allow use of null pointer as a valid cursor (implies using cursor of parent window)

gtk2_ardour/editor_canvas.cc

@@ -1012,7 +1012,7 @@ Editor::set_canvas_cursor (Gdk::Cursor* cursor)
 {
 	Glib::RefPtr<Gdk::Window> win = _track_canvas->get_window();
 
-	if (win && cursor) {
+	if (win && !_cursors->is_invalid (cursor)) {
 	        win->set_cursor (*cursor);
 	}
 }
@@ -1020,7 +1020,7 @@ Editor::set_canvas_cursor (Gdk::Cursor* cursor)
 size_t
 Editor::push_canvas_cursor (Gdk::Cursor* cursor)
 {
-	if (cursor) {
+	if (!_cursors->is_invalid (cursor)) {
 		_cursor_stack.push_back (cursor);
 		set_canvas_cursor (cursor);
 	}
@@ -1095,7 +1095,7 @@ Editor::which_trim_cursor (bool left) const
 Gdk::Cursor*
 Editor::which_mode_cursor () const
 {
-	Gdk::Cursor* mode_cursor = 0;
+	Gdk::Cursor* mode_cursor = _cursors->invalid_cursor ();
 
 	switch (mouse_mode) {
 	case MouseRange:
@@ -1161,7 +1161,7 @@ Editor::which_mode_cursor () const
 Gdk::Cursor*
 Editor::which_track_cursor () const
 {
-	Gdk::Cursor* cursor = 0;
+	Gdk::Cursor* cursor = _cursors->invalid_cursor();
 
 	switch (_join_object_range_state) {
 	case JOIN_OBJECT_RANGE_NONE:
@@ -1332,7 +1332,7 @@ Editor::choose_canvas_cursor_on_entry (ItemType type)
 
 	Gdk::Cursor* cursor = which_canvas_cursor(type);
 
-	if (cursor) {
+	if (!_cursors->is_invalid (cursor)) {
 		// Push a new enter context
 		const EnterContext ctx = { type, CursorContext::create(*this, cursor) };
 		_enter_stack.push_back(ctx);

gtk2_ardour/editor_drag.cc

@@ -234,11 +234,13 @@ Drag::swap_grab (ArdourCanvas::Item* new_item, Gdk::Cursor* cursor, uint32_t /*t
 	_item->ungrab ();
 	_item = new_item;
 
-	if (cursor == 0) {
-		_item->grab ();
+	if (!_cursor_ctx) {
+		_cursor_ctx = CursorContext::create (*_editor, cursor);
 	} else {
-		_item->grab ();
+		_cursor_ctx->change (cursor);
 	}
+
+	_item->grab ();
 }
 
 void
@@ -271,12 +273,11 @@ Drag::start_grab (GdkEvent* event, Gdk::Cursor *cursor)
 
 	_last_pointer_y = _grab_y;
 
-	if (cursor == 0) {
-		_item->grab ();
-	} else {
+	_item->grab ();
+
+	if (!_editor->cursors()->is_invalid (cursor)) {
 		/* CAIROCANVAS need a variant here that passes *cursor */
-		_item->grab ();
-		_cursor_ctx = CursorContext::create(*_editor, cursor);
+		_cursor_ctx = CursorContext::create (*_editor, cursor);
 	}
 
 	if (_editor->session() && _editor->session()->transport_rolling()) {
@@ -4151,7 +4152,7 @@ SelectionDrag::start_grab (GdkEvent* event, Gdk::Cursor*)
 		return;
 	}
 
-	Gdk::Cursor* cursor = 0;
+	Gdk::Cursor* cursor = _editor->cursors()->invalid_cursor();
 
 	switch (_operation) {
 	case CreateSelection:
@@ -4489,7 +4490,7 @@ RangeMarkerBarDrag::start_grab (GdkEvent* event, Gdk::Cursor *)
 		return;
 	}
 
-	Gdk::Cursor* cursor = 0;
+	Gdk::Cursor* cursor = _editor->cursors()->invalid_cursor();
 
 	if (!_editor->temp_location) {
 		_editor->temp_location = new Location (*_editor->session());

gtk2_ardour/mouse_cursors.cc

@@ -211,4 +211,11 @@ MouseCursors::set_cursor_set (const std::string& name)
 	midi_resize = new Cursor (SIZING);
 	midi_erase = new Cursor (DRAPED_BOX);
 	up_down = new Cursor (SB_V_DOUBLE_ARROW);
+	
+	{
+		char pix[4] = { 0, 0, 0, 0 };
+		RefPtr<Bitmap> bits = Bitmap::create (pix, 2, 2);
+		Color c;
+		_invalid = new Cursor (bits, bits, c, c, 0, 0);
+	}
 }

gtk2_ardour/mouse_cursors.h

@@ -73,11 +73,22 @@ public:
 	Gdk::Cursor* expand_left_right;
 	Gdk::Cursor* expand_up_down;
 
+	/* This cursor is not intended to be used directly, it just 
+	   serves as an out-of-bounds value when we need to indicate
+	   "no cursor". NULL/0 doesn't work for this, because it
+	   is actually a valid value for a Gdk::Cursor - it indicates
+	   "use the parent window's cursor"
+	*/
+	
+	bool is_invalid (Gdk::Cursor* c) const { return c == _invalid; }
+	Gdk::Cursor* invalid_cursor() const { return _invalid; }
+
     private:
 	std::string _cursor_set;
 	void drop_all ();
 
 	Gdk::Cursor* make_cursor (const char* name, int hotspot_x = 0, int hotspot_y = 0);
+	Gdk::Cursor* _invalid;
 };
 
 #endif /* __gtk2_ardour_mouse_cursors__ */