Help: Rhino.Geometry.HiddenLineDrawing.Compute viewport question

Scripting
,
1

Hi @stevebaer or @GregArden
I am working on a script to automate some make2d stuff of blocks and I don’t understand how viewports work in this regard.

In ordinary Make2D we can choose Cplane and this is what I am after, but in Rhino Common it seems to me that I have to define what viewport to use, but the resulting geometry doesn’t end up in a predictable place. (if I move my camera a bit then the 2D lines moves to another location, and this just seems very strange to me, so I presume I do something wrong)

This is part of the code I am working on now cleaning up now (as a version 1.2 of what I have working)

Just make a block of a box or something with insertpoint = w(0,0,0), then use top view and run the script.
I would expect the 2D result to end up underneath the geometry of the block, but it ends up somewhere unpredicable. Now pan the view a bit and run the script again, now the result ends up somewhere else… Why is that?

import rhinoscriptsyntax as rs
import Rhino
import scriptcontext as sc

def make2D_of_objects(object_ids):
    tolerance_for_2d = 0.002
    # Get the active view
    rs.CurrentView("Top")
    view = sc.doc.Views.ActiveView
    viewport = view.ActiveViewport
    
    ###########################################################################
    # Process all of the objects
    ###########################################################################
    object_geometries = []
    for obj in object_ids:
        object_geometry = obj.Geometry
        # Check meshes and repair if it is
        if rs.IsMesh(object_geometry):
            object_geometry.Faces.RemoveZeroAreaFaces(0)
            object_geometry.Weld(0.0524) # = 35 degrees
        
        object_geometries.append(object_geometry)
    
    ###########################################################################
    # Create and define hidden line drawing parameters
    ###########################################################################
    parameters = Rhino.Geometry.HiddenLineDrawingParameters()
    parameters.AbsoluteTolerance = tolerance_for_2d
    parameters.Flatten = True
    parameters.IncludeHiddenCurves = False
    parameters.IncludeTangentEdges = False
    parameters.IncludeTangentSeams = False
    parameters.SetViewport(viewport)
    # Add geometry to parameters
    for object_geometry in object_geometries:
        parameters.AddGeometry(object_geometry, None)
    
    ###########################################################################
    # Create the hidden line drawing geometry
    ###########################################################################
    hld = Rhino.Geometry.HiddenLineDrawing.Compute(parameters, True)
    if not hld:
        return False
    
    ###########################################################################
    # Process the result
    ###########################################################################
    lines=[]
    for hld_curve in hld.Segments:
            if hld_curve.SegmentVisibility == Rhino.Geometry.HiddenLineDrawingSegment.Visibility.Visible: 
                # Copy the curve, transform and add to document
                curve = hld_curve.CurveGeometry.DuplicateCurve()
                if not curve.IsShort(0.01):
                    lines.append(curve)
        
    # Join curves
    joined_curves = Rhino.Geometry.Curve.JoinCurves(lines)
    result = []
    for joined_curve in joined_curves:
        result.append(sc.doc.Objects.AddCurve(joined_curve))
    if len(result) == 0:
        return False
    
    return result

object_id = rs.GetObject()
block_objects = rs.BlockObjects(rs.BlockInstanceName(object_id))

objects=[]
for object in block_objects:
    objects.append(sc.doc.Objects.Find(object))

#print objects

make2D_of_objects(objects)

PS! I found that HiddenLineDrawing really doesn’t like bad meshes, so I added a fix for that. It would be nice if the fix could be incorperated.

2

@rajaa - is this something you can help with?

3

To be super clear, what I need is to get a way to control the outcome of HiddenLineDrawing so it is in the correct XY position of the geometry i make 2d of.

(I gather the instance xform and reapply that on the calculated geometry in the main script, so you don’t need to cover that part)

Thanks

4

It is nice that you are fixing the mesh in your sample. I will run this by @GregArden to see if he advises that we do a preprocessing of objects before passing them to HLD.

As for your questions, you will need to do some work to place your drawing in a consistent location.
Instead of taking the current active view, it will help to specify consistent plane, perhaps relative to your objects bounding box. Try something like this:

    {
    ...
    //Find bounding box of objects and adjust the projection plane origin to the center of objs bbox
    var bbox = RoughBoundingBox(obj_refs);
    Plane cplane = view.ActiveViewport.ConstructionPlane();
    ViewportInfo plan_view = GetPlanView(cplane, bbox); //see below

    //use the "plan_view " in the HLD compute
    ...
    }

    // Get the viewport for a CPlane plan view
    // Set the view frustum to loosely contain the world bounding box
    public static ViewportInfo GetPlanView(Plane cplane, BoundingBox bbox)
    {
      Point3d center = bbox.Center;
      double radius = bbox.Diagonal.Length / 2.0;
      center += 2.0 * radius * cplane.Normal;

      ViewportInfo vp = new ViewportInfo();
      vp.ChangeToParallelProjection(false);
      vp.SetCameraLocation(center);
      vp.SetCameraDirection(-cplane.Normal);
      vp.SetCameraUp(cplane.YAxis);
      vp.SetFrustum(-radius, radius, -radius, radius, radius, 3 * radius);
      return vp;
    }