storyteller-bevy/studio/assets/skyboxes/README.md

Generating Skybox and Image-Based Lighting Assets

HDRI images like those available at Poly Haven or HDRI Haven must be preprocessed before they can be used for skyboxes and image-based lighting in Bevy Engine. Ultimately, three files are required:

• An *.hdr cubemap texture for the skybox
• A *.ktx2 prefiltered diffuse irradiance cubemap for IBL
• A *.ktx2 prefiltered specular cubemap for IBL

The HDR cubemap texture currently must be generated using Blender. A helper asset with instructions is available here for Blender 3.6.

The prefiltered IBL cubemaps are generated with two CLI tools:

1. glTF IBL Sampler

   • Git clone with --recursive and build using CMake
   • Diffuse:

   ./path/to/build-output/cli \
   	-inputPath <input>.hdr \
   	-outCubeMap <output>_diffuse.ktx2 \
   	-distribution Lambertian \
   	-cubeMapResolution 32
   

   • Specular:

   ./path/to/build-output/cli \
   	-inputPath <input>.hdr \
   	-outCubeMap <output>_specular.ktx2 \
   	-distribution GGX \
   	-cubeMapResolution 512
   

2. bevy_mod_environment_map_tools

   • You can run this directly with cargo on the files generated by the previous step:

   cargo run --release -- \
   	--inputs <input>_diffuse.ktx2,<input>_specular.ktx2 \
   	--outputs <output>_diffuse.zstd.ktx2,<output>_specular.zstd.ktx2
   

The Bevy app expects the filenames to exactly match the patterns given in the examples above:

• {name}.hdr
• {name}_diffuse.zstd.ktx2
• {name}_specular.zstd.ktx2

Once the files are in place, the application's skybox module can load all of the associated files for a skybox by passing its name to a helper function.