在Unity中把一张图片转换为黑白（Blind开发日志：1月28日）

今天有个奇怪的尝试，打算实现一下让场景里一张图片直接转换成为黑白的效果，首先想到的是使用 Shader。

Shader "Custom/GrayscaleShader"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
    }
    SubShader
    {
        Tags { "RenderType"="Opaque" }
        LOD 100

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag
            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
            };

            sampler2D _MainTex;

            v2f vert (appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }
            
            fixed4 frag (v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);
                float grayscale = dot(col.rgb, float3(0.299, 0.587, 0.114));
                return fixed4(grayscale, grayscale, grayscale, col.a);
            }
            ENDCG
        }
    }
}

创建一个新的Material，并将新创建的Shader赋给这个Material。在你的场景中，找到想要转换为黑白的SpriteRenderer，并将这个新创建的Material赋给它们。

但是操作起来太麻烦了，于是尝试了一种纯粹使用代码完成的思路：

using UnityEngine;

public class ConvertSpriteToBlackAndWhite : MonoBehaviour
{
    void Start()
    {
        SpriteRenderer[] allSprites = FindObjectsOfType<SpriteRenderer>();
        foreach (SpriteRenderer spriteRenderer in allSprites)
        {
            ConvertToBlackAndWhite(spriteRenderer);
        }
    }

    void ConvertToBlackAndWhite(SpriteRenderer spriteRenderer)
    {
        if (spriteRenderer.sprite == null) return;

        Texture2D originalTexture = spriteRenderer.sprite.texture;
        Texture2D grayscaleTexture = new Texture2D(originalTexture.width, originalTexture.height);
        Color[] originalPixels = originalTexture.GetPixels();
        Color[] grayscalePixels = new Color[originalPixels.Length];

        for (int i = 0; i < originalPixels.Length; i++)
        {
            Color originalColor = originalPixels[i];
            float grayscaleValue = originalColor.grayscale;
            grayscalePixels[i] = new Color(grayscaleValue, grayscaleValue, grayscaleValue, originalColor.a);
        }

        grayscaleTexture.SetPixels(grayscalePixels);
        grayscaleTexture.Apply();

        spriteRenderer.sprite = Sprite.Create(grayscaleTexture, spriteRenderer.sprite.rect, new Vector2(0.5f, 0.5f));
    }
}

原理是，复制Sprite的原始纹理，然后对这个复制品的每个像素应用灰度转换。当然这种方法的效率非常低。

之后又改进了一下代码，可以实现渐变为黑白的效果：

using System.Collections;
using UnityEngine;

public class GradualBlackAndWhite : MonoBehaviour
{
    public float transitionDuration = 2f; // 渐变持续时间，以秒为单位

    void Start()
    {
        StartCoroutine(ApplyBlackAndWhiteGradually());
    }

    IEnumerator ApplyBlackAndWhiteGradually()
    {
        SpriteRenderer[] allSprites = FindObjectsOfType<SpriteRenderer>();
        float time = 0;

        while (time < transitionDuration)
        {
            foreach (SpriteRenderer spriteRenderer in allSprites)
            {
                ConvertToBlackAndWhite(spriteRenderer, time / transitionDuration);
            }

            time += Time.deltaTime;
            yield return null;
        }

        // 确保最终是完全黑白的
        foreach (SpriteRenderer spriteRenderer in allSprites)
        {
            ConvertToBlackAndWhite(spriteRenderer, 1);
        }
    }

    void ConvertToBlackAndWhite(SpriteRenderer spriteRenderer, float lerpFactor)
    {
        if (spriteRenderer.sprite == null) return;

        Texture2D originalTexture = spriteRenderer.sprite.texture;
        Texture2D grayscaleTexture = new Texture2D(originalTexture.width, originalTexture.height);
        Color[] originalPixels = originalTexture.GetPixels();
        Color[] grayscalePixels = new Color[originalPixels.Length];

        for (int i = 0; i < originalPixels.Length; i++)
        {
            Color originalColor = originalPixels[i];
            float grayscaleValue = originalColor.grayscale;
            Color grayscaleColor = new Color(grayscaleValue, grayscaleValue, grayscaleValue, originalColor.a);
            grayscalePixels[i] = Color.Lerp(originalColor, grayscaleColor, lerpFactor);
        }

        grayscaleTexture.SetPixels(grayscalePixels);
        grayscaleTexture.Apply();

        spriteRenderer.sprite = Sprite.Create(grayscaleTexture, spriteRenderer.sprite.rect, new Vector2(0.5f, 0.5f));
    }
}

最后测试了一下，转换为黑白的效果有点没必要，虽然代码写了，但最后没用 ……