From 45861e122dda7948f73441527a3d5813acbaa486 Mon Sep 17 00:00:00 2001
From: cosmonaut <evan@moonside.games>
Date: Fri, 22 Jan 2021 00:46:22 -0800
Subject: [PATCH] math struct layouts + change Matrix projections to use right
 handed NDC space

---
 src/Math/Matrix.cs  | 16 +++++++++-------
 src/Math/Vector2.cs |  4 ++++
 src/Math/Vector3.cs |  5 +++++
 src/Math/Vector4.cs |  6 ++++++
 4 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/src/Math/Matrix.cs b/src/Math/Matrix.cs
index 29aca4ac..65d1a2cc 100644
--- a/src/Math/Matrix.cs
+++ b/src/Math/Matrix.cs
@@ -17,6 +17,7 @@
 #region Using Statements
 using System;
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 
 #endregion
 
@@ -24,9 +25,11 @@ namespace MoonWorks.Math
 {
 	/// <summary>
 	/// Represents the right-handed 4x4 floating point matrix, which can store translation, scale and rotation information.
+	/// This differs from XNA in one major way: projections are modified to give right handed NDC space.
 	/// </summary>
 	[Serializable]
 	[DebuggerDisplay("{DebugDisplayString,nq}")]
+	[StructLayout(LayoutKind.Sequential)]
 	public struct Matrix : IEquatable<Matrix>
 	{
 		#region Public Properties
@@ -973,7 +976,7 @@ namespace MoonWorks.Math
 		) {
 			result.M11 = 2f / width;
 			result.M12 = result.M13 = result.M14 = 0f;
-			result.M22 = 2f / height;
+			result.M22 = -2f / height;
 			result.M21 = result.M23 = result.M24 = 0f;
 			result.M33 = 1f / (zNearPlane - zFarPlane);
 			result.M31 = result.M32 = result.M34 = 0f;
@@ -1037,7 +1040,7 @@ namespace MoonWorks.Math
 			result.M13 = 0.0f;
 			result.M14 = 0.0f;
 			result.M21 = 0.0f;
-			result.M22 = (float) (2.0 / ((double) top - (double) bottom));
+			result.M22 = -(float) (2.0 / ((double) top - (double) bottom));
 			result.M23 = 0.0f;
 			result.M24 = 0.0f;
 			result.M31 = 0.0f;
@@ -1107,7 +1110,7 @@ namespace MoonWorks.Math
 			}
 			result.M11 = (2f * nearPlaneDistance) / width;
 			result.M12 = result.M13 = result.M14 = 0f;
-			result.M22 = (2f * nearPlaneDistance) / height;
+			result.M22 = -(2f * nearPlaneDistance) / height;
 			result.M21 = result.M23 = result.M24 = 0f;
 			result.M33 = farPlaneDistance / (nearPlaneDistance - farPlaneDistance);
 			result.M31 = result.M32 = 0f;
@@ -1176,10 +1179,9 @@ namespace MoonWorks.Math
 				throw new ArgumentException("nearPlaneDistance >= farPlaneDistance");
 			}
 			float num = 1f / ((float) System.Math.Tan((double) (fieldOfView * 0.5f)));
-			float num9 = num / aspectRatio;
-			result.M11 = num9;
+			result.M11 = num / aspectRatio;
 			result.M12 = result.M13 = result.M14 = 0;
-			result.M22 = num;
+			result.M22 = -num;
 			result.M21 = result.M23 = result.M24 = 0;
 			result.M31 = result.M32 = 0f;
 			result.M33 = farPlaneDistance / (nearPlaneDistance - farPlaneDistance);
@@ -1255,7 +1257,7 @@ namespace MoonWorks.Math
 			}
 			result.M11 = (2f * nearPlaneDistance) / (right - left);
 			result.M12 = result.M13 = result.M14 = 0;
-			result.M22 = (2f * nearPlaneDistance) / (top - bottom);
+			result.M22 = -(2f * nearPlaneDistance) / (top - bottom);
 			result.M21 = result.M23 = result.M24 = 0;
 			result.M31 = (left + right) / (right - left);
 			result.M32 = (top + bottom) / (top - bottom);
diff --git a/src/Math/Vector2.cs b/src/Math/Vector2.cs
index 7e33e54f..f7e6c8b8 100644
--- a/src/Math/Vector2.cs
+++ b/src/Math/Vector2.cs
@@ -17,6 +17,7 @@
 #region Using Statements
 using System;
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 
 #endregion
 
@@ -27,6 +28,7 @@ namespace MoonWorks.Math
 	/// </summary>
 	[Serializable]
 	[DebuggerDisplay("{DebugDisplayString,nq}")]
+	[StructLayout(LayoutKind.Explicit)]
 	public struct Vector2 : IEquatable<Vector2>
 	{
 		#region Public Static Properties
@@ -97,11 +99,13 @@ namespace MoonWorks.Math
 		/// <summary>
 		/// The x coordinate of this <see cref="Vector2"/>.
 		/// </summary>
+		[FieldOffset(0)]
 		public float X;
 
 		/// <summary>
 		/// The y coordinate of this <see cref="Vector2"/>.
 		/// </summary>
+		[FieldOffset(4)]
 		public float Y;
 
 		#endregion
diff --git a/src/Math/Vector3.cs b/src/Math/Vector3.cs
index 2c372c40..eadaf77d 100644
--- a/src/Math/Vector3.cs
+++ b/src/Math/Vector3.cs
@@ -17,6 +17,7 @@
 #region Using Statements
 using System;
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 using System.Text;
 
 #endregion
@@ -28,6 +29,7 @@ namespace MoonWorks.Math
 	/// </summary>
 	[Serializable]
 	[DebuggerDisplay("{DebugDisplayString,nq}")]
+	[StructLayout(LayoutKind.Explicit)]
 	public struct Vector3 : IEquatable<Vector3>
 	{
 		#region Public Static Properties
@@ -192,16 +194,19 @@ namespace MoonWorks.Math
 		/// <summary>
 		/// The x coordinate of this <see cref="Vector3"/>.
 		/// </summary>
+		[FieldOffset(0)]
 		public float X;
 
 		/// <summary>
 		/// The y coordinate of this <see cref="Vector3"/>.
 		/// </summary>
+		[FieldOffset(4)]
 		public float Y;
 
 		/// <summary>
 		/// The z coordinate of this <see cref="Vector3"/>.
 		/// </summary>
+		[FieldOffset(8)]
 		public float Z;
 
 		#endregion
diff --git a/src/Math/Vector4.cs b/src/Math/Vector4.cs
index ce869f87..a78f3d27 100644
--- a/src/Math/Vector4.cs
+++ b/src/Math/Vector4.cs
@@ -17,6 +17,7 @@
 #region Using Statements
 using System;
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 
 #endregion
 
@@ -27,6 +28,7 @@ namespace MoonWorks.Math
 	/// </summary>
 	[Serializable]
 	[DebuggerDisplay("{DebugDisplayString,nq}")]
+	[StructLayout(LayoutKind.Explicit)]
 	public struct Vector4 : IEquatable<Vector4>
 	{
 		#region Public Static Properties
@@ -121,21 +123,25 @@ namespace MoonWorks.Math
 		/// <summary>
 		/// The x coordinate of this <see cref="Vector4"/>.
 		/// </summary>
+		[FieldOffset(0)]
 		public float X;
 
 		/// <summary>
 		/// The y coordinate of this <see cref="Vector4"/>.
 		/// </summary>
+		[FieldOffset(4)]
 		public float Y;
 
 		/// <summary>
 		/// The z coordinate of this <see cref="Vector4"/>.
 		/// </summary>
+		[FieldOffset(8)]
 		public float Z;
 
 		/// <summary>
 		/// The w coordinate of this <see cref="Vector4"/>.
 		/// </summary>
+		[FieldOffset(12)]
 		public float W;
 
 		#endregion