ActiveX and AutoLISP Programming Tip 1

When trying to make use of the AutoCAD^® ActiveX^® access to the object model through the AutoLISP^® "VL" commands, the vlax-dump-object function will likely become one of your best friends. The Help sections on the object model are certainly useful, but as you test bits of code to verify that they work, I have found the vlax-dump-object function invaluable in helping me to understand exactly what properties are available for a given object.

For example, I was trying to update a subroutine I had written some years back that returned certain information about the current AutoCAD^® Architecture drawing, including the drawing scale. This was before drawing scale had been added as a feature to the "vanilla" AutoCAD^® software, and I had been using a DXF "hack" to get the current drawing scale from (namedobjdict) > AEC_VARS dictionary > AEC_VARS_DWG_SETUP dictionary > 40 group. In more recent releases, the CANNOSCALEVALUE system variable will give you the current annotation scale in a drawing. When Model Space is active in a Layout Viewport, however, it is possible for the viewport scale (magnification relative to Paper Space, which is presumed to be 1:1 when plotted) to be different from the annotation scale, and I wanted to be able to report both scales. By using the vlax-dump-object function in the Visual LISP Console for the ActivePViewport object, I was able to quickly see which properties changed when I changed settings in the drawing, which helped me to understand that the inverse of the CustomScale property of the ActivePViewport object would give me the scale factor for the viewport magnification, and also allow me to sidestep dealing with the enum values reported by the StandardScale (Viewport magnification) and StandardScale2 (viewport annotation scale).

Another thing that I was able to discover by using the vlax-dump-object function was that the Paper Space Viewport does not report all of the properties that other Layout Viewports report. For example, a Layout Viewport object scaled to 1/4" = 1'-0", saved to variable objVpA, might have the following properties, which can be examined using vlax-dump-object:

_$ (vlax-dump-object objVpA)
; IAcadPViewport: IAcadPViewport Interface
; Property values:
;   Application (RO) = #
;   ArcSmoothness = 10000
;   Center = (17.8157 11.25 0.0)
;   Clipped (RO) = 0
;   CustomScale = 0.0208333
;   Direction = (0.0 0.0 6889.41)
;   DisplayLocked = 0
;   Document (RO) = #
;   GridOn = -1
;   Handle (RO) = "E84"
;   HasExtensionDictionary (RO) = -1
;   HasSheetView (RO) = 0
;   Height = 22.5
;   Hyperlinks (RO) = #
;   LabelBlockId = 0
;   LabelBlockId32 = 0
;   Layer = "G-Anno-Nplt-N"
;   LayerPropertyOverrides (RO) = 0
;   LensLength = 50.0
;   Linetype = "ByLayer"
;   LinetypeScale = 1.0
;   Lineweight = -1
;   Material = "ByLayer"
;   ModelView = nil
;   ObjectID (RO) = 60
;   ObjectID32 (RO) = 60
;   ObjectName (RO) = "AcDbViewport"
;   OwnerID (RO) = 61
;   OwnerID32 (RO) = 61
;   PlotStyleName = "ByLayer"
;   ShadePlot = 0
;   SheetView = nil
;   SnapBasePoint = (0.0 0.0)
;   SnapOn = 0
;   SnapRotationAngle = 0.0
;   StandardScale = 26
;   StandardScale2 = 7
;   Target = (1690.27 1160.54 0.0)
;   TrueColor = #
;   TwistAngle = 0.0
;   UCSIconAtOrigin = -1
;   UCSIconOn = -1
;   UCSPerViewport = -1
;   ViewportOn = -1
;   Visible = -1
;   VisualStyle = 1
;   Width = 35.3685

For the Paper Space Viewport object for that same Layout, vlax-dump-object returns the following:

_$ (vlax-dump-object objVpA)
; IAcadPViewport: IAcadPViewport Interface
; Property values:
;   Application (RO) = #
;   ArcSmoothness = 10000
;   Center = (24.3525 19.3312 0.0)
;   Clipped (RO) = 0
;   CustomScale = 1.0
;   Direction = (0.0 0.0 1.0)
;   DisplayLocked = 0
;   Document (RO) = #
;   GridOn = 0
;   Handle (RO) = "1FB"
;   HasExtensionDictionary (RO) = 0
;   HasSheetView (RO) = 0
;   Height = 36.5272
;   Hyperlinks (RO) = #
;   LabelBlockId = Exception occurred
;   LabelBlockId32 = ; error: Exception occurred: 0xC0000005 (Access Violation)
; warning: unwind skipped on exception
; error: Exception occurred: 0xC0000005 (Access Violation)
; error: Exception occurred: 0xC0000005 (Access Violation)
; error: Exception occurred: 0xC0000005 (Access Violation)

The LabelBlockID property is apparently unavailable for a Paper Space Viewport and the LabelBlockId32 property is not only unavailable, but trying to get the value causes an error that terminates the vlax-dump-object function. You can get to the properties that occur alphabetically after those two, one at a time, by using the vlax-get-property function. My routine presumes that Paper Space is plotted at 1:1 and any annotation would be scaled accordingly, so it sets the scale factors for both the viewport and the annotation at 1.0 without extracting any data from the drawing.