OpenGL如何实现多段Bezier曲线拼接

#ifndef _BEZIERCURVE_H
#define _BEZIERCURVE_H

#include "vec3.hpp"
#include <vector>
#include <iostream>
#include <gl/glut.h>

using namespace std;
//// 3次bezier曲线: 四个控制节点。曲线经过首末两个顶点。

class BezierCurve
{
public:
 //cell一共有四个控制顶点
 // -cell经过V0和V3顶点，
 // -cell的始端相切于直线：(V0, V1) 和末端相切于(V2,V3)
 class BezierCell
 {
 public:
 BezierCell(int i0, int i1, int i2, int i3)
 {
  setValue(i0, i1, i2, i3);
 }

 void setValue(int i0, int i1, int i2, int i3)
 {
  ctrlVertxIndex[0] = i0;
  ctrlVertxIndex[1] = i1;
  ctrlVertxIndex[2] = i2;
  ctrlVertxIndex[3] = i3;
 }
 const int operator[](int index) const
 {
  if (index > 3 || index < 0)
  return -1;

  return ctrlVertxIndex[index];
 }
 int ctrlVertxIndex[4];
 };

 enum eventType
 {
 LButtonDown = 0,
 MouseMove = 1,
 LButtonUp = 2
 };
 
 enum { Bezier3CtrlPnt = 4 };

 BezierCurve() { clear(); }
 ~BezierCurve(){}

 void begin()
 {
 // 开启求值器
 glEnable(GL_MAP1_VERTEX_3);
 clear();
 }
 
 void mouseSynchro(eventType type, const Vec3d& v) //响应鼠标motion
 {
 //////////////////////////////////////////////////////////////////////////
 //LButtonDown: 压入点
 if (type == LButtonDown)
 {
  if (isFirstRender)   //for the first cell
  {
  vertexVector.push_back(v); //push V0...
  vertexVector.push_back(v); //push V1...
  }
  else if ( cellRenderState() == cellRenderImple::Push ) //for any cell 
  {
  vertexVector.push_back(v); //push V2...
  vertexVector.push_back(v); //push V3... 

  cellRenderState.setChange(); //set the flag to change V3
  cellNum++;   //increase the cell counter
  }
 }
 //////////////////////////////////////////////////////////////////////////
 //MouseMove: 动态更新相应的顶点数据
 else if (type == MouseMove) 
 {
  if (isFirstRender)   //for the first cell
  { 
  vertexVector.back() = v; //change the V1 immediately
  }
  else if ( cellRenderState() == cellRenderImple::Change )//for any cell
  {
  int vecSize = vertexVector.size(); 
  vertexVector[vecSize-2] = v; //change the V2 immediately
  }
 }

 //////////////////////////////////////////////////////////////////////////
 //LButtonUp: 为拼接做准备
 else if (type == LButtonUp) 
 { 
  if (isFirstRender)
  {
  //只有第一个BezierCell可以编辑bezierCell的起始段:(V0,V1)
  isFirstRender = false;
  }
  else if ( cellRenderState() == cellRenderImple::Change)
  {
  //if finish the current cell's render
  //利用v1和中点v0计算出v2：(v1 + v2) / 2 = v0
  //next cell begin: push the next cell's V1... 
  int vecSize = vertexVector.size();
  Vec3d v0 = vertexVector[vecSize-1];
  Vec3d v1 = vertexVector[vecSize-2];
  Vec3d v2 = 2 * v0 - v1;
  vertexVector.push_back(v2);

  //重置cellRenderFlag
  cellRenderState.setPush();
  }
 }
 //////////////////////////////////////////////////////////////////////////
 //更新数组的长度
 _updateVertexNum();
 }

 void end()
 {
 glDisable(GL_MAP1_VERTEX_3);
 }

 void renderCurve()
 {
 //////////////////////////////////////////////////////////////////////////
 //rendering vertex...
 for (int i=0; i<vertexVector.size(); i++)
 {
  Vec3d v = vertexVector[i];
  glBegin(GL_POINTS); 
  glVertex3dv(v.getValue());
  glEnd();
 }

 //////////////////////////////////////////////////////////////////////////
 //rendering moving tangent(切线)
 //(vertexNum-1, vertexNum-2)
 if ( vertexNum>=2 )
 {
  glEnable(GL_LINE_STIPPLE);
  {
  glLineStipple(1, 0x0101);
  glBegin(GL_LINES);
  {
   Vec3d v1 = vertexVector[vertexNum-1];
   Vec3d v2 = vertexVector[vertexNum-2];
   glVertex3dv(v1.getValue());
   glVertex3dv(v2.getValue());
  } glEnd();
  }glDisable(GL_LINE_STIPPLE);
 }

 //////////////////////////////////////////////////////////////////////////
 //if ( !_check() )
 // return;

 //rendering bezier cells...
 system("CLS");
 for (int i=0; i<cellNum; i++)
 {
  int pos = i * 3;
  if ( (pos+3) < vertexNum )
  renderBezierCell( BezierCell(pos, pos+1, pos+2, pos+3) );
 }
 //////////////////////////////////////////////////////////////////////////
 }

 // 3次bezier曲线经过vetex0和vextex3
 void renderBezierCell(const BezierCell& cell)
 {
 double *pBuffer = new double[Bezier3CtrlPnt * 3];

 cout << "----------------------------------------------------" << endl;

 cout << "Vertex number : " << vertexNum << endl;
 cout << "Cell number : " << cellNum << endl;
 cout << "The render cell: " << cell[0] << " " << cell[1] << " " << cell[2] << " " << cell[3] << endl;

 for (int i = 0, bg = 0; i<4; i++)
 {
  Vec3d v = vertexVector[ cell[i] ];
  pBuffer[bg++] = v.x();
  pBuffer[bg++] = v.y();
  pBuffer[bg++] = v.z();
  
  cout << v.x() << " " << v.y() << " " << v.z() << endl;
 }cout << "----------------------------------------------------" << endl;

 glMap1d(GL_MAP1_VERTEX_3, 0.0, 1.0, 3, Bezier3CtrlPnt, pBuffer);
 glBegin(GL_LINE_STRIP);
 {
  for (int i = 0; i <= 30; i++) 
  glEvalCoord1f((GLfloat) i/30.0f);
 } glEnd();

 delete pBuffer; pBuffer = 0;
 }

 void clear()
 {
 cellNum = 0;
 vertexNum = 0;

 isFirstRender = true;

 vertexVector.clear();
 }
protected:
 bool _check() { vertexNum =vertexVector.size(); 
   return vertexNum == (cellNum - 1) * 3 + 4; }
 void _updateVertexNum() { vertexNum=vertexVector.size();}

 int cellNum;   //单元个数
 int vertexNum;   //顶点个数

 bool isFirstRender;   //首次标志
 std::vector<Vec3d> vertexVector; //顶点数组

 class cellRenderImple
 {
 public:
 enum RenderStep
 {
  Push = 0,
  Change = 1
 };
 cellRenderImple(){ setPush(); }
 bool operator()(void) { return flag; }
 void setPush() { flag = Push; }
 void setChange() { flag = Change; }

 RenderStep flag;  //cell的渲染状态
 } cellRenderState;
};

#include <iostream>
#include <vector>
#include <GL/glut.h>

#include "BezierCurve.h"

using namespace std;

enum WindowSize{
 WinWidth = 1024,
 WinHeight = 768
};

int  g_Viewport[4];
double g_ModelMatrix[16];
double g_ProjMatrix[16];
BezierCurve myBezier;

//////////////////////////////////////////////////////////////////////////
void init();
void display();
void reshape(int w, int h);
void keyboard(unsigned char key, int x, int y);
void mouse(int button, int state, int x, int y);
void motion(int x, int y);

int main(int argc, char** argv)
{
 glutInit(&argc, argv);
 glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
 glutInitWindowSize (WinWidth, WinHeight);
 glutInitWindowPosition (100, 100);
 glutCreateWindow (argv[0]);

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持亿速云。

 init ();
 glutDisplayFunc(display);
 glutReshapeFunc(reshape);
 glutKeyboardFunc (keyboard);
 glutMouseFunc(mouse);
 glutMotionFunc(motion);

 glutMainLoop();

 return 0;
}

void init(void)
{
 glClearColor(0.0, 0.0, 0.0, 0.0);
 glShadeModel(GL_SMOOTH);

 myBezier.begin();
}

void display(void)
{
 glClear(GL_COLOR_BUFFER_BIT);

 glColor3f(1.0, 1.0, 0.0);
 glPointSize(5.0);

 glPushMatrix();
 {
 myBezier.renderCurve();
 }glPopMatrix();

 glutSwapBuffers();
}

void reshape(int w, int h)
{
 glViewport(0, 0, (GLsizei) w, (GLsizei) h);
 glMatrixMode(GL_PROJECTION);
 glLoadIdentity();
 if (w <= h)
 glOrtho(-5.0, 5.0, -5.0*(GLfloat)h/(GLfloat)w, 
 5.0*(GLfloat)h/(GLfloat)w, -5.0, 5.0);
 else
 glOrtho(-5.0*(GLfloat)w/(GLfloat)h, 
 5.0*(GLfloat)w/(GLfloat)h, -5.0, 5.0, -5.0, 5.0);
 glMatrixMode(GL_MODELVIEW);
 glLoadIdentity();
}

void keyboard(unsigned char key, int x, int y)
{
 switch (key) {
  case 27:
  exit(0);
  break;
 }
}

void mouse(int button, int state, int x, int y)
{
 double vertex[3];

 //获取矩阵信息
 glGetIntegerv(GL_VIEWPORT, g_Viewport);
 glGetDoublev(GL_MODELVIEW_MATRIX, g_ModelMatrix);
 glGetDoublev(GL_PROJECTION_MATRIX, g_ProjMatrix);

 y = g_Viewport[3] - y;
 gluUnProject( x, y, 0,
 g_ModelMatrix, g_ProjMatrix, g_Viewport,
 &vertex[0], &vertex[1], &vertex[2] );

 if (button==GLUT_LEFT && state==GLUT_DOWN)
 {
 myBezier.mouseSynchro( BezierCurve::LButtonDown, vertex );
 glutSetCursor( GLUT_CURSOR_RIGHT_ARROW );
 }
 else if (button == GLUT_LEFT && state == GLUT_UP)
 {
 myBezier.mouseSynchro( BezierCurve::LButtonUp, vertex );
 }

 glutPostRedisplay();
}

//////////////////////////////////////////////////////////////////////////
// 计算控制节点
void motion(int x, int y)
{
 double vertex[3];

 glutSetCursor( GLUT_CURSOR_CROSSHAIR );
 y = g_Viewport[3] - y;

 gluUnProject( x, y, 0,
 g_ModelMatrix, g_ProjMatrix, g_Viewport,
 &vertex[0], &vertex[1], &vertex[2] );

 myBezier.mouseSynchro( BezierCurve::MouseMove, vertex );
 glutPostRedisplay();
}