获取unity prefab的预览图像

官方的api可以直接获取预览图像，如下所示：

Tex=AssetPreview.GetAssetPreview(Object m)as Texture;

但是如果prefab是组合体的话（即一个prefab下包含2个或多个子物体），便只返回null。可以算是unity的一个bug吧。

所以需要自己写函数来实现prefab图像预览。

思路是将Prefab实例化到场景，并利用RenderTexture进行摄像机截取图像作为预览图像，代码如下：

         /// <summary>
         /// 获取预览图象
         /// </summary>
         /// <param name="obj"></param>
         /// <returns></returns>
         private Texture GetAssetPreview(GameObject obj)
         {
             GameObject clone = GameObject.Instantiate(obj);
             Transform cloneTransform = clone.transform;
             cloneTransform.position = new Vector3(-, -, -);
             //cloneTransform.localRotation = new Quaternion(0, 0, 0, 1);

             Transform[] all = clone.GetComponentsInChildren<Transform>();
             foreach (Transform trans in all)
             {
                 trans.gameObject.layer = ;
             }

             Bounds bounds = GetBounds(clone);
             Vector3 Min = bounds.min;
             Vector3 Max = bounds.max;
             GameObject cameraObj = new GameObject("render camera");
             cameraObj.transform.position = new Vector3(cloneTransform.position.x, (Max.y + Min.y) / 2f, Max.z + (Max.z - Min.z));

             Vector3 center = new Vector3(cloneTransform.position.x, (Max.y + Min.y) / 2f, cloneTransform.position.z);

             cameraObj.transform.LookAt(center);

             Camera renderCamera = cameraObj.AddComponent<Camera>();
             renderCamera.backgroundColor = new Color(0.8f, 0.8f, 0.8f, 1f);
             renderCamera.clearFlags = CameraClearFlags.Color;
             renderCamera.cameraType = CameraType.Preview;
             renderCamera.cullingMask =  << ;
             int angle = (int)(Mathf.Atan2((Max.y - Min.y) / , (Max.z - Min.z)) *  / 3.1415f * );
             renderCamera.fieldOfView = angle;

             RenderTexture texture = new RenderTexture(, , , RenderTextureFormat.Default);
             renderCamera.targetTexture = texture;

             renderCamera.RenderDontRestore();

             RenderTexture tex = new RenderTexture(, , , RenderTextureFormat.Default);
             Graphics.Blit(texture, tex);

             Object.DestroyImmediate(clone);
             Object.DestroyImmediate(cameraObj);

             return tex;
         }
         /// <summary>
         /// 获得某物体的bounds
         /// </summary>
         /// <param name="obj"></param>
         private Bounds GetBounds(GameObject obj)
         {
             Vector3 Min = new Vector3(, , );
             Vector3 Max = new Vector3(-, -, -);
             MeshRenderer[] renders = obj.GetComponentsInChildren<MeshRenderer>();
             for (int i = ; i < renders.Length; i++)
             {
                 if (renders[i].bounds.min.x < Min.x)
                     Min.x = renders[i].bounds.min.x;
                 if (renders[i].bounds.min.y < Min.y)
                     Min.y = renders[i].bounds.min.y;
                 if (renders[i].bounds.min.z < Min.z)
                     Min.z = renders[i].bounds.min.z;

                 if (renders[i].bounds.max.x > Max.x)
                     Max.x = renders[i].bounds.max.x;
                 if (renders[i].bounds.max.y > Max.y)
                     Max.y = renders[i].bounds.max.y;
                 if (renders[i].bounds.max.z > Max.z)
                     Max.z = renders[i].bounds.max.z;
             }

             Vector3 center = (Min + Max) / ;
             Vector3 size = new Vector3(Max.x - Min.x, Max.y - Min.y, Max.z - Min.z);
             return new Bounds(center, size);
         }

后补：unity在2017.2版本已经修复了这个问题，可以放心用Tex=AssetPreview.GetAssetPreview(Object m)as Texture了。

感谢博友@跳出定向思维的发现，之前的unity旧版本也可以通过给prefab添加标签来解决问题，添加了任意标签后就可以使用自带的获取预览api了。