Fix [a01b6f7227]: WidthMMOfScreen returns 0 in VirtualBox VM using XWayland.

Actually, this is an XWayland bug, but better work-around it when possible.

1 files changed, 20 insertions, 1 deletions

diff --git a/unix/tkUnixEvent.c b/unix/tkUnixEvent.c
index a92b868..43f695c 100644
--- a/unix/tkUnixEvent.c
+++ b/unix/tkUnixEvent.c
@@ -166,7 +166,7 @@ TkpOpenDisplay(
     if (display == NULL) {
 	/*fprintf(stderr,"event=%d error=%d major=%d minor=%d reason=%d\nDisabling xkb\n",
 	event, error, major, minor, reason);*/
-	display  = XOpenDisplay(displayNameStr);
+	display = XOpenDisplay(displayNameStr);
     } else {
 	use_xkb = TK_DISPLAY_USE_XKB;
 	/*fprintf(stderr, "Using xkb %d.%d\n", major, minor);*/
@@ -188,6 +188,25 @@ TkpOpenDisplay(
 	    DisplayFileProc, dispPtr);
 
     /*
+     * Observed weird WidthMMOfScreen() in X on Wayland on a
+     * Fedora 30/i386 running in a VM. Fallback to 75 dpi,
+     * otherwise many other strange things may happen later.
+     * See: [https://core.tcl-lang.org/tk/tktview?name=a01b6f7227]
+     */
+    if (WidthMMOfScreen(DefaultScreenOfDisplay(display)) <= 0) {
+	int mm;
+
+	mm = WidthOfScreen(DefaultScreenOfDisplay(display)) * (25.4 / 75.0);
+	WidthMMOfScreen(DefaultScreenOfDisplay(display)) = mm;
+    }
+    if (HeightMMOfScreen(DefaultScreenOfDisplay(display)) <= 0) {
+	int mm;
+
+	mm = HeightOfScreen(DefaultScreenOfDisplay(display)) * (25.4 / 75.0);
+	HeightMMOfScreen(DefaultScreenOfDisplay(display)) = mm;
+    }
+
+    /*
      * Key map info must be available immediately, because of "send event".
      */
     TkpInitKeymapInfo(dispPtr);