12. Graphics Program for Flood-Fill Algorithm.

#include <GL/gl.h>
#include <GL/glut.h>
#include <math.h>
struct Point
{
GLint x;
GLint y;
};
struct Color
{
GLfloat r;
GLfloat g;
GLfloat b;
};
void init()
{
glClearColor(1.0,1.0,1.0,0.0);
glColor3f(0.0,0.0,0.0);
glPointSize(1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0,640,0,480);
}
Color getPixelColor(GLint x, GLint y)
{
Color color;
glReadPixels(x,y,1,1,GL_RGB,GL_FLOAT,&color);
return color;
}
void setPixelColor(GLint x,GLint y,Color color)
{
glColor3f(color.r,color.g,color.b);
glBegin(GL_POINTS);
glVertex2i(x,y);
glEnd();
glFlush();
}

void floodFill(GLint x, GLint y, Color oldColor, Color newColor)
{
Color color;
color=getPixelColor(x,y);
if(color.r==oldColor.r&&color.g==oldColor.g&&color.b==oldColor.b)
{
setPixelColor(x,y,newColor);
floodFill(x+1,y,oldColor,newColor);
floodFill(x,y+1,oldColor,newColor);
floodFill(x-1,y,oldColor,newColor);
floodFill(x,y-1,oldColor,newColor);
}
return;
}
void onMouseClick(int button,int state,int x,int y)
{
Color newColor={1.0f,0.0f,0.0f};
Color oldColor={1.0f,1.0f,1.0f};
floodFill(320,240,oldColor,newColor);
}
void draw_circle(Point pC,GLfloat radius)
{
GLfloat step=1/radius;
GLfloat x,y;
for(GLfloat theta=0; theta<=360; theta+=step)
{
x=pC.x+(radius*cos(theta));
y=pC.y+(radius*sin(theta));
glVertex2i(x,y);
}
}
void display(void)
{
Point pt={320,240};
GLfloat radius=50;
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_POINTS);
draw_circle(pt,radius);
glEnd();
glFlush(); }

int main(int argc,char** argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
glutInitWindowSize(640,480);
glutInitWindowPosition(200,200);
glutCreateWindow("Open GL");
init();
glutDisplayFunc(display);
glutMouseFunc(onMouseClick);
glutMainLoop();
return 0;
}