Crainiate Community

Hello,

I'm trying to make a scroll feature that will allow a user to drag & drop the diagram to scroll it (just like in Google Maps and many more...). I've overridden OnDiagramMouseDown, OnDiagramMouseUp and OnMouseMove in the Model class to capture proper mouse events (middle button in my case) and update AutoScrollPosition when mouse is moving, but it's very inefficient. It's not smooth, it looks very ugly, I don't know how to describe it well...
I think it may be caused by the fact that every time I change AutoScrollPosition the diagram is being drawn from scratch and the performance is not good enough for the OnMouseMove event, but I'm not sure... Do you know how can I make it look good ?

Best regards,
Ireneusz Patalas

Hi,

Can you post the code you use to scroll googlemaps style?

The component is optimised for smooth scrolling. When you scroll using scroll bars do you get the same effect?
You may want to attach an event hander to the Model.Render class to see if the diagram is beign re-rendered, this will cause the allocation of a new bitmap and this is an expensive operation.

Normally a diagram is only rendered if somehting has changed, or is scrolled outside of it's RenderRectangle. A RenderRectangle is normally 4 times the size of the viewable area.

It's more or less like this:

Protected Overrides Sub OnDiagramMouseDown(ByVal e As System.Windows.Forms.MouseEventArgs)
    If e.Button = Windows.Forms.MouseButtons.Middle Then
        ' remember the necessary values
        m_CanDragDiagram = True
        m_MouseDownPosition = e.Location
        m_MouseDownAutoScroll = AutoScrollPosition
        Me.Cursor = Cursors.SizeAll
    End If
    MyBase.OnDiagramMouseDown(e)
End Sub

Protected Overrides Sub OnDiagramMouseUp(ByVal e As System.Windows.Forms.MouseEventArgs)
    If e.Button = Windows.Forms.MouseButtons.Middle Then
        m_CanDragDiagram = False
        Cursor = Cursors.Default
    End If
    MyBase.OnDiagramMouseUp(e)
End Sub

Protected Overrides Sub OnMouseMove(ByVal e As System.Windows.Forms.MouseEventArgs)
    If m_CanDragDiagram Then
        ' difference between current mouse position and the position where the mouse was down
        Dim diff As Point = Point.Subtract(m_MouseDownPosition, New Size(e.Location))
        AutoScrollPosition = New Point(-m_MouseDownAutoScroll.X + diff.X, -m_MouseDownAutoScroll.Y + diff.Y)
    End If
    MyBase.OnMouseMove(e)
End Sub

When I scroll using scrollbars I do not get the same effect, so it's probably something wrong in my code. I've also attached a debug information to Render class and it seems to be called only a few times when I'm scrolling (sometimes only once).

I tried a quick sample by modifying the Editor Example to include the following subclass