1 /*
2 * Copyright 2009, Alexandre Deckner, alex@zappotek.com
3 * Distributed under the terms of the MIT License.
4 */
5
6 /*!
7 \class DragTrackingFilter
8 \brief A simple mouse drag detection filter
9 *
10 * A simple mouse filter that detects the start of a mouse drag over a
11 * threshold distance and sends a message with the 'what' field of your
12 * choice. Especially useful for drag and drop.
13 * Allows you to free your code of encumbering mouse tracking details.
14 *
15 * It can detect fast drags spanning outside of a small view by temporarily
16 * setting the B_POINTER_EVENTS flag on the view.
17 */
18
19 #include <DragTrackingFilter.h>
20
21 #include <Message.h>
22 #include <Messenger.h>
23 #include <View.h>
24
25 static const int kSquaredDragThreshold = 9;
26
DragTrackingFilter(BView * targetView,uint32 messageWhat)27 DragTrackingFilter::DragTrackingFilter(BView* targetView, uint32 messageWhat)
28 : BMessageFilter(B_ANY_DELIVERY, B_ANY_SOURCE),
29 fTargetView(targetView),
30 fMessageWhat(messageWhat),
31 fIsTracking(false),
32 fClickButtons(0)
33 {
34 }
35
36
37 filter_result
Filter(BMessage * message,BHandler **)38 DragTrackingFilter::Filter(BMessage* message, BHandler** /*_target*/)
39 {
40 if (fTargetView == NULL)
41 return B_DISPATCH_MESSAGE;
42
43 switch (message->what) {
44 case B_MOUSE_DOWN:
45 message->FindPoint("where", &fClickPoint);
46 message->FindInt32("buttons", (int32*)&fClickButtons);
47 fIsTracking = true;
48
49 fTargetView->SetMouseEventMask(B_POINTER_EVENTS);
50
51 return B_DISPATCH_MESSAGE;
52
53 case B_MOUSE_UP:
54 fIsTracking = false;
55 return B_DISPATCH_MESSAGE;
56
57 case B_MOUSE_MOVED:
58 {
59 BPoint where;
60 message->FindPoint("be:view_where", &where);
61
62 // TODO: be more flexible about buttons and pass their state
63 // in the message
64 if (fIsTracking && (fClickButtons & B_PRIMARY_MOUSE_BUTTON)) {
65
66 BPoint delta(fClickPoint - where);
67 float squaredDelta = (delta.x * delta.x) + (delta.y * delta.y);
68
69 if (squaredDelta >= kSquaredDragThreshold) {
70 BMessage dragClickMessage(fMessageWhat);
71 dragClickMessage.AddPoint("be:view_where", fClickPoint);
72 // name it "be:view_where" since BView::DragMessage
73 // positions the dragging frame/bitmap by retrieving the
74 // current message and reading that field
75 BMessenger messenger(fTargetView);
76 messenger.SendMessage(&dragClickMessage);
77
78 fIsTracking = false;
79 }
80 }
81 return B_DISPATCH_MESSAGE;
82 }
83 default:
84 break;
85 }
86
87 return B_DISPATCH_MESSAGE;
88 }
89