C++ - OpenGL - Using glRotatef() to rotate around the X, Y and Z axis

In this OpenGL 2.1 tutorial we are going to use the glRotatef() method.

This method is designed to rotate around the 3 axis: X, Y and Z.
In the example below I will use a black background and draw 3 triangles.

The green will rotate around the X axis.
The blue will rotate around the Y axis.
The red will rotate around the Z axis.

To better understand it, we have to imagine an eye seeing a point.
Now around this point all triangles will rotate.

If you still don't understand what happens in this example, try to play with values of the glTranslatef() method that is in the three triangles implementation.
For example, for the green triangle, change its values by glTranslatef(5.0f, 0.0f, 0.0f) and for the blue triangle, with glTranslatef(0.0f, -5.0f, 0.0f).

So let's get started with the OpenGL glRotatef() method.

h.h

/**
 *  BadproG.com
 *  h.h
 */

#ifndef H_H_
#define H_H_

/**
 * Define
 */
#define SCREEN_TITLE         "Hello World! :D"
#define SCREEN_WIDTH         600
#define SCREEN_HEIGHT         600
#define SCREEN_POSITION_X     100
#define SCREEN_POSITION_Y     100

/**
 * Structure
 */
typedef struct s_badprog
{
    int screenPositionX;
    int screenPositionY;

    double side;
    double hyp;
    double sideHalf;
    double sideToFind;
    double ratio;

    GLclampf bgRed;
    GLclampf bgGreen;
    GLclampf bgBlue;
    GLclampf bgAlpha;

    GLfloat    drawRed;
    GLfloat    drawGreen;
    GLfloat    drawBlue;

    GLfloat z;
    GLfloat x1;
    GLfloat x2;
    GLfloat x3;
    GLfloat y1;
    GLfloat y2;
    GLfloat y3;

} t_badprog;

#endif /* H_H_ */

main.cpp

#include <math.h>
#include <GL/glut.h>
#include <GL/freeglut.h>
#include <iostream>
#include <string>

#include "h.h"

void initValues(t_badprog *bp)
{
    bp->screenPositionX = 100;
    bp->screenPositionY = 100;

    bp->bgRed            = 0;
    bp->bgGreen        = 0;
    bp->bgBlue            = 0;
    bp->bgAlpha        = 0;

    bp->drawRed        = 0;
    bp->drawGreen        = 1;
    bp->drawBlue        = 0;

    bp->side            = 3;
    bp->hyp            = bp->side;
    bp->sideHalf        = bp->hyp / 2;

    bp->sideToFind        = pow(bp->hyp, 2) - pow(bp->sideHalf, 2);
    bp->sideToFind        = sqrt(bp->sideToFind);
    bp->ratio            = pow(bp->sideHalf, 2) / 2;

    bp->z                = -8;

    bp->x1                = -1.5;
    bp->x2                = 0;
    bp->x3                = 1.5;

    bp->y1                = 0 - bp->ratio;
    bp->y2                = bp->sideToFind - bp->ratio;
    bp->y3                = 0 - bp->ratio;
}

void initProgram(t_badprog *bp)
{
    initValues(bp);
    glClearColor(bp->bgRed, bp->bgGreen, bp->bgBlue, bp->bgAlpha);
    glColor3f(bp->drawRed, bp->drawGreen, bp->drawBlue);
}

void managerDisplay(void)
{
    t_badprog bp;
    float var = 5;
    float newAngle = 0;
    int i = 0;

    initProgram(&bp);

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_MODELVIEW);

    glLoadIdentity();
    glTranslatef(0.0f, 0.0f, -30.0f);

    while (i < 90)
    {
        // Green X
            glPushMatrix();
                glTranslatef(0.0f, 0.0f, 0.0f);
                glRotatef(newAngle += i, 1.0f, 0.0f, 0.0f);
                glColor3f(0, 1, 0);
                glBegin(GL_TRIANGLES);
                    glVertex3f(bp.x1, bp.y1, bp.z);
                    glVertex3f(bp.x2, bp.y2, bp.z);
                    glVertex3f(bp.x3, bp.y3, bp.z);
                glEnd();
            glPopMatrix();

            // Blue Y
            newAngle -= i;
            glPushMatrix();
                glTranslatef(0.0f, 0.0f, 0.0f);
                glRotatef(newAngle += i, 0.0f, 1.0f, 0.0f);
                glColor3f(0, 0, 1);
                glBegin(GL_TRIANGLES);
                    glVertex3f(bp.x1, bp.y1, bp.z);
                    glVertex3f(bp.x2, bp.y2, bp.z);
                    glVertex3f(bp.x3, bp.y3, bp.z);
                glEnd();
            glPopMatrix();

            // Red Z
            newAngle -= i;
            glPushMatrix();
                glTranslatef(0.0f, 0.0f, 0.0f);
                glRotatef(newAngle += i, 0.0f, 0.0f, 1.0f);
                glColor3f(1, 0, 0);
                glBegin(GL_TRIANGLES);
                    glVertex3f(bp.x1 + var, bp.y1, bp.z);
                    glVertex3f(bp.x2 + var, bp.y2, bp.z);
                    glVertex3f(bp.x3 + var, bp.y3, bp.z);
                glEnd();
            glPopMatrix();
        ++i;
    }
    glutSwapBuffers();
}

void managerKeyboard(unsigned char key, int x, int y)
{
    switch (key)
    {
        case 27:
        {
            exit(0);
        }
    }
    (void)(x);
    (void)(y);
}

void managerResize(int w, int h) {
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0, (double)w / (double)h, 1.0, 200.0);
}

void init(int ac, char *av[])
{
  glutInit(&ac, av);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
  glutInitWindowSize(SCREEN_WIDTH, SCREEN_HEIGHT);
  glutInitWindowPosition(SCREEN_POSITION_X, SCREEN_POSITION_Y);

  glutCreateWindow(SCREEN_TITLE);

  glEnable(GL_DEPTH_TEST);

  glutDisplayFunc(managerDisplay);
  glutKeyboardFunc(managerKeyboard);
  glutReshapeFunc(managerResize);

  glutMainLoop();
}

int  main(int ac, char *av[])
{
  init(ac, av);
  return 0;
}

Compilation

Don't forget to link your .o with the following libraries:

-lglut -lGL -lGLU

A great exercise to understand how works glRotatef(). cool

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