INFO: BeginPaint() Invalid Rectangle in Client Coordinates

SUMMARY

The BeginPaint() function returns a pointer to a PAINTSTRUCT data structure through its second parameter. The rcPaint field of this structure specifies the update rectangle in client-area coordinates (relative to the upper-left corner of the window client area).

This update rectangle also serves as the clipping area for painting in the window, unless the invalid area of the window is expanded using the InvalidateRect() function.