RenderSource.cs

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[Serializable]
public class RenderSource
{
    public Camera targetCamera;
    public RenderTexture targetTexture;

    public int width { get; private set; }
    public int height { get; private set; }
    private Texture2D texture;
    private RenderTexture renderTexture;

    bool initialized;

    public void Init(int width, int height)
    {
        this.width = width;
        this.height = height;
        texture = new Texture2D(width, height, TextureFormat.RGB24, false, true);
        renderTexture = new RenderTexture(width, height, 24);

        initialized = true;
    }

    public Texture2D FetchOnce()
    {
        var fetch = Fetch();
        Release();

        return fetch;
    }

    public Texture2D Fetch()
    {
        if (!initialized)
            throw new Exception("請先執行 Init()");

        if (targetCamera)
        {
            targetCamera.targetTexture = renderTexture;
            targetCamera.Render();

            RenderTexture.active = renderTexture;
            texture.ReadPixels(new Rect(0, 0, renderTexture.width, renderTexture.height), 0, 0);
            texture.Apply();

            targetCamera.targetTexture = null;

            return texture;
        }
        else if (targetTexture)
        {
            RenderTexture.active = targetTexture;
            texture.ReadPixels(new Rect(0, 0, renderTexture.width, renderTexture.height), 0, 0);
            texture.Apply();

            return texture;
        }
        else
        {
            throw new Exception("至少指定 targetCamera 或 targetTexture 其中一項");
        }
    }

    public void Release()
    {
        RenderTexture.active = null;
    }
}