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OpenGL编程轻松入门之NURBS曲线和曲面(2)

　2007-05-06 19:58:30　来源：WEB开发网　　　

核心提示：例12：绘制一个彩色的曲线，曲线闭合成圆，OpenGL编程轻松入门之NURBS曲线和曲面(2)，在曲线的边缘绘制8个点，如图十四所示，order NURBS曲线的阶数，阶数比维数大1， #include <windows.h> #inclu

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。