例12：绘制一个彩色的曲线，曲线闭合成圆。在曲线的边缘绘制8个点，如图十四所示。
#include <windows.h>
#include <GL/glut.h>
GLUnurbsObj *theNurb;
GLfloat ctrlpoints[12][3] = {{4,0,0},{2.828,2.828,0},{0,4,0},{-2.828,2.828,0},
{-4,0,0},{-2.828,-2.828,0},{0,-4,0},{2.828,-2.828,0},
{4,0,0},{2.828,2.828,0},{0,4,0},{2.828,2.828,0}};//控制点
GLfloat color[12][3]={{1.0,0.0,0.0},{1.0,1.0,0.0},{0.0,1.0,0.0},{-1.0,1.0,0.0},
{-1.0,0.0,0.0},{-1.0,-1.0,0.0},{0.0,-1.0,0.0},{1.0,-1.0,0.0},
{1.0,0.0,0.0},{1.0,1.0,0.0},{0.0,1.0,0.0},{1.0,1.0,0.0}};
GLfloat knots[15] = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
void myInit(void)
{
glClearColor(1.0,1.0,1.0,0.0);//设置背景色
theNurb = gluNewNurbsRenderer();//创建NURBS对象theNurb
gluNurbsProperty(theNurb,GLU_SAMPLING_TOLERANCE,10);
}
/*绘制曲线*/
void myDisplay(void)
{
int i;
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glColor3f(0.0,0.0,0.0);
glLineWidth(3.0);
/*绘制曲线*/
gluBeginCurve(theNurb);
gluNurbsCurve(theNurb,15,knots,3,&ctrlpoints[0][0],3,GL_MAP1_VERTEX_3);
gluNurbsCurve(theNurb,15,knots,3,&ctrlpoints[0][0],3,GL_MAP1_COLOR_4);
gluEndCurve(theNurb);
/*绘制点*/
glColor3f(1.0,0.0,0.0);
glPointSize(5.0);
glBegin(GL_POINTS);
for(i = 0;i < 8;i++)
glVertex2fv(&ctrlpoints[i][0]);
glEnd();
glutSwapBuffers();
}
void myReshape(GLsizei w,GLsizei h)
{
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
if(w <=h)
glOrtho(-10.0,10.0,-10.0*(GLfloat)h/(GLfloat)w,10.0*(GLfloat)h/(GLfloat)w,-10.0,10.0);
else
glOrtho(-10.0*(GLfloat)w/(GLfloat)h,10.0*(GLfloat)w/(GLfloat)h,-10.0,10.0,-10.0,10.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0,0.0,-9.0);
}
int main(int argc,char ** argv)
{
/*初始化*/
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);
glutInitWindowSize(600,400);
glutInitWindowPosition(200,200);
/*创建窗口*/
glutCreateWindow("NURBS curve");
/*绘制与显示*/
myInit();
glutReshapeFunc(myReshape);
glutDisplayFunc(myDisplay);
glutMainLoop();
return(0);
} |
·gluBeginCurve，gluEndCurve限定NURBS曲面。返回值均为void，参数均为GLUnurbsObj* nobj，为指向NURBS对象的指针。
·void gluNurbsCurve（GLUnurbsObj *nobj， GLint nknots， GLfloat *knot， Glint stride， GLfloat *ctlarray， GLint order，GLenum type）定义曲线形状。
nobj 指向NURBS对象的指针。
nknots 节点数，节点数等于控制点数加上阶数。
knot nknots数组非递减节点值。
stride相邻控制点的偏移量。
Ctlarry指向NURBS的控制点数组的指针。
order NURBS曲线的阶数，阶数比维数大1。
type曲面类型。
 图十四：NURBS曲线 |
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