System.Drawing.Imaging.ImageAttributes.SetColorKey() is set but not applied.

[KostaVlev]

I am writing test for System.Drawing.Imaging.ImageAttributes dotnet/runtime#22130:

private readonly Rectangle _rectangle = new Rectangle(0, 0, 64, 64);

[ConditionalFact(nameof(PlatformDetection) + "." + nameof(PlatformDetection.IsNotWindowsNanoServer))]
public void SetColorKey_Success()
{
    using (var bitmap = new Bitmap(_rectangle.Width, _rectangle.Height))
    using (var graphics = Graphics.FromImage(bitmap))
    using (var imageAttr = new ImageAttributes())
    {
        imageAttr.SetColorKey(Color.FromArgb(50, 50, 50), Color.FromArgb(150, 150, 150));

        bitmap.SetPixel(0, 0, Color.FromArgb(255, 100, 100, 100));
        graphics.DrawImage(bitmap, _rectangle, _rectangle.X, _rectangle.Y, _rectangle.Width, _rectangle.Height, GraphicsUnit.Pixel, imageAttr);
        Assert.Equal(Color.FromArgb(0, 0, 0, 0), bitmap.GetPixel(0, 0));
    }
}

Expected: Color.FromArgb(0, 0, 0, 0)
Actual: Color.FromArgb(255, 100, 100, 100)

I am running the test on netfx and netcoreapp and it fails on both.

Looks like transparency isn't get applied.

[EDIT] Fixed code formatting - @karelz

[karelz]

FYI: @hughbe @mellinoe

[hughbe]

From https://msdn.microsoft.com/en-us/library/windows/desktop/ms535429(v=vs.85).aspx sample code:

Ignoring the possibility i may be doing this C++ incorrectly, it looks as though this is a bug in GDI+.

int GetEncoderClsid(const WCHAR* format, CLSID* pClsid)
{
	UINT  num = 0;          // number of image encoders
	UINT  size = 0;         // size of the image encoder array in bytes

	ImageCodecInfo* pImageCodecInfo = NULL;

	GetImageEncodersSize(&num, &size);
	if (size == 0)
		return -1;  // Failure

	pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
	if (pImageCodecInfo == NULL)
		return -1;  // Failure

	GetImageEncoders(num, size, pImageCodecInfo);

	for (UINT j = 0; j < num; ++j)
	{
		if (wcscmp(pImageCodecInfo[j].MimeType, format) == 0)
		{
			*pClsid = pImageCodecInfo[j].Clsid;
			free(pImageCodecInfo);
			return j;  // Success
		}
	}

	free(pImageCodecInfo);
	return -1;  // Failure
}

static void test_imageAttributes() {
	Image image{L"C:\\Users\\hugh\\Documents\\Visual Studio 2017\\Projects\\ConsoleApplication1\\ConsoleApplication1\\173x183_indexed_8bit.bmp"};
	Graphics graphics((HWND)0);

	ImageAttributes imAtt;
	imAtt.SetColorKey(
		Color(0, 0, 0),
		Color(255, 255, 255),
		ColorAdjustTypeBitmap);

	CLSID pngClsid;
	GetEncoderClsid(L"image/png", &pngClsid);

	graphics.DrawImage(
		&image,
		Rect(20, 20, image.GetWidth(), image.GetHeight()),  // dest rect
		0, 0, image.GetWidth(), image.GetHeight(),          // source rect
		UnitPixel,
		&imAtt);

	image.Save(L"C:\\Users\\hugh\\Desktop\\stuff.png", &pngClsid);
}

In the sample code above, modified from the sample online, it shows that the C++ implementation looks broken.
I've sent @mellinoe an email with a GDI+ bug before and he wasn't sure the library has a maintainer. He also wasn't sure of the proper channel to route bugs in GDI+.

If this is indeed a GDI+ bug, I'm really not sure there's much we can do here. I think we should definitely keep the test, but maybe disable it.

[JeremyKuhne]

As this appears to be a GDI+ issue there isn't much we can do here.