{ This program opens a graphics window, fills it with a black
  background, and draws a red circle in the center.
  
  To compile this program, use the following command:
  	
	gpcgraphics myProgram myProgram.p

  The way things stand right now, two weird things will happen.
  First, you'll get a new file called "myProgram_tmp.p" in your
  current directory (assuming you use "myProgram" as the output
  file name), and second, all compiler error messages will
  refer to a line number 100 higher than the line number of the
  actual error.

  Try:
  	0. Compile and run the program as it is.
	1. Take a look at the ..._tmp.p file.  How is it different
	   from your original code?
  	2. Make the window tall and skinny.  Where does the
	   circle get drawn?  Why?
	3. Change the background color.  Can you make it white?
	4. Make the circle green.
}

program oneCircle(input,output);

import graphics;

const	radius = 20;
		windowWidth = 600;
		windowHeight = 600;
		bottom = 100;
		left = 100;

procedure StartGraphics;
begin
  { open a window }
 	initializegraphics;
	createwindow(left,bottom,left+windowWidth,bottom+windowHeight);
	
  { flood the window with a black background }
	setrgbcolor(0,0,0);
	flood; 
	flushgraphics
end;

begin
	StartGraphics;

  {"RGB" stands for red-green-blue.  The parameters for setrgbcolor
   can range in value from 0.0 to 1.0.  All zeros gives you no red,
   no green, and no blue.}

	setrgbcolor( 1, 0, 0 );
	circle( windowWidth div 2, windowHeight div 2, radius );
 
  { When you're done with drawing a particular object, you need to
    call flushgraphics, or you won't see anything.  When you get to
    more complicated programs, you can experiment leaving the
    flushgraphics calls out to see what happens. }

	flushgraphics;

  { This is here so the program won't end until the user hits the
    return key.  Otherwise, the program will end and the window will
    just disappear as soon as the drawing is done. }
	readln
end.