An application sends the WM_ERASEBKGND message 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. WM_ERASEBKGND
hdc = (HDC) wParam; // handle of device context
ParametershdcValue of wParam. Identifies the device context. Return ValuesAn 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.)
hdc = (HDC) wParam; // handle of device context
ParametershdcValue of wParam. Identifies the device context. Return ValuesAn 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.)
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这个窗体将表现出 “透明”的现象,不过由于它不会重画背景,所以一旦
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