Question

用vc6.0在mfc中调用opengl如何画三次B样条曲线，求操作步骤和程序代码。谢谢！

Answer 1

#include <stdlib.h>

#include <GL/glut.h>
#pragma comment(lib,"glut32.lib")

//

#if 0
// the points of the curve - these are the same as the bezier curve
// points demonstrated in the bezier curve example.

float Points[4][3] = {
{ 10,10,0 },
{ 5,10,2 },
{ -5,0,0 },
{-10,5,-2}
};

#define NUM_POINTS 4

// The following sets of 4 indices are the curves that need to
// be drawn to create a clamped cubic b-spline. In total there
// are 5 curve segments to draw.
//
// 0 0 0 1
// 0 0 1 2
// 0 1 2 3
// 1 2 3 3
// 2 3 3 3
//
// Remember this when trying to understand knot vectors!!
//

#else

float Points[9][3] = {
{ 10,5,0 },
{ 5,10,0 },
{ -5,15,0 },
{ -10,-5,0 },
{ 4,-4,0 },
{ 10,5,0 },
{ 5,10,0 },
{ -5,15,0 },
{ -10,-5,0 }
};

#define NUM_POINTS 9

//若绘制过首尾控制点的曲线
// 0 0 0 1
// 0 0 1 2
// 0 1 2 3
// 1 2 3 4
// 2 3 4 5
// 3 4 5 6
// 4 5 6 6
// 5 6 6 6
//
// Remember this when trying to understand knot vectors!!
//
//若绘制首尾相接的平滑曲线 ，即为当前绘制
// 0 1 2 3
// 1 2 3 4
// 2 3 4 5
// 3 4 5 6
#endif

// the level of detail for the curve
unsigned int LOD=20;

#define NUM_SEGMENTS (NUM_POINTS-3)
//

float* GetPoint(int i)
{
// return 1st point
if (i<0)
{
return Points[0];
}

if (i<NUM_POINTS)
{
return Points[i];
}
// return last point

return Points[NUM_POINTS-1];
}

//------------------------------------------------------------ OnKeyPress()
void myIdle(void)
{
glutPostRedisplay();
}

//------------------------------------------------------------ OnDraw()
void OnDraw()
{
// clear the screen & depth buffer
glClear(GL_COLOR_BUFFER_BIT);
// clear the previous transform
glLoadIdentity();
// set the camera position
// gluLookAt( 1,10,30, // eye pos
// 0,0,0, // aim point
// 0,1,0); // up direction
// glColor3f(0.5,0.2,0);
glPointSize(3);
//
// // draw curve hull
glColor3f(0.3,0,0.5);
glBegin(GL_LINE_STRIP);
for(int i=0;i!=NUM_POINTS;++i)
{
glVertex3fv( Points[i] );
}
glEnd();

glColor3f(0,1,0);

// begin drawing our curve
glBegin(GL_LINE_STRIP);

for(int start_cv=0,j=0;j<NUM_SEGMENTS;j++,start_cv++)
{
// for each section of curve, draw LOD number of divisions
for(int i=0;i!=LOD;++i)
{
// use the parametric time value 0 to 1 for this curve
// segment.
float t = (float)i/LOD;
// the t value inverted
float it = 1.0f-t;

// calculate blending functions for cubic bspline
float b0 = it*it*it/6.0f;
float b1 = (3*t*t*t - 6*t*t +4)/6.0f;
float b2 = (-3*t*t*t +3*t*t + 3*t + 1)/6.0f;
float b3 = t*t*t/6.0f;

// calculate the x,y and z of the curve point
float x = b0 * GetPoint( start_cv + 0 )[0] +
b1 * GetPoint( start_cv + 1 )[0] +
b2 * GetPoint( start_cv + 2 )[0] +
b3 * GetPoint( start_cv + 3 )[0] ;

float y = b0 * GetPoint( start_cv + 0 )[1] +
b1 * GetPoint( start_cv + 1 )[1] +
b2 * GetPoint( start_cv + 2 )[1] +
b3 * GetPoint( start_cv + 3 )[1] ;

float z = b0 * GetPoint( start_cv + 0 )[2] +
b1 * GetPoint( start_cv + 1 )[2] +
b2 * GetPoint( start_cv + 2 )[2] +
b3 * GetPoint( start_cv + 3 )[2] ;

// specify the point

glVertex2f( x,y );
}
}

// we need to specify the last point on the curve
//glVertex3fv( Points[NUM_POINTS-1] );
glEnd();

// draw CV's
glBegin(GL_POINTS);
for(int i=0;i!=NUM_POINTS;++i)
{
glVertex3fv( Points[i] );
}
glEnd();

// currently we've been drawing to the back buffer, we need
// to swap the back buffer with the front one to make the image visible
glutSwapBuffers();
}

//------------------------------------------------------------ OnInit()
void OnInit()
{
//glClearColor(1,1,1,0);
}

//------------------------------------------------------------ OnExit()
void OnExit()
{
}

//------------------------------------------------------------ OnReshape()
void OnReshape(int w, int h)
{
// prevents division by zero when minimising window
if (h==0)
{
h=1;
}

// set the drawable region of the window
glViewport(0,0,w,h);
// set up the projection matrix
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
// just use a perspective projection
//gluPerspective(45,(float)w/h,0.1,100);
if(w<=h)
{
glOrtho(-20.0,20.0,-20.0*(GLfloat)h/(GLfloat)w,20.0*(GLfloat)h/(GLfloat)w,0.0,100.0);
}
else
{
glOrtho(-20.0,20.0,-20.0*(GLfloat)h/(GLfloat)w,20.0*(GLfloat)h/(GLfloat)w,0.0,100.0);
}
// go back to modelview matrix so we can move the objects about
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}

//------------------------------------------------------------ main()
int main(int argc,char** argv)
{
// initialise glut
glutInit(&argc,argv);
// request a depth buffer, RGBA display mode, and we want double buffering
glutInitDisplayMode(GLUT_RGBA|GLUT_DOUBLE);
// set the initial window size
glutInitWindowSize(640,480);
// create the window
glutCreateWindow("Clamped B-Spline Curve");
// run our custom initialisation
OnInit();
// set the function to use to draw our scene
glutDisplayFunc(OnDraw);

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// set the function to handle changes in screen size
glutReshapeFunc(OnReshape);
glutIdleFunc(&myIdle);
// set the function to be called when we exit
atexit(OnExit);
// this function runs a while loop to keep the program running.
glutMainLoop();

return 0;

}