Hide and Display AIS_ColoredShape - C# Wrapper - Forum Open Cascade Technology

Eugenio Salguero
Wed, 02/25/2026 - 09:43

Forums:

I am loading xml files to be displayed in the screen. The xml defines shapes and colors, so for creating the object, I am using a TopoDS_Compound and an AIS_ColoredShape so each part of the shape can be displayed in a different color. Also, I'm trying to use OCAF for displaying a complex structure and to provide Undo/Redo operations.

The problem I'm facing is the following one:

When creating the object, adding to OCAF and then displaying the tree, it is working fine. Then, If I undo the operation, the object dissapear as it is expected. But finally, when I apply a redo operation, the object is displayed in black. It seems it is missing the colors of the sub_shapes

Also, I have implemented a hide selected/show hidden object operation. If I hide the object it disappears properly, but when I try to show it again (recovering it from a dictionary of <string, AIS_ColoredShapes>) it always is displayed in a unique color, missing the sub_shapes colors information

As I said, the AIS_ColoredShape is already created but the color is missed. Is there something to be done when re-displaying an AIS_ColoredShape that I am missing or has anyone faced a similar problem??

I am using c# .Net 8 and the Open Cascade c# wrapper

This is the code where I recover the info from the dictionary and the OCAF label:

AIS_ColoredShape aisC;
_coloredAisByEntry.TryGetValue(entry, out aisC);

if (aisC != null && !aisC.IsNull())
{
    int mode; _ocaf.TryGetDisplayMode(label, out mode);
    _ctx.SetDisplayMode(aisC, mode, true);
    if (!_ctx.IsDisplayed(aisC))
        _ctx.Display(aisC, true);
    _ctx.Update(aisC, false);
}

Where _ctx is the AIS_InteractiveContext.

Thank you very much in advance

Attachments:

BeforeHide.png

AfterShow.png

gkv311 n
Wed, 02/25/2026 - 11:32

AIS_ColoredShape doesn't deal with OCAF directly - it stores only TopoDS_Shape and assigning colors/materials. Hence, on its own it cannot be affected by any OCAF operations like Undo/Redo. (In contrast, XCAFPrs_AISObject computes presentation from TDF_Label, thus taking TopoDS_Shape and colors from XDE document, when recomputed).

How AIS_ColoredShape is filled in in your case and updated by Undo/Redo operation is unclear to me.

Eugenio Salguero
Wed, 02/25/2026 - 11:50

This is part of the class where the AIS_ColoredShape is created:

TopoDS_Compound compound;
TopoDS_Shape shapeCompound;
BRep_Builder builder;
AIS_ColoredShape aisCompound = null;
AIS_InteractiveContext myContext;

public class CustomCompoundAIS : AIS_Shape
{

    public CustomCompoundAIS(TopoDS_Compound shapeComp) : base(shapeComp)
    {
        compound = shapeComp;
        shapeCompound = compound;
        builder = new BRep_Builder();
        builder.MakeCompound(ref compound);
    }

    public void GenerateCompound()
    {
        aisCompound = null;

        if (shapes.Count > 0)
        {

            aisCompound = new AIS_ColoredShape(shapeCompound);

            for (int i = 0; i < shapes.Count; i++)
            {
                builder.Add(ref shapeCompound, shapes[i]);
            }


            // Triangulation
            var mesher = new BRepMesh_IncrementalMesh(shapeCompound, 0.3, false, 0.5, true);
            mesher.Perform();


            var shading = new Prs3d_ShadingAspect();
            var mat = new Graphic3d_MaterialAspect(Graphic3d_NameOfMaterial.Graphic3d_NOM_PLASTIC);
            shading.SetMaterial(mat);
            aisCompound.Attributes().SetShadingAspect(shading);


            for (int i = 0; i < shapes.Count; ++i)
            {
                var col = DecodeColor(materials[i].Color);
                aisCompound.SetCustomColor(shapes[i], col);
            }


            // Display as a single object and limit selection to the entire shape
            myContext.Display(aisCompound, true);
            myContext.SetDisplayMode(aisCompound, (int)AIS_DisplayMode.AIS_Shaded, true);
        }
    }

    public AIS_ColoredShape GetAISColoredShape()
    {
        return aisCompound;
    }
}

Then, the AIS_ColoredShape is stored in a dictionary to be recovered later

Eugenio Salguero
Wed, 02/25/2026 - 18:25

I have found what seems to be the solution. I was hiding the objects using the method Remove from AIS_InteractiveContext. Using Erase instead seems to solve my issues.

Honestly, I do not understand what is different about using one method or the other

gkv311 n
Thu, 02/26/2026 - 09:15

Honestly, I do not understand what is different about using one method or the other

The difference between AIS_InteractiveContext::Remove() and ::Erase() is that the first one removes object completely from Context and cleans up all computed presentations - so that within the next ::Display() they should be recomputed anew. ::Erase() only marks object as hidden one, but keeps it computed presentations in memory so that ::Display() later on will reuse them.

Cannot reproduce described side effects from the given code snippets - so I guess the issue happens due to some other factors or another code. Which OCCT version is used by the way?

            var mesher = new BRepMesh_IncrementalMesh(shapeCompound, 0.3, false, 0.5, true);
            mesher.Perform();

BRepMesh_IncrementalMesh called like this will perform meshing twice - within the constructor and then by called ::Perform().

            aisCompound = new AIS_ColoredShape(shapeCompound);
            for (int i = 0; i < shapes.Count; i++)
            {
                builder.Add(ref shapeCompound, shapes[i]);
            }

This works in this case, but logically you should construct TopoDS_Compound first and then pass it to AIS_ColoredShape. Once constructed, TopoDS_Shape is expected to be an immutable object, so that adding/removing subshapes shouldn't be done afterwards - instead a copy should be created and filled in. One TopoDS_Shape is added as subshape to another TopoDS_Shape it is also marked 'Frozen' and attempts to modify it via BRep_Builder::Add() and similar will throw TopoDS_FrozenShape exception.

public class CustomCompoundAIS : AIS_Shape

What AIS_Shape does here? How created AIS_ColoredShape is linked to AIS_Shape?

            myContext.Display(aisCompound, true);
            myContext.SetDisplayMode(aisCompound, (int)AIS_DisplayMode.AIS_Shaded, true);

Pay attention to theToUpdateViewer flag within AIS_InteractiveContext methods. When give it true in a row, this means that Viewer will be redrawn multiple times, and you might see intermediate steps as blinking frames.

Eugenio Salguero
Sat, 02/28/2026 - 18:22

Thank you very much. You have spotted several things in the code I did not realize about. I'm very new using the Open Cascade library and I'm learning lots of thing the hard way.

I'm using Open Cascade 8.1 with the c# wrapper comertialized by Open Cascade. Just as a comment I have found several things that work different from the c++ version due (probably) for the extra abstraction layer of the wrapper and how memory is treated