DOTween UnityEngine.UI.Image image cross fade

readme.md

DOTween Unity UI Image Crossfade

Just a quick hack to fade between UI Image sprites. I whipped up a quick shader for optimization but didn't have time to adjust it to fix sprites of different ratios when the Image component used Preserve Aspect Ratio

Works as is, simple and easy.

Here's an example of some cat pictures I found.

Example of usage

Sprite myNextSprite; // Assuming this is set
const float duration = 0.3f; // 300ms animation duration

myImage.DOKill(); // It's a good idea to kill off previous animations
myImage.DOCrossfadeImage(myNextSprite, duration, () =>
{
    //A callback for when complete. Just a hacky way of getting a callback.
    // NOTE: Will not be called if killed.
    Debug.Log("Crossfade animation completed successfully");
});

MIT License

Go ahead and use it for whatever and stuff. If you improve it please feel free to let me know and I'll update this so we can all give a little back to the community.

ImageDOCrossfade.cs

/** --
 ** Copyright (C) 2019 by Josh van den Heever
 **
 ** Permission is hereby granted, free of charge, to any person obtaining a copy of 
 ** this software and associated documentation files (the "Software"), to deal in 
 ** the Software without restriction, including without limitation the rights to 
 ** use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies 
 ** of the Software, and to permit persons to whom the Software is furnished to 
 ** do so, subject to the following conditions:
 **
 ** The above copyright notice and this permission notice shall be included in 
 ** all copies or substantial portions of the Software.
 **
 ** THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, 
 ** INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
 ** IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
 ** WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR 
 ** THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 ** --
***/
using UnityEngine;
using DG.Tweening;
using UnityEngine.UI;

public static class ImageDOCrossfade
{
    private static Image CreateTempChildImage(Image image)
    {
        Image result = null;

        string tempChildName = GetTempChildName(image);
        Transform foundTransform = image.transform.Find(tempChildName);
        GameObject tempGo = foundTransform != null ? foundTransform.gameObject : null;

        if (tempGo == null)
        {
            tempGo = new GameObject("TempCloneChild");
            var rt = image.GetComponent<RectTransform>();

            var rtPrime = tempGo.AddComponent<RectTransform>();
            rtPrime.SetParent(rt);
            rtPrime.localScale = Vector3.one;
            rtPrime.anchorMin = Vector2.zero;
            rtPrime.anchorMax = Vector2.one;
            rtPrime.sizeDelta = Vector2.zero;
            rtPrime.anchoredPosition = Vector2.zero;

            result = tempGo.AddComponent<Image>();
            result.preserveAspect = image.preserveAspect;
        }
        else
        {
            result = tempGo.GetComponent<Image>();
        }

        return result;
    }

    private static string GetTempChildName(Image target) => string.Format("TempCloneChild_{0}", target.GetInstanceID());

    public static float GetAlpha(this Image image) => image.color.a;
    public static void SetAlpha(this Image image, float alpha)
    {
        var color = image.color;
        color.a = alpha;
        image.color = color;
    }


    private static void RemoveTempChildImage(Image childImage)
    {
        if (childImage != null)
        {
            Object.Destroy(childImage.gameObject);
        }
    }

    public static Tweener DOCrossfadeImage(this Image image, Sprite to, float duration, System.Action OnComplete = null)
    {
        Image childImage = CreateTempChildImage(image);
        float progress = 0f;
        const float finalAlpha = 1f;

        childImage.SetAlpha(0f);
        childImage.sprite = to;

        return DOTween.To(
            () => progress,
            (curProgress) =>
            {
                progress = curProgress;

                float childAlpha = finalAlpha * progress;
                float imageAlpha = finalAlpha - childAlpha;
                image.SetAlpha(imageAlpha);
                childImage.SetAlpha(childAlpha);
            },
            1f, duration)
            .OnComplete(() => 
            {
                image.sprite = to;
                image.SetAlpha(childImage.GetAlpha());

                RemoveTempChildImage(childImage);

                OnComplete?.Invoke();
            })
            .OnKill(() =>
            {
                //Note: If you expect this tween will cancel and wish to halt the
                //  animation, remove this next line. It will look bad when you 
                //  start another CrossFadeImage animation on this
                RemoveTempChildImage(childImage);
            });
    }
}