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3DBugger VB .NET Tutorial

See Overview for general description and initial steps of the tutorial.

Overview of implementation

Initial tasks for starting the application are performed in DebuggerForm.Init() called from DebuggerForm.OnFormLoad(). GetVertices() method sets coordinates of the pyramid object stored in m_vert array of the form.

After that CreateGenerator() method loads DG Kernel component and obtains IDIObjGenerator interface from DIObjGenerator COM class created as new object. The interface is stored in m_iDIObjGenerator variable. The main debugging related interface I3DBugger is queried from m_iDIObjGenerator and stored as m_i3DBugger.

Notice also Plane and Segment classes in the project. They are responsible for managing and dumping relevant geometric objects. Segment object will be used to represent a single shared edge of a flat face of the pyramid.

The calculation: The algorithm will calculate interentity of all six segments of the pyramid object with the plane The interentity points will be stored in m_interentity array. These points are corners of the interentity polygon, which can also become a segment, a point or an empty set depending on position and orientation of the plane.

It is convenient to position Visual Studio and 3DBugger windows side by side as shown on picture below

Debugging the application

  • Put break point on the DumpModel() line of DebuggerForm.Calculate() method. Start the application and press Calculate button
  • Step into the DumpModel() call. This method uses IModel and IModelEx to load 3Dbugger.mdg model file, which contains model of the pyramid
  • Step Over the m_i3DBugger.DumpObject(iModel, 0, true, false) line and notice the pyramid object, which appeared in 3DBugger window. Notice the name of the object displayed in explorer window. You can view the object is 3D with all functionality of 3D Debugger available.
  • Step out of the DumpModel() method, step into m_plane.Dump(m_i3DBugger) call. and have a look at implementation of the Dump method of the Plane object. The method uses indirect dump technique. The dump is performed via IDrawUtil.Disk, at the line iDrawUtil.Disk(0, 3) Most of the code in the method is devoted to positioning and orienting the current rendering frame for IDraw because IDrawUtil.Disk renders a disk at a standard location (0,0) of the x and y axes of the current frame.
  • Notice how name of the dumped object is set at Util.SetCurrentName(strName, iDraw) line. The Util.SetCurrentName uses IKCContext to set the current Name property of the debugger to "Plane.." string. The actual dump will be performed at the i3DBugger.Dump() line of the Plane.Dump()
  • Step out of the Plane.Dump() and notice the disk representing the plane to appear in the debugger window. Name of the object containing hash of the Plane object is displayed in the Explorer
  • In DebuggerForm.Calculate() method step through several lines and step into the first call of the AddSegmentInterentity() line
  • This method calculates interentity of  a segment with the plane. Step over two lines and stop at the segment.Dump()
  • Try very useful technique, which sometimes allows debugging without adding any extra code to the application: Open Debug > Quick Watch window in Visual Studio and paste segment.Dump() into the expression line. Press Recalculate button. The segment will appear in the 3D view. Close the quick watch window
  • Step into the segment.Dump() line of DebuggerForm.AddSegmentInterentity(). The method demonstrates indirect dump using IDraw interface. Notice the iKCContext.SetBoolParam(0, true) line, which indicates the the segment must be dumped as a transient object. Notice also usage of IKCStack to save the state before the above change and restore it after the dump.
  • Step out up the call stack two times to reach the DebuggerForm.Calculate() method. Step through the repetitive loops while watching the dumped segments. Notice how previous segments are removed by the m_i3DBugger.BeginDump in the start of each loop. It is important that the segment was dumped as a transient object.
  • Notice that when the segment intersects the plane the interentity point appears in debugger window. This is accomplished in DebuggerForm.DumpPoint method.
  • Let the application to continue (Debug > Continue in Visual Studio). The final scene displayed in debugger window should look like:
  • :
  • The Interentity face is dumped by DebuggerForm.DumpInterentity() using IDraw