/// <summary>
        /// Apply new font family
        /// </summary>
        public static bool ApplyFontFamily(DrawingCanvas drawingCanvas, string value, bool addToHistory)
        {
            CommandChangeState command = new CommandChangeState(drawingCanvas);
            bool wasChange = false;

            foreach (GraphicsBase g in drawingCanvas.Selection)
            {
                GraphicsText gt = g as GraphicsText;

                if (gt != null)
                {
                    if (gt.TextFontFamilyName != value)
                    {
                        gt.TextFontFamilyName = value;
                        wasChange = true;
                    }
                }
            }

            if (wasChange  && addToHistory )
            {
                command.NewState(drawingCanvas);
                drawingCanvas.AddCommandToHistory(command);
            }

            return wasChange;
        }
 /// <summary>
 /// Add change to history.
 /// Called after finishing moving/resizing.
 /// </summary>
 public void AddChangeToHistory(DrawingCanvas drawingCanvas)
 {
     if (commandChangeState != null && wasMove)
     {
         // Keep state after moving/resizing and add command to history
         commandChangeState.NewState(drawingCanvas);
         drawingCanvas.AddCommandToHistory(commandChangeState);
         commandChangeState = null;
     }
 }
        /// <summary>
        /// Apply new color
        /// </summary>
        public static bool ApplyColor(DrawingCanvas drawingCanvas, Color value, bool addToHistory)
        {
            CommandChangeState command = new CommandChangeState(drawingCanvas);
            bool wasChange = false;

            foreach (GraphicsBase g in drawingCanvas.Selection)
            {
                if (g.ObjectColor != value)
                {
                    g.ObjectColor = value;
                    wasChange = true;
                }
            }

            if ( wasChange && addToHistory )
            {
                command.NewState(drawingCanvas);
                drawingCanvas.AddCommandToHistory(command);
            }

            return wasChange;
        }
        /// <summary>
        /// Hide in-place editing textbox.
        /// Called from TextTool, when user pressed Enter or Esc,
        /// or from this class, when user clicks on the canvas.
        /// 
        /// graphicsText passed to this function can be new text added by
        /// ToolText, or existing text opened for editing.
        /// If ToolText.OldText is empty, this is new object.
        /// If not, this is existing object.
        /// </summary>
        internal void HideTextbox(GraphicsText graphicsText)
        {
            if (toolText.TextBox == null)
            {
                return;
            }

            graphicsText.IsSelected = true;   // restore selection which was removed for better textbox appearance

            if (toolText.TextBox.Text.Trim().Length == 0)
            {
                // Textbox is empty: remove text object.

                if (!String.IsNullOrEmpty(toolText.OldText))  // existing text was edited
                {
                    // Since text object is removed now,
                    // Add Delete command to the history
                    undoManager.AddCommandToHistory(new CommandDelete(this));
                }

                // Remove empty text object
                graphicsList.Remove(graphicsText);
            }
            else
            {
                if (!String.IsNullOrEmpty(toolText.OldText))  // existing text was edited
                {
                    if (toolText.TextBox.Text.Trim() != toolText.OldText)     // text was really changed
                    {
                        // Create command
                        CommandChangeState command = new CommandChangeState(this);

                        // Make change in the text object
                        graphicsText.Text = toolText.TextBox.Text.Trim();
                        graphicsText.UpdateRectangle();

                        // Keep state after change and add command to the history
                        command.NewState(this);
                        undoManager.AddCommandToHistory(command);
                    }
                }
                else                                          // new text was added
                {
                    // Make change in the text object
                    graphicsText.Text = toolText.TextBox.Text.Trim();
                    graphicsText.UpdateRectangle();

                    // Add command to the history
                    undoManager.AddCommandToHistory(new CommandAdd(graphicsText));
                }
            }

            // Remove textbox and set it to null.
            this.Children.Remove(toolText.TextBox);
            toolText.TextBox = null;

            // This enables back all ApplicationCommands,
            // which are disabled while textbox is active.
            this.Focus();
        }
        /// <summary>
        /// Apply currently active properties to selected objects
        /// </summary>
        public static void ApplyProperties(DrawingCanvas drawingCanvas)
        {
            // Apply every property.
            // Call every Apply* function with addToHistory = false.
            // History is updated here and not in called functions.

            CommandChangeState command = new CommandChangeState(drawingCanvas);
            bool wasChange = false;

            // Line Width
            if ( ApplyLineWidth(drawingCanvas, drawingCanvas.LineWidth, false))
            {
                wasChange = true;
            }

            // Color
            if ( ApplyColor(drawingCanvas, drawingCanvas.ObjectColor, false) )
            {
                wasChange = true;
            }

            // Font properties
            if ( ApplyFontFamily(drawingCanvas, drawingCanvas.TextFontFamilyName, false) )
            {
                wasChange = true;
            }

            if ( ApplyFontSize(drawingCanvas, drawingCanvas.TextFontSize, false) )
            {
                wasChange = true;
            }

            if ( ApplyFontStretch(drawingCanvas, drawingCanvas.TextFontStretch, false) )
            {
                wasChange = true;
            }

            if ( ApplyFontStyle(drawingCanvas, drawingCanvas.TextFontStyle, false) )
            {
                wasChange = true;
            }

            if ( ApplyFontWeight(drawingCanvas, drawingCanvas.TextFontWeight, false) )
            {
                wasChange = true;
            }

            if ( wasChange )
            {
                command.NewState(drawingCanvas);
                drawingCanvas.AddCommandToHistory(command);
            }
        }
        /// <summary>
        /// Apply new line width
        /// </summary>
        public static bool ApplyLineWidth(DrawingCanvas drawingCanvas, double value, bool addToHistory)
        {
            CommandChangeState command = new CommandChangeState(drawingCanvas);
            bool wasChange = false;

            // LineWidth is set for all objects except of GraphicsText.
            // Though GraphicsText has this property, it should remain constant.

            foreach(GraphicsBase g in drawingCanvas.Selection)
            {
                if (g is GraphicsTableBlock ||
                     g is GraphicsBeacon ||
                     g is GraphicsBarrier)
                {
                    if ( g.LineWidth != value )
                    {
                        g.LineWidth = value;
                        wasChange = true;
                    }
                }
            }

            if (wasChange  && addToHistory)
            {
                command.NewState(drawingCanvas);
                drawingCanvas.AddCommandToHistory(command);
            }

            return wasChange;
        }
        /// <summary>
        /// Apply new font style
        /// </summary>
        public static bool ApplyFontStyle(DrawingCanvas drawingCanvas, FontStyle value, bool addToHistory)
        {
            CommandChangeState command = new CommandChangeState(drawingCanvas);
            bool wasChange = false;

            foreach (GraphicsBase g in drawingCanvas.GraphicsList)
            {
                if (g.IsSelected)
                {
                    GraphicsText gt = g as GraphicsText;

                    if (gt != null)
                    {
                        if (gt.TextFontStyle != value)
                        {
                            gt.TextFontStyle = value;
                            wasChange = true;
                        }
                    }
                }
            }

            if (wasChange  && addToHistory)
            {
                command.NewState(drawingCanvas);
                drawingCanvas.AddCommandToHistory(command);
            }

            return wasChange;
        }
        /// <summary>
        /// Handle mouse down.
        /// Start moving, resizing or group selection.
        /// </summary>
        public override void OnMouseDown(DrawingCanvas drawingCanvas, MouseButtonEventArgs e)
        {
            commandChangeState = null;
            wasMove = false;

            Point point = e.GetPosition(drawingCanvas);

            selectMode = SelectionMode.None;

            GraphicsBase o;
            GraphicsBase movedObject = null;
            int handleNumber;

            // Test for resizing (only if control is selected, cursor is on the handle)
            for (int i = drawingCanvas.GraphicsList.Count - 1; i >= 0; i--)
            {
                o = drawingCanvas[i];

                if ( o.IsSelected )
                {
                    handleNumber = o.MakeHitTest(point);

                    if (handleNumber > 0)
                    {
                        selectMode = SelectionMode.Size;

                        // keep resized object in class member
                        resizedObject = o;
                        resizedObjectHandle = handleNumber;

                        // Since we want to resize only one object, unselect all other objects
                        HelperFunctions.UnselectAll(drawingCanvas);
                        o.IsSelected = true;

                        commandChangeState = new CommandChangeState(drawingCanvas);

                        break;
                    }
                }
            }

            // Test for move (cursor is on the object)
            if (selectMode == SelectionMode.None)
            {
                for (int i = drawingCanvas.GraphicsList.Count - 1; i >= 0; i--)
                {
                    o = drawingCanvas[i];

                    if (o.MakeHitTest(point) == 0)
                    {
                        movedObject = o;
                        break;
                    }
                }

                if (movedObject != null)
                {
                    selectMode = SelectionMode.Move;

                    // Unselect all if Ctrl is not pressed and clicked object is not selected yet
                    if (Keyboard.Modifiers != ModifierKeys.Control  && ! movedObject.IsSelected)
                    {
                        HelperFunctions.UnselectAll(drawingCanvas);
                    }

                    // Select clicked object
                    movedObject.IsSelected = true;
                    drawingCanvas.SelectedObject = movedObject;

                    // Set move cursor
                    drawingCanvas.Cursor = Cursors.SizeAll;

                    commandChangeState = new CommandChangeState(drawingCanvas);
                }
            }

            // Click on background
            if (selectMode == SelectionMode.None)
            {
                // Unselect all if Ctrl is not pressed
                if (Keyboard.Modifiers != ModifierKeys.Control)
                {
                    HelperFunctions.UnselectAll(drawingCanvas);
                }

                // Group selection. Create selection rectangle.
                GraphicsSelectionRectangle r = new GraphicsSelectionRectangle(
                    point.X, point.Y,
                    point.X + 1, point.Y + 1,
                    drawingCanvas.ActualScale);

                r.Clip = new RectangleGeometry(new Rect(0, 0, drawingCanvas.ActualWidth, drawingCanvas.ActualHeight));

                drawingCanvas.GraphicsList.Add(r);

                selectMode = SelectionMode.GroupSelection;
            }

            lastPoint = point;

            // Capture mouse until MouseUp event is received
            drawingCanvas.CaptureMouse();
        }