How to wait for CaptureScreen to complete

I'm trying to take a screenshot of the iPhone screen either using Prime31 takeScreenShot or Application.CaptureScreenshot and then insert it into a tweet or Facebook post.

The problem I have is the async nature of both of the above calls. I can't find a way of waiting to be sure the screenshot has finished writing before trying to attach it. Everything I try ends up with no screenshot until the second time you trigger it, at which point it shows the previous one i captured. Waiting for the file to exist isn't enough, since that can mean it has started to be written but not completed.

This is what I have tried so far:

Code (csharp):

1.  
2. function WaitForFile(file : String)
3. {
4.     var t : float = 5.0;
5.     // Wait for file to become valid or 5 seconds max
6.     while (!System.IO.File.Exists(file)  t > 0f) {
7.         yield WaitForSeconds(0.1);
8.         t -= Time.deltaTime;
9.     }
10. }
11.  
12. function ShowTwitter()
13. {
14.     Application.CaptureScreenshot("screen.png");
15. //  EtceteraBinding.takeScreenShot("screen.png");
16.        
17.     #if UNITY_IPHONE
18.         var path_to_image = Application.persistentDataPath + "/screen.png";
19.     #elif UNITY_STANDALONE_OSX
20.         var path_to_image = Application.dataPath + "/Data/screen.png";
21.     #endif
22.    
23.     // Wait for capture to complete
24.     WaitForFile(path_to_image);
25.    
26.     var stars : int = PlayerPrefs.GetInt("lastStars", 0);
27.     var score : int = PlayerPrefs.GetInt("lastScore", 0);
28.                
29.     SocialNetworksAPI.Social_TW_Post_With_ScreenShot("I got a score of "+score+" and "+score+" stars on Rock Run, can you beat that?", path_to_image, "http://appstore.com/gigabytesoltionsltd/rockrun");
30. }
31.  

 

I also tried the following version, same result:

Code (csharp):

1.  
2. function WaitForFile(file : String)
3. {
4.     var t : float = 5.0;
5.     // Wait for file to become valid or 5 seconds max
6.     var fi : FileInfo = FileInfo(file);
7.     while ((fi==null || fi.Exists==false)  t > 0f) {
8.         yield WaitForSeconds(0.1);
9.         t -= Time.deltaTime;
10.         fi = FileInfo(file);
11.     }
12. }
13.  

 

I don't know about the other, but Application.CaptureScreenshot isn't async; the operation is complete and the file is closed by the next line of code. Nothing in Unity is async unless explicitly specified in the docs. So I'd suspect some logic error. (Speaking of which, not that you need it, but the WaitForFile function does nothing at all since you're not yielding on it.)

--Eric

 

It is async, there are lots of posts about this on Unity Answers stating as such.

I've managed to get it working by changing the call to WaitForFile to yield WaitForFile. I always get confused with yield in Javascript.

Thanks

 

Actually, now it isn't working again!!!!

It's back to showing the previous screenshot. Also tried this using the Prime31 plugin and still showing previous screenshot almost every time... grrr

Code (csharp):

1.  
2.     yield StartCoroutine(EtceteraBinding.takeScreenShot("screen.png"));
3.  

Why does this seem impossible!!

 

In c# I'll probably launch a first System.IO.File.Delete(yourPreviousScreenShoot) to be sure the previous screenshot goes away.

After an Application.persistentDataPath + "/screen.png";
Loading screen "please wait" locking interface with a cancel button showed.

During the update : if(System.IO.file.Exist(your screenshoot)
And if finally find it to unlock he interface and to pop the facebook window.

 

Thanks

Deleting it first has worked. Not sure why I didn't realise that was going to be a problem first

 

Hello to the past from the future! Well in unityscript it seems just to put yield between Application.CaptureScreenshot statement and any further statement is enough:

Code (csharp):

1. Application.CaptureScreenshot(fileName);
2. yield;
3. // ...now manipulate the image

I also thought thatI just need to wait for the end of frame to be able to access the captured image data but it turn out that tha capture itself happens at the very end of the frame its being called.. The simple yield with no params just postpones further statement to the next frame, thus ensuring the capture is complete.

Yields are sometimes really a bit confusing to mee too, especially th edifferent usage in C# and unityscript.

 

Bump, this is super confusing. How long should I wait for File to be completely written on mobile platform.
For Android, file is written in packets say 500KB each and it can take upto 5 seconds. So am sure file is not written in one instant. Even if I yield for File.Exists, this will not be correct as it may only contain partial data.
Is there a prescribed way to detect end of Application.captureScreenshot?

 

Bump, same here.

 

Based on my results, I believe this is incorrect. Are you certain about this?

File does not exist when next frame starts for sure. Also, I've noticed that the file is written in chunks. Let's say my image size is 5MB on Android. I've noticed that after 1 second, file exists of size 2.4 mb, then size increases to 5 mb after 3 seconds or so.

 

I've been struggling with this a bit, but I think I've got it worked out. Here's what I found...

As I see it, there are two parts to Application.CaptureScreenshot.

1. Capture the screenshot (i.e. hold it in RAM). This seems to be consistently happening before the end of the frame (when called in Update), as some have described. I think this is the behaviour you'd probably hope for, as if it takes any longer than that, then it would capture the wrong frame.
2. Save a PNG using the information captured. This is the async part, and can take a lot longer depending on the device. In the Unity Editor, this seems to happen almost instantly, but on a cheap Android tablet I tested on, it takes several seconds, as per other's experiences (I currently don't have any better Android hardware to test on, but I can imagine once you get up to the crazy high resolutions of phones like the GS6, you'll be waiting quite a while for the screenshot to save). This was the cause of my frustration, since what worked perfectly in the editor, didn't work at all in my builds!

Working around it:
One thing I did in an attempt to deal with the image not being ready by the time I come to use it, was the following line of code, which gives me a success boolean, imageLoadSuccess, so I can retry if needed. Not ideal, but the best method for dealing with it that I've come up with.

Code (CSharp):

1. Texture2D image;
2.  
3.     image = new Texture2D(Screen.width, Screen.height);
4.     bool imageLoadSuccess = image.LoadImage(System.IO.File.ReadAllBytes(path));

Hope this comes in useful for someone

 

You wouldn't use FixedUpdate, since that only applies to physics and is unrelated to the camera update.

--Eric

 

Oops, yup you're right! I meant Update() since that's per frame. I'll edit my reply to avoid confusion

I've ended up making a screenshot class that may alleviate problems for some. I wanted to be able to show the screenshot in the scene straight away, but wasn't worried about accessing the file until a bit later, so this allows me to do these things separately. I can't promise it's the best way to do things, but it's working for me. Again, I hope this helps someone:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3. using System.IO;
4.  
5. public class Screenshot : MonoBehaviour {
6.  
7.     private static Screenshot sInstance = new Screenshot();
8.  
9.     public static Screenshot Instance {
10.         get {
11.             return sInstance;
12.         }
13.     }
14.  
15.     Texture2D tex;
16.  
17.     public string getPath() {
18.         // where we want to save the image
19.         return Application.persistentDataPath + "/screentoshare.png";
20.     }
21.  
22.     public void takeNow() {
23.         //takes the screenshot, but doesn't save a file. It's stored as a Texture2D instead
24.         tex = new Texture2D(Screen.width, Screen.height, TextureFormat.RGB24, false);
25.         tex.ReadPixels(new Rect(0, 0, Screen.width, Screen.height), 0, 0);
26.         tex.Apply();
27.     }
28.  
29.     public Texture2D getTexture2D() {
30.         //call to access the texture2D from outside this class
31.         return tex;
32.     }
33.  
34.     public void saveAsFile () {
35.         //saves a PNG file to the path specified above
36.         byte[] bytes = tex.EncodeToPNG();
37.         File.WriteAllBytes(getPath (), bytes);
38.     }
39.  
40.     public bool hasSaved() {
41.         //it's not enough to just check that the file exists, since it doesn't mean it's finished saving
42.         //we have to check if it can actually be opened
43.         Texture2D image;
44.         image = new Texture2D(Screen.width, Screen.height);
45.         bool imageLoadSuccess = image.LoadImage(System.IO.File.ReadAllBytes(getPath()));
46.         Destroy (image);
47.         return imageLoadSuccess;
48.     }
49.  
50. }

No need to instantiate or anything, so to take the screenshot, just use the one line of code:

Code (CSharp):

1. Screenshot.Instance.takeNow();

To show it in your UI, access the Texture2D, using:

Code (CSharp):

1. Texture2D myScreenshotTexture = Screenshot.Instance.getTexture2D();

etc...

 

You saved my days, bro

 

File exist does not ensure that the file is written completely. File is normally written in chunks, so you have to wait till file is fully written as exists will return true even if file is partially written returning corrupt texture.

 

I had a problem with checking for file.exist because as mentioned above, the file might not be written completely. I ended up using this and it seems to work:

Code (CSharp):

1. IEnumerator delayedShare(string path, string text)
2.     {
3.  
4.         while(IsFileUnavailable(path)) {
5.             Debug.Log("file locked");
6.             yield return new WaitForSeconds(.05f);
7.         }
8.  
9.         // run your code that needs the file to be loaded here
10.  
11.  
12.     }

Code (CSharp):

1. protected virtual bool IsFileUnavailable(string path)
2.     {
3.         // if file doesn't exist, return true
4.         if (!File.Exists(path))
5.             return true;
6.  
7.         FileInfo file = new FileInfo(path);
8.         FileStream stream = null;
9.  
10.         try
11.         {
12.             stream = file.Open(FileMode.Open, FileAccess.Read, FileShare.None);
13.         }
14.         catch (IOException)
15.         {
16.             //the file is unavailable because it is:
17.             //still being written to
18.             //or being processed by another thread
19.             //or does not exist (has already been processed)
20.             return true;
21.         }
22.         finally
23.         {
24.             if (stream != null)
25.                 stream.Close();
26.         }
27.  
28.         //file is not locked
29.         return false;
30.     }

Solution was found via https://stackoverflow.com/questions/876473/is-there-a-way-to-check-if-a-file-is-in-use/937558#937558