///////////////////////////////////////////////////////////////////
//
//	graphics3.cpp
//
//	Started in Pascal by Jeff Ondich on 1/25/95
//	Last modified 5/20/98
//
//	1. Compile it, run it, figure out how it works and
//	   how to stop it.  Note that there's a warning when
//	   you compile.  Don't worry about it.
//
//	2. Complain about the flickering.  Try to get the ball to
//	   bounce from side to side instead of up and down.  Can
//	   you get the colors to change gradually from red to
//	   blue instead of abruptly?
//
///////////////////////////////////////////////////////////////////

#include	<iostream.h>
#include	<gpc-graphics++.h>

// Constants

const int radius = 40;
const int windowWidth = 600;
const int windowHeight = 600;
const int windowBottom = 100;
const int windowLeft = 100;


// Prototypes

void StartGraphics( void );
void NewCenter( int& horiz, int& vert, bool& goingUp );

// Global variables.

float	red, blue, green;


int main( void )
{
	int		x, y;
	bool	goingUp;

	StartGraphics();

	x = windowWidth / 2;
	y = radius;
	goingUp = true;
	red = 0.0;
	blue = 1.0;
	green = 0.0;

	while( true )
	{
		setrgbcolor( red, green, blue );
		circle( x, y, radius );
		flushgraphics();
		
		setrgbcolor( 0, 0, 0 );
		circle( x, y, radius );
		flushgraphics();
		NewCenter( x, y, goingUp );
	}

	return( 0 );
}


void NewCenter( int& horiz, int& vert, bool& goingUp )
{
	if( goingUp )
		vert = vert + 1;
	else
		vert = vert - 1;
	
	if( vert >= windowHeight - radius )
	{
		goingUp = false;
		red = 1.0;
		blue = 0;
	}

	else if( vert <= radius )
	{
		goingUp = true;
		red = 0;
		blue = 1.0;
	}
}


///////////////////////////////////////////////////////////////////
//	StartGraphics initializes the graphics package
//	and opens a black window for drawing.
///////////////////////////////////////////////////////////////////

void StartGraphics( void )
{
	// Call initializegraphics only once during the program,
	// before you do any other graphics
   
 	initializegraphics();


	// Open a window and flood it with a black background.

	createwindow( windowLeft, windowBottom,
					windowLeft + windowWidth, windowBottom + windowHeight );
	setrgbcolor( 0.0, 0.0, 0.0 );
	flood(); 
	flushgraphics();
}