实验4-编码裁剪算法

1、实验4-编码裁剪算法实验4编码裁剪算法1 .实验目的了解二维图形裁剪的原理(点的裁剪、直线的裁剪、多边形的裁剪),利用VC+OpenGL现直线的裁剪算法.2 .实验内容(1)理解直线裁剪的原理(Cohen-Surtherland算法、梁友栋算法)(2)利用VC+OpenG度现直线的编码裁剪算法,在屏幕上用一个封闭矩形裁剪任意一条直线.(3)调试、编译、修改程序.(4)尝试实现梁友栋裁剪算法.实验原理编码裁剪算法中,为了快速判断一条直线段与矩形窗口的位置关系,采用了如下图的空间划分和编码方案.裁剪一条线段时,先求出两端点所在的区号code1和code2,假设code1=0且code2=0,那么说

2、明线段的两个端点均在窗口内,那么整条线段必在窗口内,应取之；假设code1和code2经按位与运算的结果不为0,那么说明两个端点同在窗口的上方、下方、左方或右方.这种情况下,对线段的处理是弃之.如果上述两种条件都不成立,那么按第三种情况处理.求出线段与窗口某边的交点,在交点处把线段一分为二,其中必有一段完全在窗口外,可弃之,对另一段那么重复上述处理.实验代码#include#include#include# defineLEFT_EDGE1# defineRIGHT_EDGE2# defineBOTTOM_EDGE4# defineTOP_EDGE8voidLineGL(intx0,inty0

3、,intx1,inty1)glBegin(GL_LINES);glColor3f(1.0f,0.0f,0.0f);glVertex2f(x0,y0);glColor3f(0.0f,1.0f,0.0f);glVertex2f(x1,y1);glEnd();)structRectanglefloatxmin,xmax,ymin,ymax;);Rectanglerect;intx0,y0,x1,y1;intCompCode?ntx,inty,Rectanglerect)/求端点所在区号intcode=0x00;if(yrect.ymax)code=code|8;/1000上if(xrect.xmax

4、)code=code|2;/0010右if(xrect.xmin)code=code|1;/0001左returncode;)intcohensutherlandlineclip(Rectanglerect,int&x0,int&y0,int&x1,int&y1)intaccept,done;floatx,y;accept=0;done=0;intcode0,code1,codeout;code0=CompCode(x0,y0,rect);code1=CompCode(x1,y1,rect);doif(!(code0|code1)/端点均在视区内accept=1;/取done=1;elseif

5、(code0&code1)/端点在视区外侧x0=y0=x1=y1=0;done=1;accept=1;elseif(code0!=0)codeout=code0;elsecodeout=code1;if(codeout&LEFT_EDGE)y=y0+(y1-y0)*(rect.xmin-x0)/(x1-x0);/直线与视区边界的交点x=(float)rect.xmin;elseif(codeout&RIGHT_EDGE)y=y0+(y1-y0)*(rect.xmax-x0)/(x1-x0);x=(float)rect.xmax;elseif(codeout&BOTTOM_EDGE)x=x0+(

6、x1-x0)*(rect.ymin-y0)/(y1-y0);y=(float)rect.ymin;elseif(codeout&TOP_EDGE)x=x0+(x1-x0)*(rect.ymax-y0)/(y1-y0);y=(float)rect.ymax;if(codeout=code0)x0=x;y0=y;code0=CompCode(x0,y0,rect);elsex1=x;y1=y;code1=CompCode(x1,y1,rect);while(!done);if(accept)LineGL(x0,y0,x1,y1);returnaccept;voidmyDisplay()glClea

7、r(GL_COLOR_BUFFER_BIT);glColor3f(1.0f,0.0f,0.0f);glRectf(rect.xmin,rect.ymin,rect.xmax,rect.ymax);LineGL(x0,y0,x1,y1);glFlush();voidInit()glClearC010r(0.0,0.0,0.0,0.0);glShadeModel(GL_FLAT);rect.xmin=100;rect.ymin=100;rect.xmax=300;rect.ymax=300;x0=0,y0=0,x1=250,y1=86;printf(PresskeyctoClip!nPresske

8、yrtoRestore!n);voidReshape(intw,inth)glViewport(0,0,(GLsizei)w,(GLsizei)h);glMatrixMode(GL_PROJECTION);glLoadIdentity();gluOrtho2D(0.0,(GLdouble)w,0.0,(GLdouble)h);voidkeyboard(unsignedcharkey,intx,inty)switch(key)(casec:cohensutherlandlineclip(rect,x0,y0,x1,y1);glutPostRedisplay();break;caser:Init(

9、);glutPostRedisplay();break;casex:exit(0);break;default:break;intmain(intargc,char*argv口)(glutInit(&argc,argv);glutInitDisplayMode(GLUT_RGB|GLUT_SINGLE);glutInitWindowPosition(100,100);glutInitWindowSize(640,480);glutCreateWindow(HelloWorld!);Init();glutDisplayFunc(myDisplay);glutReshapeFunc(Reshape);glutKeyboardFunc(keyboard);glutMainLoop();return0;实验结果图1裁剪前后图2裁剪前后图3裁剪