42. Examples of Composing Several Transformations

Dated: 13-07-2025

Solar System

Use

• glutWireSphere() to generate spheres of different sizes.
• glRotatef() or glRotated() to simulate spin.
• glTranslatef() or glTranslated() to distance the planets from origin (The Sun).

Creating Sun at the origin is easy. About the planet:

1. glRotatef() or glRotated() to determine it's location in the orbit.
2. glTranslatef() or glTranslated() to place the planet in the orbit
3. glRotatef() or glRotated() to make the planet spin in its own orbit.

#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

static int year = 0, day = 0;

void init(void) {
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glShadeModel(GL_FLAT);
}

void display(void) {
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f (1.0, 1.0, 1.0);
    glPushMatrix();
    glutWireSphere(1.0, 20, 16); /* draw sun */
    glRotatef((GLfloat) year, 0.0, 1.0, 0.0);
    glTranslatef(2.0, 0.0, 0.0);
    glRotatef((GLfloat) day, 0.0, 1.0, 0.0);
    glutWireSphere(0.2, 10, 8); /* draw smaller planet */
    glPopMatrix();
    glutSwapBuffers();
}

void reshape(int w, int h) {
    glViewport (0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode (GL_PROJECTION);
    glLoadIdentity ();
    gluPerspective(60.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
}

void keyboard (unsigned char key, int x, int y) {
    switch (key) {
        case 'd':
            day = (day + 10) % 360;
            glutPostRedisplay();
           break;

        case 'D':
            day = (day - 10) % 360;
            glutPostRedisplay();
            break;

        case 'y':
            year = (year + 5) % 360;
            glutPostRedisplay();
            break;

        case 'Y':
            year = (year - 5) % 360;
            glutPostRedisplay();
            break;

        default:
            break;
    }
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize (500, 500);
    glutInitWindowPosition (100, 100);
    glutCreateWindow (argv[0]);
    init ();
    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
    return 0;
}

Code result

Articulated Robot Arm

1. Draw a segment (a cube).
2. Move the next segment towards the next pivot.
3. Draw it.

#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

static int shoulder = 0, elbow = 0;

void init(void) {
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glShadeModel(GL_FLAT);
}

void display(void) {
    glClear(GL_COLOR_BUFFER_BIT);
    glPushMatrix();
    glTranslatef(-1.0, 0.0, 0.0);
    glRotatef((GLfloat) shoulder, 0.0, 0.0, 1.0);
    glTranslatef(1.0, 0.0, 0.0);
    glPushMatrix(); 
    glScalef(2.0, 0.4, 1.0);
    glutWireCube(1.0);
    glPopMatrix();
    glTranslatef(1.0, 0.0, 0.0);
    glRotatef((GLfloat) elbow, 0.0, 0.0, 1.0);
    glTranslatef(1.0, 0.0, 0.0);
    glPushMatrix();
    glScalef(2.0, 0.4, 1.0);
    glutWireCube(1.0);
    glPopMatrix();
    glPopMatrix();
    glutSwapBuffers();
}

void reshape(int w, int h) {
    glViewport(0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(65.0, (GLfloat) w/(GLfloat) h, 1.0, 20.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(0.0, 0.0, -5.0);
}

void keyboard (unsigned char key, int x, int y) {
    switch (key) {
        case 's': /* s key rotates at shoulder */
            shoulder = (shoulder + 5) % 360;
            glutPostRedisplay();
            break;

        case 'S':
            shoulder = (shoulder - 5) % 360;
            glutPostRedisplay();
            break;

        case 'e': /* e key rotates at elbow */
            elbow = (elbow + 5) % 360;
            glutPostRedisplay();
            break;

        case 'E':
            elbow = (elbow - 5) % 360;
            glutPostRedisplay();
            break;

        default:
            break;
    }
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize (500, 500);
    glutInitWindowPosition (100, 100);
    glutCreateWindow (argv[0]);
    init ();
    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutKeyboardFunc(keyboard);
    glutMainLoop();

    return 0;
}

Code Result