Hollow Polygon implementation (C source for same)
Gretchen Helms
ghelms at hellfire.csd.sgi.com
Sat Sep 29 05:34:26 AEST 1990
The following is my implementation of Kurt Akeley's
article in the IRIS Universe regarding hollow polygons.
Object is a cube rather than a sphere as it takes less
code to implement. Read the comments.
-----------------------mangle here-----------------------
/* hollocube.c
Sample code for creating an object made up of
hollow polygons, as referenced in Kurt Akeley's
article "The Hidden Charms of Z-Buffer", IRIS
Universe issue number 11.
Implemented by G. "Murdock" Helms, SGI, 8/2/90.
Final revision 9/28/90.
Compile with cc hollocube.c -o hollocube -lgl_s
DOES NOT RUN ON NON-GT/GTXS AS PER ARTICLE.
*/
/* include the usual libs */
#include "math.h"
#include "gl.h"
#include "device.h"
main()
{
short attached; /* usual queue stuff */
short value;
int dev,val;
float box[8][3]; /* this is needed for building the walls of the cube */
float width; /* shamelessly stolen from Intro to Graphics */
foreground(); /* you can run Edge on this if you like */
initialize(box, &width); /* set up the vertices of the walls */
drawscene(box, &width); /* do drawing things */
while (TRUE) /* loop until program is killed */
{
while (qtest()||!attached) /* do the usual queue stuff */
{
dev=qread(&value);
if (dev==ESCKEY)
{
exit(0); /* can kill with esc key */
}
if (dev==REDRAW)
{
reshapeviewport();
drawscene(box, &width); /* yes, you can move the window around */
}
else if (dev==INPUTCHANGE)
attached=value;
} /* end while qtest */
} /* end while true */
} /* end main */
drawscene(box, width) /* simple draw routine */
float box[8][3];
float width;
{
czclear(0,0);
drawbeam(box);
swapbuffers();
rot(10,'x'); /* need to rotate to show off qualities */
czclear(0,0); /* wasn't apparent if viewed straight-on */
drawbeam(box);
swapbuffers();
rot(20,'y');
czclear(0,0);
drawbeam(box);
swapbuffers();
} /* end drawscene */
initbeam (x, y, z, point) /* define the values for the vertices */
register float x, y, z, point[][3];
{
point[0][0] = point[3][0] = point[4][0] = point[5][0] = -x/2.0;
point[1][0] = point[2][0] = point[6][0] = point[7][0] = x/2.0;
point[4][1] = point[5][1] = point[6][1] = point[7][1] = -y/2.0;
point[0][1] = point[1][1] = point[2][1] = point[3][1] = y/2.0;
point[2][2] = point[3][2] = point[5][2] = point[7][2] = -z/2.0;
point[0][2] = point[1][2] = point[4][2] = point[6][2] = z/2.0;
}
/* What follows are a set of small functions that
* follow the descriptions in the zbuffer article,
* in the order they appear and are used.
*/
setzbuff() /* set up Zbuffer with reverse mapping */
{
zbuffer(TRUE);
lsetdepth(0x7fffff,0x000000);
zfunction(ZF_GEQUAL);
} /* end setzbuff */
disablp() /* disable polygon pixels */
{
zbuffer(FALSE);
backbuffer(FALSE);
zdraw(TRUE);
wmpack(0x800000);
cpack(0x800000);
} /* end disablep */
enablep() /* enable pixels on perimeter */
{
cpack(0x000000);
linewidth(2);
} /* end enablep */
fillperim() /* fill poly (which actually only fills perim)*/
{
zbuffer(TRUE);
backbuffer(TRUE);
zdraw(FALSE);
wmpack(0xffffffff);
cpack(0x000000FF);
} /* end fill perim */
clearhollow() /* clear things up so no munging takes place */
{
zbuffer(FALSE);
backbuffer(FALSE);
zdraw(TRUE);
wmpack(0x800000);
cpack(0x000000);
} /* end clearhollow */
resethollow() /* reset states */
{
zbuffer(TRUE);
backbuffer(TRUE);
zdraw(FALSE);
wmpack(0xffffffff);
} /* end resethollow */
drawbeam (point) /* now let's draw. */
register float point[][3];
{
/* draw bottom facing polygon */
disablp();
bgnpolygon();
v3f( point[4] );
v3f( point[6] );
v3f( point[7] );
v3f( point[5] );
endpolygon();
enablep();
bgnclosedline();
v3f( point[4] );
v3f( point[6] );
v3f( point[7] );
v3f( point[5] );
endclosedline();
fillperim();
bgnpolygon();
v3f( point[4] );
v3f( point[6] );
v3f( point[7] );
v3f( point[5] );
endpolygon();
clearhollow();
bgnpolygon();
v3f( point[4] );
v3f( point[6] );
v3f( point[7] );
v3f( point[5] );
endpolygon();
resethollow();
/* draw left facing polygon */
disablp();
bgnpolygon();
v3f( point[3] );
v3f( point[0] );
v3f( point[4] );
v3f( point[5] );
endpolygon();
enablep();
bgnclosedline();
v3f( point[3] );
v3f( point[0] );
v3f( point[4] );
v3f( point[5] );
endclosedline();
fillperim();
bgnpolygon();
v3f( point[3] );
v3f( point[0] );
v3f( point[4] );
v3f( point[5] );
endpolygon();
clearhollow();
bgnpolygon();
v3f( point[3] );
v3f( point[0] );
v3f( point[4] );
v3f( point[5] );
endpolygon();
resethollow();
/* draw right facing polygon */
disablp();
bgnpolygon();
v3f( point[2] );
v3f( point[1] );
v3f( point[6] );
v3f( point[7] );
endpolygon();
enablep();
bgnclosedline();
v3f( point[2] );
v3f( point[1] );
v3f( point[6] );
v3f( point[7] );
endclosedline();
fillperim();
bgnpolygon();
v3f( point[2] );
v3f( point[1] );
v3f( point[6] );
v3f( point[7] );
endpolygon();
clearhollow();
bgnpolygon();
v3f( point[2] );
v3f( point[1] );
v3f( point[6] );
v3f( point[7] );
endpolygon();
resethollow();
/* draw top facing polygon */
disablp();
bgnpolygon();
v3f( point[0] );
v3f( point[1] );
v3f( point[2] );
v3f( point[3] );
endpolygon();
enablep();
bgnclosedline();
v3f( point[0] );
v3f( point[1] );
v3f( point[2] );
v3f( point[3] );
endclosedline();
fillperim();
bgnpolygon();
v3f( point[0] );
v3f( point[1] );
v3f( point[2] );
v3f( point[3] );
endpolygon();
clearhollow();
bgnpolygon();
v3f( point[0] );
v3f( point[1] );
v3f( point[2] );
v3f( point[3] );
endpolygon();
resethollow();
/* draw front facing polygon */
disablp();
bgnpolygon();
v3f( point[3] );
v3f( point[2] );
v3f( point[7] );
v3f( point[5] );
endpolygon();
enablep();
bgnclosedline();
v3f( point[3] );
v3f( point[2] );
v3f( point[7] );
v3f( point[5] );
endclosedline();
fillperim();
bgnpolygon();
v3f( point[3] );
v3f( point[2] );
v3f( point[7] );
v3f( point[5] );
endpolygon();
clearhollow();
bgnpolygon();
v3f( point[2] );
v3f( point[7] );
v3f( point[5] );
endpolygon();
resethollow();
/* draw back facing polygon */
disablp();
bgnpolygon();
v3f( point[0] );
v3f( point[1] );
v3f( point[6] );
v3f( point[4] );
endpolygon();
enablep();
bgnclosedline();
v3f( point[0] );
v3f( point[1] );
v3f( point[6] );
v3f( point[4] );
endclosedline();
fillperim();
bgnpolygon();
v3f( point[0] );
v3f( point[1] );
v3f( point[6] );
v3f( point[4] );
endpolygon();
clearhollow();
bgnpolygon();
v3f( point[0] );
v3f( point[1] );
v3f( point[6] );
v3f( point[4] );
endpolygon();
resethollow();
/* now we have to draw the cube solid inside all this stuff */
/* cuz if we don't it looks just like a normal wireframe! */
zfunction (ZF_GREATER);
cpack(0x00000000);
bgnpolygon();
v3f( point[4] );
v3f( point[6] );
v3f( point[7] );
v3f( point[5] );
endpolygon();
bgnpolygon();
v3f( point[3] );
v3f( point[0] );
v3f( point[4] );
v3f( point[5] );
endpolygon();
bgnpolygon();
v3f( point[2] );
v3f( point[1] );
v3f( point[6] );
v3f( point[7] );
endpolygon();
bgnpolygon();
v3f( point[0] );
v3f( point[1] );
v3f( point[2] );
v3f( point[3] );
endpolygon();
bgnpolygon();
v3f( point[3] );
v3f( point[2] );
v3f( point[7] );
v3f( point[5] );
endpolygon();
bgnpolygon();
v3f( point[0] );
v3f( point[1] );
v3f( point[6] );
v3f( point[4] );
endpolygon();
}
initialize(box, width) /* stuff the startup stuff here */
register float box[8][3]; /* The eight vertices of the beam */
register float *width;
{
float aspect,x,y; /* variables to perspective function */
int gid;
register float height, length; /* needed for square initialization */
prefposition(0, XMAXSCREEN/3, 0, YMAXSCREEN/3);
gid = winopen ("Hollow Polygons"); /* get the window id and name it */
RGBmode(); /* I like c3i calls, no map dependencies */
lsetdepth(0,0x7fffff); /* initialize zbuffer near and far planes */
overlay(2);
doublebuffer();
gconfig(); /* configure the hardware */
shademodel (FLAT);
qdevice (ESCKEY); /* queue all these items */
qdevice (REDRAW);
qdevice (INPUTCHANGE);
qenter (REDRAW, gid);
x = (float) XMAXSCREEN; /* set variables to perspective */
y = (float) YMAXSCREEN;
aspect = x/y;
perspective (450,aspect, 0.1,100.0); /* one viewing method */
polarview (5.0, 0, 0, 0); /* another viewing method */
*width = 2.0; height = 2.0; length = 2.0; /* static info for size of sqr */
initbeam (*width, height, length, box); /* init square */
setzbuff();
}
-----------------------mangle here-----------------------
--
G. "Murdock" Helms Is it so frightening
Silicon Graphics to have me at your shoulder?
Product Support Engineer Thunder and lightning
ghelms at sgi.sgi.com couldn't be bolder.
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