SharpGLTF/examples/SharpGLTF.Runtime.MonoGame/SceneUtils.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Microsoft.Xna.Framework;

namespace SharpGLTF.Runtime
{
    static class SceneUtils
    {
        #region helpers

        public static Matrix CreatePerspectiveFieldOfView(float fieldOfView, float aspectRatio, float nearPlaneDistance, float farPlaneDistance = float.PositiveInfinity)
        {
            CreatePerspectiveFieldOfView(fieldOfView, aspectRatio, nearPlaneDistance, farPlaneDistance, out Matrix m);
            return m;
        }

        // Microsoft recently updated this method in System.Numerics.Vectors to support farPlaneDistance infinity
        // https://github.com/dotnet/runtime/blob/e64bc548c609455652fcd4107f1f4a2ac3084ff3/src/libraries/System.Private.CoreLib/src/System/Numerics/Matrix4x4.cs#L860
        public static void CreatePerspectiveFieldOfView(float fieldOfView, float aspectRatio, float nearPlaneDistance, float farPlaneDistance, out Matrix result)
        {
            if (fieldOfView <= 0.0f || fieldOfView >= MathHelper.Pi)
                throw new ArgumentOutOfRangeException(nameof(fieldOfView));

            if (nearPlaneDistance <= 0.0f)
                throw new ArgumentOutOfRangeException(nameof(nearPlaneDistance));

            if (farPlaneDistance <= 0.0f)
                throw new ArgumentOutOfRangeException(nameof(farPlaneDistance));

            if (nearPlaneDistance >= farPlaneDistance)
                throw new ArgumentOutOfRangeException(nameof(nearPlaneDistance));

            float yScale = 1.0f / (float)Math.Tan(fieldOfView * 0.5f);
            float xScale = yScale / aspectRatio;

            result.M11 = xScale;
            result.M12 = result.M13 = result.M14 = 0.0f;

            result.M22 = yScale;
            result.M21 = result.M23 = result.M24 = 0.0f;

            result.M31 = result.M32 = 0.0f;
            float negFarRange = float.IsPositiveInfinity(farPlaneDistance) ? -1.0f : farPlaneDistance / (nearPlaneDistance - farPlaneDistance);
            result.M33 = negFarRange;
            result.M34 = -1.0f;

            result.M41 = result.M42 = result.M44 = 0.0f;
            result.M43 = nearPlaneDistance * negFarRange;
        }

        #endregion
    }
}