#include <glut.h>
#include <gl.h>
#include <glu.h>

GLint TopLeftX, TopLeftY, BottomRightX, BottomRightY;

void MyDisplay() {

glViewport(0, 0, 300, 300);
glClear(GL_COLOR_BUFFER_BIT);  // 컬러버퍼에 초기화 색을 가함
glColor3f(0.1, 0.1, 0.1);   // 회색

/*
glBegin(GL_POLYGON);    // 사각형
  glVertex3f(TopLeftX/300.0, (300-TopLeftY)/300.0, 0.0);
  glVertex3f(TopLeftX/300.0, (300-BottomRightY)/300.0, 0.0);
  glVertex3f(BottomRightX/300.0, (300-BottomRightY)/300.0, 0.0);
  glVertex3f(BottomRightX/300.0, (300-TopLeftY)/300.0, 0.0);
glEnd();
*/

glFlush();

}

void MyMouseClick(GLint Button, GLint State, GLint X, GLint Y) {

if(Button == GLUT_LEFT_BUTTON && State == GLUT_DOWN) {
  TopLeftX = X;
  TopLeftY = Y;
}

}

void MyMouseMove(GLint X, GLint Y) {

BottomRightX = X;
BottomRightY = Y;
glutPostRedisplay();

}

int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB);
glutInitWindowSize(300, 300);
glutInitWindowPosition(0, 0);
glutCreateWindow("OpenGL Reshape Example Drawing");
glClearColor(1.0, 1.0, 1.0, 1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 1.0, 0.0, 1.0, -1.0, 1.0);
glutDisplayFunc(MyDisplay);
glutMouseFunc(MyMouseClick);
glutMotionFunc(MyMouseMove);
glutMainLoop();
return 0;
}