public static void DrawDragOutline(Region region)
{
if (region == null)
return;
// Get hold of the DC for the desktop
IntPtr hDC = User32.GetDC(IntPtr.Zero);
// Define the area we are allowed to draw into
IntPtr hRegion = region.GetHrgn(Graphics.FromHdc(hDC));
Gdi32.SelectClipRgn(hDC, hRegion);
Win32.RECT rectBox = new Win32.RECT();
// Get the smallest rectangle that encloses region
Gdi32.GetClipBox(hDC, ref rectBox);
IntPtr brushHandler = GetHalfToneBrush();
// Select brush into the device context
IntPtr oldHandle = Gdi32.SelectObject(hDC, brushHandler);
// Blit to screen using provided pattern brush and invert with existing screen contents
Gdi32.PatBlt(hDC,
rectBox.left,
rectBox.top,
rectBox.right - rectBox.left,
rectBox.bottom - rectBox.top,
(uint)Win32.RasterOperations.PATINVERT);
// Put old handle back again
Gdi32.SelectObject(hDC, oldHandle);
// Reset the clipping region
Gdi32.SelectClipRgn(hDC, IntPtr.Zero);
Gdi32.DeleteObject(hRegion);
// Must remember to release the HDC resource!
User32.ReleaseDC(IntPtr.Zero, hDC);
}
public static extern int GetClipBox(IntPtr hDC, ref Win32.RECT rectBox);
public static extern IntPtr CreateRectRgnIndirect(ref Win32.RECT rect);
public static extern bool InvalidateRect(IntPtr hWnd, ref RECT rect, bool erase);
public static extern bool GetWindowRect(IntPtr hWnd, ref RECT rect);
public static extern bool DrawFocusRect(IntPtr hWnd, ref RECT rect);