using System;

namespace UnityEngine.Experimental.Rendering
{
    internal readonly struct XRView
    {
        internal readonly Matrix4x4 projMatrix;
        internal readonly Matrix4x4 viewMatrix;
        internal readonly Matrix4x4 prevViewMatrix;
        internal readonly Rect viewport;
        internal readonly Mesh occlusionMesh;
        internal readonly int textureArraySlice;
        internal readonly Vector2 eyeCenterUV;
        internal readonly bool isPrevViewMatrixValid;

        internal XRView(Matrix4x4 projMatrix, Matrix4x4 viewMatrix, Matrix4x4 prevViewMatrix, bool isPrevViewMatrixValid, Rect viewport, Mesh occlusionMesh, int textureArraySlice)
        {
            this.projMatrix = projMatrix;
            this.viewMatrix = viewMatrix;
            this.prevViewMatrix = prevViewMatrix;
            this.viewport = viewport;
            this.occlusionMesh = occlusionMesh;
            this.textureArraySlice = textureArraySlice;
            this.isPrevViewMatrixValid = isPrevViewMatrixValid;
            eyeCenterUV = ComputeEyeCenterUV(projMatrix);
        }

        private static Vector2 ComputeEyeCenterUV(Matrix4x4 proj)
        {
            var projectionParameters = proj.decomposeProjection;
            float left = Math.Abs(projectionParameters.left);
            float right = Math.Abs(projectionParameters.right);
            float top = Math.Abs(projectionParameters.top);
            float bottom = Math.Abs(projectionParameters.bottom);
            return new Vector2(left / (right + left), top / (top + bottom));
        }
    }
}