boimp

boimp is the sound a mesh makes when its lods pop. it's also a library for octahedral imposters in bevy.

versions

boimp	bevy	note
0.1.0	0.14	requires a slightly modified bevy 0.14.2 (see cargo.toml)
0.2.0	0.15

bake

generate an imposter with an ImposterBakeBundle, specifying the image size, grid count, multisampling and grid mode (spherical / hemispherical / horizontal).

commands.spawn(ImposterBakeBundle {
    camera: ImposterBakeCamera {
        radius: 10.0, // how large an area to snapshot
        grid_size: 6, // 6x6 separate snapshots
        image_size: 512, // 512x512 texture
        grid_mode: GridMode::Spherical, // how the snapshots are arranged
        multisample: 8, // how many samples to average over (^2, 8 -> 64 samples)
        ..Default::default()
    };
    transform: Transform::from_translation(Vec3::ZERO),
})

for anything to be produced, the materials used in the area must implement ImposterBakeMaterial. This is automatically implemented for StandardMaterials, other implementations can be registered by adding an ImposterBakeMaterialPlugin::<M>. the frag shader is quite simple, see the standard material version.

render

render the imposter with a MaterialMeshBundle:

commands.spawn(MaterialMeshBundle::<Imposter> {
    mesh: meshes.add(Plane3d::new(Vec3::Z, Vec2::splat(0.5)).mesh()),
    material: asset_server.load_with_settings::<_, ImposterLoaderSettings>(source, move |s| {
        s.multisample = multisample;
    }),
    ..default()
});

Use a Rectangle or Plane3d::new(Vec3::Z, Vec2::splat(0.5)) mesh.

examples:

dynamic

runs baking every frame (once 'I' is pressed, and until 'O' is pressed), and spawns a large number of imposters based on the bake results.

args:

• --grid <n> : number of separate snapshots (^2) (default 15)
• --image <n> : total size of texture image (^2) (default 1024)
• --mode [s]pherical | [h]emispherical | [H]orizontal : how the snapshots are arranged (default hemispherical)
• --count <n> : number of imposters to spawn (default 1000)
• --source <path> : gltf to load (default FlightHelmet)
• --multisample-source <n> : how many samples to average over when baking (^2) (default 1)
• --multisample-target : average samples over nearby material pixels when rendering imposters (default false)

save_asset

loads a gltf, bakes and saves an imposter, with baking params from the commandine.

args:

• --grid <n> : number of separate snapshots (^2) (default 8)
• --image <n> : total size of texture image (^2) (default 512)
• --mode [s]pherical | [h]emispherical | [H]orizontal : how the snapshots are arranged (default hemispherical)
• --source <path> : gltf to load (default FlightHelmet)
• --multisample <n> : how many samples to average over when baking (^2) (default 8)
• --output <path> : where to output to (default "assets/boimps/output.boimp")

load_asset

loads a previously baked imposter, with rendering params from the command line.

args:

• --source <path> : gltf to load (default "assets/boimps/output.boimp")
• --multisample : average samples over nearby material pixels when rendering imposters (default false)

known issues

non-opaque materials aren't well supported. a single alpha-blend texture will work fine but multiple overlapping texture layers will take only the alpha of the front-most layer.

todo

• integrate with visibility ranges
• improve asset format
• store/adjust for depths
• maybe make the storage more configurable maybe - currently 5bit/channel color and alpha, 4bit metallic and roughness, 4bit flags (only unlit flag currently passed), 24bit normal, 8bit depth
• maybe add "image" mode that records the actual view rather than the material properties
• update to 0.15 and upstream
• fix alpha issues
• use vertex instancing to avoid needing a mesh

License

boimp is free and open source. All code in this repository is dual-licensed under either:

• MIT License (LICENSE-MIT or http://opensource.org/licenses/MIT)
• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)

at your option.