src/kits/shared/DragTrackingFilter.cpp

   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
  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
  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 }