Unity3D component which enforces a certain aspect ratio to the viewport of a camera, so that the camera always renders with this aspect rather than the actual screen aspect

CameraFixedAspectViewport.cs

using UnityEngine;
using System.Collections;

namespace ZS.Tools
{
	/// <summary>
	/// Adjusts the camera viewport so the actually drawn portion is always of a specific aspect ratio,
	/// uninfluenced by the actual screen size. The viewport maximize its covered space.
	/// </summary>
	[RequireComponent(typeof(Camera)), ExecuteInEditMode]
	public class CameraFixedAspectViewport : MonoBehaviour
	{
		/// <summary>
		/// Different pre-set aspect ratios
		/// </summary>
		public enum AspectRatio
		{
			/// <summary>
			/// Custom aspect ratio, <see cref="CustomAspect">CustomAspect</see> must be set then!
			/// </summary>
			Custom,

			/// <summary>
			/// 16:9
			/// </summary>
			Aspect16to9,

			/// <summary>
			/// 16:10
			/// </summary>
			Aspect16to10,

			/// <summary>
			/// 4:3
			/// </summary>
			Aspect4to3,

			/// <summary>
			/// 5:4
			/// </summary>
			Aspect5to4,

			/// <summary>
			/// 1:1
			/// </summary>
			Aspect1to1,
		}

		[Tooltip("Which aspect the viewport should keep")]
		public AspectRatio Aspect;

		[Tooltip("When Aspect is set to Custom, this ratio (W/H) is used for aspect calculation")]
		public float CustomAspect = 1F;

		[Tooltip("Enabled continous recalculation of the viewport on each frame")]
		public bool ContinousUpdate = false;

		/// <summary>
		/// Reference to the camera component for faster access
		/// </summary>
		Camera mCamera;

		void Start()
		{
			mCamera = GetComponent<Camera>();
		}

		void Update()
		{
			if (ContinousUpdate)
			{
				ApplyToViewport();
			}
		}

		/// <summary>
		/// Corrects the viewport of the camera so the viewport resembles the intended aspect ratio
		/// </summary>
		public void ApplyToViewport()
		{
			float ratio = CustomAspect;

			switch (Aspect)
			{
				case AspectRatio.Aspect16to9:
					ratio = 16F / 9F;
					break;

				case AspectRatio.Aspect16to10:
					ratio = 16F / 10F;
					break;

				case AspectRatio.Aspect4to3:
					ratio = 4F / 3F;
					break;

				case AspectRatio.Aspect5to4:
					ratio = 5F / 4F;
					break;

				case AspectRatio.Aspect1to1:
					ratio = 1F;
					break;

				// Custom: Fall-through
			}

			// Current aspect of the whole screen
			float screenAspect = Screen.width / (float)Screen.height;

			// How much does the screen aspect be adjusted to fit the intended aspect?
			float aspectAdjustment = screenAspect / ratio;

			// >1F means bars to the left and right
			if (aspectAdjustment >= 1F)
			{
				mCamera.rect = new Rect((1F - 1F / aspectAdjustment) * 0.5F, 0F, 1F / aspectAdjustment, 1F);
			}
			// <1F means bars on the top and bottom
			else
			{
				mCamera.rect = new Rect(0F, (1F - aspectAdjustment) * 0.5F, 1F, aspectAdjustment);
			}
		}
	}
}