Applet !OPCA
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Provide Plug In Compliant Application (PCA) support.

Adds 'PCA' option to the Applets menu.

If a picture frame is not active, this option is shaded and unavailable.

If a picture frame is active, the PCA option displays a menu of all the
PCA-compatible 'remote' applications that are available. Click on an entry
in this menu to edit the picture in the 'remote' editor. All changes are
reflected immediately back in Ovation Pro.

Please note that Ovation Pro does not support 'In-place' editing.

More details about the PCA protocol are given below.

Installing Applets
------------------
In order to use this Applet, it must be copied into the !OvnPro.Applets
directory and then Ovation Pro must be re-run.

Applets may be enabled/disabled by double-clicking over them. When disabled,
an Applet's name is suffixed with a '-'.

Ovation Pro must be re-run after enabling/disabling any Applets.

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Plug In Compliant Application protocol
======================================

For latest information on the PCA protocol visit our (Clares) Web site at

http://www.stcoll.ac.uk/clares/support/


Introduction
============


The Clares Plug In Compliant Application (PCA) specification provides an
easy to implement way of allowing multiple applications to share common
objects residing in shared memory areas. A program written to the PCA
specification will work with any other which supports the standard and uses
the same type of objects.

What does PCA do for me as a user ? 

The PCA standard works at two levels. In each case a document in a common
memory area can be 'shared' between two or more applications. This is not
like the versions of OLE implemented on the Acorn platform. There is a major
difference in that OLE copies the document for the second application to
work on, thus your data takes up twice as much RAM. With PCA all
applications work on the same document thus incurring no RAM overheads.

The controlling application is called the Local application and the slave
application is called the  Remote application.

When a document is edited in a Remote application the object in the Local
application is automatically updated.

What we have up to now is a more efficient way of doing OLE. However, PCA
does not stop there. Take an application like Composition which provides a
page make up environment for bit image and vector images - all of which can
be moved and edited - a bit like Draw for bit images but with a LOT of
extras. Composition does not provide 'painting' tools but ProArtisan 24
does. If both applications are PCA compliant then a Utilities menu in Compo
will show ProArt 24 as a 'tool'. Clicking on this menu entry opens a PA24
window showing the selected Compo object. PA24 can paint into this object or
indeed perform any of its functions on the object. All changes are reflected
immediately in Compo.

This means that an application can have other applications as 'tools'. Small
'applets' can be written to provide specific functions to a PCA application
and they will be usable by any other PCA compliant application.

Imagine a simple application that does nothing else except display a
sprite and conform to the PCA standard. Another application could provide
paint tools, yet another could provide filters, another might provide
warping tools - you get the picture I'm sure. From this range of applets you
can construct the tool that you require to get the job done.

What's more, more than one remote applet can work on the same object at the
same time and changes made in any one of these will be immediately reflected
in all of them.

This is an awful lot better than OLE but there's still more.

Instead of each applet opening its own window we can use 'In-place' editing.
This means that only the  Local application displays the document. When you
click on a 'tool' entry in the Utilities menu the new tool's Toolbar opens
over the Local application's window. All tools then work on the image in the
Local's window.

Now you are really able to construct an application from a range of applets.
All you will see is one window displaying the document.

Take this a little further and imagine a DTP package supporting the PCA
standard. It could have a frame containing a graphic image and you could
link this to PA24, Compo or any other PCA application, which could
manipulate the image. The changes would be reflected immediately in the DTP
window. However, if In-place editing is used, the Toolbars would appear in
the DTP window and allow you to edit the graphic directly in the DTP window.
  
What we now have is a system whereby an application can have an infinite
number of additional tools and all applications conforming to PCA can be
used with and by all other PCA applications. An example of this could be an
image in a DTP frame linked to Compo which used this image as a 'canvas' for
a composite picture. From Compo one of the images in the composite picture
could also be linked to ProArt24 and any changes would immediately be
reflected in Compo and the DTP package.
