UPhotoFrame/Assets/Scripts/PhotoFrame.cs

using System.Collections;
using UnityEngine;
using UnityEngine.Networking;
using UnityEngine.UI;

public class PhotoFrame : MonoBehaviour
{
	const float PHOTO_INTERVAL = 5f;
	const float ANIMATION_LENGTH = 2f;

    [SerializeField]
    GameObject mainUI;

	[SerializeField]
	RectTransform imageContainer;
    [SerializeField]
    Image[] images;

    [SerializeField]
    InputField url;

	private int currentImage;

	private Image CurrentImage
	{
		get { return images[currentImage]; }
	}

	private Image NextImage
	{
		get { return images[(currentImage + 1) % images.Length]; }
	}

	public void Start()
	{
		Screen.sleepTimeout = SleepTimeout.NeverSleep;
		currentImage = 0;
		ActivateUI(true);
	}

	private void ActivateUI(bool v)
	{
		mainUI.gameObject.SetActive(v);
		for (int i = 0; i < images.Length; i++)
		{
			images[i].gameObject.SetActive(!v);
		}
	}

	Coroutine mainCoroutine;

	public void OnRunButtonClicked()
	{
		ActivateUI(false);
		mainCoroutine = StartCoroutine(SwitchImages());
	}

	public void OnStopButtonClicked()
	{
		if (mainCoroutine != null)
		{
			StopCoroutine(mainCoroutine);
			mainCoroutine = null;
		}
		for (int i = 0; i < images.Length; i++)
		{
			if (images[i].sprite != null)
			{
				Destroy(images[i].sprite.texture);
				Destroy(images[i].sprite);
				images[i].sprite = null;
			}
		}
		ActivateUI(true);
	}

	private IEnumerator SwitchImages()
	{
		yield return null;
		var loader = new ImageLoader(url.text);
		while (loader.Status == LoaderStatus.Initializing) yield return null;
		Color opaque = new Color(1, 1, 1, 1);
		Color transparent = new Color(1, 1, 1, 0);
		CurrentImage.color = transparent;
		NextImage.color = transparent;
		while (true)
		{
			var startTime = Time.realtimeSinceStartup;
			int imageIndex = Random.Range(0, loader.images.Count);
			string imageUrl = loader.images[imageIndex];

			var request = UnityWebRequest.Get(imageUrl);
			request.downloadHandler = new DownloadHandlerTexture(true);
			yield return request.SendWebRequest();

			if (request.isNetworkError || request.isHttpError)
			{
				yield return new WaitForSeconds(1f);
				continue;
			}

			var downloadTime = Time.realtimeSinceStartup - startTime;
			if (PHOTO_INTERVAL > downloadTime)
			{
				yield return new WaitForSeconds(PHOTO_INTERVAL - downloadTime);
			}

			var dh = request.downloadHandler as DownloadHandlerTexture;
			var tex = dh.texture;

			SetImageTexture(NextImage, tex);
			dh.Dispose();
			request.Dispose();

			float currentStart = CurrentImage.color.a;
			float currentFinish = transparent.a;
			float nextStart = NextImage.color.a;
			float nextFinish = opaque.a;
			startTime = Time.time;
			while (Time.time < startTime + ANIMATION_LENGTH)
			{
				float ct = Time.time;
				float x = (ct - startTime) / ANIMATION_LENGTH;
				float currentA = currentStart + x * (currentFinish - currentStart);
				Color cC = new Color(CurrentImage.color.r, CurrentImage.color.g, CurrentImage.color.b, currentA);
				CurrentImage.color = cC;
				float nextA = nextStart + x * (nextFinish - nextStart);
				Color nC = new Color(NextImage.color.r, NextImage.color.g, NextImage.color.b, nextA);
				NextImage.color = nC;
				yield return null;
			}

			currentImage = (currentImage + 1) % images.Length;
			Resources.UnloadUnusedAssets();
			System.GC.Collect();
		}
	}

	private void SetImageTexture(Image nextImage, Texture2D tex)
	{
		if (nextImage.sprite != null)
		{
			Destroy(nextImage.sprite.texture);
			Destroy(nextImage.sprite);
			nextImage.sprite = null;
		}

		float imageWidth = imageContainer.rect.width;
		float imageHeight = imageContainer.rect.height;
		//
		int maxHeight, maxWidth;
		if (imageWidth < imageHeight)
		{
			// scale to height
			maxHeight = 2048;
			maxWidth = (int)(2048 / imageHeight * imageWidth);
		}
		else
		{
			// scale to width
			maxWidth = 2048;
			maxHeight = (int)(2048 / imageWidth * imageHeight);
		}
		float factor = Mathf.Min((float) maxWidth / tex.width, (float)maxHeight / tex.height);
		int newWidth = (int)(tex.width * factor);
		int newHeight = (int)(tex.height * factor);
		TextureScale.Bilinear(tex, newWidth, newHeight);

		var sprite = Sprite.Create(tex, new Rect(0, 0, tex.width, tex.height), Vector2.zero);
		nextImage.sprite = sprite;
		nextImage.rectTransform.anchorMin = new Vector2((maxWidth - (float)newWidth) / maxWidth / 2, (maxHeight - (float)newHeight) / maxHeight / 2);
	}
}