Avoid divide by zero on buggy Xlib/Xserver implementations

Some X servers seem to report zero physical size, so our DPI
calculations would crash with divide-by-zero. Avoid this and just use
72 DPI instead.

Task-number: 258319

1 files changed, 14 insertions, 4 deletions

diff --git a/src/gui/kernel/qapplication_x11.cpp b/src/gui/kernel/qapplication_x11.cpp
index db349f0..d942519 100644
--- a/src/gui/kernel/qapplication_x11.cpp
+++ b/src/gui/kernel/qapplication_x11.cpp
@@ -1851,10 +1851,20 @@ void qt_init(QApplicationPrivate *priv, int,
             QX11InfoData *screen = X11->screens + s;
             screen->ref = 1; // ensures it doesn't get deleted
             screen->screen = s;
-            screen->dpiX = (DisplayWidth(X11->display, s) * 254 + DisplayWidthMM(X11->display, s)*5)
-                           / (DisplayWidthMM(X11->display, s)*10);
-            screen->dpiY = (DisplayHeight(X11->display, s) * 254 + DisplayHeightMM(X11->display, s)*5)
-                           / (DisplayHeightMM(X11->display, s)*10);
+
+            int widthMM = DisplayWidthMM(X11->display, s);
+            if (widthMM != 0) {
+                screen->dpiX = (DisplayWidth(X11->display, s) * 254 + widthMM * 5) / (widthMM * 10);
+            } else {
+                screen->dpiX = 72;
+            }
+
+            int heightMM = DisplayHeightMM(X11->display, s);
+            if (heightMM != 0) {
+                screen->dpiY = (DisplayHeight(X11->display, s) * 254 + heightMM * 5) / (heightMM * 10);
+            } else {
+                screen->dpiY = 72;
+            }
 
             X11->argbVisuals[s] = 0;
             X11->argbColormaps[s] = 0;