public DCMapping(HandleRef hDC, Rectangle bounds)
{
if (hDC.Handle == IntPtr.Zero)
{
throw new ArgumentNullException("hDC");
}
bool success;
NativeMethods.POINT viewportOrg = new NativeMethods.POINT();
HandleRef hOriginalClippingRegion = NativeMethods.NullHandleRef;
NativeMethods.RegionFlags originalRegionType = NativeMethods.RegionFlags.NULLREGION;
this.translatedBounds = bounds;
this.graphics = null;
this.dc = DeviceContext.FromHdc(hDC.Handle);
this.dc.SaveHdc();
// Retrieve the x-coordinates and y-coordinates of the viewport origin for the specified device context.
success = SafeNativeMethods.GetViewportOrgEx(hDC, viewportOrg);
Debug.Assert(success, "GetViewportOrgEx() failed.");
// Create a new rectangular clipping region based off of the bounds specified, shifted over by the x & y specified in the viewport origin.
HandleRef hClippingRegion = new HandleRef(null, SafeNativeMethods.CreateRectRgn(viewportOrg.x + bounds.Left, viewportOrg.y + bounds.Top, viewportOrg.x + bounds.Right, viewportOrg.y + bounds.Bottom));
Debug.Assert(hClippingRegion.Handle != IntPtr.Zero, "CreateRectRgn() failed.");
try
{
// Create an empty region oriented at 0,0 so we can populate it with the original clipping region of the hDC passed in.
hOriginalClippingRegion = new HandleRef(this, SafeNativeMethods.CreateRectRgn(0, 0, 0, 0));
Debug.Assert(hOriginalClippingRegion.Handle != IntPtr.Zero, "CreateRectRgn() failed.");
// Get the clipping region from the hDC: result = {-1 = error, 0 = no region, 1 = success} per MSDN
int result = SafeNativeMethods.GetClipRgn(hDC, hOriginalClippingRegion);
Debug.Assert(result != -1, "GetClipRgn() failed.");
// Shift the viewpoint origint by coordinates specified in "bounds".
NativeMethods.POINT lastViewPort = new NativeMethods.POINT();
success = SafeNativeMethods.SetViewportOrgEx(hDC, viewportOrg.x + bounds.Left, viewportOrg.y + bounds.Top, lastViewPort);
Debug.Assert(success, "SetViewportOrgEx() failed.");
if (result != 0)
{
// Get the origninal clipping region so we can determine its type (we'll check later if we've restored the region back properly.)
NativeMethods.RECT originalClipRect = new NativeMethods.RECT();
originalRegionType = (NativeMethods.RegionFlags)SafeNativeMethods.GetRgnBox(hOriginalClippingRegion, ref originalClipRect);
Debug.Assert(originalRegionType != NativeMethods.RegionFlags.ERROR, "ERROR returned from SelectClipRgn while selecting the original clipping region..");
if (originalRegionType == NativeMethods.RegionFlags.SIMPLEREGION)
{
// Find the intersection of our clipping region and the current clipping region (our parent's)
// Returns a NULLREGION, the two didn't intersect.
// Returns a SIMPLEREGION, the two intersected
// Resulting region (stuff that was in hOriginalClippingRegion AND hClippingRegion is placed in hClippingRegion
NativeMethods.RegionFlags combineResult = (NativeMethods.RegionFlags)SafeNativeMethods.CombineRgn(hClippingRegion, hClippingRegion, hOriginalClippingRegion, NativeMethods.RGN_AND);
Debug.Assert((combineResult == NativeMethods.RegionFlags.SIMPLEREGION) ||
(combineResult == NativeMethods.RegionFlags.NULLREGION),
"SIMPLEREGION or NULLREGION expected.");
}
}
else
{
// If there was no clipping region, then the result is a simple region.
// We don't need to keep track of the original now, since it is empty.
SafeNativeMethods.DeleteObject(hOriginalClippingRegion);
hOriginalClippingRegion = new HandleRef(null, IntPtr.Zero);
originalRegionType = NativeMethods.RegionFlags.SIMPLEREGION;
}
// Select the new clipping region; make sure it's a SIMPLEREGION or NULLREGION
NativeMethods.RegionFlags selectResult = (NativeMethods.RegionFlags)SafeNativeMethods.SelectClipRgn(hDC, hClippingRegion);
Debug.Assert((selectResult == NativeMethods.RegionFlags.SIMPLEREGION ||
selectResult == NativeMethods.RegionFlags.NULLREGION),
"SIMPLEREGION or NULLLREGION expected.");
}
catch (Exception ex)
{
if (ClientUtils.IsSecurityOrCriticalException(ex))
{
throw;
}
this.dc.RestoreHdc();
this.dc.Dispose();
}
finally {
// Delete the new clipping region, as the clipping region for the HDC is now set
// to this rectangle. Hold on to hOriginalClippingRegion, as we'll need to restore
// it when this object is disposed.
success = SafeNativeMethods.DeleteObject(hClippingRegion);
Debug.Assert(success, "DeleteObject(hClippingRegion) failed.");
if (hOriginalClippingRegion.Handle != IntPtr.Zero)
{
success = SafeNativeMethods.DeleteObject(hOriginalClippingRegion);
Debug.Assert(success, "DeleteObject(hOriginalClippingRegion) failed.");
}
}
}