#include <GL/glut.h>
#include <math.h>
#include <stdio.h>

// Define a constant for the value of PI
#define GL_PI 3.1415f

// Put here your own global variables and procedures
static int MenuID;

static float xRot = 0.0;
static float yRot = 0.0;

void ReduceToUnit(float vector[3]) {
	float length;
	
	// Calculate the length of the vector		
	length = (float)sqrt((vector[0]*vector[0]) + (vector[1]*vector[1]) + (vector[2]*vector[2]));

	// Keep the program from blowing up by providing an exceptable
	// value for vectors that may calculated too close to zero.
	if(length == 0.0f) length = 1.0f;

	// Dividing each element by the length will result in a
	// unit normal vector.
	vector[0] /= length;
	vector[1] /= length;
	vector[2] /= length;
}

void calcNormal(float vertices[3][3], float out[3]) {
	float v1[3], v2[3];
	static const int x = 0;
	static const int y = 1;
	static const int z = 2;

	// Calculate two vectors from the three points
	v1[x] = vertices[0][x] - vertices[1][x];
	v1[y] = vertices[0][y] - vertices[1][y];
	v1[z] = vertices[0][z] - vertices[1][z];

	v2[x] = vertices[1][x] - vertices[2][x];
	v2[y] = vertices[1][y] - vertices[2][y];
	v2[z] = vertices[1][z] - vertices[2][z];

	// Take the cross product of the two vectors to get
	// the normal vector which will be stored in out
	out[x] = v1[y]*v2[z] - v1[z]*v2[y];
	out[y] = v1[z]*v2[x] - v1[x]*v2[z];
	out[z] = v1[x]*v2[y] - v1[y]*v2[x];

	// Normalize the vector (shorten length to one)
	ReduceToUnit(out);
}

void drawNormalFront(float vertex[3], float normal[3]) {
	glColor3f(0.0, 0.0, 1.0);
	glBegin(GL_LINES);
		glVertex3fv(vertex);
		glVertex3f(vertex[0]+5.0*normal[0], vertex[1]+5.0*normal[1], vertex[2]+5.0*normal[2]);
	glEnd();
}

void drawNormalBack(float vertex[3], float normal[3]) {
	glColor3f(0.0, 1.0, 0.0);
	glBegin(GL_LINES);
		glVertex3fv(vertex);
		glVertex3f(vertex[0]-5.0*normal[0], vertex[1]-5.0*normal[1], vertex[2]-5.0*normal[2]);
	glEnd();
}

void StrokeText(char *string) {
	int len, i;
	len = (int) strlen (string);
	for (i = 0; i < len; i++) {
		glutStrokeCharacter (GLUT_STROKE_ROMAN, string[i]);
	}
}

// Called to draw scene
void RenderScene(void)
{
	float normal[3];
	float vertices[3][3]={{15.0, -10.0, 0.0},
			          {-15.0, -10.0, 0.0},
				    {0.0, 10.0, 0.0}};

  // Clear the window with current clearing color
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glPushMatrix();
		glRotatef(xRot, 1.0f, 0.0f, 0.0f);
		glRotatef(yRot, 0.0f, 1.0f, 0.0f);
	
		glColor3f(0.8, 0.2, 0.2);
		calcNormal(vertices, normal);
		glBegin(GL_TRIANGLES);
			glNormal3fv(normal);
			glVertex3fv(vertices[0]);
			glVertex3fv(vertices[1]);
			glVertex3fv(vertices[2]);
		glEnd();
		
		drawNormalFront(vertices[0], normal);		
		drawNormalFront(vertices[1], normal);
		drawNormalFront(vertices[2], normal);
		drawNormalBack(vertices[0], normal);		
		drawNormalBack(vertices[1], normal);
		drawNormalBack(vertices[2], normal);

	glPopMatrix();

  // Flush drawing commands
  glutSwapBuffers();
}

// This function does any needed initialization on the rendering
// context. 
void SetupRC()
{
	GLfloat  ambientLight[] = { 0.3f, 0.3f, 0.3f, 1.0f };
	GLfloat  diffuseLight[] = { 0.7f, 0.7f, 0.7f, 1.0f };
	GLfloat  specular[] = { 1.0f, 1.0f, 1.0f, 1.0f};

	// Enable lighting
	glEnable(GL_LIGHTING);

	glLightModeli(GL_LIGHT_MODEL_TWO_SIDE, GL_TRUE);

	// Setup and enable light 0
	glLightfv(GL_LIGHT0,GL_AMBIENT,ambientLight);
	glLightfv(GL_LIGHT0,GL_DIFFUSE,diffuseLight);
	glLightfv(GL_LIGHT0,GL_SPECULAR,specular);
	glEnable(GL_LIGHT0);

	// Enable color tracking
	glEnable(GL_COLOR_MATERIAL);
	
	// Set Material properties to follow glColor values
	glColorMaterial(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE);

  // Black background
  glClearColor(0.0f, 0.0f, 0.0f, 1.0f );
  glEnable(GL_DEPTH_TEST);
}

void SpecialKeys(int key, int x, int y)
{

	if(key == GLUT_KEY_UP)
		xRot-= 5.0f;

	if(key == GLUT_KEY_DOWN)
		xRot += 5.0f;

	if(key == GLUT_KEY_LEFT)
		yRot -= 5.0f;

	if(key == GLUT_KEY_RIGHT)
		yRot += 5.0f;

	if(key > 356.0f)
		xRot = 0.0f;

	if(key < -1.0f)
		xRot = 355.0f;

	if(key > 356.0f)
		yRot = 0.0f;

	if(key < -1.0f)
		yRot = 355.0f;

  // Refresh the Window
  glutPostRedisplay();
}

void Keyboard(unsigned char key, int x, int y)
{

  // ...

  glutPostRedisplay();
}

void Timer(int value)
{

  // ...

  glutPostRedisplay();
  glutTimerFunc(1000, Timer, value + 1);
}

void Idle()
{
  glutPostRedisplay();
}

void ChangeSize(GLsizei w, GLsizei h)
{
  GLfloat fAspect;
  
  // Prevent a divide by zero
  if(h == 0)
    h = 1;
  
  // Set Viewport to window dimensions
  glViewport(0, 0, w, h);
  
  fAspect = (GLfloat)w/(GLfloat)h;
  
  // Reset coordinate system
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  
  // Produce the perspective projection
  gluPerspective(60.0f,    // fovy
		 fAspect,  // aspect
		 10.0,     // zNear
		 100.0     // zFar
		 );

  // Positioning the camera
  gluLookAt(0.0, 0.0, 50.0, // eye
	    0.0, 0.0, 0.0,  // center
	    0.0, 1.0, 0.0   // up
	    );
  
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

void ProcessMenu(int value)
{
  switch(value)
    {
    case 1:
      printf("1. menupont kivalasztva.\n");
      break;
      
    case 2:
      printf("2. menupont kivalasztva.\n");
      break;
      
    case 3:
	exit(0);
      break;

    default:
      break;
    }
  
  glutPostRedisplay();
}

int main(int argc, char* argv[])
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
  glutCreateWindow("Haromszog megvilagitva");
  glutReshapeFunc(ChangeSize);
  glutSpecialFunc(SpecialKeys);
  glutKeyboardFunc(Keyboard);
  glutDisplayFunc(RenderScene);
  glutTimerFunc(1000, Timer, 1); // 1 mp mulva meghivodik a Timer() fuggveny
  glutIdleFunc(Idle); // Idle(), ha nem tortenik semmi

  MenuID = glutCreateMenu(ProcessMenu);
  glutAddMenuEntry("1. menupont", 1);
  glutAddMenuEntry("2. menupont", 2);
  glutAddMenuEntry("Kilepes", 3);
  glutAttachMenu(GLUT_RIGHT_BUTTON);

  SetupRC();
  glutMainLoop();
  
  return 0;
}