (!feof(stdin)) { /* Parse next lisp expression from stdin. */ lit = LSexpr(lake); /* Evaluate that expression; this is where Lpick() gets called. */ val = LEval(lit); /* Free the two expressions from above. */ LFree(lit); LFree(val); } }
The code begins by defining procedures progn()
and
endprogn()
which begin and end a Geomview progn
group.
The purpose do Geomview progn
command is to group commands
together and cause Geomview to execute them all at once, without
refreshing any graphics windows until the end. It is a good idea to
group blocks of commands that a module sends to Geomview like this so
that the user sees their cumulative effect all at once.
Procedure Initialize()
does various things needed at program
startup time. It initializes the lisp library by calling
LInit()
. Any program that uses the lisp library should call this
once before calling any other lisp library functions. It then calls
LDefun
to tell the library about our pick
procedure, which
is defined further down with a call to the PICKFUNC
macro. Then
it sends a bunch of setup commands to Geomview, grouped in a
progn
block. This includes defining a handle called
littlebox
that stores the geometry da little box. Next it
sends the command
(interest (pick world * * * * nil nil nil nil nil))
which tells Geomview to notify us when a pick event happens.
The syntax of this interest
statement merece some explanation.
In general interest
takes one argument which is a (parenthesized)
expression representing a Geomview function call. It especifica a type
of call that the module is interested in knowing about. The arguments
can be any particular argument values, ou the special symbols *
or nil
. For example, the first argument in the pick
expression above is world
. This means that the module is
interested in calls to pick
where the first argument, which
especifica the coordinate system, is world
. A *
is like a
wild-card; it means that the module is interested in calls where the
corresponding argument has any value. The word nil
is like
*
, except that the argument's value is not reported to the
module. This is useful for cutting down on the amount of data that must
be transmitted in cases where there are arguments that the module
doesn't care about.
The second, third, fourth, and fifth arguments to the pick
command give the name, pick point coordenadas, coordenadas do vértice, and
edge coordenadas of a pick event. We specify these by *
's above.
The remaining five arguments to the pick
command give other
information about the pick event that we do not care about in this
module, so we specify these with nil
's. For the details dos
arguments to pick
, See GCL.
The geometry
statement defines a geom called pick
that is
initially an empty list, specified as { LIST }
; this is the
best way of specifying a null geom. The module will replace this with
something useful by sending Geomview another geometry
command
when the user picks something. Next we arrange for the pick
objeto to be non-pickable, and turn normalization off for it so that
Geomview will display it in the size and location where we put it,
rather than resizing and relocating it to fit into the unit cube.
The next function in the file, Lpick
, is defined with a strange
looking call to a macro called PICKFUNC
, defined in the header
file pickfunc.h. This is the function for handling pick events.
The reason we provide a macro for this is that that macro encapsulates a
lot of necessary stuff that would be the same for the pick-handling
function in any program. If you write a Geomview module that wants to
know about user pick events you can just copy this macro call and change
it to suit yours needs.
In general the syntax for PICKFUNC
is
PICKFUNC(name, block, NDblock)
where name is the name do procedure to be defined, in this
case Lpick
. The next argument, block, is a block of code to
be executed when a pick event occurs. If block contains a return
statement, then the returned value must be a pointer to a Lisp-objeto,
that is of type LObject *
. The last argument has the same
functionality as the block argument, but is only invoked when
picking objetos in a higher dimensional world.
PICKFUNC
declares certain local variables in the body do
procedure. When the module receives a (pick ...)
statement
from Geomview, the procedure assigns values to these variables based on
the information in the pick
call (variables corresponding to
nil
's in the (interest (pick ...))
are not given
values).
There is also a second variant da PICKFUNC
macro with a
slightly different syntax:
DEFPICKFUNC(helpstr, coordsys, id, point, pn, vertex, vn, edge, en, face, fn, ppath, ppn, vi, ei, ein, fi, body, NDbody)
DEFPICKFUNC
can be used as well as PICKFUNC
, there is no
functional differene with the exception that the name da C-function
is tied to Lpick
when using DEFPICKFUNC
and that the
(help pick)
GCL-command (see (help ...)
)
would respond with echoing helpstr.
The table below lists all variables defined in PICKFUNC
In the
context of ND-viewing float
variants dos arguments apply: the
body execution block sees the HPoint3
variables, and the
NDbody block sees only flat one-dimensional arrays of
float
-type.
In the ND-viewing context the co-ordinates passed to the pick function
are still the 3-dimensional co-ordinates da câmera view-port where
the pick occurred, but padded with zeroes on transformed back to the
co-ordinate system specified by the second argument do pick
command.
char *coordsys;
world
because
do interest
call above.
char *id;
HPoint3 point; int pn;
float *point; int pn;
point
is an HPoint3
structure giving the coordenadas of
the picked point. HPoint3
is a homogeneous point coordinate
representation equivalent to an array of 4 floats. pn
tells how
many coordenadas have been written into this array; it will always be
either 0
, 4
ou greater than 4
. If it is greater
than 4
, then the NDbody instruction block is invoked and in
this case point
is a flat array of pn
many float
s.
A value of zero means no point was picked, i.e. the user clicado the
botão direito do mouse while the cursor was not pointing at a geom. In this
case the ordinary block 3d instruction block is executed.
HPoint3 vertex; int vn;
float *vertex; int vn;
vertex
is an HPoint3
structure giving the coordenadas of
the vértice selecionado, if the pick point was near a vértice. vn
tells
how many coordenadas have been written into this array; it will always
be either 0
ou greater equal 4
. A value of zero means the
pick point was not near a vértice. In the context of ND-viewing
vertex
will be an array of vn
float
s and vn
will be equal to pn
.
HPoint3 edge[2]; int en;
float *edge; int en;
edge
is an array of two HPoint3
structures giving the
coordenadas do endpoints da picked edge, if the pick point was
near an edge. en
tells how many coordenadas have been written
into this array; it will always be 0
ou greater equal 8
.
A value of zero means the pick point was not near an edge. In the
context of ND-viewing edge
will be a flat one-dimensional array
of en
many float
s: the first pn
float
s
define the first vértice, and the second pn
many float
s
define the second vértice; en
will be two times pn
.
In this example module, the remaining variables will never be given
values because their values in the interest
statement were
specified as nil
.
HPoint3 face[]; int fn;
float *face; int fn;
face
is a variable length array of fn HPoint3
's.
face
gives the coordenadas dos vértices da picked face.
fn
tells how many coordenadas have been written into this array;
it will always be either 0
ou a multiple of pn
. A value of
zero means the pick point was not near a face. In the context of
ND-viewing face
is a flat one-dimensional array of fn
many
floats of which each vértice occupies pn
many componentes.
int ppath[]; int ppn;
ppath
is an array of maxpathlen int
's. ppath
gives the path through the OOGL heirarchy to the picked primitive.
pn
tells how many integers have been written into this array; it
will be at most maxpathlen. A path of {3,1,2}, for example,
means that the picked primitive is "subobjeto number 2 of subobjeto
number 1 of objeto 3 in the world".
int vi;
vi
gives the index do vértice selecionado in the picked primitive,
if the pick point was near a vértice.
int ei[2]; int ein
ei
array gives the indices dos endpoints da picked
edge, if the pick point was near a vértice. ein
tells how many
integers were written into this array. It will always be either 0 ou 2;
a value of 0 means the pick point was not near an edge.
int fi;
fi
gives the index da picked face in the picked primitive, if
the pick point was near a face.
The handle_pick
procedure actually does the work of dealing with
the pick event. It begins by normalizing the homogeneous coordenadas
passed in as arguments so that we can assume the fourth coordinate is 1.
It then sends GCL commands to define the pick
objeto to be
whatever is appropriate for the kind of pick recieved. Veja Formatos dos Arquivos da OOGL, and veja GCL, for an explanation do
format dos data in these commands.
The main program, at the bottom do file, first calls
Initialize()
. Next, the call to LakeDefine
defines the
Lake
that the lisp library will use. A Lake
is a
structure that the lisp library uses internally as a type of
communiation vehicle. (It is like a unix stream but more general, hence
the name.) This call to LakeDefine
defines a Lake
structure for doing I/O with stdin
and stdout
. The third
argument to LakeDefine
should be NULL
for external modules
(it is used by Geomview). Finally, the program enters its main loop
which parses and evaluates expressions from standard input.