Animation in OpenGL

animationOpenGL.cpp

// We will be doing animation in OpenGL
// key concepts are:
// 1. the idle function - idle() will post a replaint and this will lead to activation of the display() function
// 2. Also we will be doing double buffering like this: glutInitDisplayMode(GLUT_DOUBLE);
// In addition we will be introducing other functions such as glPushMatrix, glPopMatrix and glSwapBuffers

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

GLfloat angle = 0.0f;


void initGL() {   // Set "clearing" or background color  
	glClearColor(0.0f, 0.0f, 0.0f, 1.0f); // Black and opaque
} 
  
void idle() { 
   glutPostRedisplay();   // Post a re-paint request to activate display()
}

void display() {  
    glClear(GL_COLOR_BUFFER_BIT);   // Clear the color buffer 

    glMatrixMode(GL_MODELVIEW);     // To operate on Model-View matrix 
    glLoadIdentity();               // Reset the model-view matrix
    glPushMatrix();                     // Save model-view matrix setting  
    //glTranslatef(-0.5f, 0.4f, 0.0f);    // Translate 
    glRotatef(angle, 0.0f, 0.0f, 1.0f); // rotate by angle in degrees  

	glBegin(GL_QUADS);                  // Each set of 4 vertices form a quad     
	    glColor3f(1.0f, 0.0f, 0.0f);     // Red   
    	glVertex2f(-0.3f, -0.3f);  
    	glColor3f(0.0, 1.0, 0.0);
		glVertex2f( 0.3f, -0.3f);   
		glColor3f(0.0, 0.0, 1.0);		   
		glVertex2f( 0.3f,  0.3f);    
		glColor3f(1.0, 1.0, 0.0);
		glVertex2f(-0.3f,  0.3f); 
	glEnd(); 
	glPopMatrix(); 
	glPushMatrix();
    glutSwapBuffers();  // Double buffered - swap the front and back buffers
    
    angle += 20.0f; // Change the rotational angle after each display()  
}


int main(int argc, char** argv) {
	glutInit(&argc, argv);          // Initialize GLUT 
    glutInitDisplayMode(GLUT_DOUBLE);  // Enable double buffered mode   
    glutInitWindowSize(640, 480);   // Set the window's initial width & height - non-square  
    glutInitWindowPosition(50, 50); // Position the window's initial top-left corner  
	glutCreateWindow("Animation via Idle Function");  // Create window with the given title   
	glutDisplayFunc(display);       // Register callback handler for window re-paint event  
	//glutReshapeFunc(reshape);       // Register callback handler for window re-size event 
	glutIdleFunc(idle);             // Register callback handler if no other event  
	initGL();                       // Our own OpenGL initialization 
	glutMainLoop();                 // Enter the infinite event-processing loop  
	return 0;
}