Hatching Clip Plane For Meshes - Forum Open Cascade Technology

Thieme Vandeput
Mon, 12/18/2023 - 14:46

Forums:

Dear developers,

I'm trying to use a clipplane on an AIS_Shape built from an stl-file. The clipplane's hatching(/Capping) works fine for .brep but shows a hollow cross-section for .stl. The way I am building it is (note that I'm using the pythonocc-wrapper of OpenCascade):

from OCC.Core.Graphic3d import Graphic3d_ClipPlane
from OCC.Core.Quantity import Quantity_Color, Quantity_TOC_RGB
from OCC.Core.TopoDS import TopoDS_Face
from OCC.Core.BRep import BRep_Builder
from OCC.Core.RWStl import rwstl

# Import stl file
stlReader = rwstl()
poly_triangulation = stlReader.ReadFile(file_name.stl)

# Convert to shape
shape = TopoDS_Face()
builder = BRep_Builder()
builder.MakeFace(shape , poly_triangulation )

# Convert to AIS_Shape
ais_shp = display.DisplayShape(shape )[0]

# Clip plane
clip_plane_1 = Graphic3d_ClipPlane()

# Set hatch on
clip_plane_1.SetCapping(True)
clip_plane_1.SetCappingHatch(True)

# Set clip plane color
aMat = clip_plane_1.CappingMaterial()
aColor = Quantity_Color(0.5, 0.6, 0.7, Quantity_TOC_RGB)
aMat.SetAmbientColor(aColor)
aMat.SetDiffuseColor(aColor)
clip_plane_1.SetCappingMaterial(aMat)

# Add clip plane
ais_shp.AddClipPlane(clip_plane_1)

In CAD Assistant it is possible to assign a hatching profile to the part. But I'm not sure how to do it in code. Any ideas?

Thanks in advance and kind Regards,
Thieme

Attachments:

Hollow Clip Plane.PNG

Hatched Clip Plane.PNG

gkv311 n
Wed, 12/20/2023 - 10:04

OCCT Viewer enables capping algorithm for watertight closed meshes only. In case of AIS_Shape - it is done for TopoDS_Solidshapes. This is because capping algorithm will produce visual artifacts on open shells.

STL files, although called 'solids', usually contain arbitrary triangulations (sometimes watertight, sometimes open shells). Do that without extra efforts AIS viewer will not consider them closed and will not enable capping.

You may try to build TopoDS_Solid out of imported STL file, or force Closed flags within AIS presentation builder (Graphic3d_Group::SetClosed()).

As sort of a hack (just for demonstration), istead of subclassing AIS object, this could be enforced also after presentation is already computed:

Handle(AIS_Shape) aShapePrs = ...
theCtx->Display(aShapePrs, AIS_Shaded, 0, false);

Handle(PrsMgr_Presentation) aPrs = theCtx->MainPrsMgr()->Presentation(aShapePrs, AIS_Shaded);
for(const Handle(Graphic3d_Group)& aGroup : aPrs->Groups()) {
 if(dynamic_cast<Graphic3d_AspectFillArea3d*>(aGroup->Aspects().get()) != nullptr) {
    aGroup->SetClosed(true);
  }
}

Thieme Vandeput
Wed, 12/27/2023 - 16:40

Thank you so much, your code did the trick!!

Thanks a lot,
Thieme