You can have your application redraw the entire contents of the client area whenever the window changes size by setting the CS_HREDRAW and CS_VREDRAW styles for the window class. Applications that adjust the size of the drawing based on the size of the window use these styles to ensure that they start with a completely empty client area when drawing.
In the following example, the window procedure draws a five-pointed star that fits neatly in the client area. It uses a common device context and must set the mapping mode as well as window and viewport extents each time the WM_PAINT message is processed.
LRESULT APIENTRY WndProc(HWMD hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
PAINTSTRUCT ps;
HDC hdc;
RECT rc;
POINT aptStar[6] = {50,2, 2,98, 98,33, 2,33, 98,98, 50,2};
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case WM_PAINT:
hdc = BeginPaint(hwnd, &ps);
GetClientRect(hwnd, &rc);
SetMapMode(hdc, MM_ANISOTROPIC);
SetWindowExtEx(hdc, 100, 100, NULL);
SetViewportExtEx(hdc, rc.right, rc.bottom, NULL);
Polyline(hdc, aptStar, 6);
EndPaint(hwnd, &ps);
return 0L;
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}
int APIENTRY WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
WNDCLASS wc;
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wc.style = CS_HREDRAW | CS_VREDRAW;
wc.lpfnWndProc = (WNDPROC) WndProc;
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RegisterClass(&wc);
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return msg.wParam;
}