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A C++ implementation of Douglas-Peucker Line Approximation Algorithm

, 3 Mar 2003
DP Line approximation algorithm is a well-known method to approximate 2D lines. It is quite fast, O(nlog_2(n)) for a n-points line and can drastically compress a data curve. Here, a fully OOP implementation is given.
// StateGL.cpp: implementation of the CStateGL class.
//
//////////////////////////////////////////////////////////////////////

#include "stdafx.h"
#include "StateGL.h"

#ifdef _DEBUG
#undef THIS_FILE
static char THIS_FILE[]=__FILE__;
#define new DEBUG_NEW
#endif


IMPLEMENT_SERIAL(CStateGL,CObject,1);

#ifdef _DEBUG
void CStateGL::AssertValid() const
{
    // call inherited AssertValid first
    CObject::AssertValid();

    // check CStateGL members...
	ASSERT((m_iPolygonMode==GL_POINT) ||
		(m_iPolygonMode==GL_LINE) ||
		(m_iPolygonMode==GL_FILL));
}

void CStateGL::Dump( CDumpContext& ch ) const
{
    // call base class function first
    CObject::Dump( ch );

    // now do the stuff for our specific class
	ch<<_T("--- CStateGL Object ---\n");
} 
#endif

void CStateGL::Serialize( CArchive& archive )
{
    // call base class function first
    // base class is CObject in this case
    CObject::Serialize( archive );
	
    // now do the stuff for our specific class
    if (archive.IsStoring())
	{
		archive<<m_bAntialias
			<<m_bBackFaceCulling
			<<m_bBlending
			<<m_bGouraud
			<<m_bLighting
			<<m_bLineStipple
			<<m_bDepthTest
			<<m_bStencilTest
			<<m_cBkgColor
			<<m_fLineWidth
			<<m_iPolygonMode;
	}
    else
	{
		archive>>m_bAntialias
			>>m_bBackFaceCulling
			>>m_bBlending
			>>m_bGouraud
			>>m_bLighting
			>>m_bLineStipple
			>>m_bDepthTest
			>>m_bStencilTest
			>>m_cBkgColor
			>>m_fLineWidth
			>>m_iPolygonMode;
	}

	// state need resetting
}

//////////////////////////////////////////////////////////////////////
// Construction/Destruction
//////////////////////////////////////////////////////////////////////

CStateGL::CStateGL()
{
	m_bPostSetState=TRUE;

	m_bAntialias=TRUE;
	m_bBackFaceCulling=TRUE;
	m_bBlending=TRUE;
	m_bDepthTest=TRUE;
	m_bStencilTest=FALSE;
	m_bLighting=TRUE;
	m_bLineStipple=FALSE;
	m_bGouraud=TRUE;
	m_fLineWidth=2;
	m_iPolygonMode=GL_FILL;
	m_cBkgColor=CVector3(1.0f,1.0f,1.0f);
}

CStateGL::CStateGL(const CStateGL &sgl)
{
	m_bPostSetState=TRUE;

	m_bAntialias=sgl.m_bAntialias;
	m_bBackFaceCulling=sgl.m_bBackFaceCulling;
	m_bBlending=sgl.m_bBlending;
	m_bDepthTest=sgl.m_bDepthTest;
	m_bStencilTest=sgl.m_bStencilTest;
	m_bLighting=sgl.m_bLighting;
	m_bLineStipple=sgl.m_bLineStipple;
	m_bGouraud=sgl.m_bGouraud;
	m_fLineWidth=sgl.m_fLineWidth;
	m_iPolygonMode=sgl.m_iPolygonMode;
	m_cBkgColor=sgl.m_cBkgColor;
}

CStateGL& CStateGL::operator =(const CStateGL &sgl)
{
	if (&sgl!=this)
	{
		m_bPostSetState=TRUE;

		m_bAntialias=sgl.m_bAntialias;
		m_bBackFaceCulling=sgl.m_bBackFaceCulling;
		m_bBlending=sgl.m_bBlending;
		m_bDepthTest=sgl.m_bDepthTest;
		m_bStencilTest=sgl.m_bStencilTest;
		m_bLighting=sgl.m_bLighting;
		m_bLineStipple=sgl.m_bLineStipple;
		m_bGouraud=sgl.m_bGouraud;
		m_iPolygonMode=sgl.m_iPolygonMode;
		m_cBkgColor=sgl.m_cBkgColor;
	}
	return *this;
}

CStateGL::~CStateGL()
{

}

BOOL CStateGL::GetStateFromDC()
{
	return TRUE;
}

void CStateGL::SetStateGL()
{
	if (!m_bPostSetState)
		return;
	m_bPostSetState=FALSE;

	// ok setting state
	glPolygonMode(GL_FRONT_AND_BACK, m_iPolygonMode);

	// Culling
	glDrawBuffer(GL_BACK);

	if (m_bBackFaceCulling)
	{
		glCullFace(GL_BACK);
		glEnable(GL_CULL_FACE);
	}
	else
		glDisable(GL_CULL_FACE);

	// lighing
	if (m_bLighting)
		glEnable(GL_LIGHTING);
	else
		glDisable(GL_LIGHTING);

	// gouraud
	if (m_bGouraud)
		glShadeModel(GL_SMOOTH);
	else
		glShadeModel(GL_FLAT);

	// background color
	glClearColor(m_cBkgColor.x, m_cBkgColor.y, m_cBkgColor.z, 0.0f);

	// depth test
	if (m_bDepthTest)
		glEnable(GL_DEPTH_TEST);
	else
		glDisable(GL_DEPTH_TEST);

	// antialiasing
	if (m_bAntialias)
	{
		glEnable(GL_LINE_SMOOTH);
		glHint(GL_LINE_SMOOTH_HINT,GL_NICEST);
//		glEnable(GL_POLYGON_SMOOTH);
//		glHint(GL_POLYGON_SMOOTH_HINT,GL_NICEST);
	}
	else
	{
		glDisable(GL_LINE_SMOOTH);
//		glDisable(GL_POLYGON_SMOOTH);
	}

	// blending
	if (m_bBlending)
	{
		glEnable(GL_BLEND);
		glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
	}
	else
	{
		glDisable(GL_BLEND);
	}

	glLineWidth(m_fLineWidth);
	// line stipple
	glLineStipple(2,0x9999);

	if (m_bLineStipple)
		glEnable(GL_LINE_STIPPLE);	
	else
		glDisable(GL_LINE_STIPPLE);	
}

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About the Author

Jonathan de Halleux
Engineer
United States United States
Jonathan de Halleux is Civil Engineer in Applied Mathematics. He finished his PhD in 2004 in the rainy country of Belgium. After 2 years in the Common Language Runtime (i.e. .net), he is now working at Microsoft Research on Pex (http://research.microsoft.com/pex).

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