Unity將粒子光效匯出成png序列幀
這個功能並不是很實用,不過美術同學有這樣的需求,那麼就花了一點時間研究了下。
我們沒有使用Unity的引擎,但是做特效的同學找了一批Unity的粒子特效,希望匯出成png序列幀的形式,然後我們的遊戲來使用。這個就相當於拿Unity做了特效編輯器的工作。這個並不是很“邪門”,因為用幻影粒子,或者3dmax,差不多也是這個思路,只不過那些軟體提供了正規的匯出功能,而Unity則沒有。
先上程式碼
using UnityEngine; using UnityEditor; using System; using System.IO; using System.Collections; using System.Collections.Generic; public class ParticleExporter : MonoBehaviour { // Default folder name where you want the animations to be output public string folder = "PNG_Animations"; // Framerate at which you want to play the animation public int frameRate = 25; // export frame rate 匯出幀率,設定Time.captureFramerate會忽略真實時間,直接使用此幀率 public float frameCount = 100; // export frame count 匯出幀的數目,100幀則相當於匯出5秒鐘的光效時間。由於匯出每一幀的時間很長,所以匯出時間會遠遠長於直觀的光效播放時間 public int screenWidth = 960; // not use 暫時沒用,希望可以直接設定螢幕的大小(即光效畫布的大小) public int screenHeight = 640; public Vector3 cameraPosition = Vector3.zero; public Vector3 cameraRotation = Vector3.zero; private string realFolder = ""; // real folder where the output files will be private float originaltimescaleTime; // track the original time scale so we can freeze the animation between frames private float currentTime = 0; private bool over = false; private int currentIndex = 0; private Camera exportCamera; // camera for export 匯出光效的攝像機,使用RenderTexture public void Start() { // set frame rate Time.captureFramerate = frameRate; // Create a folder that doesn't exist yet. Append number if necessary. realFolder = Path.Combine(folder, name); // Create the folder if (!Directory.Exists(realFolder)) { Directory.CreateDirectory(realFolder); } originaltimescaleTime = Time.timeScale; GameObject goCamera = Camera.main.gameObject; if (cameraPosition != Vector3.zero) { goCamera.transform.position = cameraPosition; } if (cameraRotation != Vector3.zero) { goCamera.transform.rotation = Quaternion.Euler(cameraRotation); } GameObject go = Instantiate(goCamera) as GameObject; exportCamera = go.GetComponent<Camera>(); currentTime = 0; } void Update() { currentTime += Time.deltaTime; if (!over && currentIndex >= frameCount) { over = true; Cleanup(); Debug.Log("Finish"); return; } // 每幀截圖 StartCoroutine(CaptureFrame()); } void Cleanup() { DestroyImmediate(exportCamera); DestroyImmediate(gameObject); } IEnumerator CaptureFrame() { // Stop time Time.timeScale = 0; // Yield to next frame and then start the rendering // this is important, otherwise will have error yield return new WaitForEndOfFrame(); string filename = String.Format("{0}/{1:D04}.png", realFolder, ++currentIndex); Debug.Log(filename); int width = Screen.width; int height = Screen.height; //Initialize and render textures RenderTexture blackCamRenderTexture = new RenderTexture(width, height, 24, RenderTextureFormat.ARGB32); RenderTexture whiteCamRenderTexture = new RenderTexture(width, height, 24, RenderTextureFormat.ARGB32); exportCamera.targetTexture = blackCamRenderTexture; exportCamera.backgroundColor = Color.black; exportCamera.Render(); RenderTexture.active = blackCamRenderTexture; Texture2D texb = GetTex2D(); //Now do it for Alpha Camera exportCamera.targetTexture = whiteCamRenderTexture; exportCamera.backgroundColor = Color.white; exportCamera.Render(); RenderTexture.active = whiteCamRenderTexture; Texture2D texw = GetTex2D(); // If we have both textures then create final output texture if (texw && texb) { Texture2D outputtex = new Texture2D(width, height, TextureFormat.ARGB32, false); // we need to check alpha ourselves,because particle use additive shader // Create Alpha from the difference between black and white camera renders for (int y = 0; y < outputtex.height; ++y) { // each row for (int x = 0; x < outputtex.width; ++x) { // each column float alpha; alpha = texw.GetPixel(x, y).r - texb.GetPixel(x, y).r; alpha = 1.0f - alpha; Color color; if (alpha == 0) { color = Color.clear; } else { color = texb.GetPixel(x, y); } color.a = alpha; outputtex.SetPixel(x, y, color); } } // Encode the resulting output texture to a byte array then write to the file byte[] pngShot = outputtex.EncodeToPNG(); File.WriteAllBytes(filename, pngShot); // cleanup, otherwise will memory leak pngShot = null; RenderTexture.active = null; DestroyImmediate(outputtex); outputtex = null; DestroyImmediate(blackCamRenderTexture); blackCamRenderTexture = null; DestroyImmediate(whiteCamRenderTexture); whiteCamRenderTexture = null; DestroyImmediate(texb); texb = null; DestroyImmediate(texw); texb = null; System.GC.Collect(); // Reset the time scale, then move on to the next frame. Time.timeScale = originaltimescaleTime; } } // Get the texture from the screen, render all or only half of the camera private Texture2D GetTex2D() { // Create a texture the size of the screen, RGB24 format int width = Screen.width; int height = Screen.height; Texture2D tex = new Texture2D(width, height, TextureFormat.ARGB32, false); // Read screen contents into the texture tex.ReadPixels(new Rect(0, 0, width, height), 0, 0); tex.Apply(); return tex; } }
這裡對幾個關鍵的知識點來做說明:
1、整體思路是這樣的,Unity中調整好攝像機,正常播放特效,然後每幀截圖,儲存成我們需要的png序列幀。這個不僅僅是特效可以這麼用,其實模型也可以。比如我們需要同屏顯示幾百上千人,或者是無關緊要的怪物、場景物件等等,就可以使用這個匯出成2d的序列幀,可以大大提高效率,使一些不可能的情況變為可能。
2、關於時間和幀率的控制。由於截圖所需要的時間遠遠大於幀間隔,所以光效如果是播放1秒,則匯出時間可能超過一分鐘。Time.captureFrameRate可以設定幀率,設定後則忽略真實時間,光效、模型會按照幀率的時間來播放。這個介面恰好就是用在視訊錄製上的。
3、光效畫布控制。這個暫時沒有找到好的方法,由於是全螢幕截圖,所以Game視窗的大小就是光效畫布的大小。
4、通過調整攝像機的位置、旋轉,控制光效的顯示資訊。
5、截圖函式就是GetTex2D()。這裡面最主要的是ReadPixels函式。需要注意,CaptureFrame函式必須要以協程的方式執行,因為裡面有一句yield return new WaitForEndOfFrame();如果沒有這一句,會報一個錯誤,大概意思就是ReadPixels不在DrawFrame裡面執行。
6、截圖時間消耗很大,所以需要在截圖開始使用Time.timeScale=0暫停時間執行,截圖後再恢復
7、注意截圖操作完成後清理各種資源,並進行GC。否則記憶體很有可能就不夠用了,截100幀圖片,記憶體很有可能就兩三G了。
8、截圖的時候使用了兩個RenderTexture,分別繪製白底和黑底的圖片,然後根據這兩張圖片計算出alpha。如果不是光效其實可以不這麼麻煩,直接把Camera的backgroundColor中的alpha設定為0就可以了。但是光效使用了特殊的shader,比如Additive,這裡涉及到alpha blend。繪製光效時如果也這樣設定的話,匯出的圖片沒有任何東西。所以必須要有實色背景。