#include <GL/glut.h>
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
int x,y;
int rFlag=0;
void draw_pixel(float x1,float y1)
{
glColor3f(0.0,0.0,1.0);
glPointSize(5.0);
glBegin(GL_POINTS);
glVertex2f(x1,y1);
glEnd();
}
void triangle()
{
glColor3f(1.0,0.0,0.0);
glBegin(GL_POLYGON);
glVertex2f(100,100);
glVertex2f(250,400);
glVertex2f(400,100);
glEnd();
}
float th=0.0;
float trX=0.0,trY=0.0;
void display()
{
glClear(GL_COLOR_BUFFER_BIT);
glLoadIdentity();
if(rFlag==1) //Rotate Around origin
{
trX=0.0;
trY=0.0;
th+=0.1;
draw_pixel(0.0,0.0);
}
if(rFlag==2) //Rotate Around Fixed Point
{
trX=x;
trY=y;
th+=0.1;
draw_pixel(x,y);
}
glTranslatef(trX,trY,0.0);
glRotatef(th,0.0,0.0,1.0);
glTranslatef(-trX,-trY,0.0);
triangle();
glutPostRedisplay();
glutSwapBuffers();
}
void myInit()
{
glClearColor(0.0,0.0,0.0,1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(-500.0, 500.0, -500.0, 500.0);
glMatrixMode(GL_MODELVIEW);
}
void rotateMenu (int option)
{
if(option==1)
rFlag=1;
if(option==2)
rFlag=2;
if(option==3)
rFlag=3;
}
int main(int argc, char **argv)
{
printf( "Enter Fixed Points (x,y) for Roration: \n");
scanf("%d %d", &x, &y);
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
glutInitWindowSize(500, 500);
glutInitWindowPosition(0, 0);
glutCreateWindow("Create and Rotate Triangle");
myInit(); glutDisplayFunc(display);
glutCreateMenu(rotateMenu);
glutAddMenuEntry("Rotate around ORIGIN",1);
glutAddMenuEntry("Rotate around FIXED POINT",2);
glutAddMenuEntry("Stop Rotation",3);
glutAttachMenu(GLUT_RIGHT_BUTTON); glutMainLoop();
}
Rotation about the origin
Rotation about the fixed point