\environment ppchtex-mkiv-style

\startcomponent ppchtex-mkiv-introduction

\title{Introduction}

The name \PPCHTEX\ covers a set of coherent macros that can be
used to typeset chemical structure formulas. The first version of
\PPCHTEX\ was ready for use in 1995 and the second release came
with the previous versions of this manual. Some 15 years later, in
the process of upgrading \CONTEXT\ to suit \LUATEX, it made sense
to reconsider the usage of \PPCHTEX.

First of all, we want basic chemical support in the kernel, so it
made sense to take the relevant code and turn it into a kernel
module. This means that in \CONTEXT\ \MKIV\ one does not need to
load any module. For compatibility we keep the old module
around.

The old code can also be used outside \CONTEXT, but the integrated
code not. This permits us to get away from the old \PICTEX\ based
approach and combine the power of \TEX, \METAPOST\ and \LUA. The
differences for \CONTEXT\ users are not that noticeable as we
already default to \METAPOST\ for rendering the lines and curves,
but in \CONTEXT\ \MKIV\ users will notice that the runtime is no
longer influenced by callouts to \METAPOST\ because there we use
the integrated library.

We have also changed a couple of aspects like dealing with fonts
and provide more control over color, as we no longer need to be
generic. The fact that we operate within \CONTEXT\ also means that
we can use all its facilities (like interaction) without special
precautions.

Of course we will keep the old variant around and fix bugs when
needed. Future extensions will happen in the integrated code and
traditional \PPCHTEX\ is frozen. Once the new code is stable, we
will disable loading the module in \CONTEXT\ \MKIV.

\stopcomponent

