我如何获得一个窗口来调整大小的C ++时保留绘制的对象

Question

My program creates random rectanges on the screen. Each time the left mouse button is clicked a new rectange of random size and colour is added to the window. However, when I resize the window, all of the rectanges are deleted - I don't want this to happen. I don't understand what the program does when it is resized, is it calling the case WM_PAINT ? If so, what do I need to include to ensure the current window state remains when resized.

Answer 1

You need to save the state and redraw whenever you receive WM_PAINT. This is simply the protocol Microsoft decided on. So make sure you keep the state of your window in memory.

In the case of a resize you also get several sizing messages, first a series of WM_SIZING events while the size is changing and then WM_SIZE when the size is finally set. You will get WM_PAINT messages in between and you are free to repaint the application upon any or all of those events.

Answer 2

See my answer to a similar question here about painting using GDI.

https://stackoverflow.com/a/12764607/682404

Basically, when your windows is resized, you should receive a WM_PAINT message from Windows. In your message handler, you need to repaint your form. The answer I linked in has some details about the painting process. Your painting code would look rougly like this:

PAINTSTRUCT stPaintStruct;
HDC hPaintDC = BeginPaint(hWnd, &stPaintStruct);

if (hPaintDC != HANDLE_NULL)
{
    // establish clipping rect using stPaintStruct.rcPaint

    if (!m_bRendering)
    {
        m_bRendering = TRUE;

        // Render() knows the how to create the output.
        Render ();

        m_bRendering = FALSE;
    }

    EndPaint (hWnd, &stPaintStruct);
    return (TRUE);
}

Every time you need to paint your window, you always need to paint from scratch, so you need to store somewhere the coordinates of your rectangles.