Draw a straight line with any slope in computer graphics (1)

Qing Dujun

Address: http://blog.csdn.net/qingdujun/article/details/40025917

This article demonstrates how to write a line function (filled with pixels) by yourself to draw a line of any slope.

1) Create CP2 class

Header file: p2.h

// P2.h: interface for the CP2 class.////////////////////////////////////////////////////////////////////////#if !defined(AFX_P2_H__85E77AD6_0704_4E12_8E74_5BE1744B3154__INCLUDED_)#define AFX_P2_H__85E77AD6_0704_4E12_8E74_5BE1744B3154__INCLUDED_#if _MSC_VER > 1000#pragma once#endif // _MSC_VER > 1000//二维点类class CP2  {public:CP2();CP2(double x,double y);virtual ~CP2();public:         //方便访问，直接定义为共有double x;double y;};#endif // !defined(AFX_P2_H__85E77AD6_0704_4E12_8E74_5BE1744B3154__INCLUDED_)

Implementation file: p2.cpp

// P2.cpp: implementation of the CP2 class.////////////////////////////////////////////////////////////////////////#include "stdafx.h"#include "DrawLine.h"#include "P2.h"#ifdef _DEBUG#undef THIS_FILEstatic char THIS_FILE[]=__FILE__;#define new DEBUG_NEW#endif//////////////////////////////////////////////////////////////////////// Construction/Destruction//////////////////////////////////////////////////////////////////////CP2::CP2(){x=0.0;y=0.0;}CP2::CP2(double x,double y){this->x=x;this->y=y;}CP2::~CP2(){}

2) create a cline class

Header file: line. h

// Line.h: interface for the CLine class.////////////////////////////////////////////////////////////////////////#if !defined(AFX_LINE_H__8A91E283_F40D_4086_8BB8_7A9D9A6DB4D5__INCLUDED_)#define AFX_LINE_H__8A91E283_F40D_4086_8BB8_7A9D9A6DB4D5__INCLUDED_#if _MSC_VER > 1000#pragma once#endif // _MSC_VER > 1000#include "P2.h"class CLine  {public:CLine();virtual ~CLine();void MoveTo(CP2 p0);          //移动到指定位置void MoveTo(double x, double y);void LineTo(CP2 p1, CDC *pDC);    //绘制直线，不含终点void LineTo(double x, double y, CDC *pDC);private:CP2 P0;      //起点CP2 P1;      //终点};#endif // !defined(AFX_LINE_H__8A91E283_F40D_4086_8BB8_7A9D9A6DB4D5__INCLUDED_)

Implementation file: line. cpp

// Line.cpp: implementation of the CLine class.////////////////////////////////////////////////////////////////////////#include "stdafx.h"#include "DrawLine.h"#include "Line.h"#include "math.h"#define Round(d) int(floor(d+0.5))//四舍五入宏定义#ifdef _DEBUG#undef THIS_FILEstatic char THIS_FILE[]=__FILE__;#define new DEBUG_NEW#endif//////////////////////////////////////////////////////////////////////// Construction/Destruction//////////////////////////////////////////////////////////////////////CLine::CLine(){}CLine::~CLine(){}void CLine::MoveTo(CP2 p0) //记录直线起点函数{P0=p0;}void CLine::MoveTo(double x, double y){P0.x = x;P0.y = y;}void CLine::LineTo(double x, double y, CDC *pDC) //绘制{CP2 p;p.x = x;p.y = y;LineTo(p, pDC);}void CLine::LineTo(CP2 p1, CDC *pDC){P1=p1;CP2 p,t;COLORREF clr = RGB(0,0,0);  //黑色像素点if(fabs(P0.x-P1.x)<1e-6)    //绘制垂线{if(P0.y>P1.y)           //交换顶点,使得起始点低于终点{t=P0;P0=P1;P1=t;}for(p=P0;p.y<P1.y;p.y++)  //执行绘制，填充像素点{pDC->SetPixelV(Round(p.x),Round(p.y),clr);}}else{double k,d;k=(P1.y-P0.y)/(P1.x-P0.x); //斜率if(k>1.0) //绘制k>1（y为主方向）{if(P0.y>P1.y){t=P0;P0=P1;P1=t;}d=1-0.5*k;    //中点初始值for(p=P0;p.y<P1.y;p.y++){pDC->SetPixelV(Round(p.x),Round(p.y), clr);                if(d>=0)  //中点位于将绘制点上方，填充下方点{p.x++;d=d+1-k;    //递推公式:当d>=0时，d(i+1)=d(i)+1-k;}else                     d+=1;       }}if(0.0<=k && k<=1.0) //绘制0<=k<=1（x为主方向）{if(P0.x>P1.x){t=P0;P0=P1;P1=t;}d=0.5-k;     //中点初始值for(p=P0;p.x<P1.x;p.x++){pDC->SetPixelV(Round(p.x),Round(p.y), clr);                if(d<0)  //中点位于将绘制点下方，填充上方点{p.y++;d=d+1-k; //递推公式:当d<0时，d(i+1)=d(i)+1-k;}else d-=k;}}if(k>=-1.0 && k<0.0)//绘制-1<=k<0（x为主方向）{if(P0.x>P1.x){t=P0;P0=P1;P1=t;}d=-0.5-k;        //中点初始化            for(p=P0;p.x<P1.x;p.x++){pDC->SetPixelV(Round(p.x),Round(p.y), clr);                if(d>0)      //中点位于将绘制点上方，填充下方点{p.y--;d=d-1-k; //递推公式:当d>0时，d(i+1)=d(i)-1-k;}else d-=k;}}if(k<-1.0)//绘制k<-1 （y为主方向）{if(P0.y<P1.y){t=P0;P0=P1;P1=t;}d=-1-0.5*k; //中点初始化for(p=P0;p.y>P1.y;p.y--){pDC->SetPixelV(Round(p.x),Round(p.y), clr);                if(d<0) //中点位于将绘制点下方，填充上方点{p.x++;d=d-1-k;//递推公式:当d>0时，d(i+1)=d(i)-1-k;}else d-=1;           }}}P0=p1;  //将终点赋值给起点}

3) ondraw Function

void CDrawLineView::OnDraw(CDC* pDC){CDrawLineDoc* pDoc = GetDocument();ASSERT_VALID(pDoc);// TODO: add draw code for native data here//绘制直线CLine *line=new CLine;//动态创建直线绘制类对象line->MoveTo(100,100);line->LineTo(500,500, pDC);}

4) The rendering effect is as follows:

Address: http://blog.csdn.net/qingdujun/article/details/40025917

References: tutorial on basic computer graphics (Visual C ++) (2nd) by Kong lingde

draw a straight line with any slope in computer graphics (1)