无限大地图：lightmap拆分

　　无缝地图涉及到地形、物件的分块加载，同样，lightmap也需要动态加载。而场景烘焙时，所有物件都是一起烘焙的，那怎么把某些物件指定烘焙到某一张lightmap贴图中？网上找了很久，也没有看到具体的实现方式，还是要自己从头造车，结合网上的一些理论，经过实践，分享2个方法

 

1. 设置自定义LightmapParameters，设置Bake tag，相同tag的物件，会烘焙到同一张lightmap中。Terrain_1_1是新创建的LightmapParameters，替换掉默认的Pamameters

 

 

2. 通过计算Renderer的uv，从完整Lightmap贴图中抠出来指定某个范围的贴图，然后与想要合并到一起的其他贴图生成一个新的lightmap贴图

 

第一个方法是最省事的，但是有一个问题，LightmapParameters看起来只有手动设置，Unity没有提供api，貌似不能用代码来实现自动化。那么只能使用黑科技了（反编译UnityEditor.dll得来的方法）

 //创建LightmapParameters资源文件
        public static void CreateLightmapParameterFile(string path, int bakeTag)
        {
            LightmapParameters lp = new LightmapParameters();
            lp.bakedLightmapTag = bakeTag;
            AssetDatabase.CreateAsset(lp, path);
            AssetDatabase.ImportAsset(path);
        }

        public static void SetRenderLightmapParameters(Renderer renderer, string giparamsFile)
        {
            SerializedObject so = new SerializedObject(renderer);
            var sp = so.FindProperty("m_LightmapParameters");
            sp.objectReferenceValue = AssetDatabase.LoadAssetAtPath(giparamsFile, typeof(LightmapParameters));
            so.ApplyModifiedProperties();
        }

重点在so.FindProperty("m_LightmapParameters");这是一个不对外的成员变量，通过反射来获取，然后设置objectReferenceValue ，关联之前创建的LightmapParameters文件。后面就简单了，自己实现吧

　　下面是第二个方法，Renderer里面有个变量lightmapScaleOffset，这个变量记录了光照uv的缩放和偏移量，通过计算可以得到该Renderer在lightmap完整贴图中的范围，然后就能扣出来

　　这里总结一下流程

　　a：通过uv2和Renderer的LightmapScaleOffset计算Lightmap贴图中的占用范围（bound）

　　b：抠图，打包图集，获得新的范围（bound）

　　c：已知新的bound和原始uv2，计算新的LightmapScaleOffset

 

//获取uv2
        public static Vector2[] GetMeshUV2(Mesh m)
        {
    //如果不存在uv2，则使用uv代替
            var uv2 = m.uv2;
            if (uv2 == null || uv2.Length == 0)
                uv2 = m.uv;

            return uv2;
        }

       //计算uv的范围
        public static Vector4 GetBounds(Vector2[] uv, Renderer r)
        {
            if (uv != null)
            {
                var __uv = new Vector2[uv.Length];
                Array.Copy(uv, __uv, uv.Length);
                uv = __uv;
                var minx = float.MaxValue;
                var miny = float.MaxValue;
                var maxx = float.MinValue;
                var maxy = float.MinValue;
                for (var _j = 0; _j < uv.Length; ++_j)
                {
                    var _uv = uv[_j];
                    if (_uv.x < minx)
                    {
                        minx = _uv.x;
                    }
                    if (_uv.y < miny)
                    {
                        miny = _uv.y;
                    }
                    if (_uv.x > maxx)
                    {
                        maxx = _uv.x;
                    }
                    if (_uv.y > maxy)
                    {
                        maxy = _uv.y;
                    }
                }
                var bounds = new Vector4(minx, miny, maxx, maxy);
                return bounds;
            }

            return Vector4.zero;
        }

//通过与LightmapScaleOffset计算出原始uv范围对应Lightmap贴图中的范围
        public static Vector4 CalcBoundWithLightmapScaleOffset(Vector4 sourceBounds, Vector4 lightmapScaleOffset)
        {
            var scaleBounds = new Vector4(sourceBounds.x * lightmapScaleOffset.x + lightmapScaleOffset.z,
                                     sourceBounds.y * lightmapScaleOffset.y + lightmapScaleOffset.w,
                                     sourceBounds.z * lightmapScaleOffset.x + lightmapScaleOffset.z,
                                     sourceBounds.w * lightmapScaleOffset.y + lightmapScaleOffset.w);

            return scaleBounds;
        }

//这里就是扣图了
public static Texture2D PickTexture(Texture2D sourceTex, Vector4 bounds)
        {
            var blockW = (int)((bounds.z - bounds.x) * sourceTex.width);
            var blockH = (int)((bounds.w - bounds.y) * sourceTex.height);
            int startX = (int)(bounds.x * sourceTex.width);
            int startY = (int)(bounds.y * sourceTex.height);

            //startY = (tex.height - startY - blockH);
            if (blockH == 0 || blockW == 0)
                return null;

            var colors = sourceTex.GetPixels(startX, startY, blockW, blockH);
            Texture2D tex2d = new Texture2D(blockW, blockH);
            tex2d.SetPixels(colors);
            tex2d.Apply();
            return tex2d;
        }

//从整lightmap贴图中扣指定物件的光照贴图
        public static Texture2D PickLightmap(GameObject go, out Vector4 bound)
        {
            bound = Vector4.zero;
            if (go == null)
                return null;

            var meshFilter = go.GetComponent<MeshFilter>();
            var renderer = go.GetComponent<Renderer>();
            if (meshFilter == null || renderer == null)
                return null;

            var tex = GetFullLightmap(renderer);
            var uv2s = GetMeshUV2(meshFilter.sharedMesh);
            //var bounds = GetBounds(uv2s, renderer);
            var sourceBounds = LightMapUtil.GetBounds(uv2s, renderer);
            var scaleBounds = CalcBoundWithLightmapScaleOffset(sourceBounds, renderer.lightmapScaleOffset);
            bound = sourceBounds;

            return PickTexture(tex, scaleBounds);
        }

以上代码，重点是uv2和LightmapScaleOffset的计算，算出一个矩形范围。这里把图扣出来了，然后是把若干抠出来的图合并到一个新的Texture。合并图集用到unity自带的接口， public Rect[] PackTextures(Texture2D[] textures, int padding, int maximumAtlasSize);

public static void CombineRendererInfos2(List<RendererInfo> rdInfoList, out Rect bound, out Rect[] packedRects)
        {
            packedRects = new Rect[0];

            //计算总面积
            int areaAll = 0;
            for(int i = 0; i < rdInfoList.Count; ++i)
            {
                areaAll += (rdInfoList[i].MyLightmap.width * rdInfoList[i].MyLightmap.height);
            }

            //计算最接近这个面积的宽高尺寸
            int size = 128;
            while(true)
            {
                if (size * size > areaAll)
                    break;
                size *= 2;
            }

            bound = new Rect(0, 0, size, size);

            if (areaAll == 0)
                return;

            while (true)
            {
                List<Rect> rectList = new List<Rect>();
                List<Texture2D> texList = new List<Texture2D>();
                rectList.Add(bound);
                for (int i = 0; i < rdInfoList.Count; ++i)
                {
                    Texture2D tex = new Texture2D(rdInfoList[i].MyLightmap.width, rdInfoList[i].MyLightmap.height);
                    texList.Add(tex);
                }

                Texture2D combined = new Texture2D((int)bound.width, (int)bound.height, TextureFormat.ARGB32, false);

                packedRects = combined.PackTextures(texList.ToArray(), 0, size);

                if (packedRects == null || packedRects.Length == 0 || packedRects[0].width * bound.width < texList[0].width)
                {
                    bound.width *= 2;
                    bound.height *= 2;
                    size *= 2;
                }
                else
                {
                    bound.width = combined.width;
                    bound.height = combined.height;
                    for (int i = 0; i < rdInfoList.Count; ++i)
                    {
                        Vector2 pos = new Vector2(packedRects[i].x, packedRects[i].y);
                        {
                            rdInfoList[i].Position = pos;
                            rdInfoList[i].Position.x *= bound.width;
                            rdInfoList[i].Position.y *= bound.height;

                            //为了消除接缝黑边
                            var ignorPixels = 1/1f;
                            var blockW = rdInfoList[i].MyLightmap.width;
                            var blockH = rdInfoList[i].MyLightmap.height;
                            var texWidth = bound.width;
                            var texHeight = bound.height;
                            var sourceBounds = rdInfoList[i].OldBound;

                            var scaleUVX = (blockW - ignorPixels) / (texWidth * (sourceBounds.z - sourceBounds.x));
                            var offsetUVX = (pos.x) / (float)texWidth - scaleUVX * sourceBounds.x;

                            var scaleUVY = (blockH - ignorPixels) / (texHeight * (sourceBounds.w - sourceBounds.y));
                            var offsetUVY = (pos.y) / (float)texHeight - scaleUVY * sourceBounds.y;

                            rdInfoList[i].MyLightmapScaleInfo = new Vector4(scaleUVX, scaleUVY, offsetUVX, offsetUVY);
                        }
                    }
                    break;
                }
            }
        }

上面重点是合并到新的lightmap后，需要重新计算Renderer的LightmapScaleOffset

var scaleUVX = (blockW) / (texWidth * (sourceBounds.z - sourceBounds.x));

var offsetUVX = pos.x / (float)texWidth - scaleUVX * sourceBounds.x;

 

var scaleUVY = (blockH) / (texHeight * (sourceBounds.w - sourceBounds.y));

var offsetUVY = pos.y / (float)texHeight - scaleUVY * sourceBounds.y

 

rdInfoList[i].MyLightmapScaleInfo = new Vector4(scaleUVX, scaleUVY, offsetUVX, offsetUVY);

 

实际上就是前面通过uv与LightmapScaleOffset计算一个范围的反推过程，现在是已知最终范围和原始uv，计算新的LightmapScaleOffset，原理还是很简单的。