S3TC image compression fails on exported project but works in editor

[ARPasescu]

Godot version: 3.0.6
OS: Windows 10 Pro

Issue description:
I'm trying to compress a viewport render image using S3TC, it works in the editor but not on the exported project, giving me this error.

This is my code:

yield(get_tree(), "idle_frame")
yield(get_tree(), "idle_frame")
var image = render_viewport.get_texture().get_data()
image.convert(Image.FORMAT_RGBA8)
image.compress(Image.COMPRESS_S3TC, Image.COMPRESS_SOURCE_GENERIC, 1.0) # Returns OK in editor but ERR_UNAVAILABLE on export

[akien-mga]

S3TC compression is done via the squish module, and is indeed only enabled for the editor binary (TOOLS_ENABLED).

Previously the whole squish module was editor-only, but @eska014 exposed the decompress method in #24017. I guess the decompression stuff might also be exposed, but needs confirmation from @reduz that this would not cause issues.

[vrmaurice]

This error is happening again on Godot 4.1 Mono.

I'm trying to use the Image.Compress() method in C#, it gives this error:
ERROR: Condition "!_image_compress_bc_func" is true. Returning: ERR_UNAVAILABLE

I've built this for a Linux server, I run the server with the --headless flag.

4.1.1.stable.mono.official [bd6af8e]

[Calinou]

I'm trying to use the Image.Compress() method in C#, it gives this error:

See this issue: #79932

Compressing textures to VRAM formats is not available in exported projects in 4.x for binary size reasons:

godot/modules/etcpak/config.py

Lines 1 to 2 in 221884e

	def can_build(env, platform):
	return env.editor_build

We could expose a SCons option to enable VRAM compressors in non-editor builds (like #73003), but it'll require you to build custom export templates to use that feature.