How to update an existing plot?

[david.sarraf]

I need to update a plot periodically using FreeBasic and DPLOT JR. I am using the example FreeBasic code to make the x-y plot. Each time I make the call it creates a new plot, rather than updating the old plot. I have spent some time with the documentation; the closest I can get is erasing the old data then replotting. That gives me two additional plots; one blank, and one with the new data.

How do I get rid of the first plot, or simply modify that one, rather than creating a whole new plot each time I make the system call?

[DPlotAdmin]

David,

I have spent some time with the documentation; the closest I can get is erasing the old data then replotting. That gives me two additional plots; one blank, and one with the new data.

This should not be, if you erased the curve before plotting your new data. Either this:

DPlot_Command(docnum,"[SelectCurve(1)][EditErase()]")
DPlot_Command(docnum,"[XYXY(...)]") ' or whatever you're doing to send the data

or this:
DPlot_Command(docnum,"[EditEraseData(1)]")
DPlot_Command(docnum,"[XYXY(...)]")

should do what you want. If not, please copy the relevant part of your code and send it to me - or paste it here if you like.

[david.sarraf]

Thanks for the help. I am now able to generate a plot and update the data at will. One other bump I had to overcome was selection of the plot to be updated. If the Select and Update commands were issued separately all data went to the first curve. If the commands were concatentated in the same command the data went to the intended curve. In short, curve selection did not appear to be "sticky". This was not a big problem, and it had the side benefit of making me more familiar with the command set.

[DPlotAdmin]

David,
That's spelled out in the documentation but I probably need to make it more clear somehow . Each call to DPlot_Command (or any other DPLOTLIB function) results in a new DDE transaction. For each new transaction, DPlot initializes several variables, including but not limited to the currently-selected curve. So this:

DPlot_Command(docnum,"[SelectCurve(3)][EditErase()]")

will delete the third curve, but this:

DPlotCommand(docnum,"[SelectCurve(3)]")
DPlotCommand(docnum,"[EditErase()]")

will delete the first (default) curve.

In any case, glad you got things working. Let me know if you have any other problems.