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GL3.2 for AIX: Graphics Library (GL) Technical Reference

cylinder1.c Example C Language Program

`/* Example C Languange Program cylinder1.c*/`
```/*
The following program illustrates how to use the Graphics
Library to perform lighting.  It draws a cylinder and rotates
it.```
```This program requires a z buffer.
*/```
```#include <gl/gl.h>
#include <math.h>
#include <stdio.h>```
```#define RADIUS 0.9
#define TWOPI 6.28318530
#define PI 3.14159265```
```/* define black RGB color */
float  blackvec[3] = {
0.0, 0.0, 0.0};```
```Matrix idmat = {
1.0,0.0,0.0,0.0, /* identity matrix */
0.0,1.0,0.0,0.0,
0.0,0.0,1.0,0.0,
0.0,0.0,0.0,1.0};```
```/*define a polygon with some structures
* -- for code readability*/
typedef struct { /* structure for a 3-D vertex */
Coord x;
Coord y;
Coord z;
} POINT;```
```typedef struct { /* 4 vertex lighted polygon struct */
POINT vertex[4];
POINT normal[4];
} POLYGON;```
```int number_of_polys;        /* cylinder polygon count */
POLYGON *polygon;           /* pointer to polygon list */```
```/*
** def_simple_light_calc()
** Tell the Graphics Library to DEFINE a simple
** lighting calculation that accounts for diffuse
** and ambient reflection.  This simple
** lighting calculation happens to use the default
** lighting parameters in the Graphics Library.
*/
def_simple_light_calc()
{
lmdef(DEFMATERIAL, 1, 0, NULL);
lmdef(DEFLIGHT, 1, 0, NULL);
lmdef(DEFLMODEL, 1, 0, NULL);
}```
```/*
** use_simple_light_calc()
** Tell the Graphics Library to USE the
** simple lighting calculation that we
** defined earlier.
*/```
```use_simple_light_calc()
{
lmbind(MATERIAL, 1);
lmbind(LIGHT0, 1);
lmbind(LMODEL, 1);
}```
```/*
** make_cylinder()
** Draw a cylinder using (2 * n) polygons
** to approximate the curvature and n
** polygons to describe the length.
** This requires (2 * n^2) polygons to
** describe the cylinder. Compute the
** surface normal at each vertex so we
** can use the Graphics Library to perform
** lighting calculations.
*/```
```make_cylinder(n)
int n;
{
POLYGON *p;                 /* pointer into polygon list */
float theta, dtheta,        /* current angle and angle */
x, dx;                /* increment around section */
/* current position and */
/* increment along cylinder side */
int vertex_i;               /* vertex counter */```
```                              /* allocate and point to enough */
/* memory for all the polygons */
number_of_polys = 2 * n * n;
p = polygon = (POLYGON *)
malloc(number_of_polys * sizeof(POLYGON));
dx = 3.0/n;                 /* n polygons for 3.0 units of length */
dtheta = PI/n;              /* length of polygon along curvature */
/* for each layer of polygons along */
/* length of cylinder ... */
for (x = -1.5; x < 1.5; x = x+dx) {
/* ... and for each polygon describing */
/* the circumference */
for (theta = 0.0; theta < TWOPI; theta += dtheta) {
/* calculate the four points */
/* describing the polygon */
p->vertex[0].x =
p->vertex[1].x = x;
p->vertex[0].y = p->vertex[3].y =
RADIUS * cos(theta);
p->vertex[0].z = p->vertex[3].z =
RADIUS * sin(theta);
p->vertex[1].y = p->vertex[2].y =
RADIUS * cos(theta + dtheta);
p->vertex[1].z = p->vertex[2].z =
RADIUS * sin(theta + dtheta);
p->vertex[2].x = p->vertex[3].x = x + dx;
/* calculate the four normals of unit length */
for (vertex_i = 0; vertex_i < 4; vertex_i++) {
p->normal[vertex_i].x = 0;
p->normal[vertex_i].y =
p->vertex[vertex_i].y / RADIUS;
p->normal[vertex_i].z =
p->vertex[vertex_i].z / RADIUS;
}
p++;
}
}
}```
```/*
** draw_cylinder()
** This subroutine increments through the 4
** vertices describing each polygon of
** the cylinder defined in make_cylinder.
** Note how a normal is sent down the
** graphics pipeline before each vertex
** so that the Graphics Library will
** compute the color for each vertex
** based on the lighting parameters that we
** are using.
*/```
```draw_cylinder()
{
POLYGON *p;        /* pointer into polygon list */
int poly_i;        /* polygon counter */
/* start at first polygon and */
/* increment through all of them */
p = polygon;
for (poly_i = 0; poly_i < number_of_polys; poly_i++) {
bgnpolygon();        /* describe the polygon */
n3f(&p->normal[0]);
v3f(&p->vertex[0]);
n3f(&p->normal[1]);
v3f(&p->vertex[1]);
n3f(&p->normal[2]);
v3f(&p->vertex[2]);
n3f(&p->normal[3]);
v3f(&p->vertex[3]);
endpolygon();
p++;                /* go to the next polygon */
}```
`}`
```/*
** main()
*/
main()
{
int i;                /* set up graphics environment */
prefposition(100, 600, 100, 600);
winopen("cylinder");
RGBmode();
doublebuffer();
gconfig();
lsetdepth(0, 0x7FFFFF);
zbuffer(TRUE);        /* Use mmode() to set up projection */
/* and viewing matrices for lighting */
mmode(MVIEWING);
perspective(400, 1.0, 4.0, 12.0);
loadmatrix(idmat);
lookat(0.0,0.0,8.0,0.0,0.0,0.0,0); /* let there be light !!!! */
def_simple_light_calc();
use_simple_light_calc();           /* Rotate cylinder in 2 deg. increments */
/* about Y and Z axis for 180 frames */
make_cylinder(25);
for (i = 0; i < 180; i++) {
c3f(blackvec);                   /* clear the frame */
clear();
zclear();
pushmatrix();                    /* make a frame */
rot(i * 2.0, 'Z');
rot(i * 2.0, 'Y');
draw_cylinder();
popmatrix();
swapbuffers();
}```
```  sleep(3);
}```

Related Information

The c subroutine, the mmode subroutine, the rot subroutine.

Lighting Basics in GL3.2 Version 4 for AIX: Programming Concepts.

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