How to use OpenGL directly in OCC？ - Forum Open Cascade Technology

X F
Sun, 09/30/2018 - 10:18

Forums:

I need to read a *.stl file,then display the shape in my program. But the *.stl is so big, there are more than 10000 triangles in it. So if using the followed code to display.

......

while(...)

{ // Will cycle >10000 times.

......// Read data from a stl file.

gp_Pnt aPnt1(vX1, vY1, vZ1);

gp_Pnt aPnt2(vX2, vY2, vZ2);

gp_Pnt aPnt3(vX3, vY3, vZ3);

if( !aPnt1.IsEqual(aPnt2, 1.0e-06) && !aPnt1.IsEqual(aPnt3, 1.0e-06) && !aPnt3.IsEqual(aPnt2, 1.0e-06) ){

TopoDS_Vertex Vertex1 = BRepBuilderAPI_MakeVertex(aPnt1);

TopoDS_Vertex Vertex2 = BRepBuilderAPI_MakeVertex(aPnt2);

TopoDS_Vertex Vertex3 = BRepBuilderAPI_MakeVertex(aPnt3);

TopoDS_Wire AktWire = BRepBuilderAPI_MakePolygon(Vertex1, Vertex2, Vertex3, Standard_True);

if(!AktWire.IsNull()){

TopoDS_Face AktFace = BRepBuilderAPI_MakeFace(AktWire);

if( !AktFace.IsNull() ){

myBuilder.Add( STLShowShape, AktFace );

}

Handle(AIS_Shape) showObj = new AIS_Shape(STLShowShape);

myAISContext()->SetColor(showObj, Quantity_NOC_WHITE);

myAISContext()->SetMaterial(showObj,Graphic3d_NOM_DEFAULT);

myAISContext()->SetDisplayMode(showObj,1,Standard_True);

myAISContext()->Display(showObj);

......

The above codes are working OK. But TOO slow. I think perhaps because the AIS_Shape is too big(Or other reason?), and I don't need those triangle shapes' BREP information. So I want to use OpenGL directly to show those Triangles. My InitView() function is copied from OCCT Sample as follow,

bool InitViewer(System::IntPtr theWnd)

{

Handle(Aspect_DisplayConnection) aDisplayConnection;

myGraphicDriver() = new OpenGl_GraphicDriver (aDisplayConnection);

myViewer() = new V3d_Viewer (myGraphicDriver());

myViewer()->SetDefaultLights();

myViewer()->SetLightOn();

myView() = myViewer()->CreateView();

Handle(WNT_Window) aWNTWindow = new WNT_Window (reinterpret_cast<HWND> (theWnd.ToPointer()));

myView()->SetWindow(aWNTWindow);

myView()->ZBufferTriedronSetup(......);

myView()->TriedronDisplay(......);

myAISContext() = new AIS_InteractiveContext( myViewer() );

myAISContext()->UpdateCurrentViewer();

myView()->Redraw();

myView()->MustBeResized();

return true;

}

During trying to find a way to solve this problem, I find the STLViewer.exe load and show the *.stl very very quickly. It based on only OpenGL. Can anyone give me some suggestions about how to use OpenGL in OCC or improving the codes' running speed? Thanks a lot!

Kirill Gavrilov
Sun, 09/30/2018 - 10:57

You don't need creating a BRep from STL with each triangle becoming a Face - this is indeed slow and inefficient.
Just use Poly_Triangulation returned by RWStl::ReadFile() - see readstl Draw Harness command.

Anton Shabalin
Mon, 10/01/2018 - 07:24

Have a look at AIS_Triangulation. You can simply create Poly_Triangulation from stl data and use it for presentations computing.

X F
Fri, 10/05/2018 - 05:01

Thank for Anton Shabalin and Kirill Gavrilov's reply.

I use AIS_Triangulation and Poly_Triangulation can display those triangles very quick. My sample code like followed:

......

TColgp_Array1OfPnt myTriNodes(1, 6);

Poly_Array1OfTriangle myTriangles(1, 2);

myTriNodes(1).SetCoord(0,0,0);

myTriNodes(2).SetCoord(0,1,0);

myTriNodes(3).SetCoord(0,0,1);

myTriNodes(4).SetCoord(0,0,0);

myTriNodes(5).SetCoord(-1,0,1);

myTriNodes(6).SetCoord(-1,0,0);

myTriangles(1).Set(1,2,3);

myTriangles(2).Set(4,5,6);

Handle(Poly_Triangulation) myPoly = new Poly_Triangulation(myTriNodes, myTriangles);

Handle(AIS_Triangulation) myAISTria = new AIS_Triangulation(myPoly);

myAISContext()->SetColor(myAISTria, Quantity_NOC_WHITE);

myAISContext()->Display(myAISTria);

......

But I have two more questions.

1. Why the SetColor(myAISTria, Quantity_NOC_WHITE) takes no effects? It always brown color. How can I set those triangles color? Further more, I want to know how to use different color to show the triangles' front and back color.

2. I read the source about StlAPI_Reader.cxx. When it read a stl file, it read the file twice. The first time, it counts the number of the "facet..." structure to decide the the parameters NUM1 and NUM2 in TColgp_Array1OfPnt nNodes(1, NUM1) and Poly_Array1OfTriangle nTriangles(1, NUM2). The second time it read the data one by one. My question is CAN I find a way like using std::vector in OCCT to instead TColgp_Array1OfPnt and Poly_Array1OfTriangle to modify the array's length and add new element later?

Kirill Gavrilov
Fri, 10/05/2018 - 06:28

1. Why the SetColor(myAISTria, Quantity_NOC_WHITE) takes no effects?

You don't need AIS_Triangulation for displaying STL triangulation.
Just use normal AIS_Shape presentation and adjust its attributes in the way you need (including back-face/front-face materials).

2. I read the source about StlAPI_Reader.cxx. When it read a stl file, it read the file twice.

You are looking into very old nonsense code - it is better upgrading OCCT to an up-to-date state with improved STL reader.
Implementing RWStl_Reader interface would allow reading STL content into application-specific structures,
but in this case you'll have to implement AIS presentation on your own.

X F
Fri, 10/05/2018 - 18:31

Thank you very much!!!

I find a way to change the color using AIS_Triangulation. Codes like followed:

......

Standard_Integer aColorRedInt = 255;

Standard_Integer aColorGreenInt = 255<<8;

Standard_Integer aColorBlueInt = 255<<16;

Handle(TColStd_HArray1OfInteger) aColorArray = new TColStd_HArray1OfInteger (1, 6);

aColorArray->SetValue(1,aColorRedInt);

aColorArray->SetValue(2,aColorRedInt);

aColorArray->SetValue(3,aColorRedInt);

aColorArray->SetValue(4,aColorGreenInt);

aColorArray->SetValue(5,aColorGreenInt);

aColorArray->SetValue(6,aColorGreenInt);// Or aColorArray->SetValue(6,aColorBlueInt )

myAISTria->SetColors (aColorArray);

myAISContext()->Display(myAISTria);

......

If one triangle's three nodes are the same color, this triangle will be the color as nodes are. If the three color are NOT the same color, this triangle will be a coloful face.

After reading your reply, I still don't know how to use AIS_Shape to show those triangles. I need to show more than 10000 triangles, Is AIS_Shape too big? How can I get Handle(AIS_Shape) from Poly_Triangulation and show them quickly? Could you give me some sample codes?

And how to set back-face/front-face materials?Could you give me some functions' name?Thanks!

Now I'm working with OCC 6.3.0 and 7.1.0 (Sure, 6.3.0 is a terrible prehistoric code, but the legacy is based on it. ), so I need to rewrite some algorithm to override the old codes.

Kirill Gavrilov
Fri, 10/05/2018 - 22:28

Now I'm working with OCC 6.3.0 and 7.1.0

OCCT 6.3.0 does not provide any efficient way for displaying middle-sized data arrays.
STL reader has been rewritten in OCCT 7.2.0 (as well as several bug-fixes and improvements for displaying triangulation-only faces using AIS_Shape) - check Release Notes.

Marco Balen
Fri, 10/05/2018 - 11:41

Hi,

I have the same problem. I am starting to understand how to display in a fast way a lot of triangles.

Can you share your test so we can proceed together to solve this ?

Marco

Marco Balen
Fri, 10/05/2018 - 17:19

I have get the below snippet of code from ReadStl of XSDRAWSTLVRML.cxx file , but the face cannot be displayed.

Handle(Poly_Triangulation) aSTLMesh = RWStl::ReadFile(aFile);
 TopoDS_Face aFace;
 BRep_Builder aB;
 aB.MakeFace(aFace);
 aB.UpdateFace(aFace, aSTLMesh);

It seems that in draw the subsequent "DBRep::Set(theArgv[1], aFace);" made the necessary job.

Have any one a method to read in a faster way a stl file or a poly_Triangulation and display them ?

Kirill Gavrilov
Fri, 10/05/2018 - 22:27

The face is displayed using normal command vdisplay creating an AIS_Shape within Draw Harness tests.
Most likely you will find Wireframe presentation not very useful for triangulation (in contrast to BRep model there will be no isolines).

pload ALL
readstl m [locate_data_file bearing.stl]
vinit View1
vdisplay -dispMode 1 m
vfit

Marco Balen
Tue, 10/09/2018 - 19:27

Hi Kirill,

I have implemented the display of the triangles with BRep_Builder.makeface and I can create an AIS_InteractiveObject and display it with shading.

But, I also need a visualization through an AIS_Triangulation because I have to set the colors of the vertex of the triangles.

I can do the visualization, but I cannot shade the surface. I get a compact coloured shape. Using the SetDisplayMode(AIS_Shaded) of the context I get no shape visualization.

How can I render a AIS_Triangulation object ?

Or can I set the color of some vertexes of the face builded with BRep-Builder ?

Marco Balen
Tue, 10/09/2018 - 20:21

Hi Kirill,

I have solved.

I have set the normals of the Poly_Triangulation object and then I can see a shaded shape.