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/*******************************************************************************
* *
* Viewmol *
* *
* E L L I P S E . C *
* *
* Copyright (c) Joerg-R. Hill, October 2003 *
* *
********************************************************************************
*
* $Id: ellipse.c,v 1.6 2003/11/07 11:00:28 jrh Exp $
* $Log: ellipse.c,v $
* Revision 1.6 2003/11/07 11:00:28 jrh
* Release 2.4
*
* Revision 1.5 2000/12/10 15:05:47 jrh
* Release 2.3
*
* Revision 1.4 1999/05/24 01:25:20 jrh
* Release 2.2.1
*
* Revision 1.3 1999/02/07 21:48:28 jrh
* Release 2.2
*
* Revision 1.2 1998/01/26 00:47:39 jrh
* Release 2.1
*
* Revision 1.1 1996/12/10 18:40:46 jrh
* Initial revision
*
*/
#include<GL/gl.h>
#include<math.h>
void ellipse(double x1, double y1, double z1, double x2, double y2, double z2,
double x3, double y3, double z3, int n)
{
const double pi2=8.*atan(1.0);
double step=pi2/(double)n;
double vx1=x2-x1, vy1=y2-y1, vz1=z2-z1;
double vx2=x3-x1, vy2=y3-y1, vz2=z3-z1;
double a, b, tmat[4][4];
register double t, aa, bb;
double vertex[3];
/* First build the transformation matrix for rotating a ellipse defined by
the points (0,0,0), (a,0,0), and (0,b,0) to the desired position */
a=sqrt(vx1*vx1+vy1*vy1+vz1*vz1);
b=sqrt(vx2*vx2+vy2*vy2+vz2*vz2);
if (a > 1.0e-3 && b > 1.0e-3)
{
tmat[0][0]=vx1/a;
tmat[1][0]=vy1/a;
tmat[2][0]=vz1/a;
tmat[0][1]=vx2/b;
tmat[1][1]=vy2/b;
tmat[2][1]=vz2/b;
vertex[0]=a*tmat[0][0]+x1;
vertex[1]=a*tmat[1][0]+y1;
vertex[2]=a*tmat[2][0]+z1;
glBegin(GL_LINE_LOOP);
glVertex3dv(vertex);
t=step;
while (t < pi2)
{
aa=a*cos(t);
bb=b*sin(t);
vertex[0]=aa*tmat[0][0]+bb*tmat[0][1]+x1;
vertex[1]=aa*tmat[1][0]+bb*tmat[1][1]+y1;
vertex[2]=aa*tmat[2][0]+bb*tmat[2][1]+z1;
t+=step;
glVertex3dv(vertex);
}
glEnd();
}
else if (a > 1.0e-3)
{
glBegin(GL_LINES);
vertex[0]=vx1+x1;
vertex[1]=vy1+y1;
vertex[2]=vz1+z1;
glVertex3dv(vertex);
vertex[0]=x1-vx1;
vertex[1]=y1-vy1;
vertex[2]=z1-vz1;
glVertex3dv(vertex);
glEnd();
}
else if (b > 1.0e-3)
{
glBegin(GL_LINES);
vertex[0]=vx2+x1;
vertex[1]=vy2+y1;
vertex[2]=vz2+z1;
glVertex3dv(vertex);
vertex[0]=x1-vx2;
vertex[1]=y1-vy2;
vertex[2]=z1-vz2;
glVertex3dv(vertex);
glEnd();
}
else
return;
}
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