BeginPaint

BeginPaint is a Windows API function used to prepare a window’s client area for painting in response to the WM_PAINT message. It validates the window’s update region and returns a device context (HDC) that should be used for drawing. A PAINTSTRUCT structure is filled by the function; the HDC in this structure is the drawing surface, and rcPaint describes the rectangle that needs repainting.

Typical usage occurs inside a window procedure when handling WM_PAINT. The pattern is to declare a PAINTSTRUCT, call BeginPaint with the window handle, perform drawing with the returned HDC, and finally call EndPaint to finish painting. The rcPaint member can guide rendering to the region that requires updates, and the clipping region is typically set to the update region to optimize drawing.

Key points: BeginPaint should only be called in response to WM_PAINT. It both provides the device context for painting and informs the system which region has to be repainted. EndPaint must be called to release the device context and to validate the painted area, allowing the system to mark the update region as complete.

If painting is needed outside of WM_PAINT, or if a DC is required without validating the update region, GetDC and ReleaseDC can be used, but they do not perform the same update-region validation that BeginPaint/EndPaint provide.

See also: EndPaint, WM_PAINT, PAINTSTRUCT, GetDC, ReleaseDC.