WM_PAINT function, how to call again?

Ok here is the situation. I loaded a bitmap to the screen using windows GDI. I did this in the WM_PAINT function. Now what I want to do is when a user clicks on a file menu, the screen must become all clear. My question is how do I call the WM_PAINT function again to clear the screen? If I just write:

Code:

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case ID_FILE_NEW:

                    WM_PAINT;
                {
                        // Just a note, never use a MessageBox from inside WM_PAINT
                        // The box will cause more WM_PAINT messages and you'll probably end up
                        // stuck in a loop

                        BITMAP bm;
                        PAINTSTRUCT ps;

                        HDC hdc = BeginPaint(hwnd, &ps);

                        HDC hdcMem = CreateCompatibleDC(hdc);
                        HBITMAP hbmOld = SelectObject(hdcMem, Logobmp);

                        GetObject(Logobmp, sizeof(bm), &bm);

                        BitBlt(hdc, 100, 50, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);
            BitBlt(hdc, 0, 0, 800, 600,hdc, 0, 0, WHITENESS);
                        SelectObject(hdcMem, hbmOld);
                        DeleteDC(hdcMem);
                        EndPaint(hwnd, &ps);
                }

---

nothing happens, the white background does't copy over the picture. However if I write the same code in the WM_PAINT function than it does.

WM_PAINT is a message sent to your window, where you handle it is a case in a switch statement not a function allthough you could call a function in the WM_PAINT case.
You can either send the WM_PAINT message yourself with SendMessage or call UpdateWindow. You can also call InvalidateRect on your window but that might not send WM_PAINT right away.

hmm, is it possible to call an if statement within WM_PAINT such as:

Code:

---

case WM_PAINT:
                {
                        // Just a note, never use a MessageBox from inside WM_PAINT
                        // The box will cause more WM_PAINT messages and you'll probably end up
                        // stuck in a loop

                        BITMAP bm;
                        PAINTSTRUCT ps;

                        HDC hdc = BeginPaint(hwnd, &ps);

                        HDC hdcMem = CreateCompatibleDC(hdc);
                        HBITMAP hbmOld = SelectObject(hdcMem, Logobmp);

                        GetObject(Logobmp, sizeof(bm), &bm);

                        BitBlt(hdc, 100, 50, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);
                        if (ClrScreen >= 0){
            BitBlt(hdc, 0, 0, 800, 600,hdc, 0, 0, WHITENESS);
            }
                         

                        SelectObject(hdcMem, hbmOld);
                        DeleteDC(hdcMem);

                        EndPaint(hwnd, &ps);
                }
                break;

---

And than set the int ClrScreen to something greater than 0 and call WM_PAIT again:

Code:

---

case ID_FILE_NEW:
                    ClrScreen = 1;
                    PostMessage(hwnd, WM_PAINT, 0, 0);

---

However this doesn't work either for some reason.

EDIT: got it working with InvalidateRect(hwnd, NULL, FALSE ); instead of postmessege