16. Rotation.cpp

#include <GL/glut.h>
#include <iostream>
#include <math.h>
#include <stdlib.h>
using namespace std;
void init() {
  glClearColor(1, 1, 1, 1.0);
  glPointSize(2.0);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D(-500, 500.0, -500.0, 500.0);
}
void makeTriangle(float x1, float y1, float x2, float y2, float x3, float y3) {
      glClear(GL_COLOR_BUFFER_BIT);
  glColor3f(1.0, 0.0, 1.0);
  glBegin(GL_TRIANGLES);
  glVertex2f(x1, y1);
  glVertex2f(x2, y2);
  glVertex2f(x3, y3);
}
// void translate(float x1, float y1, float x2, float y2, float x3, float y3,
//                float xp, float yp) {
//   glClear(GL_COLOR_BUFFER_BIT);
//   x1 = x1 + xp;
//   x2 = x2 + xp;
//   x3 = x3 + xp;
//   y1 = y1 + yp;
//   y2 = y2 + yp;
//   y3 = y3 + yp;
//   makeTriangle(x1, y1, x2, y2, x3, y3);
// }
void rotation(float x1, float y1, float x2, float y2, float x3, float y3) {
  float th = 10 * 3.14159 / 180;
  float new_x1 = x1 * cos(th) - y1 * sin(th);
  float new_y1 = x1 * sin(th) + y1 * cos(th);
  float new_x2 = x2 * cos(th) - y2  * sin(th);
  float new_y2 = x2 * sin(th) + y2 * cos(th);
  float new_x3 = x3 * cos(th) - y3 * sin(th);
  float new_y3 = x3 * sin(th) + y3  * cos(th);

  makeTriangle(new_x1, new_y1, new_x2, new_y2, new_x3, new_y3);
//   translate(new_x1, new_y1, new_x2, new_y2, new_x3, new_y3, 150, 150);
  glEnd();
//   glColor3f(0, 0.0, 0.0);
//   glBegin(GL_LINES);
//   glVertex2f(-500, 0);
//   glVertex2f(500, 0);
//   glBegin(GL_LINES);
//   glVertex2f(0, -500);
//   glVertex2f(0, 500);
//   glEnd();
  glFlush();
}
void display() {
  makeTriangle(150, 150, 180.0, 220.0, 250.0, 100.0);
  rotation(150, 150, 180.0, 220.0, 250.0, 100.0);
}
int main(int argc, char **argv) {
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
  glutInitWindowPosition(100, 100);
  glutInitWindowSize(800, 600);
  glutCreateWindow("Rotation");
  init();
  glutDisplayFunc(display);
  glutMainLoop();
}