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[]; //计算总面积
int areaAll = ;
for(int i = ; 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 = ;
while(true)
{
if (size * size > areaAll)
break;
size *= ;
} bound = new Rect(, , size, size); if (areaAll == )
return; while (true)
{
List<Rect> rectList = new List<Rect>();
List<Texture2D> texList = new List<Texture2D>();
rectList.Add(bound);
for (int i = ; 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(), , size); if (packedRects == null || packedRects.Length == || packedRects[].width * bound.width < texList[].width)
{
bound.width *= ;
bound.height *= ;
size *= ;
}
else
{
bound.width = combined.width;
bound.height = combined.height;
for (int i = ; 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 = /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。