OpenGL写的直线裁剪法

#include <GL/glut.h>
#include <stdio.h>

#define LEFT_EDGE   1  //代表0001
#define RIGHT_EDGE  2 //代表0010
#define BOTTOM_EDGE 4 //代表0100
#define TOP_EDGE    8 //代表1000

bool bInput, accept, bDraw;
struct Rectangle
{
 float xmin,xmax,ymin,ymax;
};
Rectangle  rect;

struct Point { int x, y;};
Point pt[2];

void LineGL(Point pt0, Point pt1)
{
 glBegin (GL_LINES);
 glColor3f (1.0f, 0.0f, 0.0f);   glVertex2f (pt0.x,pt0.y);
 glColor3f (0.0f, 1.0f, 0.0f);   glVertex2f (pt1.x,pt1.y); 
 glEnd ();
}

void PointGL(Point pt)
{
 glPointSize(2);
 glBegin (GL_POINTS);
 glColor3f (1.0f, 0.0f, 0.0f);   glVertex2f (pt.x,pt.y);
 glEnd ();
}

int CompCode(Point pt,Rectangle rect)
{
 int code=0x00;
 if(pt.y<rect.ymin)
  code=code|BOTTOM_EDGE;
 if(pt.y>rect.ymax)
  code=code|TOP_EDGE;
 if(pt.x>rect.xmax)
  code=code|RIGHT_EDGE;
 if(pt.x<rect.xmin)
  code=code|LEFT_EDGE;
 return code;
}

void cohensutherlandlineclip(Rectangle  rect, Point &pt0, Point &pt1)
{
 int &x0 = pt0.x;
 int &y0 = pt0.y;
 int &x1 = pt1.x;
 int &y1 = pt1.y;

 bool done = false;
 float x,y;

 int code0,code1, codeout;
 code0 = CompCode(pt0,rect);
 code1 = CompCode(pt1,rect);
 do{
  if(!(code0 | code1))//完全可见
  {
   accept=true;
   done=true;
  }
  else if(code0 & code1)//显然不可见
  {
   accept=false;
   done = true;
  }
  else
  {  
   if(code0!=0)
    codeout=code0;
   else
    codeout = code1;

   if(codeout&LEFT_EDGE){
    y=y0+(y1-y0)*(rect.xmin-x0)/(x1-x0);
    x=(float)rect.xmin;
   }
   else if(codeout&RIGHT_EDGE){
    y=y0+(y1-y0)*(rect.xmax-x0)/(x1-x0);
    x=(float)rect.xmax;
   }
   else if(codeout&BOTTOM_EDGE){
    x=x0+(x1-x0)*(rect.ymin-y0)/(y1-y0);
    y=(float)rect.ymin;
   }
   else if(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(pt0,rect);
   }
   else
   {
    x1=x;y1=y;
    code1 = CompCode(pt1,rect);
   }
  }
 }while(!done);
}

void myDisplay()
{
 glClear(GL_COLOR_BUFFER_BIT);
 glColor3f (1.0f, 0.0f, 0.0f);
 glRectf(rect.xmin,rect.ymin,rect.xmax,rect.ymax);

 if(accept)  
 {
  if(bDraw)
  {
   LineGL(pt[0],pt[1]);
  }
  else
   PointGL(pt[0]);
 }

 glFlush();
}

void Init()
{
 glClearColor(0.0, 0.0, 0.0, 0.0);
 glShadeModel(GL_FLAT);

 rect.xmin=100;
 rect.xmax=300;
 rect.ymin=100;
 rect.ymax=300;

 accept = true;
 bInput = false;
 printf("Press Left Mouse Button to Draw two Point to create a line!/nPress key 'c' to Clip!/n");
}

void Reshape(int w, int h)
{
 glViewport(0, 0, (GLsizei) w,  (GLsizei) h);
 glMatrixMode(GL_PROJECTION);
 glLoadIdentity();
 gluOrtho2D(0.0, (GLdouble) w, 0.0, (GLdouble) h);
}

void keyboard(unsigned char key, int x, int y)
{
 switch (key)
 {
 case 'c':
  cohensutherlandlineclip(rect, pt[0],pt[1]); 
  glutPostRedisplay();
  break;

 default:
  break;
 }
}

void mouse(int button, int state, int x, int y)
{
 switch (button)
 {
 case GLUT_LEFT_BUTTON:
  if (state == GLUT_DOWN)
  {
   if (bInput == false)
   {
    pt[0].x = x;
    pt[0].y = 480 - y;
    bInput = true;

    bDraw = false;
    accept = true;
    glutPostRedisplay();//
   }
   else
   {
    pt[1].x = x;
    pt[1].y = 480 - y;
    bDraw = true;
    bInput = false;
    glutPostRedisplay();//
   } 
  }
  break;
 default:
  break;
 }
}

int main(int argc, char *argv[])
{
 glutInit(&argc, argv);
 glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
 glutInitWindowPosition(100, 100);
 glutInitWindowSize(640, 480);
 glutCreateWindow("Hello World!");

 Init();
 glutDisplayFunc(myDisplay);
 glutReshapeFunc(Reshape);
 glutKeyboardFunc(keyboard);
 glutMouseFunc(mouse);
 glutMainLoop();
 return 0;
}