Transient Graphics interference with highlights


I'm trying to draw some transient graphics (in this case it's just a crosshair) in my view without affecting the default highlights.

I'm using "Visual3d_TransientManager" to do this but I'm still a little confused.

I don't really understand the difference between "BeginDraw" and "BeginAddDraw".

I guess there's a kind of redrawing with "BeginDraw"?

I managed to keep default highlights using "BeginAddDraw" and making the View Update myself.

Here's the piece of code I use (the crosshair is still a simple marker):



MyView->ConvertToGrid(px , py , x, y, z); ////grid echo is turned of

MyAISContext->MoveTo(event->win_x , event->win_y, MyView);


Graphic3d_Vertex aVertex;

aVertex.SetCoord(x, y, z);


Visual3d_TransientManager::DrawStructure (MyStructure); ///// MyStructure contains MyGroup


This works almost fine but the highlight flickers just a little due to the redraws.

Even stranger is that the default grid echo marker also interferes with the highlighting.

This code doesn't show highlights (or just shows them for a split of a second):

MyView->ConvertToGrid(px , py , x, y, z); //// grid echo is turned on

MyAISContext->MoveTo(px , py, MyView);

In this case redrawing the View doesn't seem to help.

Does anyone know a better way to do this?

I'm using Cascade release 3.1. Did this methods improved in latter versions? Thanks.

Michael Gandyra's picture

It is not clear to me, why you use Visual3D_TransientManager. Is there a special reason for doing this? Normally a crosshair is 2D. But you use Visual3D and then convert back to ViewCoordinates. Why do you want to keep default highlights? You have to give more information. Their a several possibilities. Furthermore, highlighting can be steered via the AISContext.

Best regards,

Michael Gandyra


University of Kaiserslautern

Research Group for Computer Application in Engineering Design


r-fortes's picture

Hello Michael.

Thanks for answering my post.

I'm using Visual3D_TransientManager because MyView is a "V3d_View" and the crosshair should follow x and y axis.

I also want to keep default highlights mainly because I'm still not very comfortable using AIS. I still don't know how to highlight just a detected edge.

If I call "MyAISContext->DetectedInteractive()" I get an "AIS_InteractiveObject" (wich is the only object I know how to highlight) but the entire object is highlighted not just the edge even if I call "MyAISContext->ActivateStandardMode(TopAbs_EDGE)".

If I call "MyAISContext->DetectedShape()" I get the edge (I guess if I called "MyAISContext->ActivateStandardMode(TopAbs_SHAPE)" I would get the hole shape?) but there's no method in AISContext to highlight that.

Regarding transient graphics, using "Visual3D_TransientManager" is just the only way I know.

Has you can see I'm just grasping this issues.

Nevertheless I think that if the viewer has the methods to work with AIS and manage the highlighting of entities why not use them.

Here is the code I use:

MyView->Redraw(); MyView->ConvertToGrid(px , py , x, y, z); MyAISContext->MoveTo(px , py, MyView);

MyGroup->Clear(); Visual3d_TransientManager::BeginAddDraw(MyView->View());

Graphic3d_Vertex V1, V2, V3, V4;

V1.SetCoord(x - 1000, y, z);

V2.SetCoord(x + 1000, y, z);

V3.SetCoord(x, y - 1000, z);

V4.SetCoord(x, y + 1000, z);

MyGroup->Polyline(V1, V2);

MyGroup->Polyline(V3, V4);



Would you please elucidate this newbee!?

Thanks a lot.

Michael Gandyra's picture

O.K. Newbee ! :-)

1. Rule: RTFM ! - I know, the manual is not perfect and some parts are undocumented, but the major part is quite useful in its current state. Especially AIS things are quite good documented, I think. If you don't find information in the manuals, very often there are comments in cdl- and cxx-files.

2. Rule: Learn from the samples ! Everything, what you need (without crosshair) is documented in the "SampleAISSelect" sample. Just copy and paste (if you work on linux, there are probably some similar examples, I guess). For the samples there are also some useful manuals (pdf's).

3. Rule: Learn from the source code ! Try to find inheritance correlations between the classes. This is good to practice OpenCasCade.

For your (highlighting) problem you need a local context (see sample).

Concerning the TransientManager I can send you some (undocumented) code snippets, where you can learn from, to find out how to solve this.

Best regards,

Michael Gandyra


University of Kaiserslautern

Research Group for Computer Application in Engineering Design