How to use a Render Texture to take an "Off-Screen" screen shot?

I have been looking around and nothing I have tried is working.

I would like to know if there is a way that I can setup a Canvas with some images/text that will get filled in during the game and then create a texture to file out of this Canvas without having to show it to the user.

Googling around shows that creating a RenderTexture on a camera will show the Canvas on the RenderTexture but I have not been able to create a Texture2D out of it or save it out to a file.

Any ideas??

Thanks!

 

Not a complete answer but here's what I found with quick research:

Looks like Unity API itself doesn't allow to read texture buffer but you can call GetNativeTexturePtr to get direct access to texture. From there you need to use native code and whatever rendering library is being used in your case (probably DirectX or OpenGL) to get to pixel buffer.

If you follow the documentation link to native code plugins you will find there an example of such plugin for writing to texture so it's almost what you need. Just need to read instead of writing. Also the texture reading and then exporting to file doesn't have to be integrated with Unity functionality in any way so when studying the example just drop all the "native code plugins" parts and just look at how they make use of the texture pointer returned by GetNativeTexturePtr to get to texture buffer.

 

Looks like your can create a Texture2D from the texture pointer: Texture2D.CreateExternalTexture and you should be fine from there?

 

Sweet!! That seemed to have created the texture but when I try to EncodeToPNG() I get
Unable to retrieve image reference
UnityEngine.Texture2D:EncodeToPNG()

 

Did you check your texture pointer if it's not 0 for example? For me trying to create Texture2D from a texture pointer crashes the Unity.

Here's another way.
Texture2D.ReadPixels: "This will copy a rectangular pixel area from the currently active RenderTexture". So:

Code (CSharp):

1. Texture2D tex2d = new Texture2D(rendTex.width, rendTex.height, TextureFormat.ARGB32, rendTex.useMipMap);
2. RenderTexture.active = rendTex;
3. tex2d.ReadPixels(new Rect(0, 0, rendTex.width, rendTex.height), 0, 0);
4. tex2d.Apply();
5. byte[] bytes = tex2d.EncodeToPNG();
6. File.WriteAllBytes(Application.dataPath + "/../SavedScreen.png", bytes);

When creating Texture2D I hardcoded the texture format argument because TextureFormat and RenderTextureFormat are two different enums and it turns out that TextureFormat.ARGB32 is different value then RenderTextureFormat.ARGB32 so simply casting won't work. You need to write a RenderTextureFormatToTextureFormat method to do this properly. Since you have to find int value base on matching enum labels you probably will need Reflection for that.

 

There you go:

Code (CSharp):

1. string formatName = Enum.GetName(typeof(RenderTextureFormat), rendTex.format);
2. TextureFormat? texFormat = null;
3. foreach (TextureFormat f in Enum.GetValues(typeof(TextureFormat)))
4. {
5.    string fName = Enum.GetName(typeof(TextureFormat), f);
6.    if (fName.Equals(formatName, StringComparison.Ordinal))
7.    {
8.       texFormat = f;
9.       break;
10.    }
11. }
12.  
13. if (texFormat != null)
14. {
15.    Texture2D tex2d = new Texture2D(rendTex.width, rendTex.height, (TextureFormat) texFormat, rendTex.useMipMap);
16.    RenderTexture.active = rendTex;
17.    tex2d.ReadPixels(new Rect(0, 0, rendTex.width, rendTex.height), 0, 0);
18.    tex2d.Apply();
19.    byte[] bytes = tex2d.EncodeToPNG();
20.    File.WriteAllBytes(Application.dataPath + "/../SavedScreen.png", bytes);
21. }
22. else
23.    Debug.Log("Failed to convert RenderTextureFormat to TextureFormat!");

 

Hmm... I tried doing what you show above. I have the Texture2D as a public variable so I can see if it gets updated in the inspector and it does. The image I am expecting to see is now on that public variable. But the "EncodeToPNG()" is just coming up with a grey box.

What could be wrong?

 

Perhpas you have one piece of code that updates your public Texture2D that works fine and then another piece of code that updates Texture2D before saving to file and this one is not working? No idea really. Can you show some code, give relevant details on your setup?

 

I literally used exactly what you posted above.
I somehow messed it all up now. Not exactly sure what has happened but now its just putting a grey texture using the above code rather than the actual image as it was showing a moment ago... Very Weird

But if I go ahead and use

Code (CSharp):

1. tex2d = Texture2D.CreateExternalTexture(rt.width,rt.height,TextureFormat.ARGB32,false,true,rt.GetNativeTexturePtr());

rather than

Code (CSharp):

1. tex2d.ReadPixels(new Rect(0, 0, rt.width, rt.height), 0, 0);
2. tex2d.Apply();

The texture comes out properly again but when trying to get the bytes. It says;
Unable to retrieve image reference
UnityEngine.Texture2D:EncodeToPNG()

 

I would stay far away from using the pointer now that we have a way of doing this without it. Sounds like you had it working in that the Texture2D got created correctly and then only the EncodeToPNG was causing some trouble but that was probably issue with setup. Code works, I tested it. Try reproducing the problem with minimalistic setup.

 

Thanks for your help. I have no idea why your code is not working anymore. I didn't change anything so its really confusing. I would really like to get this done though. It's very much needed.

 

Like I said, try with new scene and make as simple setup as possible to test the code. Find where exactly things go wrong and see where it leads you. Once you get the simple example working you can then compare it with your intended setup and see what's different there.

 

There's nothing in my scene besides your code and a canvas with a few child objects on it with a "Screen Space - Camera" setup for the main camera along with the main camera having a render texture applied to it.
So confused

 

Ok! I got it to work by turning off anti-aliasing completely from the Render Texture. If I put it on then it wont work. What is the reason for that?

 

No idea. You might want to make a new thread about this problem specifically cause I'm clueless.

 

Thank you. I may