This allows clients to provide their own asynchronous texture decoders
for various mime-typed images. This is a plug-in component for gltfio,
in some ways similar to MaterialProvider.
There are two motivations for this: to decouple gltfio from STB and
to make it easier to integrate support for BasisU textures.
This also has the side effect of simplifying ResourceLoader, since the
texture decoding jobs have been moved out.
As part of this work, I made the "stb" CMake target into a traditional
static library. Previously we had several files called `Image.cpp`
whose sole purpose was to enable STB_IMAGE_IMPLEMENTATION.
Note that this API is on the loader rather than the asset. This is
because the loader knows how to create Filament entities by traversing
a cgltf node hierarchy.
Animation on dynamically added instances is not yet supported.
We did not add destroyInstance() because gltfio favors flat arrays for
long term storage of entity lists and instance lists, which would be
slow to shift. We also wish to discourage create/destroy churn since it
is more efficient to pre-allocate instances and selectively add them
into the scene.
Fixes#3137.
This feature adds one new method to `FilamentAsset` and uses it in our
Kotlin, JavaScript, and C++ helpers:
utils::Entity popRenderable() noexcept;
This pops a ready renderable off an internal queue, or returns 0 if no
renderables have become ready. It provides a simple way for clients to
gradually add renderables to the scene as they become ready. Previously
clients could only get the entire list of entities, regardless of
whether they had Renderable components or complete textures.
To facilitate this feature, this PR adds a new internal-only class to
gltfio called `DependencyGraph`, which is a temporary object used for
bookkeeping during the asynchronous load.
`DependencyGraph` discovers ready-to-render entities by tracking the
textures that each entity depends on. This is a graph because
renderables connect to a set of material instances, which in turn
connect to a set of parameter names, which in turn connect to a set of
texture objects. These relationships are not easily inspectable using
the Filament API or ECS.
