MSDN描述如下: WM_ERASEBKGND Notification--------------------------------------------------------------------------------The WM_ERASEBKGND message is sent when the window background must be erased (for example, when a window is resized). The message is sent to prepare an invalidated portion of a window for painting. Syntax WM_ERASEBKGND WPARAM wParam LPARAM lParam;
ParameterswParam Handle to the device context. lParam This parameter is not used. Return ValueAn application should return nonzero if it erases the background; otherwise, it should return zero. ResThe DefWindowProc function erases the background by using the class background brush specified by the hbrBackground member of the WNDCLASS structure. If hbrBackground is NULL, the application should process the WM_ERASEBKGND message and erase the background. An application should return nonzero in response to WM_ERASEBKGND if it processes the message and erases the background; this indicates that no further erasing is required. If the application returns zero, the window will remain ed for erasing. (Typically, this indicates that the fErase member of the PAINTSTRUCT structure will be TRUE.)
WM_ERASEBKGND Notification--------------------------------------------------------------------------------The WM_ERASEBKGND message is sent when the window background must be erased (for example, when a window is resized). The message is sent to prepare an invalidated portion of a window for painting. Syntax
WM_ERASEBKGND WPARAM wParam
LPARAM lParam;
ParameterswParam
Handle to the device context.
lParam
This parameter is not used.
Return ValueAn application should return nonzero if it erases the background; otherwise, it should return zero.
ResThe DefWindowProc function erases the background by using the class background brush specified by the hbrBackground member of the WNDCLASS structure. If hbrBackground is NULL, the application should process the WM_ERASEBKGND message and erase the background. An application should return nonzero in response to WM_ERASEBKGND if it processes the message and erases the background; this indicates that no further erasing is required. If the application returns zero, the window will remain ed for erasing. (Typically, this indicates that the fErase member of the PAINTSTRUCT structure will be TRUE.)
如果pt.fErase标记为TRUE,指示应用程序应该处理背景,但是应用程序不一定需要处理,pt.fErase只是作为一个标记