{ (define LIBNAME "An Imperative Drawing Library (HtDC)")
  (include "head.tinc") }


This <code>idraw</code> package provides stateful classes and imperative methods
for a visual world. Here is its class diagram of public fields and methods:

<pre>
<code>
import colors.*; 
import geometry.*; 

  +---------------------------------+     
  | abstract World                  |
  +---------------------------------+       +------------------------------------+
  | Canvas theCanvas                |------>| Canvas                             |
  +---------------------------------+       +------------------------------------+
  | void bigBang(int,int,double)    |       +------------------------------------+
  | World endOfTime(String)         |       | void show()                        |
  | World endOfWorld(String)        |       | void close()                       |
  | abstract void onTick()          |       | void drawCircle(Posn,int,Color)    |
  | abstract void onKeyEvent(String)|       | void drawDisk(Posn,int,Color)      |
  | abstract void draw()            |       | void drawRect(Posn,int,int,Color)  |
  | abstract void erase()           |       | void drawLine(Posn,Posn,Color)     |
  +---------------------------------+       | void drawString(Posn,String)       |
                                            | void clearCircle(Posn,int,Color)   |
                                            | void clearDisk(Posn,int,Color)     |
                                            | void clearRect(Posn,int,int,Color) |
                                            | void clearLine(Posn,Posn,Color)    |
                                            +------------------------------------+
</code>
</pre>

<p>The abstract <code>World</code> class in <code>idraw</code> provides the same
methods as the <code>World</code> class in <a href="./draw.html#world">the
<code>draw</code> library</a>. Their return values are usually <code>void</code>,
however, except for <code>endOfTime</code> and <code>endOfWorld</code>, which
continue to return the last world.</p>

<p>In an analogous manner, the methods in the <code>Canvas</code> class export
the same methods as the <code>Canvas</code> class in <a
href="./draw.html#canvas">the <code>draw</code> package</a>. Their return values,
however, are <code>void</code>.  </p>

{(include "foot.tinc")}