new feature: tracking with display

[alexlib]

In the old version Tcl/Tk we had

		/* ******** Draw links now ******** */
		if (display)
			for (h=0;h<m[1];h++)
		{
			if(mega[1][h].next != -2 ) {

				strcpy(buf,"");
				sprintf(buf ,"green");

				for (j=0;j<n_img;j++)
				{
					if(c4[1][h].p[j]>0 && c4[2][mega[1][h].next].p[j]>0) {
						xp[j]=t4[1][j][c4[1][h].p[j]].x;
						yp[j]=t4[1][j][c4[1][h].p[j]].y;
						xc[j]=t4[2][j][c4[2][mega[1][h].next].p[j]].x;
						yc[j]=t4[2][j][c4[2][mega[1][h].next].p[j]].y;
						predict (xp[j], yp[j], xc[j], yc[j], &xn[j], &yn[j]);

						if ( ( fabs(xp[j]-zoom_x[j]) < imx/(2*zoom_f[j]))
							&& (fabs(yp[j]-zoom_y[j]) < imy/(2*zoom_f[j])))
						{
							strcpy(val,"");
							sprintf(val ,"orange");

							intx0 = (int)(imx/2+zoom_f[j]*(xp[j]-zoom_x[j]));
							inty0 = (int)(imy/2+zoom_f[j]*(yp[j]-zoom_y[j]));
							intx1 = (int)(imx/2+zoom_f[j]*(xc[j]-zoom_x[j]));
							inty1 = (int)(imy/2+zoom_f[j]*(yc[j]-zoom_y[j]));
							intx2 = (int)(imx/2+zoom_f[j]*(xn[j]-zoom_x[j]));
							inty2 = (int)(imy/2+zoom_f[j]*(yn[j]-zoom_y[j]));

							drawcross(interp,intx0,inty0,cr_sz,j,"green");
							drawcross(interp,intx1,inty1,cr_sz+1,j,"yellow");
							drawcross(interp,intx2,inty2,cr_sz+1,j,"white");
							drawvector (interp, intx0, inty0, intx1, inty1, 2, j, buf);
							drawvector (interp, intx1, inty1, intx2, inty2, 1, j, "white");

							if (mega[1][h].finaldecis> 0.2) {
								draw_pnr ( interp, intx0, inty0, h, j, "white");
								draw_pnr ( interp, intx0, inty0+10, mega[1][h].next, j, val);
								draw_value (interp, intx0, inty0 + 20,mega[1][h].finaldecis, j, val);
							}
						}
					}
				}
			}
		}

write at the end of the track loop. Please add it. Think how to manage it with openptv-python and pyptv