OpenGL: 填充非凸多邊形 （轉）

OpenGL多邊形填充時默認爲凸多邊形

void display()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0, 1.0, 1.0);
    glBegin(GL_POLYGON);
    {
        glVertex2i(380, 380);
        glVertex2i(320, 410);
        glVertex2i(180, 280);
        glVertex2i(90, 330);
        glVertex2i(50, 310);
        glVertex2i(50, 150);
        glVertex2i(90, 130);
        glVertex2i(180, 180);
        glVertex2i(320, 50);
        glVertex2i(380, 80);
    }
    glEnd();
    glLineWidth(2.0);
    glColor3f(1.0, 0.0, 0.0);
    glBegin(GL_LINE_LOOP);
    {
        glVertex2i(380, 380);
        glVertex2i(320, 410);
        glVertex2i(180, 280);
        glVertex2i(90, 330);
        glVertex2i(50, 310);
        glVertex2i(50, 150);
        glVertex2i(90, 130);
        glVertex2i(180, 180);
        glVertex2i(320, 50);
        glVertex2i(380, 80);
    }
    glEnd();
    glFlush();
}

填充結果：

       OpenGL中認爲合法的多邊形必須是凸多邊形，凹多邊形、自交多邊形、帶孔的多邊形等非凸的多邊形在OpenGL中繪製會出現出乎意料的結果。例如，在大多數系統中，只有多邊形的凸包被填充，而在有些系統中，並非所有的凸包都被填充。OpenGL之所以對合法多邊形類型做出限制，是爲了更方便地提供能夠對符合條件的多邊形進行快速渲染的硬件。簡單多邊形可被快速地渲染，而複雜多邊形難以快速檢測出來。爲了最大限度的提高性能，OpenGL假定多邊形是簡單的。

      非凸多邊形最簡單的填充方法最簡單的應該是GLU 網格化對象GLUtesselator

就是GLUtesselator， 能將任意多邊形，簡化爲三角形或凸多邊形的組合，從而使OpenGL能繪製出任意形狀的多邊形。

1. gluNewTess();                 //創建一個新的分格化對象
2. gluTessCallback();            //註冊回調函數，完成分格化的一些操作，照着寫就行了。
3. gluTessProperty();            //可有可無的，設置一些分格化的屬性值
4. gluTessBeginPolygon();        //開始畫多邊形
    draw polygon...              //在這裏畫多邊形，一個一個點畫就可以，最後一個點會和第一個點自動連接起來
    gluTessEdnPolygon();         //結束畫多邊形
5. gluDeleteTess();              //刪除分格化對象

#include <stdio.h>
#include <stdlib.h>
#include <GL/glut.h>

#pragma comment(lib,"glut32.lib")

GLdouble quad[12][3] = {
    {-2,3,0},   {-2,0,0},   {2,0,0},    { 2,3,0},
    {-1,2,0},   {-1,1,0},   {1,1,0},    { 1,2,0},
    {-0.5,1,0}, {-0.5,2,0}, {0.5,2,0}, { 0.5,1,0} };

void myIdle(void)
{
    glutPostRedisplay();
}
//------------------------------------------------------------  OnDraw()
//
void CALLBACK vertexCallback(GLvoid *vertex)
{
    const GLdouble *pointer = (GLdouble *) vertex;
    glColor3dv(pointer + 3);//在此設置顏色
    glVertex3dv(pointer);
}
void CALLBACK beginCallback(GLenum which)
{
    glBegin(which);
}
void CALLBACK endCallback  ()
{
    glEnd();
}
void CALLBACK errorCallback(GLenum errorCode)
{
    const GLubyte *estring;
    estring = gluErrorString(errorCode);
    fprintf(stderr, "Tessellation Error: %s\n", estring);
    exit(0);
}
void CALLBACK combineCallback(GLdouble coords[3],
                              GLdouble *vertex_data[4],
                              GLfloat weight[4], GLdouble **dataOut )
{
    GLdouble *vertex;
    int i;
    vertex = (GLdouble *) malloc(6 * sizeof(GLdouble));
    vertex[0] = coords[0];
    vertex[1] = coords[1];
    vertex[2] = coords[2];
    for (i = 3; i < 7; i++)
    {
        vertex[i] = weight[0] * vertex_data[0][i]
            + weight[1] * vertex_data[1][i]
            + weight[2] * vertex_data[2][i]
            + weight[3] * vertex_data[3][i];
    }
    *dataOut = vertex;
}
void OnDraw()
{
    // clear the screen & depth buffer
    glClear(GL_COLOR_BUFFER_BIT);

    // clear the previous transform
    glLoadIdentity();

    GLUtesselator *tobj = gluNewTess();
    if (!tobj) {    return;     }

    gluTessCallback(tobj, GLU_TESS_VERTEX, (void (CALLBACK *)())vertexCallback);
    gluTessCallback(tobj, GLU_TESS_BEGIN, (void (CALLBACK *)())beginCallback);
    gluTessCallback(tobj, GLU_TESS_END, (void (CALLBACK *)())endCallback);
    gluTessCallback(tobj, GLU_TESS_ERROR, (void (CALLBACK *)())errorCallback);
    gluTessCallback(tobj, GLU_TESS_COMBINE, (void (CALLBACK *)())combineCallback);

    // glShadeModel(GL_FLAT);

    // gluTessProperty(tobj,GLU_TESS_WINDING_RULE,GLU_TESS_WINDING_POSITIVE); //GLU_TESS_WINDING_ODD

    gluTessBeginPolygon(tobj, NULL);

    gluTessBeginContour(tobj);
    gluTessVertex(tobj, quad[0], quad[0]);
    gluTessVertex(tobj, quad[1], quad[1]);
    gluTessVertex(tobj, quad[2], quad[2]);
    gluTessVertex(tobj, quad[3], quad[3]);
    gluTessEndContour(tobj);

    gluTessBeginContour(tobj);                      // inner quad (hole)
    gluTessVertex(tobj, quad[4], quad[4]);
    gluTessVertex(tobj, quad[5], quad[5]);
    gluTessVertex(tobj, quad[6], quad[6]);
    gluTessVertex(tobj, quad[7], quad[7]);
    gluTessEndContour(tobj);

    gluTessBeginContour(tobj);                      // inner quad (hole)
    gluTessVertex(tobj, quad[8], quad[8]);
    gluTessVertex(tobj, quad[9], quad[9]);
    gluTessVertex(tobj, quad[10], quad[10]);
    gluTessVertex(tobj, quad[11], quad[11]);
    gluTessEndContour(tobj);

    gluTessEndPolygon(tobj);

    gluDeleteTess(tobj);
    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(-4.0, 4.0, -4.0 * (GLfloat)h / (GLfloat)w, 4.0 * (GLfloat)h / (GLfloat)w, 0.0, 100.0);
    }
    else
    {
        glOrtho(-4.0, 4.0, -4.0 * (GLfloat)h / (GLfloat)w, 4.0 * (GLfloat)h / (GLfloat)w, 0.0, 100.0);
    }

    // go back to model view matrix so we can move the objects about
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
//------------------------------------------------------------  main()
//
int main(int argc,char** argv)
{
    // initialize 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(480, 480);
    // create the window
    glutCreateWindow("filling");
    // run our custom initialisation
    OnInit();
    // set the function to use to draw our scene
    glutDisplayFunc(OnDraw);
    // 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;
}

簡單版：

#include <stdio.h>
#include <stdlib.h>
#include <GL/glut.h>

#pragma comment(lib,"glut32.lib")

GLdouble quad[12][3] =
{
    {5,5,0},    {15,5,0},   {15,-5,0},  { 5,-5,0},
    {0,5,0},    {-15,10,0}, {-5,-10,0}, { -10,5,0},
    {-0.5,1,0}, {-0.5,2,0}, {0.5,2,0},  { 0.5,1,0}
};
void myIdle(void)
{
    glutPostRedisplay();
}

//------------------------------------------------------------  OnDraw()
//
void CALLBACK PolyLine3DBegin(GLenum type)
{
    glBegin(type);
}

void CALLBACK PolyLine3DVertex ( GLdouble * vertex)
{
    const GLdouble *pointer = (GLdouble *) vertex;
    glColor3d(1.0,0,0);//在此設置顏色
    glVertex3dv(pointer);
}

void CALLBACK PolyLine3DEnd()
{
    glEnd();
}
GLUtesselator* tesser()
{
    GLUtesselator * tess;
    tess=gluNewTess();
    gluTessCallback(tess,GLU_TESS_BEGIN,(void (CALLBACK*)())&PolyLine3DBegin);
    gluTessCallback(tess,GLU_TESS_VERTEX,(void (CALLBACK*)())&PolyLine3DVertex);
    gluTessCallback(tess,GLU_TESS_END,(void (CALLBACK*)())&PolyLine3DEnd);
    return tess;
}

/////////////////////////////////////////////////////////////////////////////////
void OnDraw()
{

    glClear(GL_STENCIL_BUFFER_BIT);

    GLUtesselator* tess = tesser();
    if (!tess) return;
    gluTessBeginPolygon(tess,NULL);

    gluTessBeginContour(tess);
    for(int i = 0; i < 4; i++)
    {
        gluTessVertex(tess, quad[i], quad[i]);
    }
    gluTessEndContour(tess);

    gluTessBeginContour(tess);
    for(int i = 4; i < 8;i++)
    {
        gluTessVertex(tess, quad[i], quad[i]);
    }
    gluTessEndContour(tess);

    gluTessEndPolygon(tess);
    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 model view matrix so we can move the objects about
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}
//------------------------------------------------------------  main()
//
int main(int argc, char** argv)
{

    // initialize 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(480, 480);
    // create the window
    glutCreateWindow("fill tess");
    // run our custom initialization
    OnInit();
    // set the function to use to draw our scene
    glutDisplayFunc(OnDraw);
    // 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;
}

Reference：

其他填充方法：

http://www.cnblogs.com/mazhenyu/archive/2010/05/18/1738487.html

函數簡介：

http://hi.baidu.com/zhujianzhai/item/6ed52336d67e7b9ab80c03eb

http://bbs.csdn.net/topics/100086684

各種填充算法詳細講解：

http://blog.csdn.net/orbit/article/details/7368996

http://blog.csdn.net/yangtrees/article/details/9040257

轉自：http://blog.csdn.net/augusdi/article/details/20032185