Question

You know when you have a window that is frozen, but when you drag another window over the top it leaves a trail? Sometimes it looks a little bit like the end of Solitaire for Windows 3 🙂 when you get done (like my screenshot).

I’d like to make a C# windows (winforms/wpf) application that creates a surface like this and allows me to capture the image, but I’m a little bit at a loss of where to start.

Picture:

Answer 1

It would be easier with WPF. You can create a VisualBrush from any control, including a Window or FrameworkElement. Once you have that VisualBrush, you can paint it all over your form and it will create that same effect. Alternatively, you could use an ImageBrush if you want to do it with a picture rather than a UI element.

When you paint, just offset it by a couple X/Y each time and it will look just like that as it overwrites (er.. overpaints?) itself!

You can create your own class FrozenVisualHost that derives from FrameworkElement to host a DrawingVisual that you render. See: MSDN: Using DrawingVisual Objects

Overriding your FrozenVisualHost.OnRender() method would allow you to draw your ‘frozen snapshots’ as you recorded mouse movement (via MouseMove). Just make sure that you call the InvalidateVisual() method to update the host control.

One caveat: Creating a VisualBrush from a window will not capture the title bar or window border chrome. If you want that, you’ll have to grab a snapshot manually (GDI): As described here. You can use that Bitmap however for your ImageBrush and do rendering similarly.