#include <GL/glut.h>

class Polygon {
protected:
	GLfloat x, y;
	GLfloat *color;
	GLint id;
public:
	Polygon(GLfloat x, GLfloat y, GLfloat *c, GLint id) {
		this->x = x;
		this->y = y;
		this->id=id;
		color=c;
	}; 

	void setXY( GLfloat x, GLfloat y) { this->x = x; this->y = y; }

	virtual void draw(GLenum mode) abstract {};
};

class Triangle : public Polygon {
public:
	Triangle(GLfloat x, GLfloat y, GLfloat *color, GLint id) : Polygon(x, y, color, id){ }; 

	virtual void draw(GLenum mode) {
		if( mode == GL_SELECT) glLoadName(id);
		glColor3fv(color);
		glBegin(GL_POLYGON);
			glVertex2f(x-1.5, y-1.5);
			glVertex2f(x+1.0, y+1.0);
			glVertex2f(x+1.5, y+0.5);
		glEnd();
	}
};

class Rectangle : public Polygon {
public:
	Rectangle(GLfloat x, GLfloat y, GLfloat *color, GLint id) : Polygon(x, y, color, id){ };

	virtual void draw(GLenum mode) {
		if( mode == GL_SELECT) glLoadName(id);
		glColor3fv(color);
		glRectf(x-0.5, y-0.5, x+0.5, y+0.5);
	}
};

#define TRIANGLE 6
#define RECTANGLE 9

Triangle *triangle;
Rectangle *rectangle;
Polygon *object;

double d2w( int d ) {
	return (d/500.0)*4.0-2.0;
}

void display() {
	glClear(GL_COLOR_BUFFER_BIT);
	triangle->draw(GL_RENDER);
	rectangle->draw(GL_RENDER);
    glFlush();
}

/*  processHits  */
void processHits (GLint hits, GLuint buffer[], int x, int y)
{
   unsigned int i, j;
   GLuint *ptr;
   ptr = (GLuint *) buffer+3;
   if(hits == 0) return;
   switch (*ptr) {
		case TRIANGLE  : object = triangle; break;
		case RECTANGLE : object = rectangle;
   }
}

#define SIZE 8

void click( int x, int y ) {
   GLuint selectBuf[SIZE];
   GLint hits;
   GLint viewport[4];

   glGetIntegerv (GL_VIEWPORT, viewport);

   glSelectBuffer (SIZE, selectBuf);
   glRenderMode(GL_SELECT);

   glInitNames();
   glPushName(0);

   glMatrixMode (GL_PROJECTION);
   glPushMatrix ();
   glLoadIdentity ();
/* create 5x5 pixel picking region near cursor location */
   gluPickMatrix ((GLdouble) x, (GLdouble) (viewport[3] - y),
                  5.0, 5.0, viewport);
   gluOrtho2D (-2.0, 2.0, -2.0, 2.0);
   
   triangle->draw(GL_SELECT);   
   rectangle->draw(GL_SELECT);

   glMatrixMode (GL_PROJECTION);
   glPopMatrix ();
   glFlush ();

   hits = glRenderMode (GL_RENDER);
   processHits (hits, selectBuf, x, y);

   glutPostRedisplay();
}

void mouse(int button, int state, int x, int y)
{
   if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) click(x, y);
}

void motion(int x, int y){
	object->setXY(d2w(x), d2w(500-y));  
    glutPostRedisplay();
}

void reshape(int w, int h)
{
   glViewport(0, 0, w, h);
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   gluOrtho2D (-2.0, 2.0, -2.0, 2.0);
   glMatrixMode(GL_MODELVIEW);
   glLoadIdentity();
}

int main(int argc, char** argv)
{
   GLfloat red[] = {1.0,0.0,0.0}, blue[]={0.0,0.0,1.0};
   triangle = new Triangle(0,0,red, TRIANGLE);
   rectangle = new Rectangle(0,0,blue, RECTANGLE);

   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (500, 500);
   glutInitWindowPosition (0, 0);
   glutCreateWindow ("Carry");
   glClearColor (0.0, 0.0, 0.0, 0.0);
   glutReshapeFunc (reshape);
   glutDisplayFunc(display);
   glutMouseFunc (mouse);
   glutMotionFunc (motion);
   glutMainLoop();
}