rotate.cpp

#include <GL/glut.h>
#include <cmath>
void line(float x, float y)
{
    glClearColor(1.0, 1.0, 1.0, 1.0); //defining for background color
    glClear(GL_COLOR_BUFFER_BIT); //assigning the defined color to background
    glColor3f(0.0, 0.0, 0.0); // color of the object to be displayed
    glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0);//representing the real world dimensions in 2D screen and defining the coordinate limits
    glPointSize(2);
        glBegin(GL_LINES); //start drawing polygon
        glVertex2f(0.0,0.0); //defining the vertex of polygon
        glVertex2f(x,y);
        //glVertex2f(x+0.2,y+0.2);    
        glEnd();
        glFlush();
}
void rotate(float *x, float *y, float *theta);

void show()
{   float angle = 90;
    float a = 0.0, b = 0.4 ;
    //line(a,b);
    rotate(&a,&b,&angle); //calling rotation function
    line(a,b); //calling function to draw a line
    glEnd(); //ending the drawing
    glFlush(); // for execution
}

void rotate(float *x, float *y, float *theta)
{
    float *xtemp;
    xtemp  = x;
    *x = (*x)*cos(*theta) - (*y)*sin(*theta);
    *y = (*x)*sin(*theta) + (*y)*cos(*theta);
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);//initiate library functions
    glutInitDisplayMode(GLUT_SINGLE);
    glutInitWindowSize(500,500);//defining display window size
    glutInitWindowPosition(100,100);//defining display window position on the screen
    glutCreateWindow("OpenGL - Sec window demo");//defining the title of display window
    glutDisplayFunc(show);//calling the object drawing function
    glutMainLoop();    //put the program in infinite loop
    return 0;
}