Seedfill算法不起作用 - glReadPixels错误

Question

我正在尝试使用seedfill算法填充棋盘中的替代方块，但是当我右键单击这样做时，它会进入无限递归，尽管终止条件。 尽管在路径中遇到白色像素，它仍沿x方向前进填充像素。 谁能指出我哪里出错？

现在我意识到getReadPixels（）总是返回我的背景颜色，即0.0,0.0,0.0因为哪个种子填充不起作用。但我无法弄明白为什么？它与FRAME BUFFER或其他什么有关吗？

#include <GL/glut.h>
#include <iostream>
#include <cmath>
#include <cstdlib>
using namespace std;
#define WIDTH 640
#define HEIGHT 480
#define PI 3.14

float m[25][2], u[25][2];

void initialise(){

    glClearColor( 0.0, 0.0, 0.0, 0.0 );
    glClear( GL_COLOR_BUFFER_BIT );
    glPointSize( 3.0 );
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    gluOrtho2D( -WIDTH/2, WIDTH/2, -HEIGHT/2, HEIGHT/2 );
}

void setpixel( float x, float y ){

    glBegin( GL_POINTS );
        glVertex2i( x, y );
    glEnd();
    glFlush();
}

void display( void ){

    glBegin( GL_LINES );
        glVertex2i( -WIDTH/2, 0 );
        glVertex2i( WIDTH/2, 0 );
        glVertex2i(0, -HEIGHT/2 );
        glVertex2i(0, HEIGHT/2 );
    glEnd();
    glFlush();
}

//choosing the pixel color selected by the user
void getPixel( int x, int y, GLubyte *color ){
    glReadPixels( x, y, 1, 1, GL_RGB, GL_UNSIGNED_BYTE, color );
}
//----------------------------------------//

void seedfill( float x, float y ){

    GLubyte rgb[3];
    getPixel( x, y, rgb );
    if( rgb[0] == 0.0 ){
        cout << "TRUE" << endl;
    }

    if( rgb[0] == 0.0 ){
        glColor3f( 1.0, 1.0, 1.0 );
        glPointSize( 1.0 );
        setpixel( x, y );
        seedfill( x+1, y );
        seedfill( x-1, y );
        seedfill( x, y-1 );
        seedfill( x, y+1 );
    }

}

//using dda algorithm to draw line between two pixels
void dda(float x1, float y1, float x2, float y2){

    float dx = 0, dy = 0, i = 1, temp;
    float length = 0, slope = 0;
    float Dx = 0, Dy = 0;

    dx = x2 - x1;
    dy = y2 - y1;
    //slope = dy/dx;
    length = (abs(dx) >= abs(dy))?abs(dx):abs(dy);

    Dx = dx/length;
    Dy = dy/length;

    setpixel(round(x1), round(y1));

    for( ; i <= length; i++){
        x1 = x1 + Dx;
        y1 = y1 + Dy;
        setpixel(round(x1), round(y1));
        //cout << x1 << "\t" << y1 << endl;
    }
}
//----------------------------------------//

void complete( float z[25][2] ){

    int index_x, index_y;

    for( int i = 0, j = 0 ; i < 25 ; i+=5, j++ ){

        index_x = i+4;
        index_y = j+20;
        dda( z[i][0], z[i][1], z[index_x][0], z[index_x][1] );
        dda( z[j][0], z[j][1], z[index_y][0], z[index_y][1] );
    }
}

void drawBoard( int x1, int y1, int x2, int y2 ){

    int inc;
    float x, y = y1;
    inc = (x2-x1) / 4;

    for( int i = 0 ; i < 25 ; ){

        x = x1;
        for( int j = 0 ; j < 5 ; j++ ){

            m[i][0] = x;
            m[i][1] = y;
            x = x + inc;
            i++;
        }
        y = y + inc;        
    }
    complete( m );

}

void rotateBoard(){

    float r[2][2];
    int limit;
    initialise();
    display();

    r[0][0] = cos(45 * PI / 180);
    r[0][1] = sin(45 * PI / 180);
    r[1][0] = -sin(45 * PI / 180);
    r[1][1] = cos(45 * PI / 180);

    for( int i = 0 ; i < 25 ; i++ ){
        for( int k = 0 ; k < 2 ; k++ ){
            u[i][k] = 0;
            for( int j = 0 ; j < 2 ; j++ ){
                u[i][k] = u[i][k] + (m[i][j] * r[j][k]);
            }
        }
    }   
    complete( u );

    for( int i = 0 ; i < 25 ; ){

        seedfill( u[i][0] + 10, u[i][1] + 20 );
        i += 2;
        seedfill( u[i][0] + 10, u[i][1] + 20 );

        if( i+6 == 24 )break;

        if( (limit - i) % 2 == 0 ){
            i += 4;
        }
        else{
            i += 2;
        }
        limit += 5; 
    }

}

void mouse( int button, int state, int x, int y ){

    if( state == GLUT_DOWN ){

        if( button == GLUT_LEFT_BUTTON ){

            drawBoard( 0, 0, 160, 160 );
            //cout << getpixel( x, y ) << endl;
        }
        else if( button == GLUT_RIGHT_BUTTON ){
            //do something here
            rotateBoard();
        }
    }
}

int main( int argc, char **argv ){

    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_SINGLE | GLUT_RGB );
    glutInitWindowSize( WIDTH, HEIGHT );
    glutInitWindowPosition( 100, 100 );
    glutCreateWindow("CKR");

    initialise();

    glutDisplayFunc( display );

    glutMouseFunc( mouse );

    glutMainLoop();

    return 0;
}