AssimpImporter: Fix loading of embedded textures from FBX files

[Squareys]

Hi @mosra,

As promised, here's the fix for #127 .

The test file was created with Blender 3.1.0 as follows:

• Delete default scene
• Add plane
• Set the diffuse color to image texture with this image:
• File > Export > FBX, chose path mode "copy" and press the button next to the dropdown, which enables embedding images

The file now has the absolute path of the PNG embedded (C:/Users/Squareys/Desktop/embedded.png), similar to how I've seen it in "real world files", but the image data is embedded, so the loader doesn't actually access this file ever. This was ensured by renaming the image file and opening it with the Windows 3D viewer, the texture was still correctly displayed.

The test was added first, to ensure this was actually the culprit, it fails on the image expression, i.e. image was not found, exactly what I was observing in #127.

Since the GetEmbeddedImage() was added with 5.0.0, I kept the legacy path behind the ASSIMP_IS_VERSION_5_OR_GREATER, but I did not test the code (really hoping the CI does this, would be a hassle to set up the CI is testing this, luckily).

I double checked the drive-by std::string => StringView/String changes, let's hope that won't blow up in my face like on the EmscriptenApplication 😅

Looking forward to the review!

Best,
Jonathan

[Squareys]

linux-arm64 failed with StbResizeImageConverterTest sefaulting 🤔

[mosra]

Thanks! Especially for the extra care to put the test in an earlier commit.

Merged with one minor change -- I just made the #ifdef a bit less surprising in 1db2003.

[Squareys]

Amazing, thank you! 🎉 🙏