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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.
// CViewGL2D1.cpp: implementation of the CViewGL2D class.
//
//////////////////////////////////////////////////////////////////////

#include "StdAfx.h"
#include "ViewGL2D.h"


IMPLEMENT_SERIAL(CViewGL2D,CViewGL,1);

#ifdef _DEBUG
void CViewGL2D::AssertValid() const
{
    // call inherited AssertValid first
    CViewGL::AssertValid();

    // check CViewGL2D members...
}

void CViewGL2D::Dump( CDumpContext& ch ) const
{
    // call base class function first
    CViewGL::Dump( ch );

    // now do the stuff for our specific class
	ch<<_T("--- CViewGL2D Object ---\n");
} 
#endif

void CViewGL2D::Serialize( CArchive& archive )
{
    // call base class function first
    // base class is CObject in this case
    CViewGL::Serialize( archive );
	
    // now do the stuff for our specific class
    if (archive.IsStoring())
	{
		archive<<m_dLeft<<m_dRight<<m_dTop<<m_dBottom;
	}
    else
	{
		archive>>m_dLeft>>m_dRight>>m_dTop>>m_dBottom;
	}
}

CViewGL2D::CViewGL2D(GLdouble _dLeft,GLdouble _dRight, GLdouble _dTop,GLdouble _dBottom)
: CViewGL()
{
	m_dLeft=_dLeft;
	m_dRight=_dRight;
	m_dTop=_dTop;
	m_dBottom=_dBottom;

	// setting standard state
	m_StateGL.SetAntialias(TRUE);
	m_StateGL.SetBlending(TRUE);
	m_StateGL.SetBackFaceCulling(FALSE);
	m_StateGL.SetBkgColor(CVector3(1.0f,1.0f,1.0f));
	m_StateGL.SetDepthTest(FALSE);
	m_StateGL.SetStencilTest(FALSE);
	m_StateGL.SetLighting(FALSE);
	m_StateGL.SetPolygonMode(GL_LINE);
	m_StateGL.SetGouraud(TRUE);
	m_StateGL.SetLineStipple(FALSE);
}


CViewGL2D::CViewGL2D(const CViewGL2D &v2D)
: CViewGL(v2D)
{
	m_dLeft=v2D.m_dLeft;
	m_dRight=v2D.m_dRight;
	m_dTop=v2D.m_dTop;
	m_dBottom=v2D.m_dBottom;
}

CViewGL2D& CViewGL2D::operator =(const CViewGL2D &v2D)
{
	// preventing self copying
	if (&v2D!=this)
	{
		// invoke CPGLSurface copy assignement operator
		this->CViewGL::operator=(v2D);

		m_dLeft=v2D.m_dLeft;
		m_dRight=v2D.m_dRight;
		m_dTop=v2D.m_dTop;
		m_dBottom=v2D.m_dBottom;
	}

	return *this;
}

void CViewGL2D::Reshape()
{
	// stop if the view don't need reshaping...
	if (!NeedReshape())
		return;

	// intialize projection and model matrices
	glViewport(m_iTx,m_iTy,m_iWidth,m_iHeight);
 	glMatrixMode(GL_PROJECTION);
		glLoadIdentity();
		glOrtho(m_dLeft,m_dRight,m_dBottom,m_dTop,-1,1);
	glMatrixMode(GL_MODELVIEW);
		glLoadIdentity();

	// Calling base class function
	CViewGL::Reshape();

	// flushing instructions
	glFinish();
}


void CViewGL2D::InitGLState()
{
	if (!m_StateGL.NeedSetState())
		return;
	
	CViewGL::InitGLState();

	glDisable(GL_POLYGON_OFFSET_FILL);	
	glDisable(GL_POLYGON_OFFSET_LINE);	

	glDisable(GL_NORMALIZE);

	glFinish();
}

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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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