OpenGL-BoundaryFill-Square.cpp

#include <math.h>
#include <gl/glut.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 BoundaryFill(int x, int y, Color fillColor, Color boundaryColor) {
	Color currentColor = getPixelColor(x, y);
	if(currentColor.r != boundaryColor.r && currentColor.g != boundaryColor.g && currentColor.b != boundaryColor.b) {
		setPixelColor(x, y, fillColor);
		BoundaryFill(x+1, y, fillColor, boundaryColor);
		BoundaryFill(x-1, y, fillColor, boundaryColor);
		BoundaryFill(x, y+1, fillColor, boundaryColor);
		BoundaryFill(x, y-1, fillColor, boundaryColor);
	}
}

void onMouseClick(int button, int state, int x, int y)
{
	Color fillColor = {1.0f, 0.0f, 0.0f};		// red color will be filled
	Color boundaryColor = {0.0f, 0.0f, 0.0f}; // black- boundary

	Point p = {321, 241}; // a point inside the square

	BoundaryFill(p.x, p.y, fillColor, boundaryColor);
}

void draw_dda(Point p1, Point p2) {
	GLfloat dx = p2.x - p1.x;
	GLfloat dy = p2.y - p1.y;

	GLfloat x1 = p1.x;
	GLfloat y1 = p1.y;

	GLfloat step = 0;

	if(abs(dx) > abs(dy)) {
		step = abs(dx);
	} else {
		step = abs(dy);
	}

	GLfloat xInc = dx/step;
	GLfloat yInc = dy/step;

	for(float i = 1; i <= step; i++) {
		glVertex2i(x1, y1);
		x1 += xInc;
		y1 += yInc;
	}
}

void draw_square(Point a, GLint length) {
	Point b = {a.x + length, a.y},
		c = {b.x,	b.y+length},
		d = {c.x-length, c.y};

	draw_dda(a, b);
	draw_dda(b, c);
	draw_dda(c, d);
	draw_dda(d, a);	
}

void display(void) {
	Point pt = {320, 240};
	GLfloat length = 50;

	glClear(GL_COLOR_BUFFER_BIT);
	glBegin(GL_POINTS);
		draw_square(pt, length);
	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;
}