C++ - OpenGL - Using glRotatef() to animate shapes

Rotating a shape is fun, but rotating it with animation is really great.

That's what we are going to see in this glRotatef() tutorial for animating shapes on a window.

Our shape is made up of 3 squares with 3 different colours:

  • the white
  • the burgundy
  • the green

main.cpp

/*
 * main.cpp
 */

#include "BadprogRotate.h"

/*
 * Main
 */
int main(int ac, char* av[])
{
    BadprogRotate go(&ac, av);
    return 0;
}

BadprogRotate.h

/*
 * BadprogRotate.h
 */

#ifndef BADPROGROTATE_H_
#define BADPROGROTATE_H_

#include "GL/freeglut.h"

#include <string>

#define SCREEN_TITLE         "Square rotation by BadproG! :D"
#define SCREEN_WIDTH             600
#define SCREEN_HEIGHT             600
#define SCREEN_POSITION_X        100
#define SCREEN_POSITION_Y         100

class BadprogRotate {
public:
    static GLfloat S_ANGLE;

    BadprogRotate(int *ac, char *av[]);
    virtual ~BadprogRotate();

    void init(void);
    static void managerDisplay(void);
    static void managerIdle(void);
    static void managerResize(int, int);
    static void managerMouse(int, int, int, int);
    static void managerKeyboard(unsigned char, int, int);
};

#endif /* BADPROGROTATE_H_ */

BadprogRotate.cpp

Add the unistd.h file for Windows OS in order to change usleep() by Sleep() in the following managerIdle() method.

/**
 * BadprogRotate.cpp
 */

// For windows add the unistd.h file
// #include <unistd.h> 

#include "BadprogRotate.h"

/**
 * Static
 */
GLfloat BadprogRotate::S_ANGLE = 0;

/**
 * Constructor
 */
BadprogRotate::BadprogRotate(int *ac, char *av[]) {
    glutInit(ac, av);
    glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(SCREEN_WIDTH, SCREEN_HEIGHT);
    glutInitWindowPosition(SCREEN_POSITION_X, SCREEN_POSITION_Y);
    glutCreateWindow(SCREEN_TITLE);
    this->init();
    glutDisplayFunc(&managerDisplay);
    glutReshapeFunc(&managerResize);
    glutMouseFunc(&managerMouse);
    glutKeyboardFunc(&managerKeyboard);
    glutIdleFunc(&managerIdle);
    glutMainLoop();
}

/**
 * Deleting
 */
BadprogRotate::~BadprogRotate() {}

/**
 * Init
 */
void BadprogRotate::init(void)
{
   glClearColor(0.0, 0.0, 0.0, 0.0);
   glShadeModel(GL_FLAT);
}

/**
 * Display 3 squares on the screen, one rotating from left to right,
 * another from right to left and the last reducing all their dimensions
 * to 0 before recovering its original values.
 */
void BadprogRotate::managerDisplay(void)
{
   glClear(GL_COLOR_BUFFER_BIT);

   // White square
   glPushMatrix();
       glRotatef(S_ANGLE, 0.0, 0.0, 1.0);
       glColor3f(1.0, 1.0, 1.0);
       glRectf(-25.0, -25.0, 25.0, 25.0);
   glPopMatrix();

   // Burgundy square
   glPushMatrix();
       glRotatef(S_ANGLE, 0.0, 0.0, -1.0);
       glColor3f(0.7, 0.2, 0.3);
       glRectf(-10.0, -10.0, 10.0, 10.0);
   glPopMatrix();

   // Green square
   glPushMatrix();
       glRotatef(S_ANGLE, 0.0, 0.0, 0.0);
       glColor3f(0.7, 1.0, 0.3);
       glRectf(-5.0, -5.0, 5.0, 5.0);
   glPopMatrix();

   glutSwapBuffers();
}

/**
 * What's happening when the animation is activated.
   For Windows, replace usleep() by Sleep().
 */
void BadprogRotate::managerIdle(void)
{
    usleep(10000); // change it to  Sleep(5.0); for Windows
    S_ANGLE -= 1;
    glutPostRedisplay();
}

/**
 * Allow the resizing of the window, perspective is not respected.
 */
void BadprogRotate::managerResize(int w, int h)
{
   glViewport(0, 0, (GLsizei)w, (GLsizei)h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glOrtho(-50.0, 50.0, -50.0, 50.0, -1.0, 1.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

/**
 * Manage the mouse, if the left button is clicked, we revive the animation.
 * If the right button is clicked, we stop the animation.
 */
void BadprogRotate::managerMouse(int button, int state, int x, int y)
{
    switch (button) {
        case GLUT_LEFT_BUTTON:
            if (state == GLUT_DOWN)
                glutIdleFunc(&managerIdle);
        break;
        case GLUT_RIGHT_BUTTON:
            if (state == GLUT_DOWN)
                glutIdleFunc(NULL);
        break;
        default:
        break;
    }
    (void)(x);
    (void)(y);
}

/**
 * Manage the keyboard, 27 = ESC key.
 */
void BadprogRotate::managerKeyboard(unsigned char key, int x, int y)
{
    switch (key)
    {
        case 27:
        {
            exit(0);
        }
        break;
    }
    (void)(x);
    (void)(y);
}

Compiling, linking, running

g++ main.cpp BadprogRotate.cpp -o rotateMe -lglut -lGLU ; ./rotateMe

What would be OpenGL without any animation?
I don't know, but I'm sure you are on the right way to develop your own animations.

Great job, you made it. laugh

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