private void InitialiseThumbnail(IntPtr source)
{
if (IntPtr.Zero != thumb)
{
// release the old thumbnail
ReleaseThumbnail();
}
if (IntPtr.Zero != source)
{
// find our parent hwnd
target = (HwndSource)HwndSource.FromVisual(this);
// if we have one, we can attempt to register the thumbnail
if (target != null && 0 == DWM.DwmRegisterThumbnail(target.Handle, source, out this.thumb))
{
DWM.ThumbnailProperties props = new DWM.ThumbnailProperties();
props.Visible = false;
props.SourceClientAreaOnly = this.ClientAreaOnly;
props.Opacity = (byte)(255 * this.Opacity);
props.Flags = DWM.ThumbnailFlags.Visible | DWM.ThumbnailFlags.SourceClientAreaOnly
| DWM.ThumbnailFlags.Opacity;
DWM.DwmUpdateThumbnailProperties(thumb, ref props);
}
}
}
protected override Size MeasureOverride(Size availableSize)
{
try
{
DWM.Size size;
DWM.DwmQueryThumbnailSourceSize(this.thumb, out size);
double scale = 1;
// our preferred size is the thumbnail source size
// if less space is available, we scale appropriately
if (size.Width > availableSize.Width)
{
scale = availableSize.Width / size.Width;
}
if (size.Height > availableSize.Height)
{
scale = Math.Min(scale, availableSize.Height / size.Height);
}
return(new Size(size.Width * scale, size.Height * scale));
}
catch (DllNotFoundException) { }
return(new Size());
}
// this is where the magic happens
private void Thumbnail_LayoutUpdated(object sender, EventArgs e)
{
if (IntPtr.Zero == thumb)
{
InitialiseThumbnail(this.Source);
}
if (IntPtr.Zero != thumb)
{
if (!target.RootVisual.IsAncestorOf(this))
{
//we are no longer in the visual tree
ReleaseThumbnail();
return;
}
GeneralTransform transform = TransformToAncestor(target.RootVisual);
Point a = transform.Transform(new Point(0, 0));
Point b = transform.Transform(new Point(this.ActualWidth, this.ActualHeight));
DWM.ThumbnailProperties props = new DWM.ThumbnailProperties();
props.Visible = true;
props.Destination = new DWM.Rect(
(int)Math.Ceiling(a.X), (int)Math.Ceiling(a.Y),
(int)Math.Ceiling(b.X), (int)Math.Ceiling(b.Y));
props.Flags = DWM.ThumbnailFlags.Visible | DWM.ThumbnailFlags.RectDetination;
DWM.DwmUpdateThumbnailProperties(thumb, ref props);
}
}
private void UpdateThumbnail()
{
if (IntPtr.Zero != thumb)
{
DWM.ThumbnailProperties props = new DWM.ThumbnailProperties();
props.SourceClientAreaOnly = this.ClientAreaOnly;
props.Opacity = (byte)(255 * this.Opacity);
props.Flags = DWM.ThumbnailFlags.SourceClientAreaOnly | DWM.ThumbnailFlags.Opacity;
DWM.DwmUpdateThumbnailProperties(thumb, ref props);
}
}
protected override Size ArrangeOverride(Size finalSize)
{
try
{
DWM.Size size;
DWM.DwmQueryThumbnailSourceSize(this.thumb, out size);
// scale to fit whatever size we were allocated
double scale = finalSize.Width / size.Width;
scale = Math.Min(scale, finalSize.Height / size.Height);
return(new Size(size.Width * scale, size.Height * scale));
}
catch (DllNotFoundException)
{
return(default(Size));
}
}
private void ReleaseThumbnail()
{
DWM.DwmUnregisterThumbnail(thumb);
this.thumb = IntPtr.Zero;
this.target = null;
}