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Posted 3 Jan 2002

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.h: interface for the CStateGL class.

#if !defined(AFX_STATEGL_H__3EA79A79_DA8C_45B6_A6BE_12B1BB386762__INCLUDED_)
#define AFX_STATEGL_H__3EA79A79_DA8C_45B6_A6BE_12B1BB386762__INCLUDED_

#if _MSC_VER > 1000
#pragma once
#endif // _MSC_VER > 1000

#include "Vector3.h"

class CStateGL : public CObject  
	CStateGL(const CStateGL& sgl);
	CStateGL& operator =(const CStateGL &sgl);
	virtual ~CStateGL();

	BOOL GetStateFromDC();
	/// ask for state updating at next draw operation
	void PostSetState()
	{	m_bPostSetState=TRUE;};
	/// ask for state updating at next draw operation
	BOOL NeedSetState()
	{	return m_bPostSetState;};
	/// updates the OpenGL states (context must be valid)
	void SetStateGL();

	// antialiasing
	BOOL GetAntialias() const
	{	return m_bAntialias;};
	void SetAntialias(BOOL _aa=TRUE)
	{	m_bAntialias=_aa;	m_bPostSetState=TRUE;};

	// BackFaceCulling
	BOOL GetBackFaceCulling() const
	{	return m_bBackFaceCulling;};
	void SetBackFaceCulling(BOOL _bc=TRUE)
	{	m_bBackFaceCulling=_bc;	m_bPostSetState=TRUE;};

	// blending
	BOOL GetBlending() const
	{	return m_bBlending;};
	void SetBlending(BOOL _b=TRUE)
	{	m_bBlending=_b;	m_bPostSetState=TRUE;};

	// DepthTest
	BOOL GetDepthTest() const
	{	return m_bDepthTest;};
	void SetDepthTest(BOOL _dt=TRUE)
	{	m_bDepthTest=_dt;	m_bPostSetState=TRUE;};

	// StencilTest
	BOOL GetStencilTest() const
	{	return m_bStencilTest;};
	void SetStencilTest(BOOL _st=TRUE)
	{	m_bStencilTest=_st;	m_bPostSetState=TRUE;};

	// Lighting
	BOOL GetLighting() const
	{	return m_bLighting;};
	void SetLighting(BOOL _l=TRUE)
	{	m_bLighting=_l;	m_bPostSetState=TRUE;};

	// Gouraud
	BOOL GetGouraud() const
	{	return m_bGouraud;};
	void SetGouraud(BOOL _g=TRUE)
	{	m_bGouraud=_g;	m_bPostSetState=TRUE;};

	// LineWidth
	GLfloat GetLineWidth() const
	{	return m_fLineWidth;};
	void SetLineWidth(GLfloat _lw=1.5f)
	{	m_fLineWidth=(GLfloat)__max(0.0,_lw);	m_bPostSetState=TRUE;};

	// LineStipple
	BOOL GetLineStipple() const
	{	return m_bLineStipple;};
	void SetLineStipple(BOOL _ls=FALSE)
	{	m_bLineStipple=_ls;	m_bPostSetState=TRUE;};

	// Polygon mode
	GLint GetPolygonMode() const
	{	return m_iPolygonMode;};
	void SetPolygonMode(int _pm=GL_FILL)
	{	ASSERT((_pm==GL_POINT) ||
		(_pm==GL_LINE) ||
		m_iPolygonMode=_pm; m_bPostSetState=TRUE;

	// Background color
	const CVector3& GetBkgColor() const
	{	return m_cBkgColor;};
	void SetBkgColor(const CVector3& _bc)
	{	m_cBkgColor=_bc;	m_bPostSetState=TRUE;};

	/// Debugging stuff
#ifdef _DEBUG
    virtual void AssertValid() const;    // Override
    virtual void Dump( CDumpContext& dc ) const;
    /// Serialization
    void Serialize( CArchive& archive );

	BOOL m_bPostSetState;

	BOOL m_bAntialias;
	BOOL m_bBlending;
	BOOL m_bLighting;
	BOOL m_bLineStipple;
	BOOL m_bGouraud;
	BOOL m_bDepthTest;
	BOOL m_bBackFaceCulling;
	BOOL m_bStencilTest;
	GLfloat m_fLineWidth;
	GLint m_iPolygonMode; 
	CVector3 m_cBkgColor;

#endif // !defined(AFX_STATEGL_H__3EA79A79_DA8C_45B6_A6BE_12B1BB386762__INCLUDED_)

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About the Author

Jonathan de Halleux
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 (

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