Investigate the conversion between SKMatrix44 and Matrix4x4

[mattleibow]

Description

Right now we are creating a new struct each time, but it may be better to use Unsafe.As:

var m = Unsafe.As<Matrix4x4, SKMatrix44>(ref sys);

We need to benchmark and make sure.

[mattleibow]

I created a benchmark:

[Benchmark(Baseline = true)]
public SKMatrix44 UseNewStruct()
{
	SKMatrix44.UseUnsafeAs = false;

	SKMatrix44 TheSKMatrix44 = SKMatrix44.CreateRotation(10, 20, 30, 0.7f);
	var inverted = TheSKMatrix44.Invert();
	return inverted;
}

[Benchmark]
public SKMatrix44 UseUnsafeAs()
{
	SKMatrix44.UseUnsafeAs = true;

	SKMatrix44 TheSKMatrix44 = SKMatrix44.CreateRotation(10, 20, 30, 0.7f);
	var inverted = TheSKMatrix44.Invert();
	return inverted;
}

And edited the code of SKMatrix44:

public static bool UseUnsafeAs = false;

public static implicit operator Matrix4x4 (SKMatrix44 matrix) =>
	UseUnsafeAs ? Unsafe.As<SKMatrix44, Matrix4x4> (ref matrix) :
	new Matrix4x4 (
		matrix.m00, matrix.m10, matrix.m20, matrix.m30,
		matrix.m01, matrix.m11, matrix.m21, matrix.m31,
		matrix.m02, matrix.m12, matrix.m22, matrix.m32,
		matrix.m03, matrix.m13, matrix.m23, matrix.m33);

public static implicit operator SKMatrix44 (Matrix4x4 matrix) =>
	UseUnsafeAs ? Unsafe.As<Matrix4x4, SKMatrix44> (ref matrix) :
	new SKMatrix44 (
		matrix.M11, matrix.M21, matrix.M31, matrix.M41,
		matrix.M12, matrix.M22, matrix.M32, matrix.M42,
		matrix.M13, matrix.M23, matrix.M33, matrix.M43,
		matrix.M14, matrix.M24, matrix.M34, matrix.M44);

The results:

// * Summary *

BenchmarkDotNet=v0.13.5, OS=Windows 11 (10.0.22631.3155)
Intel Core i9-9980HK CPU 2.40GHz, 1 CPU, 16 logical and 8 physical cores
.NET SDK=8.0.200
  [Host]   : .NET 7.0.16 (7.0.1624.6629), X64 RyuJIT AVX2
  .NET 7.0 : .NET 7.0.16 (7.0.1624.6629), X64 RyuJIT AVX2

Job=.NET 7.0  Runtime=.NET 7.0

|       Method |      Mean |    Error |   StdDev | Ratio | RatioSD | Allocated | Alloc Ratio |
|------------- |----------:|---------:|---------:|------:|--------:|----------:|------------:|
| UseNewStruct | 100.83 ns | 3.085 ns | 8.702 ns |  1.00 |    0.00 |         - |          NA |
|  UseUnsafeAs |  59.51 ns | 1.093 ns | 0.853 ns |  0.59 |    0.05 |         - |          NA |

// * Hints *
Outliers
  TheBenchmark.UseNewStruct: .NET 7.0 -> 8 outliers were removed (132.01 ns..159.35 ns)
  TheBenchmark.UseUnsafeAs: .NET 7.0  -> 3 outliers were removed (68.31 ns..72.48 ns)