Navigation:  Programmer's Reference > Executing DPlot commands from another application

You can send a command or series of commands to DPlot from another application through a dynamic-data exchange (DDE) conversation, or "channel."  For commercial applications, you should refer to the documentation for the application to determine the method for initiating a conversation with DPlot and executing commands for another application. The DPLOTLIB DLL (not included with the DPlot distribution, available free-of-charge from the DPlot web site) hides the complexities of DDE and provides a simple interface for sending command strings to DPlot from a variety of programming environments.

Following is a brief demonstration of how to send a command to DPlot from three different environments.

 

Visual Basic 3.0

Control.LinkMode = 0

Control.LinkTopic = "DPlot|System"

Control.LinkMode = 2

Control.LinkExecute "[FileNew()]"

Control.LinkMode = 0

where Control is any label, picture box, or text box.

 

Microsoft Excel 4 macro

 

Microsoft Office products Visual Basic

Channel = DDEInitiate("DPlot", "System")

DDEExecute Channel, "[FileNew()]"

DDETerminate Channel

 

Following is a list of the commands supported by DPlot. All commands must be enclosed by square brackets. There should be no spaces in the command string, other than those embedded in character string arguments or used to delineate numeric parameters. Character arguments are always enclosed by double-quotation marks. Command names are not case-sensitive.

 

A

B

C

D

E

F

G

H

I

L

M

N

P

R

S

T

U

V

W

X

Y

Z

 

Commands may be issued in sequence or appended to each other. For example, the following command string opens and prints a DPlot file entitled "TEST.GRF" before causing DPlot to close:

[FileOpen("TEST.GRF")][FilePrint()][FileExit()]

Notes

1) Each DDE conversation has an association with a DPlot document. This association is established when the conversation is initiated, and may be changed by an Activate, FileOpen, or FileNew command.  If, for whatever reason, either DPlot or the client application terminates the conversation and the client then establishes a new conversation, this association no longer holds. The client application should re-establish the association with a document with the Activate command, else any commands sent to DPlot may not operate on the intended document.

2) Character string arguments are always enclosed by double quotation marks. In some environments (Visual Basic, for example), double quotation marks are also used to delineate character string arguments. The following example will always cause a syntax error in Visual Basic:

Control.LinkExecute "[FileOpen("myfile.grf")]"

Instead, use:

Control.LinkExecute "[FileOpen(""myfile.grf"")]"

3) For real-time applications, it is strongly suggested that the client application use the ManualScale command to force the plot coordinates to the desired value. Otherwise, DPlot will continually adjust the plot coordinates to fit the incoming data. If the ManualScale command is issued DPlot keeps the extents of the X axis constant, shifting the plot window to the right when necessary. For real-time applications that display a graph in their own window (rather than a DPlot document window), you will have much better performance using the SetOutputWindow command rather than retrieving a bitmap or metafile from DPlot after every graph update.

4) For linear X, linear Y scales, DPlot draws individual line segments rather than redrawing the entire plot every time a new data point is added with the XY command. DPlot will only redraw the plot if the incoming data point lies outside the current plot extents. Although this optimization results in significantly faster plotting, there are several drawbacks: a) Since points are added one at a time rather than drawing a series of line segments, the pattern for a line style starts over at each point. Rather than using the slower line drawing routines that use a pattern (and would be incorrect anyway), DPlot uses the faster Windows API routines MoveTo and LineTo with solid lines. b) DPlot does not create and load the color palette selected by the user. Instead, the colors used to draw the line segments are the closest match of the system colors to the desired colors. Both of these limitations apply only to line segments that are drawn individually. Once the entire plot is redrawn, the lines will be drawn correctly.

5) DPlot returns one of 3 values in response to any command. The return codes sent to the DDEML (Dynamic Data Exchange Management Library) are DDE_FACK (=0x8000), DDE_FBUSY (=0x4000), and DDE_FNOTPROCESSED (=0). The various development environments respond to these return codes in different manners, usually by displaying a MessageBox in the case of DDE_FBUSY or DDE_FNOTPROCESSED. DDE_FACK indicates success. DDE_FBUSY indicates that DPlot is currently disabled (possibly because a MessageBox or other modal dialog box is displayed). DDE_FNOTPROCESSED indicates that the command was not valid or was unsuccessful for some other reason (exceeding the array sizes, for example). Note that DPlot does not cache incoming commands if it is currently busy... it is up to the client application to re-send the commands later, if necessary. Real-time client applications should not rely on DPlot to save incoming data values.

For optimum performance with real-time applications

 

 

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