Add dragThreshold property to Event Handlers

We need drag threshold to be adjustable on each handler instance instead
of relying only on the system default drag threshold. For example in
some use cases DragHandler needs to work with a threshold of 0 or 1 to
start dragging as soon as the point is pressed or as soon as the point
is moved, with no "jump", to enable fine adjustment of a value on some
control such as a Slider.

This involves moving the dragOverThreshold() functions that handlers are
using from QQuickWindowPrivate to QQuickPointerHandlerPrivate, so that
they can use the adjustable threshold value.

Task-number: QTBUG-68075
Change-Id: Ie720cbbf9f30abb40d1731d92f8e7f1e6534eeb5
Reviewed-by: Jan Arve Sæther <jan-arve.saether@qt.io>

1 files changed, 58 insertions, 7 deletions

diff --git a/tests/manual/pointer/pointerDrag.qml b/tests/manual/pointer/pointerDrag.qml
index 79044eb0b4..2063d8fae2 100644
--- a/tests/manual/pointer/pointerDrag.qml
+++ b/tests/manual/pointer/pointerDrag.qml
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2018 The Qt Company Ltd.
+** Copyright (C) 2019 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the manual tests of the Qt Toolkit.
@@ -26,7 +26,7 @@
 **
 ****************************************************************************/
 
-import QtQuick 2.12
+import QtQuick 2.15
 import "content"
 
 Rectangle {
@@ -74,7 +74,14 @@ Rectangle {
             label: "DragHandler"
             objectName: "dragSquircle1"
             DragHandler {
-
+                dragThreshold: ckZeroDragThreshold1.checked ? 0 : undefined
+            }
+            CheckBox {
+                id: ckZeroDragThreshold1
+                label: " Zero threshold"
+                anchors.horizontalCenter: parent.horizontalCenter
+                y: 20
+                checked: false
             }
         }
 
@@ -99,7 +106,16 @@ Rectangle {
                 id: tap2
                 gesturePolicy: root.globalGesturePolicy
             }
-            DragHandler { }
+            DragHandler {
+                dragThreshold: ckZeroDragThreshold2.checked ? 0 : undefined
+            }
+            CheckBox {
+                id: ckZeroDragThreshold2
+                label: " Zero threshold"
+                anchors.horizontalCenter: parent.horizontalCenter
+                y: 32
+                checked: false
+            }
         }
 
         TextBox {
@@ -107,7 +123,16 @@ Rectangle {
             width: 100; height: 100
             label: "DragHandler\nTapHandler"
             color: queryColor(tap3.pressed)
-            DragHandler { }
+            DragHandler {
+                dragThreshold: ckZeroDragThreshold3.checked ? 0 : undefined
+            }
+            CheckBox {
+                id: ckZeroDragThreshold3
+                label: " Zero threshold"
+                anchors.horizontalCenter: parent.horizontalCenter
+                y: 32
+                checked: false
+            }
             TapHandler {
                 id: tap3
                 gesturePolicy: root.globalGesturePolicy
@@ -118,7 +143,16 @@ Rectangle {
             x: 400; y: 0
             width: 100; height: 100
             label: "DragHandler"
-            DragHandler { }
+            DragHandler {
+                dragThreshold: ckZeroDragThreshold4.checked ? 0 : undefined
+            }
+            CheckBox {
+                id: ckZeroDragThreshold4
+                label: " Zero threshold"
+                anchors.horizontalCenter: parent.horizontalCenter
+                y: 20
+                checked: false
+            }
 
             TextBox {
                 label: "TapHandler"
@@ -145,6 +179,13 @@ Rectangle {
                 label: " Greedy ↓"
                 checked: true
             }
+            CheckBox {
+                id: ckZeroDragThreshold5
+                label: " Zero threshold"
+                x: 10
+                anchors.bottom: ckGreedyDrag.top
+                checked: false
+            }
             TapHandler {
                 id: tap5
                 gesturePolicy: root.globalGesturePolicy
@@ -159,6 +200,7 @@ Rectangle {
                 DragHandler {
                     grabPermissions: ckGreedyDrag ? DragHandler.CanTakeOverFromAnything :
                         DragHandler.CanTakeOverFromItems | DragHandler.CanTakeOverFromHandlersOfDifferentType | DragHandler.ApprovesTakeOverByAnything
+                    dragThreshold: ckZeroDragThreshold5.checked ? 0 : undefined
                 }
             }
         }
@@ -174,7 +216,16 @@ Rectangle {
                 label: "DragHandler"
                 x: (parent.width - width)/2
                 y: 60
-                DragHandler { }
+                DragHandler {
+                    dragThreshold: ckZeroDragThreshold6.checked ? 0 : undefined
+                }
+            }
+            CheckBox {
+                id: ckZeroDragThreshold6
+                label: " Zero threshold"
+                anchors.horizontalCenter: parent.horizontalCenter
+                y: 20
+                checked: false
             }
         }