add TouchDoubleTapDistance platform theme hint

Double-tapping on a touchscreen typically requires a higher threshold
than double-clicking with a mouse, because it's harder to hit the
same point twice with your finger.  This is intended for use in
QtQuick's new TapHandler.

[ChangeLog][QtGui] environment variable QT_DBL_TAP_DIST customizes
the amount of movement allowed when detecting a double tap via touch.

Change-Id: I83a9be363f22c1086fd39580aa95055f2b3ff5c7
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/gui/kernel/qplatformtheme.h b/src/gui/kernel/qplatformtheme.h
index 686dbed4b1..4135e31517 100644
--- a/src/gui/kernel/qplatformtheme.h
+++ b/src/gui/kernel/qplatformtheme.h
@@ -114,7 +114,8 @@ public:
         ContextMenuOnMouseRelease,
         MousePressAndHoldInterval,
         MouseDoubleClickDistance,
-        WheelScrollLines
+        WheelScrollLines,
+        TouchDoubleTapDistance
     };
 
     enum DialogType {