在 WM_PAINT 外画一条线

Question

Usually, to draw a line we draw it in WM_PAINT

LRESULT CALLBACK Display::DisplayWindowProc(HWND hWnd,UINT msg,WPARAM wParamm,LPARAM lParam)
{
    HDC hdc;
    PAINTSTRUCT ps;

    switch(msg)
    {
    case WM_PAINT:
        hdc = BeginPaint(hWnd,&ps);
        MoveToEx(hdc,0,0,0);
        LineTo(hdc,100,100);
        EndPaint(hWnd,&ps);
        return 0;
    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }
    return DefWindowProc( hWnd, msg, wParamm, lParam);
}

But , i want to draw line whenever i want, simple example:

int WINAPI WinMain
(
HINSTANCE hInstance,
HINSTANCE hPrevInstance,
PSTR cmdLine,
int showCmd
)
{
    //Do Other Things
    Display dislpay;
    display.DrawLine();
    //Do Other Things
}

My Program is Object Oriented and i display things in Display class and i was wondering if i can do a draw line in a function like DrawLine() in Display Class.

Answer 1

You can create an off-screen DC, and select an appropriately sized bitmap, and use that to draw whenever you want. Then on WM_PAINT you blit from the off-screen DC into the windows DC.