JDK-8220272: Found the problem + possible fix

[Kevin Rushforth]

Hi Thiago,

If you are interested in contributing a fix, please see CONTRIBUTING.md 
[1] for instructions. Before we can evaluate your proposed fix, we will 
need is a signed OCA [2] from you.

Thank you.

-- Kevin

[1] 
https://github.com/javafxports/openjdk-jfx/blob/develop/.github/CONTRIBUTING.md
[2] http://www.oracle.com/technetwork/community/oca-486395.html

On 4/14/2019 5:46 PM, Thiago Milczarek Sayao wrote:
> * THE PROBLEM *
>
> In GlassApplication.cpp, the GDK_FOCUS_CHANGE event gets called from the last window to the first on my setup (I suspect "out-of-order" on some setups and even occasionally in the expected order). So the code to keep the latest enabled window fails (refering to WindowStage.java activeWindows) - that's why the "First Window" (on the code to reproduce the bug report) shows on top - because openjfx thinks it was the latest window. In WindowStage.java:
>
>      final void handleFocusDisabled() {
>          if (activeWindows.isEmpty()) {
>              return;
>          }
>          WindowStage window = activeWindows.get(activeWindows.size() - 1); //<-- HERE!!
>          window.setIconified(false);
>          window.requestToFront();
>          window.requestFocus();
>      }
>
> When there is a WINDOW_MODAL this code gets called because the modal window disable it's parents (so they do not get events - it's correct). So openjfx brings up what it thinks it's the latest window - but since the out of order GDK_FOCUS_CHANGE - it's the wrong window (activeWindows list has not the correct order).
>
> The Gtk docs states GDK_FOCUS_CHANGE is true "if the window has gained the keyboard focus" which may not be directly correlated to openjfx's WindowEvent.FOCUS_GAINED.
>
> * THE FIX *
>
> To fix this, WindowEvent.FOCUS_GAINED must be called in order of which window is shown (because the window is inserted on activeWindows at this event).
>
> So I have modified glass_window.cpp to immediately call WindowEvent.FOCUS_GAINED when showing the window:
>
> void WindowContextBase::set_visible(bool visible) {
>      if (visible) {
>          gtk_widget_show_all(gtk_widget);
>
>          //JDK-8220272 - fire event first because GDK_FOCUS_CHANGE is not always in order
>          if(jwindow && isEnabled()) {
>              mainEnv->CallVoidMethod(jwindow, jWindowNotifyFocus, com_sun_glass_events_WindowEvent_FOCUS_GAINED);
>          }
>      } else {
>          gtk_widget_hide(gtk_widget);
>          if (jview && is_mouse_entered) {
>              is_mouse_entered = false;
>              mainEnv->CallVoidMethod(jview, jViewNotifyMouse,
>                      com_sun_glass_events_MouseEvent_EXIT,
>                      com_sun_glass_events_MouseEvent_BUTTON_NONE,
>                      0, 0,
>                      0, 0,
>                      0,
>                      JNI_FALSE,
>                      JNI_FALSE);
>              CHECK_JNI_EXCEPTION(mainEnv)
>          }
>      }
> }
>
> Did some tests and it seems to fix the problem.
>
> I do not have permission to make a PR, so posting the fix here. Will happily do the PR if required.
>
> Thanks.
>