Add project files.

Assets/Cryville/Common/Unity/UI/AspectRatioLayoutElement.cs

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+using System;
+using UnityEngine;
+using UnityEngine.EventSystems;
+using UnityEngine.UI;
+
+namespace Cryville.Common.Unity.UI {
+	public class AspectRatioLayoutElement : UIBehaviour, ILayoutElement {
+		[SerializeField]
+		private RectTransform m_containerTransform = null;
+		public RectTransform ContainerTransform {
+			get { return m_containerTransform; }
+			set { SetProperty(ref m_containerTransform, value); }
+		}
+
+		[SerializeField]
+		private float m_aspectRatio = 1;
+		public float AspectRatio {
+			get { return m_aspectRatio; }
+			set { SetProperty(ref m_aspectRatio, value); }
+		}
+
+		[SerializeField]
+		private bool m_isVertical = false;
+		public bool IsVertical {
+			get { return m_isVertical; }
+			set { SetProperty(ref m_isVertical, value); }
+		}
+
+		private void SetProperty<T>(ref T prop, T value) {
+			if (Equals(prop, value)) return;
+			prop = value;
+			SetDirty();
+		}
+
+		private void SetDirty() {
+			if (!IsActive()) return;
+			LayoutRebuilder.MarkLayoutForRebuild(transform as RectTransform);
+		}
+
+		public float minWidth {
+			get {
+				return m_isVertical
+					? m_containerTransform.rect.width
+					: m_containerTransform.rect.height * m_aspectRatio;
+			}
+		}
+		public float preferredWidth { get { return minWidth; } }
+		public float flexibleWidth { get { return 0; } }
+
+		public float minHeight {
+			get {
+				return m_isVertical
+					? m_containerTransform.rect.width / m_aspectRatio
+					: m_containerTransform.rect.height;
+			}
+		}
+		public float preferredHeight { get { return minHeight; } }
+		public float flexibleHeight { get { return 0; } }
+
+		public int layoutPriority { get { return 1; } }
+
+		private bool isRootLayoutGroup {
+			get {
+				Transform parent = transform.parent;
+				return parent == null || transform.parent.GetComponent(typeof(ILayoutGroup)) == null;
+			}
+		}
+
+		public void CalculateLayoutInputHorizontal() { }
+
+		public void CalculateLayoutInputVertical() { }
+
+		protected override void OnDidApplyAnimationProperties() {
+			base.OnDidApplyAnimationProperties();
+			SetDirty();
+		}
+
+		protected override void OnDisable() {
+			LayoutRebuilder.MarkLayoutForRebuild(transform as RectTransform);
+			base.OnDisable();
+		}
+
+		protected override void OnEnable() {
+			base.OnEnable();
+			SetDirty();
+		}
+
+		protected override void OnRectTransformDimensionsChange() {
+			base.OnRectTransformDimensionsChange();
+			SetDirty();
+		}
+
+		protected override void OnTransformParentChanged() {
+			base.OnTransformParentChanged();
+			SetDirty();
+		}
+
+#pragma warning disable IDE0051
+		new void OnValidate() {
+			SetDirty();
+		}
+#pragma warning restore IDE0051
+	}
+}