float ctr_x = drag_x + drag_w/2, ctr_y = drag_y + drag_h/2;
gui->replace_x->update( plugin->config.replace_x = 100. * ctr_x / trk_w );
gui->replace_y->update( plugin->config.replace_y = 100. * ctr_y / trk_h );
float ctr_x = drag_x + drag_w/2, ctr_y = drag_y + drag_h/2;
gui->replace_x->update( plugin->config.replace_x = 100. * ctr_x / trk_w );
gui->replace_y->update( plugin->config.replace_y = 100. * ctr_y / trk_h );