#include <GL/glut.h>
#include <stdlib.h>

static int shoulder = 0, elbow = 0;

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

void display(void){
    glClear (GL_COLOR_BUFFER_BIT);
    glPushMatrix();

    /* origem posicionada no ombro */
    glTranslatef (-1.0, 0.0, 0.0);
    glRotatef ((GLfloat) shoulder, 0.0, 0.0, 1.0);

    /* origem posicionada no centro do braço */
    glTranslatef (1.0, 0.0, 0.0);
    glPushMatrix();
    glScalef (2.0, 0.4, 1.0);
    glutWireCube (1.0);
    glPopMatrix();

    /* origem posicionada no cotovelo */
    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();

    /* origem volta para o sistema de coordenadas original */
    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':
            shoulder = (shoulder + 5) % 360;
            glutPostRedisplay();
            break;
        case 'S':
            shoulder = (shoulder - 5) % 360;
            glutPostRedisplay();
            break;
        case 'e':
            elbow = (elbow + 5) % 360;
            glutPostRedisplay();
            break;
        case 'E':
            elbow = (elbow - 5) % 360;
            glutPostRedisplay();
            break;
        case 27:
            exit(0);
            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;
}