public static RenderGeometry CreateSpringGeometry(float ringRadius, float barRadius, float heightPerCycle, int segmentPerCycle, int segmentBar, bool smoothH, bool smoothV, float angle = 0, float deltaAngle = 0)
    {
        StructureGeometry structure = new StructureGeometry();

        RenderGeometry.FaceType faceType = GetFaceType(smoothH, smoothV);
        float heightPerRad = heightPerCycle / (2 * Mathf.PI);
        float slope        = heightPerRad / ringRadius;
        float scaleH       = Mathf.Sqrt(1 + slope * slope);
        int   segmentRing  = Mathf.CeilToInt(segmentPerCycle * angle / (2 * Mathf.PI) - 1e-6f);

        SurfaceComponentGeometry face = SurfaceComponentGeometries.CreatePlaneGeometry(1, 1, segmentBar, segmentRing, 1, faceType);

        var warp = new SpaceWarp(
            $" a1=(z+0.5)*{angle}",
            $" a2={deltaAngle}-x*(2*PI)",
            $" r={ringRadius}+{barRadius}*cos(a2)",
            $" X=r*cos(a1)",
            $" Y={scaleH}*{barRadius}*sin(a2)+a1*{heightPerRad}",
            $" Z=r*sin(a1)"
            );

        face.ApplySpaceWarp(warp);

        SurfaceComponentGeometry cap1 = SurfaceComponentGeometries.CreateRegularPolygonGeometry(barRadius, segmentBar, 2);
        SurfaceComponentGeometry cap2 = SurfaceComponentGeometries.CreateRegularPolygonGeometry(barRadius, segmentBar, 2);

        cap1.ApplyLinearTransform(
            Matrix4x4.Translate(Vector3.right * ringRadius) *
            Matrix4x4.Scale(new Vector3(1, scaleH, 1)) *
            Matrix4x4.Rotate(Quaternion.LookRotation(Vector3.down, Vector3.back) * Quaternion.AngleAxis(-deltaAngle * Mathf.Rad2Deg, Vector3.up)));
        cap2.ApplyLinearTransform(
            Matrix4x4.Translate(new Vector3(ringRadius * Mathf.Cos(angle), heightPerRad * angle, ringRadius * Mathf.Sin(angle))) *
            Matrix4x4.Scale(new Vector3(1, scaleH, 1)) *
            Matrix4x4.Rotate(Quaternion.LookRotation(Vector3.up, Quaternion.AngleAxis(angle * Mathf.Rad2Deg, Vector3.down) * Vector3.forward) * Quaternion.AngleAxis(deltaAngle * Mathf.Rad2Deg, Vector3.up)));

        Vertex corner1 = structure.CreateVertex();
        Vertex corner2 = structure.CreateVertex();

        structure.CreateFace(face, false, corner1, corner2, corner2, corner1);
        structure.CreateFace(cap1, false, corner1);
        structure.CreateFace(cap2, false, corner2);
        return(structure.Build());
    }
    private static void CreateStraightRampPart(
        StructureGeometry structure, bool isLeftRamp,
        Vertex cornerTopLeft1, Vertex cornerTopLeft2, Vertex cornerTopRight1, Vertex cornerTopRight2,
        Vertex cornerBottomLeft1, Vertex cornerBottomLeft2, Vertex cornerBottomRight1, Vertex cornerBottomRight2,
        bool addLeftSide, bool addRightSide, int segmentWidth, int segmentLength, float curvature, RenderGeometry.FaceType rampFaceType, RenderGeometry.FaceType sideFaceType)
    {
        bool hasBase = (cornerTopLeft1 != cornerBottomLeft1) && (cornerTopRight1 != cornerBottomRight1);

        SurfaceComponentGeometry rampFace = SurfaceComponentGeometries.CreatePlaneGeometry(1, 1, segmentWidth, segmentLength, 0, rampFaceType);
        SurfaceComponentGeometry rampBottom = SurfaceComponentGeometries.CreatePlaneGeometry(1, 1, 1, segmentLength, 1, sideFaceType);
        SurfaceComponentGeometry rampLeftSide = null, rampRightSide = null;

        if (addLeftSide && (cornerTopLeft1 != cornerBottomLeft1))
        {
            rampLeftSide = SurfaceComponentGeometries.CreatePlaneGeometry(1, 1, 1, segmentLength, 2, sideFaceType);
        }
        if (addRightSide && (cornerTopRight1 != cornerBottomRight1))
        {
            rampRightSide = SurfaceComponentGeometries.CreatePlaneGeometry(1, 1, 1, segmentLength, 3, sideFaceType);
        }

        if (curvature != 0)
        {
            float angle = -curvature * Mathf.PI / 2;
            rampFace.ApplySpaceWarp(new SpaceWarp($"sin(x*{angle})/{angle}", $"(1-cos(x*{angle}))/{angle}", "z"));
        }
        // Fit to a 45 degree ramp, then scale.
        rampFace.ApplyLinearTransform(
            Matrix4x4.Translate(cornerTopLeft1.p) *
            Matrix4x4.Scale(VectorUtil.Abs(cornerTopRight2.p - cornerTopLeft1.p)) *
            MatrixUtil.PointToPointTransform(
                rampFace.corners[0].p, rampFace.corners[3].p, rampFace.corners[1].p,
                Vector3.zero, new Vector3(1, isLeftRamp ? 1 : -1, 0), Vector3.forward));

        structure.CreateFace(rampFace, false, cornerTopLeft1, cornerTopLeft2, cornerTopRight2, cornerTopRight1);
        structure.CreateFace(rampBottom, true, cornerBottomRight1, cornerBottomRight2, cornerBottomLeft2, cornerBottomLeft1);
        if (rampLeftSide != null)
        {
            structure.CreateFace(rampLeftSide, true, cornerBottomLeft1, cornerBottomLeft2, cornerTopLeft2, cornerTopLeft1);
        }
        if (rampRightSide != null)
        {
            structure.CreateFace(rampRightSide, true, cornerTopRight1, cornerTopRight2, cornerBottomRight2, cornerBottomRight1);
        }

        var backVertices = new List <Vector3>();

        backVertices.Add(isLeftRamp ? cornerBottomRight1.p : cornerBottomLeft1.p);
        if (isLeftRamp && hasBase)
        {
            backVertices.Add(cornerBottomLeft1.p);
        }
        backVertices.Add(rampFace.boundaries[3].Last().prev.vertex.p);
        backVertices.AddRange(rampFace.boundaries[3].Select(e => e.vertex.p).Reverse());
        if (!isLeftRamp && hasBase)
        {
            backVertices.Add(cornerBottomRight1.p);
        }
        var movedBackVertices = backVertices.Select(p => p + (cornerTopLeft2.p - cornerTopLeft1.p));
        var frontVertices = movedBackVertices.Take(1).Concat(movedBackVertices.Reverse().Take(backVertices.Count - 1)).ToList();

        SurfaceComponentGeometry backFace  = SurfaceComponentGeometries.CreateStarConvexPolygonGeometry(backVertices, 4, RenderGeometry.FaceType.Smooth);
        SurfaceComponentGeometry frontFace = SurfaceComponentGeometries.CreateStarConvexPolygonGeometry(frontVertices, 5, RenderGeometry.FaceType.Smooth);

        if (hasBase)
        {
            if (isLeftRamp)
            {
                backFace.CombineBoundaries(1, 1, segmentWidth, 1);
                frontFace.CombineBoundaries(1, segmentWidth, 1, 1);
                structure.CreateFace(backFace, false, cornerBottomRight1, cornerBottomLeft1, cornerTopLeft1, cornerTopRight1);
                structure.CreateFace(frontFace, false, cornerBottomRight2, cornerTopRight2, cornerTopLeft2, cornerBottomLeft2);
            }
            else
            {
                backFace.CombineBoundaries(1, segmentWidth, 1, 1);
                frontFace.CombineBoundaries(1, 1, segmentWidth, 1);
                structure.CreateFace(backFace, false, cornerBottomLeft1, cornerTopLeft1, cornerTopRight1, cornerBottomRight1);
                structure.CreateFace(frontFace, false, cornerBottomLeft2, cornerBottomRight2, cornerTopRight2, cornerTopLeft2);
            }
        }
        else
        {
            backFace.CombineBoundaries(1, segmentWidth, 1);
            frontFace.CombineBoundaries(1, segmentWidth, 1);
            structure.CreateFace(backFace, false, isLeftRamp ? cornerBottomRight1 : cornerBottomLeft1, cornerTopLeft1, cornerTopRight1);
            structure.CreateFace(frontFace, false, isLeftRamp ? cornerBottomRight2 : cornerBottomLeft2, cornerTopRight2, cornerTopLeft2);
        }
    }