/* 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); }
The c subroutine, the mmode subroutine, the rot subroutine.
Lighting Basics in GL3.2 Version 4 for AIX: Programming Concepts.