internal unsafe static extern uint GetRegionData(
IntPtr hRgn,
uint dwCount,
NativeStructs.RGNDATA *lpRgnData);
private static unsafe void GetRegionScans(IntPtr hRgn, out Rectangle[] scans)
{
uint bytes = 0;
int countdown = 100;
int error = 0;
// HACK: It seems that sometimes the GetRegionData will return ERROR_INVALID_HANDLE
// even though the handle (the HRGN) is fine. Maybe the function is not
// re-entrant? I'm not sure, but trying it again seems to fix it.
while (countdown > 0)
{
bytes = SafeNativeMethods.GetRegionData(hRgn, 0, (NativeStructs.RGNDATA *)IntPtr.Zero);
error = Marshal.GetLastWin32Error();
if (bytes == 0)
{
--countdown;
System.Threading.Thread.Sleep(5);
}
else
{
break;
}
}
// But if we retry several times and it still messes up then we will finally give up.
if (bytes == 0)
{
throw new Win32Exception(error, "GetRegionData returned " + bytes.ToString(CultureInfo.CurrentCulture) + ", GetLastError() = " + error.ToString(CultureInfo.CurrentCulture));
}
byte *data;
// Up to 512 bytes, allocate on the stack. Otherwise allocate from the heap.
if (bytes <= 512)
{
byte *data1 = stackalloc byte[(int)bytes];
data = data1;
}
else
{
data = (byte *)Memory.Allocate(bytes, false).ToPointer();
}
try
{
NativeStructs.RGNDATA *pRgnData = (NativeStructs.RGNDATA *)data;
uint result = SafeNativeMethods.GetRegionData(hRgn, bytes, pRgnData);
if (result != bytes)
{
throw new OutOfMemoryException("SafeNativeMethods.GetRegionData returned 0");
}
NativeStructs.RECT *pRects = NativeStructs.RGNDATA.GetRectsPointer(pRgnData);
scans = new Rectangle[pRgnData->rdh.nCount];
for (int i = 0; i < scans.Length; ++i)
{
scans[i] = Rectangle.FromLTRB(pRects[i].left, pRects[i].top, pRects[i].right, pRects[i].bottom);
}
pRects = null;
pRgnData = null;
}
finally
{
if (bytes > 512)
{
Memory.Free(new IntPtr(data));
}
}
}
internal static extern unsafe uint GetRegionData([In()] IntPtr hrgn, [In()] uint nCount, [Out()] NativeStructs.RGNDATA *lpRgnData);
