Download demo project - 33 Kb
Download source files - 27 Kb
Recently, the company I CO-OP for (Bradley Ward Systems)
needed a way to show complex data reports over the web. We already have lots of
custom OCXs that present these reports in graph or chart form. These OCXs are
used in our custom applications - they were never intended to be embedded in web
Because we wanted to make the web reports as light-weight as possible, refitting
the OCXs to also be embedded in web pages was simply not an option - we didn't
want to impose stringent system requirements on the computers that would be used
to view these reports. We decided that the best way to show these reports over
the web was to take a "snapshot" of one of our OCXs and write it out to a
JPEG for display on a web page.
So, our biggest problem was how to get a picture of one of our OCXs... We tried
various ways of getting the picture by using the
HWND of a form our OCX was
embedded on. There were two major problems with this: first, a visible form
would have to appear on the screen of the webserver whenever we wanted to get
a picture of an OCX; second, a user would always have to be logged onto the
webserver in order to create the form that the OCX was embedded on. We simply
didn't find a way around these problems.
So, instead of using the
HWND to trick the OCX into painting into a DC
of our creation, we went a little deeper...
Every OCX must implement the standard
IViewObject interface - of which one of
the methods is
Draw(). Sounds perfect, right? Almost - we also have to
determine the dimensions of the OCX, functionality which
IViewObject does not
expose. We used the
GetExtents() for this.
I wrote a small ActiveX control that makes these calls, and returns an
object for embedding in a Picture control on a VB form.
This ActiveX control I present here - called ViewObjSnap - is a scaled-down
version of the one I wrote at work. It doesn't write the picture out to a
JPG or anything like that, so you would need to modify it a little to be
useful in a real world situation. It is only intended to demonstrate an
interesting solution to our problem.
The source code for the ViewObjSnap control is contained in the
ViewObjSnap_src.zip file. The source code and a demo VB project, along with
the compiled EXE for those that don't own VB, are in ViewObjSnap_demo.zip.