Fix child frame placement issues (bug#29953)

* src/nsterm.h (NS_PARENT_WINDOW_LEFT_POS):
(NS_PARENT_WINDOW_TOP_POS): Get the parent frame through the frame
struct as invisible child windows are detached from their parents in
NS.
* src/nsterm.m (x_set_offset): Offscreen frames have `nil' screen
value, so handle that gracefully.  Child frames with negative left and
top should be positioned relative to the bottom right of the parent
frame.

2 files changed, 33 insertions, 19 deletions

diff --git a/src/nsterm.h b/src/nsterm.h
index c40ddf3284a..588b9fc6443 100644
--- a/src/nsterm.h
+++ b/src/nsterm.h
@@ -1073,11 +1073,11 @@ struct x_output
    window or, if there is no parent window, the screen. */
 #define NS_PARENT_WINDOW_LEFT_POS(f)                                    \
   (FRAME_PARENT_FRAME (f) != NULL                                       \
-   ? [[FRAME_NS_VIEW (f) window] parentWindow].frame.origin.x : 0)
+   ? [FRAME_NS_VIEW (FRAME_PARENT_FRAME (f)) window].frame.origin.x : 0)
 #define NS_PARENT_WINDOW_TOP_POS(f)                                     \
   (FRAME_PARENT_FRAME (f) != NULL                                       \
-   ? ([[FRAME_NS_VIEW (f) window] parentWindow].frame.origin.y          \
-      + [[FRAME_NS_VIEW (f) window] parentWindow].frame.size.height     \
+   ? ([FRAME_NS_VIEW (FRAME_PARENT_FRAME (f)) window].frame.origin.y    \
+      + [FRAME_NS_VIEW (FRAME_PARENT_FRAME (f)) window].frame.size.height \
       - FRAME_NS_TITLEBAR_HEIGHT (FRAME_PARENT_FRAME (f)))              \
    : [[[NSScreen screens] objectAtIndex: 0] frame].size.height)
 
diff --git a/src/nsterm.m b/src/nsterm.m
index 5798f4fd0b4..419a37033f7 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -1736,7 +1736,6 @@ x_set_offset (struct frame *f, int xoff, int yoff, int change_grav)
 {
   NSView *view = FRAME_NS_VIEW (f);
   NSArray *screens = [NSScreen screens];
-  NSScreen *fscreen = [screens objectAtIndex: 0];
   NSScreen *screen = [[view window] screen];
 
   NSTRACE ("x_set_offset");
@@ -1746,26 +1745,41 @@ x_set_offset (struct frame *f, int xoff, int yoff, int change_grav)
   f->left_pos = xoff;
   f->top_pos = yoff;
 
-  if (view != nil && screen && fscreen)
+  if (view != nil)
     {
-      f->left_pos = f->size_hint_flags & XNegative
-        ? [screen visibleFrame].size.width + f->left_pos - FRAME_PIXEL_WIDTH (f)
-        : f->left_pos;
-      /* We use visibleFrame here to take menu bar into account.
-         Ideally we should also adjust left/top with visibleFrame.origin.  */
-
-      f->top_pos = f->size_hint_flags & YNegative
-        ? ([screen visibleFrame].size.height + f->top_pos
-           - FRAME_PIXEL_HEIGHT (f) - FRAME_NS_TITLEBAR_HEIGHT (f)
-           - FRAME_TOOLBAR_HEIGHT (f))
-        : f->top_pos;
+      if (FRAME_PARENT_FRAME (f) == NULL && screen)
+        {
+          f->left_pos = f->size_hint_flags & XNegative
+            ? [screen visibleFrame].size.width + f->left_pos - FRAME_PIXEL_WIDTH (f)
+            : f->left_pos;
+          /* We use visibleFrame here to take menu bar into account.
+             Ideally we should also adjust left/top with visibleFrame.origin.  */
+
+          f->top_pos = f->size_hint_flags & YNegative
+            ? ([screen visibleFrame].size.height + f->top_pos
+               - FRAME_PIXEL_HEIGHT (f) - FRAME_NS_TITLEBAR_HEIGHT (f)
+               - FRAME_TOOLBAR_HEIGHT (f))
+            : f->top_pos;
 #ifdef NS_IMPL_GNUSTEP
-      if (FRAME_PARENT_FRAME (f) == NULL)
-        {
           if (f->left_pos < 100)
             f->left_pos = 100;  /* don't overlap menu */
-        }
 #endif
+        }
+      else if (FRAME_PARENT_FRAME (f) != NULL)
+        {
+          struct frame *parent = FRAME_PARENT_FRAME (f);
+
+          /* On X negative values for child frames always result in
+             positioning relative to the bottom right corner of the
+             parent frame.  */
+          if (f->left_pos < 0)
+            f->left_pos = FRAME_PIXEL_WIDTH (parent) - FRAME_PIXEL_WIDTH (f) + f->left_pos;
+
+          if (f->top_pos < 0)
+            f->top_pos = FRAME_PIXEL_HEIGHT (parent) + FRAME_TOOLBAR_HEIGHT (parent)
+              - FRAME_PIXEL_HEIGHT (f) + f->top_pos;
+        }
+
       /* Constrain the setFrameTopLeftPoint so we don't move behind the
          menu bar.  */
       NSPoint pt = NSMakePoint (SCREENMAXBOUND (f->left_pos