MetaFun - Pragma ADE

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addto currentpicture also q shifted (0,radius/2) ;
\stopuseMPgraphic
13.6 Growing graphics
Although METAPOST is not really suited as a simulation engine, it is possible to build graphics that
are built and displayed incrementally with a sequence of mouse clicks. The following example is
the result of an email discussion David Arnold and the author had while METAFUN evolved.
Instead of defining the graphics in a separate METAPOST file, we will incorporate them in the document
source in which they are used. We can use several methods.
1. Define macros and figures in a separate file and include the graphics as external graphics.
2. Define everything in the document source as usable graphics and include the graphics using
\useMPgraphic.
3. Package the graphic components in buffers and paste those together as graphics that can be
processed at run time.
The first method is the most independent one, which has its advantages if we want to use the
graphics in other applications too. The second method works well in graphics where parts of the
definitions change between invocations of the graphic. This method follows the template:
\startuseMPgraphic{whatever}
...
\stopuseMPgraphic
\startuseMPgraphic{result}
...
\includeMPgraphic{whatever}
...
\stopuseMPgraphic
\useMPgraphic{result}
The disadvantage of this method is that it cannot be combined with btex--etex since it is nearly impossible
to determine when, how, and to what extent the content of a graphic should be expanded
before writing it to the temporary METAPOST file.
Therefore, we will demonstrate how buffers can be used. This third method closely parallels the
first way of defining graphics. A nice side effect is that we can easily typeset these buffers verbatim,
which we did to typeset this document.
We are going to do a classic compass and straightedge construction, the bisection of a line segment
joining two arbitrary points. We will construct five graphics, where each one displays one step of
the construction. We will embed each graphic in a start--stop command. Later we will see the
advantage of this strategy.
A few applications Growing graphics