bezier.cpp

wince 画BEZIER曲线的演示例子

#include "stdafx.h"
#include "Bezier.h"

/*****************************************************************************************
 *	FUNCTION    : DrawBeziers                                                            *
 *---------------------------------------------------------------------------------------*
 *	DESCRIPTION : Draws a series of connected Qubic Bezier-splines. They must be connec  *
 *	              ted so that the last point of the bezier is the same as the next ones  *
 *				  first point on the curve												 *
 *	                                                                                     *
 *	ARGUMENT    : CDC* pDC,	The device context where the beziers are drawn				 *
 *				: CPoint* pPoints, The points that make up the beziers					 *
 *				: int nPoints, The number of points on the curve						 *
 *				: int nSegments, How many points are we to compute on each bezier?		 *
 *	RETURN      : void                                                                   *
 ****************************************************************************************/

void DrawBeziers(CDC* pDC, CPoint *pPoints, int nPoints, int nSegments)
{
	VERIFY(pPoints != NULL);
	ASSERT(nSegments > 0);
	
	for(int i = 0; i + 4 <= nPoints; i += 3)
	{
		DrawBezier(pDC, &pPoints[i], nSegments);
	}
}

/*****************************************************************************************
 *	FUNCTION    : DrawBezier                                                             *
 *---------------------------------------------------------------------------------------*
 *	DESCRIPTION : Draws a Qubic bezier-spline based on four control points				 *
 *	                                                                                     *
 *	ARGUMENT    : CDC* pDC,	The device context where the bezier are drawn				 *
 *				: CPoint* pPoints, The points that make up the bezier 					 *
 *				: int nSegments, How many points are we to compute on the bezier?		 *
 *	RETURN      : void                                                                   *
 ****************************************************************************************/
void DrawBezier(CDC *pDC, CPoint *pPoints, int nSegments)
{
	pDC->MoveTo(pPoints[0]);
	fPoint fPointBezier;
	for(int i = 0; i < nSegments; i++)
	{
		BezierComputePoint(i / (float)nSegments, &fPointBezier, pPoints);
		pDC->LineTo(ROUND(fPointBezier.x), ROUND(fPointBezier.y));
	}
	pDC->LineTo(pPoints[3]);
}

/*****************************************************************************************
 *	FUNCTION    : BezierComputePoint                                                     *
 *---------------------------------------------------------------------------------------*
 *	DESCRIPTION : Computes a point on the spline using four blending functions			 *
 *	                                                                                     *
 *	ARGUMENT    : float fU, position on the spline to compute							 *
 *				: fPoint* pDstPoint, The computed point is written here					 *
 *				: CPoint* pSrcPoints, Pointer to the four control points				 *
 *	RETURN      : void                                                                   *
 ****************************************************************************************/
void BezierComputePoint(float fU, fPoint* pDstPoint, CPoint* pSrcPoints)
{
	//	
	//	Add up all the blending functions multiplied with the control points
	//
	float fBlend;
	float f1subu = 1.0f - fU;

	//	
	//	First blending function (1-u)^3
	//	
	fBlend = f1subu * f1subu * f1subu;
	pDstPoint->x = fBlend * pSrcPoints[0].x;
	pDstPoint->y = fBlend * pSrcPoints[0].y;

	//	
	//	Second blending function 3u(1-u)^2
	//
	fBlend = 3 * fU * f1subu * f1subu;
	pDstPoint->x += fBlend * pSrcPoints[1].x;
	pDstPoint->y += fBlend * pSrcPoints[1].y;

	//	
	//	Third blending function 3u^2 * (1-u)
	//
	fBlend = 3 * fU * fU * f1subu;
	pDstPoint->x += fBlend * pSrcPoints[2].x;
	pDstPoint->y += fBlend * pSrcPoints[2].y;

	//	
	//	Fourth blending function u^3
	//	
	fBlend = fU * fU * fU;
	pDstPoint->x += fBlend * pSrcPoints[3].x;
	pDstPoint->y += fBlend * pSrcPoints[3].y;
}