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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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