Wayland: Fix for "Dropdown menu moves when navigated" (#613)

This commit uses Wayland popup positionning methods to handle common
menu windows and prevents them from expanding below display bottom or above top.
The previous algorithm remains in place for menu windows higher than
the display height. Further changes for these big menus may come later.

1 files changed, 20 insertions, 4 deletions

diff --git a/src/drivers/Wayland/Fl_Wayland_Window_Driver.cxx b/src/drivers/Wayland/Fl_Wayland_Window_Driver.cxx
index 09a0feb1a..f5399af0c 100644
--- a/src/drivers/Wayland/Fl_Wayland_Window_Driver.cxx
+++ b/src/drivers/Wayland/Fl_Wayland_Window_Driver.cxx
@@ -1005,6 +1005,13 @@ Fl_X *Fl_Wayland_Window_Driver::makeWindow()
     xdg_positioner_set_size(positioner, pWindow->w() * f , pWindow->h() * f );
     xdg_positioner_set_anchor(positioner, XDG_POSITIONER_ANCHOR_TOP_LEFT);
     xdg_positioner_set_gravity(positioner, XDG_POSITIONER_GRAVITY_BOTTOM_RIGHT);
+    int XX, YY, WW, HH;
+    Fl::screen_xywh(XX, YY, WW, HH, parent_win->screen_num());
+    if (pWindow->h() <= HH) {
+      // prevent menuwindow from expanding beyond display bottom
+      xdg_positioner_set_constraint_adjustment(positioner,
+                                             XDG_POSITIONER_CONSTRAINT_ADJUSTMENT_SLIDE_Y);
+    }
     new_window->xdg_popup = xdg_surface_get_popup(new_window->xdg_surface, parent_xdg, positioner);
     xdg_positioner_destroy(positioner);
     xdg_popup_add_listener(new_window->xdg_popup, &popup_listener, new_window);
@@ -1550,10 +1557,19 @@ void Fl_Wayland_Window_Driver::reposition_menu_window(int x, int y) {
 void Fl_Wayland_Window_Driver::menu_window_area(int &X, int &Y, int &W, int &H, int nscreen) {
   Fl_Window *parent = Fl_Window_Driver::menu_parent();
   if (parent) {
-    X = parent->x();
-    Y = parent->y();
-    W = parent->w();
-    H = parent->h();
+    int XX,YY,WW,HH;
+    Fl::screen_xywh(XX, YY, WW, HH, parent->screen_num());
+    if (pWindow->h() > HH) { // the menu window is higher than the display
+      X = parent->x();
+      Y = parent->y();
+      W = parent->w();
+      H = parent->h();
+    } else { // position the menu window by wayland constraints
+      X = -50000;
+      Y = -50000;
+      W = 1000000;
+      H = 1000000;
+    }
     //printf("menu_window_area: %dx%d - %dx%d\n",X,Y,W,H);
   } else Fl_Window_Driver::menu_window_area(X, Y, W, H, nscreen);
 }