PAINTSTRUCT

PAINTSTRUCT is a structure used in the Win32 API to manage painting during a WM_PAINT message. It is populated by the BeginPaint function and passed to EndPaint when painting is complete. The PAINTSTRUCT provides the window’s device context and information about what portion of the window needs painting, enabling efficient redrawing and reducing flicker.

The structure contains the following members:

- HDC hdc: handle to the device context that should be used for drawing.

- BOOL fErase: indicates whether the background should be erased before painting.

- RECT rcPaint: the update region that requires painting, in logical coordinates.

- BOOL fRestore: reserved for system use, typically not relied upon by applications.

- BOOL fIncUpdate: indicates an incremental update, used internally by Windows.

- BYTE rgbReserved[32]: reserved for system use.

Usage context:

When a window receives a WM_PAINT message, an application calls BeginPaint, which fills a PAINTSTRUCT (ps). The application then uses ps.hdc to perform drawing, typically within the area specified by ps.rcPaint. If ps.fErase is nonzero, the system may erase the background before painting. After drawing, the application calls EndPaint, which releases the device context and validates the painted region, informing the system that the update has been handled.

PAINTSTRUCT is central to the Windows painting model, linking the update region, device context, and painting lifecycle with BeginPaint and EndPaint. It enables efficient redraws and helps manage how and what portion of a window is repainted. Related functions include BeginPaint and EndPaint.