DDA Line Drawing Algorithm 

void MainWindow::dda_line(float x1,float y1,float x2,float y2){

      float dx,dy,steps,xinc,yinc;

      int x,y;

      steps = abs(dx);

      if(abs(dy)>abs(dx)){

          steps = abs(dy);

      }

      x = x1;

      y = y1;

      int i = 0;

      while(i<steps){

          img.setPixel(x,y,qRgb(0,255,0));

          x = x+xinc;

          y = y+yinc;

          i++;

      }

}