WPF and Silverlight Pan and Zoom Controls

Question

I would like to understand the general WPF / Silverlight layout requirements for being able to implement drag and zoom. I do not mean panning and zooming the image, but for the layout of the general page (window) (or part of it) with some controls.

What features of the layout and what functions of the user controls used make the layout fixed, and panning and zooming is impossible?

Answer 1

General rule

With a few exceptions, everything in WPF can be expanded, enlarged, rotated, stretched, etc. up to your heart content. This includes individual controls, such as Button, composite controls, such as ListBox, and containers, such as StackPanel.

Exceptions

Here are the exceptions:

• If you use Adorner, and your AdornerDecorator is outside the expanded / enlarged area, then Adorners attached to your expanded / enlarged panorama area will pan, but not scale. The solution is to add an additional AdornerDecorator to the expanded / enlarged area.

• If you use Popup, it will be displayed in the expanded / enlarged location of its PlacementTarget, but it will not scale. It will also not move as you pan the area containing its PlacementTarget (basically it is on its surface above the target control). To get around this, use a zero-size canvas with a high order Z, and then when you want something to appear in the zoom / pan area.

• Any Menu context that you define will be displayed inside the popup, so menu items will be displayed in normal size, even if the area you clicked is enlarged or reduced. Due to the nature of the context menu, this is probably desirable behavior. If not, you can wrap the menu items in the ViewBox and snap the scale to your main scale.

• Your tooltips will be displayed in normal size, even if the user interface is resized or enlarged. The same solution as for ContextMenu.

• If you used WinForms integration with integrated legacy WinForms controls and the user interface, in certain situations they will not pan, zoom, and click correctly. There is an extended technique for working on this, where you manage WinForms off-screen, and then use BitBlt or a similar copy of the image in your window as an image, as well as drag and drop mouse clicks and keystrokes onto the screen window. This is a lot of work.

• If you bypass WPF and directly use GDI + or DirectX or use Win32 hWnds to display content or the user interface, then this content or the user interface will not display, scale, or snap to the window correctly unless you do it yourself in your interface code.

Final notes

• A good WPF interface always uses panels such as Grid, DockPanel, etc. to flexibly customize controls so that they automatically adjust to the size of containers, rather than fixed sizes and positions. This is also true for the inner contents of the pan / zoom area, but there is an exception to this rule: the outer element in the pan / zoom area must have a specified size. Otherwise, what will determine the area in which they will be expanded / enlarged?

• An easy way to implement pan / zoom capabilities is to configure the RenderTransform of the outermost pan / zoom control. There are many different ways to implement controls for panning and zooming, for example, you can use the toolbar buttons and sliders, scrollbars, mouse wheel, space bar + drag to pan, drag and drop areas of the most open interface, or any combination of them. Whichever interface you choose, just update the RenderTransform accordingly from the code, and you're good to go.

• If your chosen panning mechanism is a scrollbar, you can use ScrollViewer and use RenderTransform to zoom.

• Make sure you set the clipping in the pan / zoom area. Otherwise, if you enlarge or pan the elements from the side, they will still be visible outside the pan / zoom area.

Answer 2

Use the MultiScaleImage or Canvas area and place everything you need for panning and zooming.

<Canvas x:Name="panZoomPanel" Background="Transparent"> </Canvas> 

In using the code, do TranslateTransform and ScaleTransform in TransformGroup to pan and zoom

Check out another SO post or this example or this

Answer 3

In general, you can consider any composite set of interface elements in the same way as for one UIElement, so the case with the image is no different from what it does for the entire application. The best way to handle scaling based on user input (as opposed to the automatic scaling that Viewbox does) is to use ScaleTransform. This can be set on a high-level parent element, for example, in the Grid in the root of the window layout. For panning, you can combine in TranslateTransform or, in some cases, use ScrollViewer to handle moving content.

Answer 4

One very simple way to implement scaling in XAML is to use the Silverlight ViewBox. This increases XAML, not pixels. You can specify the stretch to use, and the ViewBox will scale based on this (Fill, None, Uniform, etc.). There are some great blog blog posts on the web if you are looking for Silverlight + Viewbox on Google.

Panning is easily accomplished using a similar drag-and-drop mechanism, and there are numerous blog help posts available through Google. It just comes down to capturing the MouseDown, MouseMove, and MouseUp events.