很长一段时间里，我都对游戏中各种贴图的分辨率规范认知处于一种混沌的状态，比如离镜头远的给1024分辨率，离镜头近的给2048分辨率，大物体给2048分辨率，小物体给512分辨率等等，也就是纯凭感觉，虽然不科学，但it works！

直到某天刷知乎看到了关于此类问题的讨论和技术分享，方才恍然大悟

本篇文章是对ProjectS中纹素密度选择的过程总结，以及相关工具分享

Mipmap验证工具制作

源代码来自我该给一个3D物体用多大的贴图？——游戏工程中快速确定物体贴图分辨率的实践方法，做了一些优化整理

内容也很简单，就是手动将对应分辨率的基元mipmap写入纹理中，具体优化为：

支持0-7级的mipmap指定，生成对应的纹理，实际上7级的时候纹理大小已经来到8192分辨率了，再高也没必要
- 0代表只生成一张64分辨率的纹理，仅有mip0
- 1代表生成一张128分辨率的纹理，mip1为64
- 2代表生成一张256分辨率的纹理，mip1为128，mip2为64
- 。。。
以PC平台为例，最后对纹理做了一次BC7压缩优化，可以大幅减少纹理大小和渲染压力
自动生成随机颜色
自动匹配基元mipmap纹理

这个可视化的原理也很简单，因为我们每级mipmap的分辨率都是完全匹配的

例如miplevel7为64分辨率，就使用这张64分辨率的基元图片

miplevel6为128分辨率，就用这张分辨率为64，但图片内容标识为128的基元纹理铺满整个128分辨率的mipmap

如此一来，我们严格保证了分辨率和图片显示内容一致，自然能直接将渲染结果作为指导的分辨率使用

using Sirenix.OdinInspector.Editor;
using Sirenix.OdinInspector;
using UnityEngine;
using UnityEditor;

namespace NKG.ProjectS
{
    /// <summary>
    /// 为了美观，每个基元纹理都是64分辨率
    /// mipmax为64，mipmax - 1为128，mipmax - 2为256，mipmin为 (2 ^（mipmax - mipmin） x 64)
    /// </summary>
    public class MipmapGeneratorEditor : OdinEditorWindow
    {
        [LabelText("使用说明")]
        public string wikipediaURL = "整理自：https://zhuanlan.zhihu.com/p/415919803";
        
        public const int maxMipLimit = 7;
        
        [InfoBox("mipmax为64，mipmin为8192，对应值为0-7")]
        [LabelText("Mip等级数量")][Range(0, maxMipLimit)] public int maxMipLevel = 7;

        public Texture2D[] fillrateSourceTextures;
        public Color[] fillrateSourceColors;

        [FolderPath] public string targetSavePath;

        [Button("创建")]
        void Create()
        {
            int levelCount = maxMipLevel + 1;
            
            if (fillrateSourceTextures == null || fillrateSourceTextures.Length != levelCount)
            {
                fillrateSourceTextures = new Texture2D[maxMipLimit + 1];
                fillrateSourceTextures[0] = AssetDatabase.LoadAssetAtPath<Texture2D>("Packages/com.nkg.mipmapvis/8K.png");
                fillrateSourceTextures[1] = AssetDatabase.LoadAssetAtPath<Texture2D>("Packages/com.nkg.mipmapvis/4K.png");
                fillrateSourceTextures[2] = AssetDatabase.LoadAssetAtPath<Texture2D>("Packages/com.nkg.mipmapvis/2K.png");
                fillrateSourceTextures[3] = AssetDatabase.LoadAssetAtPath<Texture2D>("Packages/com.nkg.mipmapvis/1K.png");
                fillrateSourceTextures[4] = AssetDatabase.LoadAssetAtPath<Texture2D>("Packages/com.nkg.mipmapvis/512.png");
                fillrateSourceTextures[5] = AssetDatabase.LoadAssetAtPath<Texture2D>("Packages/com.nkg.mipmapvis/256.png");
                fillrateSourceTextures[6] = AssetDatabase.LoadAssetAtPath<Texture2D>("Packages/com.nkg.mipmapvis/128.png");
                fillrateSourceTextures[7] = AssetDatabase.LoadAssetAtPath<Texture2D>("Packages/com.nkg.mipmapvis/64.png");
            }

            if (fillrateSourceColors == null || fillrateSourceColors.Length != levelCount)
            {
                fillrateSourceColors = new Color[maxMipLimit + 1];
                fillrateSourceColors[0] = new Color(Random.Range(0, 1.0f), Random.Range(0, 1.0f), Random.Range(0, 1.0f), 1f);
                fillrateSourceColors[1] = new Color(Random.Range(0, 1.0f), Random.Range(0, 1.0f), Random.Range(0, 1.0f), 1f);
                fillrateSourceColors[2] = new Color(Random.Range(0, 1.0f), Random.Range(0, 1.0f), Random.Range(0, 1.0f), 1f);
                fillrateSourceColors[3] = new Color(Random.Range(0, 1.0f), Random.Range(0, 1.0f), Random.Range(0, 1.0f), 1f);
                fillrateSourceColors[4] = new Color(Random.Range(0, 1.0f), Random.Range(0, 1.0f), Random.Range(0, 1.0f), 1f);
                fillrateSourceColors[5] = new Color(Random.Range(0, 1.0f), Random.Range(0, 1.0f), Random.Range(0, 1.0f), 1f);
                fillrateSourceColors[6] = new Color(Random.Range(0, 1.0f), Random.Range(0, 1.0f), Random.Range(0, 1.0f), 1f);
                fillrateSourceColors[7] = new Color(Random.Range(0, 1.0f), Random.Range(0, 1.0f), Random.Range(0, 1.0f), 1f);
            }

            int resolution = Mathf.FloorToInt(Mathf.Pow(2, maxMipLevel)) * 64;
            
            Texture2D texture = new Texture2D(resolution, resolution, TextureFormat.RGBA32, levelCount, true);

            // 填充从mipmax到mip0
            for (int i = 0; i < maxMipLevel + 1; i++)
            {
                int width = resolution >> i;
                int height = resolution >> i;

                Texture2D sourcePatternTexture = fillrateSourceTextures[i + maxMipLimit - maxMipLevel];
                int sourcePatternTextureWidth = sourcePatternTexture.width;
                int sourcePatternTextureHeight = sourcePatternTexture.height;
                Color fillColor = fillrateSourceColors[i + maxMipLimit - maxMipLevel];

                Color[] texCol =
                    sourcePatternTexture.GetPixels(0, 0, sourcePatternTextureWidth, sourcePatternTextureHeight);

                for (int p = 0; p < texCol.Length; ++p)
                {
                    var col = texCol[p];
                    col *= fillColor;
                    texCol[p] = col;
                }

                int copyStepX = width / sourcePatternTextureWidth;
                int copyStepY = height / sourcePatternTextureHeight;

                for (int x = 0; x < copyStepX; ++x)
                {
                    for (int y = 0; y < copyStepY; ++y)
                    {
                        texture.SetPixels(x * sourcePatternTextureWidth, y * sourcePatternTextureHeight,
                            sourcePatternTextureWidth, sourcePatternTextureHeight, texCol, i);
                    }
                }
            }

            texture.Apply(false);
            AssetDatabase.CreateAsset(texture,
                string.IsNullOrEmpty(targetSavePath)
                    ? $"Packages/com.nkg.mipmapvis/Generated/MipmapForCheck.asset"
                    : $"{targetSavePath}/MipmapForCheck.asset");
            AssetDatabase.Refresh();
            
            // BC7压缩下
            EditorUtility.CompressTexture(AssetDatabase.LoadAssetAtPath<Texture2D>( string.IsNullOrEmpty(targetSavePath)
                ? $"Packages/com.nkg.mipmapvis/Generated/MipmapForCheck.asset"
                : $"{targetSavePath}/MipmapForCheck.asset"), TextureFormat.BC7, TextureCompressionQuality.Best);
            
            AssetDatabase.Refresh();
        }

        [MonKey.Command("Mipmap Generator", Help = "生成一张用于纹理合理性检测的多Mipmap的纹理", Category = "Tool")]
        public static void ShowWindow()
        {
            GetWindow(typeof(MipmapGeneratorEditor));
        }
    }
}