Window and with animated display fade in.

WindowTest.java

import com.google.gwt.dom.client.Style.Display;
import com.google.gwt.user.client.ui.RootPanel;
import com.sencha.gxt.fx.client.FxElement;
import com.sencha.gxt.fx.client.animation.Fx;
import com.sencha.gxt.widget.core.client.Window;
import com.sencha.gxt.widget.core.client.button.TextButton;
import com.sencha.gxt.widget.core.client.event.SelectEvent;
import com.sencha.gxt.widget.core.client.event.SelectEvent.SelectHandler;

public class WindowTest {
  public WindowTest() {
    TextButton button = new TextButton("Open");
    RootPanel.get().add(button, 50, 50);
    
    button.addSelectHandler(new SelectHandler() {
      @Override
      public void onSelect(SelectEvent event) {
        displayWindow();
      }
    });
  }

  private void displayWindow() {
    Window window = new Window();
    window.setPixelSize(200, 200);
    window.setShadow(false);
    window.show();
    window.getElement().getStyle().setDisplay(Display.NONE);
    
    // use default settings
    //window.getElement().<FxElement> cast().fadeToggle();
    
    // use custom settings
    Fx fx = new Fx(700);
    window.getElement().<FxElement> cast().fadeToggle(fx);
  }
}