NMCUSTOMDRAW

NMCUSTOMDRAW is a data structure used in the Microsoft Windows operating system, specifically within the context of common controls. It is part of the Windows common control library, which provides a set of reusable UI elements such as list views, tree views, and toolbars. The NMCUSTOMDRAW structure is utilized in notification messages sent by these controls to their parent windows.

When a common control needs to perform custom drawing for one of its items, it sends a WM_NOTIFY message containing an NMHDR structure followed by an NMCUSTOMDRAW structure to its parent window. This structure contains information about the item being drawn, including its ID, state, and a handle to a device context (HDC). The parent window can then intercept this notification and use the provided information to perform custom rendering, overriding the default drawing behavior of the control.

The NMCUSTOMDRAW structure provides a mechanism for developers to significantly alter the appearance of common control elements, allowing for highly customized user interfaces. This can include changing colors, fonts, drawing custom shapes, or implementing entirely unique visual styles for individual items within a control. The specific drawing operations are performed by the parent window using the HDC provided in the structure. The control will then use the results of this drawing.