int GetUpdateRgn(hWnd,hRgn,fErase)
This function copies a window's update region into a region identified by the hRgn parameter. The coordinates of this region are relative to the upper-left corner of the window (client coordinates).
| Parameter | Type/Description |
| hWnd | HWND Identifies the window that contains the region to be updated. | |
| hRgn | HRGN Identifies the update region. | |
| fErase | BOOL Specifies whether or not the window background should be erased and nonclient areas of child windows should be drawn. If it is zero, no drawing is done. |
The return value specifies a short-integer flag that indicates the type of resulting region.
It can be any one of the following values:
| Value | Meaning |
| COMPLEXREGION | The region has overlapping borders. | |
| ERROR | No region was created. | |
| NULLREGION | The region is empty. | |
| SIMPLEREGION | The region has no overlapping borders. |
BeginPaint automatically validates the update region, so any call to GetUpdateRgn made immediately after the BeginPaint call retrieves an empty update region.