MAC: Project crash at startup - BC4 texture not supported

1After working under Windows for 10 weeks now, I’ve recently had to open the project under a Mac OS and the project crash at startup. One of the team members have to work under MacOS and is unable to open the project. I’ve added the dump log in the attachment (link text) and this is what I have found so far what causes the problem.

What: Project crash at startup.

Platform: Mac OS

Branch: Unreal Launcher

Build version: 4.5.1

Problem:[2014.11.14-22.36.53:476][ 0]LogMac:Error: appError called: Texture format ‘BC4’ not supported (sRGB=0).

Tried so far: I have deleted all textures I was able to find in the project and tried to open the project again, that ended up in success.

My conclusion: As far as I know it means that one of the many textures can not be loaded which causes the engine to crash. However it does not tell me which texture it is so I have to go manually through all the textures to find which one it cause. I have tested this on two different Mac OS, a iMac i7-core (which runs the third person template at 120 fps), and a MacBookPro i5-core (which runs the third person template at 20-30fps, due low videocard).

What to do next?

  1. Is there a better solution to tackle this problem?

  2. How can my team and I avoid this problem for future content? How can we identify if the texture is BC4 and when not?

BC4 is used for the TC_Alpha texture compression setting, but OS X doesn’t support this format and we should have been using uncompressed G8 instead. I’ve fixed the code, so 4.7 should work correctly. If you need the change sooner it is available on Github as commit 36256f5466ceac5b26c19791f12d355b0b8f015f.

Thanks for the answer and help!

This week I was able to replicate the problem. It was indeed a TC_Alpha texture, by testing all 300+ textures we have in our project.

I have tested this with the 4.7.0 version in github you mentioned and it works again at that version.

However since we are still working with 4.5.1 (UE Launcher branch) we were able to bypass this problem by using the following settings:

  • Texture saved as Targa 32-bit with an Alpha channel.
  • Load texture in Unreal Engine 4 as TC_Color instead TC_Alpha.
  • Within material shader use Texture RGB + lerp Texture Alpha for masking certain parts (as far as I can remember).

By using this method we are able to continue working within our current version of the engine.

Thanks once again and this bug-report can be solved as fixed/resolved!