基於OpenGL實現的多段Bezier曲線拼接

運行程序的交互方式有點類似corelDraw中的自由曲線繪制，或者photoShop中的鋼筆自由路徑繪制。

截圖：

將BezierCurve封裝成了一個類，代碼如下：

#ifndef _BEZIERCURVE_H
#define _BEZIERCURVE_H

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

using namespace std;
//// 3次bezier曲線: 四個控制節點。曲線經過首末兩個頂點。

class BezierCurve
{
public:
//cell一共有四個控制頂點
// -cell經過V0和V3頂點，
// -cell的始端相切於直線：(V0, V1) 和末端相切於(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()
{
// 開啟求值器
glEnable(GL_MAP1_VERTEX_3);
clear();
}

void mouseSynchro(eventType type, const Vec3d& v) //響應鼠標motion
{
//////////////////////////////////////////////////////////////////////////
//LButtonDown: 壓入點
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: 動態更新相應的頂點數據
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: 為拼接做准備
else if (type == LButtonUp)
{
if (isFirstRender)
{
//只有第一個BezierCell可以編輯bezierCell的起始段:(V0,V1)
isFirstRender = false;
}
else if ( cellRenderState() == cellRenderImple::Change)
{
//if finish the current cell's render
//利用v1和中點v0計算出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();
}
}
//////////////////////////////////////////////////////////////////////////
//更新數組的長度
_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(切線)
//(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曲線經過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; //單元個數
int vertexNum; //頂點個數

bool isFirstRender; //首次標志
std::vector<Vec3d> vertexVector; //頂點數組

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的渲染狀態
} cellRenderState;
};

測試程序如下：

#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]);

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];

//獲取矩陣信息
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();
}

//////////////////////////////////////////////////////////////////////////
// 計算控制節點
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();
}