gears.c

#include <stdlib.h>
#include <math.h>
#include <GL/gl.h>
#include "gears.h"

struct gears {
	GLint gear1, gear2, gear3;
};

static void
gear(GLfloat inner_radius, GLfloat outer_radius, GLfloat width,
     GLint teeth, GLfloat tooth_depth)
{
	GLint i;
	GLfloat r0, r1, r2;
	GLfloat angle, da;
	GLfloat u, v, len;

	r0 = inner_radius;
	r1 = outer_radius - tooth_depth / 2.0;
	r2 = outer_radius + tooth_depth / 2.0;

	da = 2.0 * M_PI / teeth / 4.0;

	glShadeModel(GL_FLAT);

	glNormal3f(0.0, 0.0, 1.0);

	/* draw front face */
	glBegin(GL_QUAD_STRIP);
	for (i = 0; i <= teeth; i++) {
		angle = i * 2.0 * M_PI / teeth;
		glVertex3f(r0 * cos(angle), r0 * sin(angle), width * 0.5);
		glVertex3f(r1 * cos(angle), r1 * sin(angle), width * 0.5);
		if (i < teeth) {
			glVertex3f(r0 * cos(angle), r0 * sin(angle), width * 0.5);
			glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), width * 0.5);
		}
	}
	glEnd();

	/* draw front sides of teeth */
	glBegin(GL_QUADS);
	da = 2.0 * M_PI / teeth / 4.0;
	for (i = 0; i < teeth; i++) {
		angle = i * 2.0 * M_PI / teeth;

		glVertex3f(r1 * cos(angle), r1 * sin(angle), width * 0.5);
		glVertex3f(r2 * cos(angle + da), r2 * sin(angle + da), width * 0.5);
		glVertex3f(r2 * cos(angle + 2 * da), r2 * sin(angle + 2 * da), width * 0.5);
		glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), width * 0.5);
	}
	glEnd();

	glNormal3f(0.0, 0.0, -1.0);

	/* draw back face */
	glBegin(GL_QUAD_STRIP);
	for (i = 0; i <= teeth; i++) {
		angle = i * 2.0 * M_PI / teeth;
		glVertex3f(r1 * cos(angle), r1 * sin(angle), -width * 0.5);
		glVertex3f(r0 * cos(angle), r0 * sin(angle), -width * 0.5);
		if (i < teeth) {
			glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), -width * 0.5);
			glVertex3f(r0 * cos(angle), r0 * sin(angle), -width * 0.5);
		}
	}
	glEnd();

	/* draw back sides of teeth */
	glBegin(GL_QUADS);
	da = 2.0 * M_PI / teeth / 4.0;
	for (i = 0; i < teeth; i++) {
		angle = i * 2.0 * M_PI / teeth;

		glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), -width * 0.5);
		glVertex3f(r2 * cos(angle + 2 * da), r2 * sin(angle + 2 * da), -width * 0.5);
		glVertex3f(r2 * cos(angle + da), r2 * sin(angle + da), -width * 0.5);
		glVertex3f(r1 * cos(angle), r1 * sin(angle), -width * 0.5);
	}
	glEnd();

	/* draw outward faces of teeth */
	glBegin(GL_QUAD_STRIP);
	for (i = 0; i < teeth; i++) {
		angle = i * 2.0 * M_PI / teeth;

		glVertex3f(r1 * cos(angle), r1 * sin(angle), width * 0.5);
		glVertex3f(r1 * cos(angle), r1 * sin(angle), -width * 0.5);
		u = r2 * cos(angle + da) - r1 * cos(angle);
		v = r2 * sin(angle + da) - r1 * sin(angle);
		len = sqrt(u * u + v * v);
		u /= len;
		v /= len;
		glNormal3f(v, -u, 0.0);
		glVertex3f(r2 * cos(angle + da), r2 * sin(angle + da), width * 0.5);
		glVertex3f(r2 * cos(angle + da), r2 * sin(angle + da), -width * 0.5);
		glNormal3f(cos(angle), sin(angle), 0.0);
		glVertex3f(r2 * cos(angle + 2 * da), r2 * sin(angle + 2 * da), width * 0.5);
		glVertex3f(r2 * cos(angle + 2 * da), r2 * sin(angle + 2 * da), -width * 0.5);
		u = r1 * cos(angle + 3 * da) - r2 * cos(angle + 2 * da);
		v = r1 * sin(angle + 3 * da) - r2 * sin(angle + 2 * da);
		glNormal3f(v, -u, 0.0);
		glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), width * 0.5);
		glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), -width * 0.5);
		glNormal3f(cos(angle), sin(angle), 0.0);
	}

	glVertex3f(r1 * cos(0), r1 * sin(0), width * 0.5);
	glVertex3f(r1 * cos(0), r1 * sin(0), -width * 0.5);

	glEnd();

	glShadeModel(GL_SMOOTH);

	/* draw inside radius cylinder */
	glBegin(GL_QUAD_STRIP);
	for (i = 0; i <= teeth; i++) {
		angle = i * 2.0 * M_PI / teeth;
		glNormal3f(-cos(angle), -sin(angle), 0.0);
		glVertex3f(r0 * cos(angle), r0 * sin(angle), -width * 0.5);
		glVertex3f(r0 * cos(angle), r0 * sin(angle), width * 0.5);
	}
	glEnd();
}

struct gears *
gears_create(GLfloat clear_red, GLfloat clear_green,
	     GLfloat clear_blue, GLfloat clear_alpha)
{
	static GLfloat red[4] = {0.8, 0.1, 0.0, 1.0};
	static GLfloat green[4] = {0.0, 0.8, 0.2, 1.0};
	static GLfloat blue[4] = {0.2, 0.2, 1.0, 1.0};
	static GLfloat pos[4] = {5.0, 5.0, 10.0, 0.0};
	struct gears *gears;

	gears = malloc(sizeof *gears);
	/* make the gears */
	gears->gear1 = glGenLists(1);
	glNewList(gears->gear1, GL_COMPILE);
	glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, red);
	gear(1.0, 4.0, 1.0, 20, 0.7);
	glEndList();

	gears->gear2 = glGenLists(1);
	glNewList(gears->gear2, GL_COMPILE);
	glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, green);
	gear(0.5, 2.0, 2.0, 10, 0.7);
	glEndList();

	gears->gear3 = glGenLists(1);
	glNewList(gears->gear3, GL_COMPILE);
	glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, blue);
	gear(1.3, 2.0, 0.5, 10, 0.7);
	glEndList();

	glEnable(GL_NORMALIZE);

	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glFrustum(-1.0, 1.0, -1.0, 1.0, 5.0, 200.0);
	glMatrixMode(GL_MODELVIEW);

	glLightfv(GL_LIGHT0, GL_POSITION, pos);
	glEnable(GL_CULL_FACE);
	glEnable(GL_LIGHTING);
	glEnable(GL_LIGHT0);
	glEnable(GL_DEPTH_TEST);

	/* We're generating premultiplied alpha so multiply in the
	 * alpha.  The gears are solid color and doesn't have
	 * anti-aliased edges, they're ok. */
	glClearColor(clear_red * clear_alpha,
		     clear_green * clear_alpha,
		     clear_blue * clear_alpha,
		     clear_alpha);

	return gears;
}

void
gears_draw(struct gears *gears, GLfloat angle)
{
	GLfloat view_rotx = 20.0, view_roty = 30.0, view_rotz = 0.0;

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glPushMatrix();

	glTranslatef(0.0, 0.0, -50);

	glRotatef(view_rotx, 1.0, 0.0, 0.0);
	glRotatef(view_roty, 0.0, 1.0, 0.0);
	glRotatef(view_rotz, 0.0, 0.0, 1.0);

	glPushMatrix();
	glTranslatef(-3.0, -2.0, 0.0);
	glRotatef(angle, 0.0, 0.0, 1.0);
	glCallList(gears->gear1);
	glPopMatrix();

	glPushMatrix();
	glTranslatef(3.1, -2.0, 0.0);
	glRotatef(-2.0 * angle - 9.0, 0.0, 0.0, 1.0);
	glCallList(gears->gear2);
	glPopMatrix();


	glPushMatrix();
	glTranslatef(-3.1, 4.2, 0.0);
	glRotatef(-2.0 * angle - 25.0, 0.0, 0.0, 1.0);
	glCallList(gears->gear3);
	glPopMatrix();

	glPopMatrix();

	glFlush();
}