#include <graphics.h>
#include <iostream>
using namespace std;

const int WINDOW_SIZE = 400;

void change_controls(int& x, int& y, int& color, int& iris_radius);
void display_controls (int color, int iris_radius);
void display_eye(int cx, int cy, int color, int iris_radius);

int main( )
{
    int x = WINDOW_SIZE/2, y = WINDOW_SIZE/2;
    int color = BLUE;
    int iris_radius = 15;
    
    initwindow(WINDOW_SIZE, WINDOW_SIZE, "Eyecon", 0, 0, true);

    do
    {
	change_controls(x, y, color, iris_radius);
	clearviewport( );
	display_eye(x, y, color, iris_radius);
	display_controls(color, iris_radius);
	swapbuffers( );
	delay(100);
    }   while (true);

    return 0;
}

void change_controls(int& x, int& y, int& color, int& iris_radius)
{
    if (ismouseclick(WM_LBUTTONDOWN))
	getmouseclick(WM_LBUTTONDOWN, x, y);
    if (kbhit( ))
    {
	switch (getch( ))
	{
	case 'C':
	case 'c': color = (color == 15) ? 1 : color+1; break;
	case '-': if (iris_radius > 0) --iris_radius; break;
	case '+': if (iris_radius < WINDOW_SIZE/4) ++iris_radius; break;
	}
    }
}

void display_controls (int color, int iris_radius)
{
    setfillstyle(SLASH_FILL, color);
    bar(0, WINDOW_SIZE-2*iris_radius, 10, WINDOW_SIZE-1);
    rectangle(0, WINDOW_SIZE-2*iris_radius, 10, WINDOW_SIZE-1);
    bgiout << "Click left mouse" << endl;
    bgiout << "Or press C or + or -" << endl;
    outstreamxy(20, WINDOW_SIZE-2*textheight("X"));
}

void display_eye(int cx, int cy, int color, int iris_radius)
{
    int eye_radius_x = int(iris_radius * 2.00);
    int eye_radius_y = int(iris_radius * 1.75);
    int path_radius_x = eye_radius_x - iris_radius;
    int path_radius_y = eye_radius_y - iris_radius;
    int mouse_x = mousex( ) - cx;
    int mouse_y = mousey( ) - cy;
    double slope, iris_x, iris_y;
    double mouse_distance_squared, iris_distance_squared;
    
    // Compute the iris_x and iris_y.
    if (mouse_x == 0)
    {   // Mouse directly above or below the the eye.
	iris_x = 0;
	iris_y = (mouse_y < 0) ? -path_radius_y : +path_radius_y;
    }
    else
    {
	slope = double(mouse_y)/double(mouse_x);
	iris_x = sqrt(
	    1.0
	    /
	    (1.0/(path_radius_x*path_radius_x) + (slope*slope)/(path_radius_y*path_radius_y))
	    );
	if (mouse_x < 0)
	    iris_x *= -1;
	iris_y = slope * iris_x;
    }

    // Adjust in case the mouse is inside the darn ellipse
    mouse_distance_squared = (mouse_x*mouse_x + mouse_y*mouse_y);
    iris_distance_squared = (iris_x*iris_x + iris_y*iris_y);
    if (mouse_distance_squared < iris_distance_squared)
    {
	iris_x = mouse_x;
	iris_y = mouse_y;
    }

    // Draw the iris
    setfillstyle(SOLID_FILL, color);
    fillellipse(cx + int(iris_x), cy + int(iris_y), iris_radius, iris_radius);
    
    // Draw the outer ellipse
    ellipse(cx, cy, 0, 360, eye_radius_x, eye_radius_y);
}