com.unity.uiwidgets/Assets/UIWidgets/painting/matrix_utils.cs

using System;
using UIWidgets.foundation;
using UIWidgets.ui;
using UnityEngine;
using Rect = UIWidgets.ui.Rect;

namespace UIWidgets.painting {
    public static class MatrixUtils {
        public static Offset transformPoint(this Matrix4x4 transform, Offset point) {
            var position3 = new Vector3((float) point.dx, (float) point.dy, 0);
            var transformed3 = transform.MultiplyPoint(position3);
            return new Offset(transformed3.x, transformed3.y);
        }

        public static Rect transformRect(this Matrix4x4 transform, Offset[] points, out bool isRect) {
            D.assert(points != null && points.Length == 4, "expected 4 points");

            var topLeft = transform.transformPoint(points[0]);
            var topRight = transform.transformPoint(points[1]);
            var bottomLeft = transform.transformPoint(points[2]);
            var bottomRight = transform.transformPoint(points[3]);

            isRect = topLeft.dy == topRight.dy
                     && topRight.dx == bottomRight.dx
                     && bottomRight.dy == bottomLeft.dy
                     && bottomLeft.dx == topLeft.dx;

            var left = Math.Min(Math.Min(Math.Min(topLeft.dx, topRight.dx), bottomLeft.dx), bottomRight.dx);
            var right = Math.Max(Math.Max(Math.Max(topLeft.dx, topRight.dx), bottomLeft.dx), bottomRight.dx);
            var top = Math.Min(Math.Min(Math.Min(topLeft.dy, topRight.dy), bottomLeft.dy), bottomRight.dy);
            var bottom = Math.Max(Math.Max(Math.Max(topLeft.dy, topRight.dy), bottomLeft.dy), bottomRight.dy);

            return Rect.fromLTRB(left, top, right, bottom);
        }

        public static Rect transformRect(this Matrix4x4 transform, Rect rect, out bool isRect) {
            return transform.transformRect(
                new[] {rect.topLeft, rect.topRight, rect.bottomLeft, rect.bottomRight},
                out isRect);
        }

        public static Rect transformRect(this Matrix4x4 transform, Offset[] points) {
            bool isRect;
            return transform.transformRect(points, out isRect);
        }

        public static Rect transformRect(this Matrix4x4 transform, Rect rect) {
            bool isRect;
            return transform.transformRect(rect, out isRect);
        }

        public static Rect inverseTransformRect(this Matrix4x4 transform, Rect rect) {
            D.assert(rect != null);
            D.assert(transform.determinant != 0.0);

            if (transform.isIdentity) {
                return rect;
            }

            var inverse = transform.inverse;
            return inverse.transformRect(rect);
        }

        public static Offset getAsTranslation(this Matrix4x4 transform) {
            if (transform.m00 == 1.0 &&
                transform.m10 == 0.0 &&
                transform.m20 == 0.0 &&
                transform.m30 == 0.0 &&
                transform.m01 == 0.0 &&
                transform.m11 == 1.0 &&
                transform.m21 == 0.0 &&
                transform.m31 == 0.0 &&
                transform.m02 == 0.0 &&
                transform.m12 == 0.0 &&
                transform.m22 == 1.0 &&
                transform.m32 == 0.0 &&
                transform.m23 == 0.0 &&
                transform.m33 == 1.0) {
                return new Offset(transform.m03, transform.m13);
            }

            return null;
        }

        public static bool isPerspective(this Matrix4x4 transform) {
            return transform[3, 0] != 0 || transform[3, 1] != 0 || transform[3, 2] != 0 || transform[3, 3] != 1;
        }
    }
}