Enable and control DWM composition

The Desktop Window Manager (DWM) composition APIs provide several functions for setting and querying for basic information that is used by the DWM. These APIs enable you to query and change the composition state. Additionally, you can set and query the rendering policy for different DWM window attributes.

Retrieving colorization information

The color of the non-client region of a window is determined by the current system color theme. The colorization value is provided through the DWM APIs to enable your application to match client UI with the system color theme.

To access this colorization value, and monitor the color change, use the DwmGetColorizationColor function and the WM_DWMCOLORIZATIONCOLORCHANGED message.

This example demonstrates how to handle the color changed message and access the new color.

...
case WM_DWMCOLORIZATIONCOLORCHANGED:
{
    DWORD newColorizationColor{ (DWORD)wParam };
    BOOL isBlendedWithOpacity{ (BOOL)lParam };
}
break;
...

Controlling non-client region rendering

Two of the visual effects that DWM enables are transparency of the non-client region of a window, and transition effects. Your application might have to disable or re-enable these effects for styling or compatibility reasons. The following functions are used to manage transparency and transition effect behavior.

• DwmGetWindowAttribute
• DwmSetWindowAttribute

To retrieve the current non-client rendering state for an application's window, call DwmGetWindowAttribute with dwAttribute set to DWMWA_NCRENDERING_ENABLED. As you can see from the documentation for DWMWA_NCRENDERING_ENABLED, when you pass that flag to DwmGetWindowAttribute, the retrieved attribute value is of type BOOL. Different flags cause DwmGetWindowAttribute to return values of different types. Here's a code example.

BOOL isNCRenderingEnabled{ FALSE };
HRESULT hr = ::DwmGetWindowAttribute(hWnd,
    DWMWA_NCRENDERING_ENABLED,
    &isNCRenderingEnabled,
    sizeof(isNCRenderingEnabled));

This next example shows how to use the DWMWA_EXTENDED_FRAME_BOUNDS flag with DwmGetWindowAttribute to retrieve the extended frame bounds rectangle of a window. The documentation for that flag tells us that the retrieved attribute value is of type RECT.

RECT extendedFrameBounds{ 0,0,0,0 };
HRESULT hr = ::DwmGetWindowAttribute(hWnd,
    DWMWA_EXTENDED_FRAME_BOUNDS,
    &extendedFrameBounds,
    sizeof(extendedFrameBounds));

DwmSetWindowAttribute enables your application to set the non-client area rendering policy. That function also determines how your application should handle DWM transition effects.

This next example disables non-client area rendering. This causes any previous calls to DwmEnableBlurBehindWindow or to DwmExtendFrameIntoClientArea to be disabled.

HRESULT DisableNCRendering(HWND hWnd)
{
    HRESULT hr = S_OK;

    DWMNCRENDERINGPOLICY ncrp = DWMNCRP_DISABLED;

    // Disable non-client area rendering on the window.
    hr = ::DwmSetWindowAttribute(hWnd,
        DWMWA_NCRENDERING_POLICY,
        &ncrp,
        sizeof(ncrp));

    if (SUCCEEDED(hr))
    {
        // ...
    }

    return hr;
}

In addition to controlling the non-client area rendering, DwmSetWindowAttribute can also control DWM transition effects. You can set transition behavior by using DWMWA_TRANSITIONS_FORCEDISABLED as the dwAttribute parameter.

Messages

The following messages provide notification of DWM events. These messages can be used to monitor changes such as composition state changes and system color theme changes.

• WM_DWMCOLORIZATIONCOLORCHANGED
• WM_DWMCOMPOSITIONCHANGED
• WM_DWMNCRENDERINGCHANGED
• WM_DWMWINDOWMAXIMIZEDCHANGE

Disabling DWM composition (Windows 7 and earlier)

Because DWM uses the graphics processing unit (GPU) for desktop composition, your application might have to disable DWM for compatibility. Applications that take full control of the desktop, such as games that run in full-screen mode, must determine whether the DWM is enabled and if it is, disable it. To do this, two functions are needed.

• DwmIsCompositionEnabled
• DwmEnableComposition

A call to DwmEnableComposition with fEnable set to DWM_EC_DISABLECOMPOSITION disables DWM composition until either the calling process has shut down, or composition has been re-enabled by calling DwmEnableComposition with fEnable set to DWM_EC_ENABLECOMPOSITION. DWM composition restarts automatically as soon as all applications that have disabled composition have either shut down or have manually re-enabled composition by calling DwmEnableComposition.