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static extern int GetRegionData(IntPtr hRgn, uint dwCount, IntPtr lpRgnData);
This is an 'unsafe' call, and thus should be led by the [SuppressUnmanagedCodeSecurity()] attribute.
Tips & Tricks:
Please add some!
// this should be defined somewhere in a class
const int RDH_RECTANGLES = 1;
unsafe RECT RectsFromRegion(IntPtr hRgn)
RECT  rects = null;
// First we call GetRegionData() with a null buffer.
// The return from this call should be the size of buffer
// we need to allocate in order to receive the data.
int dataSize = GetRegionData(hRgn, 0, IntPtr.Zero);
if (dataSize != 0)
IntPtr bytes = IntPtr.Zero;
// Allocate as much space as the GetRegionData call
// said was needed
bytes = Marshal.AllocCoTaskMem(dataSize);
// Now, make the call again to actually get the data
int retValue = GetRegionData(hRgn, dataSize, bytes);
// From here on out, we have the data in a buffer, and we
// just need to convert it into a form that is more useful
// Since pointers are used, this whole routine is 'unsafe'
// It's a small sacrifice to make in order to get this to work.
// [RBS] Added missing second pointer identifier
RGNDATAHEADER * header = (RGNDATAHEADER*)bytes;
if (header->iType == RDH_RECTANGLES)
rects = new RECT[header->nCount];
// The rectangle data follows the header, so we offset the specified
// header size and start reading rectangles.
int rectOffset = header->dwSize;
for (int i=0; i < header->nCount; i++)
// simple assignment from the buffer to our array of rectangles
// will give us what we want.
rects[i] = *((RECT *)((byte *)bytes+rectOffset+(Marshal.SizeOf(typeof(RECT)) *i)));
// Return the rectangles
Alternative Managed API:
Do you know one? Please contribute it!
The GetRegionData API
5/30/2008 8:32:45 AM - -188.8.131.52
TODO - a short description
3/16/2007 2:19:39 PM - -184.108.40.206
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