计算机图形学实验报告实验2裁剪算法实验

一、实验目的：

直线段的裁剪：编码裁剪算法，中点分割裁剪算法。

二、实验内容：

//BasicGraph.cpp

//请将下列裁剪程序补充完整，并用注释说明是何种裁剪算法

void Encode (int x,int y,int *code,int XL,int XR,int YB,int YT) {

//请将此程序补充完整

int c=0;

if(x

else if(x>XR) c=c|RIGHT;

if(y

else if(y>YT) c=c|TOP;

(*code)=c;

}

//编码裁剪算法：

void C_S_Line(POINT &p1,POINT &p2,int XL,int XR,int YB,int YT) {

//请将此程序补充完整

int x1,x2,y1,y2,x,y,code1,code2,code;

x1=p1.x; x2=p2.x; y1=p1.y; y2=p2.y;

Encode(x1,y1,&code1,XL,XR,YB,YT);

Encode(x2,y2,&code2,XL,XR,YB,YT);

while(code1!=0||code2!=0)

{

if((code1&code2)!=0) return;

code=code1;

if(code1==0) code=code2;

if((LEFT&code)!=0)

{x=XL;y=y1+(y2-y1)*(XL-x1)/(x2-x1);}

else if((RIGHT&code)!=0)

{x=XR;y=y1+(y2-y1)*(XR-x1)/(x2-x1);}

if((BOTTOM&code)!=0)

{y=YB;x=x1+(x2-x1)*(YB-y1)/(y2-y1);}

else if((TOP&code)!=0)

{y=YT;x=x1+(x2-x1)*(YT-y1)/(y2-y1);}

if(code==code1)

{x1=x;y1=y;Encode(x,y,&code1,XL,XR,YB,YT);}

else

{x2=x;y2=y;Encode(x,y,&code2,XL,XR,YB,YT);}

}

p1.x=x1;p1.y=y1;p2.x=x2;p2.y=y2;

}

int IsInArea(POINT point,int XL,int XR,int YB,int YT)

{

//请将此程序补充完整

if(point.x>=XL && point.x<=XR && point.y>YB && point.y

else return 0;

}

int NotIntersect(POINT begin,POINT end,int XL,int XR,int YB,int YT) {

//请将此程序补充完整

int maxx,maxy,minx,miny;

maxx=(begin.x>end.x)?begin.x:end.x;

minx=(begin.x

maxy=(begin.y>end.y)?begin.y:end.y;

miny=(begin.y

if(maxxXR||maxyYT) return 1;

else return 0;

}

//中点裁剪算法：

POINT ClipMid(POINT begin,POINT end,int XL,int XR,int YB,int YT)

{

//请将此程序补充完整

POINT mid,temp;

if(IsInArea(begin,XL,XR,YB,YT)) temp=begin;

else if(NotIntersect(begin,end,XL,XR,YB,YT)) temp=begin;

else

{

mid.x=(begin.x+end.x)/2;mid.y=(begin.y+end.y)/2;

if(abs(mid.x-end.x)<=1&& abs(mid.y-end.y)<=1) temp=mid;

else

{

if(NotIntersect(begin,mid,XL,XR,YB,YT))

temp=ClipMid(mid,end,XL,XR,YB,YT);

else

temp=ClipMid(begin,mid,XL,XR,YB,YT);

}

}

return temp;

}

//Liang-Barsky直线裁剪算法：

void ClipParameter(POINT &p1,POINT &p2,int XL,int XR,int YB,int YT) {

float u1=0.0,u2=1.0;

float dx=p2.x-p1.x,dy=p2.y-p1.y;

if(clipTest(-dx,p1.x-XL,&u1,&u2))

if(clipTest(dx,XR-p1.x,&u1,&u2))

if(clipTest(-dy,p1.y-YB,&u1,&u2))

if(clipTest(dy,YT-p1.y,&u1,&u2))

{

if(u2<1.0)

{

p2.x=p1.x+u2*dx;

p2.y=p1.y+u2*dy;

}

if(u1>0.0)

{

p1.x=p1.x+u1*dx;

p1.y=p1.y+u1*dy;

}

}

}

int clipTest(float p,float q,float *u1,float *u2)

{

float r;

int remainFlag=1;

if(p<0.0)

{

r=q/p;

if(r>*u2) remainFlag=0;

else if(r>*u1) *u1=r;

}

else if(p>0.0)

{

r=q/p;

if(r<*u1) remainFlag=0;

else if(r<*u2) *u2=r;

}

else //*p=0

if(q<0.0) remainFlag=0;

return remainFlag;

}

//逐边裁剪算法：

//typedef struct tRes { int yes,isIn; POINT pout;} Res;

Res TestIntersect(int edge,int type,POINT p1,POINT p2)

{//判断p2是否在所裁剪的窗边edge的内侧，是否与p1点分别在窗边edge的异侧

float dx,dy,m;

Res res;int isIn=0,yes=0;POINT pout;

dy=p2.y-p1.y;dx=p2.x-p1.x;m=dy/dx;

switch(type)

{

case 1: /*right*/

if(p2.x<=edge){isIn=1;if(p1.x>edge)yes=1;}

else if(p1.x<=edge)yes=1;break;

case 2: /*bottom*/

if(p2.y>=edge){isIn=1;if(p1.y

else if(p1.y>=edge)yes=1;break;

case 3: /*left*/

if(p2.x>=edge){isIn=1;if(p1.x

else if(p1.x>=edge)yes=1;break;

case 4: /*top*/

if(p2.y<=edge){isIn=1;if(p1.y>edge)yes=1;}

else if(p1.y<=edge)yes=1;

default: break;

}

if(yes)

{

if((type==1) || (type==3))

{ pout.x=edge;pout.y=p1.y+m*(pout.x-p1.x);}

if((type==2) || (type==4))

{ pout.y=edge;pout.x=p1.x+(pout.y-p1.y)/m;}

}

res.isIn=isIn;res.yes=yes;res.pout=pout;

return res;

}

int clipSingleEdge(int edge,int type,int nin,POINT pin[50],POINT pout[50])

/*对多边形pin与窗边edge进行裁剪，返回裁剪后的多边形pout及点数*/ {

int i,k=0;POINT p;Res res;

p.x=pin[nin-1].x;p.y=pin[nin-1].y;

for(i=0;i

{

res=TestIntersect(edge,type,p,pin[i]);

if(res.yes)

{ pout[k].x=res.pout.x;pout[k].y=res.pout.y;k++;} if(res.isIn)

{ pout[k].x=pin[i].x;pout[k].y=pin[i].y;k++;}

p.x=pin[i].x;p.y=pin[i].y;

}

return k;

}

void ClipEdgePolygon(POINT ps[50],int &n,int XL,int XR,int YB,int YT) { /*对多边形ps进行逐边裁剪*/

int n1=0,n2=0;

POINT pt[50];

n1=clipSingleEdge(XR,1,n,ps,pt);

n2=clipSingleEdge(YB,2,n1,pt,ps);

n1=clipSingleEdge(XL,3,n2,ps,pt);

n2=clipSingleEdge(YT,4,n1,pt,ps);

n=n2;

}

//多边形编码裁剪算法：

void ClipEncodePolygon(POINT ps[50],int &n,int XL,int XR,int YB,int YT) {

POINT tp[50];

int k=0,m;

int code1,code2,code;

int x,y;

for(int i=0;i

{

Encode(ps[i].x,ps[i].y,&code1,XL,XR,YB,YT);

Encode(ps[i+1].x,ps[i+1].y,&code2,XL,XR,YB,YT);

code=code1;m=i;

for(int j=0;j<2;j++)

{

if((code1 & code2)!=0) //线段两端都在窗口外的同一侧

{

switch(code)

{

case 1:x=XL;y=ps[m].y;break;

case 2:x=XR;y=ps[m].y;break;

case 4:x=ps[m].x;y=YB;break;

case 5:x=XL;y=YB;break;

case 6:x=XR;y=YB;break;

case 8:x=ps[m].x;y=YT;break;

case 9:x=XL;y=YT;break;

case 10:x=XR;y=YT;break;

}

tp[k].x=x;tp[k].y=y;k++;

}

else if((code1 & code2)==0) //线段两端不在窗口的同一侧

{

if(code==0)

{

tp[k]=ps[m];k++;

}

else if ((LEFT & code) !=0) //线段与左边界相交 {

x=XL;

y=ps[i].y+(ps[i+1].y-ps[i].y)*(XL-ps[i].x)/(ps[i+1].x-ps[i].x);

if(y>YB && y

}

else if((TOP & code)!=0) //线段与上边界相交

{

y=YT;

x=ps[i].x+(ps[i+1].x-ps[i].x)*(YT-ps[i].y)/(ps[i+1].y-ps[i].y);

if(x>XL && x

}

else if((RIGHT & code)!=0) //线段与右边界相交 {

x=XR;

y=ps[i].y+(ps[i+1].y-ps[i].y)*(XR-ps[i].x)/(ps[i+1].x-ps[i].x);

if(y>YB && y

}

else if((BOTTOM & code) != 0) //线段与下边界相交 {

y=YB;

x=ps[i].x+(ps[i+1].x-ps[i].x)*(YB-ps[i].y)/(ps[i+1].y-ps[i].y);

if(x>XL && x

}

}

code=code2;m++;

}//for(j)

}//for(i)

for(i=0;i

ps[i]=tp[i];

n=k;

}

//函数的调用，裁剪窗口的调整

//DrawView.cpp文件

//裁剪窗口的调整

CDrawView::CDrawView()

{

/************请在此函数中将裁剪窗口大小调整为长度100单位像素，宽度50单位像素的矩形********/

// TODO: add construction code here

//

m_pWidth=1;

m_pStyle=PEN_STYLE_SOLID;

m_pColor=RGB(0,0,0);

m_FFlag=0;

m_FColor=RGB(0,0,0);

m_HFlag=0;

CurrentDraw=DRAW_VCLINE;

m_Num=0;

m_Drag=0;

m_HCursor=AfxGetApp()->LoadStandardCursor(IDC_CROSS);

//

DrawType=0;

ClipFlag=0;

ClipType=-1;

XL=200;XR=300;YB=150;YT=200;

//XL=200;XR=500;YB=150;YT=400;

ClipWindowColor=RGB(192,192,50);

}

void CDrawView::OnDraw(CDC* pDC)

{

CDrawDoc* pDoc = GetDocument();

ASSERT_VALID(pDoc);

// TODO: add draw code for native data here

if(ClipFlag)

{

CPen NewPen,*pOldPen;

NewPen.CreatePen(PS_DASH,1,ClipWindowColor);

pOldPen=pDC->SelectObject(&NewPen);

pDC->MoveTo(XL,YB);

pDC->LineTo(XR,YB);

pDC->LineTo(XR,YT);

pDC->LineTo(XL,YT);

pDC->LineTo(XL,YB);

}

int index;

index=pDoc->GetShapeNumber();

for(int i=0;i

pDoc->GetShape(i)->Drawing(pDC);

}

void CDrawView::OnInitialUpdate()

{

CSize sizeTotal;

sizeTotal.cx = 640; sizeTotal.cy = 480;

SetScrollSizes(MM_TEXT, sizeTotal);

// TODO: Add your specialized code here and/or call the base class }

void CDrawView::OnLButtonDown(UINT nFlags, CPoint point)

{

// TODO: Add your message handler code here and/or call default

CClientDC dc(this);

OnPrepareDC(&dc);

dc.DPtoLP(&point);

m_pPrev=point;

m_pOrigin=point; //点击鼠标左键作为拖动绘图的第一点

m_Drag=1;

SetCapture();

RECT rect;

GetClientRect(&rect);

ClientToScreen(&rect);

ClipCursor(&rect);

CScrollView::OnLButtonDown(nFlags, point);

}

//函数调用处

void CDrawView::OnLButtonUp(UINT nFlags, CPoint point)

{

// TODO: Add your message handler code here and/or call default

if(m_Drag)

{

m_Drag=0;

ReleaseCapture();

ClipCursor(NULL);

CDrawDoc *pDoc=GetDocument();

CShape *pShape;

POINT p1,p2;

if(CurrentDraw==DRAW_VCLINE || CurrentDraw==DRAW_DDALINE ||

CurrentDraw==DRAW_MIDLINE || CurrentDraw==DRAW_BSHLINE)

{

if(ClipFlag)

{

switch(ClipType)

{

/****************编码裁剪函数调用处*************/

case CLIP_ENCODE:C_S_Line(m_pOrigin,m_pPrev,XL,XR,YB,YT); break; /****************中点分割裁剪函数调用处************/

case CLIP_MIDPOINT: ClipMid(m_pPrev,m_pOrigin,XL,XR,YB,YT);

p1=ClipMid(m_pPrev,m_pOrigin,XL,XR,YB,YT);

p2=ClipMid(m_pOrigin,m_pPrev,XL,XR,YB,YT);

m_pOrigin=p1;m_pPrev=p2;

break;

case CLIP_PARAMETER:ClipParameter(m_pOrigin,m_pPrev,XL,XR,YB,YT);

break;

}

}

pShape=new

CLine(m_pOrigin,m_pPrev,m_pWidth,m_pStyle,m_pColor,DrawType);

pDoc->AddShape(pShape);

}

if(CurrentDraw==DRAW_RECTANGLE)

{

if(ClipType==CLIP_WINDOW)

{

XL=m_pOrigin.x;XR=m_pPrev.x;

YB=m_pOrigin.y;YT=m_pPrev.y;

}

else

{

pShape=new

CRectangle(m_pOrigin,m_pPrev,m_pWidth,m_pStyle,m_pColor,

m_FFlag,m_FColor,m_HFlag,m_Hatch);

pDoc->AddShape(pShape);

}

}

if( CurrentDraw==DRAW_VCCIRCLE || CurrentDraw==DRAW_MIDCIRCLE || CurrentDraw==DRAW_BSHCIRCLE)

{

pShape=new

CCircle(m_pOrigin,m_pPrev,m_pWidth,m_pStyle,m_pColor,

m_FFlag,m_FColor,m_HFlag,m_Hatch,DrawType);

pDoc->AddShape(pShape);

}

if(CurrentDraw==DRAW_VCELLIPSE || CurrentDraw==DRAW_MIDELLIPSE) {

pShape=new

CEllipse(m_pOrigin,m_pPrev,m_pWidth,m_pStyle,m_pColor,

m_FFlag,m_FColor,m_HFlag,m_Hatch,DrawType);

pDoc->AddShape(pShape);

}

pDoc->UpdateAllViews(NULL);

}

CScrollView::OnLButtonUp(nFlags, point);

}

三实验结果：

四、实验总结

通过这次试验使我了解到如何运用计算机程序对窗口进行剪裁，了解到编码剪裁算法直观方便，速度较快，中点分割剪裁算法不用进行乘除运算，剪裁效率高,Liang-Barsky直线裁剪算法更快。