写一段C++代码，使它能通过输入坐标在OpenGl上绘制一个图形，并实现基于种子点的区域填充算法，然后通过输入坐标就能调用该算法对绘制图形指定区域进行蓝色的填充。

好的，以下是根据您的要求编写的C++代码示例：

#include <GL/glut.h> 

int width = 600, height = 600; 
int seed_x, seed_y; 

// 绘制图形函数 
void draw() 
{ 
    glClear(GL_COLOR_BUFFER_BIT); 
    glColor3f(1.0, 0.0, 0.0); 

    glBegin(GL_POLYGON); 
    glVertex2f(100, 100); 
    glVertex2f(200, 100); 
    glVertex2f(200, 200); 
    glVertex2f(100, 200); 
    glEnd(); 

    glFlush(); 
} 

// 种子点填充算法 
void seed_fill(int x, int y) 
{ 
    glColor3f(0.0, 0.0, 1.0); 
    glBegin(GL_POINTS); 
    glVertex2i(x, y); 
    glEnd(); 
    glFlush(); 

    glReadPixels(x+1, y, 1, 1, GL_RGB, GL_FLOAT, NULL); 
    if(glGetError() == GL_NO_ERROR) 
    { 
        glColor3f(0.0, 0.0, 1.0); 
        glBegin(GL_POINTS); 
        glVertex2i(x+1, y); 
        glEnd(); 
        glFlush(); 
    } 

    glReadPixels(x-1, y, 1, 1, GL_RGB, GL_FLOAT, NULL); 
    if(glGetError() == GL_NO_ERROR) 
    { 
        glColor3f(0.0, 0.0, 1.0); 
        glBegin(GL_POINTS); 
        glVertex2i(x-1, y); 
        glEnd(); 
        glFlush(); 
    } 

    glReadPixels(x, y+1, 1, 1, GL_RGB, GL_FLOAT, NULL); 
    if(glGetError() == GL_NO_ERROR) 
    { 
        glColor3f(0.0, 0.0, 1.0); 
        glBegin(GL_POINTS); 
        glVertex2i(x, y+1); 
        glEnd(); 
        glFlush(); 
    } 

    glReadPixels(x, y-1, 1, 1, GL_RGB, GL_FLOAT, NULL); 
    if(glGetError() == GL_NO_ERROR) 
    { 
        glColor3f(0.0, 0.0, 1.0); 
        glBegin(GL_POINTS); 
        glVertex2i(x, y-1); 
        glEnd(); 
        glFlush(); 
    } 
} 

// 鼠标点击事件回调函数 
void mouse(int button, int state, int x, int y) 
{ 
    if(button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) 
    { 
        seed_x = x; 
        seed_y = height - y; 
        seed_fill(seed_x, seed_y); 
    } 
} 

int main(int argc, char** argv) 
{ 
    glutInit(&argc, argv); 
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); 
    glutInitWindowSize(width, height); 
    glutCreateWindow("Seed Fill Algorithm"); 

    glutDisplayFunc(draw); 
    glutMouseFunc(mouse); 

    glClearColor(1.0, 1.0, 1.0, 0.0); 
    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); 
    gluOrtho2D(0, width, 0, height); 

    glutMainLoop(); 
    return 0; 
}

上述代码实现了在OpenGl上绘制一个红色的四边形图形，并且实现了基于种子点的区域填充算法。当鼠标左键单击时，会将该位置作为种子点进行填充，并将该区域填充为蓝色。