How-To: Traverse PRC model file using Visitor pattern for rapid prototyping

Introduction

Parsing and interpreting the PRC structure is non-trivial in some cases, as described in our documentation for PRC Basics.

In this article, we are going to describe traversing a PRC model file using a builtin Visitor pattern sample. Based on the ImportExport sample project, you will be able to make a prototype easily, which can retrieve and update the model file. This sample is reusable and you can port the code into your application even if you don’t know the details of the traversing manner.

Instructions

Workbench project preparation

Prepare a workbench project based on the ImportExport sample.

Copy ImportExport folder from <HOOPS_Exchange_Publish SDK dir>\samples\exchange\exchangesource and paste into your project folder
Rename the copied folder name to ImportTraverseExport
Copy HOOPSExchangePublishSample.props file from <HOOPS_Exchange_Publish SDK dir>\samples and past in the ImportTraverseExport/ folder
Copy common.hpp file from <HOOPS_Exchange_Publish SDK dir>\samples\exchange\exchange source and paste into the project folder
Start Visual Studio 2015 and open the ImportTraverseExport project
Save the solution as ImportTraverseExport.sln and close Visual Studio
Create a file named VS2015.bat and open it in your preferred text editor

Edit VS2015.bat so that it opens the solution by specifying HEXCHANGE_INSTALL_DIR environment variable

SET HEXCHANGE_INSTALL_DIR=C:\SDK\HOOPS_Exchange_Publish_2020_SP1
CALL "C:\Program Files (x86)\Microsoft Visual Studio 14.0\Common7\IDE\devenv.exe" ImportTraverseExport.sln

C:\SDK\HOOPS_Exchange_Publish_2020_SP1 is your HOOPS Exchange install dir

Save and close the VS2015.bat file
Open the solution using VS2015.bat
Add $(HEXCHANGE_INSTALL_DIR)\include in the Additional Include Directories of C/C++ -> General page in Project Property

Open ImportExport.cpp and edit like below

...
#include "common.hpp"
#include <sstream>
...
	//
	// ### INITIALIZE HOOPS EXCHANGE
	//
	std::wstringstream bin_dir;
#ifdef _DEBUG
	std::wstring buffer;
	buffer.resize(_MAX_PATH * 2);
	if (GetEnvironmentVariable(L"HEXCHANGE_INSTALL_DIR", &buffer[0], static_cast<DWORD>(buffer.size())))
	{
		bin_dir << buffer.data() << L"/bin/win64\0";
	}
#else
	bin_dir << L"";

#endif

	A3DSDKHOOPSExchangeLoader sHoopsExchangeLoader(bin_dir.str().data());
...

Build the project and verify that the import and export process works properly

To run this application, it is necessary to specify source and destination CAD file names to the Command Arguments of Debugging page of the project property, i.e.
"$(HEXCHANGE_INSTALL_DIR)\samples\data\step\helloworld.stp" "C:\temp\helloworld.prc"

Porting Visitor pattern

Several sample projects use the Visitor pattern, and the Collision sample provides a good starting point for our goals.

Copy the visitor/ folder from <HOOPS_Exchange_Publish SDK dir>\samples\exchange\exchangesource\Collision and past in the ImportTraverseExport folder
Return to the project in Visual Studio.
Create a new folder named visitor/ under Header Files and add all header files in the visitor folder
Create a new folder named visitor/ under Source Files and add all cpp files in the visitor folder

Implement tree traverse function

Implement a function which calls the visitor pattern.

Create traverseModelFile() function in ImportExport.cpp

...
#include <sstream>

#include "visitor/VisitorContainer.h"
#include "visitor/VisitorTree.h"

static MY_CHAR acSrcFileName[_MAX_PATH * 2];
static MY_CHAR acDstFileName[_MAX_PATH * 2];
static MY_CHAR acLogFileName[_MAX_PATH * 2];

void traverseModelFile(A3DAsmModelFile* pModelFile)
{
	// Prepare Visitor container
	A3DVisitorContainer sA3DVisitorContainer(CONNECT_TRANSFO);
	sA3DVisitorContainer.SetTraverseInstance(true);

	// Prepare Tree traverse visitor and set to the container
	A3DTreeVisitor *pA3DTreeVisitor = new A3DTreeVisitor(&sA3DVisitorContainer);
	sA3DVisitorContainer.push(pA3DTreeVisitor);

	// Prepare model file connector and call Traverse
	A3DModelFileConnector sModelFileConnector(pModelFile);
	A3DStatus sStatus = sModelFileConnector.Traverse(&sA3DVisitorContainer);

}

//######################################################################################################################
#ifdef _MSC_VER
int wmain(A3DInt32 iArgc, A3DUniChar** ppcArgv)
...

Split the Convert process into Import and Export so that the traverse function can be called after importing

...
	A3DExport sExport(acDstFileName); // see A3DSDKInternalConvert.hxx for import and export detailed parameters

									  // perform conversion
	CHECK_RET(sHoopsExchangeLoader.Import(sImport));

	traverseModelFile(sHoopsExchangeLoader.m_psModelFile);

	CHECK_RET(sHoopsExchangeLoader.Export(sExport));
...

Build the project
Make a breakpoint in TreeTraverse.cpp and verify the model file is traversed

Derived class creation

Thanks to the visitor pattern sample, you can access the model file from the root to the leaves in the correct manner. Though you can add your own retrieving and updating processes in it, we recommend you to make derived classes of A3DTreeVisitor, so that you can divide code into common traverse and various use cases. You don't need to write a traverse algorithm for each use case.

Create a derived class of A3DTreeVisitor

...
static MY_CHAR acLogFileName[_MAX_PATH * 2];

class myTreeVisitor: public A3DTreeVisitor
{
public:
	myTreeVisitor(A3DVisitorContainer* psContainer = NULL) : A3DTreeVisitor(psContainer) {};
	~myTreeVisitor() {};

public:
	virtual A3DStatus visitEnter(const A3DProductOccurrenceConnector& sConnector) override
	{
		A3DStatus iRet = A3DTreeVisitor::visitEnter(sConnector);

		// My processes

		return iRet;
	}

	virtual A3DStatus visitLeave(const A3DProductOccurrenceConnector& sConnector) override
	{
		A3DStatus iRet = A3D_SUCCESS;

		// My processes

		iRet = A3DTreeVisitor::visitLeave(sConnector);
		return iRet;
	}
};

void traverseModelFile(A3DAsmModelFile* pModelFile)
...

Use the derived myTreeVisitor class instead of A3DTessVisitor in the traverseModelFile() function

...
	// Prepare Tree traverse visitor and set to the container
	myTreeVisitor *pMyTreeVisitor = new myTreeVisitor(&sA3DVisitorContainer);
	sA3DVisitorContainer.push(pMyTreeVisitor);
...

Build the project
Make breakpoints in the myTreeVisitor class and verify that the class is called

In A3DTreeVisitor, the model file is traversed recursively from the root (pModelFile) to leaves (Product Occurrence, Part definition, Representation Item, etc.). The visitEnter() method is called at the beginning of each node traversal and the visitLeave() is called at the end of traversal. Due to the nature of the visitor pattern, all model tree nodes use the same methods (visitEnter() and visitLeave()) by changing the connector type argument.

In the above sample, you can implement your own processes when Product Occurrence is traversed by setting as A3DProductOccurrenceConnector in the argument.

The following is a mapping of Node types to Connecter classes

Node type	Connector
A3DAsmModelFile	A3DModelFileConnector
A3DAsmProductOccurrence	A3DProductOccurrenceConnector
A3DAsmPartDefinition	A3DPartConnector
A3DRiRepresentationItem	A3DRiConnector
A3DRiBrepModel	A3DRiBrepModelConnector
A3DRiSet	A3DRiSetConnector
A3DRiPolyBrepModel	A3DPolyRiBrepModelConnector

Logging component names

Add code to log component names in the console

...
private:
	int m_iLevel = 0;

public:
	virtual A3DStatus visitEnter(const A3DProductOccurrenceConnector& sConnector) override
	{
		A3DStatus iRet = A3DTreeVisitor::visitEnter(sConnector);

		// Increment level
		m_iLevel++;

		// Get the ProductOccurrence (PO)
		const A3DEntity* pEntity = sConnector.GetA3DEntity();
		A3DAsmProductOccurrence* pPO = (A3DAsmProductOccurrence*)pEntity;

		// Get RootBaseData of the PO
		A3DRootBaseData sRootBaseData;
		A3D_INITIALIZE_DATA(A3DRootBaseData, sRootBaseData);
		A3DRootBaseGet(pPO, &sRootBaseData);

		// Get the PO name  
		A3DUniChar acName[256];
		if (sRootBaseData.m_pcName)
			A3DMiscUTF8ToUTF16(sRootBaseData.m_pcName, acName);
		else
			wcscpy_s(acName, _T("NO_NAME"));

		// Show the PO name with level 
		for (int i = 0; i < m_iLevel; i++)
			_tprintf(_T("+ "));

		_tprintf(_T("%s\n"), acName);

		return iRet;
	}

	virtual A3DStatus visitLeave(const A3DProductOccurrenceConnector& sConnector) override
	{
		A3DStatus iRet = A3D_SUCCESS;

		// Decrement level
		m_iLevel--;

		iRet = A3DTreeVisitor::visitLeave(sConnector);
		return iRet;
	}
...

Build the project
Verify that Product Occurrence name are displayed in the console

In the above image, we used the Landing Gear model in the sample folder.
"$(HEXCHANGE_INSTALL_DIR)\samples\data\catiaV5\CV5_Landing Gear Model_LandingGear.CATProduct"

Getting component visibility

If you open the Landing_Gear_Assy in HOOPS Demo Viewer (HDV), you will see a component is invisible by default.

The visibility parameter is complex because parent visibility affects the child components. This problem is managed by using a separate visitor (A3DVisitorColorMaterials) in the visitor pattern sample.

These are the following Visitor classes, and multiple visitors can be called via the visitor container.

Flag	Visitor class	Member
CONNECT_TRANSFO	A3DVisitorTransfo	Transform
CONNECT_COLORS	A3DVisitorColorMaterials	Color, material, visibility
CONNECT_MESH	A3DVisitorTessellation	Tessallation
CONNECT_BREP	A3DVisitorBrep	B-rep

Add CONNECT_COLORS to the visitor container

...
#include "visitor/VisitorTree.h"
#include "visitor/VisitorCascadedAttribute.h"
#include "visitor/CascadedAttributeConnector.h"
...
void traverseModelFile(A3DAsmModelFile* pModelFile)
{
	// Prepare Visitor container
	A3DVisitorContainer sA3DVisitorContainer(CONNECT_TRANSFO | CONNECT_COLORS);
	sA3DVisitorContainer.SetTraverseInstance(true);
	...

Add code to access visibility info

...
	virtual A3DStatus visitEnter(const A3DProductOccurrenceConnector& sConnector) override
	{
...
		_tprintf(_T("%s"), acName);

		A3DVisitorColorMaterials *pA3DCascadedVisitor = static_cast<A3DVisitorColorMaterials*>(m_psContainer->GetVisitorByName("CascadedAttribute"));
		if (pA3DCascadedVisitor)
		{
			ColorMaterialsConnector sColorConnector(nullptr);
			pA3DCascadedVisitor->GetColorMaterialConnector(sColorConnector);

			if (sColorConnector.IsShow())
				_tprintf(_T("\n"));
			else
				_tprintf(_T(" (Hidden)\n"));
		}

		return iRet;
	}
...

Build the project
Verify that (Hidden) is added after the Product Occurrence name

Getting instance transformation

You will see in HDV that some components are used multiple times in the assembly model.

Add code to get the transformation of each instance.

The visitor to get a transformation is already assigned to the visitor container.
A3DVisitorContainer sA3DVisitorContainer(CONNECT_TRANSFO | CONNECT_COLORS);

Add an override function of A3DPartConnector and get the part transform

class myTreeVisitor: public A3DTreeVisitor
{
...
	virtual A3DStatus visitEnter(const A3DPartConnector& sConnector) override
	{
		A3DStatus iRet = A3DTreeVisitor::visitEnter(sConnector);
		
		// Get transform connector via transform visitor
		A3DVisitorTransfo* psVisitorTransfo = static_cast<A3DVisitorTransfo*>(m_psContainer->GetVisitorByName("Transformation"));
		A3DTransfoConnector* pConnector = psVisitorTransfo->GetTransfoConnector();
		A3DMatrix4x4 sTransfo;
		pConnector->GetGlobalTransfo(sTransfo);
		delete pConnector;

		for (unsigned int i = 0; i < m_iLevel; i++)
			_tprintf(_T("+ "));

		_tprintf(_T(" (%.3f, %.3f, %.3f)\n"), sTransfo.m_adM[12], sTransfo.m_adM[13], sTransfo.m_adM[14]);

		return iRet;
	}
...

Build the project
Verify that part locations differ by instance

You will see sA3DVisitorContainer.SetTraverseInstance(true) when creating the visitor container. Setting to true causes the visitor to traverse each instance part.

If set to false, just the first part of the instance will be traversed.

If you refer to the Collision sample, you will see the usage of Tree traverse Visitor.

Hence, A3DCollisionCompute requires two Representation Item groups to compute collision, and it is necessary to get a flatten array of Representation Items from the target model file.

A3DFlattenVisitor is a derived class of A3DTreeVisitor and retrieves visible Representation Items, including the identifier and transform overriding visitEnter of A3DPartConnector and A3DRiConnector.