与 WM_DPICHANGED 消息一起发送的建议 window 大小太大

Question

我的应用程序支持每个显示器的 DPI 感知版本 2。我有两台显示器 - 一台缩放为 100%，另一台缩放为 125%。将我的应用程序的 window 移动到具有 DPI 缩放比例的显示器并使用 WM_DPICHANGED 消息中给出的推荐大小设置新大小时，生成的客户区大小比应有的大几个像素。

例如，window 的客户区大小在我的例子中是 300x200 像素。在缩放比例为 125% 的显示器上，缩放系数为 1.25，因此生成的客户区大小应为 375x250。当我使用 WM_DPICHANGED 消息中收到的推荐大小设置 window 大小时，生成的客户区大小为 377x252。 Windows documentation claims 缩放为线性，但它无法像那样工作。

最小示例：

#include <Windows.h>

void set_window_size(HWND window, DWORD window_style, int width, int height)
{
    UINT dpi = GetDpiForWindow(window);
    float scaling_factor = static_cast<float>(dpi) / USER_DEFAULT_SCREEN_DPI;

    RECT scaled_size;
    scaled_size.left = 0;
    scaled_size.top = 0;
    scaled_size.right = static_cast<LONG>(width * scaling_factor);
    scaled_size.bottom = static_cast<LONG>(height * scaling_factor);

    // Adjust the size to account for non-client area
    AdjustWindowRectExForDpi(&scaled_size, window_style, false, 0, dpi);

    SetWindowPos(window, nullptr, 0, 0, scaled_size.right - scaled_size.left, scaled_size.bottom - scaled_size.top, SWP_NOZORDER | SWP_NOACTIVATE | SWP_NOMOVE));
}

// These sizes are for the client area
constexpr auto window_width = 300;
constexpr auto window_height = 200;

constexpr auto window_class_name = L"startup_dialog";
constexpr auto window_style = WS_OVERLAPPEDWINDOW;

LRESULT CALLBACK window_procedure(HWND window, UINT message, WPARAM w_param, LPARAM l_param)
{
    switch (message)
    {
        case WM_DESTROY:
        {
            PostQuitMessage(0);
            return 0;
        }

        case WM_DPICHANGED:
        {
            RECT* rect = reinterpret_cast<RECT*>(l_param);
            SetWindowPos(window, nullptr, rect->left, rect->top, rect->right - rect->left, rect->bottom - rect->top, SWP_NOZORDER | SWP_NOACTIVATE);
        }
    }

    return DefWindowProcW(window, message, w_param, l_param);
}

int CALLBACK wWinMain(HINSTANCE instance, HINSTANCE prev_instance, PWSTR cmd_line, int cmd_show)
{
    SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);

    WNDCLASSEXW window_class;
    window_class.cbSize = sizeof(window_class);
    window_class.style = CS_HREDRAW | CS_VREDRAW;
    window_class.lpfnWndProc = window_procedure;
    window_class.cbClsExtra = 0;
    window_class.cbWndExtra = 0;
    window_class.hInstance = instance;
    window_class.hIcon = nullptr;
    window_class.hCursor = nullptr;
    window_class.hbrBackground = reinterpret_cast<HBRUSH>(COLOR_WINDOW + 1);
    window_class.lpszMenuName = nullptr;
    window_class.lpszClassName = window_class_name;
    window_class.hIconSm = nullptr;

    RegisterClassExW(&window_class));
    HWND window = CreateWindowExW(0, window_class_name, L"Example", window_style, CW_USEDEFAULT, CW_USEDEFAULT, 0, 0, nullptr, nullptr, instance, nullptr);

    // Set the initial DPI-scaled window size
    set_window_size(window, window_style, window_width, window_height);

    ShowWindow(window, SW_SHOWNORMAL);

    // Message loop
    MSG message;
    int result;

    while ((result = GetMessageW(&message, nullptr, 0, 0)) != 0)
    {
        if (result == -1)
        {
            return 1;
        }
        else
        {
            TranslateMessage(&message);
            DispatchMessageW(&message);
        }
    }

    return static_cast<int>(message.wParam);
}

为简洁起见，删除了错误检查。
该示例需要 Windows 10 SDK 14393+ 编译和 Windows 10 1607+ 编译运行.

如何修复 WM_DPICHANGED 消息中给出的不正确的推荐 window 尺寸？

Answer 1

问题的发生是由于 Windows 错误，导致新的 window 尺寸计算不正确。可以通过处理 WM_GETDPISCALEDSIZE 消息并自己计算新的 window 大小来解决该错误。

根据问题示例处理消息的示例：

case WM_GETDPISCALEDSIZE:
{
    UINT dpi = static_cast<UINT>(w_param);
    float scaling_factor = static_cast<float>(dpi) / USER_DEFAULT_SCREEN_DPI;

    RECT client_area;
    client_area.right *= scaling_factor;
    client_area.bottom *= scaling_factor;

    RECT window_rectangle;
    window_rectangle.left = 0;
    window_rectangle.top = 0;
    window_rectangle.right = static_cast<LONG>(window_width * scaling_factor);
    window_rectangle.bottom = static_cast<LONG>(window_height * scaling_factor);

    if (!AdjustWindowRectExForDpi(&window_rectangle, window_style, false, 0, dpi))
    {
        // Error handling
        return 0;
    }

    SIZE* new_size = reinterpret_cast<SIZE*>(l_param);
    new_size->cx = window_rectangle.right - window_rectangle.left;
    new_size->cy = window_rectangle.bottom - window_rectangle.top;

    return 1;
}

请注意，使用此方法时，您必须使 window_width 和 window_height 变量在消息中可用。在问题的示例中，这是使用 constexpr 全局变量完成的。

替代方法，根据以前的客户区大小进行缩放，但速度可能稍慢：

case WM_GETDPISCALEDSIZE:
{
    UINT dpi = static_cast<UINT>(w_param);
    float scaling_factor = static_cast<float>(dpi) / USER_DEFAULT_SCREEN_DPI;

    RECT client_area;

    if (!GetClientRect(window, &client_area))
    {
        // Error handling
        return 0;
    }

    client_area.right = static_cast<LONG>(client_area.right * scaling_factor);
    client_area.bottom = static_cast<LONG>(client_area.bottom * scaling_factor);

    if (!AdjustWindowRectExForDpi(&client_area, window_style, false, 0, dpi))
    {
        // Error handling
        return 0;
    }

    SIZE* new_size = reinterpret_cast<SIZE*>(l_param);
    new_size->cx = client_area.right - client_area.left;
    new_size->cy = client_area.bottom - client_area.top;

    return 1;
}

还值得注意的是，似乎还有另一个错误，如果您在上述任一消息中设置断点，则传递给 WM_DPICHANGED 的推荐矩形将不正确。

与 WM_DPICHANGED 消息一起发送的建议 window 大小太大

The recommended window size sent with the WM_DPICHANGED message is too big

c++

winapi

dpi