Boundary fill problem

Question

hi...Im stuck in this bunch of codes...i cant get the pixel to fill up the circle??...any help

#include<iostream>
#include<glut.h>

struct Color{
    float red, green, blue;
};

Color getPixel(int x, int y){     // gets the color of the pixel at (x,y) 
    Color c;
    float color[4];
    glReadPixels(x,y,1,1,GL_RGBA, GL_FLOAT, color);
    c.red = color[0];   
    c.green = color[1];  
    c.blue = color[2];  
    return c;
}

void setPixel(int x, int y, Color c){
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glPushAttrib(GL_ALL_ATTRIB_BITS);
    glColor3f(c.red, c.green, c.blue);
    glBegin(GL_POINTS);
    glVertex2i(x,y);
    glEnd();
    glPopAttrib();
    glFlush();
}

void init()
     {
        glClearColor(1.0,1.0,1.0,0.0);
        gluOrtho2D(0.0,300.0,0.0,300.0);
     }

void drawPixel(int x,int y)
{
    glBegin(GL_POINTS);
    glVertex2i(x,y);
    glEnd();
    glFlush();
}

void Boundary_fill(int x,int y,Color thisColor){
    Color boundary_color;
    boundary_color.red=0.0;
    boundary_color.green=1.0;
    boundary_color.blue=0.0;
    Color nextpixel=getPixel(x,y);
    if((nextpixel.red!=boundary_color.red)&&(nextpixel.blue!=boundary_color.blue)&&(nextpixel.green!=boundary_color.green) && (nextpixel.red!=thisColor.red)&& (nextpixel.blue!=thisColor.blue)&& (nextpixel.green!=thisColor.green)){
        setPixel(x,y,thisColor);
        Boundary_fill((x+1),y,thisColor);
        Boundary_fill((x-1),y,thisColor);
        Boundary_fill(x,(y+1),thisColor);
        Boundary_fill(x,(y-1),thisColor);
    }

}

void draw(int x1,int y1, int x, int y){
    drawPixel(x1+x,y1+y);//quadrant1
    drawPixel(x1+x,y1-y);//quadrant2
    drawPixel(x1-x,y1+y);//quadrant3
    drawPixel(x1-x,y1-y);//quadrant4
    drawPixel(x1+y,y1+x);//quadrant5
    drawPixel(x1+y,y1-x);//quadrant6
    drawPixel(x1-y,y1+x);//quadrant7
    drawPixel(x1-y,y1-x);//quadrant8
}

void circle(int px,int py,int r){
    int a,b;
    float p;
    a=0;
    b=r;
    p=(5/4)-r;

    while(a<=b){
        draw(px,py,a,b);
        if(p<0){
            p=p+(2*a)+1;
        }
        else{
            b=b-1;
            p=p+(2*a)+1-(2*b);
        }
        a=a+1;
    }
}


void Circle(void)
{
    Color thisColor;
    thisColor.red=1.0;
    thisColor.blue=0.0;
    thisColor.green=0.0;

    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(0.0,1.0,0.0);
    glPointSize(2.0);
    int x0 = 100;
    int y0 = 150;
    circle(x0,y0,50);
    glColor3f(thisColor.red,thisColor.blue,thisColor.green);
    Boundary_fill(x0,y0,thisColor);
}

void main(int argc, char**argv)
{
    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(400,400);
    glutInitWindowPosition(1,1);
    glutCreateWindow("Boundary fill in a circle:Taaseen And Abhinav");
    init();
    glutDisplayFunc(Circle);
    glutMainLoop();
}

Answer 1

Your setPixel() routine is broken. It clears the window to white, thereby erasing all previously drawn pixels. You should remove this line and put it in your Circle() routine instead:

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

Because of that line, getPixel() will always read white pixels (except for one) and will recurse to the right. If you're lucky glReadPixels() will return some random colors when reaching the outside of the frame buffer. Otherwise it will produce a stack overflow. You should therefore also check your pixel position in Boundary_fill().