Android: Support double click event

It's impossible to get the distance between two touch events
down to 5 pixels on e.g. my Nexus 5.

This patch makes it possible to tweak the distance through
the platform theme, and sets the distance to 15% of an inch
on Android. Also provides a way to override the default minimum
of 5 pixels by using an environment variable.

[ChangeLog][Android] Fixed double click events

Task-number: QTBUG-36974
Change-Id: I23d94020c531747d6638b645133611614a2a0703
Reviewed-by: BogDan Vatra <bogdan@kde.org>

src/gui/kernel/qguiapplication.cpp

@@ -145,7 +145,7 @@ ulong QGuiApplicationPrivate::mousePressTime = 0;
 Qt::MouseButton QGuiApplicationPrivate::mousePressButton = Qt::NoButton;
 int QGuiApplicationPrivate::mousePressX = 0;
 int QGuiApplicationPrivate::mousePressY = 0;
-int QGuiApplicationPrivate::mouse_double_click_distance = 5;
+int QGuiApplicationPrivate::mouse_double_click_distance = -1;
 
 static Qt::LayoutDirection layout_direction = Qt::LeftToRight;
 static bool force_reverse = false;
@@ -1255,6 +1255,8 @@ void QGuiApplicationPrivate::init()
     initPalette();
     QFont::initialize();
 
+    mouse_double_click_distance = platformTheme()->themeHint(QPlatformTheme::MouseDoubleClickDistance).toInt();
+
 #ifndef QT_NO_CURSOR
     QCursorData::initialize();
 #endif

src/gui/kernel/qplatformtheme.cpp

@@ -499,6 +499,8 @@ QVariant QPlatformTheme::defaultThemeHint(ThemeHint hint)
         return QVariant(false);
     case MousePressAndHoldInterval:
         return QVariant(800);
+    case MouseDoubleClickDistance:
+        return QVariant(5);
     }
     return QVariant();
 }

src/gui/kernel/qplatformtheme.h

@@ -108,7 +108,8 @@ public:
         PasswordMaskCharacter,
         DialogSnapToDefaultButton,
         ContextMenuOnMouseRelease,
-        MousePressAndHoldInterval
+        MousePressAndHoldInterval,
+        MouseDoubleClickDistance
     };
 
     enum DialogType {

src/plugins/platforms/android/qandroidplatformtheme.cpp

@@ -47,6 +47,7 @@
 #include <QVariant>
 #include <QFileInfo>
 #include <QCoreApplication>
+#include <private/qguiapplication_p.h>
 #include <qandroidplatformintegration.h>
 
 QAndroidPlatformTheme::QAndroidPlatformTheme(QAndroidPlatformNativeInterface *androidPlatformNativeInterface)
@@ -179,7 +180,30 @@ QVariant QAndroidPlatformTheme::themeHint(ThemeHint hint) const
             return QStringList("android");
         }
         return QStringList("fusion");
-        break;
+
+    case MouseDoubleClickDistance:
+    {
+            int minimumDistance = qgetenv("QT_ANDROID_MINIMUM_MOUSE_DOUBLE_CLICK_DISTANCE").toInt();
+            int ret = minimumDistance;
+
+            QAndroidPlatformIntegration *platformIntegration
+                    = static_cast<QAndroidPlatformIntegration *>(QGuiApplicationPrivate::platformIntegration());
+            QAndroidPlatformScreen *platformScreen = platformIntegration->screen();
+            if (platformScreen != 0) {
+                QScreen *screen = platformScreen->screen();
+                qreal dotsPerInch = screen->physicalDotsPerInch();
+
+                // Allow 15% of an inch between clicks when double clicking
+                int distance = qRound(dotsPerInch * 0.15);
+                if (distance > minimumDistance)
+                    ret = distance;
+            }
+
+            if (ret > 0)
+                return ret;
+
+            // fall through
+    }
     default:
         return QPlatformTheme::themeHint(hint);
     }