實(shí)驗(yàn)4-編碼裁剪算法

1、實(shí)驗(yàn)4-編碼裁剪算法實(shí)驗(yàn)4編碼裁剪算法1 .實(shí)驗(yàn)?zāi)康牧私舛S圖形裁剪的原理(點(diǎn)的裁剪、直線的裁剪、多邊形的裁剪),利用VC+OpenGL現(xiàn)直線的裁剪算法.2 .實(shí)驗(yàn)內(nèi)容(1)理解直線裁剪的原理(Cohen-Surtherland算法、梁友棟算法)(2)利用VC+OpenG度現(xiàn)直線的編碼裁剪算法,在屏幕上用一個(gè)封閉矩形裁剪任意一條直線.(3)調(diào)試、編譯、修改程序.(4)嘗試實(shí)現(xiàn)梁友棟裁剪算法.實(shí)驗(yàn)原理編碼裁剪算法中,為了快速判斷一條直線段與矩形窗口的位置關(guān)系,采用了如下圖的空間劃分和編碼方案.裁剪一條線段時(shí),先求出兩端點(diǎn)所在的區(qū)號(hào)code1和code2,假設(shè)code1=0且code2=0,那么說(shuō)

2、明線段的兩個(gè)端點(diǎn)均在窗口內(nèi),那么整條線段必在窗口內(nèi),應(yīng)取之；假設(shè)code1和code2經(jīng)按位與運(yùn)算的結(jié)果不為0,那么說(shuō)明兩個(gè)端點(diǎn)同在窗口的上方、下方、左方或右方.這種情況下,對(duì)線段的處理是棄之.如果上述兩種條件都不成立,那么按第三種情況處理.求出線段與窗口某邊的交點(diǎn),在交點(diǎn)處把線段一分為二,其中必有一段完全在窗口外,可棄之,對(duì)另一段那么重復(fù)上述處理.實(shí)驗(yàn)代碼#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)/求端點(diǎn)所在區(qū)號(hào)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)/端點(diǎn)均在視區(qū)內(nèi)accept=1;/取done=1;elseif

5、(code0&code1)/端點(diǎn)在視區(qū)外側(cè)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);/直線與視區(qū)邊界的交點(diǎn)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;實(shí)驗(yàn)結(jié)果圖1裁剪前后圖2裁剪前后圖3裁剪