ColorTranslator.ToWin32 is inefficient

[JeremyKuhne]

Known colors are looked up with every property access. With system colors on windows this will cause 3 PInvokes.

runtime/src/libraries/System.Drawing.Primitives/src/System/Drawing/ColorTranslator.cs

Lines 33 to 36 in 77fb038

	public static int ToWin32(Color c)
	{
	return c.R << COLORREF_RedShift | c.G << COLORREF_GreenShift | c.B << COLORREF_BlueShift;
	}

Need to grab the full ARGB value and work with it instead to limit to a single lookup.

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[stephentoub]

With system colors on windows this will cause 3 PInvokes.

What's the call stack of the P/Invokes here?

[JeremyKuhne]

Effectively this (Windows only):

Color.R -> Color.Value -> KnownColorTable.KnownColorToArgb -> KnownColorTable->GetSystemColorArgb -> Interop.User32.GetSysColor

[ericstj]

@JeremyKuhne is this something you need for 9.0.0 or is it just something we want to fix up in future?

[JeremyKuhne]

@JeremyKuhne is this something you need for 9.0.0 or is it just something we want to fix up in future?

No, just trying to track it. I'll make a PR for it as it is pretty trivial.