Re: Graphics help please

From:

ram@zedat.fu-berlin.de (Stefan Ram)

Newsgroups:

comp.lang.java.programmer

Date:

28 Jan 2008 01:45:55 GMT

Message-ID:

<circle-20080128024321@ram.dialup.fu-berlin.de>

Knute Johnson <nospam@rabbitbrush.frazmtn.com> writes:

The JPanel is buffered so that it doesn't actually clear the
screen just the offscreen buffer. You can't draw a circle
pixel by pixel with the technique you used. It will produce
gaps because it only draws a pixel and every degree of angle
and not the points in between.

  Alan Kay was teaching five-year old children how to
  program a circle: They were asked to walk in a circle
  and to report what they did. The children would answer
  "walk a little and turn a little." After that cognition
  they could write a program to draw a circle.

  Ten-year old children already knew what a circle is:
  "The set of all point, having the same distance to a
  center." So they startet to program individual points
  starting at a center, which was more complicated; and
  the result was non a connected circle but only single
  dots.

  Fifteen-year old children already knew the formula ?r = x + y?.
  They tried to draw a circle using that formula, but
  failed. (This formula is not a good starting point for such a
  program.) Just because of their additional knowledge, it was
  actually more difficult or impossible for them to write such a
  program. At least that is what Alan Kay said in a video.

  This made me want to write a little Java program.

  It draws a part of something like a circle without AWT or Swing.

  The start of the program implements a little framework,
  then the contents of the method ?main? solely consists of
  ?Turtle commands?.

public class Turtle
{
  static double x = 0;
  static double y = 0;
  static double stepsize = 1;
  static double direction = 0;
  static char[][] screen = new char[24][78];

  static void turnALittle(){ direction += 10; }

  static void walkALittle()
  { final double angle = direction / 360 * 2 * java.lang.Math.PI;
     y = y + stepsize * java.lang.Math.sin( angle );
     x = x + stepsize * java.lang.Math.cos( angle );
     set( y, x ); }

  static
  { for( int i = 0; i < 24; ++i )for( int j = 0; j < 78; ++j )
    screen[ i ][ j ]= ' ';
    java.lang.Runtime.getRuntime().addShutdownHook
    ( new Thread
      ( new java.lang.Runnable()
        { public void run()
          { for( int i = 0; i < 24; ++i )
            { for( int j = 0; j < 78; ++j )
              java.lang.System.out.print( screen[ i ][ j ] );
              java.lang.System.out.println(); }}})); }

  static void set( final double y, final double x )
  { try{ screen[( int )( y + 11 )][( int )( x + 38 )]= '*'; }
    catch( final Exception e ){} }

  public static void main( final java.lang.String[] args )
  { walkALittle(); turnALittle();
    walkALittle(); turnALittle();
    walkALittle(); turnALittle();
    walkALittle(); turnALittle();
    walkALittle(); turnALittle();
    walkALittle(); turnALittle();
    walkALittle(); turnALittle();
    walkALittle(); turnALittle();
    walkALittle(); turnALittle();
    walkALittle(); turnALittle();
    walkALittle(); turnALittle();
    walkALittle(); turnALittle(); }}

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