#include <GL/glut.h>
#include <math.h>
#include <time.h>
#define W 512
#define H 512
int points[2][2];
int point_count=0;
void initialize(){
	glClearColor( 0.0, 0.0, 0.0, 0.0);//set background color to black
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	gluOrtho2D(0, W,0,H);
}

void setPixel(int x, int y){	//change color of a pixel
	glColor3f(1, 1, 1);
	y=H-y;
	glBegin(GL_POINTS);
	glVertex2f(x,y);
	glEnd();
}

void LineWithDDA(int x0, int y0, int x1, int y1) {//DDa line algorithm
    int dy = y1 - y0;
    int dx = x1 - x0;
    int steps,i;
    float xinc,yinc,x=x0,y=y0;
    if( fabs(dx) > fabs(dy)){
        steps=fabs(dx);
    }else{
          steps=fabs(dy);
    }
    xinc=(float) dx/ (float) steps;
    yinc=(float) dy/ (float) steps;
    setPixel(round(x), round(y));
    for(i=0;i<steps;i++){
         x+=xinc;
         y+=yinc;
         setPixel(round(x), round(y));
    }
    glutSwapBuffers();
}
void lineSegment(){
    glClear(GL_COLOR_BUFFER_BIT);
    glutSwapBuffers();
    LineWithDDA(W/2,0,W/2,H);
    LineWithDDA(0,H/2,W,H/2);
}
void Control(int button, int state, int x, int y){

  // Respond to mouse button presses.
  // If button1 pressed, mark this state so we know in motion function.

  if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN)
    {
  			setPixel(x,y);
  			if(point_count<1){
					points[0][0]=x;
					points[0][1]=y;
					point_count++;
			}else{
					points[1][0]=x;
	 			    points[1][1]=y;
			        use_dda(points[0][0],points[0][1],points[1][0],points[1][1]);
			        point_count=0;
			}
	      glutSwapBuffers();
    }
}
int main(int argc, char** argv) {
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGB);
	glutInitWindowPosition(0,0);
	glutInitWindowSize(W,H);
	glutCreateWindow("OpenGL Mouse Function");
	initialize();
	glutMouseFunc(Control);
	glutDisplayFunc(lineSegment);
	glutMainLoop();
	return 0;
}