OneSpace Modeling FAQ: DDE

How do I talk to OneSpace Modeling via DDE?

OneSpace Modeling services DDE requests, and you can also send DDE requests from OneSpace Modeling via Integration Kit functionality. See the section "DDE Interface" in the Integration Kit documentation for details.

DDE is a fairly old interprocess communication protocol. It is still used both in Windows applications and in the operating system, though. As an example, the Windows shell uses DDE to notify running applications when a user double-clicks a file which is associated with the application.

DDE uses messages which are sent to an application's message queue. The DDE protocol requires all DDE-enabled applications to continually process messages, or else DDE communication in the system will be blocked. While an DDE-enabled application is busy doing other things (parsing a file, processing a spreadsheet, or, in OneSpace Modeling's case, blending complex edges), it may not react to DDE messages for a while, and as a consequence, even DDE conversations with other apps may block for some time.

For this reason, use DDE sparingly, and only in circumstances where losing a message at least does not have catastrophic effects. That said, here is a simple example in VBA which shows how to open a conversation with OneSpace Modeling and have it execute a command.

  Sub dde()
    Dim nChannelNumber As Variant
    nChannelNumber = DDEInitiate("PESD", "GENERAL")
    DDEExecute nChannelNumber, "(CREATE_PART :name ""dde_test_part"" :owner ""/"")"
    DDETerminate nChannelNumber
  End Sub

By the way, if you want to try out DDE communication from a shell window, check out the command-line tool ddeclient.exe which is part of the Emacs distribution:

  $ echo '(CREATE_PART :name "dde_test_part" :owner "/")' | ddeclient PESD GENERAL

-- ClausBrod - 14 Jul 2005

How do I talk to other applications from OneSpace Modeling via DDE?

The Integration Kit provides the following DDE functionality to talk to external applications which support DDE:

• sd-dde-initiate
• sd-dde-execute
• sd-dde-poke
• sd-dde-request
• sd-dde-close
• sd-dde-request-timeout
• sd-dde-execute-timeout

The exact commands to be sent via DDE differ from application to application. The DDE FAQ provides information on many such applications and is a good starting point for further search.

A typical DDE session usually involves three steps:

1. Initialization
2. Communication phase
3. Teardown

In phase 1, you contact the external application using sd-dde-initiate:

  (setf dde (oli:sd-dde-initiate "EXCEL" "System")) ;; connect to Excel

In phase 2, you send commands using sd-dde-execute and inquire data from the external application using sd-dde-request.

  (oli:sd-dde-execute dde "[Select(\"r1c1:r2c2\")]")) ;; select range

In phase 3, you close the session using sd-dde-close.

  (oli:sd-dde-close dde)

-- ClausBrod - 21 Jul 2005