Windows API to get whether HDR(High Dynamic Range) is active

My environment is Windows 10 20H2(64bit) and Visual Studio 2019.
I am developing an app as C# WPF(.NET 5) project. And I want to write a code that HDR(High Dynamic Range) is active currently on the system.
In this document, I got some hints about Windows HDR. But I could only find articles about for UWP and DirectX.
I would ideally like to use the .NET API or Win32 API. Does Windows 10 provide those APIs?
Solution
You can use the Connecting and Configuring Displays (CCD) API.
specifically the DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO request (which is not really documented in MSDN but is defined in wingdi.h)
Here is some C# Console Application sample code that dumps for each monitor if it supports HDR and if it's enabled.
static void Main()
{
    var err = GetDisplayConfigBufferSizes(QDC.QDC_ONLY_ACTIVE_PATHS, out var pathCount, out var modeCount);
    if (err != 0)
        throw new Win32Exception(err);

    var paths = new DISPLAYCONFIG_PATH_INFO[pathCount];
    var modes = new DISPLAYCONFIG_MODE_INFO[modeCount];
    err = QueryDisplayConfig(QDC.QDC_ONLY_ACTIVE_PATHS, ref pathCount, paths, ref modeCount, modes, IntPtr.Zero);
    if (err != 0)
        throw new Win32Exception(err);

    foreach (var path in paths)
    {
        // get display name
        var info = new DISPLAYCONFIG_TARGET_DEVICE_NAME();
        info.header.type = DISPLAYCONFIG_DEVICE_INFO_TYPE.DISPLAYCONFIG_DEVICE_INFO_GET_TARGET_NAME;
        info.header.size = Marshal.SizeOf<DISPLAYCONFIG_TARGET_DEVICE_NAME>();
        info.header.adapterId = path.targetInfo.adapterId;
        info.header.id = path.targetInfo.id;
        err = DisplayConfigGetDeviceInfo(ref info);
        if (err != 0)
            throw new Win32Exception(err);

        var colorInfo = new DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO();
        colorInfo.header.type = DISPLAYCONFIG_DEVICE_INFO_TYPE.DISPLAYCONFIG_DEVICE_INFO_GET_ADVANCED_COLOR_INFO;
        colorInfo.header.size = Marshal.SizeOf<DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO>();
        colorInfo.header.adapterId = path.targetInfo.adapterId;
        colorInfo.header.id = path.targetInfo.id;
        err = DisplayConfigGetDeviceInfo(ref colorInfo);
        if (err != 0)
            throw new Win32Exception(err);

        Console.WriteLine(info.monitorFriendlyDeviceName);
        Console.WriteLine(" Advanced Color Supported: " + colorInfo.advancedColorSupported);
        Console.WriteLine(" Advanced Color Enabled  : " + colorInfo.advancedColorEnabled);
        Console.WriteLine();
    }
}

private enum DISPLAYCONFIG_DEVICE_INFO_TYPE
{
    DISPLAYCONFIG_DEVICE_INFO_GET_SOURCE_NAME = 1,
    DISPLAYCONFIG_DEVICE_INFO_GET_TARGET_NAME = 2,
    DISPLAYCONFIG_DEVICE_INFO_GET_TARGET_PREFERRED_MODE = 3,
    DISPLAYCONFIG_DEVICE_INFO_GET_ADAPTER_NAME = 4,
    DISPLAYCONFIG_DEVICE_INFO_SET_TARGET_PERSISTENCE = 5,
    DISPLAYCONFIG_DEVICE_INFO_GET_TARGET_BASE_TYPE = 6,
    DISPLAYCONFIG_DEVICE_INFO_GET_SUPPORT_VIRTUAL_RESOLUTION = 7,
    DISPLAYCONFIG_DEVICE_INFO_SET_SUPPORT_VIRTUAL_RESOLUTION = 8,
    DISPLAYCONFIG_DEVICE_INFO_GET_ADVANCED_COLOR_INFO = 9,
    DISPLAYCONFIG_DEVICE_INFO_SET_ADVANCED_COLOR_STATE = 10,
    DISPLAYCONFIG_DEVICE_INFO_GET_SDR_WHITE_LEVEL = 11,
}

private enum DISPLAYCONFIG_COLOR_ENCODING
{
    DISPLAYCONFIG_COLOR_ENCODING_RGB = 0,
    DISPLAYCONFIG_COLOR_ENCODING_YCBCR444 = 1,
    DISPLAYCONFIG_COLOR_ENCODING_YCBCR422 = 2,
    DISPLAYCONFIG_COLOR_ENCODING_YCBCR420 = 3,
    DISPLAYCONFIG_COLOR_ENCODING_INTENSITY = 4,
}

private enum DISPLAYCONFIG_SCALING
{
    DISPLAYCONFIG_SCALING_IDENTITY = 1,
    DISPLAYCONFIG_SCALING_CENTERED = 2,
    DISPLAYCONFIG_SCALING_STRETCHED = 3,
    DISPLAYCONFIG_SCALING_ASPECTRATIOCENTEREDMAX = 4,
    DISPLAYCONFIG_SCALING_CUSTOM = 5,
    DISPLAYCONFIG_SCALING_PREFERRED = 128,
}

private enum DISPLAYCONFIG_ROTATION
{
    DISPLAYCONFIG_ROTATION_IDENTITY = 1,
    DISPLAYCONFIG_ROTATION_ROTATE90 = 2,
    DISPLAYCONFIG_ROTATION_ROTATE180 = 3,
}

private enum DISPLAYCONFIG_VIDEO_OUTPUT_TECHNOLOGY
{
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_OTHER = -1,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_HD15 = 0,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_SVIDEO = 1,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_COMPOSITE_VIDEO = 2,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_COMPONENT_VIDEO = 3,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_DVI = 4,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_HDMI = 5,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_LVDS = 6,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_D_JPN = 8,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_SDI = 9,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_DISPLAYPORT_EXTERNAL = 10,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_DISPLAYPORT_EMBEDDED = 11,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_UDI_EXTERNAL = 12,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_UDI_EMBEDDED = 13,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_SDTVDONGLE = 14,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_MIRACAST = 15,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_INDIRECT_WIRED = 16,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_INDIRECT_VIRTUAL = 17,
    DISPLAYCONFIG_OUTPUT_TECHNOLOGY_INTERNAL = unchecked((int)0x80000000),
}

private enum DISPLAYCONFIG_TOPOLOGY_ID
{
    DISPLAYCONFIG_TOPOLOGY_INTERNAL = 0x00000001,
    DISPLAYCONFIG_TOPOLOGY_CLONE = 0x00000002,
    DISPLAYCONFIG_TOPOLOGY_EXTEND = 0x00000004,
    DISPLAYCONFIG_TOPOLOGY_EXTERNAL = 0x00000008,
}

private enum DISPLAYCONFIG_PATH
{
    DISPLAYCONFIG_PATH_ACTIVE = 0x00000001,
    DISPLAYCONFIG_PATH_PREFERRED_UNSCALED = 0x00000004,
    DISPLAYCONFIG_PATH_SUPPORT_VIRTUAL_MODE = 0x00000008,
}

private enum DISPLAYCONFIG_SOURCE_FLAGS
{
    DISPLAYCONFIG_SOURCE_IN_USE = 0x00000001,
}

private enum DISPLAYCONFIG_TARGET_FLAGS
{
    DISPLAYCONFIG_TARGET_IN_USE = 0x00000001,
    DISPLAYCONFIG_TARGET_FORCIBLE = 0x00000002,
    DISPLAYCONFIG_TARGET_FORCED_AVAILABILITY_BOOT = 0x00000004,
    DISPLAYCONFIG_TARGET_FORCED_AVAILABILITY_PATH = 0x00000008,
    DISPLAYCONFIG_TARGET_FORCED_AVAILABILITY_SYSTEM = 0x00000010,
    DISPLAYCONFIG_TARGET_IS_HMD = 0x00000020,
}

private enum QDC
{
    QDC_ALL_PATHS = 0x00000001,
    QDC_ONLY_ACTIVE_PATHS = 0x00000002,
    QDC_DATABASE_CURRENT = 0x00000004,
    QDC_VIRTUAL_MODE_AWARE = 0x00000010,
    QDC_INCLUDE_HMD = 0x00000020,
}

private enum DISPLAYCONFIG_SCANLINE_ORDERING
{
    DISPLAYCONFIG_SCANLINE_ORDERING_UNSPECIFIED = 0,
    DISPLAYCONFIG_SCANLINE_ORDERING_PROGRESSIVE = 1,
    DISPLAYCONFIG_SCANLINE_ORDERING_INTERLACED = 2,
    DISPLAYCONFIG_SCANLINE_ORDERING_INTERLACED_UPPERFIELDFIRST = DISPLAYCONFIG_SCANLINE_ORDERING_INTERLACED,
    DISPLAYCONFIG_SCANLINE_ORDERING_INTERLACED_LOWERFIELDFIRST = 3,
}

private enum DISPLAYCONFIG_PIXELFORMAT
{
    DISPLAYCONFIG_PIXELFORMAT_8BPP = 1,
    DISPLAYCONFIG_PIXELFORMAT_16BPP = 2,
    DISPLAYCONFIG_PIXELFORMAT_24BPP = 3,
    DISPLAYCONFIG_PIXELFORMAT_32BPP = 4,
    DISPLAYCONFIG_PIXELFORMAT_NONGDI = 5,
}

private enum DISPLAYCONFIG_MODE_INFO_TYPE
{
    DISPLAYCONFIG_MODE_INFO_TYPE_SOURCE = 1,
    DISPLAYCONFIG_MODE_INFO_TYPE_TARGET = 2,
    DISPLAYCONFIG_MODE_INFO_TYPE_DESKTOP_IMAGE = 3,
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_DEVICE_INFO_HEADER
{
    public DISPLAYCONFIG_DEVICE_INFO_TYPE type;
    public int size;
    public LUID adapterId;
    public uint id;
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO
{
    public DISPLAYCONFIG_DEVICE_INFO_HEADER header;
    public uint value;
    public DISPLAYCONFIG_COLOR_ENCODING colorEncoding;
    public int bitsPerColorChannel;

    public bool advancedColorSupported => (value & 0x1) == 0x1;
    public bool advancedColorEnabled => (value & 0x2) == 0x2;
    public bool wideColorEnforced => (value & 0x4) == 0x4;
    public bool advancedColorForceDisabled => (value & 0x8) == 0x8;
}

[StructLayout(LayoutKind.Sequential)]
private struct POINTL
{
    public int x;
    public int y;
}

[StructLayout(LayoutKind.Sequential)]
private struct LUID
{
    public uint LowPart;
    public int HighPart;

    public long Value => ((long)HighPart << 32) | LowPart;
    public override string ToString() => Value.ToString();
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_SOURCE_MODE
{
    public uint width;
    public uint height;
    public DISPLAYCONFIG_PIXELFORMAT pixelFormat;
    public POINTL position;
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_RATIONAL
{
    public uint Numerator;
    public uint Denominator;

    public override string ToString() => Numerator + " / " + Denominator;
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_2DREGION
{
    public uint cx;
    public uint cy;
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_DESKTOP_IMAGE_INFO
{
    public POINTL PathSourceSize;
    public RECT DesktopImageRegion;
    public RECT DesktopImageClip;
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_VIDEO_SIGNAL_INFO
{
    public ulong pixelRate;
    public DISPLAYCONFIG_RATIONAL hSyncFreq;
    public DISPLAYCONFIG_RATIONAL vSyncFreq;
    public DISPLAYCONFIG_2DREGION activeSize;
    public DISPLAYCONFIG_2DREGION totalSize;
    public uint videoStandard;
    public DISPLAYCONFIG_SCANLINE_ORDERING scanLineOrdering;
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_TARGET_MODE
{
    public DISPLAYCONFIG_VIDEO_SIGNAL_INFO targetVideoSignalInfo;
}

[StructLayout(LayoutKind.Explicit)]
private struct DISPLAYCONFIG_MODE_INFO_union
{
    [FieldOffset(0)]
    public DISPLAYCONFIG_TARGET_MODE targetMode;

    [FieldOffset(0)]
    public DISPLAYCONFIG_SOURCE_MODE sourceMode;

    [FieldOffset(0)]
    public DISPLAYCONFIG_DESKTOP_IMAGE_INFO desktopImageInfo;
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_PATH_SOURCE_INFO
{
    public LUID adapterId;
    public uint id;
    public uint modeInfoIdx;
    public DISPLAYCONFIG_SOURCE_FLAGS statusFlags;
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_PATH_TARGET_INFO
{
    public LUID adapterId;
    public uint id;
    public uint modeInfoIdx;
    public DISPLAYCONFIG_VIDEO_OUTPUT_TECHNOLOGY outputTechnology;
    public DISPLAYCONFIG_ROTATION rotation;
    public DISPLAYCONFIG_SCALING scaling;
    public DISPLAYCONFIG_RATIONAL refreshRate;
    public DISPLAYCONFIG_SCANLINE_ORDERING scanLineOrdering;
    public bool targetAvailable;
    public DISPLAYCONFIG_TARGET_FLAGS statusFlags;
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_PATH_INFO
{
    public DISPLAYCONFIG_PATH_SOURCE_INFO sourceInfo;
    public DISPLAYCONFIG_PATH_TARGET_INFO targetInfo;
    public DISPLAYCONFIG_PATH flags;
}

[StructLayout(LayoutKind.Sequential)]
private struct DISPLAYCONFIG_MODE_INFO
{
    public DISPLAYCONFIG_MODE_INFO_TYPE infoType;
    public uint id;
    public LUID adapterId;
    public DISPLAYCONFIG_MODE_INFO_union info;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
private struct DISPLAYCONFIG_SOURCE_DEVICE_NAME
{
    public DISPLAYCONFIG_DEVICE_INFO_HEADER header;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
    public string viewGdiDeviceName;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
private struct DISPLAYCONFIG_TARGET_DEVICE_NAME_FLAGS
{
    public uint value;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
private struct DISPLAYCONFIG_TARGET_DEVICE_NAME
{
    public DISPLAYCONFIG_DEVICE_INFO_HEADER header;
    public DISPLAYCONFIG_TARGET_DEVICE_NAME_FLAGS flags;
    public DISPLAYCONFIG_VIDEO_OUTPUT_TECHNOLOGY outputTechnology;
    public ushort edidManufactureId;
    public ushort edidProductCodeId;
    public uint connectorInstance;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 64)]
    public string monitorFriendlyDeviceName;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
    public string monitorDevicePat;
}

[StructLayout(LayoutKind.Sequential)]
private struct RECT
{
    public int left;
    public int top;
    public int right;
    public int bottom;
}

[DllImport("user32")]
private static extern int GetDisplayConfigBufferSizes(QDC flags, out int numPathArrayElements, out int numModeInfoArrayElements);

[DllImport("user32")]
private static extern int QueryDisplayConfig(QDC flags, ref int numPathArrayElements, [In, Out] DISPLAYCONFIG_PATH_INFO[] pathArray, ref int numModeInfoArrayElements, [In, Out] DISPLAYCONFIG_MODE_INFO[] modeInfoArray, out DISPLAYCONFIG_TOPOLOGY_ID currentTopologyId);

[DllImport("user32")]
private static extern int QueryDisplayConfig(QDC flags, ref int numPathArrayElements, [In, Out] DISPLAYCONFIG_PATH_INFO[] pathArray, ref int numModeInfoArrayElements, [In, Out] DISPLAYCONFIG_MODE_INFO[] modeInfoArray, IntPtr currentTopologyId);

[DllImport("user32")]
private static extern int DisplayConfigGetDeviceInfo(ref DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO requestPacket);

[DllImport("user32")]
private static extern int DisplayConfigGetDeviceInfo(ref DISPLAYCONFIG_SOURCE_DEVICE_NAME requestPacket);

[DllImport("user32")]
private static extern int DisplayConfigGetDeviceInfo(ref DISPLAYCONFIG_TARGET_DEVICE_NAME requestPacket);