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


This `idraw' package provides classes and imperative methods for modeling
in a visual world. Here is its class diagram of public fields and methods:

<pre>
<code>
  +---------------------------------+     
  | abstract World                  |
  +---------------------------------+       +------------------------------------+
  | Canvas theCanvas                |------>| Canvas                             |
  +---------------------------------+       +------------------------------------+
  | void bigBang(int,int,double)    |       +------------------------------------+
  | World endOfTime()               |       | void start(int,int)                |
  | World endOfWorld()              |       | void stop()                        |
  | 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)    |
                                            +------------------------------------+

                      +----------+
                      | Posn     |
                      +----------+
                      | int x    |
                      | int y    |
                      +----------+

                              +-------+
                              | Color |
                              +-------+
                                  |
                                 / \
                                 ---
                                  |
             ------------------------------------------
             |          |         |         |         |     
         +-------+  +-------+ +-------+ +-------+ +-------+  
         | Blue  |  | Green | | Red   | | White | | Yellow| 
         +-------+  +-------+ +-------+ +-------+ +-------+ 

</code>
</pre>

{(include "foot.tinc")}