为Unity的新版ugui的Prefab生成预览图

2018.3版本的unity有新的嵌套预制体功能，现在预览图很不方便。可以生成一个。

using UnityEngine;
using System.Collections;
using UnityEditor;
using System.IO;

[CustomPreview(typeof(GameObject))]
public class UIPreview : ObjectPreview
{
Texture preview;

const string cachePreviewPath = "CachePreviews";

public override bool HasPreviewGUI()
{
return true;
}


public override void OnPreviewGUI(Rect r, GUIStyle background)
{
base.OnPreviewGUI(r, background);
if (target == null)
return;

var targetGameObject = target as GameObject;

if (targetGameObject == null)
return;


GUI.Label(r, target.name + " is being previewed");
preview = AssetPreview.GetAssetPreview(target);


if (preview == null)
{
string guid = AssetDatabase.AssetPathToGUID(AssetDatabase.GetAssetPath(targetGameObject));

string pathname = Path.Combine(cachePreviewPath, guid + ".png");
preview = AssetDatabase.LoadAssetAtPath<Texture2D>(Path.Combine("Assets",pathname));
if (preview == null)
{
preview = GetAssetPreview(targetGameObject);

if (SaveTexture2D(preview as Texture2D, Path.Combine(Application.dataPath, pathname)))
{
AssetDatabase.ImportAsset(pathname);
AssetDatabase.Refresh();
Debug.Log("SaveTextureToPNG " + pathname);
}
}
}

GUI.DrawTexture(r, preview);
}

public static Texture GetAssetPreview(GameObject obj)
{
GameObject canvas_obj = null;
GameObject clone = GameObject.Instantiate(obj);
Transform cloneTransform = clone.transform;

GameObject cameraObj = new GameObject("render camera");
Camera renderCamera = cameraObj.AddComponent<Camera>();
renderCamera.backgroundColor = new Color(0.8f, 0.8f, 0.8f, 1f);
renderCamera.clearFlags = CameraClearFlags.Color;
renderCamera.cameraType = CameraType.SceneView;
renderCamera.cullingMask = 1 << 21;
renderCamera.nearClipPlane = -100;
renderCamera.farClipPlane = 100;

bool isUINode = false;
if (cloneTransform is RectTransform)
{
//如果是UGUI节点的话就要把它们放在Canvas下了
canvas_obj = new GameObject("render canvas", typeof(Canvas));
Canvas canvas = canvas_obj.GetComponent<Canvas>();
cloneTransform.parent = canvas_obj.transform;
cloneTransform.localPosition = Vector3.zero;
//canvas_obj.transform.position = new Vector3(-1000, -1000, -1000);
canvas_obj.layer = 21;//放在21层，摄像机也只渲染此层的，避免混入了奇怪的东西
canvas.renderMode = RenderMode.ScreenSpaceCamera;
canvas.worldCamera = renderCamera;

isUINode = true;
}
else
cloneTransform.position = new Vector3(-1000, -1000, -1000);

Transform[] all = clone.GetComponentsInChildren<Transform>();
foreach (Transform trans in all)
{
trans.gameObject.layer = 21;
}

Bounds bounds = GetBounds(clone);
Vector3 Min = bounds.min;
Vector3 Max = bounds.max;



if (isUINode)
{
cameraObj.transform.position = new Vector3(0, 0, -10);
//Vector3 center = new Vector3(cloneTransform.position.x, (Max.y + Min.y) / 2f, cloneTransform.position.z);
cameraObj.transform.LookAt(Vector3.zero);

renderCamera.orthographic = true;
float width = Max.x - Min.x;
float height = Max.y - Min.y;
float max_camera_size = width > height ? width : height;
renderCamera.orthographicSize = max_camera_size / 2;//预览图要尽量少点空白
}
else
{
cameraObj.transform.position = new Vector3((Max.x + Min.x) / 2f, (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);

int angle = (int)(Mathf.Atan2((Max.y - Min.y) / 2, (Max.z - Min.z)) * 180 / 3.1415f * 2);
renderCamera.fieldOfView = angle;
}
RenderTexture texture = new RenderTexture(128, 128, 0, RenderTextureFormat.Default);
renderCamera.targetTexture = texture;

var tex = RTImage(renderCamera);

Object.DestroyImmediate(canvas_obj);
Object.DestroyImmediate(cameraObj);


return tex;
}

static Texture2D RTImage(Camera camera)
{
// The Render Texture in RenderTexture.active is the one
// that will be read by ReadPixels.
var currentRT = RenderTexture.active;
RenderTexture.active = camera.targetTexture;

// Render the camera's view.
//camera.Render();

camera.Render();
// Make a new texture and read the active Render Texture into it.
Texture2D image = new Texture2D(camera.targetTexture.width, camera.targetTexture.height);
image.ReadPixels(new Rect(0, 0, camera.targetTexture.width, camera.targetTexture.height), 0, 0);
image.Apply();

// Replace the original active Render Texture.
RenderTexture.active = currentRT;
return image;
}

public static Bounds GetBounds(GameObject obj)
{
Vector3 Min = new Vector3(99999, 99999, 99999);
Vector3 Max = new Vector3(-99999, -99999, -99999);
MeshRenderer[] renders = obj.GetComponentsInChildren<MeshRenderer>();
if (renders.Length > 0)
{
for (int i = 0; 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;
}
}
else
{
RectTransform[] rectTrans = obj.GetComponentsInChildren<RectTransform>();
Vector3[] corner = new Vector3[4];
for (int i = 0; i < rectTrans.Length; i++)
{
//获取节点的四个角的世界坐标，分别按顺序为左下左上，右上右下
rectTrans[i].GetWorldCorners(corner);
if (corner[0].x < Min.x)
Min.x = corner[0].x;
if (corner[0].y < Min.y)
Min.y = corner[0].y;
if (corner[0].z < Min.z)
Min.z = corner[0].z;

if (corner[2].x > Max.x)
Max.x = corner[2].x;
if (corner[2].y > Max.y)
Max.y = corner[2].y;
if (corner[2].z > Max.z)
Max.z = corner[2].z;
}
}

Vector3 center = (Min + Max) / 2;
Vector3 size = new Vector3(Max.x - Min.x, Max.y - Min.y, Max.z - Min.z);
return new Bounds(center, size);
}

public static bool SaveTextureToPNG(Texture inputTex, string save_file_name)
{
RenderTexture temp = RenderTexture.GetTemporary(inputTex.width, inputTex.height, 0, RenderTextureFormat.ARGB32);
Graphics.Blit(inputTex, temp);
bool ret = SaveRenderTextureToPNG(temp, save_file_name);
RenderTexture.ReleaseTemporary(temp);
return ret;
}

public static bool SaveTexture2D(Texture2D png, string save_file_name)
{
byte[] bytes = png.EncodeToPNG();
string directory = Path.GetDirectoryName(save_file_name);
if (!Directory.Exists(directory))
Directory.CreateDirectory(directory);
FileStream file = File.Open(save_file_name, FileMode.Create);
BinaryWriter writer = new BinaryWriter(file);
writer.Write(bytes);
file.Close();

return true;
}

//将RenderTexture保存成一张png图片
public static bool SaveRenderTextureToPNG(RenderTexture rt, string save_file_name)
{
RenderTexture prev = RenderTexture.active;
RenderTexture.active = rt;
Texture2D png = new Texture2D(rt.width, rt.height, TextureFormat.ARGB32, false);
png.ReadPixels(new Rect(0, 0, rt.width, rt.height), 0, 0);
byte[] bytes = png.EncodeToPNG();
string directory = Path.GetDirectoryName(save_file_name);
if (!Directory.Exists(directory))
Directory.CreateDirectory(directory);
FileStream file = File.Open(save_file_name, FileMode.Create);
BinaryWriter writer = new BinaryWriter(file);
writer.Write(bytes);
file.Close(http://www.my516.com);
Texture2D.DestroyImmediate(png);
png = null;
RenderTexture.active = prev;
return true;
}


}
---------------------